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Efficient Nitrogen Fertilization: Accounting for Field Nitrogen Mineralization

Project Goals/Objectives: This project will demonstrate an enhanced soil test methodology that accounts for all sources of plant available N in the soil, including NO3-N, available NH4-N, and mineralizable N. These soil N sources provide N to crops and represent N that is not adequately accounted for by producers. The project will demonstrate the potential for reduced N runoff due to reduced N application based on this soil test methodology by establishing demonstration sites on research facilities and on private land. Crop yield, economic throughout, fertilizer cost, and water quality research data will be presented at local and national producer and scientific meetings.

Project Background: The Texas Nonpoint Source Management Program (TCEQ and TSSWCB, 2005) states that "Nutrients, pesticides, and other pollutants can come from a variety of sources including over-fertilized fields, runoff from improperly managed animal opeations and waste applications, inaccurate pesticide sprayer settings, and dozens of other sources." This project is directly aimed at reducing the potential for overapplying nitrogen (N) fertilizer based on current soil test methodology in Texas.

Traditional soil nitrogen test determine only the inorganic N in soil in the form of NO3-N, but fail to account for plant available NH4-N, plus mineralizable portion of the soil organic N pool. Organic matter in the soil provides plant available N when soil microbes mineralize organic C. Since organic C and organic N are highly linked, organic N is appreciated because of the difficulty of accurately assessing mineralization with lab techniques, especially its contribution to providing N to enhance crop production. Since traditional soil tests do not recognize the contribution of available NH4-N or mineralizable soil N in the estimation of plant available N, current soil test recommendations are often higher than necessary, which result in overapplication of N fertilizer.

The innovative soil test methodology, demonstrated in this project, represents an important agronomic advancement with the potential for major socio-economic and environmental benefits. The environment will benefit as less N will be introduced into streams and rivers. Similarly, input costs will decrease as N fertilizer inputs are reduced. The cost savings should result in increased profitability. The economic incentive associated with the enhanced soil test methodology will increase the broadscale adoption of the methodology by laboratories and landowners alike and thus measureable improvements in runoff water quality. Additional benefits of reduced N application include reduced market demand for N thereby reducing petroleum inputs required to generate N fertilizer.

Project Location: Statewide

Project Costs: Federal ($293,883); Non-Federal Match ($198,923); Total Project ($492,806)

Project Participant(s): TSSWCB and the United States Department of Agriculture - Agricultural Research Service (USDA-ARS)

Project Workplan: 08-04

Project QAPP: 08-04

"Protecting and Enhancing Natural Resources since 1939."

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