Growth, weed control, and nitrogen uptake of winter-killed cover crops, and their effects on maize in conservation agriculture

The utilization of winter-killed cover crops is increasing due to their benefits in intensive cropping systems based on summer cash crops. However, there is still a lack of knowledge about their management in temperate climates, where maize is planted early under conservation tillage techniques. For these conditions, here we document for the first time various agronomic effects of winter-killed cover crops under different management options. We evaluated the production, the nitrogen uptake, and the weed control of five pure winter-killed cover crop species, as well as the production of the subsequent maize and its nitrogen recovery, in four different sites. Several management options were compared (cover crop fertilization, sowing technique, and cover crop termination method). Legume cover crops (Trifolium alexandrinum L. and Vicia benghalensis L.) had a small above-ground biomass (on average 0.6 t DM ha(-1) in November), while for non-legumes (Avena strigosa Schreb., Sinapis alba L., and Raphanus sativus L.) the production (on average 2.4 t DM ha(-1), N uptake 89 kg N ha(-1)) was higher, as well as weed control and N uptake. The difference in the above-ground biomass between the two groups of cover crops was smaller at the end of winter (0.4 Mg DM ha(-1)), when in five out of eight site x year combinations, soil mineral N was significantly higher in a cover crop treatment compared to the no cover crop, presumably due to N release from cover crops. Cover crops did not increase maize production, and their residues did not hamper maize sowing and emergence. The recovery of cover crop N by maize was 86% for legumes and - 1% for non-legumes. We conclude that productivity, N uptake, and weed control of winter-killed cover crops (especially non-legume species) are encouraging, with no negative effects on maize yield.