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

Tomato plants (Lycopersicon esculentum Mill. cv. Momotaro) were cultured in nutrient solution supplying 35 meg or 50 meg of nitrate (NO3) per plant we ekly from the flowering stage of the first truss in two cropping seasons. T he effects of NO3 supply levels and cropping season on fruit growth of toma to were investigated. Furthermore, the relationship between the results of the plant sap analysis and fruit growth of tomato was analyzed. In the spri ng to summer cropping, NO3 supplied was almost all absorbed and high produc tivity of tomato fruits was obtained in each treatment. In the fall to wint er cropping, however, high NO3 supply did not increase the uptake of NO3, b ut tended to decrease the rate of fruit set and marketable yield. Accumulat ion 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 abi lity 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 thi s fruit truss. High NO3 supply tended to increase potassium(K) concentratio n and electrical conductivity (EC) value, and to decrease phosphate (P), ca lcium (Ca), and magnesium (Mg) concentrations in the petiole sap. On the wh ole, concentrations of these elements in the petiole sap consistently refle cted their uptake rates in two cropping seasons.