Ensuring optimum yield
The golden rule in fertilizer use remains simple: apply the right amount of nitrogen at the right time.
Fertilizers with a reliable nitrogen release profile and precise application characteristics reduce losses and improve plant uptake. In field studies, calcium ammonium nitrate and ammonium nitrate have consistently returned higher yield and better crop quality than urea and UAN. Best Farming Practice and precision farming tools can further enhance fertilizer efficiency.
Optimizing yield and quality
Different mineral sources of nitrogen have different effects on yield and crop quality. This has been well known by European farmers for decades. The different performance of mineral nitrogen sources is mainly due to losses, especially volatilization but also leaching. Some of these losses are aggravated by a mismatch between nitrogen supply and plant uptake. Scorching of leaves can also impact yield. Most of the underperformance observed with Urea and UAN can be compensated by higher nitrogen dosage, though on the cost of increased environmental burden.
France trial
In France, Arvalis and Yara conducted 122 field trials between 1987 and 2004 with winter wheat on various soil types. At an average optimum N rate of 183 kg/ha, ammonium nitrate produced 0, 26 t more yield and 0,75 points higher protein content that UAN. An additional 27 kg N/ha (15%) from UAN was needed to reach economic optimum.
Out of 122 fields fertilized at N-opt in France, 75% produced a better yield with ammonium nitrate and 25% produced a better yield with UAN.
The N response curves for the trials indicate that on average an additional 27 kg of nitrogen would have been needed with UAN to reach economic optimum.
Germany trial
In Germany, Yara conducted 55 field trials between 2004 and 2010 with winter cereals and various soil types. At an average optimum N rate of 210 kg/ha, calcium ammonium nitrate produced 2% more yield and 0,23 points higher protein content.
Out of 55 field fertilized at N-opt in Germany, 75% produced a better yield with calcium nitrate and 25% produced a better yield with urea.
The N response curves for the trials indicate that on average an additional 15 kg of nitrogen would have been needed with urea to reach economic optimum.
United Kingdom trial
The most extensive study comparing different forms of nitrogen fertilizers was performed on behalf of the UK government between 2003 and 2005 (Department for Environment , Food and Rural Affaires, Defra). Besides quantitative differences, the study highlighted the variability of results observed with urea and UAN. The required nitrogen applications rates can therefore not be predicted with the same reliability as with ammonium nitrate.
| Urea | UAN | |
| Lost yield at identical nitrogen application rates | 0.31 t/ha | 0.39 t/ha |
| Lost protein at identical nitrogen application rates | 0.3 points | 0.5 points |
| Required extra nitrogen to maintain yield | 14% | 18% |
Urea and UAN resulted in underperformance compared to ammonium nitrate on cereals in the UK
To maintain the same yield, significantly more nitrogen was needed from urea and UAN than from ammonium nitrate.
Yield was also significantly lower with urea and UAN than with ammonium nitrate.
Protein content was significantly lower on fields fertilized with urea or UAN than with ammonium nitrate.
Enhancing fertilizer efficiency
Nitrogen needs to be available in sufficient quantities so that it does not limit growth and yield. However, excess amounts of nitrogen beyond short-term plant needs may be lost to the environment or result in luxury consumption. Matching nitrogen availability precisely to current plant needs and actual soil nutrient supply maximizes yield, minimizes environmental impact and optimizes profit.
Split application is considered best agricultural practice under most conditions. Fertilizers offering a predictable release of plant-available nitrogen are best suited for split application. This is the case for ammonium nitrate and calcium ammonium nitrate, but generally not for urea. Hydrolysis of urea and volatilization losses heavily depend on climatic conditions after spreading, especially on rainfall. They cannot be predicted reliably, resulting in either under- or oversupply of nitrogen. The Defra study has highlighted the unreliability of urea, finding volatilization losses that varied from 2 to 58% of applied nitrogen!
Balanced nutrition is another prerequisite of economic fertilizer use. Insufficient supply of Phosphorus, Potassium or Sulfur can diminish nitrogen use efficiency. Frequent soil sampling provides data on actual supply of nutrients from the soil and fertilizer needs. The Yara N-Tester™ is a tool to measure plant nitrogen needs on spot and adjust fertilizer nitrogen applications correspondingly.
Matching fertilizer application with plant needs
Reducing fertilizer input by sensor controlled spreading
The Yara N-Sensor automatically applies optimum nitrogen rates (blue) based on real time mapping of biomass and chlorophyll (green), avoiding both, over- and under- fertilization. Winter wheat, Germany
Ensuring spreading precision
Spreading errors, and therefore losses, are significantly higher with urea than with CAN. Even with a spreading width of only 21 m, a light breeze of 4 m/s causes a significant spreading error of 26% with urea.
