Experimental Designs for Alley Cropping to Estimate Shrub x Grass Interaction
Alley cropping, an agroforestry system, comprises rows of perennial shrubs or trees bordering the alleys of grasses/crops. An appropriately chosen alley cropping provides improvement in feeds for small ruminants, food for human consumption, and contributes to economic and environmental sustainability. Rangeland and forage development studies aim at evaluation of interference of shrubs such as saltbush Atriplex, with the grasses or fodder/forage crops such as vetch/barley. In such studies a number purposely selected species of shrubs and grasses are evaluated under an alley cropping. This presentation discusses a number of experimental designs and statistical models for analysis of responses on the grasses/crops in the alleys. The experimental designs considered are the complete block with or without split-plot frames for the border and alley experimental units. The treatment designs include a factorial structure of shrub borders and grasses. The shrub-borders considered are of self-types, i.e. same shrub on both sides of the alley, and partial diallel-type, i.e., different shrubs on the borders. The linear models consisting of shrubs effects, grasses effects and their interaction with different structures are considered with parameters defined for shrub × grass interaction. A statistical analysis of the alley- responses has been illustrated with a simulated dataset. Key words: Alley cropping, Shrub and Grass Effects and Interaction, Self and Diallel Designs, Blocks, Split-plots.