In irrigated plantations of Punjab extensive management results in nutrient deficiency and tree growth becomes N limited on sites where non dinitrogen - fixing species are raised. The fast growing hybrid poplar and mulberry deplete the soil of its essential nutrients. The soils under Pinus roxburghii Sarg., Leucaena and Eucalyptus camaldulensis Dehn. Show increased net nitrogen mineralization rates, whereas continuously grazed and leaf-litter harvested sites of mulberry and hybrid poplar (1-214) have comparatively low total soil nitrogen, net nitrogen mineralization rates and, consequently, low N assimilation.