Multi-objective water-nitrogen regime optimization to enhance yield, quality and productivity of drip-fertigated greenhouse tomato in northwest China

Water scarcity and low nitrogen -use efficiency coexist in the arid northwest China, making precise water–nitrogen management essential for sustainable tomato production. A two-season (spring and autumn 2023) split-plot experiment was conducted on mulched drip-fertigated greenhouse tomatoes, with four irrigation levels (W1: 50 %ET C , W2: 75 %ET C , W3: 100 %ET C , and W4: 125 %ET C ) as main plots and four nitrogen rates (N1: 0, N2: 150, N3: 250, and N4: 350 kg ha⁻¹) as sub-plots, where ET C denotes crop evapotranspiration. Water–nitrogen regime significantly affected tomato yield and its components, nitrogen uptake, fruit quality, nutrient yield, water–nitrogen productivity, and nutrient water productivity. Compared with W1, W3 increased fruit yield (FY) by 80.22 %, nitrogen uptake (NU) by 38.73 %, nutrient yield of total soluble solids (NY(TSS)) by 62.31 %, nitrogen use efficiency (NUE) by 29.39 %, but significantly reduced fruit quality by 12.54 % (TSS) to 27.80 % (soluble sugars, SS), nutrient water productivity by 33.31 % (NWP(TSS)) to 45.16 % (NWP(SS)), and water productivity (WP) by 24.22 %. Further increasing irrigation amount (W4) decreased NU, FN and FY. Relative to N1, N3 increased FY by 34.91 %, NU by 38.73 %, fruit quality by 12.81 % (TSS) to 50.25 % (titratable acid, TA), NY(TSS) by 53.27 %, nutrient water productivity by 42.27 % (NWP(TSS)) to 90.06 % (NWP(TA)), and WP by 38.46 %, but reduced NUE by 9.18 %. Excessive nitrogen fertilization (N4) decreased yield and quality. W4N3 and W3N3 achieved the highest economic returns across two seasons. TOPSIS evaluation showed W3N3 was optimal for balancing yield, quality, nutrient yield and high water-nitrogen productivity. • 125 % ET C reduced fruit number but increased single fruit weight, while 350 kg N ha⁻¹ decreased both simultaneously. • Higher irrigation lowered total soluble solids and titratable acidity, while higher N raised them. • Higher irrigation increased nutrient yield of total soluble solids and titratable acidity by 62.31 % and 39.26 %. • Nutrient yield of total soluble solids is the key indicator of water-nitrogen regulation on quality. • 100 %ET C with 250 kg N ha −1 is the optimal drip-fertigation regime for greenhouse tomato under plastic mulch.