1. Rodale Institute, 611 Siegfriedale Road, Kutztown, Pennsylvania 19530, USA
2. Present address: Sustainable Systems Program, Slippery Rock University, Slippery Rock, Pennsylvania 16057, USA.

Correspondence to: L. E. Drinkwater¹ Correspondence and requests for materials should be addressed to L.E.D. (e-mail: Email: ldrink@rodaleinst.org).

Abstract

In agricultural systems, optimization of carbon and nitrogen cycling through soil organic matter can improve soil fertility and yields while reducing negative environmental impact. A basic tenet that has guided the management of soil organic matter for decades has been that equilibrium levels of carbon and nitrogen are controlled by their net input and that qualitative differences in these inputs are relatively unimportant^{1, 2, 3}. This contrasts with natural ecosystems in which there are significant effects of species composition and litter quality on carbon and nitrogen cycling⁴,⁵. Here we report the net balances of carbon and nitrogen from a 15-year study in which three distinct maize/soybean agroecosystems are compared. Quantitative differences in net primary productivity and nitrogen balance across agroecosystems do not account for the observed changes in soil carbon and nitrogen. We suggest that the use of low carbon-to-nitrogen organic residues to maintain soil fertility, combined with greater temporal diversity in cropping sequences, significantly increases the retention of soil carbon and nitrogen, which has important implications for regional and global carbon and nitrogen budgets, sustained production, and environmental quality.