Response of yield, quality, water and nitrogen use efficiency of tomato to different levels of water and nitrogen under drip irrigation in Northwestern China

The objective of this study was to investigate the effects of applying different amounts of water and nitrogen on yield, fruit quality, water use efficiency (WUE), irrigation water use efficiency (IWUE) and nitrogen use efficiency (NUE) of drip-irrigated greenhouse tomatoes in northwestern China. The plants were irrigated every seven days at various proportions of 20-cm pan evaporation (Ep). The experiment consisted of three irrigation levels (I1, 50% Ep; I2, 75% Ep; and I3, 100% Ep) and three N application levels (N1, 150 kg N ha−1; N2, 250 kg N ha−1; and N3, 350 kg N ha−1). Tomato yield increased with the amount of applied irrigation water in I2 and then decreased in I3. WUE and IWUE were the highest in I1. WUE was 16.5% lower in I2 than that in I1, but yield was 26.6% higher in I2 than that in I1. Tomato yield, WUE, and IWUE were significantly higher in N2 than that in N1 and N3. NUE decreased with increasing N levels but NUE increased with increase the amount of water applied. Increasing both water and N levels increased the foliar net photosynthetic rate. I1 and I2 treatments significantly increased the contents of total soluble solids (TSS), vitamin C (VC), lycopene, soluble sugars (SS), and organic acids (OA) and the sugar:acid ratio in the fruit and decreased the nitrate content. TSS, VC, lycopene, and SS contents were the highest in N2. The harvest index (HI) was the highest in I2N2. I2N2 provided the optimal combination of tomato yield, fruit quality, and WUE. The irrigation and fertilisation regime of 75% Ep and 250 kg N ha−1 was the best strategy of water and N management for the production of drip-irrigated greenhouse tomato.