Growth Responses, Physiological Alterations and Alleviation of Salinity Stress in Sunflower (Helianthus annuus L.) Amended with Gypsum and Composted Cow Dung

Abstract

Salt accumulation in soils poses severe challenges for crop production in arid and semi-arid regions. Scarcity of rainfall and a high evaporation rate in these regions are considered major reasons for salt accumulation. It drastically reduces the leaching of excessive salts below the root zone of crops. The toxic effects of salts on plants can be greatly reduced with the use of biological and inorganic amendments. The present study was conducted to investigate the positive influence of gypsum (GP), composted cow dung (CCD) and the combined use of gypsum and composted cow dung (GP+CCD) on the growth, seed yield, and physiological and chemical attributes of sunflowers (Helianthus annuus) in salty soil conditions. Saline-sodic soil was prepared using salts that include NaCl, Na2SO4, MgSO4, and CaCl2. It contained three levels of electrical conductivity (EC), i.e., 1.8, 6, and 12 dS m−1, and had a sodium adsorption ratio (SAR) of 15. We noted significant deleterious effects of excessive salt stress on multiple attributes of the growth, produce, physiology, and chemical factors of sunflowers. However, treatment with GP+CCD improved all these attributes in all these conditions over the control treatment. Treatment with GP+CCD also significantly increased N, P and K contents over the control in the absence of salt stress, i.e., normal conditions. Conversely, treatment with GP+CCD caused an extreme decline in antioxidant enzyme activity (APX, GPX, CAT and SOD) and Na+/K+ ratio in seeds of up to 90, 75, and 71% over control at an EC level of 1.8, 6, and 12 dS m−1, respectively. This study suggests the combined application of gypsum and composted cow dung for better production of sunflowers in salt-affected soils, and augmented growth, yield, physiology, biochemistry and nutritional value in the sunflower seeds.