Bar-Yosef, B., Agricultural Research Organization, Bet Dagan, Israel
Klaering, H.-P., Institute of Vegetable and Ornamental Crops, Großbeeren, Germany

Available water and nutrient management models (fertigation models) simulate water and nutrients transport in soil, uptake by plants, partitioning between solid and liquid phases in soil, organic matter transformations, and mass balance of water, nutrients and salts in the soil root volume, as function of weather conditions and horticultural practices. To also account for feedback relationships between plant growth and uptake from soil, abovementioned fertigation models must be coupled with crop models predicting dry matter production and yield as function of nutrients content in plant. Protected cultivation differs from open field production in several aspects: (i) both the above and below ground growth conditions can be controlled; (ii) plants grow in substrates of limited volume; and (iii) greenhouse leachate can be recirculated to save water and reduce soil pollution. Simulating crop growth in closed loop irrigation systems, particularly under conditions of high transpiration rate and low tap water quality, poses a new modeling challenge not existing under open field growth conditions. The objectives of this review are to evaluate current knowledge gaps in greenhouse fertigation modeling, and discuss the role of crop-substrate models in decision support systems designed to optimize growth conditions in semi-closed greenhouses. Discussed knowledge gaps include nitrate/ammonium nutrition and its impact on solution pH, salinity damage mechanisms, roots growth and proliferation in substrate, root uptake characteristics, and simulating water transport in growth substrates.