Tuesday, November 6, 2007
215-7

Late-Rotation Nitrogen Management in Deciduous Short Rotation Woody Crops.

Todd A. Carpenter1, Daniel Israel2, Carl Trettin3, Michael Vepraskas4, Rory Maguire5, and Mark Coleman3. (1) Soil Science, North Carolina State University, 100 Derieux St., Williams Hall, Campus Box 7619, Raleigh, NC 27695-7619, (2) 3131 Williams Hall, Box 7619, USDA-ARS, North Carolina State University, Soil Science Dept. USDA-ARS, Raleigh, NC 27695, (3) 2730 Savannah Hwy., USDA-FS (Forest Service), USDA Forest Service, South Research Station, Charleston, SC 29414, (4) PO Box 7619, North Carolina State University, North Carolina State University, Department of Soil Science, Raleigh, NC 27695, (5) Virginia Tech, Dept. of Crop and Soil Env. Sci. (0404), Smyth Hall, Blacksburg, VA 24061

Idle cropland has the potential for producing woody crops as an energy or chemical feedstock. Short rotation woody crops (SRWCs) may increase soil organic matter, sequester carbon in soil and biomass, and improve water quality in these intensively farmed fields.  Frequently, nitrogen is the limiting nutrient in these systems. Prior fertilization trials with SRWC hardwoods in the southern US have focused primarily on fertilization during establishment and early development (1-6 yrs).  While those studies show a response to N fertilization, nitrogen demands are greatest following canopy closure in hardwood plantations (e.g., typically 4-7 yrs). Thus, managing the N supply in mid- to late-rotation should maximize productivity. It is also hypothesized that N availability from litter and soil is asynchronous with crop needs. The purpose of this study is to develop the basis for managing nutrient availability in late-rotation SRWC plantations to increase productivity and reduce the time to harvest, while enhancing soil properties of formerly cultivated fields. The study site is located in Sumter County, South Carolina, in the middle coastal plain. The study was replicated in both Sycamore and Sweetgum stands. Treatments were control, single applications of 60, 100, and 160 kg N ha-1, and biennial split applications of 30, 50, and 80 kg N ha-1. Fertilizer response was measured by DBH and tree height. Soil samples were collected quarterly at 0-5, 5-15, 15-30, 30-60, and 60-90 cm. Porous cup lysimeters were installed at two depths to track N movement through the profile. Lysimeter nitrate concentrations were significantly higher at shallow depths over all sampling dates and treatments. Nitrate movement was detectable in soil samples to 90 cm, but did not exceed 3 mg kg-1 of nitrate in any treatment or date indicating no differences from control. Data indicate no significant leaching from fertilizer applications at applied rates.

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