Localized soil compaction and soil doming of the fertilizer injection zone to control nitrate leaching

Ressler, Daniel
Major Professor
Robert Horton
Committee Member
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Chemical movement is fundamental to production agriculture. Crop roots and nutrients must be in contact for optimum crop growth. In the pursuit of this goal, nitrogen that is applied in fertilizers is often leached prior to crop uptake. Means to limit fertilizer leaching to conserve resources are needed;Application method plays a role in the way chemicals move through soil. Structured soil column effluent studies suggest that leaching could be reduced if chemicals are allowed to penetrate soil aggregates prior to saturation by an infiltrating solution. In well structured soil, mixing chemicals with a limited volume of soil and destroying structure in that region further delay chemicals from traveling through the structured soil. These data suggest that isolating chemicals in zones that contain fewer large pores than the bulk soil should reduce chemical leaching from surface soils;In addition to isolating chemicals in soil that has fewer large pores (as a result of mechanical disturbance), chemical application strategies include placing chemicals under a ridge, and using a hydraulic barrier above the applied chemical. A ridge will divert surface water away from the ridge peak, so it will infiltrate the soil at the ridge valley, bypassing the chemicals below the ridge. Hydraulic barriers will serve a similar purpose, to limit water flow through chemically treated soil. A prototype N-fertilizer applicator was designed and constructed (patent pending), to apply N-fertilizer to locally tilled soil, construct a hydraulic barrier (compacted soil) over the fertilizer, and form a surface dome or ridge. This localized compaction and doming (LCD) applicator was compared with conventional knife applicators by investigating nitrate redistribution in an Iowa corn field and measuring tile drain water concentrations to determine leaching rates of surface applied chemicals;Soil nitrate concentrations were closer to the surface and less dilute when fertilizer was applied by the LCD versus the conventional knife. Tile drain water concentrations show that after 10 cm of drainage, 5% of knife injected chemicals were recovered, compared to just 1% of LCD applied chemicals. Modifying surface soils to alter water flow paths is a valuable tool to guard against ground water or tile drain contamination by N-fertilizers.