Application of Response Surface Methodology in Optimizing Soil Mixing Ratio with Sawdust in Different Soil Moisture Treatments for Greenhouse Cucumber

Cucumber is one of the important greenhouse vegetables in Iran and the world. Cucumber is a warm and temperate season crop and is very sensitive to soil moisture regimes conditions. In order to model the effect of mixing soil with sawdust on the yield of greenhouse cucumber under different moisture regimes, an experiment was conducted in a completely randomized block design with three replications. Treatments included sawdust-free treatment (control) and a combination of 5%, 10%, 20%, and 40% sawdust and amount of water were considered at two levels of 45% and 65% of field capacity and a stress-free level. Using response surface method, the results showed that, based on the variables of sawdust percentage and moisture level, the best yield model is the second degree model with a regression coefficient of 0.85. Also, the effect of available moisture levels on yield was linear and, in contrast, the effect of sawdust percentage on yield was a quadratic function. Also, assuming the least available moisture and the lowest percentage of sawdust mixing (i.e. 13.7% of sawdust and 43.6% of field capacity), the highest yield was 86.6 tons/ha with a degree of desirability of 0.6. Also, assuming the least available moisture and change of sawdust between zero to 40 % (27.6% of sawdust and 47% of field capacity), the highest yield was 93.6 tons/ha, with a degree of desirability of 0.8. The results showed that, in any specific moisture regime, with increase in the amount of sawdust, root indices, except the main root length, had an increasing trend with decrease in available water. Besides, in each of the moisture regimes treatments, an increasing trend of yield was observed with increase in the amount of sawdust. Considering the nonlinear effect of changes in moisture regime and sawdust mixing rate on greenhouse cucumber yield, in order to achieve the best yield, sawdust mixing ratio should be determined for each soil.