SOIL ORGANIC-MATTER, MICROBIAL BIOMASS AND ENZYME-ACTIVITIES IN A TROPICAL AGROFORESTRY SYSTEM

The effects of growing trees in combination with field crops on soil o rganic matter, microbial biomass C, basal respiration and dehydrogenas e and alkaline phosphatase activities were studied in soils under a 12 -year-old Dalbergia sissoo (a N-2-fixing tree) plantation intercropped with a wheat (Triticum aestivum)cowpea (Vigna sinensis) cropping sequ ence. The inputs of organic matter through D. sissoo leaf litter incre ased and crop roots decreased with the increase in tree density. Highe r organic C and total N, microbial biomass C. basal soil respiration a nd activities of dehydrogenase and alkaline phosphatase were observed in treatments with tree-crop combination than in the treatment without trees. Soil organic matter, microbial biomass C and soil enzyme activ ities increased with the decrease in the spacing of the D. sissoo plan tation. The results indicate that adoption of the agroforestry practic es led to an improved organic matter status of the soil, which is also reflected in the increased nutrient pool and microbial activities nec essary for long-term productivity of the soil. However, tree spacing s hould be properly maintained to minimize the effects of shading on the intercrops.