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Groundwater and Soil Leachate Inorganic Nitrogen in a Wisconsin Red Pine Plantation Amended with Paper Industry Sludge

Dep. of Soil Science, 1525 Observatory Dr., Univ. of Wisconsin, Madison, WI 53706;
Aspen Services, Inc., 6510 W. Forest Home Ave., Milwaukee, WI 53220;
Environ. & Applied Mathematics Res., Nekoosa Papers Inc., Port Edwards, WI 54469.

^* Corresponding author.

ABSTRACT

In late August 1984, a 2.5:1 primary/secondary paper industry sludge was applied to a row-thinned, 27-yr-old red pine (Pinus resinosa Ait.) plantation in central Wisconsin at levels of 32, 63, and 94 dry Mg ha^–1 (550, 1120, and 1670 kg N ha^–1, respectively). There were positive treatment effects on NO₃-N and NH₄-N in soil leachates and groundwater, but because of sample variability, few of these differences were significant at the p 0.05 level. Nitrate-N concentrations exceeded 10 mg L^–1 for all treatments at the 10-, 45-, and 75-cm depths, but the potability standard was exceeded at the 165-cm depth and in groundwater only on plots receiving the medium and heavy applications. Nitrate-N concentrations generally were greater in the upper 30 cm of the saturated zone than at 60 and 90 cm, suggesting a lack of vertical mixing. Whereas the maximum NO₃-N concentration decreased with depth, the time required for NO₃-N concentrations to exceed 10 mg L^–1 for a given treatment and the duration of the period when NO₃-N concentrations exceeded 10 mg L^–1 increased with depth. The seasonal trends in inorganic N concentrations in soil water collected at the 10- and 45-cm depths could be explained on the basis of N mineralization as derived from field incubation studies. A regression equation relating maximum NO₃-N in groundwater to N content of the applied sludge indicates that little groundwater degradation will occur at depths of 5.2 m in central Wisconsin when the N application to pole-sized red pine is 800 kg ha^–1 (46 dry Mg sludge ha^–1).

Research funded by Nekoosa Papers Inc. and supported by the College of Agricultural & Life Sciences and the School of Natural Resources, Univ. of Wisconsin, Madison.

Received for publication December 21, 1987.