Saturday, 15 July 2006

Changes in soil nutrient availability following land application of biosolids to forest in virginia.

Eduardo C. Arellano and Thomas R. Fox. Virginia Polytechnic Institute and State University, Department of Forestry, 228 Cheatham Hall, Blacksburg, VA 24061

Decreasing availability of agricultural land suitable for biosolids application in eastern Virginia caused by urban expansion in the Washington-Richmond-Norfolk corridor, may limit ongoing land application programs. Forestland in the Piedmont and Upper Coastal Plain of Virginia provides an alterative location for land application of biosolids. Effective specific design criteria are required for successful forestland application systems. Issues such as loading rate, nutrient assimilation rates in the ecosystem, nutrient losses, and growth response for various types of biosolids must be addressed. It may not be possible to simply extrapolate agricultural land application practices to forest settings.

The objectives of this field study is to quantify nutrient availability changes on a loblolly pine (Pinus taeda L.)plantation following the application of biosolids, determine the impact of biosolids application on cycling of N and P forest ecosystems, determine the potential for leaching of N and P from forest ecosystems following application of Biosolids, and to determine the effect of fall and winter application on the forest system.

The study have been conducted since september 2005, in a thinned loblolly pine plantation, located in the Piedmont or Upper Coastal Plain of Virginia. The study was established as a random complete block design with nine treatments, determined from different biosolids type (lime stabilized, anaerobic digested, and pelletized), conventional fertilizer, seasonal timing (fall and winter), and understory vegetation coverage.

In this work, we report the effect of the treatments on tree nutrients uptake, forest floor and mineral soil properties for a period of nine month after the first application.

Soil moisture content and temperature have been measured at 15 cm and 50 cm depths. Soil solution samples collected in the tension lysimeters have been analyzed for total N, total P, NO3-N, NH4-N, PO4-P, K, Ca, Mg, Na, pH and conductivity. Ion exchange membrane extractable total N, total P, NO3-N, NH4-N, PO4-P, K, Ca, Mg, Na have been determined. Organic forms of N and P have been determined by differences between direct measures of the total and inorganic forms.

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