Soil carbon, microbial activity and nitrogen availability in agroforestry systems on moderately alkaline soils in northern India

The present investigation aimed to analyze the role of agroforestry systems in improving soil organic matter status, microbial activity and nitrogen a vailability with a view to effective management of the fertility of moderat ely alkaline soils. The study site was located at Karnal (29 degrees 59'N, 76 degrees 51'E, 250 m.s.l.) and the systems were characterized by a rice-b erseem crop rotation; agrisilvicultural systems of Acacia, Eucalyptus and P opulus along with rice-berseem and single species tree plantations. Soil mi crobial biomass was measured using the fumigation extraction technique and nitrogen mineralization using the aerobic incubation method. Microbial biom ass carbon was low in rice-berseem crops (96.14 mug g(-1) soil) and increas ed in soils under tree plantations (109.12-143.40 mug g(-1) soil) and agris ilvicultural systems (133.80-153.40 mug g(-1) soil). Microbial biomass was higher by 42% (microbial C) and 13% (microbial N) in tree-based systems as compared to monocropping. Microbial biomass immobilized 2.32-2.57% of the s oil carbon and 4.08-4.48% of the soil nitrogen in tree-based systems. Soil carbon increased by 11-52% due to integration of trees along with the crops for 6-7 years. Cropland management practices and tree species influenced C O2-C production, biomass specific respiratory activity, and nitrogen minera lization rates. In tree-based systems, soil inorganic N levels were higher by 8-74% and nitrogen mineralization by 12-37% as compared to monocropping. On the basis of increased soil organic matter content, enlarged soil micro bial biomass pool and greater soil N availability, agrisilvicultural system s have been found to be ecologically sustainable land-use systems for utili zing moderately alkaline soils. (C) 2000 Elsevier Science B.V. All rights r eserved.