Soil Carbon Sequestration Potential as Affected by Management Practices in Northern China: A Simulation Study

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<ul><li><p>Pedosphere 24(4): 529543, 2014</p><p>ISSN 1002-0160/CN 32-1315/P</p><p>c 2014 Soil Science Society of ChinaPublished by Elsevier B.V. and Science Press</p><p>Soil Carbon Sequestration Potential as Affected by Management</p><p>Practices in Northern China: A Simulation Study1</p><p>WANG Guo-Cheng1, WANG En-Li2,2, HUANG Yao3 and XU Jing-Jing1</p><p>1State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry (LAPC), Institute of Atmospheric</p><p>Physics, Chinese Academy of Sciences, Beijing 100029 (China)2CSIRO Land &amp; Water, Black Mountain, Canberra, ACT 2601 (Australia)3State Key Laboratory of Vegetation and Environmental Change (LVEC), Institute of Botany, Chinese Academy of Sciences, Beijing</p><p>100093 (China)</p><p>(Received March 6, 2013; revised January 5, 2014)</p><p>ABSTRACTSoil has been identified as a possible carbon (C) sink for sequestering atmospheric carbon dioxide (CO2). However, soil organic</p><p>carbon (SOC) dynamics in agro-ecosystems is affected by complex interactions of various factors including climate, soil and agricultural</p><p>management practices, which hinders our understanding of the underlying mechanisms. The objectives of this study were to use the</p><p>Agricultural Production Systems sIMulator (APSIM) model to simulate the long-term SOC dynamics under different management</p><p>practices at four long-term experimental sites, Zhengzhou and Xuzhou with double cropping systems and Gongzhuling and Urumqi</p><p>with single cropping systems, located in northern China. Firstly, the model was calibrated using information from the sites and</p><p>literature, and its performance to predict crop growth and SOC dynamics was examined. The calibrated model was then used to</p><p>assess the impacts of different management practices, including fertilizer application, irrigation, and residue retention, on C dynamics</p><p>in the top 30 cm of the soil by scenario modelling. Results indicate a significant SOC sequestration potential through improved</p><p>management practices of nitrogen (N) fertilizer application, stubble retention, and irrigation. Optimal N fertilization (Nopt) and 100%</p><p>stubble retention (R100) increased SOC by about 11.2%, 208.29%, and 283.67% under irrigation at Gongzhuling, Zhengzhou, and</p><p>Xuzhou, respectively. Soil organic carbon decreased rapidly at Urumqi under irrigation, which was due to the enhanced decomposition</p><p>by increased soil moisture. Under rainfed condition, SOC remained at a higher level. The combination of Nopt and R100 increased</p><p>SOC by about 0.46% under rainfed condition at Urumqi. Generally, agricultural soils with double cropping systems (Zhengzhou and</p><p>Xuzhou) showed a greater potential to sequester C than those with single cropping systems (Gongzhuling and Urumqi).</p><p>Key Words: agro-ecosystems, APSIM model, fertilizer application, irrigation, residue retention, scenario analysis, soil organic carbon</p><p>Citation: Wang, G. C., Wang, E. L., Huang, Y. and Xu, J. J. 2014. Soil carbon sequestration potential as affected by management</p><p>practices in northern China: A simulation study. Pedosphere. 24(4): 529543.</p><p>INTRODUCTION</p><p>Soil organic carbon (SOC) has experienced signifi-cant decreases due to cultivation of natural soils inagro-ecosystems (Davidson and Ackerman, 1993; Lal,2004). It is suggested that adopting improved agricul-tural management such as stubble retention, conser-vation tillage and fertilization has the potential to en-hance SOC accumulation, thereby mitigating the cli-mate change and promoting the soil quality to supportsustainable crop productivity (Smith, 2004; Wang etal., 2013a). However, the effectiveness of any mana-gement practice on agricultural SOC balance is af-fected by the complex interaction between carbon(C) production and decomposition processes as con-</p><p>trolled by spatiotemporally changing environmentalconditions, which hampers our ability to extrapolatethe SOC dynamics over time and space (Luo et al.,2011). Process-based soil-plant system models can cap-ture the interaction between C production (input)and decomposition (output), and thus have been usedworldwide to simulate SOC dynamics under diffe-rent agricultural practices and different climatic andedaphic conditions (Smith et al., 1997b; Li et al., 2003;Lugato and Berti, 2008; Liu et al., 2009; Lehuger etal., 2010). For example, Ogle et al. (2010) simulatedthe change of SOC storage in US croplands from 1990to 2000 using the Century model, Wang et al. (2013b)modelled the regional SOC change from 1960 to 2010 inAustralian wheat growing areas based on the Agro-C</p><p>1Supported by the National Basic Research Program (973 Program) of China (No. 2010CB950604) and the National Natural ScienceFoundation of China (No. 41075108).2Corresponding author. E-mail:</p></li><li><p>530 G. C. WANG et al.</p><p>model, and Tang al. (2006) estimated the nationalSOC storage and its associated changing rates ac-ross Chinese croplands using the DeNitrification-De-Composition (DNDC) model. The advantage of adop-ting modelling method is that once the model has beenproperly validated, it can be used to predict SOC dy-namics as impacted by various management, soil andclimate conditions and their interactions across timeand space, which is impractical, if not impossible, forfield experiments.</p><p>The Agricultural Production Systems sIMulator(APSIM) model (Keating et al., 2003) was developedin Australia for simulation of both crop growth andsoil processes by providing the functionality and flexi-bility to specify complex rotation types and mana-gement options. The model has been extensively testedand applied in Australia to study the performanceof agricultural systems under different climatic con-ditions and various management scenarios (Asseng etal., 1998; Probert et al., 2005; Chen et al., 2010a,b; Wang et al., 2010; Luo et al., 2011; Yang et al.,2011). Recently, Chen et al. (2010a) and Wang etal. (2010) found that the APSIM model performed wellfor simulation of crop production under different irri-gation and fertilization treatments in the North ChinaPlain. Yang et al. (2011) also found that the APSIMmodel could reasonably simulate the dynamics of win-ter and spring wheat production in semi-arid areasof Northwest China. Luo et al. (2011) indicated thatthe model performed well in predicting SOC dyna-mics in the top 30 cm soil at an Australian semi-aridwheat belt. So far, there seems to be no study on theperformance of the APSIM model in predicting long-term SOC dynamics in different agro-ecosystems acrossChina.</p><p>Most of northern China has a semi-humid or semi-arid climate. Crop (mainly wheat and/or maize) pro-duction is highly constrained by limited water re-sources, relatively low soil fertility, and poor agricul-tural management practices (Wang et al., 2007). Irri-gation where water is available, application of mine-ral fertilizers and/or organic manure, and crop residueretention have been promoted as strategies to in-crease crop productivity and maintain soil fertility.Traditionally, only 15%25% of the crop residues werereturned to the field after harvest, with the rest re-moved mainly for cooking and heating in the rural a-reas (Wang and Feng, 2004; Li et al., 2005; Wang et al.,2007; Liu et al., 2008). Recently, residue retention isencouraged for promoting SOC sequestration. Howe-ver, the potential impact of residue return on soil Csequestration across regions is unknown.</p><p>Fertilization, particularly nitrogen (N) fertilizer ap-plication, has been widely and increasingly adoptedsince the 1970s in China, motivated by the governmentpolicies to promote grain production. However, exces-sive use of N fertilizer has caused serious environmentalproblems (Ju et al., 2009). The impact of N applica-tion on SOC status is still inconclusive. Generally, Napplication enhances crop production in areas with Ndeficiency, resulting in more crop residues incorporatedinto the soil. However, this view has been challengedby Khan et al. (2007), who reported that the intensiveuse of N fertilizers promotes the decomposition of bothcrop residues and original SOC, leading to a decreasein total SOC of the whole profile, although an increaseof C in the top soil has been widely observed. Con-sequently, optimal fertilization management aiming atbalancing the high crop productivity and SOC needsto be identified in different agro-ecosystems.</p><p>Irrigation development has lifted crop productivitysignificantly in the past three decades, particularly inthe North China Plain. However, excessive use of ir-rigation has led to cessation of river flows and rapiddepletion of groundwater resources (Wang et al., 2002,2008a). This might have profound implications on bothcrop productivity and SOC. Irrigation not only affectsthe carbon production by crops, but can also influencethe soil water status and SOC decomposition. Litera-ture studies suggest that information about the impactof irrigation change on SOC dynamics is rather lim-ited.</p><p>The objectives of this study were to: 1) use ex-perimental data from four sites distributed in nor-thern China to examine the performance of the AP-SIM model for simulation of long-term SOC dyna-mics under cropping systems with different fertilizationand residue management practices, and 2) apply thevalidated APSIM model to investigate SOC dynamicsas influenced by management scenarios with varyingN application rates, stubble retention fractions, andamounts of irrigation.</p><p>MATERIALS AND METHODS</p><p>Experimental sites and treatments</p><p>Four experimental sites from northern China, Go-ngzhuling, Urumqi, Zhengzhou, and Xuzhou, were se-lected for this study (Table I). They belong to theexperimental sites of the National Long-Term Fertili-sation Experimental Network in China (Zhao et al.,2010). Zhengzhou and Xuzhou had been in arablecropping for at least 100 years before the experi-ments started in 1980 and 1990, and Gongzhuling and</p></li><li><p>SOIL C SEQUESTRATION AND MANAGEMENT PRACTICES 531</p><p>Urumqi had been cultivated for at least 50 years be-fore the experiments started in 1990. At each site, cropbiomass and grain yields were recorded at harvest eve-ry year. SOC and soil total N in the 020 cm soillayer were also measured at the start of the experi-ment and each year after autumn harvest (i.e., du-ring SeptemberOctober). At each site, although noreplicates were designed in the experiment, but soilsamples were taken from five randomly selected loca-tions in each plot to get average values. An auger with5-cm internal diameter was used to take soil samplesin the plough layer (020 cm) at the five randomlyselected locations. The fresh soil samples were thenmixed completely, air-dried and sieved through a 2.0-mm sieve and stored for further analysis. Soil organiccarbon content in the top 30 cm soil layer was de-rived from the measured top 20-cm SOC, according toSOC vertical distribution (Jobbagy and Jackson, 2000;Mikhailova and Post, 2006; Qin and Huang, 2010), bytimes the later by 1.32. The crop and soil data wereobtained from Zhang et al. (2009, 2010) and Zhao etal. (2010). Table I shows the site information, and Ta-ble II gives the initial soil properties at the start of thefield experiments.</p><p>During the experimental period, a single crop-</p><p>ping system, continuous mono-cropping of maize atGongzhuling and a maize-wheat-wheat rotation (i.e.,maize cropping for one year and wheat cropping fornext two years) at Urumqi, was adopted. Maize forthese two sites was sowed during late April to earlyMay, spring wheat in mid-April, and winter wheat inlate September of the same year. At Zhengzhou andXuzhou, a double cropping system of winter wheatand summer maize rotation was adopted, with sum-mer maize sowed in late April to early May and win-ter wheat sowed in October of the same year. Due tothe relatively low annual precipitation and high an-nual evaporation, irrigation was routinely applied du-ring the crop growing seasons at the study sites exceptGongzhuling. Weeds were controlled by hand weedingor herbicides.</p><p>There were a total of eight treatments at thefour selected sites in the original design for fertili-zer applications, covering combinations of N, phospho-rus (P), and potassium (K) fertilizer applications andstubble management. Data from three treatments atGongzhuling, Urumqi, and Zhengzhou were used totest the APSIM model performance, including non-fertilization control (CK), application of mineral ni-trogen, phosphorus and potassium fertilizers (NPK),</p><p>TABLE I</p><p>Locations and climate conditions (19612010) at the four selected study sites in northern China</p><p>Site Latitude Longitude Absolute Climatea) Mean annual Annual Mean annual Study</p><p>altitude temperature rainfall radiation peroid</p><p>m C mm MJ m2</p><p>Gongzhuling 10330 N 12448 E 220 CT, SH 7.1 608 15.7 19902004Urumqi 4358 N 8726 E 600 MT, SA 7.8 262 16.8 19902004Zhengzhou 3447 N 11340 E 21 WT, SH 15.0 630 13.6 19902003Xuzhou 3339 N 11652 E 20 WT, H 15.0 848 15.1 19802003</p><p>a)CT = cool-temperate; MT = mild-temperate; WT = warm-temperate; SH = semi-humid; SA = semi-arid; H = humid.</p><p>TABLE II</p><p>Initial physical and chemical characteristics of the top 30 cm soil at the four selected study sites in northern Chinaa)</p><p>Site Soil type Bulk Sand Silt Clay Total pH in Initial soil organic C (030 cm)b)</p><p>density N waterFOM BIOM HUM Inert C Total C</p><p>g cm3 % g kg1 t ha1</p><p>Gongzhuling Black 1.19 38 30 32 1.42 7.2 0.40 0.53 33.00 8.45 42.37</p><p>Urumqi Grey desert 1.25 19 53 28 0.91 8.1 0.26 0.53 22.57 5.41 28.78</p><p>Zhengzhou Fluvo-aquic 1.55 27 60 13 0.67 8.3 0.13 0.26 6.73 14.78 21.91</p><p>Xuzhou Yellow fluvo-aquic 1.25 49 43 8 0.66 8.2 0.13 0.26 5.28 15.71 21.38</p><p>a)The quantity of soil organic carbon (SOC) in the 2030 cm layer (SOC20-30) was not reported in the literature, so the observed SOC</p><p>density in the topsoil (030 cm) (SOC0-30) was corrected (SOC0-30 = 1.32 SOC0-20), according to Jobbagy and Jackson (2000) andQin and Huang (2010).b)In the APSIM model, soil organic matter is divided into three conceptual pools, including fresh organic matter (FOM) pool, a more ac-</p><p>tive carbon (BIOM) pool, and a humic (HUM) pool. The FOM pool contains all the fresh organic matter, such as dead crop roots and</p><p>incorporated residues, and is further split into three subpools, i.e., carbohydrate-like (CH), cellulose-like (CL), and lignin-like (LIG)</p><p>pools. The BIOM pool represents the soil microbial biomass and microbial products. The HUM pool comprises the rest of the soil</p><p>organic matter, part of which is considered to be highly resistant to microbial decomposition (Inert C).</p></li><li><p>532 G. C. WANG et al.</p><p>and mineral NPK fertilization combined with stub-ble retention (NPKSt). Only CK and NPK were usedat Xuzhou. Under CK and NPK, wheat straw andmaize stover were cut to ground and removed from thefield after the grain harvest each year, while roots andlitters were left in the field for all the study sites. Un-der NPKSt, 7 500 kg ha1 of maize stover was scat-tered and applied as green manure around mid July atGongzhuling, all crop (maize or wheat) straw was scat-tered and applied to the field after harvest at Urumqi,and only maize stover was scattered and applied beforesowing of wheat...</p></li></ul>


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