Wheat Straw Decomposition and Changes in Decomposability during Field Exposure

Abstract

AbstractDescribing crop residue decomposition is important for assessing management practices that protect soil against wind and water erosion. Predicting wheat (Triticum aestivum L. em Thell) residue decomposition in conservation tillage systems requires information on C mineralization and changes in residue decomposability. The principal component of wheat residue is the stem. Wheat straw decomposition at the soil surface was followed during field and laboratory inclubation studies. Straw samples were collected on nine dates during 377 d of field exposure and analyzed for weight loss. Total C, soluble C, carbohydrate, N content, and C mineralization were measured periodically during the exposure period. Straw weight loss was 12% after 33 d and averaged 0.05% d−1 for the remaining exposure period. Cumulative weight loss was 33%. Total N, soluble C, and carbohydrate concentrations decreased 17, 73, and 66%, respectively, during field exposure. Total C concentration increased 6.2% after 94 d, then returned to the C concentration of the original straw. In the laboratory, C mineralization of straw taken from the field after ≥94 d was significantly (P < 0.001) lower than C mineralization of fresh residue. Cumulative CO2 evolution among samples that had been in the field for 94 to 377 d was not significantly different (P = 0.03). Amount and quality of soluble C was found to be important only during initial stages of fresh straw decomposition and was inconsequential for field exposed straw. Additions of cellobiose and N had no influence on C mineralization during laboratory incubation.