Investigating the spatial variations of water use efficiency, and fertilizer sources for irrigated and rainfed wheat systems in different regions of Iran

Chemical fertilizers have played a significant role in increasing the yield of agricultural products, especially since the 1950s, but the excessive application of these fertilizers in recent years has led to environmental pollution and a drop in agricultural productivity, food security, ecosystem and human health, and economic prosperity. Researchers believed that the best and most accessible approach to solve these problems is the improvement of the efficiency indicators of inputs. So, the purpose of the study was to evaluate the use efficiency indicators for nitrogen and phosphorus and water in wheat-irrigated and dryland systems of Iran.

In this research, provinces with more than 80% production in irrigated and rainfed systems of Iran were determined and, in each province, cities with more than 80% production of this crop were selected. The required data were collected by using face-to-face interviews and recorded statistics. Afterward, the consumption productivity of inputs was determined, and then the Pearson correlation coefficient between the productivity of different sources was computed. Also, multiple regression was used to determine the relationship between yield with climatic variables and fertilizers and water. For this purpose, the two-year average for total precipitation for irrigated and rainfed systems in each region were extracted.

The results revealed that in the main areas of wheat production, the average productivity of nitrogen consumption for irrigated was calculated as 16.69 kg of grains per kg of nitrogen compared to 17.27 kg of grains per kg of nitrogen for rainfed conditions. Contrary to nitrogen, the efficiency of phosphorus consumption in rainfed agriculture was lower than in the irrigated wheat system. Also, the highest correlation between nitrogen and phosphorus productivity for the irrigated system was computed with r=0.506 and the coefficient between nitrogen and water productivity was calculated with r=0.309 for rainfed conditions. The results for regression analysis between yield and climatic and agronomic parameters showed that increases in temperature had a positive effect on grain yield in rainfed conditions. On the other hand, increasing in other parameters such as precipitation, nitrogen, phosphorus, and irrigation in the irrigated and rainfed systems had a direct relationship with grain yield.

Excess use of nitrogen fertilizers in irrigated wheat systems led to lower nitrogen use efficiency. Although, the grain yield in irrigated conditions was higher than in dryland conditions, due to the sensitivity of using nitrogen by farmers and the adverse effects of excessive use in rainfed wheat, the consumption of nitrogen has been used with more precision and sensitivity. This ultimately led to an increase in the efficiency of nitrogen consumption in rainfed compared to irrigated systems. Unlike nitrogen, the phosphorus use efficiency was lower in rainfed compared to the irrigated system due to the direct effect of soil moisture on the release of phosphorus in the soil. According to these results, nitrogen and water were the most important factors affecting the yield in irrigated and rainfed systems. Also, the regression analysis of the relationship between wheat yield and climatic and agronomic parameters showed that in irrigated systems, nitrogen and irrigation and in rainfed conditions, nitrogen and precipitation had the most impact on grain yield.