Dobermann, Achim (University of Nebraska, Dept. of Agronomy and Horticulture, University of Nebraska Lincoln, NE, 68583-0915; Phone: 402-472-1501; Email: adobermann2@unl.edu)

Changes in Soil- and Litter-C Stocks with Progressive Farming Practices in Irrigated and Rainfed Maize-Based Agroecosystems.

A. Dobermann*, J. M. H. Knops, K. G. Cassman, D. T. Walters

Litter decomposition, and changes in soil carbon stocks were quantified in three no-till cropping systems with best-management practices that produce high yields with improved input use efficiency: (a) irrigated continuous maize, (b) irrigated maize-soybean rotation, and (c) rainfed maize-soybean rotation. Measurements were conducted in production-scale fields for a period of three years. Decomposition of maize residue was similar in both irrigated and rainfed sites, but soybean residue decomposed 10 to 24% faster than maize residue. Litter-C pools increased by about 230 g m-2 during this 3-year period in the irrigated continuous corn system because of large litter-C inputs and relatively slow decomposition rates. In irrigated corn-soybean rotation, gains in litter-C during the corn phase were largely offset by losses of similar magnitude during the soybean phase. Measurements of soil organic C stocks could not detect significant changes during the first three years of no-till farming in the three cropping systems studied despite the use of a novel approach that accounted for geospatial variation in soil properties that influence soil C dynamics