Determination of Salinity Stress Coefficient in Different Growth Stages of Forage Maize

In this research, the effect of salinity stress on the amount of evapotranspiration components of maize were investigated in mini-lysimeters (in the initial, development, mid, and late growth stages). Salinity treatments were applied by water with EC of 0.5(S0), 2.1(S1), 3.5(S2), and 5.7(S3) dS.m-1. The experiment was performed as factorial and in a completely randomized design. For the whole growth period and for S0 to S3 treatments, the values of evapotranspiration, transpiration, and evaporation were measured in the range of 420-320, 285-124, and 135-196 mm, respectively. The share of crop transpiration (T/ETc) decreased by 29% while the share of evaporation (E/ETc) increased by the same value. From S0 to S3 treatment, the values of evapotranspiration, transpiration and evaporation were measured in the range of 420-320, 1 / 285-3 / 124 and 134-7 / 195.9 mm (in the whole growth period), respectively.From S0 to S3 treatments, the values of evapotranspiration, transpiration and evaporation were measured in the range of 79-72, 19-10 and 61-62 mm (initial stage), 202-150, 150-71, and 51-79 mm (development stage), 124-84, 110-39, and 14-45 mm (mid stage), and 15-14, 6-4, and 9-10 mm (the late stage). The shares of crop transpiration decreased in the order of the developmental, mid, initial, and the late stages, while the decreasing order for the shares of evaporation was related to the initial, developmental, mid, and late stages, respectively. The dry biomass yield decreased by salinity stress, and its amount in treatments S0, S1, S2, and S3 was as 12942, 12168, 10872, and 8928 kg.ha-1, respectively. Stress coefficients of evapotranspiration (KS), transpiration (KS-T), and evaporation (KS-E) were calculated in the range of 1-0.76, 1-0.43, and 1-1.45, respectively. The results showed that for 1 dS.m-1 increase in water salinity, the amounts of relative evapotranspiration and relative transpiration decreased by 4.7% and 11.1%, respectively, and the amount of relative evaporation increased by 9%. The results showed that the transpiration component decreased with a greater slope, relative to the evapotranspiration.