ROOT DEVELOPMENT IN A SESBANIA SESBAN FALLOW-MAIZE SYSTEM IN EASTERN ZAMBIA

Roots of trees (Sesbania sesban) and crops (Zea mays) were quantified during two tree/crop cycles in a sequential tree - crop system at Chip ata, Eastern Zambia. The experiment included one- and two-year fallows as well as fertilized and unfertilized controls. The roots of S. sesb an represent a standing biomass in the soil of 3 Mg ha(-1) in the top 1.5 m after two years, with 45-60% and 70-75% being in the top 25 and 50 cm respectively. S. sesban fallow improved early rooting and growth of the following maize crop. Increased soil infiltration was also obs erved in the two-year fallow treatment, as well as decreased bulk dens ity and resistance to penetration in the soil. No differences between maize root parameters could be detected at tasselling, nor differences between nutrient status of the different treatments. Study results in dicate that under the drought-prone conditions of Eastern Zambia, wher e improved soil physical conditions are important for early deep rooti ng of crops and access to water and nutrients, tree roots could play a n important role in the fallow effect. Further studies are required to assess the relative importance of the improvement of soil chemical an d physical properties.