A field experiment was conducted in farmer's field located at Gammsa district, Dakahlya Governorate, Egypt, during two successive winter seasons 2017 and 2018, to determine and evaluate the response of watermelon grown on sandy soil to three irrigation regimes; 100%(I1), 85%(I2) and 70%(I3) of soil field capacity and four applications of bio-mineral fertilizers; F1 Applying the recommended dose of NPK (100%RNPK), F2 (85%RNPK + biofertale), F3 (70%RNPK + rhizobacterien) and F4 (55% RNPK+ mixture of biofertale + rhizobacterien).
Results showed that both of irrigation and fertilization treatments had highly significant effect on yield and its components of watermelon plants in both seasons. Maximum fruit yield and its components were achieved with I2 and F3 treatments in both seasons. Irrigation with (I2), led to increase fruit yield by (14.26 and 14.30%) compared with I1 and the corresponding values (11.72 and 12.97%) with (F3) compared with F1 in 1st and 2nd seasons, respectively. I3 achieved higher values of TSS, vitamin C, soluble sugar, PIW and water saving. Moreover, F3 followed by F4 produced the highest value of PIW in both seasons compared with F1. The combination of I2F3 has superiority in increasing fruit yield and its quality, net return and economic efficiency. Net return from water unit was resulted from the combination of (I3F4) and (I3F3) as compared with (I1F1) in both seasons, respectively.
Generally, it can be concluded that I2F3 or I2F4 is the most efficient treatment for achieving economical watermelon fruit yield, economic return and saving water and mineral fertilizers.