Optimizing yield and water productivity in arid Northwest China: A source-sink perspective on drip-fertigated potatoes

Water and nitrogen (N) availability regulate assimilate production (source) and accumulation (sink), ultimately determining potato yield and water productivity (WP c ). However, previous studies have primarily focused on final yield or static source-sink relationships, whereas the temporal dynamics of biomass allocation under different irrigation regimes and N rates remain unclear. This study quantified the effects of soil wetted proportion (P), irrigation frequency (F), and N rate on sink/source ratio dynamics, yield, WP c and tuber quality in arid Northwest China. Three-year field experiments evaluated three P levels (P1: 35%, P2: 55% and P3: 75%) in 2014–2015, and three irrigation frequencies (F1: once every 2 days, F2: once every 4 days and F3: once every 6 days) combined with three N rates (140, 220, 300 kg ha −1 ) in 2018. The results indicated that increasing P or reducing F resulted in a higher late-stage sink/source ratio. However, correlation analysis revealed that while an elevated sink/source ratio during the early-to-mid growth stages was positively associated with final yield and crop evapotranspiration, it exhibited a significant negative correlation with tuber starch and protein contents. To balance this allocation, the P2 (55%) treatment effectively maintained source-sink coordination, resulting in yield and WP c that were significantly increased by 15.5% and 22.8% relative to those under P3 in 2015. In 2018, the highest yield and WP c were recorded under the F1N3 treatment, whereas low-frequency irrigation restricted total dry matter accumulation and limited the crop's yield response to high N inputs. Consequently, based on an entropy-weight TOPSIS comprehensive evaluation, regulating spatial soil moisture through a moderate wetted proportion (P2), and adopting high-frequency irrigation (F1) with adequate nitrogen (N3), represent a promising agronomic strategy for achieving comprehensive multi-criteria performance under the tested conditions.