Potential for localized compaction to reduce leaching of injected anions

Nitrate-nitrogen (NO3-N) frequently is found in subsurface drainage waters from N-fertilized cropland at concentrations exceeding 10 mg L(-1), the drinking water standard. In this laboratory study, localized compaction during bromide (Br) application was studied as a potential method to reduce concentrations of anions such as Br- and NO3- in water percolating from the top 30 cm of soil. Rainfall simulation was used to apply water under controlled conditions to undisturbed 76 by 76 by 30 cm deep soil columns taken from chisel-plowed and no-till fields in the fall after soybean [Glycine max (L.) Merr.] harvest. Potassium bromide at 149 kg ha(-1) was broadcast or point injected with, or without, compaction around the point of injection. There were no significant differences in water volumes percolating through the columns, but concentrations and losses of Br in drainage water for the compacted point injection treatment were significantly less than those in drainage water from soil columns for point injection without compaction or broadcast application. The average Br concentration for no-till compacted point injection was about 11% of the broadcast and 7% of the uncompacted point injection. For the chisel plow, the concentration for the compacted point injection was about 15% of both the broadcast and uncompacted point injection. Losses were also of about the same percentages. Localized compaction around the point of injection significantly reduced anion leaching in these undisturbed soil columns. This concept could be implemented in the field through design of applicators that compact the soil in a zone around either point-injected or knifed-in fertilizer.