Potential and sustainability for carbon sequestration with improved soil management in agricultural soils of China

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    Agriculture, Ecosystems and Environme1. Introduction

    Agricultural soils generally have lower organic matter

    content than natural lands because of reduced C input (due to

    annual harvest and removal of crop residue, etc.), high organic

    C decomposition (due to frequent tillage), increased soil

    erosion (Paustian et al., 1997; Bowman et al., 1999; Lal,

    2002a, 2004) and other factors. Many studies have demon-

    strated that improved management practices can increase the

    C content of arable soils towards the levels found in natural

    lands (Smith et al., 2000a; West and Post, 2002; Lal, 2004).

    Increasing agricultural soil stocks has been suggested as an

    important measure to sequester CO2 from the atmosphere to

    help stabilize atmospheric CO2 concentrations and has been

    estimated that 0.40.9 Pg C year1 can be sequestered withinglobal agricultural soils (Paustian et al., 1998). The Kyoto

    Protocol under Article 3.4 includes the component of C

    uptake by soil management in the framework of controlling

    greenhouse gases emissions and hence has generated a broad

    interest in studying C sequestration of agricultural soils

    through improved managements.

    The industrial C emissions of China are about

    1 Pg C year1, second only to the United States (Marlandet al., 2005). As a signatory country of the Kyoto Protocol,

    although it currently has no obligation to cut carbon dioxide

    emissions, China is looking for ways to curb C emission and

    to enhance C sequestration. The arable land in China covers* Corresponding author. Tel.: +86 10 6488 9808; fax: +86 10 6488 9399.

    E-mail address: yanhm@lreis.ac.cn (H. Yan).

    0167-8809/$ see front matter # 2006 Elsevier B.V. All rights reserved.doi:10.1016/j.agee.2006.11.008Arable land soils generally have lower organic carbon (C) levels than soils under native vegetation; increasing the C stocks through

    improved management is suggested as an effective means to sequester CO2 from the atmosphere. Chinas arable lands, accounting for 13% of

    the worlds total, play an important role in soil C sequestration, but their potential to enhance C sequestration has not yet been quantitatively

    assessed. The C sequestration by agricultural soils is affected by many environmental factors (such as climate and soil conditions), biological

    processes (crop C fixation, decomposition and transformation), and crop and soil management (e.g. tillage and manure application).

    Estimation of the C sequestration potential requires the quantification of the combined effects of these factors and processes. In this study, we

    used a coupled remote sensing- and process-based ecosystem model to estimate the potential for C sequestration in agricultural soils of China

    and evaluated the sustainability of soil C uptake under different soil management options. The results show that practicing no-tillage on 50%

    of the arable lands and returning 50% of the crop residue to soils would lead to an annual soil C sequestration of 32.5 Tg C, which accounts for

    about 4% of Chinas current annual C emission. Soil C sequestration with improved soil management is highly time-dependent; the effect

    lasted for only 2080 years. Generally, practicing no-tillage causes higher rate and longer sustainability of soil C sequestration than only

    increasing crop residue into soils. The potential for soil C sequestration varied greatly among different regions due to the differences in

    climate, soil conditions and crop productivity.

    # 2006 Elsevier B.V. All rights reserved.

    Keywords: Carbon sequestration; Soil management; Process model; Remote sensingAbstractPotential and sustainability for c

    soil management in ag

    Huimin Yan *, Mingku

    Institute of Geographic Sciences and Natural Resource

    Anwai, Beiji

    Received 5 April 2006; received in revised f

    Available onlinon sequestration with improved

    ultural soils of China

    o, Jiyuan Liu, Bo Tao

    arch, Chinese Academy of Sciences, 11A Datun Road,

    101, China

    7 October 2006; accepted 7 November 2006

    ecember 2006

    www.elsevier.com/locate/agee

    nt 121 (2007) 325335

  • (Kern and Johnson, 1993; Freibauer et al., 2004; Lal, 2004;

    Paustian et al., 1995; Buyanovsky and Wagner, 1998).

    s andabout 124 Mha, accounting for about 13% of the worlds

    total. Chinas agricultural soils have relatively low C content

    level, because of intensive use, long cultivation history and

    the use of crop residue as fuels and feed for domestic

    animals, hence may have a great potential for C sequestra-

    tion through improved land management. It is estimated that

    about 90% of C uptake by agricultural systems would be

    emitted or returned to the atmosphere (Lin et al., 1997). C.S.

    Li et al. (2003) and K.R. Li et al. (2003) estimated that under

    conventional soil management Chinas cropland are losing

    1.6% of their soil organic carbon (SOC) while U.S.

    croplands are only losing 0.1%. However, although there

    are many studies describing agricultural SOC stocks (S.Q.

    Wang et al., 2005; X.B. Wang et al., 2005; Liu et al., 2006),

    SOC loss due to cultivation (Wu et al., 2003; Song et al.,

    2005), and the significance of improved soil management on

    increasing soil C sequestration (C.S. Li et al., 2003; K.R. Li

    et al., 2003; S.Q. Wang et al., 2005; X.B. Wang et al., 2005),

    few quantitative studies concerning agricultural soil C

    sequestration have been undertaken at the national level in

    China. Only Lin et al. (2002) and Lal (2002b) estimated soil

    C sequestration potential in China through proposed

    cropland management activities by IPCC, using the rates

    of C gain for various activities within the corresponding

    area. Therefore, there is a significant gap of spatially explicit

    quantification on C sequestration potential and its sustain-

    ability with improved soil management in the agricultural

    soils of China.

    Many studies have been conducted in other regions to

    assess the potential of agricultural soil sequestration at

    national or regional level, and have explored the options to

    enhance C sequestration (e.g. Smith et al., 2000a,b;

    Vleeshouwers and Verhagen, 2002; Marland et al., 2003;

    West and Marland, 2002, 2003; Dendoncker et al., 2004).

    Most of previous studies have used empirical approaches

    based on a comparison of measured organic C levels between

    arable and natural lands or on observations of the organic C

    change with improved management at limited sites (Lal and

    Bruce, 1999; Smith et al., 1997, 1998, 2000a,b; West and Post,

    2002). However, soil C sequestration is a complex process that

    is influenced by many factors, such as organic C inputs from

    crop residue or applied organic manure, climatic and soil

    conditions, and the original C levels, and thus has high spatio-

    temporal heterogeneity. A realistic estimate of the C

    sequestration potential at regional or national scales requires

    integrating the effects of various factors that affect C inputs to

    and loss from soils and accounting the inherent high spatial

    heterogeneity and temporal variability. Some studies have

    linked site level process-based model with GIS to extrapolate

    point measurements to regional scales (Falloon et al., 1998,

    2000; Zimmerman et al., 2005). A combination of process-

    based mechanistic modeling and satellite remote sensing is an

    effective approach to integrate the effects of various factors on

    soil C processes and to quantify the high spatial heterogeneity

    in the rates of the C sequestration. Remotely sensed surface

    H. Yan et al. / Agriculture, Ecosystem326properties combined with biogeochemical models have beenCurrently, no-tillage is practiced on only 5% of the worlds

    cropland (1379 Mha globally) (Lal, 2004). The amount of

    crop residue produced in the world is a large quantity, about

    3.5 Pg year1, but only 5060% of the residue producedmay be returned to the soil (Lal, 1999). In China, only about

    25% is returned to the fields (Ministry of Agriculture of

    China, 1998). Most crop residue was either used as fuel or

    feed for domestic animals in rural areas before 1980s, or

    burned on field after 1980s when farmers ceased taking crop

    straw as fuel due to improved living conditions. So, the

    objectives of this study were to: (1) use a coupled remote

    sensing- and process-based ecosystem model of CEVSA

    (Cao and Woodward, 1998; Cao et al., 2003) to make a

    spatially explicit quantification of the C sequestration

    potential of Chinas arable lands; (2) evaluate the effec-

    tiveness of different management options based on the

    modelled C uptake rate and its sustainability; (3) make a

    mechanistic analysis on the regional pattern of C

    sequestration potential. The soil management options

    considered in the present study are practicing no-tillage

    and increasing crop residue input into soils.

    2. Materials and methods

    Estimation of soil C sequestration requires quantification

    of the rates of C inputs and releases under improved soil

    management. The source of increment in SOC is the net C

    fixed by crops, usually measured as net primary productiv-

    ity (NPP), but only a part of the fixed C actually is

    incorporated into soils while the other parts are removed for

    harvest or for clearing the field. Soils lose C from

    heterotro

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