Three irrigation treatments were set up in northeast China to investigate soil water movement and root water uptake of greenhouse tomatoes, and the collected experimental data were simulated by HYDRUS-2D. The computation and partitioning of evapotranspiration data into soil evaporation and crop transpiration was carried out with the double-crop coefficient method. The HYDRUS-2D model successfully simulated the soil water movement, producing RMSE ranging from 0.014 to 0.027, an MRE ranging from 0.062 to 0.126, and R² ranging from 79% to 92%, when comparing model simulations with two-year field measurements. Under different water treatments, 83–90% of the total root quantity was concentrated in 0–20 cm soil layer, and the more the water deficit, the more water the deeper roots will absorb to compensate for the lack of water at the surface. The average area of soil water shortage in W₁ was 2.08 times that in W₂. W₃ treatment hardly suffered from water stress. In the model, parameter n had the highest sensitivity compared with parameters α and K_s, and sensitivity ranking was n > K_s > α. This research revealed the relationships between soil, crop and water under drip irrigation of greenhouse tomatoes, and parameter sensitivity analysis could guide the key parameter adjustment and improve the simulation efficiency of the model.

Irrigation and nitrogen application rates have significant effects on greenhouse tomato yields, as well as water and nitrogen use efficiencies, but little is known regarding how these rates affect plant–microbiome interactions and how the associated changes might impact tomato yields. In this greenhouse study conducted over two years, the effects of three irrigation levels (moderate deficit with 65–75% water holding capacity threshold, slight deficit with 75–85%, and sufficient irrigation with 85–95%) and four nitrogen application levels (60, 120, 240, and 360 kg ha⁻¹) on tomato growth, yield, water and nitrogen productivities, and rhizosphere microbial diversities and functions were investigated. The results demonstrated that the highest tomato leaf area, dry biomass, yield, and water and nitrogen productivities were obtained under the treatment with sufficient irrigation. With increasing nitrogen application, the tomato leaf area, dry biomass, yield, and water and nitrogen productivities showed a trend of first increasing and then decreasing. Overall, the treatment (N2W3) with sufficient irrigation and 240 kg ha⁻¹ N was associated with the highest tomato growth, yield, and water and nitrogen productivities. Moreover, optimal irrigation and nitrogen application obviously altered the structures of rhizosphere bacterial and fungal communities, particularly recruiting microbiota conferring benefits to tomato growth and nitrogen fixation—namely, Lysobacter and Bradyrhizobium. Ultimately, optimal irrigation and nitrogen application significantly increased the relative abundances of functions related to carbon, sulfur, and nitrogen metabolism, especially nitrogen fixation. In summary, optimal irrigation and fertilization enhanced tomato yield, as well as water and nitrogen productivities by increasing the nitrogen fixation functions of the rhizosphere microbiome. Our results provide significant implications for tomato cultivation in greenhouses, in terms of optimized irrigation and fertilization.

Accurate quantification of evapotranspiration (ET_c) and its components are critical for enhancing water use efficiency and implementing precision irrigation. A two-year experiment was conducted for greenhouse-grown tomatoes under mulched drip irrigation with three irrigation treatments during 2020–2021 in Northeast China. Three different irrigation treatments were applied by setting upper and lower soil moisture irrigation thresholds (i.e., W1, 65%θ_FC–75%θ_FC, W2, 75%θ_FC–85%θ_FC, W3, 85%θFC–95%θ_FC, respectively, where θ_FC is field capacity). In this study, a modified dual crop coefficient (K_c) model was proposed to simulate daily ET_c, plant transpiration (T_r) and soil evaporation (E_s). The simulations of the model were validated against observed data from the sap flow system combined with the soil water balance method. The controlling factors on the variations of evapotranspiration and its components were also identified by using the path analysis method. Results showed that the modified dual K_c model can accurately simulate daily ET_c, E_s, and T_r for the greenhouse tomato under different irrigation conditions, with the coefficients of determination ranging from 0.88 to 0.98 and the index of agreement higher than 0.90. The seasonal cumulative ET_c of tomato for W1–W3 were 138.5–194.4 mm, of which 9.5–15.8% was consumed by E_s. Path analysis showed that the net radiation (R_n) was the dominant factor controlling the variations of T_r and ET_c during the growing seasons. The canopy coverage degree (K_cc) was the dominant controlling factor of E_s, while the temperature (T_a) was the primary limiting factor affecting E_s. This study can provide reference information for developing proper irrigation management in a greenhouse-grown tomato in the north cold climate regions.