Ammonia Impacts on Atrazine Leaching Through Undisturbed Soil Columns

Ammonia-based fertilizers, such as anhydrous ammonia, aqua ammonia, and urea, initially increase soil pH, reducing atrazine (2-chloro-4- ethylamino- 6-isopropylamino-1,3,5-triazine) sorption and increasing atrazine desorption. Increased amounts of atrazine in soil solution may increase atrazine\u27s leaching potential. This laboratory study investigated atrazine leaching behavior when ammonia and atrazine applications overlap. Nondisturbed 15-cm diam. by 15-cm depth soil columns were excavated from a Brandt silty clay loam (fine silty, Pachic Udic Haploboroll) and a Ves clay loam (fine silty, mixed mesic Typic Hapludalf). Concentrated NH4OH was applied to the soil surface at 0 or 220 kg N ha-1. Immediately after fertilizer application, 1.9 kg atrazine (spiked with ring-labeled 14C-atrazine) ha-1 was applied. One day after chemical application, soil columns were leached with 5.4 L of water. The ammonia application increased leachate and surface soil pH by about 2.5 and 3.5 pH units, respectively. The amount of 14C collected in leachate from ammonia-treated columns was 60 and 30% greater for the Brandt and Ves soils, respectively, compared with untreated columns. Less 14C remained in the surface of the ammonia-treated columns than in the surface of the untreated columns. These data indicate that the interaction between ammonia-based fertilizers and atrazine must be considered when evaluating atrazine movement through soil. Applications of atrazine and ammonia-based fertilizers that increase pH should be physically separated to limit the leaching potential of atrazine