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Title: SOIL ORGANIC C AND N POOLS UNDER LONG-TERM PASTURE MANAGEMENT IN THE SOUTHERN PIEDMONT USA

Author
item Franzluebbers, Alan
item Stuedemann, John
item Schomberg, Harry
item WILKINSON, S - USDA-ARS RETIRED

Submitted to: Soil Biology and Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/28/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary: Storage of carbon (C) in soil has become a topic of great interest following the Kyoto Protocol because of concerns about rising CO2 concentration and its role in potential global warming. Soil is the largest terrestrial reservoir of carbon and has potential to store more carbon with improved management. An increasing proportion of land in the Southern Piedmont USA has been converted to various pasture management systems. We investigated the effects of harvest technique, stand age, species composition, and previous land use on potential soil C and N storage under pasture. We found that (1) typical tall fescue-common bermudagrass pastures in the Southern Piedmont USA can increase soil organic C and N storage more than conservation-tillage cropland, (2) grazing of pastures with cattle is beneficial to storage of soil organic C and N compared with haying, (3) storage of soil organic C occurs at a rate of 654 kg/ha/yr during the first 30 years of establishment under grazed tall fescue and at a rate of 221 kg/ha/yr under hayed bermudagrass, (4) pasture established following clearing of forestland has greater potential soil organic C and N storage than following cropland, and (5) in the long-term, grass management systems have nearly equivalent potential to store soil organic C as forestland.

Technical Abstract: We compared soil C and N pools (total, particulate, and microbial) under pastures that varied due to harvest technique (grazing or haying), species composition (cool- or warm-season), age, and previous land use. Conversion of conventionally tilled cropland to grazed pasture 20 years ago resulted in 31% greater soil organic C, 34% greater total N, 66% greater particulate organic C, 2.4-times greater particulate organic N, and 28% greater soil microbial biomass C at a depth of 0-200 mm than land converted to conservation-tillage cropland. Soil organic C and total N at a depth of 0-200 mm averaged 38 and 2.9 Mg/ha, respectively, under grazed bermudagrass and 31 and 2.2 Mg/ha, respectively, under hayed bermudagrass. A chronosequence of grazed tall fescue suggested soil organic N sequestration rates of 73, 44, and 6 kg/ha/yr to a depth of 200 mm during 0-10, 10-30, and 30-50 years, respectively. Soil C storage under long-term grazed tall fescue was 85 to 88% of that under forest, whereas soil N storage was 77 to 90% greater under grazed tall fescue than under forest. Properly grazed pastures in the Southern Piedmont USA have great potential to restore natural soil fertility, sequester soil organic C and N, and increase soil biological activity.