Effects of cover crops and their residues on weed suppression and subsequent composite cross populations of maize in organic cropping system

In organic cropping systems cover crops have the potential to develop into a crucial factor of an ecological weed management strategy. To determine the effects of various cover crop species and their residues on the weed suppression and agronomic performance of composite cross populations (CCPs) of maize (Zea mays L.), the field experiment was set up under suboptimal climatic conditions in the period from September 2011 to October 2012. The following three cover crop types were grown between cash crop: (1) Brassica juncea (L.) Czern. cv. ISCI 20; (2) Vicia villosa Roth cv. Latigo; and (3) a mix of seven cover crop species (Fagopyrum esculentum Moench, Lupinus albus L., Phacelia tanacetifolia Benth., Pisum sativum L., Trifolium alexandrinum L., Trifolium incarnatum L. and V. villosa). The results obtained were compared with no-cover crop plots and two maize hybrids, conventional and organic. V. villosa in pure stand was the most productive and stable cover crop (509,43 gm-2), with the highest weed suppressive effect (63,24% weed reduction). Consequently as a leguminous species, residues of V. villosa significantly increased development and growth of the maize cultivars (2,102 tha-1) compared to the control plots (1,85 tha-1). The lowest weed suppression effect (only 23% weed reduction) and total maize biomass production (1,42 tha-1) was observed under Mix 7 treatment, as a result of poor establishment and adaptation of that cover crop type (188,75 gm-2). Multiple comparisons of the different maize cultivars showed that CCPs and organic hybrid achieved similar dry grain production value, while the conventional hybrid had the best agronomic performance. The whole-grain analysis indicated that the choice of cultivar and not the green manure treatment, had the high significance on the quality of the final product. These findings showed that weed suppression and green manure effects of the cover crops under abiotic stress conditions are greatly influenced by individual species adaptation, agronomic management and within system compatibility of the subsequent maize genotype.