Winter cover crops influence weed establishment and nitrogen supply to maize

Cover crops (CC) and crop rotation are key components of a sustainable crop production system. The objectives of this study were to (i) evaluate the effect of winter CC on nitrogen (N) supply to the subsequent maize crop, and to (ii) evaluate the effect of CC on soil cover and weed population. Three winter CC were evaluated: black oat (BO) (Avena strigosa Schieb), white lupin (WL) (Lupinus albus), and oilseed radish (OR) (Raphanus sativus L.), as single species and in a mix. The three CC mixes included: BO+WL; BO+OR; and OR+WL. In addition to CC treatments a set of five N application rates (0, 60, 120, 180, and 240 kg N ha-1) were included on plots under winter fallow (WF). The winter CC supplied plant-available N to the subsequent maize crop varying from 25 to 53 kg N ha-1 with BO and WL, respectively. The mix of CC varied less in N supply (38-42 kg N ha-1). Soil cover and weed suppression varied between CC. The results suggest that BO can be used to attain rapid soil cover. Black oats also provided better soil cover after CC flattening, likely due to the higher C:N ratio and slower residue decomposition. The higher C:N ratio may result in some N immobilization and reduced plant available N to the maize crop. However, BO also showed great weed suppression. Mixing CC is an alternative to merge the benefits of the individual species, enhancing the overall ecosystem services provided by them.