ABOVEGROUND AND BELOWGROUND INTERACTIONS IN A LEUCAENA/MILLET ALLEY CROPPING SYSTEM .2. LIGHT INTERCEPTION AND DRY-MATTER PRODUCTION

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 and five, six and six rows of millet, respectively. LM6P differed from LM6 in that a vertical polytene barrier separated the root systems of leucaena and millet to a depth of 50 cm. Dry matter production and light interception data for millet and leucaena are presented to allow comparison of light capture and utilisation efficiency by the two species under contrasting hedge management in the rainy seasons of 1986 and 1987. Dry matter yields of leucaena did not differ significantly between treatments in either rainy season, but were much higher in 1987 than in 1986 because of the less severe lopping regime. The higher yields in 1987 resulted from a greater mean fractional light interception by leucaena, which increased shading of alley cropped millet when compared with 1986. The dry matter yields of millet in treatments LM5 and LM6 were reduced relative to the sole crop in both years. In 1986, this reduction appeared to result primarily from shading, while in 1987 the mean fractional light interception and the pre-anthesis conversion coefficient were both lower in LM5 than in SM. Above- and below-ground competition interacted in 1986, so that when root competition was reduced (LM6P) the millet was able to grow taller, eventually matching the leucaena in height and partially escaping the shading and yield reduction experienced in LM5 and LM6. In 1987, the hedges were always more than 1 m taller than the millet and the root barrier failed to remove the detrimental competition between leucaena and millet.