Crop residue decomposition and nitrogen release in single and mixed cover crops

Dynamics of decomposition and nitrogen (N) release of cover crop residues in mixed and single cultures was evaluated in a field experiment. The following materials were used: (a) black oat (Avena strigosa Schieb); (b) common vetch (Vicia sativa L.); (c) oilseed radish (Raphanus sativus L. var. oleiferus Metzg.); (d) 32 % black oat + 68 % common vetch, and (e) 51 % black oat + 49 % common vetch. To monitor the residue decomposition, air-dried plant material was inserted in 0.5 mm mesh nylon-bags (0.2 by 0.2 m), which were placed on the surface of the soil and collected after 15, 29, 43, 59, 71, 82, 112, and 182 days. Remaining dry matter amounts (DM) and N concentrations were determined in the collected materials. Nonlinear models were fit to the values obtained for the remaining amounts of dry matter and nitrogen, which separated the DM and N of crop residues in two compartments, one more easily decomposable and the other more recalcitrant. Among the single crops, common vetch presented the highest decomposition rate (0.06119 day(-1)) of DM within the more easily decomposable compartment. Where oat was mixed with common vetch there were reductions of 30 % (0.04264 day(-1)) and 50 % (0.03113 day(-1)) in the DM decomposition of this compartment when the DM proportion of the grass was 32 and 51 %, respectively. The highest amount of totally released N occurred during the first 15 days of the experiment, which lasted 182 days. Results show that an association of oat and common vetch does not reduce the N release rate of the more easily mineralizable compartment, compared to single common vetch. However, cultural residues of common vetch - oat mixtures presented a higher persistence in the soil than those of single common vetch and released higher amounts of N than single oat and single oilseed radish.