Enhanced Soil Test Methods for Determining Fertilizer Application Rates Rick Haney, Daren Harmel, and Alan Franzluebbers Introduction  Agricultural fertilizer has been in the spotlight recently because:  it is a difficult time for agriculture (high costs of inputs, equipment, land; rapidly changing commodity prices; uncertain weather).  excess nutrients in water diminish ecological function, reduce recreational opportunities, increase treatment costs.  The traditional approach for determining fertilizer rates contributes to water quality concerns and decreased farm profits.  Traditional Approach - Apply excess fertilizer so yields aren’t limited by nutrient deficiency under ideal growing conditions.  New Approach - Apply optimal fertilizer to meet realistic yield goals based on a balance between nutrients removed and whole plant requirements.  The objective of this research was to determine the impacts of using Enhanced Soil Test methods to determine fertilizer application rates. Methods  Established sites in seven TX counties  determined ARS-recommended rate with Enhanced Soil Test methods  collected data on: fertilizer rate, cost; crop yield, price  determined profit (“throughput” = revenue – fertilizer cost)  evaluated corn, wheat, oats, milo, hay grazer production  evaluated runoff water quality at USDA-ARS Riesel Watersheds. Results and Discussion  Based on preliminary data:  Fertilizer N application rates were reduced by 35% (corn), 30% (oats), 39% (wheat), 31% (milo), and 13% (hay grazer).  Changes in yields ranged from +2% (oats) to -18% (haygrazer)  Changes in profit (throughput) ranged from +12% (oats) to -23% (haygrazer).  Poor growing conditions prevalent in the study to date resulted in the control scenario being the most profitable for all crops except oats.  For oats, the ARS-recommended rates based on the Enhanced Soil Tests were most profitable. Summary  Poor growing conditions have dominated the study to date, but improved conditions will hopefully occur in future study years.  With further research and development, these Enhanced Soil Test methods will contribute to:  better farmer and rancher understanding of the soil- plant system and crop nutrient requirements  greater farm and ranch profitability  improved environmental quality. Enhanced Soil Test Methods  Account for organic and inorganic plant available N, P based on soil microbial activity and a soil extractant that contains naturally occurring organic acids from root exudates:  NO 3 -N, NH 4 -N, mineralizable organic N  Inorganic P, mineralizable organic P.  In contrast, conventional soil test methods typically  only account for NO 3 -N  usually determine P with highly buffered soil extractants which alter the soil pH to unnatural levels. This project was funded by a Clean Water Act §319(h) grant from USEPA and TSSWCB. For more information contact: (254) Field sites on private land and on USDA-ARS farms. Nutrients required per unit of crop production is a vital, but often overlooked, component of optimal fertilizer rate determination. Results to date for corn. Poor growing conditions, specifically drought in this case, contributed to the unfertilized control having the highest profits.