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Peter C. Andersen, Fred M. Rhoads, Steven M. Olson and Brent V. Brodbeck

`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 NO3-N, free amino acids, total amino acids, and total-N (the sum of NO3-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 NO3-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 NO3-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. NO3-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 NO3-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 NO3-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 NO3-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, NO3-N, or total-N in petiole sap.

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Peter C. Andersen, Fred M. Rhoads, Steven M. Olson and Kristen D. Hill

Carbon and nitrogen budgets were determined for `Colonial' (spring) and `Equinox' (fall) tomato (Lycopersicon esculentum Mill.) plants grown on raised beds with black polyethylene mulch and supplied with preplant-N at 0, 67, 134, 202, or 269 kg·ha–1. For both spring and fall experiments, we quantified the partitioning of dry matter, N, and C, and determined marketable and total yield. In the spring study, the concentration of N in leaves, stems, and in total plants increased linearly with level of N fertilization, whereas a quadratic relationship described the amount of N contained in the fruit (maximum with 202 kg·ha–1). Quadratic relationships occurred between rate of fertilization and leaf weight, stem weight, total plant weight, marketable yield, and total yield in the spring study, with maximum values at 134 or 202 kg·ha–1 rates of N fertilization. In the fall crop, fewer significant relationships occurred between dependent variables and rate of N fertilization, and coefficients of determination tended to be much lower than in the spring study. The fraction of N in leaves, stems, and roots (fall study only) was influenced by N fertilization. Effects of N fertilization on the fraction of C partitioned to any plant part was either nonsignificant or significant at P = 0.05. Total yield was related to N fertilization in a quadratic manner, but marketable yield was significantly affected only in the spring study. In both studies, increasing the rate of N fertilization reduced the C: N linearly for all tissues. In all cases, the quantity of N partitioned to vegetative tissue was at least 65% of that partitioned to the fruit, and the quantity of C in the plant was at least 74% of that in the fruit. In conclusion, although N fertilization above 202 kg·ha–1 generally increased the concentration and total amount of N in vegetative tissues, it did not increase yield. Also, the highest rate of N fertilization (269 kg·ha–1) resulted in a much lower efficiency of applied N [defined as: (N plant + N fruit)/N applied], and a much higher level of residual soil nitrate-N.

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Salvadore J. Locascio, George J. Hochmuth, Fred M. Rhoads, Steve M. Olson, Alan G. Smajstrla and Ed A. Hanlon

Tomato (Lycopersicon esculentum Mill.) was grown with drip irrigation on an Arredondo fine sand and on an Orangeburg fine sandy loam to evaluate the effect of N and K time of application on petiole sap, leaf-N and -K concentrations, fruit yield, and to determine N and K sufficiency ranges in leaf tissue. On the sandy soil, N—K at 196-112 kg·ha-1 were applied 0%, 40%, or 100% preplant with the remainder applied in 6 or 12 equal or in variable applications in 12 weeks. With the variable application rate, most nutrients were applied between weeks 5 and 10 after transplanting. On the sandy loam soil that tested high in K, only N (196 kg·ha-1) was applied as above. Petiole sap K concentration declined during the season, but was not greatly affected by treatment. Petiole NO3-N concentrations decreased during the season from 1100 to 200 mg·L-1, and the decrease was greater with preplant N treatments. On the sandy soil, marketable fruit yields were lowest with 100% preplant, intermediate with 100% drip applied (no preplant N), and highest with 40% preplant and 60% drip applied. With 100% drip applied, yields were higher with 12 even applications than with either six even weekly applications or with 12 variable N and K applications. With 40% preplant, timing of application had little effect on yield. On the sandy loam soil in 1993, yields were highest with 100% preplant, intermediate with 40% preplant and 60% drip applied, and lowest with all N drip applied. In 1994 when excessive rains occurred, yields were similar with all preplant and with split N applications. Petiole N concentration was correlated with tomato yield, especially at 10 weeks after transplanting. The best correlation between sap-N and total yields occurred between 4 and 6 weeks at Gainesville and between 4 and 10 weeks at Quincy.