Effect of nitrogen on growth, fruit quality and nutrient uptake of tomatoes grown in sand culture

Abstract

The effect of nitrogen (N) application level on fruit yield and quality, growth and nutrient uptake ofthe tomato cv. Flora-Dade was investigated in a sand culture experiment. Plants were harvested at regular intervals over a 16-week period and N levels (1.07, 5.36, 10.71 and 32.14 mmol L-1 of N as nitrate) were applied each day in a complete nutrient solution which was formulated to provide a stable and balanced nutrient supply. A response surface model fitted actual growth and nutrient uptake data quite precisely (R2> 0.96) over the range 1-32 mmol L-1 of N. From this model predicted growth and nutrient uptake rates were derived. At final harvest, increases in the level of applied N increased the number of fruit set and increased the dry weight of roots, leaf, stem and fruit. Fresh and dry weight of fruit responded to N up to 32 mmol L-I, whereas vegetative and root dry weight failed to respond beyond 11 mmol L-1 N. The firmest fruit with the highest dry matter content were grown at N levels of 11 and 32 mmol L-1. Fruit with the highest total soluble solids content were grown at N levels of 1 and 32 mmol L-1. Fruit dominated top growth over the last 6 weeks of the growth period, when the maximum predicted growth rate by tops of 151 g plant-1 week-1 was calculated to occur 10 weeks after transplanting at an N application level of 2 1 mmol L-1. Similar growth rates were predicted over the N range 18-32 mmol L-1, with rates increasing rapidly up to early fruit harvest and remaining high. Predicted nutrient uptake rates followed a similar response to growth rates. The maximum uptake rates (g plant-1 week-1) were 3.65 N, 6.19 potassium, 0.83 phosphorus, 2.03 calcium and 0.59 magnesium. We conclude that, in order to achieve optimum nutrition and hence maximum growth rates and quality of tomatoes under field conditions, the application of N and K fertilisers should be matched to the high demand which occurs over the fruit growth period.