Carbon sequestration in a nectarine orchard as affected by ... · built and nectarine trees were planted exactly same as T 2. The cuttings of A. pintoi were planted within the terraces

208 E u r o p e a n J o u r n a l o f H o r t i c u l t u r a l S c i e n c e

Eur. J. Hortic. Sci. 80(5), 208–215 | ISSN 1611-4426 print, 1611-4434 online | http://dx.doi.org/10.17660/eJHS.2015/80.5.2 | © ISHS 2015

Carbon sequestration in a nectarine orchard as affected by green manure in ChinaY.X. Wang, B.Q. Weng, J. Ye, Z.M. Zhong and Y.B. HuangInstitute of Agricultural Ecology, Fujian Academy of Agricultural Sciences, Fuzhou, China

Original article

The topsoil organic carbon (SOC) content (Grossman and DeJong, 1998; Robertson et al., 2000; Janssens et al., 2003), soil organic carbon density (SOCD) (Wang et al., 2010), and total carbon storage (Ordόñez et al., 2008) of or-chards were higher than those of annual herbaceous crops, grasslands and agriculture, but lower than forests. Novara et al. (2012) found that the conversion of natural vegeta-tion to orchards (vineyards and olive groves) decreased SOC. However, other studies found that SOC density (Fang et al., 2012) and SOC sequestration (Chen et al., 2007) of orchards were lower than grassland, shrubland, and aban-doned cropland. These controversial results indicated the need to further research on carbon sequestration of or-chards.

Carbon sequestration is related to not only land-use types, but also soil management practices of orchards (e.g., no tillage, straw and grass as so-called ‘green manure’). Orchards often employ conventional management with a lack of soil cover to reduce the competition between trees and weeds for water and nutrients; this management can induce roughness and may have serious impacts on vege-tation and soil carbon storage, by increasing erosion and emission of soil carbon to atmosphere (Francia Martínez et al., 2006; Freibauer et al., 2004). However, reducing tillage intensity, such as no tillage, can be positive effec-tive for SOC sequestration (Zibilske et al., 2002; Ramos et al., 2011), and conservation tillage systems, such as green manure, are more effective in retaining SOC, thereby main-taining a relatively higher level of SOC than conventional tillage systems (Zhang et al., 2005; Wu et al., 2011; Ramos

German Society for Horticultural Science

SummaryInformation is scarce on long-term effects of

green manure on carbon storage in fruit orchards, an important issue for carbon footprinting according to PAS 2050-1 not only in Europe. Thus, for assessing carbon sequestration, the carbon distribution in the vegetation, litter and soil within the same nectar-ine orchard was compared with three management practices such as sloping plot without conservation measures (T1), a terraced plot without conservation measures (T2), and a terraced plot with green ma-nure of Arachis pintoi ‘Amarillo’ as mulch (T3), with the following results: (a) carbon storages of fruit tree and litter in the nectarine orchard ranged from 13.0 to 14.7 t carbon ha-1, and 0.54 to 0.59 kg carbon per plant, respectively. No significant difference was found between different treatments. However, the carbon storage from A. pintoi increased to 5.12 t car-bon ha-1 in the T3 treatment. (b) Soil organic carbon (SOC) and soil organic carbon density (SOCD) in T3

treatment significantly increased compared with T1 and T2 treatments, and decreased with the increase of soil depth. A significant difference was observed between every soil layers in T3 treatment. (c) During the 13 years after orchard establishment, the soil organic carbon sources influenced the δ13C distribu-tion with depth and carbon originate. The upper soil layer SOC turnover in T3 treatment (a mean 63.1% of replacement in the 0–20 cm soil layer after 13 years) was 1.59 and 1.41 times greater than those of T1 and T2 treatments, respectively, indicating that terraced nectarine orchard with A. pintoi as green manure could rapidly sequester SOC in subtropical China.

Keywordscarbon footprint, soil organic carbon, δ13C, carbon sequestration, nectarine, PAS 2050-1

Significance of this studyWhat is already known on this subject? • Orchards, as one of the semi-permanent cultivation

practices, occupy over 4.8×105 km2 in the world. Information is scarce on long-term effects of green manure on carbon storage in fruit orchards, an im-portant issue for carbon footprinting according to PAS 2050-1 not only in Europe.

What are the new findings? • The green manure mulch practice had no significant

impact on fruit tree biomass carbon storage, and sig-nificantly increased organic carbon storage in 0–100 cm soil layer.

What is the expected impact on horticulture? • The adoption of Arachis pintoi in terraced orchards

rapidly increases carbon sink and offers great eco-logical benefits.

IntroductionDuring the last century, the carbon dioxide (CO2) con-

centration in the atmosphere increased from 280 to 367 ppm. The land-use to land-cover change, including conver-sion of forest and grassland to cultivation, is the second most important source of CO2 emissions (IPCC, 2001; Lal., 2004, 2007; Ceschia et al., 2010). Orchards, as one of the semi-permanent cultivation practices, occupy over 4.8×105 km2 in the world. China is the largest fruit grower world-wide with 1.1×105 km2 in 2009, accounting for 1.14% of the land area of China and 23% of orchard areas of the world, respectively.

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Wang et al. | Carbon sequestration in a nectarine orchard as affected by green manure in China

et al., 20 11). Wu et al. (2011) found higher organic carbon in Citrus orchards intercropped with green manure such as white clover and straw mulching than with conventional management. Na varro-Cerrillo et al. (2009) indicated that the soil under green manure had higher soil organic mat-ter levels in comparison to the cultivated soil in Mediter-ranean afforestation, and the response of green manure differed between species and environmental conditions. It illustrated that carbon sequestrations of orchards is af-fected by not only green manure, and related to covered grass species.

As a special practice of vegetation management, the carbon sequestration of orchards is affected by texture, topography and climatic conditions, especially land-use practices (e.g., trim, fertilization and harvest of fruits) (Vesterdal et al., 2002; Zinn et al., 2005; Homann et al., 2004; Shukla and Lal, 2005), which increased the complex-ity and uncertainty of ecosystem carbon cycle research. Despite efforts made in recent years to determine the pro-cess of carbon sequestration there is still a lot of uncer-tainty about the effects of different management practices on carbon sequestration of a nectarine orchard in a hillside red soil. This study estimated the carbon stocks, distribu-tion and δ13C value in a nectarine orchard under different management practices. In PAS 2050-1, any accounted car-bon sequestration can be offset in the carbon footprint of a fruit crop. The aim of this paper was to assess the effects of different management practices on carbon sequestration using a fruit orchard in a hillside region of China.

Materials and methods

Site descriptions and soil characteristicsThe study site was a nectarine orchard planted in 1996

on YuChi village of SanMing City, Fujian Province, China (26°25’N, 117°57’E); it was located about 150 m above sea level. The region is a mild, subtropical monsoon cli-mate with high temperature and humidity in summer and cool climate in winter. The annual average temperature is 19.2°C, with the lowest in January reaching from 9.0 to 12.0°C and the highest in July, from 26.6 to 28.9°C. Annual rainfall during the period of study was 1,620 mm and an-nual sunshine 4,289 h. The soil type is a red loam. The basic physical and chemical properties of soils sampled in 1996 are summarized in Table 1. The constructive species of original vegetation was Miscanthus (Miscanthus flordulus) and Mans (M. sinensis) in the site, which were all C4 plants. The grassland (denoted G) was reclaimed into orchard in 1996.

Experiment designThe experiment started from 1996. Nine plots were

used to assess the management measures on carbon se-questration in a randomized complete block design with three replicates. The nine plots were separated by concrete borders that extended 15 cm aboveground. The size of each experimental plot was 100 m2 (4 x 25 m). The treatments were: a sl op ing nectarine plot without conservation mea-sures, denoted as T1. In T1 treatment, eight rows of nectar-ine trees spacing at 80 x 80 cm were planted on the slope, weeds were allowed growing in natural conditions but re-moved by hand-pulling 3–4 times per year. Terraced nec-tarine orchard without conservation measures, denoted as T2. In T2 treatment, eight terraces were built on the natural slope, each with a soil ridge (approximately 15 cm high) in

front and a shallow ditch (with width and depth of 15 cm) behind the ridge. In the middle of each terrace, four pits with the diameter of 80 cm were dug to 80 cm for nectarine tree planting; weeds were managed in the same as T1. The t erraced nectarine orchard with Arachis pintoi as green manure, denoted as T3. In T3 treatment, eight terraces were built and nectarine trees were planted exactly same as T2. The cuttings of A. pintoi were planted within the terraces on April, 1996. They withered aboveground shoots in win-ter, and naturally emerged in the next spring.

Each nectarine tree was fertilized in April, with 0.35 kg FCMP (calcium-magnesium phosphate fertilizer), 0.5 kg specialty fertilizer for fruit (N: P: K=16:16:16 or 15:15:15), 0.25 kg superphosphate and 0.25 kg potassium chloride ev-ery years and their necta rine fruits harvested when ripe.

Sampling methods 1. Plant sampling. All fruit trees (including tree height, crown size and ground diameter) in each plot were sur-veyed on November, 2008. Two fruit trees representing the stand-specific ground-diameter and height range were selected and sampled destructively in each plot. The trees were cut at a height of 20 cm above the ground. Prior to branch removal, representative branches from the low-est to the highest throughout the crown were sampled. All branches were then clipped from the tree, and fresh weights were determined using balance. The stems of each tree were cut in 50 cm sections and weighted using balance. A disk (approximately 5 cm wide) was cut from the stump to the top of each stem section to determine moisture con-tent. The entire root system was dug up and washed lightly to remove soil particles. All tissues were oven-dried at 70°C to determine moisture content. The total dry weight for each component (branches, stem, and root) was calculated. The fruits of 5 trees, randomly chosen in nine plots, were harvested and weighed to determine the production dur-ing the harvest seasons from 2006 to 2008.2. Litterfall sampling. Litter was collected with the use of three 4 x 4 m litter traps per plot. The traps were located permanently, about 20 cm off the ground and 2 m from fruit trunk along the canopy waterdrip. During the 12-month period, from March 2006 to April 2007, litter was collected at monthly intervals and sorted into four categories: (1) foliage; (2) flower; (3) branches; and (4) fruit, and an oven-dry weight (70°C) was determined for individual samples. Individual samples from each category were then bulked and ground in a rotary mill (sieve ±0.5 mm mesh) prior to chemical analysis.3. Grass sampling. Three squares of 50 x 50cm were ran-domly established in T3 treatments. In each square, the above-ground grasses were cut along ground and collected for the classes of green part and litter, and then the entire root system of grasses were collected and weighted indi-vidually. All samples were dried at 70°C and weighted.4. Soil sampling. Three samples in each plot were ran-domly selected by collecting of the following layers: 0–20 cm, 20–40 cm, 40–60 cm, 60–80 cm and 80–100 cm depth. The samples were immediately taken to the laboratory, sieved through a 0.9 mm sieve to determine soil organic carbon.

Organic carbon determination methods 1. Organic carbon content in plant. The organic carbon storage was calculated by multiplying the dry biomasses of fruit, litter and grass with their organic carbon concen-




trations, and converted to kg C ha-1. The organic carbon concentrations in plant samples were determined by the potassium dichromate oxidation method (Liu et al., 1996).2. Soil organic carbon content. Soil organic carbon was measured on a 0,5 g sample using wet chemistry (Walkley and Black, 1934). Soil organic carbon density (SOCD, t C ha-1) was calculated with the following formula:

(1)

where Ci is the soil organic carbon content (g kg-1), Hi is the depth of each soil layer (cm), and Bi is soil bulk density of each soil layer (g kg-1).

Organic carbon stable isotopic analysisThe δ13C of organic materials (litter and soil samples)

are measured was conducted with an isotope ratio mass spectrometer (Finnigan MAT-251) in Chinese Academy of Forestry Science, Beijing, China. The 13C abundance is ex-pressed in delta (d) per mil (‰) and calculated as follows (Peri et al., 2012):

δ13C(‰) = [(Rsample / Rstandard) -1] × 1000 (2)

where, Rsample and Rstandard are respectively the isotope ra-tio 13C/12C of a sample and a reference material, the latter is from a belemnite carbonate from the Pee Dee formation of North Carolina, USA.

According to Wang et al. (2007), a modified linear model equation applied to estimate plantation (C3) and grass(C4)-derived SOC proportions is given by:

δS = f δA + (1 – f ) δ0 (3)

where, δS is the δ13C of the soil organic carbon(SOC) in the surface soil horizon of the orchard, δA is the δ13C of fruit trees litter, δ0 is the δ13C of the SOC in the surface soil hori-zon of the virgin grassland, f is the fraction of SOC originat-ing from the litter (fruit trees or groundcover).

Statistical analysisThe SPSS 12.0 software was used for statistical analy-

sis. One-way ANOVA was performed to calculate the Fish-er’s LSD (least significant difference). Significance was determined at α=0.05 from each treatment separately.

Results

Carbon in the litterLitter biomasses of nectarine orchard pointed out a

seasonal in the litter production because of plant growth characteristics and phenological regularity. Two peaks of litter production were found throughout the year, with the first in March and April, 2006, and the second in Au-gust and September, 2007 (Figure 1). The annual litter bio-masses for the three treatments were from 0.54 kg carbon per plant to 0.59 kg carbon per plant without significant differences among T1, T2 and T3 treatments. There was a great difference in the components of annual litter among them; the percentage of leaf litter was the highest, ranging from 94.5% to 97.4%.

Carbon in the fruit trees and groundcover vegetationThe measure of fruit biomass was taken in November,

when nectarine leaves had already dropped so that carbon storage in leaves was not calculated. The vegetation carbon stocks of nectarine orchard under different management practices ranged from 13.0 to 14.7 t carbon ha-1 (Figure 2). No significant differences were found between treatments T1, T2 and T3. Most of the carbon storage in the nectarine trees came from branches, ranging from 63–67% of total vegetation carbon storage, the second pool was from roots, ranging from 21–28%, and the least was from the tree trunk with only 9–14%. The order of fruit productions was: T1>T2>T3, but there were no significant differences among the three treatments. In addition, the carbon storage in Arachis pintoi ‘Amarillo’ in T3 treatment was 5.12 t carbon ha-1.

Soil organic carbon (SOC) content and soil organic carbon density (SOCD)

Two-way ANOVA indicated that orchard management practices and soil depth had a significant effect on SOC content (Figure 3). Compared with treatments T1 and T2, SOC content for T3 treatment significantly increased from 14.9% to 46.5% and from 7.4% to 15.3%, respectively, and it decreased with the increase of soil depth in all the treat-ments. There were no significant differences in SOC con-tent among the soil layers of 0–20 cm, 20–40 cm and 40–60 cm for treatments T1 and T2. However they for T1 increased by 165% and 244%, 149% and 223%, 136% and 196% than that for the soil layers of 60–80 cm and 80–100 cm, respec-tively, and for T2 treatment increased by 229% and 309%, 177% and 245%, 138% and 206%. In T3 treatment, there were significant differences among different soil layers, and SOC contents in the soil layers of 0–20 cm, 20–40 cm and 40–60 cm increased by 165% and 245%, 121% and 188%, 68.0% and 118% than that for the soil layers of 60–80 cm and 80–100 cm, respectively.

Orchard management practices and soil depths had a significant effect on soil organic carbon density SOCD, and the change trend was similar to the SOC content. SOCD of T3 treatment significantly increased from 4.75% to 27.0% and from 0.42% to 4.13% compared to T1 and T2 treatments, re-spectively, whereas SOCD decreased with depth increase in T1, T2 and T3 treatments. In T1, T2 and T3 treatment, SOCD in the soil layers of 0–20 cm, 20–40 cm and 40–60 cm was significantly higher than those of in the soil layers of 60–80 cm and 80–100 cm, ranging from 134%–260%, 87.2%–190%, 63.7%–178%, respectively.

Soil δ13C value and source of organic carbon in the nectarine orchard1. Soil δ13C value. Plants with a C3 pathway have δ13C val-ues in the range of -35‰ to -20‰, while those with a C4 pathway have higher δ13C values, ranging from -19‰ to -9‰ (Bernoux et al., 1998; Staddon, 2004). Because values of soil δ13C are close to that of adjacent vegetation, changes in soil δ13C during transitions from C3 to C4 vegetation could be used to estimate turnover times of soil organic carbon (Bernoux et al., 1998). Conversion from grassland to orchard plantation (C4→C3) caused a decrease in the soil δ13C values of nectarine trees and A. pintoi. The soil δ13C value of original grassland (G) was -20.5‰. Constructive Miscanthus and Mans were C4 plants, whose leaf of organic carbon δ13C values were between -13.4‰ and -13.7‰. In our study, the mean value of δ13C from the litters of fruit trees (C3) and green manure (C3) were -28.5‰ and -29.9‰, respectively. When the original grasslands were reclaimed

brancheswerethenclippedfromthetree,andfreshweightsweredeterminedusingbalance.Thestemsofeachtreewerecutin50cmsectionsandweightedusingbalance.Adisk(approximately5cmwide)wascutfromthestumpto the topofeachstemsection todeterminemoisturecontent.Theentirerootsystemwasdiggingandwashedlightlytoremovesoilparticles.Alltissueswereoven-driedat70°Ctodeterminemoisturecontent.Thetotaldryweightforeachcomponent(branches,stem,androot)wascalculated.Thefruitsof5trees,randomlychoseninnineplots,wereharvestedandweighedtodeterminetheproductionduringtheharvestseasonsfrom2006to2008.2. Litterfall sampling.Litterwascollectedwiththeuseofthree4x4mlittertrapsperplot.Thetrapswerelocatedpermanently,about20cmoffthegroundand2mfromfruittrunkalongthecanopywaterdrip.Duringthe12-monthperiod,fromMarch2006toApril2007,litterwascollectedatmonthlyintervalsandsortedintofourcate-gories:(1)foliage;(2)flower;(3)branches;and(4)fruit,andanoven-dryweight(70°C)wasdeterminedforindi-vidualsamples.Individualsamplesfromeachcategorywerethenbulkedandgroundinarotarymill(sieve±0.5mmmesh)priortochemicalanalysis.3. Grass sampling. Threesquaresof50x50cmwererandomlyestablishedinT3treatments.Ineachsquare,theabove-groundgrasseswerecutalonggroundandcollectedfortheclassesofgreenpartandlitter,andthentheentire root system of grasses were collected and weighted individually. All samples were dried at 70°C andweighted.4. Soil sampling. Threesamplesineachplotwererandomlyselectedbycollectingofthefollowinglayers:0–20cm,20–40cm,40–60cm,60–80cmand80–100cmdepth.Thesampleswereimmediatelytakentothelaboratory,sievedthrougha0.9mmsievetodeterminesoilorganiccarbon.Organic carbon determination methods 1. Organic carbon content in plant. Theorganiccarbonstoragewascalculatedbymultiplyingthedrybiomassesoffruit,litterandgrasswiththeirorganiccarbonconcentrations,andconvertedtokgCha-1.Theorganiccarbonconcentrationsinplantsamplesweredeterminedbythepotassiumdichromateoxidationmethod(Liuetal.,1996).2. Soil organic carbon content. Soilorganiccarbonwasmeasuredona0,5gsampleusingwetchemistry(WalkleyandBlack,1934).Soilorganiccarbondensity(SOCD,t C ha-1)wascalculatedwiththefollowingformula:

SOC � �� × �� × �� × 10�

�

(1) whereCiisthesoilorganiccarboncontent(g kg-1),Hiisthedepthofeachsoillayer(cm),andBiissoilbulkdensityofeachsoillayer(g kg-1).Organic carbon stable isotopic analysis

Theδ13Coforganicmaterials(litterandsoilsamples)aremeasuredwasconductedwithanisotoperatiomassspectrometer(FinniganMAT-251)inChineseAcademyofForestryScience,Beijing,China.The13Cabundanceisexpressedindelta(d)permil(‰)andcalculatedasfollows(Perietal.,2012):

δ13C(‰)=[(Rsample/Rstandard)-1]×1000 (2)where,RsampleandRstandardarerespectivelytheisotoperatio13C/12Cofasampleandareferencematerial,the

latterisfromabelemnitecarbonatefromthePeeDeeformationofNorthCarolina,USA.According toWangetal. (2007),amodified linearmodelequationapplied toestimateplantation(C3)and

grass(C4)-derivedSOCproportionsisgivenby:δS=fδA+(1–f)δ0 (3)

where,δSistheδ13Cofthesoilorganiccarbon(SOC)inthesurfacesoilhorizonoftheorchard,δAistheδ13Coffruittreeslitter,δ0istheδ13CoftheSOCinthesurfacesoilhorizonofthevirgingrassland,fisthefractionofSOCorigi-natingfromthelitter(fruittreesorgroundcover).Statistical analysis

TheSPSS12.0 softwarewasused for statistical analysis.One-wayANOVAwasperformed to calculate theFisher’sLSD(leastsignificantdifference).Significancewasdeterminedatα=0.05fromeachtreatmentseparately.

Results




Figure 1. Dynamics of litter biomass from nec-tarine orchards under different management practices from March 2006 to March 2007. T1: sloping nectarine orchard without conserva-tion measures; T2: terraced nectarine orchard without conservation measures; T3: terraced nectarine orchard with A. pintoi as green manure mulch.

Figure 2. Amount of carbon in fruit tree vegeta-tion under different management practices. T1: sloping nectarine orchard without conserva-tion measures; T2: terraced nectarine orchard without conservation measures; T3: terracednectarine orchard with A. pintoi as green manure mulch. Different small letters mean significant difference between different treat-ments at 0.05 level.

Figure 3. Variation of soil organic carbon (SOC) content in different soil layers. T1: sloping nectarine orchard without conservation mea-sures; T2: terraced nectarine orchard without conservation measures; T3: terraced nectarine orchard with A. pintoi as green manure mulch. Different small letters mean significant differ-ence between different treatments in the same soil layer at 0.05 level.

Figure 4. Soil organic carbon density (SOCD) in different soil layers. T1: sloping nectarine orchard without conservation measures; T2: terraced nectarine orchard without conserva-tion measures; T3: terraced nectarine orchard with A. pintoi as green manure mulch. Differ-ent small letters mean significant difference between different treatments in the same soil layer at 0.05 level.

Figure1.DynamicsoflitterbiomassfromnectarineorchardsunderdifferentmanagementpracticesfromMarch2006toMarch2007.T1:slopingnectarineorchardwithoutconservationmeasures;T2:terracednectarineorchardwithoutconservationmeasures;T3:terracednectarineorchardwithA.pintoiasgreenmanuremulch.

Figure2.Amountofcarboninfruittreevegetationunderdifferentmanagementpractices.T1:slopingnectarineorchardwithoutconservationmeasures;T2:terracednectarineorchardwithoutconservationmeasures;T3:ter-racednectarineorchardwithA.pintoiasgreenmanuremulch.Differentsmalllettersmeansignificantdifferencebetweendifferenttreatmentsat0.05level.

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Figure 3. Variation of soil organic carbon (SOC) content in different soil layers. T1: sloping nectarine orchard with-out conservation measures; T2: terraced nectarine orchard without conservation measures; T3: terraced nectarine orchard with A.pintoi as green manure mulch. Different small letters mean significant difference between different treatments in the same soil layer at 0.05 level.

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Figure 4. Soil organic carbon density (SOCD) in different soil layers. T1: sloping nectarine orchard without conser-vation measures, T2; terraced nectarine orchard without conservation measures; T3: terraced nectarine orchard with A.pintoi as green manure mulch. Different small letters mean significant difference between different treat-ments in the same soil layer at 0.05 level.

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Figure 3. Variation of soil organic carbon (SOC) content in different soil layers. T1: sloping nectarine orchard with-out conservation measures; T2: terraced nectarine orchard without conservation measures; T3: terraced nectarine orchard with A.pintoi as green manure mulch. Different small letters mean significant difference between different treatments in the same soil layer at 0.05 level.

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Fig. 4 Soil organic carbon density (SOCD) in different soil layers

T1: sloping nectarine orchard without conservation measures,T2: terraced nectarine orchard without conservation measures, T3:terraced nectarine orchard with A.pintoi as green manure mulch. Different small letters mean significant difference between dif-

ferent treatments in the same soil layer at 0.05 level.

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orchard, the soil δ13C value changed. Figure 5 shows the dif-ference among δ13C values for the different orchard man-agement practices. Within different management practices, the order of soil δ13C value was T1>T2>T3; soil δ13C values of T1 and T2 treatments were similar, but significantly higher than T3 treatment. In T3 treatment, the litters were formed not only from nectarine trees but also A. pintoi with a low δ13C value (-29.9‰). Therefore the litter residues into soil would show a decreasing δ13C value. We also found that the soil δ13C values increased with the increase of soil depth in the three treatments; it may be caused by isotopic fraction-ation effects during decomposition process.2. Fruit trees and grass contribution to SOC. Equation (3) was used to estimate the proportion of grass-derived and planted fruit trees and green manure derived C in the soil surface layer. Table 2 showed that grass-derived SOC is a very high proportion of the total SOC in T1 and T2 treatments, accounting for 55.3%–60.4% of the total. Meanwhile, there was a slight difference in SOC composi-tion between T1 and T2 treatments; it may be caused by the

different amount of litter removed by runoffs. The lowest proportion of grass-derived SOC (36.9%) and the highest proportion (63.1%) of SOC derived from fruit trees and green manure were in T3 treatment. Because no significant differences of organic carbon from fruit litter were found between T2 and T3 treatments (Figure 1), we assumed that SOC derived from fruit trees in T3 treatment was the same as the amount of T2 treatment, and estimated the propor-tion of green manure-derived SOC (25.22%). This result, from another point of view, indicated that conversion of wild grasslands to orchards was not supported; however, soil organic carbon pool was stabilized by green manure mulch.

Discussion

Carbon storage in soil Carbon sequestration in soils is considered to be an

important option for the mitigation of increasing atmo-spheric CO2 concentrations as a result of climate change. Thus, management strategies to increase SOC were stud-ied (Leinfelder, 2012; Lal and Kimble, 2000). For example, conservation tillage practices, such as no tillage and with grass coverage, increase the soil organic carbon because it reduces disturbances from tillage and the risks of erosion, enhances organic residues into soil, and thus improves soil carbon sequestration (Castro et al., 2008; Sainju et al., 2002; Pulleman et al., 2005). Effect of green manure mulch and management practices in fruit orchard on soil organic carbon storage was not very well defined. On the other hand, plant communities, covering soil surface, contribute to soil carbon sequestration through the deposition of leaf litter, dead root material, and rhizodeposition (Saner et al., 2007; Peri et al., 2012). The addition of organic residues is

Figure 5. The value of δ13C in orchard soil un-der different management practices. T1: slop-ing nectarine orchard without conservation measures; T2: terraced nectarine orchard without conservation measures; T3: terraced nectarine orchard with A. pintoi as green manure mulch.

Table 1. Physical and chemical properties of orchard soil sampled in 1996.

Soil layerClay particle (%)

pH Organic matter (g kg-1)

CEC (cmol kg-1)

Water soluble acid (cmol kg-1)>0.01 mm <0.01 mm

0~20 cm 45.1 55.0 4.35 23.1 73.5 57.420~40 cm 42.0 58.0 4.39 20.3 61.0 51.5

Soil layer Total nitrogen(g kg-1)

Total phosphorus (g kg-1)

Available nitrogen (mg kg-1)

Available phosphorus (mg kg-1)

Available potassium (mg kg-1)

0~20 cm 0.96 0.23 101 / 31.620~40 cm 0.79 0.23 92.4 / 19.6

Table 2. The composition of soil organic carbon from orchards under different management practices.

TreatmentTotal SOC

(g kg-1)

SOC from wild

grassland (g kg-1)

SOC from

nectarine (g kg-1)

SOC from green

manure (g kg-1)

T1 14.8 8.95 5.87 –T2 17.9 9.88 7.98 –T3 21.1 7.80 7.98 5.32G 19.5 19.5 – –

Figure5.Thevalueofδ13Cinorchardsoilunderdifferentmanagementpractices.T1:slopingnectarineorchardwithoutconservationmeasures,T2:terracednectarineorchardwithoutconservationmeasures,T3:terracednec-tarineorchardwithA.pintoiasgreenmanuremulch.

.

-27

-26

-25

-24

-23

-22

-21

δ13 C(‰

)

0-20 cm 20-40 cm

T1 T2 T3




the only way to increase soil organic carbon levels (Fage-ria, 2007). The green manure mulch was expected to have a significant positive influence on soil carbon sequestra-tion. In this study, the result was also positive. Compared to the sloping and terraced nectarine orchards without conservation measures, the SOC content and SOCD in the terraced nectarine orchard with A. pintoi mulch increased from 4.75% to 27.0% and from 0.42% to 4.13%, respec-tively. This result coincides with those published by Mar-quez-Garcia et al. (2013), who observed that organic car-bon of 0–25 cm soil layer in olive orchard with crop cover increased by 38.1% with respect to conventional tillage. However, the result reported by Wilson et al. (2010) indi-cated that soil organic carbon was stable in the upper soil profile for two years after planting two cover crops species (Trifolium repens and Medicago sativa). The effect of green manure on soil organic carbon content is highly related to the amount and only weakly to the type of residue applied (Fageria, 2007). The reason for this discrepancy could be related to a longer period in our case (13 years resp. 2 years); in our study long-term application of green manure const ituted the larger C sink.

Carbon storage of orchard ecosystem At present, research activities on the role of orchard

ecosystems in sequestering atmospheric CO2 remain scarce. Unlike annual crops, orchards for fruit production are able to sequester C for a lifetime period of at least 20–25 consecutive years (Liguori et al., 2009). This study proved that nectarine orchard ecosystems had a high pote ntial for carbon sequestration. Carbon storage of nectarine tree was from 13.0 to 14.7 t C ha-1, being equivalent to 35% of the mean carbon density of forest vegetation in China (Fang et al., 2007). Distribution of total carbon sequestration also showed that carbon stock in aboveground biomass is more than ground biomass, which conforms to the results in Sofo et al. (2005). In addition, green manure can increase CO2 fixation in the nectarine orchard ecosystem. The adoption of specie with a high biomass production is recommended, A. pintoi, with a dry matter of 5.12 t C ha-1, equivalent to 18.77 t ha-1 of CO2. Moreover, in the hillside red soil region, the use of green manure enhances SOC accumulation and can also reduce soil carbon losses to the atmosphere in the form of CO2 (Nieto et al., 2013). In our study, the green ma-nure mulch practice had no significant impact on fruit tree biomass carbon storage and fruit production, and signifi-cantly increased organic carbon storage in 0–100 cm soil layer, suggesting the green manure mulch system was ap-propriate for promoting carbon sequestration of orchard ecosystem. Such results have been reported in some stud-ies focused on biomass growth. For example, Wilson et al. (2010) reported that the cover crop management practice and species selection had no significant impact on height growth and needle dry weight of Abies fraseri. Liu et al. (2013) also found orchard sod cultivation did not signifi-cantly affect the economic performance of orchard produc-tion. However, there are also several reports on competi-tion for nutrients leading to depressed growth (Walsh et al., 1996). The reason for this discrepancy could be related to the adoption of species and management measures. Thus our conclusion is that careful management is necessary to capitalize on the benefits of green manure and avoid the competition from trees and grass.

SOC derived from fruit trees and green manure SOC originates from the litter of aboveground vegeta-

tion, so the litter from these vegetation species may affect soil δ13C variation (Hobbie et al., 2002). Fruit trees and A. pintoi as green manure had low δ13C value, input of organic matters from dead root material, litters and root exudates of them into soil had decreased leading to the decrease in 13C composition in the soil surface layer. Soil organic car-bon from previous plant communities will gradually decay out of the SOC pool and be replaced by new C derived from the subsequent plant communities. In this study we used stable isotopes (δ13C) to evaluate the impact of conversion from grasslands to nectarine orchard with different man-agement p ractices on SOC dynamics. We found that in 0–20 cm soil layer of nectarine orchards without green manure mulch converted from original grassland, 55.3%–60.4% of total C was derived from grassland soils after 13 years, sug-gesting a relatively slow turnover rate of SOC. However, the turnover rate of SOC under nectarine orchard with green manure mulch was slightly faster than those in nectarine orchards without green manure, with SOC derived from fruit tree being 37.8% total C, and from green manure being 25.2%. These results demonstrated that orchard green ma-nure mulch management could rap idly sequester SOC into long-term storage pools in subtropical China. Some studies have also found that orchard sod cultivation had the poten-tial to increase soil C stocks (Liu et al., 2013; Weng et al., 2013). In fact, soil carbon sequestration was affected not only by management, but also by soil and climatic condi-tions (Nieder et al., 2003). Further studies of this type could provide useful information about the relative importance and effects of green manure on soil carbon sequestration in a wide range of soil types, climates and species that may help improve orchard management practices in the future.

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Received: Sep. 16, 2014Accepted: Jun. 23, 2015

Addresses of authors: Y.X. Wang*, B.Q. Weng, J. Ye, Z.M. Zhong and Y.B. HuangInstitute of Agricultural Ecology, Fujian Academy of Agri-cultural Sciences, Fuzhou, Fujian Province, 350003, China* Corresponding author; E-mail: [email protected] Tel.: (011886) 591-83838017 (Office)


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Carbon sequestration in a nectarine orchard as affected by ... · built and nectarine trees were planted exactly same as T 2. The cuttings of A. pintoi were planted within the terraces