|Ressler, Daniel - IOWA STATE UNIVERSITY|
|Horton, Robert - IOWA STATE UNIVERSITY|
|Baker, James - IOWA STATE UNIVERSITY|
Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 3, 1998
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 test 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. This study showed that the applicator successfully reduced nitrogen leaching and increased corn yield per unit of nitrogen in growing seasons with above average rainfall. 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: Fertilizer nitrogen (N) applied for corn production can be lost through leaching of nitrate-nitrogen (NO3-N). This loss is an inefficient use of N and can result in water contamination. A fertilizer applicator was developed to alter physical properties of the soil surrounding a knife-injected fertilizer band. Soil alterations include smearing macropores below the fertilizer injection slot, formation of a localized compaction soil layer over the injected fertilizer band, and formation of a surface dome to cover the compacted soil layer and the fertilizer band. The applicator, termed LCD, was compared with a conventional knife applicator (without a covering disk) to evaluate its effect on leaching by determining NO3-N and bromide (Br-) tracer redistribution during the growing season and by measuring corn yield. The NO3-N and Br- distributions were determined by intensive soil sampling to 0.8 m below the soil surface. Four fertilization rates (67, 112, 157, and 202 kg N ha-1) were used to characterize yield response. During seasons when rainfall was below average, neither NO3-N redistribution nor crop yield showed a response to fertilizer application technique. During a growing season with above average rainfall, 20% more of the applied NO3-N and 18% of the applied Br- was recovered in the top 0.8 m of soil when applied with the LCD applicator. Use of the LCD applicator increased crop yield approximately 0.48 Mg ha-1 over yield using the conventional knife applicator during an above average rainfall season, suggesting that one-fifth of the conventional knife applied N was lost prior to crop uptake. These findings suggest the LCD applicator was effective at reducing leaching losses when rainfall was abundant.