Optimizing nutrient availability and potential carbon sequestration in an agroecosystem

The uniformity, low cost and ease of application associated with inorganic fertilizers have diminished the use of organic nutrient sources. Concern for food safety, the environment and the need to dispose of animal and municipal wastes have focused attention on organic sources of N such as animal-derived amendments, green manures, and crop rotations. Managing organic N sources to provide sufficient N for crop growth requires knowledge of C and N decomposition over several years, particularly where manure and compost are applied. We report a comparison of compost and chemical fertilizer, use of a corn-corn-soybean-wheat rotation compared to continuous corn and the use of cover crops. Nitrogen (150 d) and C incubations (317 d) were conducted to determine the effect of cropping system and nutrient management on: N mineralization potential (NMP), the mineralizable organic N pool (N_o), the mean residence time (MRT) of No, C mineralization (C_min), and soil organic carbon (SOC) pool sizes and fluxes. Compost applications over 6 y increased the resistant pool of C by 30% and the slow pool of C by 10%. The compost treatment contained 14% greater soil organic C than the fertilizer management. Nitrogen was limiting on all compost treatments with the exception of first year corn following wheat fallow and clover cover crop. The clover cover crop and wheat-fallow increased inorganic N in both nutrient managements. We recommend that growers adjust their N fertilizer recommendation to reflect the quantity and timing of N mineralized from organic N sources and the N immobilization that can be associated with compost or other residue applications. Proper management of nutrients from compost, cover crops and rotations can maintain soil fertility and increase C sequestration.