|Ressler, Daniel - IOWA STATE UNIVERSITY|
|Horton, Robert - IOWA STATE UNIVERSITY|
|Baker, James - IOWA STATE UNIVERSITY|
Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 1, 1997
Publication Date: N/A
Interpretive Summary: Nitrogen fertilizers have been widely used in American crop production for the last half century. In 1993, 724,940 tons of nitrogen were applied in Iowa. Unfortunately, nitrate-nitrogen moves through the soil readily in water and can degrade the quality of surface and ground water supplies. Subsurface banding of fertilizer nitrogen with a knife applicator is the most commonly used application technique in the Midwestern states. In Iowa, greater than 50% of the fertilizer nitrogen is knife injected. With knife injection, a small furrow partly filled with loose soil remains above the fertilizer band. This furrow provides an ideal place for rainwater to accumulate, allows rapid infiltration, increases the amount of water flowing through the nitrogen fertilizer band, and therefore, increases the potential for nitrate movement. In this study we describe a nitrogen fertilizer applicator that reduces the flow of water through the fertilizer band. To divert water flow, the applicator compacts the soil above the fertilizer band, fills the knife furrow with soil, and builds a ridge of soil over the knife furrow. A field study showed that the applicator successfully modified the soil conditions above the fertilizer resulting in reduced water infiltration and nitrate movement. The potential impact of widespread use of this applicator would be to reduce losses of nitrate from farming systems and to reduce nitrate contamination of ground and surface water supplies. Additionally, reducing nitrate movement would result in greater uptake of the applied fertilizer by the crop and may allow lower fertilizer inputs while maintaining yield.
Technical Abstract: Conventional practices for nitrogen fertilization of corn produce soil conditions that are conducive to preferential water flow and nitrate leaching. Reducing water flow through the fertilizer band will reduce nitrate movement. A new fertilizer applicator is proposed that will more effectively protect the fertilizer from infiltrating water and thus reduce the potential for leaching. The new localized compaction and doming applicator (LCD) forms a small compacted layer of soil above the subsurface fertilizer band, fills in the knife furrow, and then builds a soil dome on the surface above the band. The LCD applicator was evaluated in a field study by measuring penetration resistance, bulk density, infiltration rate, and nitrate movement above the fertilizer band and comparing these measurements to those made within a conventional knife applicator system. The LCD applicator increased penetration resistance from 0.50 to 0.75 MPa and bulk density from 1.2 to 1.4 g/cm3 above the fertilizer band as compared with the knife applicator. The ponded infiltration rate through the fertilizer band was reduced from 19.7 cm/hr in the conventional knife system to 10.1 cm/hr in the LCD system. Nitrate movement was measured during a growing season in a corn field using sequential soil grid sampling of a trench wall. Nitrate applied with the LCD applicator moved downward only 60% as deep as nitrate applied with the conventional knife applicator The ability to reduce nitrate movement by modifying the soil above the N application band with the LCD applicator represents a simple yet effective strategy to reduce nitrate leaching losses and nitrate degradation of surface and ground water quality.