Removal of Nutrients from the Soil

Table 4 lists amounts of certain nutrient elements that are removed by vegetable crops. It includes both the amounts removed by harvest and those that remain in crop residue and are returned to the soil. These figures for crop removal should be considered approximate. They can be used as a basis for adjusting your own application rates up or down on a trial basis. Keep in mind that nutrient removal varies with factors such as soil moisture, temperature, and pH. Plants can absorb large amounts of a nutrient if it is in abundance; but this may not increase yield. Excess levels of some nutrients can reduce the yield and/or quality of some crops.

Nutrients that are relatively immobile in the soil, such as phosphorus, calcium, magnesium, and the micronutrients, are not all extracted by plants because the roots do not come in contact with all of the nutrients. This is especially true of certain vegetables that have small or sparse root systems. Most of the phosphorous applied to the soil becomes fixed in a form unavailable to plants. Thus, it is necessary to provide some excess amounts of nutrients when soil test levels are below the optimum range, and this is why rates sufficient to replace the amount removed by crops are sometimes recommended for soils that test in the optimum range.

Table 4: Approximate Nutrient Removal by Selected Vegetable Crops