Fertigation versus conventional fertilization of flatwoods grapefruit

A four-year field experiment was conducted to compare conventional fertilization by broadcasting granular material with a combination broadcast/fertigation program. The experiment was conducted on mature 'Ruby Red' grapefruit trees in a south Florida Flatwoods grove. The conventional fertilization (CONV) consisted of broadcast applications 3 times per year (Feb/Mar, May/Jun, Oct/Nov). The combination treatment (COMB) had a broadcast application of 33% of the annual N and K2O in Feb/Mar followed by the remainder applied as fertigation at 2-week intervals beginning in April. The CONV plots received 33% of the annual N and K2O (plus minor elements) during an application in late winter plus additional applications, each with a third of the annual N and K2O in the May/June and Oct/Nov time periods. During the four-year period, the COMB trees out-produced the CONV trees in 3 of the 4 years. The 4-year cumulative fresh fruit yield advantage of the COMB trees averaged 4150 kg ha(-1) (108 boxes ha(-1)) per year advantage over the CONV program. The cumulative total soluble solids (TSS) produced over four years with the COMB trees averaged 10.9 Mg ha(-1) versus 10.1 Mg ha(-1) for the CONV treatment. The production increases by the COMB treatment over the CONV program represent 8% and 9% advantages for the TSS and fruit yield, respectively. The combination dry + fertigation treatment provided a higher fertilizer use efficiency (greater production for similar application rates) than the conventional dry broadcast applications alone.