Improve water quality
It has been shown that both losses from leaching (an issue for water quality) and denitrification (an issue for climate change) are minimal at N rates that are lower or equal to corn demand. With more precise N inputs applied at sidedress, there will be fewer losses to the environment. When more fertilizer is applied than is needed by the crop, especially when it is applied long before the crop is able to use it, losses to the environment increase exponentially.
Nitrate pollution in groundwater causes human health risks. High nitrate concentrations transported into sensitive estuarine systems can cause hypoxia (low oxygen content), fish kills, and collapse of estuarine ecosystems. These problems are currently experienced in the Gulf of Mexico, Chesapeake Bay, Great Bay, and many other locations world-wide. With more precisely estimated N inputs, mostly applied at sidedress, nitrate leaching will be minimized, because most of the applied nitrogen will be taken up by the crop.
Mitigate Climate Change
According to the EPA’s most recent report, agriculture produces 8% of U.S. greenhouse gas (GHG) emissions. This is arguably a disproportionate contribution, since agriculture only contributes 1.2% of the U.S. GDP. However, managing nitrogen better could go a long way toward mitigation efforts.
Nitrogen-related activities make up the largest fraction of agricultural GHG’s. Not only is N manufacture energy intensive (thus producing CO2), but nitrous oxide (N2O) emissions make up the largest portion of agriculture’s contribution, and the global warming potential of N2O is about 300 times that of CO2. Agricultural N applications to land accounts for 92% of agricultural N2O emissions. This is a larger impact than all of U.S. aviation and is 1.5 times the effect of methane from livestock (enteric fermentation)! Because of the large acreage of corn in the US (90 million), the high nitrogen inputs, and the dynamics with weather (discussed here), corn is by far the largest contributor to this concern.
Applying all N at planting or in excess specifically leads to high levels of denitrification (N2O emissions), especially during wet springs, but also during wet falls when there is excess N left over. There are higher emissions under no till or minimum tillage and on poorly drained soils when N is poorly managed. When an appropriate amount of N is applied mostly at sidedress, this will result in less denitrification.