Recent trends in salinity control for soilless growing systems management

Abstract

The consequences of closed hydroponic systems, the impact of salinity build-up on crop yield and product quality are reviewed. Soilless cultivation, especially in closed-loop systems offers a great option for water saving in greenhouses. Capture and recycling of the drainage will considerably improve the water use efficiency in horticultural crops and restrict water pollution by nutrients and pesticides. However, accumulation of undesired ions in the root environment constrains the potential of complete recycling. This is due to the presence of undesired ions in irrigation water, which is the case in many regions, especially in the Mediterranean countries. For fruit vegetables, high salinity of the nutrient solution in the root environment will induce inhibition of growth and production at one hand, but it may increase fruit quality on the other hand and thus offers possibilities for product quality control. Therefore the maximum acceptable salt accumulation will depend on the expected yield and quality responses at one hand, and the desire for the highest water and nutrient use efficiencies on the other. To enable growers of regions with low quality water to adopt recycling of the excess irrigation water, efficient solutions have to be found to control, manage and minimize salt accumulation. Taking into account that the effects of salinity - apart from the water quality itself - strongly depend on (i) crop characteristics, (ii) greenhouse climate, (iii) irrigation and drainage management method and (iv) fertilization level, the above issues are analysed and the relevant literature is discussed. Alternative methods to overcome the problem of salt accumulation and increase water and fertilisers use efficiency, such as desalination of poor quality irrigation water are also presented. Finally, efforts for development of decision support systems with on-line measurement or model-based prediction of the salt concentrations in the drainage solution for semi-closed soilless systems management under different environmental conditions are also presented and discussed.