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bushels/acre). By A.D. 395, farmers in Campania in southern Italy had abandoned 330,000 acres of land (Simkhovitch, 1937). While the quotation that intro- duces this paper oversimplifies the story, the conservation record of past civilizations has not been good. How has western civilization managed its ? Did our European ancestors Reviews learn anything from the mistakes of earlier cultures? And how do our cur- rent soil husbandry practices compare to those of past cultures? Fallow and early European farming The Historical of Living The farmer has always had to deal with soil depletion. The first and most long-standing method of restoring soil and Related productivity has been the simple fal- lowing of the land (Fussell, 1965). Practices While the use of and green manures was known in very early times, fallowing has, until very recently, been Laura K. Paine1 and Helen Harrison2 the most common practice in dealing with declining soil productivity. Early European farmers followed the path of “Civilized man has marched across the Romans, growing mostly soil-de- Additional index words. , the face of the earth and left a cover , intercrop, , pleting grain and depending on desert in his footprints” (Carter and conservation . fallow to ameliorate the effects (Fussell, Dale, 1974). 1972). Europe was “saved” from agri- Summary. Since the domestication of cultural decline by another, more-dev- the first crop species, farmers have Few people consider the impor- astating disaster—the bubonic plague, dealt with the problem of soil tance of or soil conserva- which rose to epidemic proportions in depletion and declining crop yields. tion in the development of cultures. Europe in the middle of the 14th Fallowing of land was the first The rise ofcivilizations depends on the century. The precipitous decline in approach to restoring soil fertility, ability of a culture to produce not just population initiated long-term and and is still the most commonly used enough food for survival, but a surplus method among indigenous farmers. ultimately beneficial changes in Euro- of food. It is only with the production pean agriculture. Alternatives to fallow, such as crop of surpluses and cash crops that popu- rotation and green manures, devel- It is estimated that Europe lost oped in a number of areas. The lation growth, trade, and the trappings between one-eighth and one-third of earliest record of their use is in of civilization can develop. Maintain- its population to the plague between Chinese writings from ca. 500 B.C. ing the productivity of the soil that 1347 and 1351 (Goetz, 1990). This Discussion of these practices is found feeds a population is essential to this population decrease greatly lessened in European agricultural publications process. Inevitably, as population in- the pressure to produce grain for sub- dating from the 16th century. While creases, the pressure on the land to sistence, and created a serious labor these ancient techniques have proven feed it increases. Historical records deficit as well. The large, communal value for , their use show that lands that sustained early in modern agriculture is quite limited. fields of the open field system were civilizations, such as Mesopotamia, divided among individual farmers. Renewed interest within the agricul- Greece, Egypt, and Rome, were de- ture community in recent decades has There was a shift toward less labor- resulted in a greater research effort in pleted by pressure intensive methods: pasturage and live- the areas of green manures, cover and poor soil husbandry (Carter and stock production, and a concomitant crops, and living-mulch cropping Dale, 1974). This factor contributed increase in the application of systems. significantly to the decline of these to the land (Fussell, 1972). A result of cultures. During the last decades of these changes was the development of the Roman Empire, for example, yields crop rotation theory. This practice and of wheat and barley averaged 4 to 6 other conservation methods have bushels per acre. Columella advised served to sustain the productivity of farmers to switch to grapes, “for none Europe’s soils. in Italy can remember when grain in- creased four-fold” (this would result Crop rotation in a “good” yield for that time, of 7 The development of crop rota-

HortTechnology · Apr./June 1993 3(2) 137 tion theory rested on an understand- low seasons, and many involved green “Tillage is breaking and dividing ing that different crops vary in the manure crops for the first time. the Ground by Spade, Plough, Hoe or amount of nutrients they take from the other Instruments, which divide by a soil, and that some (notably ) Tillage fort of Attrition (or Contusion) as serve to enhance the soil’s ability to “The finer Land is made by Till- Dung does by Fermentation” (Tull, sustain subsequent crops. There was age, the richer will it become, and the 1731). no accompanying understanding of more Plants it will maintain” (Tull, Furthermore, he was quick to , a science that was not 1731). point out the other advantage of his to mature until the middle of the 19th system—tillage not only killed sprout- century With these words, Jethro Tull ing in the field, but, by reducing Thomas Tusser’s Five Hundred started what became a revolution in the amount of manure used, one could Points of Good Husbandry, published the practice of agriculture. Born in cut down the amount of seed in 1580, was one of the earliest widely 1674, Tull was an organist and gentle- introduced into the field in the first distributed volumes on agriculture. man farmer (Fussell, 1973). He ap- place. Thus, tillage served to: The following excerpt (with interpre- proached farming scientifically, con- “. . . force open her (the land’s) tation in parentheses) reflects 16th ducting comparative experiments on Magazines with the Hoe, which will century understanding of soil conser- his Oxfordshire, England, estate. Here, thence procure (for) them at all times vation and crop rotation: Tull explored the role of tillage in Provision in abundance, and also free making land more productive. Noth- them from Intruders; I mean, their Otes, rie or else barlie, and wheat ing in the agricultural system of the spurious Kindred, the Weeds, that that is gray 18th century was conducive to the use robbed them of their too scanty Al- brings land out of comfort, and soon of tillage. implements were simple lowance” (Tull, 1731). to decay. and crude. A farmer’s entire array of While Tull’s theories did not have One after another, no comfort machinery often consisted of a plow an immediate impact on farming in betweene, and a harrow (Fussell, 1965). The Europe, their long-term effect on ag- is crop upon crop, as will quickly be draft animals used to power these riculture has been great. In the de- seen implements did not have the benefit of cades since Tull introduced the con- (, , barley and wheat deplete the breeding for size and strength. Only cept of tillage, it has become an inte- soil) the top few inches of soil were ever gral part of western agriculture. Today disturbed. Seed was broadcast by hand tillage, with its attendant drawbacks, Still crop upon crop many fermers do in the spring and maintenance of the can be an obstacle to sustainability. take. field during the cropping season was Goals of and and reape little profit for greediness minimal. advocates in recent years have been the sake. Thus, Tull was forced to invent amelioration of the negative effects of Though breadcorne and drinkcorn the equipment he needed—the seed tillage. such croppers do stand: drill and the cultivator, which he is said Count peason or brank, as a comfort to have constructed from pipe organ Soil fertility theory after to land. parts. The seed drill allowed for the Tull (Some greedy farmers sow crop af- planting of seed in distinct rows, so There were many other research- ter crop of wheat or barley, but receive that cultivation between rows during ers working in the 18th century to diminishing returns. Peas or the growing season was made possible. unlock the secrets of the soil and plant help to restore soil fertility.) The benefits derived from this ap- nutrition. Several important concepts proach included reduction of seed were derived from this work, such as Some useth at first a good fallow to waste and reduction in weed pressure the knowledge that resulted make. on the crop. Using this system, Tull’s from the decomposition of plants and To sowe thereon barlie, the better to yields far outstripped those of his neigh- provided water-holding capacity as well take. bors, even without the regular addi- as sustenance for crops. Humus im- Next that to sowe pease, and of that to tion of manure. He recorded his ob- parts a dark color to soil, and the sowe wheat, servations of this phenomenon in a degree of darkness was held to reflect Then fallow againe, or lie lay for thy book entitled Horse Hoeing Hus- the richness of the soil. The culmina- neat. bandrie: An Essay on the Principles of tion of this research was the “Humus (In this verse, Tusser sets out a Vegetation and Tillage (Tull, 1731). Theory,” which was developed in the rotation that calls for fallow, barley, Like Tusser, Tull worked without the last decades of the 18th century (Fus- peas, wheat, then fallow again or pas- benefit of an understanding of plant sell, 1971). The Humus Theory went ture. The term “neat” refers to .) nutrition. While the value of manure beyond the above-mentioned obser- (Tusser, 1580, p. 19-20, in Ras- and for increasing yields were vations (which were substantially true) mussen, 1975) well-known, the mechanism by which and held, wrongly, that all necessary this occurred was not understood. substances for plant growth came from Numerous crop rotation schemes Thus, Tull came to the conclusion the humus, or , in the were developed involving the major through his observations that, what- soil. The Humus Theory’s main pro- crops of the period: wheat, barley, ever affect manure had on the soil, its ponent was Albrecht Daniel Thaer of , peas, and pasture grasses (Whit- effects could be simulated with tillage. Germany. Thaer’s great influence in ing, 1971). All systems included fal- His reasoning was as follows: the scientific community caused this

138 HortTechnology · Apr./June 1993 3(2) theory, incomplete as it was, to domi- eral categories, based on how they tit impeded the adoption of these prac- nate scientific thought for many years. into the farmer’s crop rotation. They tices. It was not until the 19th century Finally, in the 1830s, a number of are : that green manures and cover crops workers accumulated scientific evi- 1) Main Crop, which is a green were used to any great extent in Eu- dence for proposing a mineral basis for manure crop grown during the regular rope. plant nutrition. Research from this growing season, in place of any other In North America, the acceptance period provided the basis for our knowl- crop. This is done only in cases of very of green manures has been even more edge today. The scientist who is given poor soil that will grow no other crop minimal than in Europe. The abun- credit for these theories is Justus van because there is an expenditure of dance of cheap, fertile land on this Liebig, a German chemist. In 1840, he money and effort with no return. continent discouraged most practice published a work that set out the fol- 2) Catch Crop, which is a green of soil conservation; many farmers sim- lowing facts about plant nutrition: manure planted after the main crop ply moved west when the fertility of 1) The carbon that the plant uses has been harvested. their land declined. Among those who is derived from carbon dioxide. 3) Winter Cover Crop, which of- continued to farm in the Eastern states, 2) The hydrogen and oxygen it ten serves purposes other than as green however, the 19th century saw a trend uses comes from water. manure. Planted in the fall, this plant- toward the use of fertility-enhancing 3) Plants absorb other necessary ing serves to cover the soil in winter, practices. Agricultural scientist Rich- elements from the soil. thus protecting it from . It may ard Allen observed that, by 1846, “this 4) Growth is proportional to the be allowed to mature and be harvested system (green manuring) has, within a amount of mineral substances avail- for grain, in the case of winter wheat or few years been extensively adopted in able to the plant (Fussell, 1971). rye, or for hay, in the case of many some of the older, settled portions of Liebig is best known for his “Law legumes and grasses. the United States” (Allen, 1852). of the Minimum,” which states that 4) Companion Crop. This was plant growth is restricted by that nutri- Pieters’ name for what we are calling Beginnings of the soil ent that is in lowest supply in propor- today a “”; a species conservation movement tion to the plant’s requirement for that planted at the same time as the main As grew in nutrient. crop or with the final cultivation and prominence during the 1800s, there Liebig and his colleagues ushered allowed to grow up during the grow- was an increasing awareness of the in the modern era in crop nutrition ing season between crop rows as well factors involved in soil productivity. and soil fertility study. Once an under- as after the crop is harvested. At the Soil depletion gradually became a con- standing of how plants derive needed time this method was used primarily in cern within the agricultural commu- nutrients from the soil was gained, grain production and in . nity. During the latter half of the 19th research efforts branched out to en- The plant species used as green century, several long-term research compass a wide range ofapproaches to manures, cover crops, and living projects were initiated in England and maintaining soil fertility. It was now are many and varied. Green in the United States, in efforts to docu- known that the value of manure was manures species are most often le- ment the effects of various soil hus- not only in its organic matter content gumes or fast-growing forbs and bandry systems (continuous cultiva- but in its mineral content as well. grasses. The earliest recorded use of tion vs. various rotations, manures, Manure remained the main type of soil green manures comes from China. In and green manures as well as compari- amendment used. However, much at- 500 B.C. the writer Chia Szu Hsieh son to natural grasslands). Now-fa- tention was turned to green manures, advised “For manuring the field, lu mous studies were begun at the Univ. which act in much the same way. In tou (Phaseolus mungo L. var. radiatus) of Illinois and at experiment stations in this era of scientific investigation, re- is best, and siao tou (P. mungo L.) and Pennsylvania, Ohio, and Missouri, as searchers began comparing these soil sesame rank second. They are broad- well as at Rothhamsted in England amendments and investigating their cast in the 5th or 6th month and (White et al., 1945; Williams, 1926). chemical and physical effects on crop plowed under in the 7th or 8th There remained a strong belief that growth and on the soil. month . . . Their fertilizing value is as organic matter was a major factor in good as silk worm excrement and well- soil fertility and, even as the first large- Green manures and cover rotted manure.” (Pieters, 1927). scale productions ofartificial crops Unlike the agriculture of the Ori- was beginning, research was focused The term “green manure” en- ent, western agriculture, until recently, on maintenance of organic matter lev- compasses a wide range of practices. has never involved large-scale growing els and the effect of crop production As defined by the Soil Science Society, of legumes, either as a food source or on their depletion. Many of these stud- a green manure is a “plant material as a green manure. In addition, the ies are ongoing today, and continue to incorporated with the soil while green, persistence of the feudal open field document the long-term effects of our or soon after maturity, for improving system ofagriculture throughout much crop production systems. the soil” (Soil Science Society, 1973). of Europe’s history further discour- In 1917, Adrian Pieters published In practice, green manuring takes on aged the use of green manures or cover a review of green manure research many variations on this theme and crops by greatly limiting the individual conducted at American agricultural includes both cover crops and living farmer’s options (Fussell, 1965). Fi- experiment stations. Pieters cited nearly mulches. Adrien Pieters, in his 1927 nally, the rise of the concept of tillage 200 studies, conducted in the 30 years book entitled Green Manuring Prin- and the view that a “clean-tilled” field since the establishment of the experi- ciples and Practice, presents four gen- was a sign of good husbandry further ment station system in 1887. It is

HortTechnology · Apr./June 1993 3(2) 139 apparent that many of these early prac- little general adoption of these conser- age was sod-planting. It was found titioners of soil science were concerned vation methods. Before the introduc- that, when cultivation is reduced, soil about the depletion of soils. Their re- tion of herbicides, farmers were de- aeration and nitrification also decrease search indicates that green manures and pendent on tillage for weed control. and soil crusting and erosion often cover crops were considered to be valu- As tractors became more widely avail- increase. Sod-planting, in which row able tools in the soil conservation effort. able in the 1920s and 1930s, the use of crops are planted into sod killed with The concern within the scientific tillage increased in most areas. herbicides, was developed to address community manifested itself in a num- A milestone on the road toward these problems (Shear, 1985). Work ber of ways in the early decades of the greater acceptance of limited tillage in this area led directly to the develop- 20th century. In 1925, the American systems was the publication in 1943 of ment of the living mulch concept. Society of hosted a sympo- Plowman's Folly by Edward Faulkner. An outgrowth of this research sium on “soil deterioration,” which This work directly called into question was that the herbicides used in sod explored the causes and effects of soil the necessity for and the value of till- planting, when applied at reduced rates, depletion (Haskcll, 1926). This sym- age. The suggestion that plowing— could regulate growth of the sod with- posium focused on how various agri- which had come to be considered fun- out killing it. A 1965 article entitled cultural practices contribute to soil damental to crop husbandry—was “The Sleeping Sod” describes the con- deterioration and the role that public unnecessary, perhaps even wrong, was cept of producing crops in a grass sod policy plays in this process. One par- quite revolutionary. In his book, Faulk- that has been “put to sleep” with a ticipant reviewed the results of the ner, a farmer and county agriculture selective herbicide for the duration of long-term studies on crop rotation agent in Ohio, maintained that “no the growing season. The author, J. and soil fertility at Rothhamsted and at one has ever advanced a scientific rea- Paul Lilly, discusses the practice in American experiment stations, some son for plowing” (Faulkner, 1943). light of the productivity goals of that of which had been in progress at that Faulkner’s theories were based on period; living mulches (or sleeping time for over 70 years. Conclusions the premise that the soil should be dis- sods) were seen as a way to 1) put drawn from these studies were that turbed as little as possible in the pro- highly erodible and otherwise untillable crop rotation alone, even when le- cess of raising crops and that, in this hillsides into production and 2) pro- gumes are included, was not able to way, it will more closely simulate a na- duce two crops: a summer row crop maintain soil productivity over the long tural ecosystem. Crop residue was to and spring and fall pasturage in the term. Additionally, research showed be left at the soil surface, not incorpo- same field in the space of year. that “though three times as much plant rated, thus providing erosion protec- The goal of increased productiv- food has been applied in continuous tion, moisture conservation, and a slow- ity during the 1950s and 1960s was culture as in rotation farming, it has release source of nutrients. His theo- met largely, however, through in- not produced as large a gross return” ries were derived from knowledge gain- creased inputs of agricultural chemi- (Williams, 1926). ed from the long-term soil manage- cals and fossil fuels. The emphasis was ment studies mentioned previously. on the use of technology in food pro- Conservation tillage While the thrust of Faulkner’s book duction. Conservation and soil hus- Another major problem facing was reduction of tillage-not the use bandry often were looked upon as an American farmers was . A of cover crops and green manures— unnecessary hindrance to the efficient 1926 headline in the USDA weekly the acceptance of his ideas opened the operation of the farm. As this approach Official Record stated that erosion was door for a whole range of limited-till- became established, some of its draw- costing the American farmer age options. The efforts of conserva- backs were brought to light. The prob- $200,000,000 each year. While public tion tillage advocates were greatly facili- lems that faced agriculture in the early awareness of erosion and the adoption tated by the development of herbi- part of the century had not been ad- of soil conservation techniques has cides in the late 1940s. Now, with cul- dressed and actually had been exacer- been slow overall, several events in the tivation no longer required for weed bated by much of the new technology. 20th century forced changes to be control, the concept of reducing till- A growing group of and made in some areas. A prolonged age gained greater acceptance. Some environmentalists began again to look drought in the Great Plains states in agronomists of this period predicted for alternatives to the poor crop hus- the 1930s was the first such event. that herbicides would make tillage bandry practices that have character- Many dryland farmers in what came to obsolete. ized American agriculture (Shear, be known as the Dust Bowl were forced A number of minimum tillage 1985). to either adopt soil conservation prac- systems were devised and equipment In the 1960s, many of those con- tices or risk major crop losses (Hurt, was designed to perform these new cerned about these developments 1981). To lessen the impact of wind tillage operations. These systems in- joined the growing Organic Move- and drought conditions, farmers were cluded plow-planting, in which nar- ment. There was a call for returning to encouraged to reduce tillage and to row strips were plowed and planted in traditional farming practices, involv- make use of cover crops and mulches. a single pass over the field, and stubble ing reduced inputs and an emphasis on Research continues today on living mulch farming, which involved shal- use of “natural” fertilizers, such as mulch/cover crop systems for wind low cultivation with crop residue left manures and legumes. Living mulches protection in sugar beets and other on the soil surface (Shear, 1985). and green manures had a place in this crops grown in the west (Lauer and scheme as a nonchemical means of Fornstrom, 1988). The idea of a living mulch weed control and as organic soil con- Outside the Dust Bowl, there was Another approach to reducing till- ditions.

140 HortTechnology · Apr./June 1993 3(2) In the 1970s, the concerns of made plans for future work and dis- of Illinois agronomists, showed that organic farmers became concerns for cussed how best to design studies of the crucial nutrients in the competi- all farmers. The 1973 Arab Oil Em- these complex systems (Miller and Bell, tion picture are nitrogen and water bargo drove the costs of fuel and pe- 1982). (Kurtz et al., 1957). Competition can troleum-based farm chemicals up One of the top priorities high- be reduced by regulating the intercrop’s steeply and sent shock waves through lighted in this workshop was the screen- use of these nutrients or by choosing the agricultural community. Reduced ing ofpotential mulch species for quali- mulch species that are drought-toler- tillage systems were put forth as a ties important in an intercrop system. ant or nitrogen-fixing. Screening work solution to the energy crisis and, by These characteristics are summarized on new species, particularly legumes necessity, the concept of conservation in William’s 1987 Oregon State Univ. such asvetches and dwarf , con- tillage became more widely accepted Extension Circular on living mulches tinues (Lanini et al., 1989). (Triplett and VanDoren, 1977). Al- and include: Mulch suppression can be accom- though the main thrust of this move- 1) Rapid establishment to sup- plished in several ways. By far the most ment was based on simply allowing press weeds and provide early traffica- successful to date has been with use of crop residues to remain at the soil bility and . reduced dosages of herbicides—the surface, the living mulch idea was again 2) Adequate wear tolerance and sleeping sod approach. A large amount looked into and more research was persistence. of this work has been done by agrono- done, mainly with agronomic crops. 3) Tolerance of drought and low mists using suppressed grass sods fertility. mainly in field corn production (Lewis The direction of living 4) Reduction of costs associated and Martin, 1967; Loughran and mulch research with mowing intervals, needs, Hartwig, 1987). In horticultural crops, Toward the end of the 1970s, thatch removal or chemical mowing. researchers have examined several ap- Robert Sweet began research at Cornell 5) Enhancement of crop yield proaches to mulch suppression. A rep- Univ. that applied the concept of com- and quality (William, 1987). resentative work is a 1982 study by panion crops/living mulches for the Two major screening studies con- Vrabel, Minotti, and Sweet at Cornell. first time to vegetable production. It ducted in the mid-1980s tested a com- In this study, researchers compared was he who invented the name “living bined total of 139 grass and five herbicides, plus mowing, for sup- mulch” to differentiate this practice species for these qualities. From each pression of white clover mulch in sweet from the many other manifestations of of these trials, several promising living corn. Their results indicate that both the green manure idea (Hughes and mulches were chosen for further study. methods can suppress mulch growth Sweet, 1979). Many horticulturists The more expansive of the two was effectively, and acceptable yields can believe that it is in vegetable produc- conducted at Cornell Univ. by Nichol- be maintained with either method. tion and other small-scale, intensively son and Wien (1983). They grew in- A recent development in the sup- managed cropping systems that living tercrops of five grasses and three white pression of living mulches is the use of mulches can be used most effectively. clover species with either sweet corn or rototilling in legume mulches (Gru- Much of the recent research has been cabbage. They characterized an in- binger and Minotti, 1990). Yield of done in the area of vegetable produc- verse linear relationship between mulch sweet corn was compared in mowed tion. dry weight and crop yield. vs. rototilled white clover living mulch. The Cornell Vegetable Crops The second study, conducted at The rototilled treatments compare fa- Dept. gradually developed a fairly large the Univ. of Connecticut by DeGreg- vorably, not only with mowed plots, and ongoing research program in the orio and Ashley (1985), differed from but with clean-cultivated check plots years since Sweet’s first study was pub- the Cornell study in that it compared as well. This response is very likely due lished in 1979. Meanwhile, Ray Will- mulch competition with weed compe- the contribution of fixed nitrogen made iam and his colleagues at Oregon State tition rather than with a bare ground available by the rototilling of the le- Univ. began another, complementary control. Mulches were all grassy spe- gume, and the more effective suppres- research program on living mulch sys- cies; no legumes were included. This sion achieved by this method. tems, focusing mainly on wind erosion study points out one of the underlying In spite of these successes, overall control and on woody crops-tree ideas behind living mulch systems— research results present a mixed pic- fruits, Christmas trees, and nursery that an intentional, regulated ground ture of the benefits and risks associated stock (R. Sweet, personal correspon- cover may be preferable to the uncer- with living mulch systems. The possi- dence). These two programs laid a tainties of weed competition. bility of crop damage when herbicides foundation upon which many other Controlling competition is the are used to suppress the mulch has horticulturists have built. key to the successful use of living been noted (Lindgren and Ashley, In Apr. 1982, a group of living mulches and has been a persistent ob- 1986) and, while some researchers have mulch researchers gathered at Oregon stacle to widespread acceptance of this been able to control competition (Gru- State Univ. for a workshop entitled practice. In his 1911 book entitled binger and Minotti, 1990; Lanini et “Crop Production using Cover Crops Field Notes on Apple Culture, Liberty al., 1989), studies on a variety of crops and Sods as Living Mulches.” Sweet Hyde Bailey suggested that manage- show yield reductions even with sup- was an invited speaker, along with ment of cover crops in orchards should pression of the mulch (Neilsen and others from California, Oregon, Wash- involve increasing manure application Anderson, 1989; Wiles et al., 1989). ington, and British Columbia. In addi- and suppressing the sod through graz- Living mulch systems can be more tion to sharing results from their re- ing of hogs or sheep. difficult to manage than conventional spective programs, the participants A 1952 study, conducted by Univ. cropping systems and often require

HortTechnology · Apr./June 1993 3(2) 141 specialized equipment or changes in a natural ecosystem. In a natural eco- corn production with partial rototilling. Amer. scheduling. Changes in the soil envi- system, energy and nutrient flow is J. of Alt. Agr. 5(1):4-12. ronment can occur as a result of both relatively stable and self-regulating. Haskell, S.B. (ed.). 1926. Symp. on Soil Dete- the reduction of tillage and the pres- Living mulches, green manures, and rioration. J. Amer. Soc. Agron. 18(2):89- ence of a living ground cover in the cover crops act to increase the amount 165. field (Haynes, 1980; Thomas and Frye, of biomass that remains in place and Haynes, R.J. 1980. Influence of soil manage- 1984). Living mulch often alters soil thus contribute to sustaining the sys- ment practice on the agro-ecosys- temperature and moisture levels and tem over the long term (Allison, 1973; tem. Agro-Ecosystems. 6(1980):3-30. can affect seed germination and dis- Kononova, 1961). Their value lies in Hughes, B.J. and R.D. Sweet. 1979. Living ease incidence. Insect and vertebrate their role in maintaining and conserv- mulch: a preliminary report on grassy cover problems sometimes increase un- ing the soil and, as such, these practices crops interplanted with vegetables. In: R.B. der living mulch systems (deCalesta, will remain, as they have been in past Taylorson (ed.). Proc. Northeast Weed Sci- 1982; Norris, 1986), although they eras, a useful tool for solving the prob- ence Soc., Vol. 33. Evans, Salisbury, Md. have been found to support beneficial lems that face agriculture today. Hurt, R.D. 1981. The Dust Bowl: an agricul- insects as well, in some cases (Andow tural and social history. Nelson-Hall, Chi- et al., 1986; William, 1981). cago. Overall, a living mulch system is Literature Cited Kononova, M.M. 1961. : more complex than conventional, Allen, R.L. 1852. The American farm book or Its nature, its role in soil formation and a compend of American agriculture. C.M. clean-tilled systems, and for this rea- fertility. Pergamon, New York. son living mulches, like other no-till Saxton and Co., New York. systems, are not suited to all situations. Kurtz, T., S.W. Melsted, and R.H. Bray. 1957. Allison, F.E. 1973. Soil organic matter and its The importance of nitrogen and water in There are many instances, however, in role in crop production. Elsevier, New York. reducing competition between intercrops and which living mulches can be used ef- Andow, D.A., A.G. Nicholson, H.C. Wien, corn. Agron. J. 44(1):13-17. fectively. In recent years, the study of and H.R. Willson. 1986. Insect populations Lanini, W.T, D.R. Pittenger; W.L. Graves, F. this practice has been incorporated on cabbage grown with living mulches. Munoz, and H.S. Agamalian. 1989. Environ. Entomol. 15(2):293-299. into complex studies that take a sys- Subclovers as living mulches for managing tems approach to crop production. Bailey, L.H. 1911. Field notes on apple cul- weeds in vegetables. Calif. Agr. 43(6):25-27. Ideally, these studies involve a ture. Orange Judd, New York. multidisciplinary team, including hor- Lauer, J.G. and K.J. Fornstrom. 1988. A liv- ing mulch system for sugarbeet establish- ticulturists, entomologists, plant pa- Carter, V.G. and T. Dale. 1974. and civilization. Univ. of Oklahoma Press, Nor- ment, Wyoming Agr. Sta., Laramie. Bul. thologists, ecologists, agronomists, and man. 907:50-53. agricultural economists. Living mulches, cover crops, and green ma- de Calesta, D.S. 1982. Potential rodent prob- Lewis, W.M. and C.K. Martin. 1967. Sod planting with band and broadcast herbicide nures integrate well into many crop- lems in a living mulch system. In: J.C. Miller and S.M. Bell (eds.). Crop production using application. Proc. 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