Land management effects on nitrogen and carbon cycling in an Ultisol

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  • This article was downloaded by: [Ams/Girona*barri Lib]On: 17 October 2014, At: 03:23Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number:1072954 Registered office: Mortimer House, 37-41 Mortimer Street,London W1T 3JH, UK

    Communications in SoilScience and Plant AnalysisPublication details, including instructions forauthors and subscription information:http://www.tandfonline.com/loi/lcss20

    Land management effectson nitrogen and carboncycling in an UltisolH. A. Torbert a , S. A. Prior b & D.W. Reeves ba USDAARS Grassland , Soil and WaterResearch Laboratory , 808 East BlacklandRoad, Temple, TX, 76502 E-mail:b USDAARS , National Soil DynamicsLaboratory , 411 South Donahue Drive,Auburn, AL, 36832Published online: 11 Nov 2008.

    To cite this article: H. A. Torbert , S. A. Prior & D.W. Reeves (1999)Land management effects on nitrogen and carbon cycling in an Ultisol,Communications in Soil Science and Plant Analysis, 30:9-10, 1345-1349, DOI:10.1080/00103629909370290

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    http://www.tandfonline.com/page/terms-and-conditionshttp://www.tandfonline.com/page/terms-and-conditions

  • COMMUN. SOIL SCI. PLANT ANAL., 30(9&10), 1345-1359 (1999)

    Land Management Effects on Nitrogen andCarbon Cycling in an Ultisol

    H. A. Torbert,a,1 S. A. Prior,b and D.W. Reevesb

    aUSDA-ARS Grassland, Soil and Water Research Laboratory, 808 EastBlackland Road, Temple TX, 76502bUSDA-ARS National Soil Dynamics Laboratory, 411 South Donahue Drive,Auburn, AL 36832

    ABSTRACT

    Soil carbon (C) content in agro-ecosystems is important in a global contextbecause of the potential for soil to act as a sink for atmospheric CO2. However,soil C storage in agro-ecosystems can be sensitive to land managementpractices. The objective of this study was to examine the impact of landmanagement systems on C and nitrogen (N) cycling in an Ultisol in Alabama.Soil samples (0-10, 10-20, and 20-30 cm depths) were collected from a Marvynsandy loam soil (fine-loamy, siliceous, thermic Typic Hapludults) under fivedifferent farm scale management systems for at least 5 years. The five systemswere cotton (Gossypium hirsutum L.) production managed with 1)conventional tillage only, 2) conventional tillage with a grazed winter covercrop (wheat, Triticum aestivum L.), 3) conservation tillage with a winter covercrop grown for cover only with strip tillage; or taken out of cotton productionwith either 4) long-term fallow (mowed), or 5) Conservation Reserve Program

    1Corresponding author (e-mail address: torbert@brc.tamus.edu).

    1345

    Copyright 1999 by Marcel Dekker, Inc. www.dekker.com

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  • 1346 TORBERT, PRIOR, AND REEVES

    with loblolly pine (Pinus taeda L.) (CRP-pine). Total N, total organic C(TOC), total P, and soil C:N ratios were determined. Potential Cmineralization, N mineralization, C turnover and C:N mineralization ratioswere determined on samples during a 30-day laboratory incubation study.The fallow system had significantly higher TOC concentration (7.7 g kg-1 C)while the CRP-pine system had lower TOC concentration (3.1 g kg-1 C)compared with the farmed management systems (=4.7 g kg-1 C). The fallowsystem had a significantly lower C turnover at all three soil depths comparedwith the other management systems. At the 0-10 cm depth, the highest C:Nmineralization ratio levels were observed in management systems receivingthe most tillage. Our results indicate that for Ultisols in the Southeast the useof surface tillage in land management systems is a controlling factor whichmay limit soil C sequestration.

    INTRODUCTION

    The combined impact of population increases, industrial expansion, anddeforestation has resulted in increased atmospheric CO2 concentration (Holland,1978; Smil, 1985;Warneck, 1988), which is projected to double in the next century(Bolin, 1986). The implications of these changes, while highly debated, are forglobal warming and local climate shifts. Soils play a major role in the global Cbudget not only because of the large amount of C stored in soil, with estimatesranging from 1,395 to 1,636x10" g (Ajtay et al., 1979; Post et al., 1992;Schlesinger, 1984), but also because the soil contribution to the annual flux ofCO2 to the atmosphere is 10 times that contributed by fossil fuel usage (Post et al.,1990). Jackson (1992) estimated that 1.3x10" g of gross CO2 is removed fromthe atmosphere by crops each year. Agro-ecosystems are important in the globalcontext not only because of CO2 flux to the atmosphere, but also because C storagein agro-ecosystems can be sensitive to management practices such as tillage andcropping systems (Kern and Johnson, 1993). Lai (1997) estimated that if 15% ofthe world production of residue could be converted to a passive soil organic Cpool it could lead to a C sequestration rate of 0.2x10" g CO2 yr

    1. Therefore, anessential question is how residue management impacts the sequestration of C insoil.

    Conservation tillage leads to increases in TOC concentration near the soil surface(Franzluebbersetal., 1995;Torbertetal., 1997; Potter etal., 1997;Reeves, 1997),but the ability of the soil to sequester C may be dependent not only on residuemanagement, but also on the amount of plant residues added to the soil (Wood etal., 1990,1991), crop sequence (Potter et al., 1997), and climate (Reeves, 1997;Potter etal., 1998).

    The ability of residue management to impact soil C sequestration is unclear andis dependent on climate and soil type (Reeves, 1997; Lai, 1997). Dick (1996),using the Erosion Productivity Impact Calculator (EPIC) model, examined the

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  • LAND MANAGEMENT EFFECTS ON N AND C CYCLING 1347

    impact of widespread conversion to no-till production in the Corn Belt of theUnited States. He estimated that 3.3xlO12 g of C could be conserved andsequestered each year for the next 100 years. Likewise, Mitchell et al. (1996)used EPIC with the National Resources Inventory (NRI) database to examine theimpact of the CRP (a USDA government program aimed at long-term conversionof marginal farm land out of crop production) and conservation tillage on Csequestration and found that agricultural soils would be a sink for C in the centralUnited States. Converting crop production land to perennial grass cover associatedwith CRP in Texas, Kansas, and Nebraska would result in an estimated increaseinTOCof 1.1 x lO'gofCha^yr'CGebhartetal., 1994). However, Huggins et al.(1996) reported that land converted from cropland to CRP seldom expressed anincrease in TOC when measured in fields in the Corn Belt, Northern Great Plains,and the Columbia Plateau of the United States. Likewise, Allan et al. (1996)reported that while conversion of cropland to CRP resulted in changes in soilphysical and chemical properties of soil, no change in TOC was found in 6-7years of CRP in Minnesota.

    Much less research has been conducted on the impact of conservation tillageand CRP conversion in the humid Southeast, United States. In the Southeast,CRP conversion has been largely in the form of planting loblolly pine (Pinustaeda L.). The objective of this study was to examine the impact of residuemanagement systems on C and N cycling in an Ultisol in central Alabama, includingthe impact of CRP-pine production compared to cotton production, a major cropof the region.

    MATERIALS AND METHODS

    A study area was identified in central Alabama where continuous cotton hadbeen produced for at least 50 years on a Marvyn sandy loam soil with a 6% slope.Sites were identified where the land use had been maintained under five differentmanagement systems: 1) conventional tilled winter fallowed cotton (20 y), 2)winter grazed cover crop with conventional tilled cotton (5 y), 3) strip-tilled cotton(5 y), 4) fallow (10 y), and 5) CRP-pine (5 y). At the time of

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