Impact of pasture cropping system and phosphorous rate on weed management in cool- season pastures

Temperate forage species can complement natural rangelands to curb animal malnutrition during winter in communal areas where feeding depends solely on rangelands. However, weed infestation poses threatens cool-season pastures via competition for soil nutrients, largely phosphorous, thereby reducing forage productivity. This study assessed the influence of various pasture stand types (PSTs) and varying P rates on weed density, composition, richness and diversity. A grass species, Oats ( Avena sativa ), broadleaved species ( Raphanus sativus ) and two forage legumes [Bird’s-foot-trefoil ( Lotus corniculatus ) and Vetch ( Vicia sativa )] were planted in monocultures and grass-legume mixtures in communal gardens of Amakhuze communities in the Eastern Cape Province of South Africa. These monoculture and mixed PSTs were assigned varying rates of 0, 25, 45, 65 and 85 kg P/ha, totalling 30 treatment combinations, each replicated three times. The responses of the weeds along P gradient were species-specific, with Cynodon dactylon and Cyperus rotundus being the codominant graminoid species across all PSTs while Ciclospermum leptophyllum was the most dominant forb species. C. rotundus exhibited low relative abundance at 45 kg P/ha except for Lotus monoculture, whereas C. dactylon abundance was suppressed at 65 and 85 kg P/ha for all PSTs except Radish stands. Pure legume stands increased weed densities, whereas Radish, Oats monocultures and mixtures suppressed weed densities and richness at 65 kg P/ha. Hence, we conclude that 65 kg P/ha is optimal for weed suppression and that legume-grass intercropping, Oats monoculture and Radish are crucial for sustainable weed management in cool-season pastures.