Winter cover crops to reduce herbicide inputs into spring-planted maize pastoral systems in New Zealand

The use of cover crops can improve the environmental sustainability of intensive cropping systems. A five-year field trial was undertaken to evaluate the effect of multi-season cover cropping on weed suppression within a no-till spring-planted maize system in the Waikato region in New Zealand. Five cover crop treatments were compared: gland clover (Trifolium glanduliferum Boiss.); faba bean (Vicia faba L); oats (Avena sativa L.); and Italian ryegrass (Lolium multiflorum Lam.), and winter fallow. The results demonstrated that in this system, herbicide treatments can be reduced to one application to terminate the winter cover crop and a single maize post-emergence application, thus reducing selection pressure for herbicide-resistance, without any loss in silage or grain production. Furthermore, a legume-based cover crop gave higher yields than the grass cover-crops and reduced the damage by the maize and grass pest cosmopolitan armyworm (Mythimna separata Walker). The build-up of crop residue over time was detrimental to the establishment of the small-seeded clover and ryegrass cover crops but good weed suppression and grain yields were achieved in the final season by replacing them respectively with the larger seeded woolly pod vetch (Vicia eriocarpa (Hausskn.) Halácsy) and a blue lupin (Lupinus angustifolius L.)/ mustard (Sinapis alba L.) mix.