Impact of NPK Fertilization Regimes on the Phenology, Growth, and Yield of Common Buckwheat (Fagopyrum esculentum Moench) Under Arid Conditions in Jazan, Saudi Arabia

Common buckwheat (Fagopyrum esculentum Moench) is considered phosphorus efficient, but its response to fertilizer regime in hot, arid, irrigated soils is poorly known. We tested whether a P-dominant NPK regime advances flowering and alters grain composition relative to balanced NPK and no fertilizer. In a drip-irrigated field trial in Jazan, Saudi Arabia (randomized complete block design, five blocks), we compared an unfertilized control (C), balanced NPK (F1; 40 kg N, 17.5 kg P, 33.2 kg K ha⁻¹), and P-dominant NPK (F2; 5.8 kg N, 13.1 kg P, 4.8 kg K ha⁻¹), applied by fertigation. The control reached 50% flowering 43.4 days after sowing, F1 after 39.0 days (10.1% earlier), and F2 after 35.2 days (18.9% earlier; p < 0.001). Vegetative traits and seed yield (0.37 to 0.49 t ha⁻¹) did not differ significantly. Grain K was 7.7% lower and crude fiber 12.6% lower under F1 than in the control, and grain Mn was 44.3% higher under F2 than under F1. Fertilizer regime therefore changed flowering time without changing growth or yield. F2 flowered earliest although it supplied less P than F1, which suggests that the N to P ratio matters as well as the P dose.