Speaking about nutrient solutions in soilless cultivation, different solutions can be discerned. Originally, in soilless culture only one nutrient solution was taken into account, being the solution in the containers in which the plants were grown. Such solutions were intensively moved by air bubbling and thus, the composition of the solution in the whole root environment was equal. The root environment was restricted to the container in which the plants were grown and thus, the whole root system of the plant was surrounded by the same nutrient solution. However, this is not the case for hydroponics and substrate systems under practical growing conditions, where great differences occur in time and place within the root environment. The main reason for these differences of salt concentrations between spots within the root environment are the inequality of water supply and water uptake by the crop as discussed in Section 6.3, at the one hand and the lack of movement of the solution within the root environment to equalize them on the other. In Chapter 8 some examples were shown of the inequality of the distribution of nutrients and salts within the root environment of substrate grown plants and the consequences of it on plant development.