Science and nitrogen use efficiency

Nitrogen use efficiency (NUE) is a term maintaining its currency. Worldwide, NUE is 33%. Once a concern primarily due to groundwater quality and health concerns, rising natural gas prices have moved economic concerns to the forefront. Economics must certainly have resonated in the government NUE workshop "Roadmaps to more N efficiency" held in Germany recently and mentioned in a previous article. Climate change concerns have increased interest as well as the availability of grant funding for research. NUE is affected by many factors: fertilizer form and placement, irrigation management, climate, soil characteristics and CO2 levels.
Nitrogen loss due to denitrification is caused by microbial respiration when soil oxygen levels are depleted. It is negligible in some parts of the planet and the dominant form of loses in others. This from the University of Kentucky, somewhat buried in an article about economic concerns:

Worldwide nitrogen use efficiency is only about 33 percent, so 33 percent actually makes it into the crop. A lot of nitrogen is applied that never gets used by the crop. In the United States, the rate is 50 to 60 percent, but still half the nitrogen never makes it to the crop.

In Kentucky the biggest loss of nitrogen comes from denitrification, when nitrate is converted to nitrogen gas and dissipates into the air. By controlling denitrification, a farmer can potentially reduce the amount of nitrogen needed to produce a crop.

The other forms of reduced efficiency are leaching of nitrate and volatization of ammonia. Part of the loss to percolation can be attributed to uniformity of application and even off-target losses. Necessary to complete a zero-sum balance point of view is accounting for microbially fixed nitrogen, and changes in soil biomass,both microbial and plant roots.
Those of us who work in support of permitted land application of waste water and waste water solids are very interested in advances in understanding of NUE. Our client projects are generally held to a land treatment capacity based on a design philosophy that an NUE of 100% is a reasonable target, the legacy of a simpler time in history. With the higher level of information and better technology available today, this simplistic design standard may well be approaching the end of its useful life.

Tech Tags: soil science fertility nitrogen-use-efficiency nitrogen denitrification management research government environmental economics farm survival agriculture crop waste recycling