The term corn fertilizer may refer to fertilizer for corn, or fertilizer made from corn. Fertilizer for corn usually is a blend of synthetic chemical fertilizers designed to meet corn's specific needs. Fertilizer made from corn is a corn gluten product used for natural weed control and fertilization for lawns.
Corn needs high amounts of nitrogen and phosphorus in order to get started and grow well, and it usually requires further applications of phosphorus and potassium when it gets ready to flower. While garden stores might sell fertilizers designed for corn, there is no specific type of corn fertilizer. Instead, corn fertilizer is managed during different parts of the growing season to make sure the corn is getting the specific elements it needs at certain times.
Most types of corn fertilizer are very high in nitrogen because corn is a heavy nitrogen feeder throughout its growth cycle. Some types of fertilizers for corn, called starter fertilizers, are a mixture of nitrogen and phosphorus. These fertilizers are designed to give plant roots an extra boost while they're still very young to help them overcome the slow growth and poor nutrient uptake associated with cold weather early in the season. Starter fertilizers are spread around corn seeds before they sprout. When the corn is 4 to 6 feet (1.2-1.8 meters) tall, fertilizers with nitrogen, phosphorus and potassium are often applied into the soil or as foliar spray.
Corn is such a heavy feeder that synthetic corn fertilizer can be quite expensive, and the toll on the soil and groundwater is disproportionate to the benefits. Instead of applying chemical fertilizers, organic farmers supply corn with nitrogen by cover cropping either when the corn is very young, or over the winter before it's planted. Cover crops like crimson clover or vetch draw their nitrogen from the air and fix it in the soil. Corn can also be rotated with soybean or alfalfa crops to increase the nitrogen in the soil. The other chemical elements corn needs can come from manures or compost. Corn plants fertilized organically take up as many nutrients as those fed with synthetic fertilizers.
A type of fertilizer made from corn, called corn gluten fertilizer, is a nitrogen-rich by-product of cornstarch production. Sold as pellets or powder, this corn fertilizer is generally used on lawns. Manufacturers claim that it effectively suppresses weeds before they can grow, but controlled studies on the product have shown mixed results. The apparent weed suppression is probably due to the high nitrogen content of this fertilizer, which gives grass a big boost and allows it to out-compete the weeds. Although corn fertilizer is natural and safe for people and pets, it is still a serious pollutant because the unused nitrogen converts to nitrates and enters the groundwater.