Our most effective nitrogen (N) fertilizer, ammonium nitrate, has become extremely hard to find in most areas. It’s been used to make explosives and could soon come under federal regulation, requiring too much paperwork for dealers to want to stock the product.
Growers are increasingly turning to urea and urea-based formulations to meet their N fertilizer needs. Although there can be substantial N losses when urea is used for forage production, new research is proving that growers can cut these losses and make urea more effective.
Ammonium nitrate fertilizer provides N in a form that the plant can readily use. When applied, it splits into its chemical halves: ammonium and nitrate.
The nitrate is quickly taken up by roots while the ammonium latches onto soil particles, is taken up by roots or ultimately is converted by soil bacteria into nitrate and absorbed up by roots. There’s little risk that any will escape as gas.
Urea, on the other hand, has to be broken down to form ammonium, and a substantial amount of N from urea is often lost to the atmosphere as ammonia gas. University of Georgia research has recorded ammonia losses as high as 48% of the applied N. Other research shows that urea N losses are typically around 20% of total N applied.
With N fertilizer prices being as high as they currently are, these losses are a major economic drain on profitability. It also makes for poor stewardship of our natural resources.
Recently, several so-called “enhanced-efficiency” products have been introduced to the market to curb these N losses. Some act by controlling the breakdown of urea to ammonium – specifically, the rate of urease activity. Others create a barrier, such as a polymer coating, that slowly allows urea encapsulated inside to moisten and seep out.
University researchers around the U.S. have begun comparing these products. We recently looked at three on bermudagrass hayfields harvested four times a year in a multi-year study at two Georgia locations. They were Agrotain and Nutrisphere-N urease inhibitors and ESN Smart Nitrogen, a polymer-coated urea product.
We measured ammonia volatilization loss in field studies using an acid trap. As expected, we saw very high losses – an average of 17% of applied N – in areas where urea was applied. Agrotain and ESN Smart Nitrogen prevented a majority of the volatilization. Nutrisphere-N didn’t effectively reduce ammonia loss in our study.
With ammonia loss controlled, forage yielded similar to that treated with ammonium nitrate. For example, field areas with Agrotain-treated urea produced an average of 11% more yield than areas provided conventional urea – about the same yield if ammonium nitrate were applied.
In the initial studies, ESN Smart Nitrogen produced lower yields than urea because it released N too slowly for our fast-growing bermudagrass. In other experiments, we have found that, when conventional urea is blended with the ESN Smart Nitrogen, yields can rival those of ammonium nitrate-treated crops. Forage yields were not different between areas treated with conventional urea or Nutrisphere-N-treated urea.
Work with these fertilizer treatments will continue. These results are promising and the current cost structure appears to be beneficial. Most of these products add only 5-8% to the cost of urea (60¢/lb of N in Georgia). Spending to prevent up to a 20% atmospheric loss of N is more cost-effective than just adding more N to make up for that loss.