Preface. I: Introduction. 1. The History of Agroforestry. 2. Definition and Concepts of Agroforestry. II: Agroforestry Systems and Practices. 3. Classification of Agroforestry Systems. 4. Distribution of Agroforestry Systems in the Tropics. 5. Shifting Cultivation and Improved Fallows. 6. Taungya. 7. Homegardens. 8. Plantation Crop Combinations. 9. Alley Cropping. 10. Other Agroforestry Systems and Practices. III: Agroforestry Species. 11. General Principles of Plant Productivity. 12. Agroforestry Species: the Multipurpose Trees. 13. Component Interactions. IV: Soil Productivity and Protection. 14. Tropical Soils. 15. Effects of Trees on Soils. 16. Nutrient Cycling and Soil Organic Matter. 17. Nitrogen Fixation. 18. Soil Conservation. V: Design and Evaluation of Agroforestry Systems. 19. The Diagnosis and Design (D&D) Methodology. 20. Field Experiments in Agroforestry. 21. On-Farm Research. 22. Economic Considerations. 23. Sociocultural Considerations. 24. Evaluation of Agroforestry Systems. 25. Agroforestry in the Temperate Zone. Glossary. SI Units and Conversion Factors. List of Acronyms and Abbreviations. Subject Index.

An introduction to agroforestry

The topics addressed in this volume of a continuing series on the soil sciences are soil-water repellency, nutrient transformations in soils amended by green manures, and the physical fractionation of soil and organic matter in primary particle size and density separates.

Advances in Soil Science

Publisher Summary This chapter describes the various aspects of cereal-legume intercropping systems Intercropping is the growing of two or more crop species simultaneously in the same field during a growing season The intercropping of legumes with cereals offers scope for developing energy-efficient and sustainable agriculture The main types of intercropping include mixed intercropping, row intercropping, and strip intercropping Crop combinations differ with geographical location and there may be intercropping of tree crops, intercropping of tree and field crops, or intercropping of field crops Combinations of crops are determined primarily by the length of the growing season and the adaptation of crops to particular environments Different indices have been suggested for evaluating productivity and efficiency per unit area of land of cereal-legume intercrop systems These include comparisons of absolute yields, protein yields, caloric equivalent, and in economic terms, gross returns from intercrops and sole crops Differences in competitive ability affect the relative performance of component crops and thus the land equivalent ratio values of different cereal-legume intercrop systems It is found that phosphorus is a major nutrient that determines the production potential of most grain legumes usually intercropped with cereals

Cereal–Legume Intercropping Systems

The evolution of natural ecosystems is controled by a high level of biodiversity, In sharp contrast, intensive agricultural systems involve monocultures associated with high input of chemical fertilisers and pesticides. Intensive agricultural systems have clearly negative impacts on soil and water quality and on biodiversity conservation. Alternatively, cropping systems based on carefully designed species mixtures reveal many potential advantages under various conditions, both in temperate and tropical agriculture. This article reviews those potential advantages by addressing the reasons for mixing plant species; the concepts and tools required for understanding and designing cropping systems with mixed species; and the ways of simulating multispecies cropping systems with models. Multispecies systems are diverse and may include annual and perennial crops on a gradient of complexity from 2 to n species. A literature survey shows potential advantages such as (1) higher overall productivity, (2) better control of pests and diseases, (3) enhanced ecological services and (4) greater economic profitability. Agronomic and ecological conceptual frameworks are examined for a clearer understanding of cropping systems, including the concepts of competition and facilitation, above- and belowground interactions and the types of biological interactions between species that enable better pest management in the system. After a review of existing models, future directions in modelling plant mixtures are proposed. We conclude on the need to enhance agricultural research on these multispecies systems, combining both agronomic and ecological concepts and tools.

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Mixing plant species in cropping systems: concepts, tools and models. A review

Intercropping, the agricultural practice of cultivating two or more crops in the same space at the same time, is an old and commonly used cropping practice which aims to match efficiently crop demands to the available growth resources and labor. The most common advantage of intercropping is the production of greater yield on a given piece of land by making more efficient use of the available growth resources using a mixture of crops of different rooting ability, canopy structure, height, and nutrient requirements based on the complementary utilization of growth resources by the component crops. Moreover, intercropping improves soil fertility through biological nitrogen fixation with the use of legumes, increases soil conservation through greater ground cover than sole cropping, and provides better lodging resistance for crops susceptible to lodging than when grown in monoculture. Intercrops often reduce pest incidence and improve forage quality by increasing crude protein yield of forage. Intercropping provides insurance against crop failure or against unstable market prices for a given commodity, especially in areas subject to extreme weather conditions such as frost, drought, and flood. Thus, it offers greater financial stability than sole cropping, which makes the system particularly suitable for labor-intensive small farms. Besides, intercropping allows lower inputs through reduced fertilizer and pesticide requirements, thus minimizing environmental impacts of agriculture. However, intercropping has some disadvantages such as the selection of the appropriate crop species and the appropriate sowing densities, including extra work in preparing and planting the seed mixture and also extra work during crop management practices, including harvest. The selection of an appropriate intercropping system for each case is quite complex as the success of intercropping systems depend much on the interactions between the component species, the available management practices, and the environmental conditions. Plant breeding can contribute determinedly to increase of productivity of intercropping systems by investigating and exploiting the genetic variability to intercrop adaptation. This paper provides an overall view and evaluation of annual intercropping, summarizing its main advantages supported by a number of key examples from the literature which point out its great value in the context of sustainable agriculture.

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Annual intercrops: an alternative pathway for sustainable agriculture.

Criteria for evaluating different intercropping situations are suggested, and the Land Equivalent Ratio (LER) concept is considered for situations where intercropping must be compared with growing each crop sole. The need to use different standardizing sole crop yields in forming LERs is discussed, and a method of calculating an ‘effective LER’ is proposed to evaluate situations where the yield proportions achieved in intercropping are different from those that might be required by a farmer. The possible importance of effective LERs in indicating the proportions of crops likely to give biggest yield advantages is discussed.

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The Concept of a ‘Land Equivalent Ratio’ and Advantages in Yields from Intercropping

A simple competitive ratio (CR) is proposed as a measure of intercrop competition, to indicate the number of times by which one component crop is more competitive than the other. Intercropping data show that this CR term could be useful in (i) comparing the competitive ability of different crops, (ii) measuring competitive changes within a given combination, (iii) identifying which plant characters are associated with competitive ability, and (iv) determining what competitive balance between components is most likely to give maximum yield advantages.

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A competitive ratio for quantifying competition between intercrops.

Data from 94 experiments on sorghum/pigeonpea intercropping were examined for evidence that the stability of yield is greater with intercropping than sole cropping. Stability of the major component (sorghum) was examined by calculating the distribution of yields; stability of the overall intercropping system was examined by calculating coefficients of variation, by computing regressions of yield against an environmental index, and by estimating the probability of monetary returns falling below given ‘disaster’ levels. All these approaches have some merit; taking the last as an example, it was found that for a particular ‘disaster’ level quoted, sole pigeonpea would fail one year in five, sole sorghum one year in eight, but intercropping only one year in thirty-six. Intercropping gave yield advantages under a wide range of environmental conditions and there was no significant evidence that advantages were greater under stress. This is discussed in relation to possible mechanisms contributing to greater yield stability.

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Evaluation of Yield Stability in Intercropping: Studies on Sorghum/Pigeonpea

It is proposed that two distinct objectives should be recognized in the evaluation of intercropping advantages: (i) a biological objective to determine the increased biological efficiency of intercropping and (ii) a practical objective to determine the advantages that are likely to be obtained by a farmer. The sole crop systems with which intercropping must be compared to satisfy these objectives are defined. Evaluation in relative, absolute, monetary and nutritional units is discussed and some aspects of presenting intercropping data in graphical form are illustrated.

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Evaluation and Presentation of Intercropping Advantages

A field technique is described in which trenches were dug and vertical polythene partitions installed to eliminate below-ground interactions between component crops in intercropping. With pearl millet/groundnut the control intercrop (i.e. not dug out) gave a yield advantage of 22% compared with sole cropping. A treatment dug out but refilled without polythene partitions was very similar to the control intercrop, indicating that the digging procedure per se had little effect on growth. An intercrop treatment in which below-ground partitions were installed gave a yield advantage of 19% over sole cropping, suggesting that the main determinant of yield advantage was an above-ground interaction between the canopies. However, partitioning decreased millet yield and increased groundnut yield, indicating that below-ground interactions were important in determining the competitive balance of the two crops. It is concluded that the partitioning technique is promising.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0014479700011613

R. W. Willey

Papers

The Concept of a ‘Land Equivalent Ratio’ and Advantages in Yields from Intercropping

A competitive ratio for quantifying competition between intercrops.

Evaluation of Yield Stability in Intercropping: Studies on Sorghum/Pigeonpea

Evaluation and Presentation of Intercropping Advantages

A Field Technique for Separating Above- and Below-Ground Interactions in Intercropping: an Experiment With Pearl Millet/Groundnut