Foliar applications of urea as a tool to reduce nitrate contamination in greenhouse crops.

摘要

This study investigates the ability of foliar N sprays to supply N to the crop, in order to minimize the N supplied to the roots and reduce nitrate leaching to the soil. Sweet pepper plants were used to determine the optimal urea concentration to be sprayed on the leaves, inside the greenhouse. The experiment consisted of the application of two different nutrient solutions (standard and deficient) containing 12.5 and 3.5 mM NO3- respectively. To the plants grown in the N-deficient nutrient solution, foliar urea was applied every fortnight at different concentrations (5, 10, or 15 g L-1). The results show that plant fresh weight (stem and leaves) was greater for the treatment that received higher nitrate concentration in the nutrient solution, than for any of the foliar-fertilized treatments. Leaf growth was also affected by the fertilization strategy and a differential effect was found between crop stages. Total N was increased, especially for those plants that received the higher urea concentration; however, only a minor effect was found on growth and total yield. Further work, involving different frequency during the crop cycle and taking into account the phenological stage, could show further benefits of foliar urea in horticulture.