Water and Fertilizer Management in Soilless Rocket

Sensor-based irrigation is a promising and increasingly adopted strategy to reduce water and fertilizers consumption and losses, and to improve the overall crop performance and product quality in soilless greenhouse cultivation. This study aimed to test two irrigation scheduling approaches (timer- or sensor-based) and two fertilization levels (high or low, with reference to the standard dosage range recommended for the specific fertilizers used) of open-cycle soilless rocket salad (Diplotaxis tenuifolia) in Mediterranean autumn-winter unheated greenhouse conditions. Rocket plants (cv. Dallas, Isi Sementi) were grown in a peat: perlite (3:1) mixture in 4.5 L plastic pots. Four treatments were compared: timer with high or low fertilization (T-HF, T-LF), and sensor-based with high or low fertilization (S-HF, S-LF). In timer-based treatments, irrigation schedule was periodically adjusted based on leaching fraction measurements (≈35% was set as a target, according to common practice). In sensor-based treatments, on-demand irrigation was operated based on substrate EC/temperature/moisture sensors (GS3, Decagon Devices). These were connected to a CR1000 datalogger programmed to automatically open irrigation valves and supply water enough to constantly maintain volumetric water content to a pre-defined set-point (0.35 m3 m^-3, close to maximum water holding capacity), with no leaching. Slow release fertilizers (Osmocote Exact and CalMag, ICL) were mixed with the substrate at high (3.75 and 1 g L^-1, respectively) or low dosage (2.25 and 0.6 g L^-1). Yield, quality, water use and substrate parameters trends were evaluated. Sensors improved water use efficiency compared to timer (34.4 vs 21.4 g FW l^-1, on average) matching water supply with plant needs, preventing leaching and providing the best plant growth conditions. The highest and the lowest cumulative (three harvests) yield values were obtained in S-HF and T-LF respectively (144.8 and 102.2 g FW pot^-1), while similar values were observed in S-LF and T-HF (131.4 g FW pot^-1, on average).