Nitrogen Fertilizer Options and Technologies

August 25, 2008 at 7:00 am

Below is an article I wrote for the August 24, 2008 Lima News.

The financial cost of fertilizer used in agriculture is intimately linked to the oil market. As the cost of a barrel of oil rises, so do agricultural fertilizer prices. One of the most basic sources of fertilizer is ammonium nitrogen, also referred to as anhydrous ammonia. Used directly in corn to supply nitrogen to a growing corn crop, anhydrous ammonia is also used to develop other nitrogen-containing fertilizers for corn, soybeans and wheat. Anhydrous ammonia costs have risen sharply in the past year and farmers are looking for technologies and other options to supply nitrogen. Below I have summarized some of these options and technologies.

Optical Sensors. Optical reflectance sensors can be used to measure light reflectance from leafy corn crop canopies, which can be used to estimate the nitrogen status of plants and ultimately estimate how much additional nitrogen needs to be applied. Healthy, large plants reflect light differently than struggling, smaller plants and plants with adequate nitrogen reflect light differently than nitrogen deficient plants. Optical sensors help farmers recognize and quantify differences in the nitrogen content of plants in areas of a field. The nitrogen rate can be controlled manually or electronically to change application rates based on reflectance differences in a field. There are two primary commercialized sensors in use in the United States, Crop Circle™ and GreenSeeker™. Both units emit near infrared rays and visible light wavelengths. Currently, Purdue leads the Midwest in research on this subject.

Cover Crops. There are some research publications that show nitrogen contributions from legume cover crops. Late July/early August is an excellent time to be planting a cover crop into wheat stubble fields. Summer seeded legume cover crops include: winter pea, red clover, crimson clover, hairy vetch, soybean, and cowpea. Many of the legume species require overwintering and producing significant spring growth in order to supply significant amounts of nitrogen. Establishment of cover crops solely for the purpose of supplementing nitrogen should be approached with caution. The earlier the crop is established the greater the chance of good growth prior to the onset of winter, and the greater the chance that the cover crop can contribute nitrogen. Ohio State University Extension has resources in this area, and the CORN Newsletter ( is a good place to get the latest information on cover crops.

Manure Application. Sidedressing pre-emergent corn in the spring with swine manure produces yields comparable to applying commercial fertilizer. Manure application, mostly practiced in the fall, can be just valuable in the spring, and place the available nitrogen nutrient much closer to when the corn crop can utilize nitrogen. Also in consideration is dry poultry manure, which can be brokered, delivered, stored and spread easier than liquid manure. Livestock manure is a source of nitrogen for growing crops. Manure can be an inexpensive option farmers have for applying fertilizer – especially in no-till situations. Bulletin 604, published by OSU Extension, is a good place to start for information on manure use (

Hyper-Efficient Crops. The next big thing coming out of the laboratory is hyper-efficient crops. These are crops that are bred and altered to produce the same amount of yield on 25% less fertilizer than would normally be required to achieve similar yield. In some cases, single genes are being inserted in to soybeans, canola and rice which increase yield by 10%. There is an obvious push to introduce these genes in to corn, one of the most nutrient intensive crops grown in Northwest Ohio. Expect this technology to be introduced in to the marketplace by 2014.

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