Evaluation of Basil (Ocimum basilicum) and Cowpea (Vigna unguiculata) Intercropping at Different Nitrogen Fertilizer Levels and its Effect on Weed Density

To study the effect of different levels of nitrogen and intercropping systems of basil (Ocimum basiilicum L.) and cowpea (Vigna unguiculata L.) on weed population structure، an experiment was carried out as a split-split plot a randomized complete blocks design with three replications during 2010-2011 at Sari Agricultural Science and Natural Resources University. Treatments included weed control and weed infested as the main plots، levels of nitrogen (0، 50 and 100 kg/ha) as sub plots، Sole cropping of cowpea and basil، and additive planting ratios of 25، 50 and 75% basil as sub-sub plots. Under weed control conditions، the highest yield of cowpea (685 kg ha-1) and maximum dry matter yield of basil (430 kg ha-1) were obtained from 50% basil ratio with 50 and 100 kg ha-1N fertilizer application، respectively. The highest yield of basil (139 kg ha-1) was observed in weed infested plots of 25% basil planting ratio and 100 kg ha-1 nitrogen fertilizer with the highest invasive coefficient of 1. 66 and competition coefficient of 3. 42. The highest land equivalent ratio (1. 43) belonged to 50% additive ratio of basil in weed free and the lowest (0. 87) belonged to 75% ratio and without nitrogen fertilizer in weed infested condition. Generally، existence of cowpea in additive intercropping reduced the population and biomass of weeds compared to basil sole cropping. Increasing nitrogen fertilizer application caused faster closed canopy of plant species in intercropping which led to reduced weeds population and biomass.