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

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<ul><li><p>arb</p><p>ric</p><p>i Ca</p><p>s Rese</p><p>ng 100</p><p>orm 2</p><p>e 12 D</p><p>Agriculture, Ecosystems and Environme1. Introduction</p><p>Agricultural soils generally have lower organic matter</p><p>content than natural lands because of reduced C input (due to</p><p>annual harvest and removal of crop residue, etc.), high organic</p><p>C decomposition (due to frequent tillage), increased soil</p><p>erosion (Paustian et al., 1997; Bowman et al., 1999; Lal,</p><p>2002a, 2004) and other factors. Many studies have demon-</p><p>strated that improved management practices can increase the</p><p>C content of arable soils towards the levels found in natural</p><p>lands (Smith et al., 2000a; West and Post, 2002; Lal, 2004).</p><p>Increasing agricultural soil stocks has been suggested as an</p><p>important measure to sequester CO2 from the atmosphere to</p><p>help stabilize atmospheric CO2 concentrations and has been</p><p>estimated that 0.40.9 Pg C year1 can be sequestered withinglobal agricultural soils (Paustian et al., 1998). The Kyoto</p><p>Protocol under Article 3.4 includes the component of C</p><p>uptake by soil management in the framework of controlling</p><p>greenhouse gases emissions and hence has generated a broad</p><p>interest in studying C sequestration of agricultural soils</p><p>through improved managements.</p><p>The industrial C emissions of China are about</p><p>1 Pg C year1, second only to the United States (Marlandet al., 2005). As a signatory country of the Kyoto Protocol,</p><p>although it currently has no obligation to cut carbon dioxide</p><p>emissions, China is looking for ways to curb C emission and</p><p>to enhance C sequestration. The arable land in China covers* Corresponding author. Tel.: +86 10 6488 9808; fax: +86 10 6488 9399.</p><p>E-mail address: yanhm@lreis.ac.cn (H. Yan).</p><p>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</p><p>improved management is suggested as an effective means to sequester CO2 from the atmosphere. Chinas arable lands, accounting for 13% of</p><p>the worlds total, play an important role in soil C sequestration, but their potential to enhance C sequestration has not yet been quantitatively</p><p>assessed. The C sequestration by agricultural soils is affected by many environmental factors (such as climate and soil conditions), biological</p><p>processes (crop C fixation, decomposition and transformation), and crop and soil management (e.g. tillage and manure application).</p><p>Estimation of the C sequestration potential requires the quantification of the combined effects of these factors and processes. In this study, we</p><p>used a coupled remote sensing- and process-based ecosystem model to estimate the potential for C sequestration in agricultural soils of China</p><p>and evaluated the sustainability of soil C uptake under different soil management options. The results show that practicing no-tillage on 50%</p><p>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</p><p>about 4% of Chinas current annual C emission. Soil C sequestration with improved soil management is highly time-dependent; the effect</p><p>lasted for only 2080 years. Generally, practicing no-tillage causes higher rate and longer sustainability of soil C sequestration than only</p><p>increasing crop residue into soils. The potential for soil C sequestration varied greatly among different regions due to the differences in</p><p>climate, soil conditions and crop productivity.</p><p># 2006 Elsevier B.V. All rights reserved.</p><p>Keywords: Carbon sequestration; Soil management; Process model; Remote sensingAbstractPotential and sustainability for c</p><p>soil management in ag</p><p>Huimin Yan *, Mingku</p><p>Institute of Geographic Sciences and Natural Resource</p><p>Anwai, Beiji</p><p>Received 5 April 2006; received in revised f</p><p>Available onlinon sequestration with improved</p><p>ultural soils of China</p><p>o, Jiyuan Liu, Bo Tao</p><p>arch, Chinese Academy of Sciences, 11A Datun Road,</p><p>101, China</p><p>7 October 2006; accepted 7 November 2006</p><p>ecember 2006</p><p>www.elsevier.com/locate/agee</p><p>nt 121 (2007) 325335</p></li><li><p>(Kern and Johnson, 1993; Freibauer et al., 2004; Lal, 2004;</p><p>Paustian et al., 1995; Buyanovsky and Wagner, 1998).</p><p>s andabout 124 Mha, accounting for about 13% of the worlds</p><p>total. Chinas agricultural soils have relatively low C content</p><p>level, because of intensive use, long cultivation history and</p><p>the use of crop residue as fuels and feed for domestic</p><p>animals, hence may have a great potential for C sequestra-</p><p>tion through improved land management. It is estimated that</p><p>about 90% of C uptake by agricultural systems would be</p><p>emitted or returned to the atmosphere (Lin et al., 1997). C.S.</p><p>Li et al. (2003) and K.R. Li et al. (2003) estimated that under</p><p>conventional soil management Chinas cropland are losing</p><p>1.6% of their soil organic carbon (SOC) while U.S.</p><p>croplands are only losing 0.1%. However, although there</p><p>are many studies describing agricultural SOC stocks (S.Q.</p><p>Wang et al., 2005; X.B. Wang et al., 2005; Liu et al., 2006),</p><p>SOC loss due to cultivation (Wu et al., 2003; Song et al.,</p><p>2005), and the significance of improved soil management on</p><p>increasing soil C sequestration (C.S. Li et al., 2003; K.R. Li</p><p>et al., 2003; S.Q. Wang et al., 2005; X.B. Wang et al., 2005),</p><p>few quantitative studies concerning agricultural soil C</p><p>sequestration have been undertaken at the national level in</p><p>China. Only Lin et al. (2002) and Lal (2002b) estimated soil</p><p>C sequestration potential in China through proposed</p><p>cropland management activities by IPCC, using the rates</p><p>of C gain for various activities within the corresponding</p><p>area. Therefore, there is a significant gap of spatially explicit</p><p>quantification on C sequestration potential and its sustain-</p><p>ability with improved soil management in the agricultural</p><p>soils of China.</p><p>Many studies have been conducted in other regions to</p><p>assess the potential of agricultural soil sequestration at</p><p>national or regional level, and have explored the options to</p><p>enhance C sequestration (e.g. Smith et al., 2000a,b;</p><p>Vleeshouwers and Verhagen, 2002; Marland et al., 2003;</p><p>West and Marland, 2002, 2003; Dendoncker et al., 2004).</p><p>Most of previous studies have used empirical approaches</p><p>based on a comparison of measured organic C levels between</p><p>arable and natural lands or on observations of the organic C</p><p>change with improved management at limited sites (Lal and</p><p>Bruce, 1999; Smith et al., 1997, 1998, 2000a,b; West and Post,</p><p>2002). However, soil C sequestration is a complex process that</p><p>is influenced by many factors, such as organic C inputs from</p><p>crop residue or applied organic manure, climatic and soil</p><p>conditions, and the original C levels, and thus has high spatio-</p><p>temporal heterogeneity. A realistic estimate of the C</p><p>sequestration potential at regional or national scales requires</p><p>integrating the effects of various factors that affect C inputs to</p><p>and loss from soils and accounting the inherent high spatial</p><p>heterogeneity and temporal variability. Some studies have</p><p>linked site level process-based model with GIS to extrapolate</p><p>point measurements to regional scales (Falloon et al., 1998,</p><p>2000; Zimmerman et al., 2005). A combination of process-</p><p>based mechanistic modeling and satellite remote sensing is an</p><p>effective approach to integrate the effects of various factors on</p><p>soil C processes and to quantify the high spatial heterogeneity</p><p>in the rates of the C sequestration. Remotely sensed surface</p><p>H. Yan et al. / Agriculture, Ecosystem326properties combined with biogeochemical models have beenCurrently, no-tillage is practiced on only 5% of the worlds</p><p>cropland (1379 Mha globally) (Lal, 2004). The amount of</p><p>crop residue produced in the world is a large quantity, about</p><p>3.5 Pg year1, but only 5060% of the residue producedmay be returned to the soil (Lal, 1999). In China, only about</p><p>25% is returned to the fields (Ministry of Agriculture of</p><p>China, 1998). Most crop residue was either used as fuel or</p><p>feed for domestic animals in rural areas before 1980s, or</p><p>burned on field after 1980s when farmers ceased taking crop</p><p>straw as fuel due to improved living conditions. So, the</p><p>objectives of this study were to: (1) use a coupled remote</p><p>sensing- and process-based ecosystem model of CEVSA</p><p>(Cao and Woodward, 1998; Cao et al., 2003) to make a</p><p>spatially explicit quantification of the C sequestration</p><p>potential of Chinas arable lands; (2) evaluate the effec-</p><p>tiveness of different management options based on the</p><p>modelled C uptake rate and its sustainability; (3) make a</p><p>mechanistic analysis on the regional pattern of C</p><p>sequestration potential. The soil management options</p><p>considered in the present study are practicing no-tillage</p><p>and increasing crop residue input into soils.</p><p>2. Materials and methods</p><p>Estimation of soil C sequestration requires quantification</p><p>of the rates of C inputs and releases under improved soil</p><p>management. The source of increment in SOC is the net C</p><p>fixed by crops, usually measured as net primary productiv-</p><p>ity (NPP), but only a part of the fixed C actually is</p><p>incorporated into soils while the other parts are removed for</p><p>harvest or for clearing the field. Soils lose C from</p><p>heterotrophic respiration (HR), soil erosion by wind and</p><p>water. In the present study, only HR is included in</p><p>calculating soil C loss. The soil C sequestration was</p><p>estimated using a coupled remote sensing- and process-</p><p>based model (Fig. 1) that calculates the C inputs from crop</p><p>growth and the decomposition of C under differentused to predict C fluxes into and out of ecosystems and to</p><p>evaluate potential mechanisms of terrestrial CO2 sequestra-</p><p>tion (Nemani et al., 2003; Cao et al., 2004).</p><p>Soil C sequestration can be achieved by increasing the net</p><p>flux of C from the atmosphere to the terrestrial biosphere by</p><p>storing more of the C from net primary production in the</p><p>longer-term C pools in the soil or by slowing decomposition.</p><p>No-tillage can significantly reduce soil C release by</p><p>reducing the turnover of soil aggregates and the exposing</p><p>of young and labile organic matter to microbe decomposi-</p><p>tion (Paustian et al., 2000). This method has been taken as an</p><p>effective and environmentally friendly soil C sequestration</p><p>strategy (Lal, 2004). No-tillage and preferential crop</p><p>residues management (increasing C input) are two important</p><p>and widely recognized measures to enhance C sequestration</p><p>Environment 121 (2007) 325335management options.</p></li><li><p>s and2.1. Crop NPP and C inputs into soils</p><p>The rate of C input into agricultural soils was calculated</p><p>as the proportion of crop NPP that is returned into soils,</p><p>including crop residues and manure application. The NPP in</p><p>a given area at the present time was estimated using a remote</p><p>sensing-based production efficiency model, GLO-PEM. The</p><p>model consists of linked components that describe processes</p><p>of canopy radiation absorption, utilization, autotrophic</p><p>respiration, and the regulation of these processes by</p><p>environmental factors such as temperature, water vapor</p><p>pressure deficit, and soil moisture (Prince and Goward,</p><p>1995; Cao et al., 2004). It calculates NPP as follows:</p><p>H. Yan et al. / Agriculture, Ecosystem</p><p>Fig. 1. A schematic representation of the model for estimating soil carbon</p><p>sequestration. The meaning of acronyms are as follows: fraction of photo-</p><p>synthetically active radiation (FPAR), light use efficiency (LUE), auto-</p><p>trophic respiration (Ra), gross primary production (GPP), net primary</p><p>production (NPP), soil organic matter (SOM).NPP X</p><p>tStNteg Ra (1)</p><p>where St is the incident PAR in time t, Nt the fraction of</p><p>incident photosynthetically active radiation (PAR) absorbed</p><p>by vegetation canopy (FPAR) calculated as a linear function</p><p>of NDVI (Prince and Goward, 1995), eg the light useefficiency of the absorbed PAR by vegetation in terms of</p><p>gross primary production, and Ra is the autotrophic respira-</p><p>tion calculated as a function of standing aboveground bio-</p><p>mass, air temperature, and photosynthetic rate.</p><p>The NPP of crops consists of the organic C in the</p><p>economic products (e.g. grain), roots and straw (stems,</p><p>leaves, stalks, etc.), which were calculated using the C</p><p>allocation parameters as given in Table 1.</p><p>The C in the economic products of crops is usually</p><p>removed from crop lands; a part of the C in straw and roots is</p><p>removed away for other uses (e.g. fuel and livestock feed) or</p><p>is burned for clearing the field, and only the remaining C</p><p>enters into soil as the source of C. In addition, organic</p><p>manure is also an important C source for agricultural soils,</p><p>however, in China most of organic manure originated fromcrop products. At present, according to the national statistic</p><p>data, altogether 25% residues are returned into soils with</p><p>17% being directly incorporated into soils and 8% as organic</p><p>manure input into soils in China (State Environmental</p><p>Protection Administration of China, 2000). In the present</p><p>study, the rate of C input into the soil was estimated as a part</p><p>of NPP based on the C allocation among crop organs and the</p><p>survey of actual data inputs, including from the applied</p><p>organic manure. C input included all roots and returned</p><p>straw, and the proportions of NPP to roots and straws were</p><p>calculated by the mean value of different crops listed in</p><p>Table 1 because the crop types are unavailable for the</p><p>present.</p><p>2.2. SOC decomposition</p><p>The rate of C release from agricultural soils was</p><p>calculated as the rate of heterotrophic respiration using a</p><p>process-based ecosystem model, CEVSA (Cao and Wood-</p><p>ward, 1998; Cao et al., 2003). In simulating organic carbon</p><p>transformation, decomposition and accumulation, CEVSA</p><p>divides soil organic matter into surface litter, root litter,</p><p>microbes, and slow and passive C pools, each of which has a</p><p>specific decay rate (Cao et al., 2003). All SOC transforma-</p><p>tions and decomposition in these pools are treated as first-</p><p>order rate reactions that are affected by temperature, soil</p><p>moisture, nitrogen availability, soil texture, and the lignin/</p><p>nitrogen ratio.</p><p>The original CEVSA did not consider the effects of</p><p>tillage on SOC dynamics. In natural lands, soil organic</p><p>matter is physically protected in microaggregates to</p><p>microbial decomposition. Tillage of arable lands enhances</p><p>soil organic matter decomposition by disturbing the physical</p><p>protection. It is estimated that the decay rate of SOM in</p><p>cultivated soils is several times higher than that of natural</p><p>Environment 121 (2007) 325335 327</p><p>Table 1</p><p>Carbon allocation to economic products, straw and roots (Li et al., 1994)</p><p>Cropa Grain Straw Root</p><p>Wheat 0.28 0.42 0.3</p><p>Corn 0.3 0.44 0.26</p><p>Cotton 0.19 0.48 0.33</p><p>Soybeans 0.28 0.44 0.28</p><p>a Scientific names: wheat (Triticum aestivum), corn (Zea mays), cotton</p><p>(Gossypium hirsutum) and soybeans (Glycine max).lands (Balesdent et al., 2000; Six et al., 1998; Li et al., 1994).</p><p>In the present study, The CEVSA model was modified to</p><p>account the effect of tillage by using a parameter that</p><p>measures the increases on the decay rates of different C</p><p>pools relative to that in soils with no tillage (Leite et al.,</p><p>2004) (Table 2).</p><p>2.3. Data sources and model running</p><p>We use the coupled models of GLO...</p></li></ul>

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