The Influence of Different Amounts of Nitrogen and Weed Interference on Yield and Yield Components of Corn under Two Irrigation Systems

Introduction: Corn (Zea mays L.) is one of the most important crops in the world that need high water requirement during its developmental stages. Improvement of water management system increases crop production all over the world, especially in aired and semiarid climates. For instance, drip irrigation system can be used to provide accurate and adequately nitrogenous fertilizers while conventional systems such as flood irrigation has lower efficiency in the use of nitrogen fertilizers. An improved understanding of the effects of nitrogen (N) on crop–weed interactions is needed for development of integrated weed management systems where reasonable application of N fertilizers is considered too. Moreover, maize competition with weeds is another important factor that affects its yield. So this study was conducted to evaluate the effect of nitrogen on yield and yield components of corn and weed interference under two systems of flood and drip irrigation. Materials and Methods: In order to evaluate the effect of irrigation methods and nitrogen under weed-infest condition on yield and yield components of maize, a field experiment was conducted in split-split plot design based on randomized complete blocks during 2012 growing season at the Collage of Agriculture, Shiraz University. Factors were irrigation type as main plots (flooding and drip), nitrogen levels as sub plots (0, 75 and 150 kg ha-1) and weed interference as sub-sub plots (weed infest and weed free). Drip irrigation system was carried out by using strips with 20 cm output, 0.175 mm thickness and 16.5 mm internal diameter. Urea 46% was used to supply nitrogen. A control (weed free) was used in this experiment. Statistical analysis of the data was performed by using SAS 9.1 software and comparing of the means was done by the least significant difference test (LSD) at 5% level. Result and Discussion: The results showed that under weed interference, grain yield (51.0%) and yield components (number of rows and kernels per ear, ear length and diameter and seed weight) decreased significantly. In the former studies weed competition had been expressed a major limitation for corn production. It seems that weeds caused corn yield losses indirectly through their influence on the resources required for crop growth and competition for light and belowground resources. It was also shown that weeds are high nitrogen consumers cause to reduce the amount of available nitrogen for crops growth. Therefore when corn and weeds emerge simultaneously in a mixture, weeds competitiveness increases with increasing nitrogen supply. However, nitrogen addition has a positive effect on both corn and weeds growth, but weeds tends to respond more to nitrogen addition than corn. In this study we observed similar results and increasing of nitrogen application from 75 to 150 kg ha-1 which increased grain yield by 44.4% and ear length by 4.9 %, but under weedy condition decreased ear length by 25.8%. Nitrogen application caused a different response in each irrigation system, so that the application of 75 and 150 kg ha-1nitrogen under drip irrigation system reduced weed biomass by 62.6 % and 64.4 % compared to flooding system respectively. Applying drip irrigation system also reduced weed density (56.8%) and biomass (54.3%) and increased corn grain yield compared to flooding irrigation system. Under weed free condition and using of drip irrigation system number of grain per ear increased by 50.1% significantly. In drip and flooding irrigation systems under weed free condition compared to weedy plots, number of grain per ear increased by 17.0% and 7.9% respectively whilst drip irrigation system compared to flooding irrigation system increased ear diameter by 50.5%. However hundred grain weights were affected by all treatments, under weed free condition compared to weedy condition, in drip irrigation system hundred grain weights increased by 18.2 %, but in flooding irrigation system no significant differences was observed. Performance comparison of grain yield under irrigation systems revealed that drip irrigation increased grain yield by 62.0 %. Conclusion: The results showed that the effectiveness of nitrogen was much higher under drip irrigation compared to flooding irrigation. It can be because of that drip irrigation system directly provide water for plants and prevent from water availability for weeds. Therefore, appropriate irrigation system as an agronomical practice affects the growth and weed competition ability in cor