Effect of salicylic acid on physiological N efficiency and water use efficiency of barley in cut irrigation condition

Drought stress has osmotic and physiological effects on plants, resulting in reduced growth, metabolic disorders and oxidative stress in plants. Different plants use several strategies to cope with drought stress. External application of different compounds such as organic solvents and minerals is a solution to increase drought tolerance in plants. Salicylic acid was recognized as a plant hormone and its role in defense mechanisms against biological and non-biological stressors is well defined. The purpose of this experiment was to evaluate the effect of salicylic acid on reducing the effects of drought stress on yield, water use efficiency and some physiological characteristics of the barely.

This study was conducted a split plot experiment based on randomized complete block design with three replications in Sabzevar in 2017. The altitude of this area is 1195 m above sea level and is 36° 5 N latitude and 44° 3' E longitude. The treatments included irrigation at two levels of drought stress (irrigation cut from booting to harvesting stage) and complete irrigation and salicylic acid spraying treatment at four levels of zero (control), two, four and six mM at stage of shoots on barley. Data were analyzed with the SAS software ver 9.1 and the means were compared with LSD test.

The results showed that in both conditions of irrigation and drought stress, the highest number of spikes, number of seeds, seed yield and biological yield per m2 were obtained in two to six mM of salicylic acid, respectively, and the lowest was related to control treatment. The lowest water use efficiency was obtained under full irrigation conditions without salicylic acid and with the consumption of salicylic acid up to six mM, water use efficiency increased. In addition, salicylic acid spraying in drought stress conditions compared to full irrigation led to increase water use efficiency. In both conditions, full irrigation and irrigation cut, the highest and lowest grain yields were obtained from 6 mM salicylic acid and control treatments (without salicylic acid spraying), respectively. Under full irrigation and drought stress, spraying with 6 mM of salicylic acid increased the grain yield by 44% and 48% compared to control (without salicylic acid spraying). It seems that the effect of salicylic acid spraying in drought stress conditions was more effective than irrigation conditions compared to irrigation treatment. Physiological efficiency of N increased with increasing salicylic acid consumption, and consumption of six milligrams of salicylic acid with ratios of 124.6 and 132.1, respectively, in both conditions of irrigation and cut irrigation, had the highest physiological N, respectively. Cut irrigation conditions increased N remobilization, also increased the physiological efficiency of N to 113.95%. On the other hand, salicylic acid reduced drought stress by increasing physiological efficiency N and N remobilization, which improved wheat grain yield under stress conditions compared to complete irrigation.

The physiological efficiency of N, which was produced from the total dry matter divided by the absorbed nitrogen, in fact, indicates the relation between N and dry matter production and, irrespective of salicylic acid consumption and irrigation conditions, the physiological efficiency of N increased to about 135, water use efficiency was added linearly. Therefore, it can be said that the N flow within the tissue has a positive effect on the water use efficiency.