Perennial pigeonpea (Cajanus cajan (L) Millsp.) was grown as a multipurpose tree species in strips or blocks with annual crops (sorghum, sunflower and chickpea) on a shallow Vertisol from 1987 to 1989. The interaction between the perennial pigeonpea and annual crops was measured at the tree-crop interface (TCI) by comparing the plants at the interface (I) and in the middle of the block planting (N).
Perennial pigeonpea I plants had significantly more branches and bigger stems than N plants at the onset of the following rainy season. The greater number of flowers and grains of the I pigeonpea plants was partly due to a better lateral light level and partly due to a better access to water. On the other hand the negative effect on annual crops at the TCI extended to 1.5 m during the rainy season and to 2.5 m during the post-rainy season. Significant reduction in the growth of annual crops occurred at 30-40 days after sowing and was associated with the shading by the taller pigeonpea. Measurements of root profile of pigeonpea at the interface indicated that competition for moisture was the major cause for yield reduction of chickpea during the post-rainy season but an allelopathetic effect may also be involved. The results are compared with other TCI studies especially with Leucaena leucocephala in the semi-arid crops and the possible mechanisms for moisture interaction at the TCI are discussed.