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Abstract
Metabolism of foliar-applied [14C]urea and accumulation of 14C by developing fruits was investigated in trimmed tomato (Lycopersicon esculentum) plants. Carrier-free, high-specific-activity [14C]urea, applied to the single source leaf, resulted in production of 14C-labeled neutral compounds (presumably sugars) that were exported from this leaf and recovered from the single developing fruit after 6 and 24 hr. [14C]urea also was recovered from the fruit, but it possessed only one-half as much 14C activity as neutral compounds. Using an in vivo assay, leaf pieces also exhibited linear rates of urea-dependent NH3 production (2.17 ± μpmol°g−1 fresh weight per hour) that was inhibited (96%) by acetohydroxamate, a compound specific for the enzyme urease. Thus, urea is metabolized to NH3 and CO2 in tomato leaves via the enzyme urease, and the released CO2 is assimilated in a fashion similar to that of external CO2. Foliar application of [14C]urea may be useful for studying source-sink relations in tomato plants.
The influence of various crop rotations on the marketable yield of processing tomatoes (Lvcopersicon esculentum) in southwestern Ontario was investigated. The study was conducted for three years using nine and eight crop rotations at Leamington and Dresden, respectively. Four rates of nitrogen, 0, 45, 90, and 135 kg/ha were applied to each rotation. The treatments were arranged in a split-plot experimental design. Tomato yields were generally higher at both locations for all rotations compared to continuously grown tomatoes (control). The highest yields were obtained when tomatoes were grown in an alfalfa (Medicago sativa) rotation and rotations involving rye (Secale cereale) or winter wheat (Triticum aestivum). Tomato yields from the soybean (Glycine max) rotation and from continuously grown tomatoes were similar. At both locations, yields from continuously grown tomatoes increased with increasing rates of nitrogen fertilizer. Optimal yields for each rotation varied with each individual rate of nitrogen. Tomatoes grown in the alfalfa rotation showed the least response to higher rates of applied nitrogen. Our data indicates that certain crop rotations and nitrogen fertilization rates can be used together to enhance the yield of processing tomatoes.
A study was conducted from 1989 to 1991 to examine the effects of continuous tomato cropping, short-term crop rotation and, nitrogen fertilization rates on processing tomato quality. Research was conducted at two sites in southwestern Ontario, Leamington and Dresden, in split-plot experimental design. The rotations included tomato (Lycopersicon esculentum) - winter wheat (Triticum aestivum) (underseeded with red clover (Trifolium pratense), tomato-winter wheat-soybean (Glycine max), tomato-alfalfa (Medicago sativa), and tomato-rye (Secale cereale). Nitrogen fertilization rates of 0, 45, 90 and 135 kg/ha were used. Processing tomato cv. Heniz 9230 and Nabisco Brands Ltd. 7107 were assessed for colour, % soluble solids and total solids, and blossom end rot [BER]. In most instances, continuous tomato [C-T] had significantly poorer colour, soluble solids, and total solids than fruit from the various crop rotations. High nitrogen rates for C-T at Leamington, resulted in improved soluble solids and total solids, but had no significant effect on colour. A lower incidence of BER consistently occurred with low rates of nitrogen. Our results indicate that short-term crop rotation and nitrogen management in processing tomatoes can enhance fruit quality when compared to C-T.