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United States Department of Agriculture

Agricultural Research Service

Research Project: GRASSLAND PRODUCTIVITY AND CARBON DYNAMICS: CONSEQUENCES OF CHANGE IN ATMOSPHERIC CO2, PRECIPITATION, AND PLANT SPECIES COMPOSITION, ...

Location: Grassland, Soil and Water Research Laboratory

Title: Initial field evaluation of the agro-economic effects of determining nitrogen fertilizer rates with a recently-developed soil test methodology

Authors
item Harmel, Daren
item Haney, Richard

Submitted to: Open Journal of Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 10, 2013
Publication Date: June 1, 2013
Citation: Harmel, R.D., Haney, R.L. 2013. Initial field evaluation of the agro-economic effects of determining nitrogen fertilizer rates with a recently-developed soil test methodology. Open Journal of Soil Science. 3:91-99.

Interpretive Summary: Although agricultural is not the only contributor of excess nutrients in US waters, agriculture is an important contributor and should do its part to reduce its nutrient contribution. One important step in reducing agricultural contribution is to accurately account for all sources of plant available nutrients so that only needed fertilizer is applied. In this study, three fertilizer rate treatments were evaluated: no fertilizer (control), traditional rate, and reduced rate based on an enhanced soil test method. For each of nine sites in Texas, fertilizer data (formulation, rate, cost, and application date) and crop data (yield, price, and harvest date) were recorded, and net profit was determined. In this four year study, fertilizer rates were reduced 30-50% (and fertilizer costs reduced 23-39%) based on enhanced soil test method recommendations for wheat, corn, oats, and grain sorghum, but yields were not significantly reduced (0-6%) and oat yields actually increased 5%. Profit decreased < 1% for corn and increased 7-18% for wheat, oats, and grain sorghum with reduced fertilizer rates, and although these changes were not significant, they do represent potential benefit through increased profit and decreased input cost and production risk. In only 6% of the time was the traditional fertilizer rate the most profitable, compared to 51% for the unfertilized treatment and for the 43% for the enhanced soil test treatment. These results do not indicate that fertilizer application should be avoided but that fertilizer rates should be carefully chosen considering all sources of plant available nutrients to ensure that fertilizer is applied at the optimal rate.

Technical Abstract: Although agricultural is not the only contributor of excess nutrients in US waters, agriculture is an important contributor and should do its part to reduce nutrient loading. One important step in reducing agricultural contribution is to accurately account for all sources of plant available nutrients so that only needed nutrients are applied. In this study, three fertilizer rate treatments were evaluated: no fertilizer (control), traditional rate, and reduced rate based on an enhanced soil test method. For each of nine sites in Texas, fertilizer data (formulation, rate, cost, and application date) and crop data (yield, price, and harvest date) were recorded, and economic throughput (profit) was determined. In this four year study (35 site years), fertilizer rates were reduced 30-50% (and fertilizer costs reduced 23-39%) based on enhanced soil test method recommendations for wheat, corn, oats, and grain sorghum, but yields were not significantly reduced (0-6%) and oat yields actually increased 5%. Profit decreased < 1% for corn and increased 7-18% for wheat, oats, and grain sorghum with reduced fertilizer rates, and although these changes were not significant, they do represent potential benefit through increased profit and decreased input cost and production risk. In only 6% of the time was the traditional fertilizer rate the most profitable, compared to 51% for the unfertilized treatment and for the 43% for the enhanced soil test treatment. These results do not indicate that fertilizer application should be avoided but that fertilizer rates should be carefully chosen considering all sources of plant available nutrients (e.g., mineralization, irrigation water, nutrients deeper in the soil profile) to ensure that fertilizer is applied at the optimal rate.

Last Modified: 7/25/2014