Umudike Journal of Engineering and Technology

Drip fertigation is the dominant means of water and nutrient delivery in protected cultivation, yet the effect of its controllable variables on crop response has not been consolidated quantitatively. This study quantified the effect of five drip variables, namely irrigation level, emitter discharge, fertigation rate, fertigation frequency and number of split doses, on nitrogen, phosphorus and potassium uptake, on nutrient use efficiency and on marketable yield. Ten databases were searched systematically; thirty-five records were assessed and seventeen included, yielding 177 treatment observations. Effect sizes were computed as log response ratios referenced to each study’s own full-irrigation treatment and pooled at study level. Uptake could not be synthesised: nitrogen uptake was recoverable for 18 observations from one study, and phosphorus and potassium uptake for none. Deficit irrigation reduced marketable yield by 13.9% (95% CI 21.4 to 5.8%; p = 0.005; 70 contrasts, 10 studies), robustly across five sensitivity analyses. Neither nutrient use efficiency nor irrigation water use efficiency changed significantly. In multilevel meta-regression, irrigation level predicted yield (p = 0.0005) while emitter discharge and number of splits did not, and 95.2% of variance lay between studies. The water saved under deficit irrigation was approximately offset by the yield forgone.