Soil Nitrates Following Four Years Continuous Corn and as Surveyed in Irrigated Farm Fields of Central and Eastern Colorado
1976
Ludwick, A. E. | Reuss, J. O. | Langin, E. J.
High rates of fertilizer N used in many intensive farm management systems have been cited as a potential pollution hazard to surface and ground waters. The purpose of this study was to evaluate soil NO₃⁻ accumulations following 4 years continuous corn (Zea mays L.) grown with different nitrogen and irrigation regimes, and to compare these results to present NO₃⁻ concentrations found in irrigated farm fields of central and eastern Colorado. Soil NO₃⁻ content in the 300-cm sampled profile was significantly influenced by both fertilizer N and irrigation treatments; the greater accumulations were associated with the two higher fertilizer N rates and two lower irrigation rates. Nitrate increased linearly in relation to fertilizer N between 67 and 269 kg N/ha and could be described by two simple regression equations separating the irrigation treatments into two groups (l-2 and l-3, low rates; l-4 and l-5, high rates). Coefficients of determination for the two groups were 0.981 and 0.975, respectively. Two hundred and seventy irrigated farm fields were sampled to a depth of 90 cm in central and eastern Colorado. Mean soil NO₃⁻-N content was 173 kg/ha and contents were not significantly different between coarse and fine textured groupings. Fields sampled immediately following beans (Phaseolus vulgaris L.) contained similar amounts as those following corn. Mean soil NO₃⁻ content decreased with greater soil depth. Observed NO₃⁻ concentrations appear to be the result of gradual accumulations from annual or near-annual fertilizer N and/or manure applied over a period of time. Data from the 4-year corn experiment clearly illustrate that NO₃⁻ can accumulate in a soil profile even when fertilizer N is applied at rates below that required for maximum production.
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