Nutrient Requirements of Solanaceous Vegetable Crops

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The solanaceous group of vegetables (tomato, eggplant, chili and bell peppers) generally take up large amounts of nutrients. The amount of nutrients they take up depends on the quantity of fruit and dry matter they produce, which in turn is influenced by a number of genetic and environmental variables. For tomato to produce 1 mt of fresh fruit, plants need to absorb, on average, 2.5 to 3 kg N, 0.2 to 0.3 kg P and 3 to 3.5 kg K. Eggplant need 3 to 3.5 kg N, 0.2 to 0.3 kg P, and 2.5 to 3 kg K, while chili and bell peppers need 3 to 3.5 kg N, 0.8 to 1 kg P, and 5 to 6 kg K. In the absence of any other production constraints, nutrient uptake and yield are very closely related.

Fruit and fruiting parts in this group of vegetables contain 45 to 60% of total N, 50 to 60% of total P, and 55 to 70% of total K absorbed by the plants. The major proportion of the nutrients in fruit are absorbed from the time of flowering. The proportion of nutrients found in fruit declines with an increase in nutrient applications. A small proportion of the N, and still smaller proportions of the P and K, found in fruit are translocated from the vegetative parts.

The period of greatest nutrient requirements for N, P and K is from about ten days after flowering to just before the fruit begins to ripen. There is diurnal variation in nutrient absorption. A higher proportion of P tends to be absorbed during the night than N or K.

These crops use only a small proportion of N from organic sources. Eggplant is very effective in making use of plant nutrients already available in the soil, whereas tomato, and chili and bell peppers, are not. All these crops prefer NO3-N as a source of N. High concentrations of NH4-N in the growing medium greatly reduces their growth and productivity, especially of tomato and pepper.

For tomato, the ideal anion and cation ratios were found to be 58:36:6 for N:S:P, and 39:32:29 for K:Ca:Mg. To monitor the level of NPK in tomato plants, the fifth leaf from the top, sampled between flowering and the beginning of fruit ripening, was found to be ideal.

The quantity of nutrients to be applied depends on the yield potential of the cultivar, the level of available nutrients in the soil, and growing conditions. Because in these crops vegetative and reproductive stages overlap, and because the plants need nutrients even up to fruit ripening, application methods such as fertigation, split application of fertilizers, use of slow release N fertilizers, and integrated use of fertilizers and organic sources of nutrients have proved very effective in increasing nutrient use efficiency and crop productivity, and reducing nutrient losses.

D.M. Hegde
Food & Fertilizer Technology Center