What is Denitrification and Why You Should Care

Jarrod O. Miller, Extension Agronomist, jarrod@udel.edu and Amy Shober, Extension Specialist – Nutrient Management and Environmental Quality, University of Delaware, ashober@udel.edu

Nitrogen (N) is a complex element that can undergo many transformations in the environment. The most likely form of N found in soils is nitrate (NO3), which can be lost from the root zone by leaching or through denitrification. When soils are saturated with water for more than 48 hours, microbes can transform nitrate into gases, allowing them to escape to the atmosphere. Many studies have observed denitrification increasing when water filled pore space is above 60%. With heavy rainfall across the state, soils are definitely under those conditions. Dense or heavier textured soils are at an increased risk for denitrification.

Denitrification will only occur if microbes have access to a food source in the form of soil organic matter, crop residues, or manure. Since organic matter content typically decreases as you go deeper into the soil profile, the chance for denitrification also drops with depth. Some researchers have observed maximum denitrification within the upper 2-8 inches of the soil. So keep in mind that adding N fertilizers to soils that are already saturated may cause gaseous N losses. In contrast, waiting for the upper few inches of soils to dry out reduces the chances that you will lose applied N through denitrification.

The USDA-NRCS has some guidelines for determining soil moisture in the field by hand, including photos for different soil textures. However, if you squeeze your soil into a ball and water comes out it is too wet to do anything, let alone apply fertilizer.

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