Effect of deficit irrigation on Relative Water Content (RWC), Proline concentration, antioxidant enzymes content, chlorophyll concentration and forage yield of five clover species

In order to study the effect of deficit irrigation on RWC, proline concentration, antioxidant enzymes content, chlorophyll concentration and forage yield of five clover species, a field experiment was conducted during the cropping season 2019-2020.  The experimental design was split plots arranged based on randomized complete blocks design (RCBD) with three replications. Deficit irrigation  at three levels (0 (Full irrigation), 20 and 40% less than the irrigation requirement) were considered as main plots and  five clover species (Trifolium resupinatum ، T. alexandrium ، T. lapaceaum ، T. echinatum و T. diffusum) were allocated as sub plots.The results showed by increasing deficit irrigation up to 40%, proline concentration increased by 93% and the content of antioxidant enzymes catalase, peroxidase and superoxide dismutase increased by 12, 98 and 83% respectively. However, RWC, yield of fresh and dry fodder decreased by 22, 24 and 29% respectively. The highest RWC, chlorophyll concentration and content of antioxidant enzymes were observed without significant difference in T. resupinatum and T. alexandrium species. The interaction effect of two factors (deficit irrigation × species) showed by increasing deficit irrigation, fresh and dry forage yield of all five species decreased significantly. In all three levels of deficit irrigation, the highest yield of fresh (20.39, 18.81 and 13.94 t/h) and dry forage (4.59, 4.25 and 3.06 t/h) were obtained in T. resupinatum species. In general, the results showed that all 5 species do not have the required stability under stress conditions. Therefore, deficit irrigation for the proposed species will be justified only if a 20 and 40 percent irrigation water reduction is more beneficial than the yield reduction.