Effect of water and Salinity Stress on Root Morphological Characteristics and Tomato Yield and Determination of Optimum Yield Point Using Response Surface Methodology (RSM)

In order to model the effect of salinity stress on the yield of greenhouse tomato under moisture regimes conditions, an experiment was conducted in a completely randomized block design with three replications. Treatments included salinity stress at levels 1.5, 2.5, 4, 7 (dsm-1). and amount of water stress at three levels of 50, 60 and 70% of field capacity.  Using a response surface method, the results showed that the best yield model based on the variables of salinity stress and moisture level is the second degree model with a regression coefficient of 0.93., The highest yield, assuming the least available moisture and the highest salinity stress, was 117.9 (gr per plant) with a degree of desirability of 0.6, in 3 (dsm-1) of salinity and 63.6% depletion of field capacity. Other root indices had an increasing trend, except for the main root length, with decrease available water and also in a specific moisture regime with increasing the amount of salinity.  Also, a decreasing trend of yield in each of the moisture regimes treatments was observed with increasing the amount of salinity. Considering the nonlinear effect of changes in moisture regime and salinity greenhouse tomato yield, in order to achieve the best yield, salinity stress should be determined first for each plants