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DIVISION S-7—FOREST & RANGE SOILS

Soil Organic Matter Fractions under Managed Pine Plantations of the Southeastern USA

Daniel B. Warnell School of Forest Resources, Univ. of Georgia, D.W. Brooks Dr., Athens, GA 30602-2153

^* Corresponding author (dmarke{at}forestry.uga.edu).

Herbicide application in plantation forests may affect soil productive capacity through its effect on the quantity and characteristics of soil C. We examined changes in surface soil (<10 cm) soil organic matter (SOM) fractions in 12- to 18-yr-old pine stands from the Lower Coastal Plain and Piedmont of the southeastern USA that were receiving complete competition control treatments (n = 13 paired plots). Light (LF) (<1.6 g cm^–3), medium (MF) (1.6–2.0 g cm^–3), and heavy (HF) fraction (2.0 g cm^–3) SOM were isolated by density separation and the HF was hydrolyzed isolating a hydrolyzable (H-HF) and residual fraction (R-HF). Herbicide treated surface soils had lower whole soil C (12.8 g kg^–1) and N (0.51 g kg^–1) compared with untreated controls, 16.1 g C kg^–1 and 0.63 g N kg^–1. Across all sites, the greatest decreases in soil C and N occurred in the LF and MF fractions. The majority of C and N in Lower Coastal Plain surface soils (90% sand) is partitioned in the LF + MF, while in the Piedmont soils (60% sand) it is in the H-HF. Decreases in these SOM fractions were only slightly greater than decreases in whole soil SOM. Additionally, there was a significant decrease of 27, 41, and 31% in net N mineralization (7-d anaerobic incubation) due to treatment in a Piedmont site for whole soil (WS), WS + L/MF, and WS + HF, respectively. For the Lower Coastal Plain site, there was an 18% decrease in the WS + L/MF mixture only. Complete competition control in both the Piedmont and Coastal Plain clearly decreased SOM quantity. Decreases in SOM quality as indicated by decreased net N mineralization potential were also evident. The results suggest herbicide treatments may decrease the productive capacity of surface soils.

Abbreviations: HF, heavy fraction • H-HF, hydrolyzable heavy fraction • LF, light fraction, MF, medium fraction • R-HF, residual heavy fraction • RPM, revolutions per minute • SOM, soil organic matter • SPT, sodium polytungstate • WS, whole soil

This article has been cited by other articles:

				D. V. Sarkhot, N. B. Comerford, E. J. Jokela, J. B. Reeves III, and W. G. Harris Aggregation and Aggregate Carbon in a Forested Southeastern Coastal Plain Spodosol Soil Sci. Soc. Am. J., September 28, 2007; 71(6): 1779 - 1787. [Abstract] [Full Text] [PDF]