The Influence of Nitrogen Application Under Aerated Drip Irrigation on the Hydraulic Characteristics and Photosynthetic Capacity of Tomato

The objective of this study is to investigate the effect of water and nitrogen coupling on tomato yield and water use efficiency (WUE) under aerated drip irrigation, and to provide a scientific basis for water and nitrogen management for tomato cultivation in Northwest China.

Two greenhouse experiments were carried out in 2023 and 2024, and three irrigation levels W1 (50% ET_C), W2 (75% ET_C) and W3 (100% ET_C) were set under aerated drip irrigation with micro and nano bubble generating devices (ET_C is the actual crop evaptranspiration). Three nitrogen application levels were N1 (0), N2 (150 kg·hm^-2) and N3 (250 kg·hm^-2), and W3 (100% ET_C) N3 (250 kg·hm^-2) under traditional drip irrigation was used as control treatment (CK). The effects on soil moisture content, hydraulic characteristics, photosynthetic characteristics and yield of tomato were studied.

Aerated drip irrigation promoted the uptake and utilization of soil water in tomato, improved plant hydraulic characteristics and leaf photosynthetic characteristics, and increased yield and WUE by 1.21% to 1.84% and 1.84% to 2.25%, respectively. Optimized water and nitrogen management under aerated drip irrigation could further promote tomato growth and yield. Soil moisture content increased with increasing irrigation but decreased with increasing nitrogen application, reaching a maximum in the W3N1 treatment, which was 0.31% to 19.37% higher than other treatments; tomato stem water potential, Pn, Gs, and SPAD all increased with increasing irrigation and nitrogen application, reaching maximum values in the W3N3 and W2N3 treatments, respectively, and increasing by 0.95% to 104.86% compared with other treatments. PLC decreased with the increase of irrigation water and N application and decreased to the minimum value in W3N3 treatment, which was 11.27% to 69.24% lower than other treatments. Nitrogen application under deficit irrigation alleviated water stress in tomato plants, and soil moisture content, stem water potential, PLC, Pn, Gs and SPAD were significantly improved by 17.37% to 21.16% under deficit irrigation W2 compared with W1. Yields of both spring-summer and autumn-winter tomato reached the maximum in the W2N3 treatment, WUE reached the maximum in the W2N3 and W1N3 treatments, respectively, and autumn-winter tomato WUE was increased by 1.02% in the W1N3 treatment compared with W2N3, but yield was significantly decreased by 15.25%. Path analysis revealed that the direct effect coefficient of soil moisture content on yield under aerated drip irrigation was 0.439, while the indirect effect coefficients of soil moisture content on yield through stem water potential, PLC, Pn and Gs were 0.952, 0.852, 0.582 and 0.494, respectively.

Nitrogen application under aerated drip irrigation can improve the hydraulic characteristics of tomato under different irrigation conditions, enhance the photosynthetic capacity of leaves, and then improve the tomato yield. Considering the yield and WUE, the appropriate irrigation volume and nitrogen application rate for tomato in Northwest China are 75% ET_C and 250 kg·hm^-2, respectively.