SOME EFFECTS OF THE ENVIRONMENT ON THE NUTRITION OF GREENHOUSE TOMATOES

The nutritional requirement of greenhouse tomatoes depends on plant size and on the growth rate of both the vegetative parts and the fruit. The rates of growth and nutrient uptake, and the distribution of nutrients within the plant, depend on the aerial and root environments. For example, with tomato grown in NFT, the uptake of N, K and Ca were closely related to solar radiation and air temperature whereas P uptake was more dependent on root temperature. Low humidity increased the K and Ca content of the leaves but decreased the Ca content of the fruit. The availability of nutrients, and the ability of the roots to absorb them, depends on factors such as the pH, aeration and salinity of the substrate. High pH decreased the availability of several nutrients whilst poor aeration and high salinity decreased nutrient uptake. High salinity always decreased the K, Ca and Mg contents of tomato fruit. The integration of cultural conditions with fruit growth behaviour is discussed in relation to blossom-end rot.