Optimizing fertilization under ridge-furrow rainfall harvesting system to improve foxtail millet yield and water use in a semiarid region, China

Effects on the soil water and foxtail millet yield of different fertilizer rates coupled with the ridge-furrow rainfall harvesting system (RFRHS) are unclear, which could guide improvements to productivity in dryland farming. We conducted field experiments using RFRHS and traditional flat planting (TFP) at four different fertilizer rates: (i) no fertilizer (CK); (ii) low (L), N 90 + P2O5 60 kg ha(-1); (iii) medium (M), N 180 + P2O5 120 kg ha(-1); and (iv) high (H), N 270 + P2O5 180 kg ha(-1). RFRHS significantly improved the topsoil water content (by 4.7-8.5% in 0-40 cm layer) and topsoil temperature (by 0.4-0.7 degrees C), which stimulated stable seedling establishment and accelerated millet growth. Fertilization significantly enhanced water absorption in 0-140 cm profile, prolonged the growth period of millet and significantly increased dry matter accumulation. Finally, under RFRHS, the grain yield and water use efficiency (WUE) of foxtail millet increased by 6.2% and 6.7%, respectively, compared with TFP, and they tended to increase more as fertilizer rate increases, indicating a positive interaction between water and nutrients. However, under RFRHS, the M fertilizer rate obtained a higher yield (average 6748.6 kg ha(-1)), WUE (average 18.6 kg ha(-1) mm(-1)) compared with CK and L rates, and made a greater contribution to the grain yield (average 32.1%), but no further significant increases were observed with the H fertilizer rate where RFRFS showed a tendency to decrease grain yield compared to TFP in wet years. Therefore, RFRHS with fertilizer application at a rate of N 180 + P2O5 120 kg ha(-1) may be suitable for high-efficiency farming management to improve the yield and WUE for foxtail millet in this semiarid region.