Effects of Forest Management Intensity on Carbon and Nitrogen Content in Different Soil Size Fractions of a North Florida Spodosol

Authors: SARKHOT, D - UNIV. OF FL/SOIL & WATER; COMERFORD, N - UNIV. OF FL/SOIL & WATER; JOKELA, E - UNIV. OF FL/FOREST RES.; Reeves Iii, James

Submitted to: Plant and Soil
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/21/2007
Publication Date: 5/15/2007
Citation: Sarkhot, D., Comerford, N.E., Jokela, E.J., Reeves III, J.B. 2007. Effects of Forest Management Intensity on Carbon and Nitrogen Content in Different Soil Size Fractions of a North Florida Spodosol. Plant and Soil Journal. 294:291-303.

Interpretive Summary: As a result of concerns about global warming, there is a great interest in whether soils can be used to sequester C. In order to estimate how much C might sequestered information is needed on how the process works and is affected by various parameters including how measurements of C are carried out. Pine plantations of the southeastern US are regional carbon sinks. In spite of huge increases in woody biomass, studies have shown little or even negative effects on the carbon content of the extremely sandy soils of this region. Hence, it is important to understand the mechanisms that determine the impact of intensive management on carbon sequestration in these soils. This study was conducted to examine the carbon profile and to make a preliminary evaluation of soil carbon and nitrogen pools as influenced by forest management. Evaluation of methods for very sandy soils was a necessary first step. The study objectives were to evaluate the difference between dry and wet sieving for size fractionation, and use the preferred method to determine the sensitivity of the size fractions to the management-related changes in soil organic carbon (SOC). A 4-year-old loblolly plantation in north Florida with two contrasting forest management regimes, replicated in 3 blocks was the study site. Dry sieving was the preferred method for soil particle size fractionation, as it preserved more soil structure; it did not loose water-soluble organic components, such as esters and amides; and it did not affect N distribution. Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) spectra were used to indicate the chemical composition of the size fractions and helped to infer the presence of recently added organic matter in the largest sand fraction, as well as more decomposed organic matter in the silt + clay fraction. Intensive management reduced C in all the three sand size fractions, probably due to the reduced input of understory roots. The largest sand fraction (2000 to 250 'm) was found to contain nearly half of the total SOC and showed a 23% decrease in C content due to intensive management.

Technical Abstract: Pine plantations of the southeastern US are regional carbon sinks. In spite of huge increases in woody biomass, studies have shown little or even negative effects on the carbon content of the extremely sandy soils of this region. Hence, it is important to understand the mechanisms that determine the impact of intensive management on carbon sequestration in these soils. This study was conducted to examine the carbon profile and to make a preliminary evaluation of soil carbon and nitrogen pools as influenced by forest management. Evaluation of methods for very sandy soils was a necessary first step. The study objectives were to evaluate the difference between dry and wet sieving for size fractionation, and use the preferred method to determine the sensitivity of the size fractions to the management-related changes in soil organic carbon (SOC). A 4-year-old loblolly plantation in north Florida with two contrasting forest management regimes, replicated in 3 blocks was the study site. Dry sieving was the preferred method for soil particle size fractionation, as it preserved more soil structure; it did not loose water-soluble OC components, such as esters and amides; and it did not affect N distribution. Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) spectra were used to indicate the chemical composition of the size fractions and helped to infer the presence of recently added organic matter in the largest sand fraction, as well as more decomposed organic matter in the silt + clay fraction. Intensive management reduced C in all the three sand size fractions, probably due to the reduced input of understory roots. The largest sand fraction (2000 to 250 'm) was found to contain nearly half of the total SOC and showed a 23% decrease in C content due to intensive management.