Crop Residue Decomposition in Intercropped and Sole Cropped Agroecosystems in the Argentine Pampas.

Argentina is currently one of the world’s biggest maize and soybean producers, and the current cropping area is expected to expand. Cultivation of soybeans has increased from 5 to 14.5 million hectares in the last 10 years. However, intensive sole cropping results in soil degradation and lowered soil organic matter (SOM). In addition, soybeans have low biomass productivity and therefore low carbon (C) return to the soil. Depletion of soil organic carbon (SOC) contributes to greenhouse gases (GHG) and lowered crop productivity. Knowledge of plant residue input and their rate of decomposition help to understand SOC dynamics. In Latin America, there is a need to conduct more studies in agricultural systems regarding the potential of the soils of intercropped agroecosystems to sequester C and reduce GHG fluxes. In this study, C and nitrogen (N) input from crop biomass was evaluated. The experimental site at Balcarce, Argentina (37º 45´S, 58º 18´W; elevation 130 m) was a randomized complete block design (RCBD) with 3 replications consisting of two maize-soybean intercrop agroecosystems, a maize sole crop and a soybean sole crop. The rate of soybean and maize residue decomposition was evaluated by placing approximately 20 g of oven-dry crop residue in 25 cm x 25 cm bags with a 2 mm mesh size. Litterbags were collected monthly and the residue was analyzed for C and N. The C- and N-input from crop residue was sampled during harvest within a 1 m x 0.52 m area in each plot. Crops were separated into above- and belowground plant components and dried material was sampled for C and N.