The Effect of Deficit Irrigation Management and Nitrogen Fertilizer Levels on Yield and Water use Productivity in Soybean

The deficit irrigation method with the aim of saving water consumption can be presented as a useful strategy in low water conditions and with the proper use of the amount of water consumption. Optimum use of water and proper use of fertilizer, in addition to increasing plant yield, increases the water productivity and fertilizer. Nitrogen is one of the main elements in plant nutrition, because of its importance in the plant's vital processes; its deficiency reduces performance more than other elements. The present research was conducted with the aim of investigating the effect of water stress and different levels of nitrogen fertilizer on the yield and productivity of Williams cultivar soybeans in Hormozgan province.

This experiment was conducted in the form of split plots in the form of randomized complete blocks in three replications in Hajiabad city (Hormozgan province) in two crop years 2021 and 2022. The main factor was irrigation in 6 levels without irrigation and providing 40, 60, 80, 100 and 120% of water requirement and the secondary factor was the amounts of nitrogen fertilizer (urea source) in four levels including zero, 50, 100, 150 and 200 kg/ha. Each experimental unit had dimensions of 5×20 m2 and had 10 cultivation rows.

The interaction effect of irrigation and nitrogen fertilizer on biological, pod and seed yields, harvest index, thousand seed weight, number of seeds per plant, pod length, water consumption efficiency in biological, pod and seed were significant at 1% level. The interaction effect of irrigation and fertilizer showed that the highest amount of biological, pod and seed yields in the conditions of 100% water requirement and 150 kg N/ha consumption were 6051, 4941 and 3049 kg/ha respectively. The maximum harvest index due to the interaction effect of irrigation and nitrogen fertilizer was in the conditions of 100% water requirement and with 100 and 150 kgN/ha fertilizer with an average of 0.43%. The interaction effect of irrigation and nitrogen fertilizer showed that the maximum thousand seed weight was with 120.8 g in the condition of 100 percent water requirement and fertilizer consumption of 200 kg/ha. The highest efficiency of water consumption based on biological, pod and seed yields were observed in conditions without irrigation and 150 kg N/ha in the amount of 5.61, 3.71 and 2.28 kg/m3 respectively.

According to the results, the availability of water and sufficient nitrogen are two very important factors that affect the growth and yield of soybean. Therefore, in addition to the lack of water, the lack of nitrogen also causes stress on the growth and yield of soybean. With the upward trend of nitrogen fertilizer consumption, the yield decreased and if there is not enough water, the increase in nitrogen fertilizer consumption aggravates the effect of moisture stress and as a result the yield of the plant decreases, therefore, in water shortage conditions, Excessive use of nitrogen fertilizer is not recommended. According to the results, full irrigation and nitrogen consumption up to 150 kg/ha are suggested for the studied area.