Simplified models for the water relations of soilless cultures: what they do or suggest for sustainable water use in intensive horticulture

In intensive horticulture (including in this term both greenhouse cultivation and the outdoor production of containerised nursery stocks) there is an increasing application of closed-loop (no-drain) soilless cultures, in consideration of their positive environmental implications. In these systems, water use efficiency may depend on how the mineral supply is controlled. Crop modelling and the use of recently-marketed devices (like chemo-sensors) are promising tools for the development of a sort of ‘on-demand’ fertigation strategy. The management of closed systems is much more complicated when saline water is available to the growers, since the progressive accumulation of ions (such as Na and Cl) that are scarcely taken up by the plants, makes it necessary to discharge, more or less frequently, the recycling nutrient solution, with consequent loss of water and fertilisers. The paper illustrates some simplified models for the water relations of soilless culture and discusses what these models suggest, in terms of strategical, tactical or operational implementations, for a sustainable use of hydric resources, particularly in cultivations conducted under saline conditions. The analysis of the effect of salinity on crop productivity suggests that the most valuable strategy is likely the improvement of water quality, by means of desalinisation or the use of rainwater. Nevertheless, on species with moderate tolerance to salinity, like tomato, the application of some particular procedures for the control of nutrient supply may have positive results in terms of both crop sustainability.