Results Growth response to P fertilization on a 20 yr old loblolly pine plantation in coastal SC.

1. Cn * 0 -10 Cn * 10-20 Fert * 10-20 Fert * 0-10 Bradley W. Miller Department of Forestry Corresponding Author: bwmillergk@hotmail.com Long-term changes in Hedley phosphorus pools in response to a single P fertilization in a southeastern US loblolly pine plantation. Thomas R. Fox Department of Forestry • Environmental & Social Considerations • Phosphorus (P) fertilization can dramatically increase tree growth in nutrient deficient soils of the southeastern US (NCSFNC, 2004). Increased productivity could reduce the hectares required to meet our societies wood product needs. • Phosphorus applied to soils is rapidly sequestered by plants, microbes, or chemically sorbed to soil mineral becoming less plant available (labile) over time (Turner and Lambert, 1988) . • Phosphorus runoff into streams and rivers is a major contributor to the eutrophication of our waterways (Vadas et al., 2005) . • Understanding how much Hedley P remains labile over time may lead to a reduction of P fertilizer prescribed during planting, and therefore reduce the chance of P pollution of our waterways. • Phosphorus fertilization at stand establishment. Discussion Results Growth response to P fertilization on a 20 yr old loblolly pine plantation in coastal SC. • Ha: Twenty years after fertilization Hedley labile P and Mehlich-3 P are significantly higher in the 0-10 cm soil horizon of the fertilized plots. • Hedley Po pools increased by 72% in 0-10 cm soil horizon of the fertilized sites. These Po pools may be acting as a long-term source of labile P for loblolly pine growth. • Mehlich-3 extracts P using an organic chelator to solubilize P from recalcitrant P pools. Soil microbes produce analogous compounds in situ, therefore these P pools may be labile. 0 lbs/ac P at Planting 50 lbs/ac P at Planting • Loblolly pine tree growth increased by greater than 2 meters on many sites in the southeastern US. • P fertilization resulted in a sustained growth increase compared to control sites. • Conclusion • The increase in Hedley labile P suggest there is a long-term impact of a single P fertilization in loblolly pine forests, and therefore some sites may not require P fertilization at establishment of subsequent rotations. • Understanding how soil microbes affect organic P, moderately labile P, and recalcitrant P pools may lead to more accurate soil based predictions of labile P pools. • Research Objectives • Determine the long-term effects of P fertilization on soil biogeochemical phosphorus pools using the Hedley sequential fractionation procedure. • Determine the long-term effects of P fertilization on labile P pools in forest soils. • Hypothesis • Ha: Fertilized sites would have greater labile P content than the control sites. Hedley P fractions from a loblolly pine plantation soil 20 years after fertilization in SC. Mehlich-1, Mehlich-3, and Hedley P fractions from a loblolly pine plantation 20 yrs after fertilization in SC. Acknowledgement Funding provided by USDA NRI Competitive Grant Program. Dissertation Committee: J. Burger and L. Zelanzy, Virginia Tech. L. Allen, NCSU. F. Sanchez , USFS-SRS. “Leaves grow trees, Resources grow leaves” Forest Nutrition Co-Op References NCSFNC. 2004. Responses to nutrient additions in young loblolly pine plantations: Regionwide 18 fifth report. Department of Forestry, NCSU and Virginia Tech., Raleigh, NC. Tiessen, H., and J.O. Moir. 1993. Characterization of available P by sequential extraction. Lewis Publishers. Turner, J., and M.J. Lambert. 1988. Long-term effects of phosphorus fertilization on forests., p. 125-133, In B. B. and W. C. H., eds. Forest site evaluation and long-term productivity. University of Washington Press, Seattle, WA. Vadas, P.A., P.J.A. Kleinman, A.N. Sharpley, and B.L. Turner. 2005. Relating Soil Phosphorus to Dissolved Phosphorus in Runoff: A Single Extraction Coefficient for Water Quality Modeling. J Environ Qual 34:572-580. Methods Hedley Fractionation Procedure • Routine soil analyses were performed: Mehlich-1 and Mehlich-3 soil P test. • Modified Hedley fractionation uses 0.5 g soil subjected to a series of extracting solutions of increasing strength(Tiessen and Moir 1993). • Fractions represent the strength of P held by soil colloids and can be grouped based on the bio-availability of the P pool: • Labile – Plant available during one growing season. • Moderately Labile – Plant available over time • Recalcitrant – Not plant available Treatment * Depth (cm) Treatment * Depth (cm) • Labile P pools (green) remain significantly higher (p=0.04) in the 0-10 cm soil horizon of the fertilized plots 20 years after application. • Labile P decreased with depth. • A majority of P is found in the Hedley NaOH recalcitrant fraction which represents P bound to Fe and Al oxides. • Mehlich-3 results show a significant (p=0.02) increase in extractable P in the 0-10 cm soil horizon of the fertilized sites. • Results suggest that Mehlich-3 extracts from recalcitrant P pools including P bound to Fe and Al oxides. • Mehlich-1 P was less than Hedley labile P pools in the 0-10 cm soil horizon. Photo: D. Blevins