Although agriculture is not the only
contributor of excess nutrients to 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 a recently-developed enhanced soil test
methodology. 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, fertilizer rates were reduced
30%-50% (and fertilizer costs reduced 23%-39%) based on enhanced soil test
methodology 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. Although these changes were not statistically
significant, they do represent benefit through increased profit potential 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 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.