Optimal coupling combinations between irrigation frequency and rate for drip-irrigated maize grown on sandy soil

This study was conducted over 2 years (2007 and 2008) to establish the optimal combinations between irrigation frequency and rate for drip-irrigated maize using water production functions and water use-yield relationships. A field experiment was conducted using a randomized complete block split plot design with four irrigation frequencies (F₁, F₂, F₃ and F₄, irrigation events once every 1, 2, 3 or 4 days, respectively) and three drip irrigation rates (I₁: 1.00, I₂: 0.80, and I₃: 0.60 of the estimated evapotranspiration, ET) as the main and split plots, respectively. Our results show that yield variables and water use efficiencies (WUEs) increased with increasing irrigation frequency and rate, with non-significant differences between F₁ and F₂ in yield variables and between I₁ and I₂ in WUEs. Moreover, the combination between various irrigation frequencies and rates had an important effect on yield variables and WUEs, with the highest values being found for F₁I₂ and F₂I₁ and the lowest for F₃I₃ and F₄I₃. The F₁I₃ treatment had grain yield and yield components values similar to those obtained for the F₃I₂ and F₄I₁ treatments and WUEs values similar to those obtained for the F₂I₁ and F₂I₂ treatments. Seasonal yield response factors (k_y) were 1.81 and 1.86 in 2007 and 2008, respectively. Production functions of yield versus seasonal crop ET were linear for all combinations of irrigation frequency and rate and for all irrigation frequency treatments with the exception of the F₁ treatment, which instead showed a second order relationship. The relationship between WUE and grain yield was best represented by a power equation. In conclusion, we identified the optimal coupling combinations between irrigation frequency and water application rate to achieve the maximum yield and WUEs under either sufficient (F₂I₁) or limited irrigation (F₁I₃) water supplies.