Impacts of cropping systems on soil nitrogen storage and loss

Organic and low-input cropping systems that use more C inputs are alternati ves to conventional systems for sustaining long-term soil fertility. An und erstanding of the impacts of these cropping systems on N balance (N applied minus N removed in harvested plant material), storage and loss is necessar y to improve long-term soil fertility and minimize the risk of environmenta l pollution. An evaluation of 4-year rotations of organic (N from legumes a nd composted manures), low-input (N from legumes and reduced amounts of syn thetic fertilizers), and conventional (conv-4, N from synthetic fertilizers ) and a conventional 2-year rotation (conv-2, N from synthetic fertilizers) on N balance, storage and loss was conducted from 1989 to 1998. Compared t o the conv-2 system, the organic and conv-4 systems showed 119 and 8% great er cumulative N balances, respectively, over the duration of the study. How ever, N balance in the low-input system was 19% less than in conv-2 system. After 10 years of differential management, total N in the top 15 cm of soi l was 1.46 g kg(-1) in the organic, 1.26 g kg-l in the low-input, 1.13 g kg (-1) in the conv-4, and 1.1 g kg(-1) in the conv-2 system. Compared to the conv-2 system, cumulative N losses for the organic, low-input and conv-4 sy stems were lower by 80, 92, and 10%, respectively. These findings suggest t hat organic and low-input cropping systems that add C to soil have the pote ntial for storing N and making it available for future crop use, while mini mizing the risk of environmental pollution. (C) 2001 Elsevier Science Ltd. All rights reserved.