Effect of Drought and Salinity Stress on Estimation of Forage Maize Yield through Periodic Evapotranspiration Using Different Models

Determining the intra-seasonal sensitivity of maize evapotranspiration to environmental stresses has an important effect on modeling of yield. In this research, the effect of drought and salinity stresses were investigated on the relative evapotranspiration (during initial, development, mid, and late stages) and relative yield of maize, in a field with sandy loam soil texture. 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. Drought treatments included four irrigation levels of 100% (I0), 80% (I1), 60% (I2), and 40% (I3) of the crop water requirement. The experiment was performed as factorial in a randomized complete block design, with three replications. The relative evapotranspiration of maize in the initial, development, middle and final stages was estimated between 63.5-100%, 62.6-100%, 55.2-100%, and 66.4-100%, respectively. The relative yield of maize in the I0S0 to I3S3 treatments was calculated between 42.6-100%. The results showed that salinity and drought stresses reduced both the evapotranspiration and maize yield. Also, evapotranspiration decreased with a steeper slope in sensitive growth stages compared to yield. Effect of the mentioned stresses at sensitive growth stages caused disruption in the flowering and fruiting of maize. In this study, the relative yield of maize was modeled by additive models of Blank, Stuart, Singh and multipliable models of Jensen, Rao, and Minhas. According to the results, Stewart model with sensitivity coefficients (in four growth stages) of 0.227, 0.416, 0.604, 0.14 and Jensen model with sensitivity coefficients of 0.301, 0.41, 0.608, and 0.147 were selected as the optimal models. However, Rao, Blank, Singh, and Minhas models were chosen as the next priorities. Therefore, under salinity and drought stress, the relative yield of maize was modeled based on the amount of evapotranspiration in the growth stages.