Design and Analysis of Mixed Cropping Experiments for Indigenous Pacific Island Agroforestry

Mixed cropping (including agroforestry) often gives yield advantages as opposed to monocropping. Many criteria have been used to assess yield advantage in crop mixtures. Some of these are presented. In addition, the relative merits of replacement, additive and bivariate factorial designs are discussed. The concepts of analysis of mixed cropping are applied to an example of an alley cropping (a type of agroforestry) experiment, and a basic agroforestry research guide is described. Mixed cropping is the growing of two or more crops simultaneously on the same land, either with or without distinct row arrangement (Andrews and Kassam 1976), and includes the practice of agroforestry. Mixed cropping was probably the first type of organized crop production (Francis 1986, Plucknett and Smith 1986) and is still widely practiced in the developing world (Osiru and Willey 1972). The fact that intercropping is still widely used in developing countries indicates that the advantages of mixed cropping commonly outweigh the disadvantages in regions where mechanization is rare, inputs are low, and stability of yield is important (Andrews and Kassam 1976, Harwood and Price 1976, Okigbo and Greenland 1976, Francis and others 1976). The fact that mixed cropping is also being seriously considered for certain conditions in developed countries further indicates that this strategy may also be applicable to some forms of mechanized agriculture. Measuring Yield Advantages Nazer and others (1987) have commented on the confusingly large number of indices for assessing the yield advantage of crop mixtures compared to pure stands. The large number of indices partly reflects the differences in criteria used to appraise “advantages,” often encompassing aspects of quality or value as well as yield, but also reflect the different reasons for which an assessment is made, i.e., an ecological vs. an agronomic assessment.