Investigating the Interaction of salinity, drought and nitrogen fertilizer stresses on some physiological traits, yield and yield components of maize (Zea mays L.)

Introduction Environmental stresses are considered as the most important limiting factors in agricultural production in the world. About two-thirds of Iran's agricultural lands are located in arid and semi-arid regions and face drought stress. After drying, salinity is one of the most important environmental stresses in the world and in Iran. Environmental stresses have a negative effect on the growth and development of reproductive organs and decrease the economic and biological yeild of the plant. These stresses also affect many physiological processes of the plant and cause changes in plant physiological traits. Studies have shown that the absorption of the most of nutrients in plants under salt and drought stress is reduced. Nitrogen is the first food ingredient that is lacking in saline areas and is an essential nutritious element of the plant. Considering the major contribution of maize in providing human food, livestock and industrial uses, as well as soil conditions of the country, organic matter shortages and climate change, the comprehensive study of the mutual relations of consumption and non-use of fertilizers is essential in the presence and absence of water stresses and salinity, according to optimal management of water and soil resources and fertilizers and finally the achievement of optimal yields. Materials and methods The experiment was conducted as split- split plot design in a randomized complete block design with three replications at the Research Farm of the Faculty of Agricultural, University of Ilam in 2017. The treatments consisted of four levels of salinity (S1 =fresh water, S2 = 2, S3 = 4 and S4 = 6 ds / m) from salt rock source as the main factor, three levels of irrigation (I1 = 100, I2 = 80 and I3 = 60 percentage of water requirement of the plant) as a sub factor and three levels of nitrogen fertilizer from urea source (N1 = 0, N2 = 100 and N3 = 150 kg/ha) were considered as the sub- sub factor. Treatments were applied, in the 5_6 leaf stage. Sampling was performed to measure physiological traits at flowering time and yield and yield components at harvest time. Data analysis was performed by SAS.9.2 software and the mean comparison test was performed by LSD test. Charts is drawn by Excel. Results and discussion Based on the results, the highest yield was obtained in non stress conditions and application of 150 kg ha-1 nitrogen. Interaction of stresses among functional traits had the most negative effect in grain yield with a 69% reduction, also, among three physiological traits, electrolyte leakage showed a three-fold increase in the effect of interaction treatments with increasing tensions. The number of seeds per ear, number of rows per ear, number of seeds per row, biological yield and harvest index were decreased by 59%, 40.6%, 40%, 65% and 46%, respectively. Application of nitrogen at all levels of stress also reduced the effects of stresses and increased yield. The relative water content of leaf, chlorophyll a, chlorophyll b, total chlorophyll and carotenoid were also significantly reduced by the dual effects of treatments. It was also observed that all examined traits at the highest level of stress had an almost identical response to N2 and N3 treatments. Therefore, it seems that application of 100 kg ha-1 of nitrogen in maize under stress is appropriate for increasing the plant resistance and reaching maximum yields. Conclusions The results indicated that salinity and irrigation stress in all studied traits were significant. Increasing stresses increased ion leakage and decreased other traits. Nitrogen consumption under stress condition improved all traits. There was no significant difference between treatments for consumption of 100 and 150 kg ha-1 nitrogen except for biological yield. As a result, under severe stresses, consumption of 100 kg ha-1 of nitrogen seems to be more optimal.