Water status diagnosis in greenhouse drip-irrigated tomato and celery using leaf turgor dynamics and machine learning

Accurate crop water status monitoring is crucial for optimized irrigation in controlled environments, but traditional approaches relying on damaging measurements or sporadic sampling frequently restrict real-time evaluation.

This study explored the non-invasive leaf patch clamp pressure (LPCP) probe to evaluate the water status of drip-irrigated tomato and celery. Leaf turgor dynamics analysis enabled the characterization of the LPCP probe's output parameter (P_p) and its environmental drivers, and the development of predictive machine learning models.

The results indicated that diurnal patterns of P_p in drip-irrigated tomato and celery exhibited two distinct states: State I (unimodal) and State II (troughed), corresponding to moisture conditions with no or mild stress, and severe stress, respectively. The soil water content (SWC) thresholds for State I were set at SWC > 20% (tomato) and SWC > 19% (celery), whereas those for State II were set at SWC < 18% (tomato) and SWC < 16% (celery). For State I, P_p was positively associated with solar radiation but negatively associated with SWC (in tomato) and wind speed (in celery). For State II, the associations between P_p and environmental parameters were less than those in State I. Interestingly, compared to full irrigation, non-full irrigation treatments not only showed a higher proportion of State II but also resulted in an increase in both P_p,max and P_p,min by 15.39%-138.39% in tomato and 3.44%-94.02% in celery. These analytical results yielded four model parameter combinations based on the inclusion of SWC and the management of distinct P_p states. The prediction model that integrated Combination 4 (substate P_p prediction based on meteorological factors and SWC) with the random forest approach exhibited the highest accuracy (R₂ = 0.995, MSE = 2.419, RMSE = 1.540, and MAE = 0.531), with SWC identified as its key feature parameter.

These findings provide a scientific foundation for optimizing the precision irrigation of greenhouse vegetables in drip systems.