Effect of Simultaneous Cropping With Some of Legumes and Different Levels of Urea Application on Nitrogen Agronomic Efficiency in Corn

Introduction
Mixed cultivation of plants is one of the most important scientific methods to help maintain the balance of the living system of the soil and to improve the fertility of the soil. Using the method of growing pulses and grains is one of the factors that improves soil fertility. An increase in the antioxidant compounds of corn in culture with soybeans compared to single culture has been reported. In a study, the cultivation of one-year alfalfa and corn compared to its pure cultivation caused an increase of 10.52% in corn protein. In a research, the most fodder and dry corn (67 and 14.94 tons) was produced from the cultivation of 100% corn + 100% alfalfa. One of the optimal methods of weed control is living plant mulch. In a research, living mulch (flowering mallow, holly and barsim clover) had a significant effect on the growth of corn and weeds. The least amount of weeds was observed in the presence of the cover plant of Bersim clover. Nitrogen plays an important role in the structure of proteins, enzymes and cytochromes. Consumption of 184 kg of nitrogen increased the yield of one ton of corn grain. According to the increase of nitrogen application in corn cultivation up to 200 kg, the protein percentage improves from 10.38 to 11.73 percent. To study of nitrogen agronomic efficiency of corn and some of legumes in simultaneous cropping with different levels of urea application.
 Materials and methods
A factorial arrangement of treatment in a randomized complete block design with three replications was used. Urea manure levels [N₀= without urea (Control), consumption of urea N₁= 75 Kg ha^-1, N₂= 150 Kg ha^-1, N₃= 225 Kg ha^-1) and Simultaneous cropping treatment, (S₁= Cultivation of corn, S₂= Cultivation of corn + chickpea, S₃= Cultivation of corn + cowpea, S₄= Cultivation of corn + mung bean) were assigned in plots. In this study characteristics such as: panicule length, dry weight of stem and leaves, surface of ear leaf, height of poding in legumes, productivity index of plant, grain yield of legumes, protein yield of corn, number of corn + legumes grain per m^-2 and nitrogen agronomy efficiency of corn + legumes were assessed.
 
 Results and discussion
Results indicated that the effect of different levels of urea on the characteristics such as: dry weight of corn stem and leaves, height of poding in legumes, corn productivity index, grain yield of legumes, protein yield of corn, number of corn + legumes grain per m^-2 and nitrogen agronomy efficiency of corn+legumes was significant. Effect of Simultaneous cropping treatment on the characteristics such as: surface of ear leaf, height of poding in legumes, grain yield of legumes and nitrogen agronomy efficiency of corn + legumes was significant, too. The maximum and minimum of nitrogen agronomy efficiency (10.19 and 0.22 Kg Kg ^-1) were obtained with the (75 Kg ha^-1 urea + Simultaneous cropping of chickpea and corn) and (225 Kg ha^-1 urea + Simultaneous cropping of corn and cowpea) treatments, respectively.
 
Conclusions
With the increase in urea fertilizer consumption, the agronomic efficiency of nitrogen decreased.  Urea, nitrogen agronomic efficiency decreased. So, the lowest agronomic efficiency of nitrogen was obtained with the consumption of 225 kg of urea fertilizer. Among the plants of the leguminous family, corn and chickpeas at the same time had a noticeable advantage in terms of nitrogen agricultural efficiency compared to the eye-bean and mung bean at the same time.Simultaneous multi-planting of leguminous plants (nitrogen fixation capability) with other crops, while reducing the consumption of chemical fertilizers, can be recommended to achieve sustainable agriculture