Yield of greenhouse tomato in response to supplemental nitrogen and potassium

A supply of nitrogen or potassium greater than required or taken up by the plants should not influence the yield and quality of greenhouse tomato. To test this hypothesis, yields were compared for plants grown in rock-wool medium with sufficient nitrogen (N) and potassium (K), or with N- and/or K-supplements that increased the concentrations in nutrient solution by about 30% during fruit production. Twelve cultivars were grown and harvested over a 3-month period in each of three years. In 1999, N-supplement in the form of NH4NO3 decreased yield and fruit size. In 2000, N-supplement in the form of Mg(NO3)(2) increased yield and fruit size early in production, but it did not affect total yield. In 2001, when NH4NO3 and Mg(NO3)2 were compared directly without K-supplement, they had no significant effects on yield or fruit size. The K-supplement alone caused a non-significant increase in yield and fruit size in 1999 and 2000, but in combination with N-supplement, it significantly decreased yield, compared to the effect of N-supplement alone. The fraction of fruit with radial cracks in the skin varied according to fruit size and was affected in the same way by the nutrition treatments. The NH4NO3 supplement increased blossom end rot. Mg(NO3)(2) tended to decrease yield and size of small-fruited cultivars, but increased yield and size of large fruited cultivars. Other cultivar-specific effects of the nutrient regimes were not consistent from year to year.