Management of Periodic Nutrient Supply Independent of Water Supply Based on Solar Radiation and Crop Models in a Soilless Culture

Recently, periodic nutrient supply in a soilless culture was suggested by some researchers. A defined amount of nutrient elements that is independent of water supply is supplied in a short period such as a day or a week. The aim of the periodic nutrient supply is to supply nutrients just enough for plant growth during the short period, thus achieving a decrease in fertilizer consumption without decreasing yield. In this report, we review the periodic nutrient supply and suggest optimal methods of the supply. Reports on the periodic nutrient supply showed indirectly that, if excess nutrients were not supplied to plants, dry matter production was positively correlated with uptake of nutrients such as nitrate and phosphate. Thus, to decrease fertilizer consumption, the amount of nutrient supply should be maximized within a range where the correlation between nutrient uptake and dry matter production is observed. To determine such an optimal amount of nutrient supply required by the plants in a short period, we have to predict the rate of dry mater production during the period. Although it is feasible to measure the rate of dry matter production by destructive measurements, it is not practical in commercial greenhouses. The rate of dry matter production is predictable by solar radiation and crop growth models. The models can simulate dry matter production using leaf area index (LAI), light extinction coefficient and solar radiation. Although it is often difficult to estimate LAI practically, LAI could be predictable with a transpiration model, water uptake and environmental data such as solar radiation. Because water uptake by plants and solar radiation are usually measured on line in a greenhouse, the rate of dry matter production and thus the amount of nutrient supply could be predicted continuously.