Nitrogen and potassium concentration in the nutrients solution for the production of tomato (Solanum lycopersicum)

This study viewed to determine the effects of N and K concentrations in the nutrients solution on the productivity and fruit quality of tomato plants growing in a hydroponic medium. The experiment was carried out from January through April of 2011, in Jaboticabal, Sao Paulo, Brazil. The experiment was divided in two phases – the first took place during the vegetative development of the plants and it consisted of the doses of N of 137.5, 192.5, 247.5, and 302.5 mg L-1, keeping K concentration at 275 mg L-1. In the second phase, during plant reproductive growth, the treatments consisted of the K doses of 137.5, 206.25, and 275 mg L-1 and the N dose which yielded the best results during the previous phase. At the end of the vegetative phase, leaf N content, first raceme height, internode length, and stem diameter were determined, and it was verified to have no significant effect of treatments upon the characteristics, and therefore considered the lowest N rate (135.5 mg L-1) as most appropriate. At the reproductive phase, increasing doses of N caused yield reductions of clusters 1 and 2. As to K concentrations, the largest yield of cluster 2 resulted from the concentration of 202.5 mg L-1. The largest fruit yield resulted from the N and K concentrations of 177.2 and 188.7 mg L-1 respectively, this means N:K relation of 1:1.1. The soluble solids content of fruits from clusters 1 and 2 was not influenced by variations in N and K concentrations.   Key words: Greenhouse, hydroponic system, nitrogen:potassium ratio, productivity.