NUTRITION OF GREENHOUSE VEGETABLES IN NFT AND HYDROPONIC SYSTEMS

The uptake of nutrients by cucumber increased with the applied concentrations of N, P, and K. The ratio of absorbed K:N did not increase with plant development. With tomato, however, the K:N ratio increased with the fruit load from 1.1:1 to a maximum of 2.6:1, after which it declined to about 2:1. Increasing the concentration of K in the nutrient solution reduced the incidence of uneven ripening and increased the organic acid and K contents of tomato fruit. Low levels of Ca and Mg reduced cucumber yields, the proportion of high quality fruit, and the uptake of the respective elements.

The uptake of water, N and K by tomato was closely related to solar radiation whereas the uptake of P was highly correlated with solution temperature. Nevertheless, increasing solution temperature increased the uptake of most nutrients which resulted in marked increases in nutrient accumulation in the leaves. The uptakes of N and K were both highly correlated with that of water.

High humidity at night reduced the dry weight of cucumber leaves and caused a greater reduction in Ca content than high humidity during the day. Increasing salinity decreased the dry weight and Ca uptake of cucumber plants, but increased the proportion of the total dry weight and Ca in the fruit. With tomato, the uptake of water and nutrients increased with salinity up to 4.8 mS cm^-1 and then decreased at higher salinity. The occurrence of blossom-end rot is related to environmental factors that affect both the uptake and distribution of Ca and the rate of fruit growth.