Effectbof biochar amendment

Plant Soil (2012) 351:263–275 DOI 10.1007/s11104-011-0957-x

REGULAR ARTICLE

Effect of biochar amendment on maize yield and greenhouse gas emissions from a soil organic carbon poor calcareous loamy soil from Central China Plain Afeng Zhang & Yuming Liu & Genxing Pan & Qaiser Hussain & Lianqing Li & Jinwei Zheng & Xuhui Zhang

Received: 24 May 2011 / Accepted: 9 August 2011 / Published online: 10 September 2011 # Springer Science+Business Media B.V. 2011

Abstract Aims A field experiment was conducted to investigate the effect of biochar on maize yield and greenhouse gases (GHGs) in a calcareous loamy soil poor in organic carbon from Henan, central great plain, China.

Methods Biochar was applied at rates of 0, 20 and 40 tha−1 with or without N fertilization. With N fertilization, urea was applied at 300 kg N ha−1, of which 60% was applied as basal fertilizer and 40% as supplementary fertilizer during crop growth. Soil emissions of CO2, CH4 and N2O were monitored using closed chambers at 7 days intervals throughout the whole maize growing season (WMGS).

Results Biochar amendments significantly increased maize production but decreased GHGs. Maize yield was increased by 15.8% and 7.3% without N fertiliza-

tion, and by 8.8% and 12.1% with N fertilization under biochar amendment at 20 tha−1 and 40 tha−1, respectively. Total N2O emission was decreased by 10.7% and by 41.8% under biochar amendment at 20 tha−1 and 40 tha−1 compared to no biochar amendment with N fertilization. The high rate of biochar (40 tha−1) increased the total CO2 emission by 12% without N fertilization. Overall, biochar amendments of 20 tha−1 and 40 tha−1 decreased the total global warming potential (GWP) of CH4 and N2O by 9.8% and by 41.5% without N fertilization, and by 23.8% and 47.6% with N fertilization, respectively. Biochar amendments also decreased soil bulk density and increased soil total N contents but had no effect on soil mineral N. Conclusions These results suggest that application of biochar to calcareous and infertile dry croplands poor in soil organic carbon will enhance crop productivity and reduce GHGs emissions.

Responsible Editor: Johannes Lehmann.

A. Zhang : Y. Liu : G. Pan (*) : Q. Hussain : L. Li : J. Zheng : X. Zhang Institute of Resource, Ecosystem and Environment of Agriculture, Nanjing Agricultural University, 1 Weigang, Nanjing 210095, China e-mail: gxpan@njau.edu.cn G. Pan e-mail: gxpan1@hotmail.com G. Pan e-mail: pangenxing@yahoo.com.cn

Keywords Biochar . CO2 emission . CH4 emission .

N2O emission . Maize productivity Abbreviations AEN Agronomic N use efficiency EF N fertilizer-induced emission factor of N2O GHGs Greenhouse gases GWP Global warming potential GHGI Greenhouse gas intensity WMGS Whole maize growing season SOC Soil organic carbon

264

Introduction Atmospheric carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) are the key long-lived greenhouse gases (GHGs) forcing global warming. World agriculture accounted for an estimated emission of 5.1–6.1 Pg CO2-equivalents yr−1, contributing 10–12% to the total global anthropogenic emissions of GHGs in 2005 (Smith et al. 2007). While agriculture releases a significant amount of CH4 and N2O to the atmosphere, the net GHGs emission of CO2 equivalents from farming activities can potentially be decreased by changing agricultural management to increase soil organic matter content and/or decrease CH4 and N2O emissions (Mosier et al. 2006; Smith et al. 2008).

Biochar production and application from crop straw has been proposed as one effective countermeasure to mitigate climate change (Lehmann 2007) through increasing soil carbon storage (Lehmann et al. 2006; Fowles 2007) while decreasing direct GHGs emission and improving soil fertility and crop productivity (Major et al. 2010a). The high porosity of biochar may also be very beneficial for improving soil structure and water holding capacity (Karhu et al. 2011; Vaccari et al. 2011) and, therefore, mitigating the increasing drought stress in dryland agriculture due to climate change. Biochar amendment to cropland may have indirect effects on reducing N demand by crop production through enhanced N use efficiency which in turn may reduce the indirect emission of GHGs from N fertilizer industry (Gaunt and Lehmann 2008; Zhang et al. 2010).

Wide variations in the rates of CO2 emissions from soils treated with biochar have been reported in the literature. Major et al. (2010a) reported greater CO2 emissions from a savanna Oxisol in Colombia under amendment of biochar from old mango (Mangifera indica L.) trees. In a field study of biochar from lump-wood applied to an arable soil in Northeast England, Bell and Worrall (2011) observed a significantly higher soil respiration from unplanted plots but no significant increase in carbon emissions from vegetated plots. Karhu et al. (2011) reported no effect of birch biochar on soil respiration from a wheat field in Southern Finland. Nevertheless, an amended Swiss loam soil showed no increase in CO2 evolution with pine wood-derived biochar but with grass-derived biochar (Hilscher et al. 2009). Such effects may also depend on soil organic carbon

Plant Soil (2012) 351:263–275

status. Kimetu and Lehmann (2010) reported a finding that application of biochar led to a reduction in CO2 evolution from SOC-poor soil but to an increased CO2 evolution from SOC-rich soil. More recently, Jones et al. (2011) argued that biochar application to soil could repress the breakdown of native SOC, which could be referred to as a negative priming effect. They concluded that a small shortterm C releases in biochar-amended soil should not overshadow its potential for long-term C sequestration in soil environments.

The emission of CH4 and N2O from croplands is a major concern; therefore their mitigation from agriculture is urgently required (Forster et al. 2007). The substantial effect of biochar amendment on decreasing N2O emissions has been well addressed despite variable effect on CH4 emissions. Rondon et al.

(2005) observed a complete suppression of CH4 emissions from a grass stand (Brachiaria humidicola) and soybean cropland under biochar treatment. Karhu et al. (2011) reported no changes in N2O emission but increased CH4 uptake by wheat field under birch biochar in Southern Finland. As shown in our previous study, Zhang et al. (2010) reported a decrease in total N2O emission by 40–51% and by 21–28% with and without N fertilization, respectively, and also observed a 34–41% increase in total CH4 emissions regardless of N fertilization under amendment of wheat straw-derived biochar from a rice paddy of China. Therefore, the field effects of biochar amendments on crop yield and GHGs emissions may vary with crop and soil types, site condition as well as the properties of biochar used (Spokas and Reicosky 2009; Major et al. 2010a; Wardle et al. 2008; Zhang et al. 2010; Karhu et al. 2011; Zimmerman et al. 2011; Kimetu and Lehmann 2010; Hilscher et al. 2009).

However, there are still few studies addressing the overall effects of biochar on the total global warming potential, integrating the three key greenhouse gases from croplands with regard to crop productivity.

China is one of the largest agricultural countries in the world possessing 12% of the world’s total crop harvest area (FAOSTAT 2002) and consuming almost 1/3 of the world’s chemical N fertilizers (Heffer 2009). Maize (Zea mays L.) is one of the most important staple crops in China, comprising 30 million hectare of harvested area and 155 million metric tons of production in 2010 (Anonymous 2011). With the increasing use of chemical N fertilizers, high C

Plant Soil (2012) 351:263–275

Materials and methods Experiment site The field experiment was situated in Linzhuang Village (34°32′N, 115°30′E), Liangyuan District, Shangqiu City, Henan Province, China, lying in the Central Great Plain of Yellow River-Huaihe River in North China. Under a semi-humid temperate monsoon climate, the local area has a mean annual temperature of 13.9°C, an annual sunshine time of 2510 h and frost-free days of 230 day as well as precipitation of 780 mm and potential evaporation of 1735 mm. During the growing season, the mean air temperature of the site changed from 34°C in early July to 17°C in late September. Data for precipitation and temperature during the whole maize growing season were presented in Fig. 1. Derived from alluvial

100

Precipitation Max.temperature

Min.temperature

40

80

60 20 40

Temperature(

)

30 Precipitation(mm)

intensity in China’s agricultural production has become a serious concern (Cheng et al. 2011). While sustaining a high crop productivity, enhancement of soil organic carbon and reductions in CO2, CH4 and N2O emissions from croplands would be of particular importance for the commitment of China’s target to reduce total C emission per unit of GDP by 40–45% by 2020 (Anonymous 2010). Biochar production technology, with continuous pyrolysis system using vertical kilns, has been proposed as one mitigation strategy and biochar application is now under development in China’s agriculture (Pan et al. 2011).

The greenhouse gas intensity (GHGI) is being used to relate agricultural production to global warming potential (GWP) (Mosier et al. 2006; Qin et al. 2010; Shang et al. 2011; Zhang et al. 2010), however no knowledge is available about the impacts of biochar amendment on GHGI in maize farming systems.

Greenhouse gas accounting of GWP and GHGI as affected by biochar application in maize fields may provide the rationale for developing a low carbon technology as part of China’s agricultural industry and may further help to optimize agricultural management strategies for simultaneously achieving grain yields and mitigating climatic impacts of maize production in China.

The objectives of this study is to gain a holistic insight into the effects of biochar amendment on maize productivity and on net GHGs emissions during the whole maize growing season (WMGS) in central China.

265

10 20

0 5 Jul

15 Jul 25 Jul 4 Aug 14 Aug 24 Aug 3 Sep 13 Sep 23 Sep Date (dd-mm)

0

Fig. 1 Daily precipitation (bars) and max air temperature (above curve) and min air temperature (under curve) in the maize growing season

sediments of the Yellow River, the soil is a calcareous, fluvo-aquic loamy classified as aquic Fluvent in US Soil Taxonomy (Soil Survey Staff, USDA 1994) and a calcaric Aqui-Alluvic Primisol in Chinese Soil Taxonomy (Gong 1999).

Biochar amended Biochar used for the field experiment was produced from wheat straw by pyrolysis at 350–550°C in a vertical kiln made of refractory bricks in Sanli New Energy Company, Henan, China. With such a technology, 35% in mass of wheat straw would be expected to be converted to biochar (Pan et al. 2011). For the field study, the biochar mass originally in a particulate form was ground to pass through a 2 mm sieve, and mixed thoroughly to obtain a fine granular consistency that would mix more uniformly with the soil mass.

Measurements of basic properties of the soil and biochar were conducted following the protocol described by Lu (2000), the pH (H2O) was determined with a glass electrode (Seven Easy Mettler Toledo, China, 2008). Total organic C and N contents were analyzed with an Elementar Vario max CNS Analyser (German Elementar Company, 2003). Soil samples were extracted with 2 molL−1 KCl solutions (soil:water=1:5), ammonium was determined by the micro-Kjeldahl method, and nitrate was determined by the Devarda’s alloy method and the obtained values were normalized to soil dry weight. Total ash content of biochar was determined with 720°C ignition in a muffle furnace for 3 h, and the mineral element content and elemental analysis by atomic adsorption spectroscopy following

266

Plant Soil (2012) 351:263–275

an acid digestion as described by Cui et al. (2011). Soil bulk density was measured of samples collected in field plots using a cylinder of 100 cm3. The specific surface area of the biochar material was tested using the Brunauer–Emmett–Teller (BET) method. In brief, the N adsorption- desorption isotherms at 77 K were measured by an automated gas adsorption analyzer ASAP2000 (Micromeritics, Norcross, GA) with +5% accuracy. The high ash content measured was likely due to soil particles that attached to the straw while collected in the field. The basic properties of the studied topsoil (0–15 cm) and biochar are given in Table 1.

Field experiment The biochar was applied at rates of 0, 20 and 40 tha−1 (C0, C1 and C2, respectively) with or without N fertilization (N1 and N0, respectively). With N fertilization, urea was applied at 300 kg N ha−1, of which 60% was applied as basal fertilizer and 40% as supplementary fertilizer during crop growth. Also as basal fertilizers, calcium superphosphate and potassium sulfate were applied at 75 kg P2O5 ha−1 and 90 kg K2O ha−1 respectively to all plots. Prior to sowing, biochar and the fertilizers were broadcasted evenly onto soil surface by hand and immediately mixed in the plow layer (0–15 cm) with a tilling tractor. Sowing of maize seeds (zea mays, Zhengdan 958) was performed on the mixed soil surface by hand on 17 June 2010. For maize growth, a row spacing and a distance in the row was designed as 50 cm and 21 cm, respectively (Fig. 2). After 2 weeks, the maize seedlings were thinned to approximately 55,000 per hectare. The mature maize was harvested on 26 September 2010. The experiment used a randomized complete block design with three replicate plots. Each treatment plot was 4 m×5 m in area. The plots were separated by a protection row 0.5 m in width, each with a drainage outlet.

Greenhouse gas emission monitoring For measuring soil flux of greenhouse gases, an aluminum flux collar was installed in between the maize plants in each plot. The top edge of the collar had a groove filled with water to seal the rim of chamber that was attached to the collar during gas collection. The chamber was equipped with a circulating fan to ensure complete gas mixing and wrapped with a layer of sponge and aluminum foil to minimize air temperature variability inside the chamber during the sampling period. The cross-sectional area of the chamber was 0.12 m2 (0.35 m×0.35 m). The gas sampling for flux measurements were performed once a week throughout the growing period except for once a day for 1 week after fertilizer was applied. As reported by Zou et al. (2005), gas flux during 8 and 10 a.m. could be an approximation of the daily average, gas sampling in this study was done between 8–10 a.m. on a fine day and gas evolved was sampled using a syringe 0, 10, 20, and 30 min after chamber closure which allowed a calculation of the flux under a treatment. Adjustments in sampling dates and frequency were made in case of a rainfall event.

The concentrations of CO2, CH4 and N2O in a gas sample were simultaneously analyzed with a gas chromatograph (Agilent 7890D) equipped with a flame ionization detector (FID) and an electron capture detector (ECD). N2 was used as the carrier gases and an Ar-CH4 gas mixture as the make-up gas for ECD analysis of CO2, CH4 and N2O. N2O was separated by two stainless steel columns (column 1 with 1 m length and 2.2 mm in diameter, column 2 with 3 m length and 2.2 mm in diameter) that were packed with 80–100 mesh Porapack Q. N2O was detected by ECD, while CO2 and CH4 was detected

by FID. The oven temperature was controlled at 55°C, and the temperatures of the ECD and FID were set at 330°C and 200°C, respectively. Fluxes were determined from the slope of the mixing ratio change with the four

Table 1 Basic properties of the topsoil (0–15 cm) and biochar pH (H2O)

Topsoil Biochar

8.38 10.4

Organic carbon (g kg−1) 9.87 467

Total N (g kg−1)

Bulk density (g cm−3)

Surface area (m2 g−1)

Ash content (%)

0.94

1.46

/

/

5.9

/

8.92

20.8

As components of the ash content in the biochar, 1% of Ca, 0.6% of Mg, 0.4% of Fe and 2.6% of K

Plant Soil (2012) 351:263–275

267 Inter Row

Maize 35 cm

Fertilizer Chamber

35 cm Soil sampling

21 cm 50 cm

Fig. 2 Schematic diagram of chamber placement

sequential samples, taken at 0, 10, 20, and 30 min after chamber closure. Sample sets were rejected unless they yielded a linear regression value of r2 greater than 0.90.

The total emissions of CO2, CH4 and N2O over the WMGS were sequentially accumulated from the emissions averaged on every two adjacent intervals of the measurements. The detailed calculation of a flux using these sequential samples was described in detail

by Zou et al. (2005).

Soil sampling and analysis Composite samples of topsoil at 0–15 cm depth were collected with an Eijkelkamp soil core sampler from each plot after maize harvest on 26 September 2010.

The samples were sealed in plastic bags and shipped to the laboratory within 2 days after sampling and stored at 4°C in a refrigerator before further analysis or treatments. Root detritus was removed and the soil was air-dried and ground to pass a 2 mm sieve prior to analysis. A portion of each soil sample was ground to pass a 0.15 mm sieve for C and N analysis. Samples for bulk density measurement were also conducted for each plot using a 100 cm3 cylinder hand-pressed into the soil to a depth of 0–10 cm. For these soil sampling and treatments, the protocol described by Lu (2000) was followed.

comparison of maize yield between treatment plots with or without applied N. The N fertilizer-induced emission factor of N2O (EF hereafter) was calculated by the difference in total N2O emission of measurements over the WMGS between treatments with or without N fertilizer application divided by the fertilized N with a biochar treatment.

For assessing trade-off effects between GHGs mitigation and production using biochar in agriculture, an overall gross GWP in CO2-e, per hectare was also calculated using the following equation: GWP ¼ 25 E CH4 þ 298 E N2 O

ð1Þ

where, GWP is the total emission in CO2-equivalents per hectare, E-CH4 and E-N2O is the total emission per hectare of CH4 and N2O during the WMGS respectively. Hence, following a calculation reported

by Mosier et al. (2006), Qin et al. (2010), Shang et al.

(2011) and Zhang et al. (2010), an overall GHGI was also calculated as the overall gross GWP divided by the grain yield of maize produced under biochar treatment, using the equation as follows: GHGI ¼ GWP=Y

ð2Þ

where, GWP is the overall total emission of CH4 and N2O (kg CO2-e ha−1), Y is the grain yield of maize in t ha−1, and GHGI is the total overall emission intensity with grain production (kg CO2-e t−1).

All data were expressed as means plus or minus one standard deviation. Differences between the treatments comparing the effects of biochar amendment, N fertilization, and their interaction were examined using a two-way analysis of variance (ANOVA). The significance of difference was tested using LSD test at level of 0.05. The effects of biochar on the fertilizer induced N2O-N emission factor and agronomic N use efficiency were examined considering the interaction of biochar with N fertilization. All statistical analyses were carried out using JMP, version 7.0 (SAS Institute 2007).

Data processing and statistics Results Calculation of the direct emission factors and total GWP values for CH4 and N2O was performed following the IPCC methodology (Forster et al. 2007).

The agronomic N use efficiency (AEN, kg grain yield increase per kg N applied) was estimated based on a

Soil properties and maize productivity Results for soil physical and chemical properties sampled after maize harvest under the different

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Plant Soil (2012) 351:263–275

biochar/N treatments are presented in Table 2. The effects of biochar treatment and other factors were tested and presented in Table 3. Biochar amendments increased soil organic carbon and total N and decreased soil bulk density but had no effect on pH (H2O) in treatments both with and without N fertilization (Table 3). Biochar amendment at 40 t ha−1 caused a significant decrease in soil bulk density by 0.17 gcm−3 and by 0.28 gcm−3 with and without N fertilization. In treatments without N fertilization, SOC was found to increase by 57.8% under biochar amendment at 40 tha−1 (C2N0) and by 44.0% under biochar amendment at 20 tha−1 (C1N0) as compared to no biochar treatment (C0N0), respectively. However, in treatments with N fertilization, SOC was increased by 42.2% under biochar amendment at 40 t ha−1 (C2N1) and by 25.0% under biochar amendment at 20 t ha−1 (C1N1) as compared to no bichar amendment (C0N1), respectively. Without N fertilization, total soil N content was enhanced by 31.0% under C2N0 and by 24.1% under C1N0 respectively as compared to under C0N0, while there was no significant difference between the biochar treatments with N fertilization.

Without N fertilization, an increase in maize yield was observed by 7.3% and by 15.8% under C2N0 and C1N0 treatments, respectively, as compared to C0N0.

Moreover, the maize yield was increased by 11.6% under C2N1 and by 18.2% under C1N1 as compared to under C0N1 (Table 4).

As shown in Fig. 3, the estimated AEN value was increased from 1.25 kg kg−1 N under no biochar to

2.28 kg kg−1 N under biochar amendment at 40 tha−1.

While biochar amendment increased soil total N content. It had no effect on soil mineral N contents.

Greenhouse gases emissions Results for the measured GHGs emissions from the treatments plots are reported in Table 4 and their emission dynamic during the WMGS is shown in Fig. 4. The mean flux of CO2-C over the WMGS ranged from 82.4±5.5 mg CO2-C m−2 h−1 under C0N0 to 92.3±1.2 mg CO2-C m−2 h−1 under C2N0 without N fertilization, and from 74.5±6.1 mg CO2-C m−2 h−1 under C0N1 to 72.6±1.6 mg CO2-C m−2 h−1 under C2N1 with N fertilization, respectively. Total CO2 emissions from soil depended on the N fertilization regardless of biochar amendment (Table 5). While there was no difference in total CO2 emission between treatments of C1N0 and C0N0, total CO2 emission was increased by 12% under C2N0 compared to under C0N0. There was no effect of N fertilization on CO2 emissions under a single rate of biochar amendment.

As shown in Fig. 4, there were obvious N2O emission peaks about 5 days after supplementary fertilizer application. The mean fluxes of N2O-N over the WMGS ranged from 35.0±2.7 μg N2O-N m−2 h−1 to 60.6±5.0 μg N2O-N m−2 h−1 and 10.4±0.67 μg N2O-N m−2 h−1 to 11.7±0.84 μg N2O-N m−2 h−1 under biochar amendments with and without N fertilization, respectively. Total N2O emissions over the WMGS were very obviously affected by biochar

Table 2 Soil pH (H2O), Soil organic carbon (SOC), Total N and bulk density (mean±S.D., n=3) of topsoil (0–15 cm) following biochar amendment with or without N fertilization

No N fertilization

N fertilization

a

(Treatments)a

pH(H2O)

SOC (g kg−1)

Total N (g kg−1)

NH4+-N (mg kg−1)

NO3−-N (mg kg−1)

Bulk density (g cm−3)c

C0N0

8.15±0.21(b)b

10.9±1.0(c)

0.87±0.06(c)

1.30±0.14

20.4±3.9

1.37±0.1(a)

C1N0

8.24±0.04(ab)

15.7±0.5(ab)

1.08±0.02(ab)

1.63±0.29

20.3±1.0

1.23±0.03(b)

C2N0

8.38±0.06(a)

17.2±1.6(a)

1.14±0.003(a)

1.98±0.75

20.0±0.31

1.09±0.001(c)

C0N1

8.28±0.03(ab)

11. 6±0.7(c)

1.04±0.01(b)

1.35±0.25

22.9±2.3

1.36±0.02(a)

C1N1

8.38±0.02(a)

14.5±0.2(b)

1.12±0.11(ab)

1.34±0.23

21.9±0.82

1.23±0.11(b)

C2N1

8.23±0.05(ab)

16.5±0.5(a)

1.11±0.003(ab)

1.60±0.93

20.5±0.75

1.19±0.005(bc)

Biochar amendment at 0, 20 and 40 tha−1 (C0, C1 and C2, respectively) with and without N fertilization

b

Letters within parenthesis in a single column represent statistical class among the treatments at p<0.05. Mean±S.D. with the same small letters are not significantly different at p=0.05. It represents biochar×N fertilization interaction effects c

Samples for bulk density measurement were conducted for each plot using a 100 cm3 cylinder hand-pressed into the soil to a depth of 0–10 cm

1.5

0.52 52.0 3.3 0.047 0.032 9.2 0.106 12

0.71 0.35

0.89 19.26

3.05 0.76

0.61 0.74

0.28 0.15

1.01 0.17

0.01 0.018

0.0003

0.27

0.156

3.01 0.036

0.08

2

2.6 0.116 5

2

102.8

4.45 0.078

26.8

amendment, N fertilization and their interactions (Tables 4 and 5). With N fertilization, addition of biochar amendments resulted in a reduction in N 2O emission by 10.7% and by 71.8% under C1N1 and C2N1 as compared to C0N1. However, there were no significant differences observed between biochar treatments without N fertilization, showing no effect on N 2O emission from soil indigenous N (Table 4). The estimated EF values from the applied chemical N fertilizer ranged from 1.6 ± 0.2 g N 2O-N kg−1 N under biochar amendment at 40 t ha −1 to 3.4 ± 0.3 g N2O-N kg−1 N under no biochar amendment. Accordingly, the EF for N 2O emission was decreased by approximately 18% and 53% under biochar amendment at 20 tha−1 and 40 tha−1 compared to no biochar amendment, respectively (Fig. 5).

Results for CH4 emission rates (Table 4) showed a small but insignificant “sink effect” in the dry cropland over the WMGS as the mean flux of CH4 across the growing stages ranged from −0.0059± 0.0027 m CH4-C gm−2 h−1 to 0.018±0.0086 mg CH4C m−2 h−1 in all treatments. There was a small increase in total CH4 emission under biochar amendments at higher rate of 40 t ha−1 (Tables 4 and 5) regardless of N fertilization.

Seasonal GWP and GHGI As shown in Table 4, there was a significant decrease in the overall total GWP and GHGI for the CH4 and N2O when calculated over a 100-year time frame.

Compared to C0N1, the overall total GWP was decreased by 9.8% under C1N1 and by 41.5% under C2N1 with N fertilization, but there was no difference between treatments without N fertilization. Furthermore, there was no significant difference in GHGI between treatments with and without N fertilization.

Overall, GHGI was decreased by 23.8% under C1N1 and by 47.6% under C2N1 compared to under C0N1, respectively.

Discussions

Model

B×N

Effect of biochar on maize productivity Error

0.9

8.8

5.7

11.7

0.0312 0.18

<0.0001

0.001

0.52

0.15 2.36

0.69 6.0

10.2 0.42

0.33 1.2

0.69 0.19

0.67 0.158

0.004 0.027

0.0001 64.5

0.36 6.4 0.36 0.42 N fertilization

0.2

0.69 0.69 0.006

2

1

Biochar

P

99.07 1.82 0.032

0.9

20 20.3 0.108

0.017

<0.0001

0.0001

P F SS P F SS F SS

F

SOC(g kg−1)

P

F

P SS F SS P

SS

NO3−-N (mg kg-1) Bulk density(g cm−3) Total N(g kg−1)

NH4+-N (mg kg−1)

269

pH(H2O) DF Factor

Table 3 A two-way ANOVA for the effects of biochar (B) and N fertilization (N) on pH (H2O), soil organic carbon(SOC), total N, bulk density of topsoil NH4+-N, and NO3−-N (0–15 cm)

Plant Soil (2012) 351:263–275

Biochar amendments have previously been shown to increase crop productivity by improving the

270

Plant Soil (2012) 351:263–275

Table 4 Maize yield and total emissions (mean±S.D., n=3) of carbon dioxide (CO2), methane(CH4) and nitrous oxide (N2O) over the WMGS from the field and global warming potential

No N fertilization

N fertilization

a

(GWP) and greenhouse gas intensity (GHGI) as affected by biochar amendment and N fertilization

(Treatments)a

Yield (t ha−1)

C0N0

6.28±0.26(d)

C1N0

7.27±0.30(b)

1709.2±9.9(b)

0.36±0.17(a)

0.24±0.02(d)

122.8±13(d)

16.9±1.9(d)

C2N0

6.74±0.18(c)

1860.8±25(a)

−0.55±0.15(c)

0.23±0.03(d)

91.1±13(d)

13.6±2.2(d)

C0N1

6.65±0.006(c)

1501.6±123(c)

−0.39±0.06(c)

1.22±0.1(a)

559.2±48(a)

84.0±7.2(a)

C1N1

7.86±0.05(a)

1520.3±56(c)

−0.13±0.05(b) 1.09±0.06(b)

504.8±28(b)

64.2±3.9(b)

C2N1

7.42±0.07(b)

1465.1±32(c)

−0.11±0.05(b) 0.71±0.05(c)

327.0±26(c)

44.0±3.1(c)

b

CO2-C (kg ha−1)

CH4-C (kg ha−1)

N2O-N (kg ha−1)

1661.5±110(b)

−0.12±0.05(b) 0.21±0.01(d)

GWP(CH4+N2O) (kg ha−1) c 94.0±6(d)

GHGI (kgCO2-equivalents t−1grain yield )d 15.0±1.2(d)

Biochar amendment at 0, 20 and 40 tha−1 (C0, C1 and C2, respectively) with and without N fertilization

b

Letters within parenthesis in a single column represent statistical class among the treatments at p<0.05. Mean±S.D. with the same small letters are not significantly different at p=0.05. It represents biochar×N fertilization interaction effects. c

GWP (kg CO2-equivalent ha−1 )=25×CH4 +298× N2O (Forster et al. 2007)

d

GHGI (kg CO2-equivalent t−1 grain yield)=GWP/per ton grain yield of corn

physical and biochemical properties of cultivated soils (Asai et al. 2009; Major et al. 2010b). Crop response to biochar amendment depends on the chemical and physical properties of the biochar, climatic conditions, soil conditions and crop type (Zwieten et al. 2010; Yamato et al. 2006; Gaskin et al. 2010; Haefele et al. 2011). Asai et al. (2009) reported a decreased yield of upland rice (Oryza sativa L.) following application of biochar amendment without N fertilization in a N deficient soil. But in a degraded Ultisol (an acid, highly weathered and nutrient poor soil) from Kenya, Kimetu et al.

(2008) reported the cumulative maize yield to double AEN(kg of increased maize production per kg N fertilized)

3.0

a a 2.0

b 1.0

0.0 C0N1

C1N1

C2N1

Treatments

Fig. 3 Agronomic N use efficiency (AEN, kg of increased maize production per kg of N fertilized) under biochar amendment at 0, 20 and 40 tha−1 (C0, C1 and C2, respectively) with N fertilization (mean±S.D., n=3). Different letters above bars represent differences at p<0.05

after three repeated biochar applications of 7 tha−1 over 2 years. However, Major et al. (2010b) showed no change of maize yield in the first year and significant increase in the subsequent 3 years following a single dose of wood biochar at 20 tha−1 in a Colombian savanna Oxisol (similar in chemical properties to Ultisols). In the present study, maize yield was increased by 11.6%–18.2% with N fertilization and by 7%–16% without N fertilization under biochar amendment at rates of 20–40 tha−1, respectively (Table 4). The increased maize yield in biochar amended soil could be attributed to increased nutrient availability (Chan et al. 2007, 2008; Zhang et al. 2010) and to improved soil physical properties indicated by decreased soil bulk density. But the increase in yield seemed not proportional to biochar amendment rate for N availability could be decreased under high biochar application (Lehmann et al. 2003) as a C/N ratio of 15 was observed under C2N1 compared to of 13 under C1N1. In a previous study, an increased agronomic N use efficiency and higher rice productivity was found in an acidic SOC-rich paddy soil following biochar application at the rate of 10 tha−1 and 40 tha−1 (Zhang et al. 2010). In this study with SOC-poor calcareous soil, the agronomic N use efficiency was also significantly increased under biochar amendments (Fig. 3). High levels of soil organic carbon accumulation due to biochar amendment could enhance N efficiency and increase crop productivity (Pan et al. 2009).

Plant Soil (2012) 351:263–275

271

Fig. 4 Dynamic of CO2 (a), N2O (b) and CH4 (c) emissions from the field during the whole maize growing season (mean±S.D., n=3).

Negative flux suggests CH4 uptake by soil. Arrows indicate the date of supplementary fertilizer application

180 160

a

CO 2 -C(mg m-2 h-1)

140 120 100 80 60 40 20 0 400

b

350

N2 O-N(µ g m-2 h-1

(

300 250 200 150 100 50 0

0.4

c

CH 4 -C(mg m-2 h-1)

0.3 0.2 0.1 0 -0.1 -0.2 -0.3 -0.4

5 Jul

19 Jul

28 Jul

30 Jul

10 Aug Date

25 Aug

11 Sep

26 Sep

Table 5 A two-way ANOVA for the effects of biochar (B) and N fertilization (N) on greenhouse gas emissions and maize yield from the field Factor

DF

CO2-C (kg ha−1) SS

Biochar

2

20097

Fertilization

1

277213

B×N

2

49639

Model

5

346949

Error

12

64122

F 1.9 52 4.6 13

P

CH4-C (kg ha−1)

N2O-N (kg Nha−1)

Yield (t ha−1)

SS

F

P

SS

SS

F

P

F

P

0.19

0.68

31

<0.0001

0.2

33

<0.0001

3.6

55

<0.0001

<.0001

0.052

5

0.049

2.7

893

<0.0001

1.4

41

<0.0001

0.03

0.73

34

<0.0001

0.23

38

<0.0001

0.08

1.47

27

<0.0001

3.2

207

<0.0001

5.1

0.0002

0.13

0.04

0.4

1.1 31

0.35 <0.0001

272

Plant Soil (2012) 351:263–275

-1

EF[gN2O-N(kgN) ]

4

a b

3

c

2 1 0

0 t/ha

20 t/ha Biochar amendment

40 t/ha

Fig. 5 Change in the N fertilizer-induced emissions factor for N2O (EF) from the field amended with biochar at different application rates (mean±S.D., n=3). Different letters above bars represent differences at p<0.05

Effect of biochar on greenhouse gas emission Effect of biochar amendment on soil C cycling and emission of N2O and CH4 may vary greatly with soil and biochar types. The priming effect induced by biochar addition may be either positive or negative, depending on the biochar type and the soil water regime (Zimmerman et al. 2011). As biochar amendment may enhance microbial activity, decomposition of soil organic carbon may be accelerated (Wardle et al.

2008). Major et al. (2010a) found that biochar from old mango (Mangifera indica L.) trees applied to a savanna Oxisol in Colombia at the rate of 23.2 tha−1 induced greater CO2 emissions, which was attributed to the enhanced below-ground net primary productivity under biochar addition. Ethylene, more or less present in biochar, could act as a microbial inhibitor (Spokas et al. 2010) and the magnitude of its effect would depend on the native soil carbon content (Kimetu and Lehmann 2010). Nevertheless, biochar amendment at rates less than 10 tha−1 may have no effect on soil respiration from croplands (Knoblauch et al. 2010; Karhu et al. 2011). In the study reported here, changes in total CO2 emissions from maize cultivated soil with biochar amendment were observed depending on whether or not N fertilizer was applied, regardless of biochar amendment rates (Table 5). Overall, total CO2 emission was increased by 12% under biochar amendment at 40 t ha−1 without N fertilization compared to no biochar and N fertilization treatment, being affected by the labile carbon content of biochar. In a laboratory incubation study using δ13C labeling technology, Smith et al. (2010) found an increased CO2 flux from

decomposing organic matter from soil amendment with switchgrass biochar. However, the total CO2 emission in their study was unchanged with N fertilization.

Previous studies have shown contradictory effects of N fertilization on soil microbial processes: suppression by Fisk and Fahey (2001) and Iqbal et al. (2009), enhancement by Allen and Schlesinger (2004) and no effect by Lee et al. (2007). In this study, N fertilization decreased microbial respiration by 10.6%, 12.4% and 27% under biochar application at rates of 0, 20 and 40 tha−1, respectively. These results seem consistent with the finding by Iqbal et al. (2009) that biochar amendments suppressed microbial respiration from a subtropical rice paddy fertilized with N alone. N fertilizer-induced reductions in soil microbial respiration could be partly explained by a decrease in phenol oxidase activity (a lignin-degrading enzyme) resulting from N suppression of white-rot fungi (Frey et al.

2004; Waldrop et al. 2004).

Decreases in net emissions of CH4 and N2O from some very acid and nutrient- limited soils following biochar amendment have been well documented (Rondon et al. 2005, 2006). Recently, Karhu et al.

(2011) showed that application of birch biochar at rate of 9 tha−1 had no effect on N2O emission but increased CH4 uptake in a wheat field from Southern Finland. However, a significant decrease in N2O emission from rice paddy was reported in a previous study (Zhang et al. 2010) and in a cross-site study (Liu et al. 2011). The results here indicated a sharp decrease in N2O emission following biochar amendment with N fertilization which was proportional to the rate of biochar addition. However, a significant but small effect was noticed on CH4 emission. Finally, the GWP and GHGI of CH4 and N2O emissions decreased significantly following biochar amendment.

N dynamic is subject to changes with soil aeration, pH and the C/N ratio of the material (Cavigelli and Robertson 2001; Yanai et al. 2007; Rondon et al. 2007; Warnock et al. 2007; Zwieten et al. 2009). Biochar amendment could potentially favor the activity of N2O reductase from denitrifying microorganisms as soil pH was increased (Yanai et al. 2007) while inhibiting the activity of reductases involved in the conversion of nitrite and nitrate to nitrous oxide (Zwieten et al. 2009).

As soil aeration improvement would also lead to changes in the functionality and diversity of denitrifiers in soils (Cavigelli and Robertson 2001), improved aeration with decreased bulk density (Table 2) would

Plant Soil (2012) 351:263–275

also tend to depress the activity of denitrifiers in soils amended with biochar. As a consequence, the emission factor for N2O from N fertilization was decreased and agronomic N use efficiency increased considerably under biochar amendment in this study.

The emission factor of fertilizer N for N2O was estimated to be 0.0034 kg N2O - N/kg N, 0.0028 kg N2O - N/kg N and 0.0016 kg N2O - N/kg N under biochar amendment at 0 tha−1, 20 tha−1 and 40 t ha−1, respectively. It is obviously lower than IPCC default value of soil N2O resulting from N fertilizer (0.01 kg N2O - N/kg N) (Intergovernmental Panel on Climate Change IPCC 2006).

Furthermore, biochar amendments would have additional potential for offsetting N fertilizer production emission through the increased agronomic N use efficiency observed here. Thus, in addition to direct reduction in N2O emissions in field, biochar amendments in croplands would have great benefits for reductions in GHGs emission from the fertilizer industry (Zhang et al. 2010; Gaunt and Lehmann 2008).

Conclusions As agricultural production has strong impacts on greenhouse gas emissions, effective and applicable countermeasures for mitigating these emissions are urgently required globally. This study provided an insight into greenhouse gas emissions and greenhouse gas intensity as affected by biochar amendments in maizecropping systems of the Central China Plain. Biochar amendments increased soil organic carbon and total N but decreased soil bulk density in line with an increase in maize yield. Increased CO2 emission from the maize field amended with biochar was observable only in the absence of N fertilization. However, biochar amendments significantly decreased the total direct N2O emission from the maize field during the whole maize growing season and indirect CO2 emissions by increasing agronomic N use efficiency and by reducing the N fertilizer-induced emission factor of N2O. The present study suggests the use of biochar as a soil amendment could be adopted as an effective and applicable measure to achieve simultaneously high grain yield and low global warming potential intensity of maize production in croplands of calcareous soil poor in organic carbon, which are very extensive and critical for maize production in North China. Moreover, the application

273

of biochar from crop residues may offer additional carbon negative benefits though avoiding burning in field and bio-resource recycling, which have been a great concern with air pollution of China’s agriculture.

Acknowledgements This study was partially supported by the Ministry of Science and Technology of China under a grant number of 2008BAD95B13-1. Biochar was produced in Sanli New Energy Company, Henan Province, China. The authors are grateful to the anonymous reviewers for their constructive comments on the manuscript.

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