Relative to Ammonium Nitrate and Conventional Urea in No-till Corn​

Picture of field with measurements
Measuring the nitrogen volatilization for individual nitrogen treatments, above, was part of a recent study conducted by the University of Tennessee Institute of Agriculture to determine the effects of enhanced efficiency urea fertilizers relative to ammonium nitrate and conventional urea on no-till corn yields and net returns in Tennessee.  Photo by R. Sharp, courtesy UTIA.

KNOXVILLE, Tenn. — Nitrogen is an important and expensive input for corn production, with fertilizer expenses including nitrogen comprising 37 to 45 percent of annual total operating expenses for corn in the United States between 2010 and 2016. Researchers at the University of Tennessee Institute of Agriculture studied the effects of replacing ammonium nitrate fertilizer with enhanced efficiency (EE) urea fertilizers on no-till corn yields and net returns in Tennessee.

This study is timely, as increasing security concerns regarding ammonium nitrate have led to more government regulation, increased prices and reduced availability of the product. Tennessee no-till corn producers were directly affected by the changes, as the state was the second-leading user of ammonium nitrate in the U.S. in 2011. In 2016, harvested corn for grain in Tennessee covered 830,000 acres, and approximately 75 percent of that acreage was planted using no-till.

An additional challenge for producers is the fact that nitrogen is a difficult nutrient to manage in farm fields, and the inefficient use of nitrogen fertilizer can adversely impact the environment and net returns.

Although urea is a less-expensive, widely available nitrogen fertilizer alternative, considerable amounts of nitrogen can be lost through ammonia volatilization – the amount of nitrogen lost to the air – when broadcast on the soil surface in no-till crop production.

EE nitrogen fertilizers have been developed to reduce nitrogen losses when applied to the soil and to improve nitrogen use efficiency in crop production.

The UTIA study determined the effects of EE urea fertilizers relative to ammonium nitrate on no-till corn yields and net returns in Tennessee. Results showed:

• Urea + nitrogen-(n-butyl)-thiophosphoric triamide (NBPT) and polymer-coated urea (PCU) produced significantly higher yields and net returns than conventional urea and produced the highest yields and net returns among the EE urea products; however, these nitrogen fertilizers did not perform as well as ammonium nitrate under the no-till growing conditions in Tennessee.

• Urea + NBPT and PCU offer greater potential to improve net returns than urea + maleic-itaconic acid copolymer (MICP). The addition of MICP to urea improved neither yields nor net returns compared with conventional urea. In fact, yields were significantly lower with MICP compared with the other EE treatments.

• Conventional urea provided higher yields but with net returns similar to no nitrogen fertilizer control. The additional revenue from increased yields was offset by the additional cost of urea.

The study was a multidisciplinary effort undertaken by UTIA researchers in the Department of Plant Sciences; the Department of Biosystems Engineering and Soil Science; and the Department of Agricultural and Resource Economics.

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James A. Larson, Professor, 865-974-7231,