Cover crops to secure weed control strategies in a maize crop with reduced tillage

To better understand the ability of cover crops to control weeds in a maize crop (Zea mays, L.) grown with reduced tillage, four field experiments were set up from 2009 to 2014 in the western part of Switzerland. Ten non-wintering cover crop species were compared to a no cover crop control in strip plot experiments including different weeding strategies. The weeding strategies included no or minimum tillage before maize seeding. Soil coverage by weeds at early maize stage (2-4 leaf stage) varied drastically between weeding strategies and years. In most cases, cover crops allowed to reduce the weed pressure compared to the no cover crop control. The most efficient cover crop species varied from year to year, but niger (Guizotia abyssinica, (L.f.) Cass.), sunflower (Helianthus annuus, L.), field pea (Piston sativum, L.) and phacelia (Phacelia tanacetifolia, Benth.) gave the best overall results. Maize yield differed significantly between weeding strategies only one year, with higher yield observed with minimum tillage. In some situation, cover crops cultivated in autumn still showed a significant impact on maize yield, with common vetch (Vicia saliva, L.) as the most successful species. Interestingly, the effect of cover crop on weed cover and maize yield was not limited to the less intense strategy (no tillage). These results show that cultivating cover crops before maize in this type of conditions is a promising method to help controlling weeds. In addition, cover crops are known for providing multiple ecosystem services which could altogether improve the sustainability of cropping systems on the long term.