Effect of potassium fertilizer on yield of three cultivars of watermelon under salt stress conditions

To investigate the effect of K fertilizer on yield and yield components of three watermelon cultivars, a two-year study (2007-2008) was conducted in Ardestan Agricultural Research Center (Isfahan province) by using of split plot randomized based on complete block design in three replications. Three watermelon cultivars (‘Sugar baby’, ‘Charleston Grey’ and ‘Mahbubi’), were assigned as main plots and four K fertilizer levels (zero, 50, 100, and 150 kg K.ha-1) were assigned as subplots. Two and three times higher than consumption of K fertilizer (100 and 150 kg K.ha-1) in compared to normal conditions (without salinity), led to a 24.8 and 18.5 percent increase in yield of ‘Charlston Gray’ and ‘Sugar Baby’, respectively. The highest fruit yield (39112 kg.ha-1), was obtained using 150 kg K.ha-1 in ‘Charleston Gray’ cultivar. Potassium applications at all levels, increased fruit number in ‘Sugar Baby’ and fruit weight in ‘Charleston Gray’, were considered as the main reason for increasing yield. By increasing of K application, the ratio of Na/K in the leaves from 0.61 to 0.33 and in the stems from 0.81 to 0.4 was decreased. The results indicated that in saline conditions, higher levels of K fertilizers can reduce the deleterious effects of salinity and thus may improve watermelon yield.