The main factor that distinguishes between fertilisation management of soil-grown from that of soilless-grown plants is the lower buffer capacity for solution composition and limited supply of nutrients. Consequently, soilless culture methods offer unique benefits such as capabilities to control water availability, pH and nutrient concentrations in the root zone. At the same time there are higher risks because of the smaller root system and low buffering capacity for water, nutrients and because of the increased risk of exposure to extreme ambient temperatures. The general objective of this chapter is to exemplify nutritional issues of substrate-grown plants and to discuss differences between fertilisation/nutrition of soil-grown plants and of soilless-grown ones. The specific objectives are: (i) to present the nutritional requirements of soilless-grown crops; (ii) to illustrate the impacts of the NH4/NO3 ratio in the irrigation water on rhizosphere-pH and on the development of soilless-grown plants under various temperatures and aeration conditions; (iii) to discuss the integrated effect of irrigation frequency and nutrient availability on crop growth; (iv) to present the crop responses to changes in the electrical conductivity of the root-zone solution and to the ionic composition of the water, in soilless culture; (v) to describe the mode of fertilisation and the potential nutrient sources; and (vi) to discuss possible interactions among various fertilisers, and between the roots, the solution and the substrate, including the effects of the medium, temperature and oxygen concentration. Special attention will be devoted to pH effects on plant root functions and on availability of specific nutrients.
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