Coupling effects of irrigation amount and fertilization rate on yield, quality, water and fertilizer use efficiency of different potato varieties in Northwest China

Water shortage, excessive fertilization and improper variety selection have seriously restricted the sustainable development of potato in Northwest China. Two-year field experiments were conducted in 2021 and 2022 to explore the effects of irrigation amount and fertilizer application rate on the growth, yield, nutrient uptake, quality, water, and fertilizer use efficiency, soil enzyme activity and economic benefits of different potato varieties. Three irrigation levels were W1 (100% crop evapotranspiration (ETC)), W2 (80% ETC) and W3 (60% ETC). Three fertilization rates were F1 (240 kg N ha−1), F2 (180 kg N ha−1) and F3 (120 kg N ha−1). Three locally grown potato cultivars were V1 (Feiurita), V2 (Longshu 7), and V3 (Qingshu 9). The results showed that irrigation amount, fertilization rate and potato variety significantly influenced tuber yield, commercial tubers, maximum tubers, tuber weight, reduced sugar content, irrigation water productivity (WPI), partial fertilizer productivity (PFP), soil catalase activity (SCA), total income, net income, and input-output ratio. The chlorophyll content, net photosynthetic rate, dry matter accumulation, maximum tuber weight, starch content, vitamin C content, and crude protein content increased with the increase of irrigation amount. With the increase of fertilizer application rate, chlorophyll content, net photosynthetic rate, dry matter accumulation, tuber yield, plant nitrogen (N), phosphorus (P), potassium (K) absorption, starch content, crude protein content, vitamin C content, WPI, soil enzyme activity and net income increased first and then tended to stabilize or even decline. On average, the tuber yield, starch content, crude protein content, vitamin C content, WPI and net income of F2 were 19.3% (6.9%), 1.6% (1.6%), 8.8% (10.4%), 3.8% (10.5%) and 21.1% (7.8%), 34.6% (14.9%) higher than those of F1 in 2021 (2022), respectively. In two years, the average potato yield, WPI, PFP and SCA of V3 treatment were 13.1%, 14.5%, 16.4% and 4.8% higher than those of V2 treatment, respectively. Among all treatments, T5 (W2F2V3) had the highest tuber yield, commercial tuber yield, total P accumulation, crude protein content, SCA, soil alkaline phosphatase activity (SPA), soil sucrase activity (SSA) and net income, and the lowest reducing sugar content. Plant accumulation of N, P and K was closely related to tuber yield, and potato tuber yield showed a significant positive correlation with SCA and SSA. Based on the comprehensive differential combination evaluation model, considering potato growth and development, yield, quality, water, and fertilizer use efficiency and economic benefits, T5 treatment was the best treatment. After comprehensive evaluation, the optimal irrigation and fertilizer ranges were 270–290 mm and 167 kg N ha−1 to 193 kg N ha−1, respectively. The present study provides a basis for evaluating and selecting better management practices for effective irrigation and fertilization management of the best potato varieties in Northwest China.