Biochar is a beneficial soil amendment but the changes in its surface properties during the aging process, especially the oxygen-containing functional groups and the associated adsorption behaviors, ...are not well documented. In this paper, the aged wheat straw biochar was simulated by chemical oxidation with HNO3-H2SO4 and NaOH-H2O2 systems. Characterization results showed that carbon loss and oxygen incorporation ran throughout the aging process. Surface oxygen-containing functional groups were found to be increased in all treated biochars, especially for carboxyl. Much more developed mesopores were observed in aging biochar, specific surface area was increased by 126% for biochar treated with NaOH-H2O2, and 226% for biochar treated with 40% of HNO3-H2SO4. Thermogravimetric analysis showed that the increasing oxygen-containing functional groups led to 14% and 30% mass loss by treating biochar with alkali and acid, respectively. The improved biochar surface through the increase of oxygen-containing functional groups enhanced the cadmium sorption capacity, and the sorption capacity increased by 21.2% in maximum. Roughed surface from oxidation was another reason for increasing cadmium adsorption. Results indicated that the adsorption performance of biochar on pollutant would be changed during aging process along with the changing surface properties.
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•Carbon loss and oxygen incorporation ran throughout the oxidation.•Aging layer formed on the biochar surface.•Oxidant destroyed surface structure and developed much more mesopores.•More oxygen-containing functional groups increased cadmium complexation.•Long-term field remediated biochar showed much more carboxyl groups.
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 fertilization, 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.
▶ Biochar increased rice yield at 10% while N fertilization could be saved for a rice yield of 9t/ha. ▶ Biochar increased methane emission but reduced N2O emission. ▶ Biochar significantly reduced ...emission factor of N fertilizer.
A field trial was performed to investigate the effect of biochar at rates of 0, 10 and 40tha−1 on rice yield and CH4 and N2O emissions with or without N fertilization in a rice paddy from Tai Lake plain, China. The paddy was cultivated with rice (Oryza sativa L., cv. Wuyunjing 7) under a conventional water regime. Soil emissions of CH4 and N2O were monitored with a closed chamber method throughout the whole rice growing season (WRGS) at 10 day intervals. Biochar amendments of 10tha−1 and 40tha−1 increased rice yields by 12% and 14% in unfertilized soils, and by 8.8% and 12.1% in soils with N fertilization, respectively. Total soil CH4-C emissions were increased by 34% and 41% in soils amended with biochar at 40tha−1 compared to the treatments without biochar and with or without N fertilization, respectively. However, total N2O emissions were sharply decreased by 40–51% and by 21–28%, respectively in biochar amended soils with or without N fertilization. The emission factor (EF) was reduced from 0.0042kgN2O-Nkg−1 N fertilized with no biochar to 0.0013kgN2O-Nkg−1 N fertilized with biochar at 40tha−1. The results show that biochar significantly increased rice yields and decreased N2O emission, but increased total CH4 emissions. Summary calculations based on this experiment data set provide a basis for estimating the potential reductions in GHG emissions that may be achieved by incorporating biochar into rice paddy soils in south-eastern China.
This review summarizes the influences of pyrolysis conditions and feedstock types on biochar properties and how biochar properties in turn affect soil properties. Mechanistic evidence of biochar's ...potential for enhancing crop productivity, carbon sequestration, and nutrient use efficiency are also discussed. The review identifies the knowledge gaps, limitations, and future research directions for large‐scale use of biochar. Both pyrolytic parameters and feedstock types are considered to be the main factors controlling biochar properties such as nutrient content, recalcitrance, and pH. Biochar produced at low temperatures may improve nutrient availability and crop yield in acidic and alkaline soils, whereas high‐temperature biochar may enhance long‐term soil carbon sequestration. Biochar can also improve the efficiency of inorganic and organic fertilizers by enhancing microbial functions and reducing nutrient loss, thereby making nutrients more available to plants. Integration of biochar and chemical or organic fertilizers generally provides for better nutrient management and crop yield in most types of soils. Although biochar can improve degraded soils, it is not a panacea; as such, soil‐ and crop‐specific biochar are needed in order to ensure optimum crop yield and agricultural sustainability.
Fenton-like system formed in a natural soil environment deemed to be significant in the aging process of biochar. Aged biochars have distinct physico-chemical and surface properties compared to ...non-aged biochar. The aged biochar proved to be useful soil amendment due to its improved elements contents and surface properties. The biochar aging process resulted in increased surface area and pore volume, as well as carbon and oxygen-containing functional groups (such as C=O, -COOH, O-C=O etc.) on its surface, which were also associated with the adsorption behavior of 2,4,6-trichlorophenol (2,4,6-TCP). The biochar aging increased the adsorption capacity of 2,4,6-TCP, which was maximum at pH 3.0. The 2,4,6-TCP adsorption capacity of aged-bush biochar (ABB) and aged-peanut shell biochar (APB) was increased by 1.0-11.0% and 7.4-38.8%, respectively compared with bush biochar (BB) and peanut shell biochar (PB) at the same initial concentration of 2,4,6-TCP. All biochars had similar 2,4,6-TCP desorption rates ranging from 33.2 to 73.3% at different sorption temperatures and times. The desorbed components were mainly 2,4,6-TCP and other degraded components, which were low in concentration with small molecule substance. The results indicated that the aged-biochar could be effective for the long-term remediation of naturally organic polluted soils.
► Biochar amendment of 10tha−1, 20tha−1 and 40tha−1 increased rice productivity in both rice cropping cycles. ► Biochar amendment seemed no effect on soil respiration in two cycles, decreased nitrous ...oxide emission but increased methane emission which significantly decreased in the second cycle compared to that of in the first cycle. ► Biochar amendment decreased global warming potential and C intensity of rice production in the second cycle but in the first cycle.
Biochar production and application from crop straw had been proposed as one effective countermeasure to mitigate climate change. We conducted a 2-year consecutive field experiment in 2009 and 2010 in rice paddy to gain insight into the consistency over years of biochar effects on rice production and greenhouse gases emissions. Biochar was amended in 2009 before rice transplanting at rates of 0, 10, 20 and 40tha−1, soil emissions of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) were monitored with closed chamber method at 7 days interval throughout the whole rice growing season (WRGS) both in 2009 and 2010. The results showed that biochar amendment increased rice productivity, soil pH, soil organic carbon, total nitrogen but decreased soil bulk density in both cycles of rice growth. Soil respiration observed no significant difference between biochar amendment and the corresponding control both in the first and second cycle, respectively. However, biochar amendment decreased nitrous oxide emission but increased methane emission in both cycles. No significant difference in carbon intensity of rice production (GHGI) and global warming potential (GWP) were observed between the biochar amendment at the rate of 10tha−1 and 40tha−1 and control though the GWP and GHGI was increased by 39% and 26% at the rate of 20tha−1 respectively, in the first cycle. However, in the second cycle, both of overall GWP and GHGI were observed significantly decreased under biochar amendment as compared to control, ranging from 7.1% to 18.7% and from 12.4% to 34.8%, respectively. The biochar effect intensity on global warming potential were observed from −2.5% to 39.2% in the first cycle, and from −18.7% to −7.1% in the second cycle. However, the biochar effect intensity on C intensity of rice production was observed from −10.2% to 25.8% in the first cycle, and from −36.9% to −18.6% in the second cycle. Therefore, biochar effect on reducing the overall C intensity of rice production could become stronger in the subsequent cycles than that in the first cycle though a consistently strong effect on reducing N2O emission in a single crop cycle after biochar amendment. Nevertheless, these effects were not found in proportional to biochar amendment rates and a high rice yield but lowest C intensity was achieved under biochar amendment at 10tha−1 in both cycles of the rice paddy in the present study.
Cadmium (Cd) pollution in agricultural soils has exerted a serious threat due to continuous application of pesticides, fertilizers, and wastewater irrigation. The present study aimed to test the ...efficiency of KOH-modified and non-modified rice straw-derived biochar (KBC and BC, respectively) for reducing Cd solubility and bioavailability in Cd-contaminated soil. Cadmium-contaminated soil was incubated for 60 d with 15 and 30 g kg−1 BC and KBC. At the end of incubation, Cd mobility was estimated by the European Community Bureau of Reference sequential extraction and toxicity characteristic leaching procedure (TCLP), while bioavailability was determined using 1 mol L−1 NH4NO3 extraction. The bioavailability risk index and bioaccessibility, assessed by a simple bioaccessibility extraction test, of Cd were used to examine the potential effects of Cd on living organisms. The results indicated that application of both KBC and BC significantly increased soil pH, cation exchange capacity, nutrients, and organic carbon. The soluble fraction of Cd was significantly decreased by 30.3% and 27.4%, respectively, with the addition of KBC and BC at 30 g kg−1 compared to the control (without biochar addition). Similarly, the bioaccessible Cd was significantly decreased by 32.4% and 25.2%, respectively, with the addition of KBC and BC at 30 g kg−1 compared to the control. In addition, both KBC and BC significantly reduced Cd leaching in the TCLP and NH4NO3-extractable Cd in the amended soil compared to the control. The reduction in Cd solubility and bioaccessibility by KBC and BC may be due to significant increases in soil pH and surface complexation. Overall, KBC at an application rate of 30 g kg−1 demonstrated positive results as soil amendment for Cd immobilization, and reduced bioaccessible Cd in contaminated soil.
Purpose
Our knowledge of biochar as a tool for soil carbon (C) sequestration and soil quality in semi-arid regions remains limited in recent years. Moreover, there is a lack of understanding on the ...comparison between effects of biochar rates on soil organic C (SOC) and nitrogen (N) mineralization in organic C poor soils.
Materials and methods
Interactive effects of corncob-biochar (B), prepared at 450 °C pyrolysis temperature, and wheat straw (W) on soil native and fresh organic matter were investigated in sandy loam alkaline calcareous soil. The corncob-biochar was applied alone and in combination with wheat straw (WB) at rates equivalent to 0 t ha
-1
(unamended control), 22.5 t ha
-1
(B1, W1, W1B1), and 45 t ha
-1
(B2, W2, W2B2). After treatment applications, soils were incubated under laboratory conditions for 61 days and periodic CO
2
evolution rates were measured to calculate the cumulative CO
2
efflux and priming effects.
Results and discussion
The lowest CO
2
efflux was found in B2 treatment, whereas CO
2
efflux was lower in W1B1 than in W1 treatment. Biochar alone and with wheat straw significantly reduced net C mineralization (NCM) compared to wheat straw only treatments and the effects became stronger as biochar rate increased. This was reflected in data on the priming effect, which also showed that increased biochar rates induced a stronger negative priming (− 87 to − 67%) on SOC. Biochar with wheat straw at both rates enhanced microbial biomass C (MBC) compared to the control, W1, B1, and B2 treatments. However, the W1B1 and W2B2 treatments decreased water-extractable organic C (WEOC) contents compared to W1 and W2. Microbial metabolic quotient (
q
CO
2
) and MBC/TOC ratio increased with biochar rate, suggesting more efficient utilization of labile C by microorganisms at higher biochar rate. Biochar alone and with wheat straw reduced soil mineral nitrogen (N) contents than the control treatment and resulted in net negative N mineralization or net N immobilization.
Conclusions
Our findings indicate that biochar can reduce decomposition of soil organic matter to facilitate C and N sequestration in low organic C soils. However, our study also suggests the co-application of biochar and organic amendments/residues as labile C source to induce co-metabolism to improve microbial functions and C utilization efficiency in soils that are deficient in organic C.
Long-term soil chronosequences are valuable model systems for investigating pedogenesis and investigating the process of element coupling. Here, we assessed the coupling relationships among C, Fe, ...and Fe-reducing bacteria (
Anaeromyxobacter
,
Geobacter
, and
Shewanella
) in a paddy soil chronosequence of approximately 50 to 1000 years. Soils of the chronosequence originated from tidal marsh under nearly identical landscape and climate conditions. During 1000 years of rice cultivation, soil organic carbon (SOC) contents in surface horizons (0–20 cm) increased from 10.4 to 21.8 g kg
−1
. In contrast, total Fe contents declined from 59.6 to 45.1 g kg
−1
during the initial 50 years of paddy rice cultivation and then further decreased at a low rate of 0.004 g kg
−1
soil year
−1
(equivalent to 10 kg ha
−1
soil year
−1
). Organically complexed Fe oxides (Fe
p
) increased from 219 to 642 mg g
−1
with increasing time of pedogenesis, but free total Fe oxides (Fe
d
) and amorphous Fe oxides (Fe
o
) declined at early stage of soil development, followed by a slow accumulation at later stages of the chronosequence. Gene copy numbers of
Anaeromyxobacter
and
Geobacter
increased from 4.6 × 10
5
and 3.6 × 10
6
copies g
−1
to 3.8 × 10
7
and 3.6 × 10
7
copies g
−1
dry soil with continuous paddy rice cultivation, while concurrently
Shewanella
gene abundance decreased gradually from 4.5 × 10
5
to 9.3 × 10
4
copies g
−1
dry soil. Using structural equation modeling (SEM), different coupling relationships were observed among C, Fe, and Fe-reducing bacteria for the first 300 years of paddy chronosequence and thereafter. Overall, all Fe-reducing bacteria did not show consistent variation. With the stable microbial community and iron oxide fractions, the microbially mediated dissimilatory coupling relationship between C and Fe becomes simple during 1000 years of paddy soil development.
Purpose
Biochar, due to its heterogeneity, may not be equally effective for cationic and anionic metals/metalloid immobilization in soil. Biochar modification could facilitate the immobilization of ...specific metals/metalloids in soil.
Materials and methods
This study explored the potential of unmodified and modified (with KMnO
4
) biochars derived from sawdust and rice husk at two different temperatures (300 and 700 °C) on the mobility of arsenic (As) in contaminated soil. Soil column leaching experiments were performed with two application rates (2% and 5%; w/w) of different biochars, and the pore waters at different time intervals were analyzed for As and other cations and anion concentrations.
Results and discussion
In general, all the biochars increased As mobility in soil. The biochars produced at 300 °C significantly and highly increased As concentrations (up to 341%) in pore waters, as compared with the unamended soil. However, the modified biochars showed As immobilization in soil as compared with their unmodified counterparts. The mechanisms of biochar interaction with As in soil were investigated by developing correlations of As with various chemical constituents. It was inferred that As mobilization was increased due to competition between As and PO
4
3−
. Contrarily, immobilization of As in soil by modified biochars was related to sorption onto Fe- and Mn-oxides.
Conclusions
Pristine biochar may not be an efficient remediation measure for As-contaminated soil. There could be a risk of As leaching into groundwater from soils amended with biochar. However, it is recommended that modification of biochar may assist the immobilization of As in soil.
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