SOILLESS CULTURE: MANAGEMENT OF GROWING SUBSTRATE, WATER, NUTRIENT, SALINITY, MICROORGANISM AND PRODUCT QUALITY

The present article reviews the scientific literature on soilless culture and provided a critical examination of the micro-environmental factors that can affect horticultural crop growth and productivity, including, soilless substrate, fertigation solution, salinity, nutrient content and pH and plant-microorganism interaction. In addition, the role of precision agriculture such as, remote sensing in soilless system performance is reviewed. Soilless substrate source (organic and inorganic) and particle size can affect mineral content, oxygen level, salinity and pH of the nutrient solution, as well as the microorganism diversity and abundance. Organic substrates had more microorganism communities compared to inorganic substrates. Microorganism inoculation (e.g. fungi) of inorganic substrate to increase microorganism abundance is completely ineffective. However, environmentalists do not recommend the use of peat-based organic substrates because it leads to loss of soil organic carbon and destruction of wetlands. Agricultural demands for sustainable, environmental friendly soilless system highlights the benefits of using inorganic substrate (rock-wool and volcanic tuff) and the re-use of nutrient solution (closed systems) to avoid water and nutrient losses. Interestingly, biological control of root rot pathogens in closed soilless systems is more effective than open or conventional due to the lower variety of microorganism community in closed structures. However, substrate salinity is the main challenge in closed soilless systems. The use of salt-tolerance cultivars, large volume tanks to minimize electrical conductivity and pH changes and sub irrigation with low concentration nutrient solution are the main approaches to reduce salinity in growing substrates. Several precision agricultural techniques based on advanced sensing technologies such as smart irrigation systems and surface reflectance data from crop canopy may increase soilless system efficiency. These techniques are based on crop water demands, not fixed watering schedules and have the potential to optimize water and nutrient use efficiency.