Efficient Nitrogen Fertilization

Project Work Plan

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Problem/Need Statement

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 operations 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 tests determine only the inorganic N in soil in the form of NO3-N, but fail to account for plant available NH4-N, plus a 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 broken down to plant available N. This very important component of soil microbiology has been traditionally under-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.

This excess application increases N inputs into Texas rivers and lakes, which can accelerate eutrophication and substantially increase water treatment costs. Excess N in the Mississippi River, some of which is contributed by Texas watersheds, contributes to a major environmental problem - Gulf of Mexico hypoxia. Steve DiMarco, a Texas A&M researcher, has also recently claimed the existence of a Texas Gulf Coast hypoxic zone. Such hypoxic (low oxygen) areas are absent of most marine life and threaten to inexorably damage important ecosystems.

The Texas Commission on Environmental Quality (TCEQ) is currently in the process of revising Texas Surface Water Quality Standards for the 2009 triennial review. Major revisions to the Standards are being drafted, including the establishment of numeric nutrient criteria for reservoirs and modifications to contact recreation use and bacteria criteria. Numeric nutrient criteria will also be established for major rivers and small streams over the next decade. As a result numerous Texas water bodies which currently have concerns for nutrients will likely be impaired once the nutrient criteria are adopted.

In addition to adverse environmental effects, excess N fertilizer application increases input costs for agricultural producers. Overapplying N fertilizer wastes money on unnecessary inputs and reduces profitability. The problem is that traditional soil test procedures and resulting recommendations fail to account for mineralizable N in the soil that is released and made plant available. Thus, farmers do not knowingly apply excess N; they apply at the recommended N rates. The issue lies with fertilizer recommendations based on conventional soil test results.

Although agriculture is not the only contributor to the problem of excess N in our Nation's waters, agriculture should do its part to reduce N loading. Basing fertilizer application rates on soil tests that more accurately account for the total amount of plant available N in the soil, including mineralizable N, could have tremendous socio-economic and environmental benefits. Very few scenarios present such a likely "win-win" outcome.

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 willdecrease 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 measurable 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.

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