The role of legume cover crops in the ecological intensification of winter wheat to manage weeds under different soil tillage regime

Ecological intensification by means of legume cover crops undersown in winter wheat has the potential to control weeds and reduce the herbicides adoption in cereal cultivation. They may also provide high biomass to be used for feeding livestock in case of cash crop failure due to the climate changes consequences. Field experiments were conducted to investigate the effect of legume cover crops undersown in wheat (Triticum aestivum L. cv. Baharan)to suppress weeds under different tillage systems at the research station of Ilam University (Iran) during 2018-2019 and 2019-2020. The treatments were three soil tillage systems (conventional tillage, minimum tillage and no-tillage); and four legume cover crop [Persian clover (Trifolium resupinatum L. var. Haftchin), vetch (Vicia villosacv. Maragheh), grass pea (Lathyrus sativusL.) and bitter vetch (Vicia ervilia (L.) Willd.)]. In addition, wheat monoculture with and without weeds, monoculture of each legume cover crop and a fallow plot were included. Legume cover crops were sown at 50% and wheat at 100% of the seed rate adopted by the farmers. In 2018-2019, weed aboveground biomass was reduced of 43.0, 86.5, 68.4 and 3.5% when Persian clover, vetch, bitter vetch and grass pea, respectively, were undersown in wheat under no tillage system. The reduction for the same treatments was of 54.0, 98.0, 85.0 and 84.9 %, respectively, under minimum tillage and 70.0, 95.8, 65.8 and 50.8%, respectively, under conventional tillage. In 2019-2020, the reduction in weed aboveground biomass under no-tillage system was significant only for vetch and bitter vetch (33.4 and 10.3%, respectively), while no reduction was observed in Parsian clover and grass pea. Under minimum tillage, the reduction was 28.2, 62.0, 58.5 and 55.5% in wheat undersown with Persian clover, vetch, bitter vetch and grass pea, respectively, and 43.9, 57.4, 44.3 and 46.3%, respectively, under conventional tillage. Vetch adopted for ecological intensification of wheat showed the greatest impact in reducing weed dry weight. As expected, the highest wheat grain yield (8422 kg ha-1) was obtained in wheat monoculture with weed control followed by wheat + bitter vetch intercropping (6267 kg ha-1) under minimum tillage. The forage quality in legume crops and soil factors were also improved under intercropping system. The land equality ratio was more than one in all intercropping patterns. We concluded that the intercropping of wheat with the legume cover crops present promising environmental-friendly approaches for managing weeds in a sustainable way while maintaining the crop production system.