Weed abundance in alfalfa crop and alfalfa mixtures under nitrogen fertilization

摘要

The aim of the research was to determine the incidence of weeds in pure alfalfa crop and its mixtures, whether growing in mixtures can significantly reduce the proportion of weeds. Also, it should be determined how N fertilization affects the expansion of weed species.The experiment included two legume (alfalfa and sainfoin) and two grass species (orchardgrass and tall fescue). Alfalfa was sawn in pure crop and in mixtures with grasses and sainfoin: alfalfa+orchardgrass (50:50), alfalfa + orchardgrass + tall fescue (33.3:33.3:33.3) and alfalfa + orchardgrass + tall fescue + sainfoin (25:25:25:25).The plots were fertilized with 0, 70, 140 and 210 kgN ha"1 per year. Weed proportion in the mixtures, compared to pure alfalfa, was reduced by 46.8 to 55.6%. There was no significant variation among mixtures in the proportion of weeds. Nitrogen fertilization significantly increased weed pressure in canopy structure. N fertilization increased weedproportion more in pure alfalfa then in their mixtures with grasses and sainfoin.