Corn Cob Residue Carbon and Nutrient Dynamics during Decomposition

The cob fraction of corn (Zea mays L.) residue has characteristics that reduce concerns associated with residue removal making it a potential biofuel feedstock. The contribution the cob makes to soil C and nutrient dynamics is unknown. A litterbag study was conducted in no-tillage plots under irrigated and rainfed conditions in eastern Nebraska. Litterbags containing cobs were placed in corn rows on the soil surface or vertically in the 0- to 10-cm soil depth following grain harvest and collected aft er 63, 122, 183, 246, 304, and 370 d. Samples were analyzed for dry matter, C, N, P, K, S, Ca, Mg, Fe, Mn, Cu, and Zn. Dry matter loss was greater for buried (59% loss rainfed site vs. 64% irrigated site) than surface cobs (49% loss rainfed site vs. 42% irrigated site). Cob N, P, S, content did not change over the duration of the study and these nutrients would play a limited role in nutrition for the subsequent crop. Cob K content declined exponentially over the study suggesting that cob K would be available to the subsequent crop. Cob Ca, Mg, Zn, Fe, Mn, and Cu content increased during the study representing immobilization. With the exception of K, nutrients contained in the cob are immobilized the year following harvest and play a minor role in mineral nutrition of the subsequent crop. As cellulosic conversion technology becomes available cobs represent a feedstock that can be harvested with minor effect on crop nutrient availability.