Relationships of Nitrogenous Compounds in Petiole Sap of Tomato to Nitrogen Fertilization and the Value of these Compounds as a Predictor of Yield

`Colonial' tomato ( Lycopersicon esculentum Mill.) plants were grown on raised beds with black polyethylene mulch, drip irrigation, and preplant-N rates of 0, 67, 134, 202, or 269 kg·ha -1 . Petiole sap was collected 7 and 13 weeks after transplanting. Concentrations of NO 3 -N, free amino acids, total amino acids, and total-N (the sum of NO 3 -N and amino acid-N) were examined as functions of the rate of N fertilization. Also, each of these compounds was used as an independent variable as a predictor of fruit yield. Seven weeks after planting, the concentrations of NO 3 -N and 15 of 18 of the free amino acids were correlated with the rate of N fertilization, but concentrations of bound or total amino acids were not. The amount of NO 3 -N accounted for 37% of the total-N in the 0 kg·ha -1 treatment, and up to 83% in the 202 kg·ha -1 treatment. NO 3 -N was highly correlated with total-N for both nonhydrolyzed and hydrolyzed sap ( R 2 = 0.98). Thirteen weeks after transplanting, neither the concentration of NO 3 -N nor that of amino acids, other than asparagine, glutamine, and proline, were significantly related to the rate of N fertilization. On both dates, concentrations of glutamine plus glutamic acid were correlated with rate of N fertilization whether expressed as absolute values or as percentage values. N fertilization rate and the concentration of NO 3 -N or total-N were related to total fruit yield ( R 2 = 0.69 to 0.74), and marketable fruit yield ( R 2 = 0.78 to 0.82). N-fertilization rate and petiole sap concentrations of NO 3 -N or total-N were also correlated with the N contained in total or marketable yield. Petiole sap variables measured 13 weeks after transplanting were not significantly correlated with fruit yield or the quantity of N contained in the fruit. Free, bound, or total amino acids in petiole sap were not as well correlated with fruit yield parameters as were N-fertilization rate, NO 3 -N, or total-N in petiole sap.