Response to nitrogen and potassium of tomatoes grown in sand culture

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The effects of different rates of application of nitrogen (N) and potassium (K) on several parameters of growth and development were investigated in plants of the determinate tomato cultivar Sunny grown in sand culture. Parameters included fruit set, yield of fresh fruit, fruit firmness, yield of dry matter and nutrient accumulation. Three levels of N applied until first fruit set and three levels of N applied after first fruit set were compared in the presence of two levels of K in a factorial experiment. The soil solution concentrations of N were N/5, N/1 and 2N (N/1 = 8.07 mM N as NO3-) and the K concentrations were K/5 and K/1 (W1 = 3.26 mM K+). The treatments were supplied in a complete nutrient solution every two days. Low N increased the time to fruit set, reduced dry matter yield in leaf, stem, roots and fruit and fresh fruit yield. A reduction in all yield parameters was recorded, irrespective of whether N was low during the pre- or post-fruit set period. Low K and doubling the standard N level had no effect on any fruit set or yield variables. These treatments had no effect on the time from transplanting to fruit maturity or on the temporal spread of harvest. A combination of the lowest N and K levels produced the softest fruit while the highest N and K combination produced the firmest fruit. High levels of N increased the concentration of N in leaf, stem and fruit and the magnesium (Mg) concentration in leaf and fruit but reduced the K concentration in fruit.