Based on soil test results from across their fields, farmers can vary the rate of application depending on soil conditions. Precision application of fertilizer is becoming more common as global positioning technology develops. Global positioning uses satellite technology to help the farmer apply the proper amount of fertilizer based on the soil tests results when traveling across the field. The late spring test for soil nitrate allows many corn growers to reduce the amount of nitrogen they apply to their cornfields. Farmers sample their fields when the corn is about 6 inches tall, and apply only the amount of nitrogen needed for crop growth.
Farmers apply a variety of fertilizer materials.
Manure is recognized as an excellent source of plant nutrients as well as a source of organic matter. Farmers with access to livestock manure often find that manure alone can meet the nutrient needs of their crops. Commercial sources of nitrogen are commonly applied by farmers with limited access to manure. One source of nitrogen that many farmers use is anhydrous ammonia. Green manure crops and crop rotations involving legumes also provide farmers with an additional source of plant nutrients.