Nitrogen Fertilization and Ground Cover in a Hybrid Poplar Plantation: Effects on Nitrate Leaching1
- Richard A. Mc Laughlin,
- Phillip E. Pope and
- Edward A. Hansen2
A 3-yr study in northern Wisconsin measured the effects of ground cover treatments and N fertilization on tree growth, NO3−-N leaching, and N mineralization in an irrigated hybrid poplar (Populus deltoides Bartr. × P. trichocarpa Torr. and Gray, clone NC-9922) plantation. Annually fertilized (112 kg N/ha per year) and unfertilized plots were either maintained weed-free (bare soil), allowed to revegetate with native weeds, or seeded to birdsfoot trefoil (Lotus corniculatus L.). Soil solution NO3−-N was monitored in samples from permanently installed cup lysimeters. During the first two growing seasons, fertilization in bare soil plots increased NO3−-N concentrations below the rooting zone to over 150 mg N/L. Tree growth response to fertilization in these plots occurred primarily in the third growing season, and NO3−-N concentrations were much lower in and below the rooting zone relative to previous years. Fertilization increased NO3−-N concentrations in the rooting zone during growing seasons two through four in trefoil plots and three and four in native weed plots. Nitrate-N concentrations below the rooting zone in all trefoil and native weed plots averaged ≤ 11 mg/L until the end of the fourth growing season when it averaged 20 to 24 mg/L in fertilized plots. Fertilization significantly increased soil N mineralization in buried plastic bags only in plots with a ground cover and was 42 to 47% greater in these plots compared with fertilized bare soil plots. This study indicates that ground cover plays an important role in preventing leaching losses of fertilizer and native soil N in young biomass plantations.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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