Agroforestry Systems 20:199--212, 1992. © 1992 Kluwer Academic Publishers. Printed in the Netherlands. Increasing Gliricidia sepium and Cassia spectabilis biomass production R. H. MACLEAN, 1 J. A. LITSINGER, 1 K. MOODY 1 and A. K. WATSON 2 i International Rice Research Institute, P.O. Box 933, 1099 Manila, Philippines," 2 Department of Plant Science, Macdonald Campus of McGill University 21 111 Lakeshore Road, Ste-Anne de Bellevue, Quebec, H9X 1CO Canada Key words: mixed hedgerows, inter- and intra-specific competition Abstract. This paper examines the impact of spacing on biomass production of monocropped and mixed hedgerows of seedlings and cuttings of Gliricidia sepium and Cassia spectabilis. The impact of lime on G. sepium biomass production was also evaluated. Seedlings survived better than cuttings; and no differences were observed between seedlings in either pattern at the highest density tested. Although spacing reduced inter-and intra-specific competition, total biomass production was greatest at higher densities. Mixing hedgerow species reduced intraspecific competition within C. spectabilis, resulting in increased biomass production. Six, 8 and 12 tons of lime per hectare significantly increased fresh G. sepium biomass production at all harvest dates except the first. Extrapolated to an alley cropping system, applying 6 t/ha of lime increased fresh cumulative G. sepium biomass production by almost 39 t/ha over the no lime treatment representing more than 200 kg N/ha. Introduction Alley cropping, a system in which food crops are grown between hedgerows of perennial leguminous, woody shrubs and/or grasses, is an agroforestry system addressing some of the problems facing upland farmers [14]. Benefits of alley cropping include: (1) the amelioration of soil chemical and physical properties [18, 19, 38], (2) the reduction of soil erosion by contoured hedgerows and mulched biomass ]17], (3) the potential uptake and recycling of leachates by deep rooted perennials [9, 15], (4) improved weed control [39], and (5) increased availability of fuelwood and/or fodder. The degree to which alley cropping can provide the above benefits partially depends on the quantity of biomass hedgerows can produce. Hedgerow biomass production is governed by species selection, spatial arrangement and management prac- ticed [40]. Acid soils represent almost two thirds of the world's humid tropics [30]. Phosphorus, an essential nutrient for lateral and fibrous rootlet development, can be adsorbed and made unavailable by aluminum and iron complexes in acid soils, thus reducing the plant's growth rate and increasing its suscep- tibility to drought [5, 6, 31]. Acid soils are particularly unfavorable for