Although only 1% of the total plant weight is made up of inorganic nutrients, fertilizer application is critical; it influences greatly the growth and development of the crop, as well as the quantity and quality of the fruit. A tomato crop absorbs the major nutrients at the following average rates: nitrogen, 370 kg/ha; phosphorus, 50 kg/ha; potassium, 680 kg/ha; magnesium, 290 kg/ha; and calcium, 45 kg/ha.
Over a season a grower should apparently apply twice as much potassium as nitrogen and almost as much magnesium as nitrogen to fulfill the plant's needs. However, that interpretation is too simplistic. In fact, fertilizer feeding programs are adjusted regularly throughout the production season to suit the changing nutritional needs of the crop according to crop and environmental conditions. Furthermore, the fertilizer feed is used as a tool to control crop growth and fruit quality.
The role of each nutrient in the growth and productivity of tomatoes is described in the sections that follow.
This nutrient contributes more toward the vegetative components (leaves and stems) of the plant than the reproductive components (fruit). High rates of nitrogen induce vigorous vegetative growth to the detriment of fruit production. However, under hot and bright conditions, the nitrogen level must be increased to enable the plant to continue growing and to realize the maximum production potential of the fruit.
An excess of nitrogen is marked by strong thick stems, curled leaves in the head of the plant, large clusters and flowers, and poor fruit set. A deficiency of nitrogen expresses itself in hard plants with thin heads, light green foliage, and pale yellow flowers.
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