Effects of Sensor-Guided Irrigation on Post-Harvest Soil Nutrient Status, Yield, and Resource Use Efficiency in Greenhouse-Fertigated Tomato: A Single-Season Case Study

Most evidence on integrated water–fertilizer management for greenhouse tomatoes comes from arid and semi-arid systems; whether sensor-guided irrigation provides comparable benefits under humid subtropical conditions, where rainfall does not enter the greenhouse water balance, is unclear. This single-season trial (Anhui Province, China; randomized complete block design, n = 3) compared an unfertilized control (CK), conventional practice (T1), the provision of optimized nutrients with empirical irrigation (T2), and the same nutrient program delivered with sensor-triggered irrigation (T3). T2 and T3 shared an identical fertilizer program, providing the most direct comparison of the irrigation regime within the same optimized nutrient program. Compared to T2, T3 showed 16.2% and 13.6% (adjusted block contrasts, p = 0.013 and 0.036) increases in post-harvest soil-available phosphorus and potassium; the increase in the AHN value was not significant (18.2%, p = 0.062). The highest yield (84.43 t/ha, 86.4% higher than for CK), apparent nitrogen recovery efficiency (35.63%) and irrigation water productivity (34.83 kg/m3) were achieved with 37.4% less nitrogen and 21.1% less water usage in comparison to the levels for T1. Among the differences between T2 and T3, only the irrigation water productivity increase (31.8%, p < 0.001) and dry matter accumulation were confirmed; yield (6.9%, p = 0.076), apparent nitrogen recovery efficiency (18.5%, p = 0.19) and net profit (CNY 28.46 × 104/ha for T3 vs. CNY 27.02 × 104/ha for T2, p = 0.32) exhibited numerical, but not significant, advantages in this sample. The exploratory PCA/Pearson correlation (n = 12) associated soil P and K contents with productivity descriptively but not causally (AP yield, r = 0.858; AK yield, r = 0.854; both, p < 0.001). Therefore, it can be observed that sensor-driven irrigation added to the optimization of fertilizer application, confirming an irrigation water productivity increase and some numerically advantageous results in the single-season trial; further factorial multi-season trials are needed before broader recommendations can be made.