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Masters Theses 1911 - February 2014
1985
Intercropping corn and soybean :: planting pattern, plant density, and nitrogen fertilizer responses /
Antonio Vargas University of Massachusetts Amherst
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INTERCROPPING CORN AND SOYBEAN: PLANTING PATTERN,
PLANT DENSITY AND NITROGEN FERTILIZER RESPONSES
A Thesis Presented
By
ANTONIO VARGAS
Submitted to the Graduate School of the University of Massachusetts in partial fulfillment of the requirements for the degree of
MASTER OF SCIENCE
February 1985
Department of Plant and Soil Sciences INTERCROPPING CORN AND SOYBEAN: PLANTING PATTERN, PLANT DENSITY AND NITROGEN FERTILIZER RESPONSES
A Thesis Presented
By
ANTONIO VARGAS
Approved as to style and content by: /I
Stephen J. Herbert, Chairperson of committee
Mack Drake, Member
Richard A. Damon, Jr^;
Allen V. Barker, Department Head Department of Plant and Soil Sciences
ii DEDICATION
To my wife
Ginger
whose patience, love and support permitted me to complete this thesis.
iii ACKNOWLEDGEMENTS
I wish to acknowledge the valuable advice, experience and profesional training provided by Professor Stephen J. Herbert whose help and friendship have been of inestimable value throughout my academic training as well as in preparation of this thesis. Also I would like to thank the members of my thesis committee, Professors
Mack Drake and Richard A. Damon, Jr. for their time and helpful comments.
In addition, my appreciation goes to all the professors, fellow students, and friends who transmitted awareness of new ideas through their lectures and conversations. Especially I must acknowledge the hours and assistance provided by Daniel Putnam, Jerry Litchfield, Jack
Creighton, Dr. Benjamin Rodriguez, Dr. Francisco Chapman, Sharon
Lenpicki, Ronald Lavigne, Steven Bodine, Charles Mancino, Asa
Thompson, Evelyn Morales, Franklin Linares and Jenny Ruth. Many thanks go to Greg Thompson for his editorial assistance.
Finally, I would like to acknowledge my parents who taught me how to live life.
Partial support for this research comes from the Massachusetts
Agricultural Experiment Station Hatch Project 476, and the Department of Plant and Soil Sciences.
iv TABLES OF CONTENTS
DEDICATION.1±i
ACKNOWLEDGEMENTS . iv
LIST OF TABLES ..
LIST OF FIGURES ..
Chapter
I. INTRODUCTION. 1
II. LITERATURE REVIEW . 7
Relevance of Intercropping to Tropical Agriculture . 9 Temperate Regions . 10 Intercropping Systems and Potential .... 11 Mixed Intercropping. 12 Row Intercropping. 13 Relay Intercropping. 14 Strip Intercropping. 14 Basic Concept of Intercropping Competition . 15 Competition for Light . 16 Reasons for Practicing Intercropping .... 19 Spatial Arrangement and Plant Density ... 22 Effect of Shade. 26 Nitrogen in Crop Mixture. 30 Weeds and Intercropping Systems. 35 Nutrient and Water Competition ...... 36
III. MATERIALS AND METHODS . 38
1982 Field Study. 38 1983 Field Study. 43
IV. RESULTS AND DISCUSSIONS. 49
1982 Results. 49 1982 Discussion. 67
v 1933 Results . 72 1983 Discussion. 89 Conclusion. 92
V. SUMMARY. 94
LITERATURE CITED . 98
APPENDIX.114
vi LIST OF TABLES
Table 1. Rainfall 1982 and 1983 39 2. Treatment planting patterns and densities forming a replacement series . 40 3. Planting patterns and nitrogen treatments .... 46 4. Silage yield and percent soybean in the final yield mixture. 50 5. Ear dry matter yield and number of ears on a row-equivalent basis. 51 6. Ear number per plant and dry weight per ear ... 52 7. Kernel dry weight and kernels per row. 53 8. Percent crude protein and crude protein yields on a dry matter basis. 57 9. Ears as a percentage of corn and as percentage of the total yield mixture-1982 . 63 10. Row-equivalent dry matter yield of corn bordered by corn, soybean, or corn and soybean on either side. 64 11. Row-equivalent yields of soybeans and number pods per plant. 65 12. Silage yield (70% moisture) in South Deerfield (S.D.) and Belchertown (Belch)-1983 . 73 13. Dry matter yields for corn and soybean components of monocultures and intercrops in South Deerfield-1983 75 14. Dry matter yields for corn and soybean components of monocultures and intercrops in Belchertown-1983 . 77 15. Dry matter yield ear corn-1983 79 16. Dry matter yield of shelled corn-1983 . 80 17. Crude protein yield dry basis-1982 82 18. Percent crude protein dry basis-1983 83 19. Nodule number in South Deerfield-1983 . 87 20. Nodule dry weight in South Deerfield-1983 .... 88
vii LIST OF FIGURES
Figure 1. Arrangement of rows for corn and soybean in monoculture (A,B) and intercropped con and soybeans (C). 45 2. Forage composition dry matter basis . 55 3. Contribution of the various yield components to total protein yield on a dry matter basis. 58 4. Planted area comparison of intercrops and monocultures. 59 5. Silage yields on a harvested ratio basis .... 60 6. Ear dry matter yield on an equivalent row basis. 62 7. Total and component Land Equivalent Ratios ... 66 8. Effect of nitrogen fertilizer on protein yield on corn (C-C) and soybean (S-S) monocultures and a corn-corn-soybean-soybean intercrop where nitrogen was applied to both corn and soybean (C-C-S-S) and only corn (C-C-S-S). 85
viii CHAPTER I
INTRODUCTION
Today there is great concern about energy conservation. Grass crops require nitrogen fertilizers to reach their maximum yields, and the supply and cost of chemical nitrogen fertilizers are closely linked to availability of petroleum products (Hoffman & Melton, 1981).
Therefore, energy can be saved by growing a grass with a legume (a nitrogen-fixing species).
Many of the so-called new experimental approaches to farming are little more than resurgence of a method that was once popular, since been left behind by what is considered to be progress. This has been true of such practices as minimum tillage, double cropping, controlled field traffic, and many soil and water conservation techniques.
Intercropping can also be added to that list (Crookston, 1976).
Intercropping is not a new agricultural practice. In fact, it was once a common American farming method. The early European settlers who learned to grow corn from the Indians often planted beans and corn together. Perhaps, the bean plants used the growing corn stalks as bean poles.
Most small farmers in tropical developing countries in Asia,
Africa, and South America have been using many different cropping practices to increase production. There are several cropping combinations presently being employed in the tropics. Multiple cropping systems can be classified according to the degree of
1 2
intensification in time and space (Sanchez, 1976; Harwood, 1979;
Andrews and Kassam, 1981).
Multiple cropping. The intensification of cropping in time and space dimensions. May use two or more crops on the same field in a year.
Intercropping. Is growing two or more crops simultaneously on the same field per year. Crop intensification is in both time and space dimensions. There is intercrop competition during all or part of crop growth; nevertheless farmers manage more than one crop at a time in the same field. These crops can be in alternating rows or even mixed together within rows (Crookston, 1976). There are many succesful intercropping combinations practiced in the world today.
The following are examples.
1. Corn ( Zea mays L.) and dry beans ( Phaseolus L.) in Latin
America. 2. Dryland rice ( Qriza sativa L.) and corn in the
Philippines. 3* Sorghum ( Sorghum bicolor (L.) Moench) and sweet potatoes ( Solanum tuberosum L.) or cowpeas ( Vigna sinensis Savi) in
Africa. 4. Corn and soybeans ( Glycine max (L.) Merr.) in China.
5. Millet ( Setaria faberri Herm.) and sorghum in Nigeria.
Mixed intercropping. Growing two or more crops simultaneously with no distinct row arrangement. 3
Strip intercropping. Growing two or more crops simultaneously in different strips wide enough to permit independent cultivation but narrow enough for the crops to interact agronomically.
Row intercropping. Growing two or more crops simultaneously with one or more crops planted in rows.
Relay intercropping. Growing two or more crops simultaneously during part of each one’s life cycle. A second crop is planted after the first crop has reached its reproductive stage of growth but before it is ready for harvest.
Sequential cropping. Growing two or more crops in sequence on the same field per year. The succeeding crop is planted after the preceding one has been harvested. Crop intensification is only in the time dimension. There is no intercrop competition. Farmers manage only one crop at a time in the same field.
Double cropping. Growing two crops a year in sequence.
Triple cropping. Growing three crops a year in sequence.
Quadruple cropping. Growing four crops a year in sequence.
Single stands. Growing one crop cultivar alone in pure stands at the normal density. Synonymous with "solid planting". Opposite of
"multiple cropping". 4
Monoculture. Repetitive growing of the same crop on the same land.
Rotation. Repetitive growing of two or more sole crops or multiple cropping combination on the same land.
Cropping pattern. Yearly sequence and spatial arrangement of the crops and fallow on a given area.
Cropping system. The cropping patterns used on a farm and their interactions with farm resources, other farm interprises, and available technology that determines their make up.
Mixed farming. Cropping systems that involve raising of crops and animals.
Croping index. Number of crops growing per annum on a given area of land x 100. Cordero and Mac Collum (1979) indicated that a cropping index is greater than one .
Relative yield total (RYT). Sum of intercropped yields divided by yields of sole crops. This is the same concept as Land Equivalent
Ratios. "Yield" can be measured as dry matter production, grain yield, nutrient uptake, energy, or protein production, as well as market value of crops.
Land equivalent ratio (LER). Ratio of area needed under sole cropping to the one under intercropping to yield equal amounts of intercrops relative to sole crop yields. It is equivalent to RYT, 5
expressed in commercial yields.
Maximum cropping. The attaiment of the highest possible production per unit area per time without regard to cost or net return.
The planting patterns of crop by farmers across the United States have shifted away from intercropping and progressed to large, uniform, monocropped fields. However, increasing management pressure of higher land costs, decreasing energy supplies, and low market prices, may bring intercropping into the American farming scene again (Crookston,
1976).
There is a need to re-evaluate intercropping practices for modern agricultural programs. There is a need to study intercropping possibilities with combinations of many crops such as corn, soybeans, small grains, summer annual hay or pasture crops, and vegetable crops.
These mixtures of species could be applicable to the mechanized systems of North America if specific yield aspirations are met. Yield goals addressed in this study are associated with dairy operations, where in the Northeast, the on-farm production of protein is frequently deficient (Smith, 1981).
Percentage crude protein-dairy. Fourteen percent crude protein in the ration is considered adequate for a high producing dairy cow during the first 23 weeks of lactation (Holter et al., 1982). If most of this protein is made up from on-farm forage sources, the amount of grain concentrates required could be reduced, which would both be more economical and a better feed source for the animal. A lactating dairy 6
cow consuming a high fiber diet is less likely to develop metabolic or digestive problems (Miller & OfDell, 1969)* and fiber is often considered an essential nutrient for this reason. Therefore, a high quality forage diet with few concentrates is considered much better than a low quality forage diet with high concentrates (Miller, 1979).
Moreover, higher quality forage would enable the farmer to reduce costs by cutting back on concentrates since less would be required
(Church, 1977; Miller, 1979). For farmers an increase in forage protein production without reduced yield quantity is important.
The purpose of this study was to evaluate yield relationships of a corn—soybean intercrop system under different planting patterns and densities (1982) and nitrogen rates and placement (1983). CHAPTER II
REVIEW OF LITERATURE
According to Harwood (1979) and Sanchez (1976), most small farms in tropical Asia, Central America, and Africa have employed multiple cropping combinations for intensifying crop production per unit area.
The number or multiple cropping combinations in actual use in the tropics must be on the order of several thousand.
Small farms are by far the most numerous type in the tropics. In tropical Asia, 75 percent of all farms are smaller than 2 hectares; in
Central America, 69 percent are smaller than 5 hectares; and for 20 tropical African countries, the average farm size is 5.4 hectare
(Gomes & Zandstra, 1977; Sanchez, 1976; Mac Arthur , 1971; and Uehara,
1977).
Data from Uehara (1977) showed the per capita cultivated land expressed in hectares was estimated at 0.9 for North America, 0.88 for
Russia, 0.34 for Africa and Latin America, 0.33 for Europe, and 0.17 for Asia.
The largest populations live in countries in which the posibility for expansion of arable land is extremely remote.
Gomes and Zanstra (1977) indicated that there were several important considerations in designing adequate multiple cropping systems for small farmers. First, land and not labor is the more
7 8
limiting resource. Second, access to market is poor. Third, cash resource are limited and cash flow is an important consideration.
Finally, there is a premium for crops that are edible and that can be stored or preserved since they can be used in the household if the market is unfavorable.
Legumes must occupy an important role in cropping patterns of small farmers in the tropics to be competitive with other crops.
Multiple cropping has been used to diversify agricultural products and to satisfy the needs of subsistence farming by increasing productivity and income. Technically, advanced countries of Asia, Europe, and
North America which enjoy high unit area yields, are better off or at least as well off in per capita cultivated land as the developing countries of tropics. Some reports illustrated the potential of multiple cropping with intensity index 1.4-4.0 for upland crops in the
Philippines, 1.1 in Burna, 1.8 in Taiwan,and 1.3-2.0 in the South East
Atlantic (Gomes & Zandstra, 1977; Cordero & Me Collum, 1979;
Borgstorm, 1973; and Arnon, 1972). Yet a major limiting factor for intensive cropping in the farm field is water. People tend to congregate in places where water and soil fertility do not limit food production (Uehara, 1977). 9
Relevance of Intercropping to Tropical Agriculture
The need to increase food production in tropical areas is one of the major world problems where physical areas under cultivation cannot be increased. There is a possibility of increasing productivity by relay, multiple or sequential cropping and intercropping in order to produce more per unit area and time, and to stabilize overall production. One objective in intercropping is to produce an additional crop without much effect on the base crop yield, or to obtain higher total economic returns even though there is ; some marginal sacrifice of the base crop (Annand et al., 1978).
Multiple cropping systems are often characterized by high plant species diversity, better erosion control, low but stable yield and an intensive exploitation of limited land resources (Altieri et al.,
1978; and Dickinson, 1977). Traditional small farm systems in many regions are characterized by low use of technology, low but relatively stable yields and low investment and risk.
Spanish conquerors and other explorers observed crop associations during their exploitation of the Americas (Patino, 1965). These associated cropping patterns have evolved with generations of farmers with small holdings, and still ocuppy an important role for food production in Latin America. Estimates of the proportion of beans produced in associated cropping systems are 40$ in Mexico (Lepiz,
1972; 73$ in Guatemala, 90$ in Colombia and 80$ in Brazil (Gutierres,
1975). Surveys from various national programs indicate that about 60$ of maize and 80$ of beans are produced in associated cropping systems in Latin America (Dickinson, 1977). This makes intercropping studies 10
highly relevant to my particular region and agricultural experience.
Temperate Regions
Quantity of silage, or yield per acre, is of vital importance in
New England. The area possible to devote to tilled crops is usually limited and crop production frequently becomes a question of securing the highest yield possible. Therefore, unless a combination of corn and soybean gives a yield increase or maintains yield at an acceptable level of over corn alone, the economic value of the intercrop may be questioned, although increased quality though higher protein should not be disregarded (Cummins, 1973)• Boss (1917) found that a corn-soybean combination produced an increase in total nutrients and protein over corn alone as a result of two years' work at the
Minnesota Experiment Station. Stemple (1977) at West Virginia obtained the following data in a one year's test: corn and soybeans
10.16 tons silage; corn alone 8.97 tons silage. Hughes and Wilkins
(1925), after 10 years of work with corn and soybeans in Iowa, concluded that larger yields of silage may be secured by planting the intercrop and that it is a desirable practice to plant soybeans in corn for "hogging down".
Corn is capable of producing more high quality energy per acre as silage than any other forage crop in the temperate zone. However, supplemental protein is needed to balance the ration for livestock feeding. Urea can furnish the additional nitrogen necessary for ruminant protein synthesis, but declining petroleum reserves and recent increased nitrogen cost make it necessary to re-examine other 11
alternatives for increasing silage protein levels (Anderson & Daigger,
1982).
If the forage yield of corn-soybean mixtures can be maintained at an acceptable level and yield quality can be increased, then corn-soybean mixtures are worth considering for temperate regions
(Cummins, 1973).
Intercropping Systems and Potential
Sanchez (1976) indicated that intercropping was the simultaneous growing of two or more crops in the same field at the same time.
Unlike sequential cropping where intensification is in the time dimension, intercropping involves intensification in both space and time.
Harwood (1979) reported that intercropping of annual crops, planting two different crops together in the same field at the same time, is the least understood of all cropping methods. A few generalizations can be made about intercropping. First, crop types in many possible intercropping patterns should be compatible with each other. Second, a particular intercropping pattern is almost always chosen to alleviate a particular limitation in resources. Third, intercropping is almost always associated with farms of less than 2 hectares. Fourth, intercropping patterns must be designed with careful attention to details of plant type, planting arrangements, timing and other factors. Finally, intercropping combinations make it difficult if not impossible to cultivate between the rows with animal or tractor drawn equipment 12
Furthermore, there are several types of intercropping mixtures using annual crops. The most common type is a mixture of short and tall types in which both crops are planted at the same time, but the
taller crop is harvested first. Maize might be the tall crop harvested after three months, for example, with the intercrop of peanut, sweet potato, or rice harvested after four months. Such intercrops of different plant types with little competition between
crops during the reproductive stage are usually the most productive.
Sanchez (1976) described four types of intercropping: mixed
intercropping, row intercropping, relay intercropping, and strip
intercropping.
Mixed Intercropping
Mixed intercropping encompasses a wide array of apparently random
arrangements of several crops in a field. Mixed cropping is common when cereals, grain legumes, and root crops are growing together and
no tillage is practiced. The differences in plant size and growth
duration probably decrease the competition for solar radiation. Mixed
cropping in Costa Rica with a bean-corn-cassava obtained RYT of 1.4
for yields and 1.3 for net income compared with growing the three
crops in single stands.
Arnon (1972) indicated that mixed cropping was a method which
attempted to make the most of the potentialities of the enviroment.
By planting together a succession of crops with varying harvesting
times and growth habits, plant nutrients in different soil layers were
better exploited and light energy was utilized more effectively. 13
Limited water supply was utilized more efficiently in a mixed cropping system than in pure stands.
Row Intercropping
Sanchez (1976) and Harwood in (1979) reported that row
intercropped occured when one or more crops were planted at about the
same time in rows close to each other. Row intercropping is common in
tilled areas and is perhaps the central concept of intercropping.
Competition among species for light, water, and nutrients is in the
row basis. Corn and upland rice are commonly grow in this fashion in
Asian and Central American lowlands.
Row intercropping is most advantageous when a tall-statured crop
is grown with a short-statured one, and when the crops have different
growth durations. Competition for light is minimized when tall crops
have an erect leaf habit and shorter crops more horizontal leaf angle.
When the crops have diffent growth durations, and advantages of row
intercropping increase further. Then stages of maximum demand for
light, water, and nutrients occur at different times even though the
crops are planted at about the same time.
Row intercropping of annual crops under perennials is common.
Tall growing crops such as corn, cassava and bananas are planted on
young coffe ( Coffea sp. ) or rubber ( Hevea brasiliensis ) and
produce income while the permanent crops develop. At normaj. spacings
and plant densities, the yields of intercropped cowpeas ( Vigna
sinensis ) and sugar cane ( Saccharum officinarum ) were identical to
monoculture yields (RY of 2.0) in Northeast Brazil. In Taiwan, sugar 14
cane was intercropped with several species (Sanchez, 1976).
Relay Intercropping
When a second crop is planted after the first has entered the reproductive growth phase but before harvest the system is called
*1 "relay intercropping" (Sanchez, 1976; Harwood, 1979).
In South America, tall photoperiod-sensitive corn cultivars require 6 to 10 months to mature. When the ears are well formed but not mature
(33-35 percent water in kernels), farmers break the stalks just below the ears and plant climbing bean cultivars. Relay cropping is also very common in rice-based Taiwan. Planted rice-melons are followed by rice again relaying with cabbages ( Brassica oleracea capitata) and corn.
Competition is minimized in relay intercropping by reducing the time during which two crops are grown together. For this system to be successful, the crop planted during the reproductive stage of another must be tolerant to the shading by the first crop. Due to the shorter competition period, relay intercropping generally provides higher relative yield totals than mixed or row intercropping. Also relay intercropping is advantageous in separating root systems.
Strip Intercropping
Pattern occurs when individual crops are grown in the same field in strips wide enough to permit independent cultivation but close enough to produce some agronomic interaction. There is little competition between crops except in the border rows, but the benefits of wind protection and water conservation may give positive RYT 15
values.
Harwood (1979) indicated that intercropping can be used to achieve a number of agricultural objectives. For each objective, certain specific intercrop combinations are more appropriate:higher over-all productivity, reduced tillage during the growing period, weed control simplifying, improvement in the control of insect pests and disease, insurance factor, and inherent stability of crop mixtures.
Basic Concept of Intercropping Competition
The first step in understanding intercropping is learning how plants react to each other*s mixtures. A different response of
individual plants or species to their environment as modified by the presence of another individual plant or another has been shown. Such interference occurs when different plants share a growth factor
(light, water, nutrients) that is present in unlimited amounts. Plant
yields are not affected by this type of interference. Competitive
interference or supply competition occurs when one or more growth
factors are limiting. In such cases, the plant or species better
equipped to utilize a growth factor increases its yield at the expense
of the other plant or species, which suffers a yield decrease.
Complementary interference, occurs when one plant helps another as in
the case of legumes supplying nitrogen to grasses via symbiotic
Interference occurs among plants of the same species in single
stands and among plants of the same and differnt species in
intercropping system. Plant interference resulting in a relative 16
yield total (RYT) of dry matter production close to 1.0 suggests no advantage of intercropping. The RYT of a mixture ranging from 1.1-1.7 or more indicates an advantage of intercropping, and an RYT less than
1.0, indicates clear disadvantage.
RYT can be expressed in terms of crop yields (LER) and gross income (IER). When three or four crops are intercropped, RYT values increase even more. The yield advantages of successful intercropping
systems are probably selected to minimize interspecific competition
for light, water and nutrients.
Competition for Light
Trang and Joel (1980) emphasized that plants with no shade
produced more dry matter, nitrogen, non—extructural carbohydrates, and
higher nodule mass and number than when shaded. Mann et al., (1980)
found that the quality of solar radiation penetrating a crop canopy
and reaching the soil surface greatly affected the micro environment
beneath the canopy. The leaf area index (LAI), is the ratio of total
leaf area above some specified ground area to this ground area.
Gangwar and Kalra (1982) found that the average increase of total
corn grain production by intercropping with legumes ranged from 29.5
to 92.5 percent greater yield over pure cropping of corn. Aplication
of 80-120 kg N per hectare increased total production by 29.0-37.5
percent compared with 40 kg N per hectare. However, application of 80
kg N per ha was more economical. 17
Gardiner and Craker (1981) concluded that bean-corn intercrop planting increased light reflection compared with bean monocrop.
Furthermore, Dale et al. (1982) observed the effect of leaf area, incident radiation, and moisture stress on reflectance of near infra red radiation from a corn canopy. Differences in reflectance first appeared to increase with increasing moisture stress and then decreased with further increase in moisture stress as rolling reduced the ratio of green plant cover (RGPC).
In 1967, Pendleton emphasized that light appears to be the primary ecological factor limiting the grain yield of corn when grown under low light conditions. Border plants in the light rich environment had more tillers, more plants with two ears, shorter stalks with greater diameters and slightly larger leaf area than plants from inner rows or normal border rows. Kitamura et al. (1981) investigated legume growth and nitrogen fixation affected by plant competition for light and soil nitrogen. The green leaf, Dismodlum intortum was a better competitor for light, probably due to its thin horizontal leaves which probably have lower light compensation buds than nandi, Setaria sp. However green leaf yields were reduced and nandi yields were increased when the two species shared a common rooting volume indicating that green leaf was a poor competitor for nutrients. Nodulation of green leaf was reduced by both top and root competition, but the plants were apparently able to compensate for reduced nodule members by increased weight per nodule and increased specific activity once nodule strength was fully developed. Root development was restricted by top compensation, more so in green leaf 18
than nandi.
Shaw and Weber (1967) studied the effect of canopy arrangement on light interception and yield of soybeans. The yield correlated positively with both the amount of leaf area and volume of canopy above the compensation point. Greater oil content was generally associated with greater light penetration. The effect of shading in adjacent rows was greater in 1 meter row spacing than an 1.5 meter row spacing.
Sanchez (1976) indicated that when crops have different growth duration, the advantages of row intercropping increases further.
Stages of maximum demand for light, water and nutrients occur at different times even though both crops are planted at about the same time; corn-mungbean intercropping is an example. Mungbean reaches its flowering stage 35 days after planting before it is shared by corn.
It is harvested at 60 days, when corn demands are at a maximum. There is little shading at the seedling stage of either crop, which is an advantage because both are very susceptible to light stress.
Sivakumar and Virmani (1980) investigated the growth and interception of photosynthetially active radiation (PAR) in a corn/pigeonpea intercrop and sole corn, sole pigeonpea crops grown in large plots. The growth and yield of the corn crop in pure stands and intercropped were not significantly different. Efficiency of dry matter production, calculated from the relations between dry matter production and comulative intercepted PAR, was highest for the corn/pigeonpea intercrop followed by sole corn and sole pigeonpea, proving the utility of such intercrops in making better use of 19
resources in the semi-arid tropics (SAT).
Reasons for Practicing Intercropping
Intercropping is a traditional practice that predominates among farmers in developing tropical and subtropical countries (Andrews and
Kassam 1976; Harwood and Price, 1976; Okigbo and Greenland, 1976;
Francis et al«, 1976). In traditional agriculture, it has been practiced at a low level of technology and largely for risk reduction
(Krantz et al., 1976). But, an understanding of the technical, socio-economic, and physical factors associated with crop mixtures
(Norman, 1970) has revealed that, under the prevailing and aberrant weather situations in the semi-arid tropics, intercropping has greater yield potential, stability of production, and advantages in pest, disease and weed management (Aiyer, 1949; Andrews, 1972; Rao and
Shetty, 1977). Intercropping results in increased efficiency of utilization of environmental factors, insurance against crop failure, maintenance of soil fertility, protection of soil against erosion and a built-in balanced nutritional supply of energy and protein (Aukland,
1970; Ruthenberg, 1971; Norman, 1974; Banta and Harwood, 1975; Okigbo,
1978; Rachie, 1978).
Intercropping may be a potential farming method to increase land
productivity, especially in developing countries where land shortage
is a problem. This is because the evaluation of land productivity in
terms of the Land Equivalent Ratio (LER) has shown that this farming
practice may have yield advantages of to 60% over sole crops (Munro,
I960; Norman, 1970; Bantilan and Harwood, 1973), not only with low 20
levels of technology, but also at high levels of input (Andrews, 1972;
International Rice Research Institute, 1972, 1973> 1974; Searle et al., 1981; Krantz et al., 1976). Although it has been argued that the practical management of intercropping can be more difficult than for sole crops, this argument is only valid for developed agriculture where crop management is highly mechanized.
Beneficial effects of intercropping grain legumes with maize, in terms of total grain production per unit area of land, have been reported by many workers (Evans, I960; Alexander and Genter, 1962;
Pendleton et al., 1963; Gautam et al., 1964; Narang et al.,1969;
Willey and Osiru, 1972). Mohta and De (1980) reported an increase in total land productivity of 31% and 48%, when soybean was intercropped with sorghum and maize, respectively.
The yield advantages of intercropping may be viewed in two ways; that is, intercropping can give stability of yield from season to season and higher yields in a good season than sole cropping. In a assessment of the second advantage, which has received much more attention, Willey (1979) recognized that intercrops may be judged by different criteria, depending upon the farmer’s objectives. The first situation where intercropping must give full yield of a main crop and may provide some yield of minor crop. This criterion is common where the objective of a farmer is to get full yield of a staple cereal and a second crop is acceptable only if its yield is additional. A second situation is where the combined intercrop yield must exceed the yield of the higher yielding crop. This situation occurs in grass mixtures
(Donal, 1963) and in mixtures of genotypes within a given crop 21
(Trenbath, 1974b), where the criterion is to obtain maximum yield irrespective of which crop it comes from. The third situation is where intercropping must give a higher yield than the growing of the component crops separately. The criterion here is that the grower would like to have both component crops for security, social and dietary requirement reasons.
Research has shown that there are physiological aspects to yield advantages for intercrops. Yield advantages, or LERs, greater than unity, have been obtained where annidation occurs in component crops, i.e., where supplementary use of resources occurs. Annidation may occur in time and space. It has been shown that biggest advantages may occur where there is temporal complementarity, i.e., where the major demands on resources by the component crops occur at different times because they have different growing or fruiting periods
(Andrews, 1972; Baker and Yusuh, 1976; Dalai, 1974; Osiru and Willey,
1976; Willey and Osiru, 1972; Natarajan and Willey, 1980a, b; Rao and
Willey, 1980). Another aspect of annidation in time occurs where crops have different durations of growing season, such that when one matures the conditions become favorable for the other component
(Harper, 1968; Trenbath, 1974b; Schepers and sibma, 1976).
Annidation in space may occur where leaf canopies of the intercrops occupy different vertical layers and the tallest component modifies the microclimatic conditions of the other (Aiyer, 1949;
Baldy, 1963; Hadfield,1974). Another potential annidation in space where LERs may increase concerns the root systems. Component crops may exploit different layers of soil Whittington and O’Brien, 1968; 22
Trenbath, 1975b).
Other yield advantages have been attributed to the utilization of fixed nitrogen by a non-legume intercropped with a legume when the legume mature earlier than the non-legume (Centro Internacional de
Agriculture Tropical, 1974; Finlay, 1974; Wien and Nangju, 1976).
Yield Advantages also been attributed to better weed control through intercropping (Harwood and Bantilan, 1974; Rao and Shetty,
1977), and, although controversial, to better control of pest and deseases by the intercropping system (Baker and Norman, 1975; Batra,
1962; Trenbath, 1975a; International Rice Research Institute, 1972,
1975; Finlay, 1974).
Spatial Arrangement and Plant Density
Spatial arrangement and plant density are factors that are known to affect the perfomance of crops in both monoculture and intercropping systems.
In monoculture, spatial arrangement may be defined as the distribution of plants over the ground and plant density as the number of plants per unit area. In intercropping, the situation is different, spatial arrangement has to incorporate the space allocation of the two crops. Plant density in intercropping also poses some confusion because it has two aspects, and though interrelated, they may have quite distinguishable and independent effects. One aspect is total plant density or the combined density of all component crops.
This determines the overall pressure on resources, and consequently, the extent of their use. The second aspect is the density of 23
components, which relates to the ratio of intercrops.
Spatial arrangement and plant density are bound to affect the geometry of plant spacing and leaf distribution, and these in turn, would affect light penetration into the canopy as well as to the shorter components.
In intercropping, the intensity of the interaction between the components, therefore, would depend on the proportion of interplant contacts between individuals of the different components. This would imply that, by choice of appropriate plant arrangement for the components, one could maximize favorable interactions between them.
In most situations where the ratio of component crops is the same, and the intercrops are planted on alternate rows with constant row width, the proportional areas allocated to them are equal. But, this relationship can be changed in order to reduce interspecific contact. Research has shown that, where the dominant crop is allocated a relatively smaller proportional area by grouping its rows close together, its competition on the dominated crop is reduced.
This has been found to increase yield of the dominated crop, while at the same time maintaining yield of the dominant crop (cereal), better than if the dominant crop's population density was simply reduced (All
India Coordinated Research Project for Dryland Agriculture, 1972;
Freyman and Venkateswarlu, 1977; Singh, 1977; Singh et al., 1973)*
There are some contradictory reports on how intimate associated crops should be. Andrews (1972) and IRRI Research (International Rice
Research Institute, 1973) suggests that maximum benefit from any complementary effects can accrue if crops are as intimately associated 24
as possible. Other investigations show that increasing intimacy has no effect (Evans, I960; Herrera and Harwood, 1975), but, in cases where the lowest components are susceptible to shading, it has reduced
their yields (Osiru, 1974). Osiru (1974), in the same context,
reported that where intimacy of components was less the light
penetration to the lower component was improved and yield advantages
occurred.
There is evidence that, for many intercropping situations,
utilization of resources and therefore, yield advantages, are
maximized where total plant density is greater than that which is
optimum for the components as sole crops (International Rice Research
Institute, 1974; Osiru and Willey, 1972; Willey and Osiru, 1972).
This seems most likely to be so where there are large temporal
differences in the growth patterns of the components, as was suggested
by de Wit (I960). In this situation, the intercrops utilize a greater
total amount of environmental resources. This would seem to indicate
that the advantage is not at its maximum until there is sufficient
intensity of competition between the species to make them fully
utilize their respective parts of the environment. But one problem
observed is that, when total plant density is increased, a dominant
crop may become even more dominant, even though the ratio between the
component plant density remains constant. However, Harper (1961) has
stressed that increasing plant density does not necessarily increase
the advantage of a more competitive species. 25
An important aspect which has emerged from recent experimentation is that where intercropping gives a yield advantage, the total population optimum may be higher than that of either sole crop
(Herbert & Putnam, 1982).
When the space allocated to component crops is directly related to component populations, the intimacy of the arrangement can still vary. It has often been suggested that to get maximum benefit from any complementary effects, crops should be as intimately associated as possible and there have been experiments which support this (Anderson
& Kassam, 1975; Herbert & Putnam, 1982).
Varying the component plant densities may change the interaction relationship between the component crops. In fact, observations have indicated that increasing the density of a crop may increase its relative competitive ability (Lakhani, 1976; Osiru and Willey, 1972).
The importance of high component plant density has been demonstrated. Osiru and Willey (1972), using the replacement series technique, examined four plant densities of maize and beans as intercrops. They estimated the optimum plant density of pure stands of maize by yield determination. In the higher maize plant densities, the maize was replaced by beans to bring it nearer its optimum plant density. Results showed that where one third of the pure maize stand was replaced by beans, the yield of maize remained good. In fact, any yield of beans was, in effect, a bonus, thus resulting in a high level of total yield. They also reported similar results using sorghum. In these experiments, when competitive ability was analyzed, they found that, regardless of the maize density that remained after replacement 26
by beans, maize remained dominant. But, when sorghum was used instead of maize, they found that when two thirds of sorghum was replaced by beans, the beans achieved greater competitive ability and reduced the yield of sorghum markedly. These effects were attributed to the heights of the cereals, tall maize and short sorghum, which contributed to the shading effect on beans.
Effect of Shade
The energy required by plants for different growth functions is derived from photosynthesis, which, in turn, depends on light. Watson
(1971) observed that the output of the photosynthetic system, and the potential supply of photosynthate to the useful plant parts, depends on how much of the light falling on the crop is intercepted by leaves.
Shibles and Weber (1965) found that the rate of dry matter production in soybean was linearly related to percent of light interception, with a LAI of aproximately 3.2 needed for 95% interception. Depriving plants of light, therefore, may cause stress. Donal (1963) reported that competition for light may occur whenever one plant casts a shadow on another, or within a plant when one leaf shades another leaf.
Several authors have indicated that leaf display, rate of leaf surface expansion, maintenance of leaf area and plant height are some of the morphological and physiological characteristics that would contribute to competition for light energy (Black, I960; Aquino, 1968; Donal,
1961 and Trenbath, 1976). 27
Shading legume plants has been observed to change their
morphological and physiological responses and interactions with the
enviroment. Crookston et al., (1975) reported that shading soybeans
caused them to grow tall and to have fewer stomata per unit leaf area.
Hedley and Ambrose (1979) using different degrees of artificial
shading, observed that, at high degrees of shading, pea (Pisum sativum
L) relative growth rate and biological and economic yield were
significant reduced. Dart and Mercer (1965) reported that, among
•* other factors in a controlled enviroment, cowpea root nodulation, dry
weight production and plant combined nitrogen uptake were controlled
by light.
There are numerous reports of shading on soybeans. Johnston et
al., (1969) and Lawn and Brun (1974) showed that shade reduce soybean
photosynthesis. It has been observed that, when soybeans are
subjected to inadequate light or shade during flowering, pod and
flower abortion is a common phenomenon (Howell, I960; Mann and
Jaworski, 1970; Carter and Hartwig, 1962). Other reports show that
lodging and reduction of seed set (Mann and Jaworski, 1970; and seed
yield (Beets, 1977; Singh et al., 1973; Mohta and De, 1980; Dalai,
1977; Prine, 1979; and Wahua and Miller, 1978).
Intercropping species which usually differ in height, leaf
distribution in space, and other morphological characteristics, may
cause plants to compete for light energy. Research has shown that,
although mutual shading is inevitable, the shorter crops in mixtures
have been found to experience the greatest shading effect from the
taller component crops. Searle et al. (1981) observed a great 28
reduction of solar radiation reaching the top of legumes, soybean and
groundnut ( Arachis hypogaea L.) when they were intercropped with maize. Evans (I960) also found that, even when maize was planted on a
alternate rows and in groups, the shade provided by maize to the groundnuts still reduced the yield of the legume significantly.
Similar results were obtained by growing maize and cowpeas in
alternate rows, same rows and the same hill (Agboola and Fayemi, 1971;
Mongi er al., 1976; Dalai, 1977) found that the poor perfomance of
soybeans in a maize intercrop was due to the reduction of
photosynthetic photo flux density by maize. Although most of the
shading effect in an intercropping is imposed upon the undercrop
species, Enyi (1973) and Wahua and Miller (1978) reported that a
observed grain yield reduction of sorghum in a soybean intercropping
was probably mainly due to reduction of photosynthesis of the lower
leaves that were shaded by the soybean canopy.
The energy for N2-fixation is derived from photosynthesis. Using
artificial shading, Wahua and Miller (1978) and Lawn and Brun (1974)
observed that the ability of soybeans to fix nitrogen was reduced.
This same phenomenon was observed when maize was intercropped with
calopo, greengram and cowpeas (Algboola and Fayemi, 1971) beans
(Graham and Rosas, 1978) and groundnuts and soybeans (Searle et al.,
1981).
Shading another plant might change its competitive ability. Hall
(1974) stated that a plant shaded by its neighbors to an extent that
light is limiting its growth may, by virtue of its reduced
development, have a smaller root system and, hence, possibly be "less 29
competitive” for minerals and water. Hall (1974) also pointed out that shading one plant by another could render the local temperature regime either more or less favorable, and so further affect the growth process.
The adaptive characteristics of the shaded species or crop spatial arrangement manipulations by man may alleviate the problem of light competition in mixtures. Extension growth of internodes
(Trenbath, 1974) leaf blades (Kamel, 1959) petioles (Clark, 1975) and fewer branches (Cohen, 1969) are some of the characteristics of shaded plants.
Trenbath and Harper (1973) reported that when shorter types of oats ( Avena sativa L.) were interplanted in a mixture with taller ones, the shorter types grew taller than in monoculture. The stem extension facilitated more light interception, and calculations indicated a gain of 20$ in average weight per seed over that which would have been realized by nonelongated plants. Osiru (1974) observed that, with increasing intimacy in an alternate row arrangement of sorghum genotypes of different heights, the shorter genotypes grew very poorly and overall yield decreased. But, when these genotypes were in less intimate arrangements, the shorter genotypes yielded better and yield advantages were realized.
Pendleton and Seif (1962) observed similar effects with maize genotypes. Cohen (1969) summarizing the shade influences of adjacent plants, stated than competitive stress is exerted on a plant by the spatial arrangement and the phenotype of the surrounding plants. 30
In summary, intercrops in maize seem to be poor competitors for light mainlly due to their shorter stature, allowing maize to shade them. This fact is supported by (Whyte et al., 1953), who indicated that the yield reduction of legumes in a maize intercrop was due to the reduction in photosynthetic photon flux density, which reduced the rate of their photosynthesis.
Nitrogen in Crop Mixtures
Cereal—legume mixtures have formed very important combinations, and, with the high cost of nitrogen fertilizer, they are likely to
continue to do so (Willey & Lakhani, 1976). The component of a
mixture may be complementary in a spatial sense by exploiting
different layers of the soil with their root systems. Roots of maize
are longer and denser than those of cow-peas and soybeans
(S.U.Remison, unpublished) and presumably exploit resources at lower
soil levels. Components of a mixture may also complement each other
nutritionaly, one requiring much of an element of which the other
component needs little (Davis & Snayou, 1973)*
There is a belief that intercropped cereals benefit from of
nitrogen transferred from the legumes. In fact, research has revealed
that tropical legumes are capable of excreting nitrogen during growth
(Agboola & Fayemi, 1971, 1972), and there are some findings where
non-legume yields has been increased when intercropped with a legume
compared to when sole cropped, even when high levels of nitrogen have
been applied (Centro Internacional de Agricultura Tropical, 1974;
Finlay, 1974; Wien & Nangju, 1976). Although reports of Vallis et al. 31
(1967) and Wahua & Miller (1978) indicated lack of evidence for direct transfer of microbially fixed nitrogen from the legume to non-legume in a mixture, the beneficial effects mentioned above are found to be dictated by time. Investigations have shown that the benefit accrues depending on the relative growth patterns of the intercrops. That is, when the legume mature earlier than the non-legume, the nitrogen from the mineralized, sloughed-off and dead nodules and roots may be transferred to the non-legume of longer growth duration (Walker et al., 1954; Trumble & Shapter, 1973; Agboola & Fayemi, 1971, 1972;
Henzel & Vallis, 1977).
Competition for soil nitrogen between cereals and intercropped legumes seems indisputale. This is because legumes have been found to demand more nitrogen than they can supply for themselves by
N2-fixation. Ezedina (1964) and Pate & Dart (1961) reported that cowpea relies on mineral N early in the growing season before nodules are sufficiently developed. In support to this view, Eaglesham et al.
(1977) indicated that cowpea can only fix about 8056 of its nitrogen needs. Dart et al. (1977) also showed that cowpea needed some soil nitrogen in order to obtain early vegetatitive growth and maximum seed yields. Some studies on soybeans also have led to the conclusion that symbiotic N2-fixation must be supplemented with combined N from the soil or fertilizer for maximum growth and yield (Alios & Bartolomew,
1959; Fred & Graul, 1916; Norman, 1974; Norman & Krampitz, 1945; and
Thornton, 1946). Maple & Keogh (1969) increased vegetatitive growth of soybeans with 9 and 18 kg N application in southern type plants. 32
However, application of N fertilizer could have detrimental effects on intercropped legumes. Some investigators have shown that fixation of atmospheric nitrogen by soybeans and other legume crops is usually reduced when inorganic nitrogen is added to the soil or rooting medium, due to the inhibition of nodulation and loss of nodule efficiency. They have also observed that the amount of symbiotic N produced is inversely related to the amount of combined N available
(Orcutt & Wilson, 1935; Norman & Krampitz, 1945; Virtamen et al.,1947;
Allen & Baldwin, 1954; Moustafa et al., 1969; Hardy et al., 1971;
Harper & Cooper 1971; Johnson & Hume, 1972).
Dalai (1974) showed that, although in an intercrop of maize and pigeon peas [ Cajanus cajan (L.) Mill ] the legume responded to N application up to 20 kg N per hectare, the amount required by maize for maximum grain yield (200 kg N/ha) would have adverse effects on the grain yield of pigeon peas when they are grown together. It has also been shown that, on low nitrogen soils, the non-legume is either suppressed (Stern and Donal, 1962) or has little advantage (MacLeod and Bradfield, 1963), but on high nitrogen soils the strong growth response of the non-legume usually causes it to dominate the legume by snading it (Tranble & Shapter, 1937; Stern & Donal, 1962; Searle et al., 1981).
Shading of legumes in an intercrop may augment the N2-fixation problem. In shaded legumes, especially where degree of shading is hlgn, M2-fization has been found to experience severe reductions (Dart
4 Keroer, 1965; Weber, 1968; Mann 4 Jarworski, 1970; La wn & Brun,
1974; Graham 4 Rosas, 1978). Intercropping soybean with a tall 33
sorghum showed that N-fixation was reduced 99% due to reduction in number of nodules per plant, weight per nodule and specific nodule activity (Wahua and Miller, 1978).
The problem anticipated from nitrogen fertilizer application in a legume intercrop is seen to be confounded with the competitive ability of a legume for soil nitrogen. Henzel & Vallis (1977) found that legumes are generally weaker competitors for soil nitrogen than are non-legumes during early growth. On the other hand, depletion of soil nitrogen by a cereal may stimulate nodulation, and, therefore, enhance
N2-fixation (Hinson, 1975; Criswell et al., 1976).
Maize requires a heavy nitrogen application for maximum grain yield (Beets, 1978; Dalai, 1974). This fact, together with lack of evidence for direct nitrogen transfer in a cereal-legume mixture, would mean that nitrogen fertilizer application in a maize intercrop would be indispensable. Kurtz et al. (1952) observed that, where water is not limiting, sufficient nitrogen fertilizer reduces the competition between maize and intercropped legumes and grasses.
However, a decrease in a legume yield is a common observation in a cereal-legume mixture.
Dalai (1977) found that the reduction in soybean yield that occurs when it is intercropped with maize was not alleviated by the application of nitrogen. Searle et al. (1981) and IRRI research
(1974) showed that the reduction of intercropped groundnuts and soybean increased with increasing N levels as the balance was shifted in favor of maize. Another report by Dalai (1977) showed that where N fertilizer was applied in an intercropping system, both total grain 34
yield and maize grain were always higher, whereas soybean yield was not different compared to plots where no N fertilizer was applied.
In summary, legumes in cereal intercrops seem to experience direct competition for soil nitrogen, and the shading effect from cereals impairs their effectiveness in nitrogen fixation. The nitrogen fixation problem is enhanced by the application of nitrogen fertilizer. There could be two reason underlying this phenomenon.
One is that the fertilizer reduces the nodulation of legumes and, secondly, it could stimulate the vegetative growth of the cereal, thus increasing the shade on the legume and, therefore, resulting in inhibition of nitrogen fixation. If these two aspects are concomitantly experienced, then the legume perfomance could be increasingly jeopardized, as is usually observed in most intercroppings. It is likely that, given these conditions, the legumes might be in such a high demand of the N supply that there is no likelihood of some N excretion to benefit the component cereal crop.
On the other hand, if the legume in a mixture fixes N2 effectively, and if it is assumed that the legume would not compete for N, then the cereal environment might be changed.
It is likely that in such a situation, if the cereal-legume mixture was sown at the same total plant density as that of the monoculture, each cereal plant might have a larger supply of N than in monoculture, as the legume supplies the major portion of its needs from atmospheric N2. Therefore, under limiting N conditions, a yield advantage from cereal-legume mixtures could be expected. 35
The beneficial effects of legumes in cereal intercrops are likely to depend on relative growth patterns. Because evidence for any direct benefits is far from conclusive, it is likely that, despite the enhanced decrease in the yield of legumes due to N fertilizer
application, the use of N in cereal-legume mixtures will continue
because the reduced yield of legumes is usually more than compensated
for by the increased yield of the cereal, and higher total grain
yields are realized.
Weeds and Intercropping Systems
Most intercropping systems were designed to utilize the spatial
arrangement and time dimension more completely (Willian & Chang,
1980). For instance, Asian farmers normally combine mixtures of crops
having broad and narrow leaves or horizontal and vertical canopy
arrangements, with varying maturity or harvest dates in either mixed,
row or strip-intercropping systems. Weed emergence and growth were
suppressed following the formation of the crop canopies due to the
more competitive planting patterns.
In 15 experiments, Staniforth and Charles (1956) found that weed
infested planting averaged 248 kg/ha approximately 10 percent of the
weed-free beans when weeds were grown the entire season. As
illustrated, the dry weight total for purslane ( Portulaca oleracea )
and goose grass ( Galium aparine ) was about 2.1 kg/m2 in corn alone;
it was 0.9 kg/m2 weeds in mungbeans alone; and 0.3 for weeds in corn
plus mungbeans. 36
The modern and sound management strategies were designed to minimize competition and enhance complementary species within the agro-ecosystem (William & Chang, 1980).
Nutrient and Water Competition
According to Kurth et al. (1952) generally all nutrients excepts nitrogen and water in the soil are immobile. It has been shown that a soil must contain 150 ppm of exchangeable potassium for maximum yield of corn. A soil fertile for a maximum corn crop should also be capable of supplying these nutrients to an intercrop without greatly affecting corn yields. A crop growing between the rows of corn will compete with corn for the mobile nutrients such as N and water. If the soil contains just enough N for a full corn crop, then an intercrop will reduce corn yield to the extent that it competes with corn for N provided water is not limiting. It follows then, that within rather wide limits, the competition between a corn crop and an intercrop can be reduced to a minimum by the use of N and water.
Natarajan and Willey (1980), tested sorghum-pigeon intercropping.
The total water use was affected very little by cropping system.
During the sorghum growing period, total water use by sole sorghum, sole pigeonpea and intercropping, was 434, 430, and 417 mm respectively; after sorghum was harvested, it was 154 and 168 mm for sole and intercrop pigeonpea, giving virtually identical seasonal totals of 584 and 585 mm for these two treatments. Nutrient uptake on a whole plant basis, the N concentrations of sole and intercropped sorghum showed no significant differences at any of the five sampling 37
times. In contrast, the P and K concentrations in earlier samples were higher in the intercrop (and occasionally significant), suggesting that at this stage the sorghum was more competitive for
these nutrients. CHAPTER III
MATERIALS AND METHODS
1982 Field Study
The experiment was conducted during the 1982 growing season at
the University of Massachusetts Agricultural Experiment Station Farm
in South Deerfield at 42 degrees 27 minutes north latitude 72 degrees
35 minutes west longitude at an elevation 146 meter. Growing season
precipitation for 1982 was 511 mm from May-September (Table 1). The
soil was predominantly a Hadley fine, sandy loam (Typic Udifluvent). •
Cornell 281 field corn was intercropped with Williams soybeans consisting of treatments in a modified factorial randomized block design, with planting pattern and corn density as variables, forming
the complete factorial and a single soybean monoculture treatment
creating the modification. The planting patterns, as described in
Table 2 were as follows: 1. Soybean alone planted in double rows 35 cm apart on 91 cm centers (soybean-soybean). 2. Corn planted alone
in rows 91 cm apart (corn-corn). 3« Corn and soybean in a 50/50 ratio with third and fourth rows of corn replaced by two double rows,
35 cm apart. 4. Corn and soybean in a 50/50 ratio with alternate
rows of corn replaced by a double row of soybean 35 cm apart.
38 39
TABLE 1. Rainfall 1982 and 1983.
MONTH RAINFALL
SOUTH DEERFIELD BELCHERTOWN & SOUTH DEERFIELD 1982 1983
nun
MAY 74 140
JUNE 226 58
JULY 107 64
AUGUST 68 59
SEPTEMBER 76 61
TOTAL 551 382 TABLE 2. Treatments planting patterns and densities forming a replacement series. Two rows of soybeans replace one row of corn when intercropped-1982. X H >—( Du < Z Z O Ou H < H w aS z Q Z C/3 M H >* w CJ o 2 z CO >* O CQ 25 z o 3 s H Q X M o X U-l | Q. 03 'J3 B o w C 1 O 3 1 1 1 1 1 1 I l 1 1 :v t¥ : v oo m ON 00 sC »—H CN 1 • • • ¥ ¥ ¥ t •- 00 v£> ON rH CN 00 • • sO tn CN 00 00 • • CJ e 40 41
The soybean population was held constant, 18 plants/meter of row which is equivalent to 395,360 plants/ha in monoculture. Three densities of corn were plantedslow, medium, and high with 5.9 > 8.6 and 11.2 plants/meter of row. This corresponds to 64,246, 93>898, and
123>550 plants/ha in monoculture. These variables were factorially
• combined as follows: 3 corn populations x 3 planting patterns involving corn plus one soybean monoculture x 4 replication = 40 plots.
Both corn and soybean were planted on 20 May. The corn was overplanted to 7.4 (low), 10.8 (medium), and 14.1 (high) plants/meter of row. After two weeks of emergence, corn was thinned to 5.9 > 8.6, and 11.2 plants/meter of row respectively. The soybeans was overplanted to 22 plants/meter of row and then thinned to 18 plants/meter of row.
The rows were oriented in a north-south direction to receive maximum light. Corn was planted using a cone-type seeder. The soybean with a 90 percent germination were inoculated with Rhizobium japonium prior to sowing and fertilization. They were mechanically planted with a cone-type seeder.
Weeds were controlled by a preemergence application of 1.7 kg/ha-1 a.i. alachlor ((2-chloro-2*, 6*-diethyl -N- (Methoxymethyl) acetanilide) and 0.85 kg/ha-1 a.i.linuron (3- (3> 4 - dichlorophenyl)
-1- methox -1- methylurea).
Prior to planting, nitrogen, phosphorus and potasium were applied at the rates of 153-3 N kg/ha, 35.2 P kg/ha, and 100.5 K kg/ha respectively. 42
Corn and soybean densities in the intercropping were part of a
replacement series. They were directly comparable to the monocultures
on a row equivalent basis rather than a land-area basis. Plots were
7.62 meters long by eight (row-equivalent) rows wide.
During the growing season, samples of corn and soybean were taken
every two weeks, beginning 9 June, 29 days after sowing. Each sample
consisted of 36 cm (0.33m2) on a simple corn row and on a double
soybeans row. The samples measured were as follows: 1. Fresh weight.
2. Leaf area. 3« Leaf, stem and pod dry weight. 4. Height. 5.
Growth stage..
Leaf area measurements were taken on all soybeans and corn leaves
using a Licor Li-3100 area meter. Height was measured on soybean from
the ground to the growing point and on corn from the soil to the
tallest leaf or tassel.
Final harvests were measured on 14 September. Total harvested
area for each plot of corn and soybean was 2.73 meters of row (5m2).
Plant number, plant height, ear number and ear weight (first and
second ear), fresh weight of corn stover and fresh weight of soybean
plants were recorded. For dry matter determination, subsamples of
corn ear, corn stover and soybean plants were taken. Finally a
soybean subsample of 15 plants was taken for determination of fresh
weight, height, pod weight, node number, branch number, and growth
stage.
Corn and soybean subsamples were dried and weighed, then ground
to a 1mm size. Crude protein determination was made separately for
each yield component of corn and soybeans (kernel, cob, stover, for 43
corn and pod, stem, leaves for soybean), using the macro-Kjeldahl method.
The variables were analyzed using analysis of variance and single degree of feedom comparisons. There were 9 comparisons for the total yields, 8 comparisons for corn yields and 6 comparisons for soybean yields.
1983 Field Study
In 1983, identical experiments were conducted at two sites at the
University of Massachusets Agricultural Experiment Station Farm in
South Deerfield at 42 degrees 27 minutes N latitude, 72 degrees 35 minutes W longitude at an elevation of 146 meter. and at the
Belchertown State School Farm in Belchertown at 42 degrees 16 minutes
N latitude, 72 degrees 25 minutes W longitude at an elevation of 152 meter. Average growing season precipitation for South Deerfield and
Belchertown was 382 mm and 405 mm from May-September respectively
(Table 1).
The soil in South Deerfield was predominantly a Hadley fine, sandy loam (Typic Udifluvent) and in Belchertown the soil was a
Ninigret fine, sandy loam (Aquic Dystrochcept). Both sites were planted with Cornell 281 corn intercropped with Williams soybeans
(maturity III group) in a corn-corn-soybean-soybean pattern along with corn and soybean monocultures, with nitrogen rate and method of 44
application as additional variables Figure 1. A modified factorial, randomized block design was used. The variation in nitrogen rates between the two intercrop application methods described below, created the modification for the complete factorial. The corn and soybean in
South Deerfield were planted on May 17, 1983 and in Belchertown on May
18, 1983.
A basal application of 15 kg/ha of nitrogen fertilizer was distributed in all plots prior to planting. For the monoculture and one of the intercrop the nitrogen rates were 0, 90 and 180 kg/ha. The
i remaining intercrop treatment had three rates of nitrogen (45, 90, 180 kg/ha) applied only between the corn rows, thus the effective rates
available to these corn rows were 90, 180 and 360 kg/ha, since the
soybean occupying half the cropped area received zero nitrogen (Table
3). The nitrogen applied after planting was spread across soil
surface beneath the plant canopy.
Corn population was high density, 11.2 plants per meter of row
(equivalent to 123,550 plants/ha) and soybean population was 18 plants
per meter of row (equivalent to 395,360 plants/ha).
The rows were oriented in a north-south direction to receive
maximum light. Corn was planted using a cone-Type seeder. Soybean
seeds with 90$ germination were inoculated using a peat-based granular
inoculant containing Rhizobium japonium prior to sowing and
fertilization. They were mechanically planted with a cone-Type
seeder. 45
T3 C 03 a < G) S-i 4->3 r-H 3 0 o c o e c w c (0 0) ua >. o • w ^ u T3 —' C 03 m c C 3 U Q) O 13 U >i O V4 CO o y-1 T3 c W (0 £ 0 c i4 S4 o 4-1 O 0 03 4-> O C 04 Weeds were controlled by a pre-emergence application of 1.7 kg/ha-1 a.i.alachlor ((2-chloro -2f6’- diethyl -N- Methoxymethyl) acetanilide) and 0.85 kg/ha-1 a.i.linuron (3- (3> 4- dichlorophenyl) -1- methoxylurea). Before sowing, both areas were fertilized at the rates of 49kg P/ha, 93kg K/ha and 3,628.8 kg/ha of lime. Ammonia nitrate was weighed and divided in plastic bags, then was equally distributed and applied between the corn and soybean rows except for one intercropping treatment where it was applied only between corn rows. Corn and soybean densities in the intercropping were part of a replacement series. They were directly comparable to the monoculture on a row equivalent basis rather than a land-area basis. Plots were 9.1 meter long by 6 (row equivalent) rows wide for monocultures and 8 (rows equivalent) rows wide for intercropping. The following parameters were measured biweekly from a 0.33m2 sample of corn and soybean: 1. Fresh weight. 2. Leaf area. 3» Leaf, stem and pod dry weight. 4. Height. 5. Grow stage. Leaf area measurements were taken on all soybean and corn leaves i using a Licor Li-3100 area meter. Height was measured on soybean from the ground to the growing point and on corn from the soil to the tallest leaf or tassel. Final harvests were measured on 17 September for South Deerfield and 18 September for Belchertown. Total harvested area for each plot of corn and soybean was 2.73 meters of row (5m2). Plant number, plant height, ear number and ear weight (first and second ear), fresh weight of corn stover and fresh weight of soybean plants were recorded. For 48 dry matter determination, subsamples of corn ear, corn stover and soybean plants were taken. Finally, a soybean subsample of 15 plants was taken for determination of fresh weight, height, pod number, node number, branch number and growth stage. Corn and soybean subsamples were dried and weighed, then ground to a 1mm size. Crude protein determination was made separately as follows scorn stover, ears and soybean plants. The method used was the macro-Kjeldahl. The variables were analyzed using analysis of variance and single degree of freedom comparisons. There were 11 such comparisons for the total yields and 8 comparisons for the separate corn and soybean component yields CHAPTER IV RESULTS AND DISCUSSIONS 1982 Results Forage yields of density treatments and diverse planting pattern are shown in Table 4. Corn monoculture yields were more than twice those of soybean grown alone. After analysis, significant differences in corn monoculture yields at the three densities (low, medium, and high) were not found. Intercropping densities augmented the yield from low to high. In the high intercropping densities there were significant differences between the two intercropping patterns. Total yields (from 40.4 to 52.5 t/ha 70$ moisture) were lower in intercropping compared to corn monoculture(54.8-55.6 t/ha). Ear yield of the area planted to corn was greatly enhanced in intercropping especially at high densities with a increase of 32$ and 63$ in the corn-soybean pattern at the medium and high densities respectively compared with corn alone (Table 5). Intercropped corn plants produced heavier ears and kernels, greater number of the first and second ears and more kernel/row than monoculture (Table 5,6,7). In both intercropped patterns this effect was enhanced by increased density as compared with corn monoculture. Soybean yield and pod 49 TABLE 4. Silage yield and percent soybean in the final yield mixture-1982. CO w o H o w J a K C4 CO w « u W 2 o Eh >h OQ w 2 &H a M c a, < Eh w a< X < Eh 2 2 o co co CO u CJ U I U I CO u CO CO U u u CO Eh CO CO CJ 2 >• i I I 1 1 1 1 1 l \ p X 05 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0M m O I r—IVO>H 1 • •'T 1—1 ■nor- CN CO o CJ 05 w CQ ¥ 2 *P % o ■*r oc 88 88 2 cn V oo o •%. • • «>. • u 2 1 — cn ^ cn rH p s ? o o > 05 o § o § < Ml 8 04 >1 63 n V 00 ~8 5 u I n- 00 o g i g & a) s 2 >i A >. 05 ft1 *8 63 X I >1 g * g ■p o Eh •H 8 W I V < g & 21 8 o 2 co CO CM M • • 6 in r- in Eh in m co cn co 2 < i-3 a CU CO CM I CO u o cn oc 6 cn CM in *IT> 05 cn < 4J 63 m 8 1 co u-» UJ r- o CM a a CM CO cn o> o +J 4-> m M-l MH •H •H Ed & M & & t-3 CO •H 03 D 5 CO < w Eh SB X TABLE 6. Ear number per plant and dry weiqht per ear-1982. 04 < o z Eh M z cx < Eh os E-< w z < OS 2 w D y os o Z < OS w M Eh CO a s K w u V U g u g CO CO ¥ CO co u co T u T I 1 1 I i \ JU i—i 4-> ? in d3 Sh tX> I j I 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 •H H in CD CD in £ CN CTV co in CN co • • o rr CN o ov rH m o m rH in CN VO Q 5 CO g £ • • 00 00 <7\ <7\ o 00 a> rH VO rH CO VO CO VO CO a • •H •H •H Hh U-l •H •-HSh CO 4-J o u 4J .+Jp j-o 3 Ml 04 in 4-) 8 o s C 0) CD 03 a gw I 03 > in c 0) Sh o S' rH 4J o -hy O >(r-j VII 050 Nl c •H •H •H M-i Ml CO 4-1 ■H Ml c O 0) O U Si 04 M 04 -H 4-> CP o 4J X o So s in £ & u C co c 03 — c • sQ, c cn • . > • Sh S! 04 52 TABLE 7. Kernel dry weight and kernels per row-1982. & PI < 2 Eh H 2 O CX < Eh Eh W « 2 w w PI ++ o X Eh H •H •H co •H «p X> c CP •H a o Q •H x> +j PI H cx o o .—* Ml 8 \|| O -H P XI 3 PI P -H a) c O pL, H 18 ^ 4J CX 4-> c 'll (T3 cn p Cp c ++ • • X) •H •H CO •H UH CP c XJ ■—• 8 cn • -H cx Ml o W (U P c s X) H -H 0 XI c 0 o '- p a cn yields were depressed in the intercrops and with increased corn densities compared with soybean monoculture. The soybean and stover yield and the greater kernel yield in the intercropping augmented yield quality of the mixtures. The forage composition (dry basis) for all treatment combinations are given in Figure 2. In corn monocultures, there was no significant effect of corn density on forage composition. In the intercrops, the increased weight of ears and number of ears compared with monocultures (Table 5) resulted from a increased contribution of kernels to the total forage mixture with increased corn density. The greatest yield contribution for the total forage mixture was produced by kernels, while corn stover and cob in intercropping remained relatively constant across corn densities. i The final percentage crude protein of the yield mixture reflected changes in the percentage of soybean in the silage (Figure 3 and Table 8). The corn-corn-soybean-soybean row pattern at low corn density elevated the percentage of protein in the silage to 10.3% with a increase of 47.1% compared to the best corn monoculture treatment. A larger protein content is found in the corn-corn- soybean-soybean pattern, making this pattern more attractive for the yield goals of this research. Percentage of crude protein of the soybean monoculture was significantly greater than the corn monoculture or intercrops. There was a signicant linear effect for percentage protein for both density and planting pattern. Soybean produced significantly more protein than corn alone. However, some of the intercropping treatments produced higher protein rates than 55 56 soybean grown alone (Table 8). The contribution of the any given component to the total protein production of the cropping system is a function of both the % protein of the that component (showed in Figure 3) and its yield. Soybean contribution to protein yields of the intercropping decreased as density increased. While contribution of the kernel component increased with higher densities, corn stover, cob and second ear component contributions remained relatively constant. Pod and kernel components had the highest crude protein contents of the two species and contributed to over 60% of protein yield (Figure 3)« Total corn, ear, and soybean yield components of the silage obtained in intercropping can be compared to those expected if the intercrop competition was the same as the intra-crop competition (Figure 4). Corn intercropping yields were more than expected, while soybean yields were less than expected from equivalent proportions of monoculture corn and soybean. The intercropped corn yield more than compensated for the loss in soybean yields, with the result that the total yield mixture was greater than expected in all cases. A stricter test of yield advantage is comparison of treatments on a harvested proportion rather than on a planted proportion (Willey, 1979). The yield advantage for low density treatments shown in Figure 4 does not appear in corn-corn- soybean-soybean pattern when the treatments are compared with sole crops on a harvested ratio basis (Figure 5). However, all of the intercrops rendered more yield than expected from monocultures at the ratio of corn:soybean in the harvested intercrop mixture except for the low density TABLE 8. Percent crude protein and crude protein yields on a dry matter basis-1982. ++ M PI Eh Q O o 04 >4 04 U 2 Eh U § Q 04 05 Eh w D Q a g W H W 05 W W a 04 tJ < 2 Eh H 2 O 04 < E-i OS Eh W 2 CO u u CO CO u u CO CO u u CO u CO CO CO CO u u u H 2 CO Eh >4 1 1 1 1 1 1 I 1 1 1 1 1 1 \ X <#> 03 1 1 1 1 1 1 1 1 1 I 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 i } 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 rH rH 00 O r~ mill m 1 1 1 • rH iH rH rH co a> rH CN cn rH rH VO m I—1 o PJ O 2 00 o o 1 • • • U M P a -3 4J II 10 ■u c s 3 a 5 >i u J-l o 'O 4J y-i fl 01C '4-io c C O >1 O 0,-P E -H T3 O U3 rH O C O O •H>< iu T3 .0 P sac •pmu ua P O -P O >p p cu c c ipm Pm *H10 -u P 0 P GJ P c a a OOP p e a masO -C p c c * a -h cn 3 0 p o -p a AO C oE toP P a a 73 JC P HU O a -w -P *J >iCU a a m m a 3 a a o p x •h am p a 3 p ^ > w c c a s p r. c a -p .c p p m p3 0 m a, p c a 0 .c c •P g ■ H P 3 -P 3 Z C JO 3 •p • —l • p m a -3 P *p c c m p 3 0 3 0 0 U -0 -1 p (san^STOUi %oL})CTC3IA< PLANTING PATTERN 1 r-i o rH o <*p (JP U CO o os >H z ca o o lo un o o o & w os w o CO OS M CL CP4-> -P 3O 33 3 3 Oa-p C 4Jp-H 3 33COC 3 >i-P P CO 3 CO>t 3 O-H 0 3 U <—l3 L-l E co-i Cl r-i 3 p CO 3-H o • 3-H c o 33 3 Cl rH U Cl -H O C CL -P CO 01 i—i a) 3 c E ■P ^ o C 33 •h x 0 -H O >,CW 3 -H a. 3 3 33 -P T3 P CO a) • co o co c cu CO XI C5 o *H o c c 3 h 3tr i « C XO ■P 3 CL 3 -P4J Ci 3 3 Ci 3 <+4 u 3 P -P 0 Cl o CL Cl a o 3 CL a _ 3-H i-H 3 -P O C 3 a c Cl O ■P E o c 0 O 3 p 3 a» o o e a a) i -p o Cl O CL u o E 3 59 60 X SOYKANO 20 40 60 80 100 HARVESTED MIXTURE FIGURE 5. Silage yields on a harvested ratio basis. Solid curved lines indicate yields ex¬ pected if equivalent yield proportions were obtained from monoculture. 61 corn-corn-soybean-soybean mixture. The increase in corn yields with increased densities in intercropping enhanced the contribution of the ears to the total mixture at harvest (Figure 4 and Table 9). Row equivalent yields of corn bordered by corn, soybean, or corn and soybean on either sides were measured (Table 10). Intercropped corn rows produced more dry matter than monoculture rows at all corn densities. The largest corn dry matter contribution was attained in corn ear. The corn-soybean planting pattern produced the highest corn ear yields which increased 41$ with increasing density (Figure 6 and Table 10). For corn monoculture ear yield peaked at medium density and high density declined slightly from 955 to 915 g/m2. Yields of the soybean monoculture were larger than row equivalent yield of both intercropping patterns. However, silage yield of soybean intercropping corn-soybean was higher than soybean monoculture yield at low density (Table 11). The number of pods and nodes per plant was significantly greater for the monoculture soybeans than the intercropped soybean rows (Table 11). The Land Equivalent Ratio (LER) for all intercrops were larger than 1.0 (Figure 7). Land "efficiency" increased as density $ increased, especially in the corn-soybean pattern where the highest LER was obtained at high density. 1800 1600 19 8 2 H 1400 CM I E 1200 w> 1000 800 600 cf c-c c-c-s-s c -s PLANTING PATTERN FIGURE 6. Ear dry matter yield on an equivalent row basis. 63 T3 to VO i—1 1 a) u oo r- •P ro 'sr IX o iH ia Ml •P cu 0 ■p to 1 c a) $ P 1 a) ■p u s 00 CM in ■p 1 00 'S* ■P • *p tj (0 0 CU rH 2 O 20 • o •H -H o E a (0 -P c tn cn E E- •H *H O U C QJ x: o •H U O C O 73 3 tO 3 (U , TJ • c -P o w OS r—i T3 ■p ■p OQ -H ■p u OS o x 0 0 C T3 o O 'p S -u aj= O 0 c 0 -p C 5 03 cr 5 > (13 0 >1 C 3 0 a) o1 c o m e P -P O -H 0 1982 Discussion Intercropping has been reported as one of the farming methods that is capable of increasing crop productivity per unit land area. But one common observation in this culture practice is that when unrelated economic species are mixed, they are forced to compete interspecifically for at least a part of their respective life cycles, causing a depression of the weaker competitor species. The production of total dry matter is of primary concern in a ruminant feeding program as this is the primary determinant of the energy value of corn silage (Church, 1977). However, composition of the dry matter is also of major importance as protein, digestibility, and palatability are prime factors in determining the productivity of a animal (Miller, 1979). This study was designed to minimize competition between dissimilar species through application of soil and crop management principles, i.e., by applying nutrients and manipulating spatial arrangement of maize crop to accomodate a soybean intercrop. The silage yields in corn-soybean intercropping at high density were maintained at a level similar to corn alone. In both planting patterns intercropping yields increased as density increased. The greater yield contribution for the mixtures was obtained from corn yields especially at high densities. This demonstrates the competitive ability of corn also shown by the LER and Competitive Ratio trends. Although the individual yields of the legumes, and some 68 time the maize, were reduced in the intercrop as opposed to their yields in sole stands, their combined (total) yields per unit area in the intercrop were mostly higher than planting the same relative cropped area as sole crops. This resulted in LER values greater than one. However yield compared to corn monoculture is more important in this study. The spatial arrangement of maize used severely reduced the seed yield of the intercropping soybean but caused no significant depression on the maize grain yield, a common finding in other studies showing the greater competitive ability of corn (Putnam, 1983). Aplication of nitrogen significantly increased maize grain yield, whereas it tended to lower that of soybeans, except in the monoculture soybeans. These findings have been observed by Beets (1977) and Searle et al. (1981) and many other workers experimenting on intercrops. Although total intercropped yields and yield advantages were largest compared to monocultures at high density in all patterns, there was a decrease in percentage of soybeans with increased corn densities in the mixtures. However, there was yield complementarity when intercrops were compared with monocultures on a yield-ratio basis. The intercropping planting (corn-soybean) yields of forage were superior to the yields of intercropping corn-corn- soybean-soybean. This is a finding similar to Herbert et al. (1984) and shows that the more the intercrop approaches the planting pattern of monocultures the less is the yield advantage to the intercrops. In this situation each 69 component of the intercrop is subjected to more intra-crop competition than inter-crop competition. This is detrimental to the yield compensation from the dominant crop component, corn in this case which also happened to be the higher yielding component. The average reduction (9 - 7%) of soybean yield in intercropping corn-soybean was not as large as the increase of corn yield (35.9%). The corn-corn-soybean-soybean treatment followed the same trend with a reduction of 7.6% in the soybean yield and an increase of 20% for the corn yield. The LERs were larger for the corn-soybean treatmen than for the corn-corn-soybean-soybean. This comparison of row equivalents in the different treatments and the LERs also demonstrates the complementarity that exists between the two crops in a replacement series is increased by mixing the crops more thoroughly. The corn rows bordered by soybeans produced more stover, a larger yield of ears, more ears per square meter, heavier ears, more kernels per row, number of rows per ear, and a percentage of ears higher than monoculture rows at corresponding densities. Increased corn density suppressed kernel weight in monoculture but not at all or less so in the intercrops. Kernels per row and cob weight were suppressed by higher densities in all patterns, though this was more severe in monoculture than in intercrops. There was no density effect on the number of rows per ear. The increased number of ears produced per area planted with corn was the result of more ears produced per plant in the intercrop and less of a reduction in numbers of ears per plant with increased corn densities in intercropping than in monoculture. Some of the above effects had been found earlier by Putnam (1983) and 70 this study extends this information. Cattle feeders often desire a high grain/stover ratio (Genter and Camper, 1973)• The ear component of corn ranks higher in digestibility trials than stalks and leaves. In addition corn stover is about 6.8$ crude protein, mature ears range from 9.3$ to 10.2$ crude protein (National Academy of Sciences, 1971). A high ear-stover ratio would tend to increase the percentage of crude protein in the silage, which is shown by the corn monoculture data, where medium density silage (57$) was higher in protein than low and high density (53$ and 55$ ears in silage respectively). Protein production on a land area basis was greater in the intercrops than corn but similar to soybean protein production. In contrast to the negative effect of corn density in monoculture on crude protein content, increased corn densities tended to increase or at least maintain crude protein yields in the intercrops, adding to the complementarity of the intercrop. The corn-corn-soybean-soybean intercrop at low corn density produced the highest percentage of crude protein, while the highest yield of protein was produced by the corn-soybean intercropping at the low corn density on a land area basis. Total yield in both treatments (corn-corn- soybean-soybean and corn-soybean) were 46.3 t/ha and 47.1 t/ha compared to a maximum of 52 to 56.4 t/ha for corn monoculture and some intercrops. This yield might be considered acceptable because of the higher protein content. That is some yield reduction of the mixture might be neccessary and acceptable to optimize the protein production from intercropping mixtures. However the advantages of 71 increased % protein and protein yield in intercropping must be weighed against total forage yield reductions of these systems when compared with corn silage. The soybean treatment produced more protein on a land area basis than corn monoculture or the intercrops except for the corn-soybean at low density. In the intercrops with increasing corn densities the soybean and especially the pod production to the protein yield declined. The pod and kernel components had the highest crude protein contents of the two species and contributed to over 60% of the protein yield. The fact that crude protein yields with increased densities did not decline is a result of the higher dry matter yields of the higher quality kernel component and lack of a severe suppression of the pod component in the intercrops. The protein complementarity in the mixture was due to compensation of any pod contribution loss by an increase in kernel yield. However, crude protein yield in the context of this experiment must be viewed only as biologicy. Crude protein content is a more practical measure of yield quality in this situation, as feed ration formulation for dairy cows in the United States, is based in percentage of protein. In conclusion, intercropping dry matter yields increased as corn density increased. Intercropping yields were maintained similar to corn monoculture at high densities. Mixtures of corn and soybean were able to tolerate higher corn densities better than corn alone. The ear component contribution was the best in mixtures for forage and protein. Although increases in protein were found at high intercropped densities, it must be that to optimize protein content, 72 some reduction in total dry matter must be required, a decision to be based upon the requirements of each farm situation. 1983 Results Silage yields of intercropping and monoculture treatments and N rates of fertilizers of South Deerfield and Belchertown experimental sites are given in Table 12. Forage yields in all treatments were greater for the South Deerfield site compared to equivalent treatments in Belchertown. However, mostly the trends were similar at both sites. Corn monoculture yields were nearly twice those of soybeans grown alone. Corn monoculture yields increased as N rates increased at both sites. In South Deerfield there were no significant differences in soybean monoculture yields at the three N rates, with a slight reduction at the high N rate. In Belchertown, however, soybean monoculture yields responded to N fertilizer increasing yields from the low to high N rate. Yield increase was less pronounced in the treatments where each two rows of corn were replaced with two double rows of soybeans (corn-corn-soybean-soybean). There were two sets of treatments planted in this pattern. The first intercropped plot, where nitrogen was evenly distributed, showed a increase in yield with increased nitrogen application. The second intercropped plot, where nitrogen TABLE 12. Silage yield (70% moisture) in South Deerfield (S.D.) and Eelchertown (Belch.)-1983. * 2 M o E-* os u W 2 u u cn cn u u cn cn u u cn 1 cn 1 i | i 1 i i i i i &4 U DC Eh M J M N a OS cn *H x: Q CQ cn Q i-4 xz cn xz i-4 0 cn Q 0 r—I CQ XZ cn Q 0 0 cn a) o 0 0 • • • • • • • . • • • • \ X x: \ xz A3 Cn 4-> 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 (CJ 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 O N* 00 CN ID o cn O ID CN o rH o n" Csl in in • 1 a • 1 • • • in 00 'T cn CN 00 m 1 1 1 1 1 1 • • o\ o CN in t" cn 00 cn n- o CN in cn rr r-' ID cn O i-4 ID in »H o a a a • a • • • rH 00 1 o ID m i-4 n- CN cn CN CN cn 00 in r-H i-4 ''3' 1 m | cn T in 00 cn o 00 • a a . . • 1 • • ! 1 1 I i r4 0 O 4-1 •H T3 •H T3 X! 44 i-4 •H rH •H 4-1 i-4 0 XZ P 4-> 4-1 4-1 •H C XZ >1 CO 0 O 4J CU O 54 0 0 >4 4-> •H C 54 >4 3 o CO S 54 4-1 0 -H O CO > 0 0 0 3 C 0 54 XZ 0 Cn ■p 0 z c xz 0 54 N CD 54 U CT3 3 cn 0 0 o > 0 u 0 0 c CO 0 0 •rH •H •H 4-i 4-1 fj 4-1 --. in Q TJ •H 2 c 0 CO PS 4-1 o &, in O cn 0 aa 4-5 ° VI o c VI ~ X) cn xz O 0 ■P aa 0 CT cu 0 54 0 o 3 o 1 0 >lM 0 c > cn 0) u cn a a M ■P 4-> cu 0 54 CN 3 > cn -p 54 o a) C 0 54 O a CO X c — SYI O 54 • O CU r—l c O >4 o 5h CU a rH o O PUI 2 •P DS VII -P V a«i 0 C 54 P O• O >iO 0 O CO CU .Qi-4 1 a •H •H •rH 44 to 44 cn rH —- 4J tJ XZ •H CQ cn e 2 DS 4-5 o 0 J cu C cn ^1 0 xz aa 0 o o o ■p 0 cu aa 0 c 0 0 54 (1) — (0 • c > 1 co u to 0 a 2 oz 4-> X M 4-5 cu VI 0 0 54 54 o c 0 o cu 1 73 74 was applied only to the corn rows, showed respectively a larger increase in yield from the medium nitrogen application. However, there was a decrease in yield from medium to high nitrogen application. Intercropping yields were greater than those of soybean monocultures. Yields from intercropped plots where nitrogen was evenly distributed was lower than yields from plots containing only corn. Yields from intercropped plots where nitrogen was applied only to the corn rows were higher than yields from plots containing only corn, with the exception of high N rate intercropped plots, where yields were reduced compared to the medium N rate plots. The greatest forage yield was produced by corn monoculture at high N rate. However, the medium N rate intercrop treatment produced 93% of the maximum corn monoculture yields for a given site. Dry matter yields for corn and soybean components of monoculture and intercrops in South Deerfield are given in Table 13* Dry matter yields of corn monoculture were larger than those of soybeans grown alone. Dry matter yields of corn monocultures increased as N rates increased. Dry matter yield of soybeans grown alone were similar with a slight reduction at high N rates. Dry matter of corn intercropping where nitrogen was evenly distributed in the plot indicated an increase in dry matter yield with increased nitrogen application. However, in this planting pattern dry matter yield of soybean in the intercrop decreased as N rates increased. Dry matter yield of corn intercropping where the nitrogen was distributed only in the corn rows showed an increase from low to medium N rates. In this treatment the TABLE 13. Dry matter yields for com ^ and soybean tconponents of monocultures and inter- •H •H O r—l TS uv oo •5 p OH co T3 fc. 4J 03 Q <8 >, o 03 o P p 5 03 03 •-* dry matter yield decreased from medium to high. Also in this treatment dry matter yields of soybean intercopping decreased from low to medium as N rate increased. However, dry matter yield increased at high N rates. The component dry matter produced in both planting patterns of corn and soybean intercropping was higher than equivalent row yield of corn but lower for soybean monocultures (Table 13)• The dry matter yields of corn intercropping where nitrogen was distributed evenly were lower than those of intercropping where nitrogen was applied only in corn rows. However, in this treatment dry matter yields of soybean intercropping were greater than intercropping where nitrogen was applied only in corn rows. The highest dry matter yield was produced by corn monoculture at the high N rate. However, medium N rate intercrop treatment rendered 79$ of the maximum corn monoculture yield and 158$ on a row equivalent basis. Dry matter yields for corn and soybean components of monoculture and intercrops in Belchertown are given in Table 14. Dry matter yields of corn monoculture were greater than those of soybean monoculture. Dry matter yields of corn and soybean monocultures were augmented as N rates were augmented. Dry matter of corn intercropping where nitrogen was evenly distributed in the plot showed an increase in dry matter yield with increased N application. However, in this treatment dry matter yields of soybean intercropping decreased as N rates increased. Dry matter yields of corn intercropping where nitrogen was applied only in corn rows indicated an increase from low to medium N rates. However, in this treatment dry matter yield TABLE 14. Dry matter yields for corn and soybean! components of monoculture and intercrops in Belchertown-1983. For row equivalent comparisons dry matter yields of intercrop components should be doubled. * 2 W M OS Eh OS o W N 2 W - u u CO CO u u CO CO u u CO CO 1 1 1 1 1 1 1 1 1 1 1 OS X H -3 -H u o OS 2 CO O >H CQ w < 2 o OS 2 CO o 03 w < 2 u o OS 2 CO O >H H CQ < 2 \ 0* x cn \ XC X i l l i i i l l i 1 Cn (C i i l i i i l i i i i i i l i l l i i i i 1 | i i i i i i i i i i i i i i i 1 I i 1 l i i i i i i i o r~ 00 I-H o VO o i-H OV TT o i-H CO in VO (—i 1 | 1 | 'vr in VO r- vo r~ CO o 00 CM 1 1 1 1 1 1 1 1 (Ti O i-H (X in CM CM r» in VO ov VO rH in CTv CM 00 r- r^- decreased at high N rates. Also in this planting pattern dry matter yields of soybeans decreased from low to high as N rates increased. The dry matter yields of corn intercropping where nitrogen was applied evenly were lower than those of intercrops, where nitrogen was applied only in corn rows. However, in this treatment dry matter yields of soybean intercropping were greater than in intercrops where nitrogen was applied only to corn rows. The highest dry matter yield was produced by corn monoculture. Dry matter yield of ear corn of monoculture and intercrop in South Deerfield and Belchertown sites are given in Table 15. Dry matter yields of ear corn of corn monoculture were greater than intercroppings. However, the medium N rate intercrop treatment where nitrogen was applied only in corn rows produced 13% more ear corn compared with medium N rate treatment of the monoculture. In this pattern monoculture production increased as N rates increased. Dry matter yield of ear corn of the intercropping where N was evenly distributed was lower than the yield of ear corn of the intercropping where N was applied only to corn rows. However, the yield of ear corn of high N rates was larger than those of the intercropping where nitrogen was applied only to corn rows, for both sites. The corn monoculture produced the largest corn yield at the high N rate. However, the medium N-rate intercrop treatment rendered 78$ of the maximum corn monoculture ear corn yield for South Deerfield. Shelled corn yield of the monoculture and intercrop in South Deerfield and Belchertown sites are given in Table 16. Shelled corn yields in the corn monoculture were greater than in the intercropping. Eh 9 a 15. Dry matter yield ear corn-1983. « P4 2 Eh OS o o W 2 o u u o CO CO u u cn 1 1 cn 1 1 1 1 1 1 1 1 H OS Eh M M PO (S3 OS u X4 43 CO 1—1 Q CQ CO x: a r-i 03 CQ o CO i—i a x: 0Q a) 0 14J o O 03 -P rH •H p 03 -P 03 03 C 3 p a) o -P 4H CP -P Q> x: c 03 u 03 <13 o p o o s a 03 P cn o c o p O •rH ■H 4H ■rH W 4-J cn 44 -—. cn Q •H 2 OS rH CP C O 8 -P t-Q o 03 c Oj o cn VI u • • 03 (U C <13 H mi 03 p -P o m —^ o 1 1 0 • «k p c > cn c 03 p o p 0 a cn • • • • -H •H •H 4H cn H 44 r—1 44 xz QQ T3 -H •H o CP c 2 CNH O 03 OS ^-P w in Ml cn• G ■P Nl o o G in 4-4 — 03 cn la °Ml 04 >— • 03 0 rH • M P 03 CL, <0 Ml0 a1 •0 03 m -p a • 3 0a p •»O4 0 P• M 2 -p os 1 c 3 0 •- P 03 cn P o Ml C3 P C4 > 'H cn — C 1 ai <3 P 4-3 0 X 0 (13 p a • • H • 0 p o O c o u 79 TABLE 16. Dry matter yield of shelled corn-1983. * U u u cn cn u u CO cn I 2 CP M W O M i E-i OS OS £-• U J W M 2 N 1 1 1 1 1 W OS CO Q rH sz OQ CO Q SZ rH 0 o Q3 CO Q rH J3 rH vw vw •H G vw >1-p O 03 0 in P 03 ■P rH G p 0 0 p 5 c in -P n3 vw P 0 0) 5 03 > in ■H C3 in 03 -P C 3 Sh 03 0 ■P On -p 0) £ C 03 03 SZ P 0 N rH P -p 0) 0 3 03 w • 03 03 > 0 P 03 03 0 p e 0) u 0 Qu flj SH cn 0 G SZ 0 p 0 P •p •rH •P VW u 'SI vw --. -p •P cn ■— Q rH ■p 2 o o Nl os 03 Cl cp G ■P O 03 Nl CJ —r C « M o o rH 03 cn ■P However, the medium N rate intercrop treatment produced higher kernel yields than the medium N rate treatment of the monoculture in a given site. In the treatment where nitrogen was applied only in corn rows kernel yield increased from low to medium and decreased in the high N rate treatment. Kernel yields of the intercropping where nitrogen was evenly distributed was lower than the kernel yields of the intercropping where nitrogen was applied only in corn rows. However, the kernel yields of the high N rate intercropping was larger than those of intercropping where nitrogen was applied only to corn rows, for both sites. The corn monoculture produced the highest shelled corn yield at the high N rate. However, the medium N rate intercrop treatment rendered 73% and 68% of the maximum corn monoculture kernel yield for South Deerfield and Belchertown respectively. The percentage of crude protein in the final mixture reflected the changes in percentage of soybeans in the silage (Table 17). Crude protein yields of the corn monoculture were significantly less than those of soybeans and the intercrops (Table 18). In this treatment crude protein yield of corn increased as N rates increased. Crude protein yields of soybeans were significantly twice those of corn grown alone. In this treatment crude protein yields of soybean at South Deerfield were similar across N rates. However, crude protein yields of soybeans at Belchertown responded sligtly to increased rates. Crude protein yields of the intercrop where nitrogen was applied evenly were less than the intercrop where nitrogen was applied only to corn rows, except for the high N rate intercropped plots where yields were reduced compared to the medium N rate plots for both TABLE 17. Percent crude protein dry basis-1983. o u M W Eh OS « E* O H O 2 Pu W M 2 N cn cn CJ u cn cn u u cn cn i i I i i i i i oc w X rH cn rH x Q i—i CQ cn a x CQ i—t x cn cn CQ m 0 P N U (CJ c x: >1 cn o p 0 C >-i cn 5 aj -h o cn sites. The largest crude protein yields were obtained by intercropping where nitrogen was applied only in corn rows at the medium N rate for both sites. The mean protein yields of the intercropping treatments produced significantly more protein per hectare than either corn or soybeans alone. The percentage of crude protein in the final yield mixture are given in Table 17. The intercrop row pattern where nitrogen was distributed evenly in corn rows at low N rates raised the percentage of protein in silage to 12.5%. This was an increase of 68•9% compared to the best corn monoculture treatment and also an increase of 45.9% and 52.1% was found compared to corn alone in medium and high N rates respectively for given site. Percentage of crude protein of the soybean monoculture was significantly higher than the corn monoculture or the intercrops. Percentage of crude protein of the intercropping where nitrogen was appied only in corn rows, was significantly higher than in the intercropping where nitrogen was applied evenly. However, low N-rate intercropped plots where nitrogen was distributed evenly produced higher protein yields. There was a significant linear effect for percentage of protein for N rates. Belchertown intercrops produced more protein per hectare when compared to the soybean with zero nitrogen at the basal rate. Total corn stover, ear and soybean crude protein yield components of silage are given in Figure 8. Generally soybean produced the largest yield of protein. However, intercrop treatment with 90 kg/ha where nitrogen was applied only in corn rows produced slightly higher o u u XI XI >4 c C oo W OS o a CM (bm/8)|) p|9|A maiojd 86 protein yield than soybean monoculture. Nodule weight for soybean monoculture and intercrops in South Deerfield are given in Table 19- Dry nodule weight for soybean monoculture was significantly greater than intercrops and decreased slightly as N rate increased. Nodule weight for intercropping where nitrogen was evenly distributed decreased more as N rate increased. A significant difference in this pattern decreasing from 18.2 g/m2 to 6.8 g/m2 was found. While the nodule weight of intercropping where nitrogen was applied only in the corn rows showed a decrease from low to medium maintaining the same weight in the medium and high N-rate treatments. Nodule numbers for soybean monoculture and intercrops are shown in Table 20. Nodule number for soybean monoculture were significantly greater than intercrops. In this pattern nodule number decreased from low to medium N-rates. However, the nodule number augmented slightly in the high N-rate. Nodule number for the intercropping where nitrogen was evenly distributed increased from low to medium N-rate and decreased significantly in the high N-rate. Nodule number intercrop where nitrogen was applied only in the corn rows were greater than the other intercrop except in the medium N-rate treatment. In this planting pattern the nodule number decreased from low to medium N-rate. However, increased in the high N-rate treatment TABLE 19. Nodule dry weight in South Deerfield-1983. NITROGEN FERTILIZER S-S C-C-S-S C-C-S-S * kg/ha 0 19.8 18.2 - 45 - - 14.7 90 18.7 13.2 11.9 180 17.0 6.8 11.8 Only corn rows received nitrogen fertilizer, thus effective rate for comparison of these corn rows is double the whole plot rate. Significant Effects: N-Rate Linear (P^0.05) ; Soybean vs. Intercrops (P^O.Ol). TABLE 20. Nodule number in South Deerfield-1983. NITROGEN FERTILIZER S-S C-C-S-S C-C-S-S* kg/ha 0 106 73 - 45 - - 76 90 90 77 74 180 93 42 80 * Only com rows received nitrogen fertilizer, thus ef¬ fective rate for comparison of these corn rows is double the whole plot rate. Significant Effects: Soybean vs. Intercrops (Ps^O.Ol). 89 1983 Discussion There can be no doubt that the majority of experiments in the tropics and even in temperate areas indicate that mixed cropping systems are more productive than pure stands* though this does not neccessarily imply that such systems should be encouraged as more sophisticated production methods are adopted. The present results from this area support the general findings in two years of research (1982-1983) that maize-soybean mixtures were significantly more productive than planting the same relative cropped area in stands. In 1983, two experiments were established to examine the possibilities for nitrogen economy with a intercrop. The reasoning for this is that soybean being a legume is capable of fixing atmospheric nitrogen when properly nodulated, and so is less dependent for growth on sources of nitrogen from the soil. For these studies the corn-corn-soybean-soybean intercrop pattern was chosen to ensure in certain treatments that nitrogen fertilizer was only applied to corn, that is between neighboring corn rows. Forage yields in all treatments were greater for the South Deerfield site compared to equivalent treatments in Belchertown. However, even though one site was more productive than the other, the yield trends were similar at both sites. As found in other studies corn monoculture yields were about twice those than soybeans grown alone. Corn monoculture yields increased as N-rates increased in both sites. In South Deerfield soybean monoculture yields did not respond 90 to increasing rates of nitrogen, while in Belchertown increasing nitrogen increased soybean yields. The South Deerfield site has had a history of growing soybeans and thus soybean plants may have been better nodulated and were more able to fix nitrogen than soybean plants in Belchertown where soybeans were being grown for the first time. The spatial arrangement of maize used severely reduced the forage yield of intercropped soybean, but caused no significant depression on the maize forage yield, except in the high N rate in intercropping where nitrogen was applied only in corn rows. In this treatment the nitrogen was applied only in corn rows and therefore, in the high N rate the nitrogen concentration (360 kg/ha) was shown to be too elevated causing a depression in corn yield. The intercropping pattern yields of forage where nitrogen was applied only in corn rows were superior to the yields of intercropping where nitrogen was distributed evenly, except in the high N-rate treatment. Applying N only to corn rows greatly increased this component of the intercrop yield, but at the same time soybean component yields were not significantly different compared to spreading N evenly between corn and soybean rows. There was evidence of greater efficiency of N use in addition to production economies for farmers. The LERs were also greater for the intercropping where nitrogen was applied only in corn rows than the other intercrop. This indicating also that there was an increase in biological efficiency for the former intercrop. 91 The corn rows bordered by soybean produced more stover, a greater yield of ears, heavier ears, more kernel per row, and a percentage of ears higher than monoculture rows in corresponding N-rates. Increased N rate increased kernel weight in monoculture, but not at all in intercrops. Kernel weight was suppressed in high N rates in the intercropping where nitrogen was applied only in corn rows, perhaps further showing an intensification of moisture stress caused by the high N-rate in this treatment. Soybeans produced the greatest yields of protein, but this was equalled or surpassed by the best intercrop treatment with 90 kg/ha of nitrogen all applied to corn rows. However, crude protein yield decreased in the high N rate treatment. This probably ocurred due to excessive nitrogen application reducing the corn component contribution to protein yield. Kurtz et al., (1952) observed that nitrogen fertilizer reduces the competition between intercropping and maize, but the optimum requirement of nitrogen fertilizer for maize would have adverse effects on grain yield of legumes when they are grown together. Normally well nodulated soybean would not be fertilized with nitrogen, since the yield response is usually that found in South Deerfield, while in Belchertown the intercrops yielded more protein per hectare when compared to the soybean with zero nitrogen above the basal rate. In the intercrop where nitrogen was distributed evenly, the crude protein increased as N rates increased. The fact that crude protein yields in this intercropping pattern with increased N rates did not decline is partially due to the high quality of the kernel component. 92 For corn monoculture nitrogen applications improved protein yield. However, intercrops where nitrogen was applied only in corn rows were more effective, producing more protein with less nitrogen applied. Dry nodule weight for soybean was greater than intercrops and decreased slightly as N rate increased. However, the nodule weight of intercropping where N was evenly distributed decreased significantly as N rates increased. There was probably severe root competition between maize and soybeans. Nodulation ability of legumes can be reduced by the application of N fertilizer. There could be two reasons underlying this phenomenon. One is that the supply of N fertilizer reduces the need for nodulation and N fixation by legumes and, secondly, it could stimulate the vegetative growth of the cereal, thus increasing the shade on the legume resulting in an inhibition of nodulation and nitrogen fixation. If these two aspects are concomitantly experienced, then when soil available N supply is raised the legume performance could be increasingly jeopardized, as is usually observed in most intercropping (Beets, 1978 and Dalai, 1974). Conclusions Mixtures of corn and soybeans gave considerably higher yields than could be achieved by growing the two crops separately and then mixing. The maize/soybean mixtures suggest that an important component of this greater efficiency may have been improved utilization of light because of the very different heights of the crops. It is also probable that there was better utilization of soil resources because 93 of the large difference in rooting depths which are known to exist between corn and soybean. A further posibility is that the different growth cycles of the crops produced an over-all utilization of resources, although as pointed out by Andrews (1972) this factor is likely to be of more importance under longer growing seasons conditions. Maize was the dominant species. The pronounced seasonal differences in rainfall are reflected in the yields of crops between 1982 and 1983. CHAPTER V SUMMARY In the 1982 and 1983 seasons two field experiments were conducted to evaluate yield relationships of a corn-soybean intercrop system under different planting patterns and densities (1982) and nitrogen rates and placements (1983). In 1982 three densities of corn in 91 cm rows (5.9, 8.6, and 11.2 seeds per meter of row) and double rows of soybean, 35 cm apart on 91 cm centers (18 seeds per meter of each row) were planted as monoculture crops and in two intercropped treatments, where alternate and every third and fourth row of corn was replaced with two rows of soybeans 35 cm apart (a replacement series). Corn monoculture produced 54.8, 56.4, and 55.6 t/ha (low, medium, and high respectively) compared to soybean monoculture 25.4 t/ha silage for soybean alone. Intercropping where each row of corn was replaced with double rows of soybean density treatments (low, medium, and high) produced yields of 47.7, 48.4, and 52.5 t/ha silage respectively. Intercropping where the third and fourth rows were replaced by two double rows of soybean, density treatments (low, medium, and high) yielded 40.4, 46.3, and 48.6 t/ha silage respectively. Intercropping yields were greatly enhanced in high corn densities, but not in monoculture yields. 94 95 The percentage of ears of corn component for both intercrop patterns was maintained at nearly 56$ from low to high corn densities while in corn monoculture decreased it at high density. Also, ear number per plant and weight per ear was reduced less severely and ears/m2 increased to a greater level in intercropping with increased corn densities compared to corn monoculture. Similarly, a greater ear yield was obtained in both intercropped patterns than in monoculture at medium and high densities. The higher corn densities needed to maintain yield in intercropping reduced the soybean contribution to yield, but the percentage of soybean in the 50/50$ intercropping (corn—corn—soybean-soybean) pattern was sufficient to significantly raise the percentage crude protein from 6.8 to 7.0$ in corn monoculture to 10.3, 10.1, and 9.0 for the low, medium, and high densities, respectively. For the total cropped area, intercropped patterns and soybean alone produced significantly more protein than corn alone. Increasing corn density competitive ratios at harvest indicated that the superior competitive ability of corn increased while the soybean competitive ability decreased. In all intercropping treatments, Land Equivalent Ratios were greater than 1.0. Corn LAI increased with increased corn densities while that soybean maintained at the same level. In 1983 nitrogen rates of fertilizer were applied in all plots. For the monoculture and one of the intercrops, the nitrogen rates were 0, 90, and 180 kg/ha. The remaining intercrop treatment had three 96 rates of nitrogen (45, 90, 180 kg/ha) applied only between the corn rows. N-rate and the three planting patterns (corn-corn, soybean-soybean, and corn-corn - soybean-soybean) were combined factorially. In addition, only corn rows of an extra pattern (corn-corn - soybean-soybean) were fertilized with the same overall rate of N, twice the rate of fertilizer for the corn rows themselves. Corn was planted with a high density (11.2 seeds/m of row) and soybean population (18 seeds/m of each row) where corn and soybean densities in intercroping were part of a replacement series. Corn monoculture produced 44.8, 52.7, and 65.1 t/ha (low, medium, and high N-rate) compared to 30.6, 30.4, and 29.3 t/ha silage respectively for soybean alone for a given site. Intercropping where nitrogen was distributed evenly in corn rows produced 40.4, 47.6, and 51.1 t/ha silage in low, medium, and high N-rates respectively. Intercropping where nitrogen was applied only in corn rows produced 48.9, 60.5, and 45.8 t/ha silage in low, medium, and high N-rates respectively for a given site. Corn monoculture and intercropping yields were greatly enhanced by medium and high N-rates in both sites, but not soybean alone whose yields were maintained at the same level. The greatest forage yield was produced by corn monoculture (65.1 t/ha) at high N-rate. However, the medium N-rate intercrop treatment produced 93% of the maximum corn monoculture yields (60.5 t/ha) for a given site. 97 Dry matter yields reflected these changes in silage yields where the greatest dry matter yield was produced by corn monoculture (19550 kg/ha) at high N-rate while the greatest dry matter yield intercropping (15471 kg/ha) was obtained in the treatment where nitrogen was applied only in corn at the medium N-rate. The higher corn N-rates required to maintain yield in intercropping reduced the contribution to yield, but the percentage of soybean in intercropping where nitrogen was distributed evenly was sufficient to raise significantly the percentage crude protein from 4.8 to 7.4$ in corn monoculture to 12.5, 10.8, and 10.8 for the low, medium, and high N-rates respectively for a given site. In addition, intercropping and soybean patterns produced significantly more protein than corn alone, except in intercrops at high N-rate for both sites. 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Mean yields of corn, soybean, and total dry matter accumulation over time (1982). 3 3 m co rn i> z -H o 3 a O co o -< r* ~n 70 • • • o O o o • • / > —i z —i —( CD 70 Z z m “O r~ 1 1 1 1 1 1 1 1 1 I 1 i 1 1 1 co CO CO o o oo co —1 —< -H 3 CO co co o o o o o co CO o co co *—* m o o c~> o oo o CO o m + s: o 43 VI 43 30 00 I-* 43 co vo cn VIH VOIHHVI 43 vl 43 vo 00 !-• 43 o OO CJ 43 43 3-> vj 03 (41 43 W M H h-» M cn ro vo co CO VO CO t—• vj vj! co 43 o CO CJ 43 43 H* 03 ro 43 o CO t-* CO 03 vl 43 IM 3-3 \j oj no vo 03 vo o 03 ro i—* VO 03 O 43 VO VO VO vi oi co ro m OOoihnhh vo ro 03 m ro 03 vi co co ui o vi ro co O 03 vo 43 o ro I—* M 43 VI vj 03 CO 03 vi Caj vj a» m co 1—» H-* cn ro vo oo 03 vo co 3—* vi cn co h-* 3—1 CO 03 CO oo vi cn co cn 03 o 1—* 3—* 03 CO 43 VO 03 ro vj vo t—* cn oo O 1—* »—» ^ » en k-* cti i—» ro oi ro co 03 30 43 03 vo ro vn m ai co ro 3-* co oo co o 03 vo 43 o ro i—* H—• 43 VI VI 03 00 03 vj w ro vi oi • co 03 vl 43 ro I-* co co vi cn 03 i—* i—* ►—» no vo vi co m-» vi co ro o vi ro cn ID f\3 MN M H430003MM • •••••• 0(43 03 03rOHH • •••••• 3 o m vi co m cj ro 43 M-» O 03 vo cn i—* 43 ro VI M 03 H Vi I—* 1—• CO CO 03 VI -si 43 4* VO 43 03 00 vi oi oi 43 co ro i-* no m O CO 03 M 43 oo OJ 3—* VO O 43 1—» 03 4» viawvjro M 43 30 03 43 M ro col i—• ro -43 vj -v4 03 m in od co ro 03 03 -43 CO I—* 03 ro CO CO 03 03 43 vi co h* as vi ro h nhh no m r0 03 30 03 H cn ai auD cn 43003CJ3-* 43 43 U1 VI O ro M l\3 30 O 43 o H <41 ro i—* 4» ro -sj ro cn i—* 30 43 43 03 30 H> M 03 43 CO H* 03 t—• 30 vi oo o cn VO CO CO O 03 43 03 O 03 VO 341 M O co cn i—* -43 co oo VI M M VO OJ 03 VI 43HVIUH O 03 cn 43 ro 43 ro vo cn o ro vo vo vo M H-» wrorovjmoo rOVOMMOH zc 1—* CD □C • mi-* at ro 03 oo a ro 03 ■& -vi cn cn 4^ co ro *—■ OOUOU1H vo i—1i cn co ''j ro cn 4* 03 i—• cn cti cti rOHH MO^SIOWN no f\3 »—* (JIOO'UIH ro O'* oo co cD ro >—• no 00 uo '•o ro MOroM^-&si o 4» co 03 cn co o I— -C» 00 O t—> CO *WCDO-t>vlO sjuico roM 03 0UCOCOSKD OMncoroM i>o no m ro m ji o -t» t» VIWVJAM VI SI Vi I\3 03 ro H 03 co -e» oo vo or -c* io h* 03 co ni ro vi O * n O oi ro H-* 1—* M-» U O a\ -si M M H* (O ro VJ OJ CO 03 ji OMX»coroHO »—» H-» co vi o 30 h* 03 ro ro mm 003C0 03H ai a cn m ui ai ai oiroo^H co co ro co oi ro m ca O ui ai h m m CO VI H- CO CD 43 ♦Density does not apply to soybean monoculture. Table 22. Mean yields of corn, soybean, and total dry matter accumulation over time (1983). —1 o —H 1“ • > o -< 03 z “T| CO m o o a is • o 30 Z o o *T| o • • —t 30 Z2L “O —( G3 m —1 H-« z z “O r* + ♦ 1 1 1 1 1 1 ♦ 1 1 1 1 1 1 1 1 1 1 co 00 1 1 o o 1 o CO CO CO co o o o o o CO o o co co CO CO CO co o o o o o —1 m o Z —1 “< C/3 o m HW x: o r“ . i—* ro *« o> cn O O vj i—* I—* co 1—'' CO VJ * H U1030HOH 03 * * vj co ro 03 co 03 -vi co ro ►—* ro cn cn ro cn cn h cn 03 h 03 xx oo ro ro ro co I—1• vj co cn vj O co 03 CO cn u h 03 co h c_n h-» <_n cn ►—» 00 CO vj co ro^o vjHsi O cn h h cn oo CO OO 03 00 CO CO H-* o -e» x» ro cn o> cn 03 oo i—» ro cn oo O oo o • ••••• co cn * ro 03 CO 03 * Vl H cn oo co »-* ro cr» m vj H-* ►—» ro cn cn no cn ui H*cn m cn -c* co ro ro ro co I—1> vi co cn vi HU V* ro co cn oo o t—* H-* ro * co cn m LTl Ol CJ1 ^ M M -Vl co 03 o o o CO CO vj CO * 03 CD VI vl CO O cn hh * co H 1—» 03 1—• 00 vj 03 co HUOIUCOU ro ^vi >—» ^vi CO 00 03 03 CO CO • ••••• 03 cn * co i\3 h 3 o m rx3 cn cn co co M 03 H * OO H »—» OCO vl* VI * * * CO H 03 V 03 * V H 03O3C0OH03 O -e» no ►-* 03 H*VO vj CJ CO*CJ*OOH 03 ro cn cn 03 h rx) id id cn w JIHID^H* -vi _c» co rx3 co co co co CD * CO V CD co 03 co co i—* cn CO* VOHA H-* co cn x» rxj ui O -& cn v h 03 V 03 03 H cn 30 03 *03 0103 • ••••• co cn x» ro VIOOOO Vll\) cn*30 0n0H 43030WH03 co cn -p. 1X3 03 VI 03 VI H 03 03 CD O H 03 O vj x» ro h-* 03 *WO*H “vl -C^ 1X3 03 1—* CO VJ IX) 00 1X3 VJ CO 03 -D. CO r\3 O M* X6H-t3XO co co co co CO 03 CO 03 ►—* -P» cn 03 rxj co O COK003H cn cn x* co ro i—* CD ■& CO vl ® 30 * VOH03 • ••••• H-* z h-* zn O H—1 -t« 03 cn rx) SSVKTO 03 CO CO -C* CO H-* 00 H-* -C» 03 CO •—* K-* h-* H* O vj OJ vi co cn co vi I—» oo o cn co co 1—* vl vl H OO >—» uiroui vcoh t—• O ro ro o oj H—* ♦—» O MNJ OJH Ol ^ VI M 03 CO 00 I—1 -P. cn x» cn 03 ro cn VI03 WlOH O ►—**—* X» CO Xi ^ ^ 00 H* W f\) • ••••• WH03H030 x» 03 cn rx> HOMMOOJ M O Ol lO Ol M CO 03 CO CO Nitrogen fertilizer was only applied between corn rows, thus the effective rate is doubled for corn. Table 23. Mean leaf area index of corn and soybean and total area index over time (1982). > 1— > -< ao > —1 —1 > J» 1— -n 30 ►—« o T| CO o m z r~ >—4 *—* o o o r~ z —1 3> z CTO “O » —1 z TD 1— —1 m 1 1 1 1 1 1 1 1 1 1 1 CO CO co —1 -< ■H 3 CO o o oo o co o o o CO CO CO a m z co *—4 m o o o CO o CO C/1 co o o CO H—4 o ♦ z: o r* .& -& co ro o O O VOCUl AWPOM CJ -& 03 -& 03 PO PO co-ftCorcoMAO OvAUHOO l\3 PO 03 IN) v co ro vcooo vivcom -e» -p» co co i—* o O ro ror\) ro mo o ao oo v co a po o O co co oo cn on oo PO PO PO co o O O roPOwcoMOo 03 ctn o O cn co o cn oo oo co m o O w roo h oi co v ctn CTN -e> PO o o o ro co oo CD m co O cn oo ctn co i—* o O co po o m ai co v 03 ao vi co -c* po o O co co on cn cn on cn co w co ro m o ro o o v ro o PO PO oo-b 03 co oo VI ID 4i V cn CO 00 VCO03 V VCJH-* roNPOPOMOO H U V CJ O * -t» cn co on -vi co co • •••••• • •••••• UUO^HOICJM 3 m o ACJftftroOO V OUT * W l\3 M V PO .fi CO CO -C» M n cn w po co ro m *U**POOO ■OWU-ftPOOO co oo cn co cn -c» m» rouiOHOiuiO uicn-ftNOOO co co h> o cn co o po o cn i—* co cn co COJiUCJMOO co cn po co po cn i—* co -vi co cn vj co m* co vo cn cn cn co vj po o cn i—* co cn co OOIAPOHOO co cn ai vi cj cj m co m o cn-ft po v Ji^UWHOO co co i—* o on co O cn -t* co co ►—* o O O co co o cn co m* ai oo oi vi 03 co ^ m ac co oo oi v a z H—1 3: O OlUl * CO f\3 I-* O OKfl VI UlUl M OW^OMOO-C* i—* ro cn 00 ro cn >—* U1 cn co ro no ro ro .& Ol***UOO >—* CO -vl 1—* O ro CTN aim^WHOO m* cn a: co cn ro m* 00 CO 00 CO V (Jl M H* H* 00 H* VIM 00 ACIVOOHCOM CO K-• CTN 1—i1 o -E» CTN Ol V -t» CO h* o o oo vi ai m w oo m ai co CTiai w m O co co ro o o -e» cn cn -c» -e» ro O O ooow vaiuiM OIOIft*POOO co co —i i—* 03 cn o> vl co A W VI ♦Density does not apply to soybean monoculture. Table 24. Mean leaf area index of corn and soybean and total leaf area index over time (1983). z -< CD m —i —i i> 73 Z 4—4 O “T1 OO o o 4—4 -n cn o r~ r~ r~ 4—4 O 1— -a > —i —i -o z —1 z an m 73 Z 4—4 1— * ♦ =4- 1 1 1 1 1 1 1 1 1 1 1 1 1 CO CO 3 cn o cn o OO CO o m z oo ►—4 —1 -c -i 4—4 m cn o cn CO CO cn CO co co co cn cn co co cn cn CO co cn co o o CO •£. o r— m co co ro m o AVIOIAMO rocn oo m co oo -A. VI 'vj o O OD a cn oo ro m ro o cn m* o vj co cn oo a m o m co co co ♦Nitrogen fertilizer was only applied between rows, thus the effective rate is doubled for corn.