Chapter V Multiple Cropping Systems: A Basis for Developing an Alternative Agriculture Dr. Stephen R. Gliessman Environmental Studies University of California Contents Page Abstract . 69 Introduction . 69 Concepts and Definitions . 70 The Basis of Multiple Cropping. 71 Yield Advantages of Crop Mixtures . 71 General Resource Use . 73 Specific Resource Use, Conservation, and Management . 75 Agroforestry: A Multiple Cropping System . 79 Socioeconomic Implications of Multiple Cropping Systems: Perspectives for the Future . 80 References. 82 List of Tables Table No. Page l. Definitions of the Principle Multiple Cropping Patterns . 71 2. Related Terminology Used in Multiple Cropping Systems . 71 3. Biological and Physical Factors: The Advantages and Disadvantages of Multiple Cropping Systems Compared to Sole-Cropping or Monoculture Systems. 72 4. Social and Economic Factors: The Advantages and Disadvantages of Multiple Cropping Systems Compared to Sole-Cropping or Monoculture Systems . 73 S. Yields of Corn, Beans, and Squash Planted in Polyculture as Compared to Low and High Densities of Each Crop in Monoculture . 74 6. Effects of Mixed and Row Intercropping on Yields and Nutrient Uptake of Corn and Pigeon Peas in St. Augustine, Trinidad, Expressed as Relative Yield Totals . 76 7. Biomass Distribution of Dry Matter in a Corn/Bean Polyculture as Compared to a Corn Monoculture, in Tacotalpa, Tabasco, Mexico . 76 8. Classification and Examples of Agroforestry Technologies. 80 Figure Figure No. Page l. Distribution of the Relative Yield Totals of Mixtures Based on 572 Published Experiments . 72 Chapter V Multiple Cropping Systems: A Basis for Developing an Alternative Agriculture This paper presents a general discussion of Specific examples of the effects of multiple the concept of multiple cropping, including a cropping systems on resource use, conserva- description of the different types of systems, tion, and management are discussed, Variables and the advantages and disadvantages of their considered include microclimate, light, soil, widespread use, both biological and socio- water, pests, diseases, weeds, crop interac- economical. These systems are designed to in- tions, space, and time. The special case of tensify agricultural production both in terms agroforestry, which combines trees with crops of yields per unit area and through the more and grasses, is discussed. efficient use of space and time. In conclusion, the socioeconomic implica- Examples of yield increases with multiple tions, both advantageous and disadvantageous, cropping systems are expressed in terms of are discussed. Also, the great potential for Relative Yield Totals (RYT) or Land Equivalent multiple cropping systems in agriculture in the Use (LER) where the production per unit area United States is presented. Research needs to with the multiple crops is greater than the sum be directed to test these alternatives. of equivalent areas planted to monoculture. This increase in production is explained by higher overall efficiency of resource use. Multiple cropping is not a new form of agri- cropping systems is more prevalent. Though cultural technology, but instead is an ancient the history of multiple cropping is old, the con- means of intensive farming. Multiple cropping cept has received very little attention from agri- has been practiced in many parts of the world cultural scientists, and what limited interest ex- as a way to maximize land productivity in a ists has come about very recently. specific area in a growing season. Generally, the practice of planting two or more crops on Why was this interest increased so dramat- the same field is more common in tropical re- ically in such a short time? Food shortages in gions where more rainfall, higher tempera- many parts of the world, as well as the threat tures, and longer growing seasons are more of insufficient supplies in the near future, con- favorable for continual crop production. As tinues to stimulate more intensive agricultural population has increased, increasing the need investigation in a search for more productive for agricultural production, the use of multi- alternatives. As a consequence, it appears that 69 70 we are about to embark on a new phase of agri- best agricultural lands–areas with good soil cultural research. Exactly what form it will take and easy water control. Future increases in is still not known, but the reasons for this new production, therefore, will demand a new and approach are rapidly becoming apparent. innovative way of managing these highly pro- ductive lands, as well as looking for methods First, we have begun to observe a leveling off to make marginal lands increasingly produc- in yield increases brought about by the types tive. Only 20 percent of Asia rice land, for ex- of genetic manipulation that gave us such rapid ample, is irrigated, and the new high yielding and impressive yield increases during the rice varieties (which also require high levels of “Green Revolution.” It is as if we have reached fertilizers, water use, and pest control) have not a “yield plateau” with the current lines of r - e penetrated much beyond this boundary (16). search and crop selections. Large-scale use of single varieties (e.g., some of the International The third factor is the oil crisis. Oil prices Rice Research Institute (IRRI) varieties of rice), continue to soar, and with them, the cost offer- with broad adaptability, produced major break- tilizers, pesticides, and fuel needed to build and throughs in yields. But it appears that these va- run farm equipment and move irrigation water. rieties have almost reached their maximum Costs continue to mount for those inputs most yield potentials. In many areas with specific responsible for achieving the dramatic yield in- soil and climatic conditions, they have not per- creases of the “Green Revolution. ” We are formed as well as hoped, especially on land faced with the necessity of having to consider more difficult to mechanize or irrigate. Thus other alternatives that might allow us to sub- we must begin to look for varieties with more stitute innovative biological or agronomic prac- specific adaptability and selected for specific tices and varieties for these high cost inputs. environments, or else consider alternative Multiple cropping offers one of the most im- cropping systems. portant and promising of these alternatives. Second, most of the dramatic yield increases during the past few decades have been on the CONCEPTS AND DEFINITIONS Multiple cropping systems use management tial cropping, where two or more crops are practices where the total crop production from grown on the same piece of land, but one fol- a single piece of land is achieved by growing lowing the other. single crops in close sequence, growing sev- Some additional terms used in multiple crop- eral crops simultaneously, or combining single ping are presented in table 2. Agroforestry, as and mixed crops in some sequence. The most a particular type of intercropping system, will important aspect of multiple cropping is the be discussed in some detail. Also, “mixed crop- intensification of crop production into addi- ping, “ “polyculture,” and “multiple cropping” tional dimensions. Multiple cropping includes will be used interchangeably in this review. By the dimensions of time and space; for exam- combining different aspects of simultaneous ple, when two crops share the same space at and sequential cropping systems, it is possible the same time. to visualize a truly complex pattern of different A classification of types of multiple cropping multiple cropping systems. This classification systems is presented in table 1. Note that will be used throughout the following discus- special emphasis is placed on the distinction sion, based on a symposium sponsored by the between intercropping, where two or more American Society of Agronomy, in support of crops are grown at the same time, and sequen- the need to standardize terminology (34). — 71 Table 1 .—Definitions of the Principal Multiple Table 2.— Related Terminology Used in Multiple Cropping Patterns Cropping Systems ● Multiple Cropping: The intensification of cropping in time Single Stands: The growing of one crop variety alone in pure and space dimensions. Growing two or more crops on the stands at normal density. Synonymous with “solid plant- same field in a year. ing, “ “sole cropping. ” Opposite of ‘(multiple cropping. ” c Intercropping: Growing two or more crops simultaneously Monoculture: The repetitive growing of the same crop on the on the same field per year. Crop intensification is in both same land. time and space dimensions. There is intercrop competi- Rotation: The repetitive growing of two or more sole crops tion during all or part of crop growth. Farmers manage more or multiple cropping combinations on the same field. than one crop at a time in the same field. Cropping Pattern: The yearly sequence and spatial arrange- —Mixed intercropping: Growing two or more crops simul- ment of crops, or of crops and fallow on a given area. taneously with no distinct row arrangement. Cropping System: The cropping patterns used on a farm and —Row intercropping: growing two or more crops their interactions with farm resources, other farm enter- simultaneously with one or more crops planted in rows. prises, and available technology that determine their —Strip intercropping: Growing two or more crops simul- makeup. taneously in different strips wide enough to permit in- Mixed Farming: Cropping systems that involve the raising dependent cultivation but narrow enough for the crops of crops and animals. to interact agronomically. Cropping Index: The number of crops grown per annum on —Relay intercropping: Growing two or more crops simul- a given area of land multiplied by 100. taneously during part of each one’s life cycle. A second Relative Yield Total (RYT): The sum of the intercropped yields crop is planted after the first crop has reached its divided by yields of sole crops. The same concept as land reproductive stage of growth, but before it is ready for equivalent ratios. “Yield” can be measured as dry matter harvest.