Study of forage corn (Zea maize L.) yield as affected by faba bean (Vicia faba L.) density and mineral nitrogen in no-till system.

Nitrogen fertilizers are commonly used to increase economic performance in corn production. However, it should be noted that nitrogen added to the soil in crop ecosystems is not fully available to the plant and may be leached. In this context, many studies have investigated various crop production methods to improve soil health and reduce soil nitrogen losses. Crop rotation and no-till may be an appropriate method to improve soil health and increase soil organic carbon and total nitrogen. In this experiment, it was assumed that growing faba beans in rotation with forage corn and applying sustainable agriculture can greatly reduce the need for nitrogen fertilizer in corn and increase nitrogen use efficiency compared to monoculture corn. The objective of this experiment was to determine the appropriate plant density of faba bean and its effect on crop rotation with forage corn, and to evaluate the nitrogen fertilization efficiency of corn.
 
A two-year experiment was conducted in 2018-2019 as a factorial experiment based on a randomized complete block design with three replicates at the research farm of the Faculty of Agriculture and Natural Resources, university of Mohaghegh Ardabili, Ardabil, Iran. The experimental treatments were different plant densities of faba bean (25, 35, 40 and 80 plants m-2) and different nitrogen (N) fertilizer rates (0, 100, 200 and 300 kg ha-1) in forage corn. Shadan cultivar of faba bean was planted in this experiment and it was harvested manually at the physiological maturity stage. The corn variety was the single cross hybrid 201, which was planted at the density of 80000 plants ha-1 in the residue rows of faba bean. Nitrogen fertilizer (as urea) was applied three times at the V5 stage of corn. Three corn plants were harvested at the milk stage and then oven dried at 70 °C for 72 h and weighed. Traits studied in this experiment were include grain yield, 100-grain weight, harvest index, biological yield and weed control efficiency in faba bean and fresh and dry forage yield, protein yield, nitrogen recovery efficiency, nitrogen agronomic efficiency and nitrogen productivity in forage corn. Statistical analysis of data was performed using SAS 9.4 software, and significant differences between treatment means were tested using the Duncan's Multiple Range Test at P < 0.05.
 
Faba bean
The highest grain yield was obtained at plant density of 80 plants.m-2, 100-grain weight, and HI were observed at plant densities 40 plant.m-2 and the densities of 80 and 40 plants had the highest Reduction percentage in dry weight of weeds and biological yield. It seems that an increase in plant density, especially at the beginning of the growing season, results in complete coverage of the soil with plants and reduces the competitive ability of weeds. In addition, with higher plant density, solar radiation on the plant canopy increases, so less light is available for weeds and the germination rate of weed seeds decreases. The result of cultivation shows higher competitive power and the results were obtained.
Corn
Our results showed that using faba bean in rotation with forage corn can reduce the need for nitrogen fertilizer. The results of the mean comparisons showed that the highest dry forage yield of corn was obtained at the density of 40 faba bean plants+200 kg N ha-1, representing an increase of 155% compared to the control treatment. Corn yield is very sensitive to nitrogen deficiency. On the other hand, using of legumes in crop rotations can improve crop access to nitrogen. Addition, the highest protein yield was observed at the density of 40 faba bean plants+200 kg N ha-1 and 35 faba bean plants+200 kg N ha-1. Density of 40 faba bean plants+no application of N fertilizer had the highest nitrogen recovery efficiency and nitrogen agronomic efficiency. Thus, it can be concluded that the combined application of nitrogen fertilizer and the use of faba bean in the crop rotation increases the availability and uptake of nitrogen and also increases the efficiency of this element at a stage of plant growth when nitrogen uptake is high. Therefore, the corn yield was higher in these treatments
 
In this experiment, the effects of plant density of faba bean on the yield of this crop and the effects of crop rotation on nitrogen yield and efficiency of forage corn were studied. The results showed that the highest grain yield, 100-grain weight, biological yield, and bean harvest index were obtained at plant densities 40 and 80 plant. The results also showed that the density of 40 bean plants+200 kg N ha-1 had the highest increase in dry forage yield of corn compared to the control. It can be concluded that the density of 40 faba bean plants+200 kg N ha-1 in forage corn under similar climatic conditions may be a suitable method to reduce the use of chemical N fertilizer.