Effect of different level of irrigation regimes and nitrogen fertilizer on yield and water use efficiency in kidney bean (Phaseolus vulgaris L.)

Drought is the most important stress factor that affects agricultural production in the arid and semiarid areas and reduce crop production. Iran is a country with a warm and dry climate that more than 85% of it located in arid and semi-arid areas. Improving the water use efficiency through agronomic management is one of the most effective and low cost approches for water management in the agricultural fields. The main objective of this study was to investigate the growth and yield response of kidney bean to deficit irrigation with the aim of increasing water use efficiency. In addition, the other objective of this study was to determine the desired level of nitrogen fertilizer at each level of water stress that make improve water uses efficiency.

In order to study the effect of irrigation and nitrogen fertilizer on yield and water use efficiency of kidney bean, an experiment was conducted as a randomized complete block design with a split plot arrangement of tratment in 2016 in Saveh, Iran. The deficit irrigation treatments as a main plot were irrigation at 40% of soil moisture depletion (non-stress treatment), irrigation at 50% of soil moisture deplation and at 60% of soil moisture deplation. The irrgation at 40% soil moisture depletion was considered as an acceptable moisture discharge rate for achieving maximum yield and other irrigation treatments considered as deficit irrigation. Sub-plot was included nitrogen fertilizer application rate at 0 (control), 25, 50 and 100% of maximum nitrogen requirement of dry bean plant. The middle two rows of 60 cm length were harvested for seed yield and LAI determination. At harvest time, a sub-sample of 10 plants were sampled from each plot to determine the number of pods per plantand seeds per pod.Biomass was obtained by drying plants at 70◦C. After drying and threshing, grain yield was determined.

The results showed that drought stress under irrigation after 60% soil moisture depletion decreased leaf area index, dry matter, seed number per unit area and finally kidney bean seed yield. However, mild stress treatment (50% soil moisture deplation) had a significant decrease in seed number per unit area and seed yield compared to optimal irrigation treatment. Furthermore, water use efficiency in kidney bean was increased at both levels of deficit irrigation compared to the full irrigation treatment. The results also showed that growth and yield traits and water use efficiency of kidney bean improved with nitrogen fertilizer application compare to no nitrogen application. The results also showed that the response of seed yield to nitrogen fertilizer was dependent on the amount of applied irrigation water in different irrigation regimes. At irrigation regime by 40% soil moisture depletion, seed yield of kidney bean increased by 11, 16 and 13% with nitrogen application rates of 50, 100 and 200 kg ha-1, respectively. While, seed yield was increased by 9, 14 and 10% with nitrogen application rates of 50, 100 and 200 kg ha-1, respectively, when kidney bean plants irrigated at 60% soil moisture depletion. The water use efficiency of kidney bean had no significant differences between 100 and 200 kg N ha-1. However, the N application rate less than 100 N ha-1 caused a significant reduction in water use efficiency of kidney bean plant. The regression analysis also showed that the responses of seed yield and water use efficiency to nitrogen fertilizer application rate at all irrigation levels were quadratic, and this quadratic response explaind 99 % of varion in these traits.

The results showed that the irrigation of kidney bean at 50% soil moisture depletion compared to irrigation at 40% soil moisture depletion could increase water use efficiency without any significant reduction in seed yield. The irrigation at 50% soil moisture depletion saved irrigation water about 270 m-3 ha-1 compared to the irrigation at 40% soil moisture depletion. We also concluded that the application of 50 % of maximum nitrogen requirement for bean plant could produce maximum seed yield and water use efficiency in all irrigation regimes.