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 availability with a view to effective management of the fertility of moderately alkaline soils. The study site was located at Karnal (29◦59′N, 76◦51′E, 250 m.s.l.) and the systems were characterized by a rice–berseem crop rotation; agrisilvicultural systems of Acacia, Eucalyptus and Populus along with rice–berseem and single species tree plantations. Soil microbial biomass was measured using the fumigation extraction technique and nitrogen mineralization using the aerobic incubation method. Microbial biomass carbon was low in rice–berseem crops (96.14 mg g−1 soil) and increased in soils under tree plantations (109.12–143.40 mg g−1 soil) and agrisilvicultural systems (133.80–153.40 mg 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 soil 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 CO2-C production, biomass specific respiratory activity, and nitrogen mineralization 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 microbial biomass pool and greater soil N availability, agrisilvicultural systems have been found to be ecologically sustainable land-use systems for utilizing moderately alkaline soils. © 2000 Elsevier Science B.V. All rights reserved.