Water and Nutrient Supply in Horticultural Crops Grown in Soilless Culture: Resource Efficiency in Dynamic and Intensive Systems

Abstract

It is currently possible to exploit specialised and standardised growing techniques in a context in which both land and water are becoming scarce. Agronomic innovation and automation are being coupled to an increasing sensitivity towards environment protection and a reduction in input losses. Consequently, modern horticulture is shifting from traditional culture systems, in the open field, to protected cultivation and soilless culture systems (SCS). Protected cultivation and SCS allow the provision of water and nutrients to the plant root system to be controlled and regulated, thus favouring root oxygenation. The punctual and real crop needs are satisfied by the hydroponic nutrient solution (HNS) . SCS introduce both resource optimisation and a reduction in losses, and thus increase food security and profitability in modern dynamic and intensive systems. Some SCS require the use of substrates or substrate mixes that must be chemically stable and should prevent the release of elements that can interfere with the HNS composition, thus inducing both phytotoxicity and microbial contamination. An HNS should be formulated using microbiologically safe water, and calibrating the macro-, meso- and micronutrients on the basis of the chemical composition of the water. However, it is also necessary to consider the interactions that occur in an HNS formulation between the individual elements that can affect plant growth, crop yield and injury susceptibility. Indicators, such as pH, electrical conductivity, oxygen content and temperature, should be checked periodically. The HNS supply period per day, volume per unit area or per plant, and the number of events during the day should be determined and tailored for a proper plant production in SCS. The HNS supply, whether continuous or discontinuous, can be supplied directly to the root using sub-irrigation or nebulisation systems, or from the aerial part using drip irrigation or sprinkling systems. The water and nutrient supply in SCS can be organized either through open-cycle hydroponic systems, in which the plants are fed with a specifically prepared HNS, without recovering the drainage, or through closed-cycle hydroponic systems, in which the drainage is collected, analysed, sanitised, integrated with the absorbed nutrients and re-inserted into the system. Each horticultural crop has its own specific water and nutrient supply needs that arise from specific physiological responses.