During this same period, corn yields have continued to increase at a rate exceeding 1.5 percent per year. These practices reduce nutrient losses and produce a cropping system that more efficiently utilizes all inputs, including commercial fertilizer. In the case of P and K, many corn farmers have succeeded in building their fields to the optimum soil test range where only maintenance amounts of P and K are now required for optimum production. Crop Nutrition and Nutrient Losses from Soils Crops require an adequate supply of nutrients to maintain satisfactory yields and quality. Commercial fertilizer and organic nutrient sources are used to make up the difference between crop needs and soil supplying ability.
Soil testing is the major tool used in determining supplemental nutrient needs.
Nutrient removal in the harvested portion of crops represents the largest single loss of nutrients from soils. Table 2 shows nutrients removed in the harvested portion of several North American crops. Table 2 Nutrients removal in the harvested portion of several crops. K. Once soil supplies are depleted through crop removal, the only method of replacement is through the importation of outside sources. The source can be organic residues or commercial fertilizer.