Previous field studies of soil fertility effects on the processing quality of tomatoes have been inconclusive. To adequately assess the relationship of various nutrients to fruit quality, it is necessary to more closely control the nutrition of the plant. Therefore, techniques were developed and a series of experiments were initiated in the greenhouse to study the effect of individual nutrients on pH, soluble solids, and color, as well as on yield. This article analyzes the effect of one nutrient–nitrogen–on tomato processing quality.