Effects of water and fertilizer coupling on the yield and quality of processing tomato under aerated drip irrigation

Optimizing water and fertilization management is a critical component for maximizing crop production and water-fertilizer use efficiency. Aerated irrigation is widely recognized to improve soil aeration and water productivity. However, information about crop yield and quality of processing tomato responds to water-nitrogen-gas coupling remains unclear. To explore the effects of water and fertilizer coupling under aerated irrigation on yield, quality, and water-fertilizer use efficiency of processing tomato (Solanum lycopersicum), and to determine the optimal water-nitrogen rate for improving quality under aerated irrigation, a field experiment was conducted in 2019 at the Key Laboratory of Modern Water-Saving Irrigation of the Xinjiang Production and Construction Corps at Shihezi University in Xinjiang, China. Two irrigation levels (4 950 and 4 050 m3/hm2), four nitrogen levels (280, 250, 220, and 190 kg/hm2), and two aerated rates (15% and 0) were tested using a completely randomized design. A local processing tomato cultivar, Jinfan 3166, was selected transplanted on May 5th manually and harvested on August 24th. Subsurface drip irrigation was adopted in this study. Air was injected into a drip line using Mazzei air injector (Mazzei air injector 1078, American), and the aerated rate was approximately 15%. Plant height, stem diameter, yield, water-use efficiency, nitrogen partial factor productivity, and fruit quality parameter of processing tomato were determined. The results showed that irrigation and nitrogen fertilization significantly affected plant height and stem diameter of processing tomato (P<0.05). The plant height of processing tomato was greater as the irrigation and nitrogen level increased. However, excessive irrigation and fertilization had a major negative impact on stem diameter. Furthermore, Aerated irrigation enhanced plant height and stem diameter more under higher irrigation levels. Processing tomato yield was greater at a high irrigation level by 2.18% to 16.95% than that in the low irrigation level. Under the same irrigation amount, processing tomato yield increased firstly and then decreased relative to nitrogen levels. Compared to no aerated irrigation, aerated irrigation significantly increased processing tomato yield by 2.32% to 10.02% (P<0.05). Compared to low irrigation amount, more irrigation amount significantly decreased irrigation water-use efficiency by 4.31% to 16.40% (P<0.05), but increased nitrogen partial factor productivity by 2.18% to 16.95% (P<0.05). Under the same irrigation amount, irrigation water-use efficiency first increased and then decreased with the increase of nitrogen levels, and nitrogen partial factor productivity showed a negative correlation with the nitrogen amount. Aerated irrigation enhanced irrigation water-use efficiency and nitrogen partial factor productivity by an average of 6.12% and 6.19%, respectively, comparing to no aerated irrigation. Water-nitrogen-gas coupling had a stronger effect on the quality index of the processing tomato. Compared to low irrigation level, the average soluble sugar, organic acid, Vitamin C, and the soluble solid content was 5.84%, 4.85%, 2.50%, and 3.34% smaller in high irrigation amount. And soluble sugar, Vitamin C, and soluble solid content increased firstly and then decreased with the increase of nitrogen application. Aerated irrigation increased soluble sugar, organic acid, Vitamin C, and soluble solid content of processing tomato significantly (P<0.05). Meanwhile, compared to no-aerated irrigation, the ratio of sugar to acid was significantly lower by 1.17% in aerated irrigation (P<0.05). The principal component analysis was applied to evaluate and compare the water and nitrogen fertilization management technology with the fruit quality parameter of processing tomato. Two components were extracted from the quality index matrix which the accumulative contribution rate was 87.043%. Based on the principal component analysis, the comprehensive rankings revealed the suitable irrigation amount was 4 050 m3/hm2 and the suitable nitrogen amount was 250 kg/hm2 under aerated irrigation conditions, which ranked first. Under this pattern, the irrigation water-use efficiency was 46.85 kg/m3, which was significantly higher than other treatments (P<0.05). These results could provide theoretical support for improving water-fertilizer use efficiency of processing tomato in Xinjiang.