Effect of restricted supply of nitrate on fruit growth and nutrient concentrations in the petiole sap of tomato cultured hydroponically

Abstract

Tomato plants (Lycopersicon esculentum Mill. cv. Momotaro) were cultured in nutrient solution supplying 35 meq or 50 meq of nitrate (NO₃) per plant weekly from the flowering stage of the first truss in two cropping seasons. The effects of NO₃ supply levels and cropping season on fruit growth of tomato were investigated. Furthermore, the relationship between the results of the plant sap analysis and fruit growth of tomato was analyzed. In the spring to summer cropping, NO₃ supplied was almost all absorbed and high productivity of tomato fruits was obtained in each treatment. In the fall to winter cropping, however, high NO₃ supply did not increase the uptake of NO₃, but tended to decrease the rate of fruit set and marketable yield. Accumulation of NO₃ in the petiole sap was found with high NO₃ supply in the fall to winter cropping. Cropping season greatly influenced not only fruit growth but also the concentration of NO₃ in the petiole sap in relation to the ability of tomato plants to use available nitrogen (N). Furthermore, reduction in the rate of fruit set and weight of tomato fruit were found to relate to the low concentration of NO₃ in the petiole sap of the leaf just below this fruit truss. High NO₃ supply tended to increase potassium (K) concentration and electrical conductivity (EC) value, and to decrease phosphate (P), calcium (Ca), and magnesium (Mg) concentrations in the petiole sap. On the whole, concentrations of these elements in the petiole sap consistently reflected their uptake rates in two cropping seasons.