Optimum Use of Saline Waters in Cotton Production

Increasing population growth, necessity of food production, increase use of fresh water in industrial expansion, urbanization and cultivation expansion and ultimately low amount of rainfall in arid and semi-arid regions of the country increases the pressure for using saline waters in crop production. Application of proper saline irrigation water managements could maintain optimum crop production and moreover soil salt balance. In this study seven saline irrigation water management treatments were used on Varamin cotton cultivar (Gossypium.hirsutum) production in three replicate in RCBD for three years. The treatments consisted ;application of three saline irrigation waters of  2.9,6.3 and 10.2 dS.m^-1 (M1, M2 and M3) during whole growing  season , irrigation with water salinity of 2.9 dS.m^-1 in early season (the germination and establishment stages) followed by irrigation  water salinity of 6.3 dS.m^-1(M4) or 10.5 dS.m^-1 (M5) for the rest of growing season and two alternative saline irrigation water  application managements  of 2.9 dS.m^-1 along with 6.3 (M6) or 10.5 dS.m^-1 (M7). The results shows that  cotton lint yield reduction in M2 and M3 treatments were about 33 and 66 percent compare with M1 (2.9 dS.m^-1) treatment, respectively. Cotton lint yield reduction in M4 and M5 irrigation water management treatments also were 21 and 49 percent relative to M1 treatment respectively. Alternative irrigation of fresh water (2.9 dS.m^-1) and moderately saline water (6.3 dS.m^-1) or high saline water (10.5 dS.m^-1) caused 13 and 40 percent cotton lint yield reduction with respect to M1 treatment. As a result alternative managements of irrigation water application (M6 and M7) could save about 50 percent of fresh water (2.9 dS.m^-1) and meantime maintain optimum amount of yield.  The linear regression analysis of the relationship between relative cotton lint yield (Ry) and average salinity of saturated soil paste extract (ECe) during growth period resulted the b ( line slope, expressing percentage yield depression per dS.m^-1 ) and a (threshold value) equal to 8.2 and 6.5 dS.m^-1 respectively (Ry=100-8.2 (ECe-6.5))with high correlation coefficient (R²=0.88).