Cultivation in soilless cropping systems (SCS) provides multiple benefits in greenhouse production due to their inherent ability to decouple plant cultivation from the constraints imposed by the greenhouse soil. Nutrient supply in soilless culture can be both an advantage, as it can be precisely controlled, but also a disadvantage if inappropriately managed, due to the limited rooting volume and concomitantly due to the low buffering capacity in the root zone. Due to differences in uptake mechanisms between individual nutrients, the nutrient concentrations and mutual ratios in the root solution (RS) are different than those in the supplied solution (SS). Therefore, optimal control of nutrition in SCS must be based on standard recommendations for the composition of both the SS and the RS. Closed-loop soilless cropping systems (CLS) can eliminate pollution of surface and underground water resources as they do not allow for discharge of any nutrient solution (NS) effluents to the environment. However, the risk for occurrence of nutrient imbalances is higher in CLS, because the nutrient concentrations in the recycled NS are poorly predictable variables impacting the composition of the SS. The current strategy to cope with this uncertainty is to regularly analyze samples of drainage or recirculating NS but this has the drawback that the analysis results, when available, are not actual, as they depict the nutrient status that was prevailing in the root zone some days ago. To address this problem, ion-selective electrodes (ISEs) have been proposed as means to monitor the nutrient concentrations in the root zone of the plants. However, their commercial application requires high credibility and robustness of the ISEs under greenhouse conditions. Furthermore, a special decision support system is needed to process the measurements in real time and automatically readjust the nutrient supply rates, and a special fertigation system with multiple stock solution tanks to implement the output of the DSS. To minimize or even eliminate discharge of NS in CLS, new approaches are needed to manage salt accumulation in CLS if raw water with sub-optimal Na concentrations is used. Due to the low buffering capacity in the root zone of SCS, optimal control of pH is very important and some critical factors for achieving this goal are discussed. Finally, a new trend in soilless culture is the use of organic fertilisers in these systems, and even the organic soilless culture production, which is not uniquely considered in different countries.

The physical and chemical properties of growing media significantly influence their hydraulic properties, affecting plant growth and development. Key physical properties include air-filled porosity, dry matter content, bulk density, shrinkage, and particle size distribution. Organic matter content, a physio-chemical property, also plays a role in enhancing water retention and facilitating nutrient availability. As the UK horticulture industry transitions to peat-free growing media, a range of organic and inorganic ingredients including wood fibre, bark, coir, composts, sand, and clay are increasingly being used in combination to formulate growing media. Variations in the physical and chemical properties of the ingredients, and variations in the ratios with which they are combined, result in diverse hydraulic properties of formulations and impact their effectiveness as growing media. Understanding the links between physio-chemical properties and optimum irrigation management is crucial, especially considering the intrinsic link between irrigation and nutrition. This study investigated the relationships between volumetric moisture content VMC (%), growing media dry matter content and bulk density in peat-reduced and peat-free growing media. The trials involved crops of Aubrieta gracilis (1L pots), Salvia nemorosa (3L pots), Lupinus polyphyllus (3L pots), Euonymus japonicus (5L pots) and Pieris japonica (7.5L pots) monitored with dielectric moisture sensors in commercial nursery settings. Results indicate that peat-free growing media can achieve similar or greater VMC (%) compared to peat-reduced nursery control media, although some mixes exhibit lower VMC (%).

The study discusses the correlation between the sensor-based readings and the physical properties of the growing media. By adjusting irrigation duration and frequency significant water savings can be achieved while maintaining moisture levels comparable to peat-based controls. This has positive implications for nutritional use efficiency and reduces nutrient loss through leachates caused by over-watering.

Further research is necessary to determine the ideal moisture levels based on growing media and plant demand and to establish a reliable sensor-based irrigation management approach to optimise the performance in peat-free growing media, particularly in terms of irrigation and nutritional management.

Adequate nitrogen supply is crucial for producing high-quality vegetable seedlings in press pots. Even slight nitrogen shortage impairs plant growth and might extend the cultivation period. On the other hand, high amounts of nitrogen at the end of the cultivation period might lead to unwanted large leaves that complicates planting. Due to the increasing substitution of peat in growing media by wood fiber, the importance of continuous control of nitrogen supply will increase. However, usual nitrogen analysis in the lab is not well suited to assess nitrogen stocks in press pots as it takes too long until growers receive the results. Thus, an easy on-site method for analysis of ammonium and nitrate in press pots was established. The method is based on the extraction of entire press pots without any sample preparation. Eight pots are taken, mixed with 300 ml of a 0.0125 M CaCl₂ solution and homogenized with a handheld blender. The volume of the suspension is recorded and an aliquot of 50 ml is mixed again with another 300 ml of a 0.0125 M CaCl₂ solution. The suspension is filtered and ammonium and nitrate are measured using a handheld spectrometer with test strips (RQFlex 20). Over a period of about nine months, 600 samples were taken from five growers and analyzed for mineral nitrogen using both the on-site method and the lab method. The results revealed a close correlation between the two methods (R² = 0.78). The root mean square error was about 4 mg nitrogen per press pots, which allows at least a classification of N supply of press pots into five levels (very low, low, adequate, high, very high).

Frequency Domain Reflectometry (FDR) soil moisture sensors offer valuable insights into growing media by providing both moisture content and electrical conductivity (EC) data. However, most FDR sensors measure the bulk EC, not the EC values commonly used by growers and researchers. Bulk EC can fluctuate based on moisture levels and media type, leading to several attempts to convert it into a more practical EC value. While the Hilhorst equation can convert bulk EC to pore water EC in soils, it requires recalculating the pore water EC to approximate the saturated extract EC for practical use in soilless substrates. Consequently, proper conversion of FDR sensor measurement is essential for effective in situ monitoring and control of EC levels, which ensures optimal water and nutrient management in the soilless cultivation of horticultural crops. This study used FDR sensors (TEROS 12, Meter Group, USA) to continuously measure the saturated extract EC of soilless substrates in situ. This was achieved by calibrating medium-specific constants and conversion factors. Adjusting the medium-specific constants (i.e., dielectric constant when bulk EC is zero) for different substrates significantly improved the precision of pore water EC estimations. Further refinement through regression calibration of pore water EC to saturated extract EC could enable continuous, reliable in situ EC measurement for soilless substrates. By utilizing this calibration of FDR sensors, improved water and nutrient management for soilless cultivation can be achieved through continuous in situ monitoring of substrate moisture and EC.

Efficient fertilizer use is essential for sustainable food production in greenhouses, particularly for fast growing crops like cucumber (Cucumis sativus), to ensure both high yield and quality. In this study, Lebanese and Continental cucumber varieties were cultivated in a high-tech greenhouse to evaluate their productivity, gene expression and resource use efficiency at three different electrical conductivity (EC) levels (1.0, 2.5, and 3.5 dS/m) during the flowering and maturity stages. We demonstrate that an EC level of 2.5 produced the best yield compared to the other EC levels throughout flowering and maturity stages. Photosynthetic rate and stomatal conductance showed no significant variations across different EC levels at both stages of plant development; however, electron transport rate was significantly higher in the plants grown in EC 2.5 of Lebanese and Continental cucumbers. The shelf life of cucumbers was best maintained at by an EC level of 2.5, while a greater water loss was observed at EC 1.0 for Lebanese variety during maturity stages at a temperature of 2 °C. Moreover, relative expression analysis of cucumber leaves and fruits revealed the decreased expression of a potassium genes like HKT1 and channels including TPK5 in response to higher ECs. Additionally, a cost-benefit analysis indicated that the greenhouse cucumber business in Australia could break even in 3 to 5 years and a fertigation efficiency of 1010 L·m⁻²·year⁻¹ was observed at an EC level of 2.5, highlighting its optimal economic fertigation performance. We conclude that efficient fertigation promotes sustainable resource usage, enhances crop productivity, and ensures cost-effective production in greenhouse-grown cucumbers.