Nitrogen Budgeting

Nitrogen Budgeting

Photo by Derek, Lena and Mike

Nitrogen Budgeting

Location: ISU Boyd Farm, Outside Ames, IA
Featuring: Dr. Tom Kaspar, Plant Physiologist, USDA/ARS

Can plant scientists help farmers adopt farming practices that maximize the benefits of nitrogen fertilizer while reducing the threat of contaminating groundwater?

Farmers can document the benefits of applied fertilizer by establishing a nitrogen budget to track nutrients entering and leaving a field. Nitrogen can be added with fertilizer, through irrigation water, residual plant-available nitrogen already in the soil, from legumes that fix atmospheric nitrogen, from the decomposition of plant and animal residues, and from the mineralization of soil organic matter. Conversely, nitrogen can be lost though leaching and denitrification, and in the case of manure or urea-containing fertilizers lost into the air through volatilization.

Precisely timed fertilizer applications and carefully managed water use can allow commodity crops like corn to uptake most of the available nitrogen in the soil through its roots. After a corn or soybean harvest, when there are no live plant roots in the soil, water moving downward can carry soluble nitrogen into drainage tiles or groundwater. Incorporating the off-season planting of legumes and cover crops like winter rye into corn and soybean rotations allows these nutrients to be taken up in the soil, thereby reducing agricultural runoff.

“How do we keep track of our nitrogen budget? The answer is not very well. But we are making attempts to measure it as best we can, and what we learn from our research helps us understand how and when nitrogen is lost.”

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