Effect of water superabsorbent levels, nutrition management and salicylic acid on soil characteristics, water use efficiency and morphological characteristics and yield of bean (Phaseolous vulgaris L.) in drought stress

Today, more than a third of the worlds land is located in arid and semi-arid areas that are subject to water constrains. Drought stress causes different physiological changes in the plant, such as increasing shading temperature, increasing concentration of proline amino acid, decreasing leaf relative humidity, increasing soluble sugars concentration, increasing stomatal resistance and increasing concentration of antioxidant compounds of plant. Considering the destructive effects of drought stress, in recent years, many efforts have been made to increase water use efficiency. The use of superabsorbents and spraying of humic acid and salicylic acid are considered as essential solutions for saving and optimizing water use. Regarding insufficient water availability in the country and the importance of using ecofriendly inputs in increasing water productivity and conducting few studies on the use of statistical techniques to identify the factors affecting water use efficiency, this research in order to investigate the effect of water superabsorbent, humic acid and salicylic acid on water use efficiency and some morphological characteristics and yield and tolerance indicators of bean (Phaseolous vulgaris L.) under drought stress was done.

In order to determine factors affecting water use efficiencis of common bean (Derakhshan cultivar) affected by different inputs in conditions of drought stress, a split plot experiment based on RCBD design with three replications was used during 2015-16 growing season, at Research Farm of Ferdowsi University of Mashhad, Iran. Irrigation levels (50 and 100% of water requirement) and nutritional treatments (75 kg.ha-1 Nitrogen+80 kg.ha-1 Superabsorbent, 80 kg.ha-1 Superabsorbent+6 kg.ha-1 Humic acid+1 Mm Salicylic acid, 6 kg.ha-1 Humic acid+1 Mm Salicylic acid+75 kg.ha-1 Nitrogen, 6 kg.ha-1 Humic acid+1 Mm Salicylic acid+75 kg.ha-1 Nitrogen+80 kg.ha-1 Superabsorbent and Control) assigned to the main and sub plots, respectively. In this research, traits shuch as seed yield, dry matter yield, harvest index, weight seed per plant, height plant, LAI, CGR, soil nitrogen, phosphorous, EC and pH was estimated.

The result showed that all of the nutritional treatments had significantly effects on water use efficiency, but in both conditions of 50 and 100% of water requirement, the highest water use efficiency were obtained in Humic acid+Salicylic acid+Nitrogen+Superabsorbent, so that this treatment increased water use efficiency 63 and 55% compared to control in 50 and 100% of water requirement, respectively. All of the nutritional treatments decreased damages caused by drought stress, but in this conditions (50% of water requirement), the highest LAI (7.24), CGR (6.47 g.m-2.day-1), soil nitrogen (0.32%) and phosphorous (0.0183%) observed in treatment of nitrogen+superabsorbent+humic acid+salicylic acid. Application of nitrogen+superabsorbent, superabsorbent+humic acid+salicylic acid, nitrogen+humic acid+salicylic acid and nitrogen+superabsorbent+humic acid+salicylic acid increased mean productivity (MP) 19, 54 and 47 and 59%, geometric mean productivity (GMP) 18, 55 and 48 and 59% and harmonic mean (HM) 17, 55 and 48 and 60% compared to control, respectively. Effect of nutritional treatments on stress susceptibility (SSI) and stress tolerance index (STI) was significant and the lowest SSI (0.59) and the highest STI (1.51) obtained in treatment of nitrogen+superabsorbent+humic acid+salicylic acid.

In general, the results showed that although all nutritional treatments were effective in reducing drought stress damages, but the highest seed yield, dry matter yield, harvest index, weight seed per plant, leaf area index, crop growth rate, soil nitrogen and water use efficiency observed in treatment of nitrogen+superabsorbent+humic acid+salicylic acid. MP, GMP and HM in all nutritional treatments was more than control, significantly. Application of superabsorbent+humic acid and salicylic acid, nitrogen+humic acid+salicylic acid, nitrogen+superabsorbent+humic acid+salicylic acid decrease SSI compared to control and the highest STI obtained in treatment of nitrogen+superabsorbent+humic acid+salicylic acid.