Determination of Grain Yield Inputs of the Maize Hybrid Giza 168 Using a Six-Factor Central Composite Design in Mediterranean Regions Under Irrigation

The maize single hybrid Giza 168 was evaluated for grain yield in a six-factor central composite design in 2015 and 2016 summer seasons. The six factors included; surface irrigation level (I), potassium (K), phosphorus (P), nitrogen (N), sowing date (SD), and plant density (PD). The CROPWAT schedule module was applied for evaluation of irrigation practices and to develop alternative improved water delivery schedules. The six studied factors explained 57% of the variation in grain yield, with significant linear effects for PD (0.48*), I×K interaction (-0.45*), and P×N interaction (-0.69*). The highest grain yields (8.05 and 8.06 t/ha) were obtained from two combinations, i.e., high irrigation with high K, low P, high N, late SD, and high PD; and low irrigation with high K, high P, low N, late SD, and low PD, respectively. Simulation of irrigation scheduling indicated that the quantity of irrigation water could be reduced by 22% and the irrigation interval extended to 15 days without any loss in grain yield. The results showed that application of 270 kg N/ha, 100 kg K2O/ha, 34.5 kg P2O5/ha, and sowing at 20 to 30 May with a plant density of 65,000 plants/ha will realize the highest yield potential of the hybrid Giza 168.