Effect of Cereals Intercropping Systems and Application of Nitrogen Fertilizer on Nitrogen and Micronutrients Content of Weeds Shoot and Grain Yield

Introduction[1]
Weed management is a key issue in ecological management of agroecosystems, and weed control should be tackled primarily by altering the competitive balance between crop and weeds. This can be through measures such as the correct choice of rotation, the choice of crop species and cultivars with more competitive ability and precision nutrient management. The infestation of weeds may also be significantly reduced by crop species diversification in cropping systems. Therefore, intercropping system is one of the ways to diversity. It is likely that intercrops promote the use of the available resources by crops, thus, leaving less opportunity for the establishment and growth of weeds. In addition to cropping system components, the absorption of nutrients may be affected and in some cases be increased by nitrogen. Reduction of available nutrients to weeds is one of the ecological approaches for to weaken weeds and to increase crop yield. This experiment was conducted to investigate the effects of cereals intercropping systems and nitrogen levels on nitrogen and micro-nutrients (Fe, Zn, Cu and Mn) content of weeds shoot and crop grain yield. This experiment was carried out at the Darab faculty of Agriculture and Natural Resources, Shiraz University, Iran during 2013-14 cropping season. Treatments were arranged in a factorial experiment based on randomized complete block design (RCBD) with three replicates. Treatments were five different sowing ratios of wheat: triticale consisted of 100: 0, 75: 25, 50: 50, 25: 75, 0: 100, four different sowing ratios of barley: triticale consisted of 100: 0, 75: 25, 50: 50, 25: 75 and two nitrogen levels (100 and 200 kg N ha-1). Nitrogen and micro-nutrients (Fe, Zn, Cu and Mn) content of weeds shoot and grain yield were measured and compared statistically. The lowest and the highest nitrogen content of weeds shoot was observed in the monoculture of triticale with 200 kg N ha-1 and in the monoculture of wheat with 200 kg N ha-1 respectively. The interaction of intercropping systems and nitrogen levels led to decrease of nitrogen content in weeds tissue. There were the lowest Fe and Mn content of weeds shoot in W50T50 and B50T5050 intercropping systems with 200 kg N ha-1. The W25T75 and monoculture of barley (B100) showed the lowest Zn content for weeds shoot and increasing nitrogen fertilizer resulted in an increase in Zn content of weeds. The Cu content of weed shoot was higher in monocultures than that in intercropping systems. The lowest Cu content in weeds shoot was observed in W50T50 and B75T25 where 100 kg N ha-1 applied to the experimental plots. Furthermore, grain yield in wheat: triticale intercropping was greater than that in monoculture of wheat. In this study, B50T50 cropping system with 200 kg N ha-1 showed the highest grain yield. Generally, grain yield of crops increased with rising nitrogen amount in intercropping systems. The results of this study showed that nitrogen, Fe and Mn content of weeds shoot decreased where they grew in intercropping systems with the highest nitrogen fertilizer level. However, Cu content of weeds shoot decreased in intercropping systems and lower nitrogen fertilizer level. Furthermore, Zn content of weeds shoot decreased in intercropping systems and high amount of nitrogen fertilizer increased this micro-nutrient in weeds shoot. According to the results, crop grain yield increased significantly (P≤0.01) where a higher amount of nitrogen fertilizer applied to cereal intercropping systems. These findings have implications for ecological management of weeds in cropping systems and increasing crop yield through increasing cereal crop diversity and management of nitrogen and micro-nutrients (Fe, Zn, Cu and Mn).