Nitrogen Uptake and Losses

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Soil Savvy

By Gurbir Dhillon Ph.D.

To continue the conversation around soil nitrogen in agriculture, let’s talk about how plants uptake nitrogen from the soil in nitrate (NO3) and ammonium (NH4+) forms.

Ammonium ions convert into nitrite and subsequently to nitrate form through the enzymatic action of soil bacteria in a process known as nitrification.

The nitrate forms of soil nitrogen are highly mobile, whether added as fertilizer or produced in the soils though the nitrification process. Soils lose nitrates via leaching in drainage water or through volatilization to the atmosphere in gaseous forms.

Thus, the challenge in field management of nitrogen fertilizers is to ensure soil nitrogen availability at the right time and in suitable amounts. The nitrification inhibitors (such as Centuro or eNtrench) can inhibit the activity of soil bacteria that convert ammonium to nitrates, thus slowing down its losses in denitrification and leaching.

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Urease inhibitors (such as Agrotain and Limus) reduce the breakdown of urea into ammonium thus reducing the losses due to volatilization of ammonium into gaseous forms. Certain dual inhibitors (such as SuperU and Tribune) contain both urease and nitrification inhibitors.

ESN granules
ESN granules for display at a field day.

Slow-release nitrogen fertilizers offer another option to reduce nitrogen losses from fertilized soils. These fertilizers release nitrogen slowly and synchronize its availability better with plant requirements and uptake. One of the widely available products is ESN (Environmentally Smart Nitrogen) that contains polymer coating on urea granules that slows down urea dissolution through controlled diffusion of moisture into the granules.

Other products such as urea formaldehyde control urea dissolution and hydrolysis through linear and cross-linked polymers of varying chemical complexity. The performance of slow-release products can be significantly affected by soil conditions such as its texture, pH, moisture content, and microbial activity.