Nitrogen and Chloride Movement in Small Upland Piedmont Watersheds: I. Nitrate-Nitrogen and Chloride Distribution in Soil Profiles

Soil profile characteristics of many soils are related to the partitioning of fertilizers for soil pool, plant uptake, overland transport, and deep seepage. Chloride and NO₃-N distribution patterns were studied on variable soil profiles of two small agricultural watersheds planted to corn (Zea mays L.). Management variables included grassed waterways, graded terraces, and winter rye (Secale cereale L.) cover crops. Landscape slope and soil characteristics of the surface and control section layers were inherent variables within and among watersheds. Average soil Cl concentrations decreased from 275 ppm to background levels (30 ppm) at the 0- to 8-cm soil depth within 40 days after spring-incorporated applications of Cl fertilizer (112 kg Cl/ha as KCl). Nitrogen fertilizers (∼140 kg N/ha per year) were applied in split applications to meet optimum corn-growth demands. Average NO₃-N concentrations ranged from 20 to 40 ppm at the 0- to 8-cm depth immediately after N-fertilizer applications, but decreased rapidly because of biological assimilation. Nitrate-N below 25-cm soil depths were consistently ± 10 ppm and unrelated to watershed management or soil characteristics because of the low concentrations. Chloride distribution in soil profiles was significantly related to the depth of the B21t soil horizon below the soil surface and to surface soil texture only when the B21t horizon was uniformly located in the soil profile. Most anions available for leaching are below the B21t horizon following summer leaching, and move below the soil solum during winter leaching. A Cl balance suggests that most unaccounted for N (30 kg/ha) may be lost through winter leaching or denitrification. Recommended applications of applied N-fertilizer for corn production provide little opportunity for overland transport and small increases in deep seepage during winter months to drainage waters. Heavy applications of Cl in April or May suggest that similar applications of commercial N-fertilizers have little chance of overland transport because of rapid movement below the surface cm depths. The overland transport quantities may increase significantly on severely eroded Piedmont soils because of shallow B21t horizons and usually steep slopes associated with these lands.