Nitrogen Fertilization: II. Effect on the Soil Solution Composition, Acidity, and Nitrate Adsorption

Analyses were performed on soil solution extracts of samples obtained from depths where nitrate accumulation occurred due to ammonium nitrate applications on three different soils, i.e., Cecil fine sandy loam (Typic, Hapludult; clayey, kaolinitic, thermic), Groseclose silt loam (Typic, Hapludult; clayey, mixed, mesic), and Davidson clay loam (Rhodic, Paleudult; clayey, kaolinitic, thermic). Comparisons were made between treatments of moderate and high N applications in all three soils and between irrigated and nonirrigated conditions on the Cecil and Davidson soils. Nitrate movement and accumulation resulted in markedly different effects on the soil solution composition in the various soils. In the Groseclose silt loam, which has a subsurface layer of low permeability, high nitrate and electrolyte concentrations accompanied by lower pH values and higher amounts of Zn, Mn, and Al in the soil solution were encountered. In the Cecil fine sandy loam and Davidson clay loam, substantial amounts of nitrate were in an adsorbed state which resulted in lower electrolyte concentrations in soil solution. The degree of adsorption was dependent on pH conditions which were affected by movement of acidity. The high NO 3 ‐N adsorbed/NO 3 ‐N solution ratios in the Cecil and Davidson soils indicate that denitrification was not predominant at lower depths in these soils. The fact that applications of acid‐forming N fertilizers may affect the plant root environment mardedly in some soils and result in increased Mn and Al concentrations in the soil solution also suggest that toxic levels for some plants and crops may occur.