The Effect of Different Levels of Nitrogen Fertilizer on Yield and Agronomic Characteristics of Basil (Ocimum basilicum L.) Intercropped with Cowpea (Vigna unguiculata L.) and Affected by Weed Competition

In order to study the intercropping of basil (Ocimum basiilicum L.) and cowpea (Vigna unguiculata L.) under different levels of nitrogen supply and weed competition conditions, a field experiment was carried out in split-split plot arrangement based on a randomized complete block design with three replications during 2010 and 2011 at Sari Agricultural Science and Natural Resources University. Experimental factors included weed treatment (weed free and weed infested), three levels of nitrogen fertilizer (0, 50 and 100 kg ha-1), and different planting ratios (monoculture of cowpea and basil, additive planting ratio 25, 50 and 75% basil). In weed control conditions, the maximum yield of cowpea (684 kg ha-1) and dry matter yield of basil (420 kg ha-1) were belonged to 20, 50 percent of basil ratio and 50 and100 kg ha-1 nitrogen fertilizers, respectively. The highest amount of essence yield in weed free and weed infested were 69.24 and 70.40 percent as compared to the basil monocropping which belonged to 50 and 25 percent of additive basil intercropping with 100 kg ha-1 nitrogen application, respectively. Also, the dry weight of shoot and oil yield in monoculture treatments were significantly higher than intercropping. The leaf percent and the ratio of leaf and flower to stem in basil plant were significantly lower in monocropping than intercropping. In weed infested conditions, the highest percentage of stem (62.18) and basil dry yield (160 kg ha-1) were recorded in 25 percent of basil ratio and 100 kg ha-1 of nitrogen application. Also, the highest system productivity index (1517) and land equivalent ratio (LER=1.31) were belonged to 50 percent of basil ratio and 50 kg ha-1of nitrogen fertilizer in weed free conditions which shows that intercropping is more efficient than monocropping.