Submitted to: World Wide Web
Publication Type: Other
Publication Acceptance Date: 10/19/1999
Publication Date: N/A
Citation: OLNESS, A.E., LOPEZ, D., ARCHER, D.W., CORDES, J., SWEENEY, C., MATTSON, N., RINKE, J.L., VOORHEES, W.B. THE ARS NITROGEN DECISION AID. AVAILABLE FROM: HTTP://WWW.MORRIS.ARS.USDA.GOV 
Interpretive Summary: Nitrogen (N) usually limits crop yields and is often added to crops in excess of plant needs. About $1.5 to $2.5 billion in N costs are wasted each year. Some of the waste occurs because soil microbes produce mineral N that can be used by crops, but this source of N is not adequately considered at the time when synthetic N fertilizer is applied. Furthermore, the amount of mineral N produced by soil microbes varies with climate and soil type. A complex computer program, called the ARS Nitrogen Decision Aid, uses soil and climate data to predict the amount of N produced by the soil microbes. This amount of N is added to the amount originally present in soil; these amounts are subtracted from 160 lbs of N per acre. The difference is the amount of N that needs to be added as fertilizer N. Over 1500 copies of the N decision aid have been distributed to farmers, consultants, USDA-NRCS staff, extension specialists and other interested individuals. Application of the decision aid enhances N fertilizer use efficiency by more than 10% relative to current general methods of N fertilizer application. Producers benefit from better yields through appropriate applications of N fertilizer and reduced input costs.
Technical Abstract: Nitrogen is the element that most often limits crop production. Each year about 10 billion kg of fertilizer N is applied to US crops, but it is estimated that less than half of this application is found in the crop at harvest. A computerized decision aid has been developed that has the potential to increase N fertilizer use efficiency. The decision aid relies on four basic soil characteristics (soil texture, pH, organic matter content and bulk density) and two climatic characteristics (temperature and rainfall). General Energy Model for Limited Systems describe the components in the model and these are then assembled into a single function that predicts the rate of nitrate-N production. The amount of nitrate generated in the soil is added to the amount of nitrate present at planting (determined by sampling) and the amount of nitrate-N leached from the soil is subtracted; the amount remaining is subtracted from 160 kg nitrate-N per hectare. This difference is the amount of fertilizer N needed to achieve optimal N fertilizer use efficiency.