Reduce Nitrous Oxide Emissions

Nitrous oxide (N₂O) is a greenhouse gas hundreds of times more powerful than carbon dioxide. Agricultural operations account for 60% of N₂O emissions in California. For more in-depth coverage about N₂O emissions, check out our N₂O emissions focus topic page.

Large bursts of N₂O result when soil N levels are elevated and soils are relatively wet. Avoiding excess soil nitrate, particularly when soils are wet, can help minimize N₂O emissions from agriculturally managed soils.

While some N₂O emissions are unavoidable, emissions can be minimized by taking the steps outlined on this page. In general, practices that reduce N₂O emissions also increase fertilizer efficiency.

Soil management practices influence rates of nitrous oxide production

Minimize Excess Soil Nitrogen

Nitrogen that remains in the soil after crop uptake can be utilized by microbes that produce N₂O. Applying the proper amount of nitrogen fertilizer can therefore help limit the production of this greenhouse gas.

Construct a Nutrient Management Plan

Nitrate present in irrigation water is an often overlooked source of nitrogen (photo credit: USDA)

A well-constructed nutrient management plan incorporates residual nitrogen (N) remaining from previous seasons, N that will be plant available following the mineralization of soil organic matter or incorporated cover crops, N in irrigation water, and a variety of aspects related to fertilizer N.

Considering all these potential N sources when determining N application rates reduces N₂O emissions by limiting the amount of N available to microbes that produce N₂O.

For more information about nutrient budgeting, take a look at our nitrogen management and budgeting page.

Adjust Fertilization Rates Mid-season

Changes in temperature and precipitation can alter how N behaves in the soil, so pre-season N management plans should be adjusted based on in-season N levels. An easy, on-farm 'quick test' for soil nitrate allows for the adjustment of N application rates on the fly.

Comparing results of the ‘quick test’ to established threshold values can tell you whether crops will show yield responses with additional fertilization. Threshold values have been identified for a variety of California crops.

For each crop, three threshold values are supplied. The early season level refers to pre-plant soil nitrate tests, whereas the mid-season and late-season refer to those two points in the plant growth cycle. The exact time point considered "mid-season" or "late-season" varies depending on the crop. The values found under "mid-season" and "late-season" refer to the amount of time into the crop growth cycle that the supplied values are relevant. For a summer lettuce crop with an expected 70 day growth period, the mid-season threshold level would be relevant at 14 days (0.2 x 70 = 14) and the late-season value at about 52-53 days (0.75 x 70 = 52.5).

A visual depiction of soil nitrate threshold values

Time Fertilizer Applications to Peak Crop Demands

Crops N requirements change over the course of the season. Timing N applications to periods of maximum N demand can limit excess soil N and suppress N₂O emissions.

For example, a fall planted barley crop takes up a relatively small amount of N through the winter and N demand peaks at the stem elongation stage. Therefore N applied at tillering, if followed by rain or irrigation, ensures efficient fertilizer uptake while limiting excess soil N and associated N₂O emissions. [1]

Timing of nutrient requirements vary depending on the crop. Visit the CDFA fertilization guidelines for crop specific information.

Barley nitrogen requirements are highest during stem elongation (photo credit: CDFA)

Minimize Excess Soil Moisture

Targeted irrigation systems allow for the application of smaller amounts of water throughout the season. By minimizing excess soil water, rates of N₂O production can be kept in check.

Subsurface drip irrigation has been shown to reliably reduce N₂O emissions. In almond orchards, microsprinkler irrigation has been shown to reduce N₂O emissions even more than surface drip. [2]

To learn more about implementing targeted irrigation systems, visit the Irrigation Training and Research Center website.

Buried drip irrigation systems help to minimize nitrous oxide production

Sources

Baethgen, W.E., C.B. Christianson, and A.G. Lamothe, Nitrogen fertilizer effects on growth, grain yield, and yield components of malting barley. Field Crops Research, 1995. 43(2): p. 87-99.
Alsina, M.M., A.C. Fanton-Borges, and D.R. Smart, Spatiotemporal variation of event related N2O and CH4 emissions during fertigation in a California almond orchard. Ecosphere, 2013. 4(1).