Above- and below-ground interactions in a leucaena/millet alley cropping system. I. Experimental design, instrumentation and diurnal trends

Abstract

Leucaena ( Leucaena leucocephala (Lam.) de Wit) and pearl millet ( Pennisetum glaucum (L.) R.Br.) were grown together in an alley cropping system in a semi-arid area of India. The five treatments included sole millet (SM), sole leucaena (SL) planted in double rows to form hedges with an alley width of 2.8 m, and alley cropping treatments LM5, LM6 and LM6P with alley widths of 2.8, 3.3 and 3.3 m, respectively. Millet rows within the alleys were spaced at 47 cm, giving five rows in LM5 and six rows in both LM6 and LM6P. LM6P differed from LM6 in that a vertical polythene barrier separated the root systems of leucaena and millet to a depth of 50cm. Light interception, wind speed, saturation deficit and air, soil and leaf temperatures were monitored during the 1986 and 1987 rainy seasons in treatments SM, SL and LM5. This paper describes the experimental design and instrumentation and presents representative diurnal time courses illustrating the nature of the microclimatic changes associated with alley cropping. These indicate that alley cropping altered the microclimate experienced by millet to an extent which depended on its proximity to the hedge, hedge shape and the relative size of the two components. The larger leucaena canopy in 1987 than in 1986 resulted in more substantial reductions in wind speed and incident light in the alleys of LM5 as compared with SM. Leaf and soil temperatures within the alleys tended to be warmer during the night and cooler during the day than in SM and temperature differences between rows within LM5 were related to the degree of shading by leucaena. Analysis of integrated data predicted little effect of the observed changes in saturation deficit on the productivity of millet, while thermal time analysis for 1987 suggested a 2—3 day delay in flowering for millet adjacent to the hedge as compared with sole millet.