Soil Solution

The characteristics of the soil solution in the root environment in the greenhouse industry differ much from those for field grown crops. This is caused firstly by the growing conditions in the greenhouse, which strongly differ from those in the field and secondly the function attributed to the soil solution with respect to plant development. One of the most striking differences between growing in the greenhouse and in the field is the exclusion of the natural precipitation in greenhouses, which offers opportunities for a full control of the water supply. Another difference is the heavy fertilizer application, related to the high nutrient uptake. In addition these application fertilizers are for the greater part added by fertigation. Furthermore, the irrigation and fertilizer addition not only has a function with respect to supply the plant with sufficient nutrients and water, but in greenhouses these actions are also a tool to control plant growth and produce quality. Sometimes, low osmotic potentials in the soil solution are maintained to prevent a lush growth or to improve fruit quality. Such effects on plant development, especially makes sense in substrate growing, where plants are grown in small rooting volumes and thus the composition of the soil (substrate) solution easily can be adjusted, for example on the demand of the crop under changing growing conditions. Thus, in principle it seems possible to supply plants under greenhouse conditions at the right time with the right quantity of water and nutrients, and losses of water and nutrients to the environment can be minimized. However, this is often frustrated by a heterogeneous water supply of irrigation systems, a heterogeneous water uptake by plants and accumulation of salts in the root environment from the irrigation water used. Thus, a precise matching on the demand by the water supply is hindered by an overdose of irrigation water to equalize the differences between wet and dry spots and to prevent too high accumulations of residual salts.