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Biochar-based fertilizer effects on crop productivity: a meta-analysis

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Leônidas C. A. Melo at Universidade Federal de Lavras (UFLA)
Leônidas C. A. Melo
Johannes Lehmann at Cornell University
Johannes Lehmann
Jefferson Santana da Silva Carneiro at Universidade Federal de Lavras (UFLA)
Jefferson Santana da Silva Carneiro
Marta Camps Arbestain at Massey University
Marta Camps Arbestain
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Abstract and Figures

Aim Biochar-based fertilizers (BBF) have gained increasing interest in recent years, yet their effects on crop productivity have not been reviewed. Methods We conducted a meta-analysis of the published literature (2011-2021) using 148 pairwise comparisons between crop productivity after additions of BBF, of conventional fertilizers (fertilized control), and a non-fertilized control. Results On average, BBF applied at very low application rates (mean of 0.9 t ha⁻¹) increased crop productivity by 10% compared with fertilized controls and 186% compared with non-fertilized controls. This mean crop productivity increase is comparable to that reported when biochar is used as a soil conditioner (i.e., 15 t-30 t ha⁻¹ to increase crop productivity by 10%). This crop yield increase suggests that biochar acts as a matrix to increase fertilizer use efficiency to a larger extent than conventional fertilizer alone. Cluster analysis revealed that BBFs have the potential to increase crop productivity by 15% when added to soils that are not responsive to conventional fertilizers. BBF produced at a highest heating temperature (HHT) of >400 °C increased crop productivity by 12% as opposed to those produced at a HHT of ≤400 °C that showed no increase. BBF with C contents >30% in the final mixture caused the largest increase in crop productivity by 17%, whereas those with C contents ≤30% had no effect. Conclusion This study has shown that biochar can be an effective constituent of novel fertilizers with enhanced efficiency, which may contribute to lower nutrient losses and lower negative environmental impacts.
Change in crop productivity as a result of additions of biochar-based fertilizers (BBF) in comparison with the fertilized control (red dotted line). The comparison is for the grand mean effect size and for several categories related to the climate, soil characteristics and fertilizer characteristics. The circles represent the mean value and the bars represent the 95% confidence interval. The difference is considered significant (p < 0.05) from the fertilized control when the bars do not overlap with the dotted line. Sub-categories were considered to differ between them when their 95% confidence intervals did not overlap. The numbers in parenthesis represent the number of pairwise comparisons (on the left)/number of independent studies (on the right) from which the comparisons were made. * Soil categories were divided in highly-weathered soils (HWS), weakly-developed soils (WDS), and others
Change in crop productivity as a result of additions of biochar-based fertilizers (BBF) in comparison with the fertilized control (red dotted line). The comparison is for the grand mean effect size and for several categories related to the climate, soil characteristics and fertilizer characteristics. The circles represent the mean value and the bars represent the 95% confidence interval. The difference is considered significant (p < 0.05) from the fertilized control when the bars do not overlap with the dotted line. Sub-categories were considered to differ between them when their 95% confidence intervals did not overlap. The numbers in parenthesis represent the number of pairwise comparisons (on the left)/number of independent studies (on the right) from which the comparisons were made. * Soil categories were divided in highly-weathered soils (HWS), weakly-developed soils (WDS), and others
… 
(a) Cluster analysis for crop productivity response (ln RR); (b) detailed cluster categorized by soil categories (HWS, WDS, and “others”); and (c) correlation between the fertilized control (FC) versus non-fertilized control (UFC) (“Fertilizer effect” - x-axis) and BBF versus fertilized control (FC) (“Biochar effect” - y-axis) (grey shading indicates 95% confidence interval; n = 86)
(a) Cluster analysis for crop productivity response (ln RR); (b) detailed cluster categorized by soil categories (HWS, WDS, and “others”); and (c) correlation between the fertilized control (FC) versus non-fertilized control (UFC) (“Fertilizer effect” - x-axis) and BBF versus fertilized control (FC) (“Biochar effect” - y-axis) (grey shading indicates 95% confidence interval; n = 86)
… 
Change in crop productivity as a result of additions of biochar-based fertilizers (BBF) in comparison with the fertilized control (red dotted line). The comparison is for pyrolysis temperature combined with carbon content (a) or feedstock nutrient content combined with carbon content in BBF (b). “High T” represents pyrolysis of biochar at >400 °C and “Low T” represents pyrolysis of biochar at ≤400 °C. “High C” represents BBF containing >30% C, and “Low C” represents BBF containing ≤30% C. “Poor Nu” represents biochar derived from wood and other plant derived feedstocks; “Rich Nu” represents biochar derived from manures, sludges and other ash-rich feedstocks. The circles represent the mean value and the bars represent the 95% confidence interval. The difference is considered significant (p < 0.05) from the fertilized control when the bars do not overlap with the dotted line. The numbers in parenthesis represent the number of pairwise comparisons (on the left)/number of independent studies (on the right) from which the comparisons were made
Change in crop productivity as a result of additions of biochar-based fertilizers (BBF) in comparison with the fertilized control (red dotted line). The comparison is for pyrolysis temperature combined with carbon content (a) or feedstock nutrient content combined with carbon content in BBF (b). “High T” represents pyrolysis of biochar at >400 °C and “Low T” represents pyrolysis of biochar at ≤400 °C. “High C” represents BBF containing >30% C, and “Low C” represents BBF containing ≤30% C. “Poor Nu” represents biochar derived from wood and other plant derived feedstocks; “Rich Nu” represents biochar derived from manures, sludges and other ash-rich feedstocks. The circles represent the mean value and the bars represent the 95% confidence interval. The difference is considered significant (p < 0.05) from the fertilized control when the bars do not overlap with the dotted line. The numbers in parenthesis represent the number of pairwise comparisons (on the left)/number of independent studies (on the right) from which the comparisons were made
… 
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Vol.: (0123456789)
1 3
https://doi.org/10.1007/s11104-021-05276-2
REVIEW ARTICLE
Biochar-based fertilizer effects oncrop productivity:
ameta-analysis
LeônidasCarrijoAzevedoMelo · JohannesLehmann· JeffersonSantana da SilvaCarneiro·
MartaCamps-Arbestain
Received: 5 March 2021 / Accepted: 13 December 2021
© The Author(s), under exclusive licence to Springer Nature Switzerland AG 2021
mean crop productivity increase is comparable to that
reported when biochar is used as a soil conditioner
(i.e., 15t-30t ha−1 to increase crop productivity by
10%). This crop yield increase suggests that biochar
acts as a matrix to increase fertilizer use efficiency
to a larger extent than conventional fertilizer alone.
Cluster analysis revealed that BBFs have the poten-
tial to increase crop productivity by 15% when added
to soils that are not responsive to conventional ferti-
lizers. BBF produced at a highest heating tempera-
ture (HHT) of >400°C increased crop productivity
by 12% as opposed to those produced at a HHT of
≤400°C that showed no increase. BBF with C con-
tents >30% in the final mixture caused the largest
increase in crop productivity by 17%, whereas those
with C contents ≤30% had no effect.
Conclusion This study has shown that biochar can be
an effective constituent of novel fertilizers with enhanced
efficiency, which may contribute to lower nutrient losses
and lower negative environmental impacts.
Keywords Biochar· Crop production· Enhanced-
efficiency fertilizer· Nutrient use efficiency· Organo-
mineral fertilizers
Introduction
Global food production is expected to increase by
50-70% between 2010 and 2050, whereas food and
non-food needs (e.g., fibers, bioenergy) are expected
Abstract
Aim Biochar-based fertilizers (BBF) have gained
increasing interest in recent years, yet their effects on
crop productivity have not been reviewed.
Methods We conducted a meta-analysis of the pub-
lished literature (2011-2021) using 148 pairwise com-
parisons between crop productivity after additions of
BBF, of conventional fertilizers (fertilized control),
and a non-fertilized control.
Results On average, BBF applied at very low appli-
cation rates (mean of 0.9t ha−1) increased crop pro-
ductivity by 10% compared with fertilized controls
and 186% compared with non-fertilized controls. This
Responsible Editor: Didier Lesueur.
Supplementary Information The online version
contains supplementary material available at https:// doi.
org/ 10. 1007/ s11104- 021- 05276-2.
L.C.A.Melo(*)· J.S.Carneiro
Soil Science Department, School ofAgricultural Sciences,
Federal University ofLavras, Lavras, MG37200-900,
Brazil
e-mail: leonidas.melo@ufla.br
J.Lehmann
Soil andCrop Sciences, School ofIntegrative Plant
Science, Cornell University, Ithaca, NY, USA
M.Camps-Arbestain
New Zealand Biochar Research Centre, School
ofAgriculture andEnvironment, Massey University,
PalmerstonNorth, NewZealand
/ Published online: 27 January 2022
Plant Soil (2022) 472:45–58
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
... Whereas prepyrolysis methods result in an enrichment of highly stable forms of N (Suo et al. 2021), which are less readily available to plants, postpyrolysis methods often achieve an enrichment in plant-available N (Castejóndel Pino et al. 2023a). A recent meta-analysis (Melo et al. 2022) found that BBFs enriched with N, among other nutrients, produced from high-pyrolysis temperature biochars (> 400°C) and feedstocks with high C content, stimulate root development and microbial communities and lead to the highest crop productivity. However, there is still a lack of field research examining the influence of BBFs on crop productivity and N losses, specifically focusing on gaseous losses such as N 2 O and NH 3 . ...
... This indicates a slow release of N from the BBF since it was applied only once at the beginning of the experiment while SF was divided into two applications. Most field studies assessing the effectiveness of BBFs have been carried out in grain crops, but studies assessing their influence on vegetable crops and their comparison to other optimized fertilization strategies are notably scarce (Melo et al. 2022). Grafmüller et al. (2022) found similar yields after the application of N-enriched biochars compared to urea or NH 4 NO 3 in white cabbage. ...
... The impact of BBF on crop yields and N efficiency is highly dependent on BBF characteristics, and they should be carefully considered (Osman et al. 2022). In a recent meta-analysis, Melo et al. (2022) found that BBFs with high C and nutrient concentrations were the most effective in enhancing nutrient use efficiency and crop yields compared to mineral fertilizers, although it should be cautiously interpreted as research on BBFs is still limited. According to their findings, the BBF used in our study had optimal characteristics, that is, with high C concentration (biochar from wood-based feedstock produced at high temperature) and high N concentration (N-doped through postpyrolysis treatments). ...
Field Assessment of Biochar Interactions With Chemical and Biological N Fertilization in Pointed White Cabbage
Article
Full-text available
  • Oct 2024
The interaction of biochar with mineral fertilization has attracted attention as a strategy to reduce N losses and enhance nitrogen use efficiency. In this study, we investigated the coapplication of biochar with two optimized fertilization strategies based on split urea and a microbial inoculant (Azospirillum brasilense) in a commercial pointed white cabbage crop. Additionally, we evaluated a third optimized N fertilization alternative, a biochar‐based fertilizer (BBF) enriched in plant‐available N, which was developed from the same biochar. We assessed environmental impacts such as greenhouse gasses (GHG) and NH3 emissions, yield‐scaled N2O emissions, and global warming potential (GWP). Additionally, we evaluated agronomical outcomes such as crop yield, plant N, and chlorophyll concentration. Moreover, we examined the N‐fixing gene's total and relative abundance (nifH and nifH/16S). Biochar and BBF exhibited similar crop yield, GHG, and NH3 emissions compared to split applications of the synthetic fertilizer. The main difference was associated with the higher soil C sequestration in biochar and BBF treatments that reduced the associated GWP of these fertilization strategies. Finally, biochar favored the activity of the N‐fixing bacteria spread, compared to the sole application of bacteria and BBF demonstrated a promoting effect in the soil's total abundance of natural N‐fixing bacteria.
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... Many studies have highlighted the positive impact of biochar application on crop productivity when used as an amendment [36,52,53] and a nutrient source [54,55]. Biochars mixed with fertilizers to produce BBF have been shown to increase yield above unenriched biochars in several field trials [56]. For example, Ng et al. [57] modified a peanut shell biochar with K 3 PO 4 and observed that 3% and 5% by mass amendment to soil resulted in a 69% and 136% yield increase in P. heterophylla. ...
... These results support the conclusion that the recycled P added to the biochars from the wastewater was beneficial to plant growth. Melo et al. [56] did a meta-analysis of field studies that compared the potential of BBF as replacements for conventional fertilizers. They found that the average crop productivity increased by 10% in fields that were amended with BBF. ...
... They found that the average crop productivity increased by 10% in fields that were amended with BBF. However, the Melo et al. [56] meta-analysis did not show any overall effect of increased P availability on crop productivity from using BBF. In contrast, the Fe-amended biochar used in the WRRF showed increased P availability that resulted in greater above-ground plant tissue concentrations. ...
Availability of Recycled Phosphorus on Biochar Reacted with Wastewater to Support Growth of Lactuca sativa
Article
Full-text available
  • Aug 2024
The use of biochar in water resource and recovery facilities (WRRF) shows promise for recovery of phosphorus (P) to use as a biochar-based fertilizer (BBF) that can replace conventional fertilizers, promote carbon sequestration, and improve soil quality. In this study, biochar was recovered after being dosed into secondary-treated discharge from a municipal WRRF. The value of the recovered biochar as a BBF was tested in a lettuce (Lactuca sativa) growth trial. The BBF was compared to an inorganic fertilizer, raw biochar, and controls that had either only nitrogen (N) fertilizer or no amendment. The ability of the treatments to support plant growth was determined by measuring plant height, biomass, leaf tissue total N and P concentration, and plant quality. Plant quality for the Fe-modified biochar used in the WRRF was 9.05 (±0.44) on a 10-point scale compared to 9.61 (±0.46) for the inorganic fertilizer treatment and 2.22 (±0.82) for the untreated control. Plant tissue P concentrations were 6.28 (±0.83), 9.88 (±0.90), 15.46 (±2.54), and 6.36 (±1.91) g plant −1 for the raw biochar, Fe-modified biochar used in the WRRF, inorganic fertilizer, and no amendment treatments, respectively. Soil P availability and P uptake amount in the leaves indicated that the BBF released P more slowly than the inorganic P fertilizer; however, it was sufficiently available for uptake to support plant growth to maturity. Results from these experiments show that Fe-modified biochar used in WRRF can supply adequate P to plants. The slow release will reduce P leaching into surface waters.
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... Among strategies available, pyrolysis (thermal conversion under inert condition) of biowastes can produce P-rich biochars that can be directly used as slow release fertilizers [5,6]. After pyrolysis the P is retained in the solid product (i.e., biochar), often in the form of orthophosphate (PO 4 3-) bound to cations like calcium (Ca) and magnesium (Mg) [7][8][9]. ...
Temperature-Dependent Phosphorus Speciation and Release from Magnesium-Rich Biochars
Article
Full-text available
  • Nov 2024
Thermal conversion of biomasses into biochar-based slow-release fertilizers presents an attractive approach to recover and reuse phosphorus (P) in agriculture, and the presence of magnesium (Mg) can stabilize the P into poorly leachable yet plant-available forms. Nevertheless, the effect of pyrolysis temperature on P speciation and release from Mg-rich biochars is poorly understood. To understand this, spent green tea leaves were treated with magnesium oxide (MgO) and phosphoric acid (H3PO4) and pyrolyzed at 300–700 °C. By using X-ray diffraction (XRD) and FTIR spectroscopy, three types of Mg phosphate forms were identified in the Mg/P-modified biochars: (i) crystalline Mg pyrophosphate (Mg2P2O7) at 400–700 °C, (ii) crystalline Mg orthophosphate (Mg3(PO4)2) at 700 °C, and (iii) an amorphous ortho-/condensed phosphate phase. Sequential (Hedley) extraction confirmed that increasing the pyrolysis temperature from 300 to 500 °C decreased the orthophosphate (Pi) extractability and increased that of polyphosphate (Px), and the readily available P (in H2O and 0.5 M NaHCO3) was high at 300–500 °C. Biochars produced at 600 and especially 700 °C contained primarily long-term available P species (extractable in 1 M HCl). This temperature-dependent extractability was ascribed to phosphate phase transformations and increased crystallinity at higher temperatures. Similar trends in P release with pyrolysis temperature were found in kinetic release in water, and post-kinetics characterization confirmed that struvite or struvite-K and Mg2P2O7 were rate-limiting phases for phosphate dissolution. These results provide mechanistic insights into the P transformations for the design of more efficient Mg-rich biochar-based slow-release fertilizers with minimal P risk losses. Graphical Abstract
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... 7 To overcome this limitation, significant efforts are being made to modify and activate biochar, 8,9 leading to the development of so-called biochar-based fertilizers (BBF). [10][11][12] These biocharnutrient-enriched composites can serve as slow-release fertilizers to enhance nutrient use efficiency. 13 In addition to its nutritional value, other properties of biochar can affect seed germination and plant growth in different crop species, as recently reviewed by Joseph et al. 14 These effects can be either positive or negative, depending on several factors that are mainly related to the characteristics of the biochar (origin; production process; post-production treatments; aging, toxic compounds, capacity to alter the pH), biochar use conditions (biochar rate; soil or substrate properties), and plant sensitivity to abiotic and biotic factors. ...
Effects of biochar, N‐enriched biochar and urea on tomato seed germination, vegetative growth, and fruit traits
Article
Full-text available
BACKGROUND Agronomic uses of biochar have been intensely explored in the last 15 years. Recently, a new generation of biochar‐based fertilizers has been developed. Raw biochar (BCH), nitrogen‐enriched biochar (N + BCH) or urea were added to a coir fiber‐based substrate for tomato cultivation, to assess seed germination, growth and fruiting of two cultivars (Cuarenteno and Moneymaker). RESULTS BCH stimulated seed germination and early radicle growth, possibly because of the presence of karrikins detected in both BCH and N‐BCH (0.039 and 0.044 mg kg⁻¹, respectively). However, BCH reduced growth in adult plants in both cultivars, probably because of ammonium retention, causing low‐N‐stress‐related symptoms such as accumulation of flavonoids in the leaf. Urea was toxic for seed germination because of the fast release of ammonium, but caused a positive effect on adult plant growth and yield, increasing chlorophyll in both cultivars, quantum yield and ascorbic acid in cv. Cuarenteno, and decreasing flavonoids and peroxide in leaves of both cultivars. Unlike urea, N + BCH showed a positive impact on plant growth and yield, but without releasing high amounts of ammonium or negatively affecting seed germination. Nitrogen‐rich amendments reduced phosphorus and increased iron leaf content in both cultivars. CONCLUSION BCH can be effectively used as a growth medium constituent in nurseries for seedling production, whereas N + BCH offers a promising alternative to urea or other nitrogen mineral fertilizers for crop cultivation. © 2024 The Author(s). Journal of the Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.
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... The observed increase in crop yield suggests that biochar can be an effective component of fertilizers, enhancing efficiency and boosting plant productivity compared to conventional fertilizers. The results of a meta-analysis of 148 observations indicated that biochar-based fertilizers resulted in a 10% increase in crop productivity compared to conventional fertilizers (Melo et al. 2022). Nevertheless, as Table 3 shows, the effectiveness of biochar may vary depending on factors such as soil type, biochar properties, and crop species. ...
The potential of biochar incorporation into agricultural soils to promote sustainable agriculture: insights from soil health, crop productivity, greenhouse gas emission mitigation and feasibility perspectives—a critical review
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Biochar is a carbon-rich material produced through the pyrolysis of organic biomass. Its unique properties make it a versatile asset in agricultural and environmental management. This review paper provides scientific insights into how biochar affects soil’s physical, chemical, and biological properties. It then discusses how these changes can impact crop growth and yield, addressing a key concern for farmers while also considering the potential for biochar to mitigate greenhouse gas (GHG) emissions such as carbon dioxide (CO2), Nitrous oxide (N2O), and methane (CH4), which is of public interest. Additionally, it examines the costs and benefits associated with biochar use, aiming to guide its adoption and suggest future research directions in agricultural applications. Biochar incorporation improves soil properties by enhancing structure, water retention, aeration, nutrient availability, and microbial activity. Different processes impact the effects of biochar on soil, plants, and agricultural systems, influenced by factors like biochar type, soil type, and application rate. Understanding the interaction of these elements, especially over the long term, is vital for promoting the widespread use of biochar in agriculture. Moreover, assessing the economic benefits and costs of biochar in each region is key to convincing farmers to adopt this practice. Graphical abstract
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... Solid organic wastes, as well as human urine, are rich in macronutrients, consistently produced in human settlements and widely available globally. Many treated and untreated organic wastes have been demonstrated to be effective crop fertilisers either alone (Marchuk et al., 2023;Melo et al., 2022;Roy et al., 2006;Schiemenz and Eichler-Löbermann, 2010) or combined with other organic wastes, provided that their properties (e.g. pH, dry matter) do not diminish each other's fertiliser efficacy (Brod et al., 2014). ...
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... The biochar, a carbon rich solid byproduct of biomass thermochemical conversion, has attracted increasing interest for its ability to retain soil nutrients (Azeem et al., 2019) and improve soil fertility . Hence, biochar and organic fertilizers combined application might be an alternative to compensate potential disadvantages of organic fertilizers applied alone, and to enhance their performance in terms of soil quality and sustainable crop production (Melo et al., 2022;Yan et al., 2023). Compared to the organic fertilizer alone, integrating biochar with organic fertilizers has significant positive effects on nutrient use efficiency and crop productivity in low-fertility soil. ...
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Quantification of soil organic carbon: the challenge of biochar-induced spatial heterogeneity
Article
Full-text available
  • Jul 2024
Introduction Soil organic carbon (SOC) content can vary significantly across a given plot. Therefore, a representative sampling is a prerequisite to obtain meaningful results from analysis and of utter importance when SOC quantification is used to quantify (temporary) carbon dioxide removal (CDR). However, certain management practices aiming to increase SOC further increase the level of heterogeneity and may challenge representative sampling schemes. This includes concentrated root-zone application of biochar, which immediately increases SOC with the input of biochar-C and may promote the local enrichment of non-biochar SOC over time. Methods Here, we used numerical modelling to quantify the number of single sampling points (soil cores) needed to achieve a representative sample of biochar-C and total SOC on a plot after application of biochar in rows, e.g., for growing vegetables, or in the circumference of trees in agroforestry systems. Results After row application of 5 t ha ⁻¹ biochar in soil with rather low SOC content (26 t ha ⁻¹ ), 140 soil cores (per 0.25 ha plot) where necessary to achieve representative sampling of C-stocks (±5% error) in 90% of the repeated sampling simulation cases. Compared to realistic and cost-effective soil sampling scenarios in agronomic practice, we conclude that concentrated root zone application of biochar makes representative sampling for quantification of SOC in soils with low baseline C-stocks virtually impossible. Discussion This finding calls into question the soil-sampling and SOC-analysis-based (“result-based”) monitoring of SOC as a (temporary) CDR when biochar might have been applied. Considering the rapid scaling of biochar production and use in agriculture, this is a considerable challenge for SOC certification. Instead, action-based incentives, rewarding farmers for carrying out specific practices, could be applied to promote carbon farming practices.
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Biochar effects on crop yield variability
Article
  • Jul 2024
  • FIELD CROP RES
Context or Problem Numerous studies have demonstrated that biochar application can increase crop yield by improving soil properties and health. Yet, these studies, however, neglected how biochar alters yield variability across years – reflecting the yield stability. Objective or Research question This study aimed to investigate the effects of biochar application on crop yield variability. Methods Published data from 38 experimental sites were collected from the Web-of-Science. Two-thirds of the data were originated from three main staple crops: maize, wheat, and rice. The remaining were from rapeseed, soybean, sweet potato, and peppermint. Biochar effects on crop yield and its variability as well as their driving factors were analyzed by linear mixed models depending on soil conditions, field management practices, and climate types. Results Biochar increased the crop yield globally by 14 %, especially in soils with low pH (< 5.5), low nitrogen (N) and phosphorus (P) inputs (≤ 120 kg N ha−1, < 35 kg P ha−1), with high biochar inputs (≥ 20 Mg ha−1), and under crop rotation. Biochar increased crop yields by 12 % in short-term (≤ 5 years) and 21 % in long-term (> 5 years) experiments. Biochar increased yield variability by 42 % in acidic soils (pH < 5.5) and by 24 % with low N inputs (≤ 120 kg N ha−1), mainly because its liming and fertilization effects were short-lasting within the first few years. The yield variability after biochar application decreased with the increase in mean annual temperature, inter-annual variabilities of temperature and precipitation, but with the decrease in mean annual precipitation in the growing season. Yield variability under biochar increased in short-term experiments by 27 %, but there was no change (0 %) in long-term experiments because of the higher yield gains and resistance to fluctuating weather conditions. Therefore, crop yield variability decreased with increasing yield in long-term experiments. Conclusions Biochar application increased short-term variability of crop yields, but its long-term variability remained unaffected. Implications or Significance This study highlights that biochar can support steadily future crop production in the long run.
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Combined application of biochar with fertilizer promotes nitrogen uptake in maize by increasing nitrogen retention in soil
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Combined application of biochar with fertilizers has been used to increase soil fertility and crop yield. However, the coupling mechanisms through which biochar improves crop yield at field scale and the time span over which biochar affects carbon and nitrogen transformation and crop yield are still little known. In this study, a long-term field trial (2013–2019) was performed in brown soil planting maize. Six treatments were designed: CK—control; NPK—application of chemical fertilizers; C 1 PK—low biochar without nitrogen fertilizer; C 1 NPK, C 2 NPK and C 3 NPK—biochar at 1.5, 3 and 6 t ha ⁻¹ , respectively, combined with chemical fertilizers. Results showed that the δ ¹⁵ N value in the topsoil of 0–20 cm layer in the C 3 NPK treatment reached a peak of 291 ‰ at the third year (2018), and demonstrated a peak of 402 ‰ in the NPK treatment in the initial isotope trial in 2016. Synchronously, SOC was not affected until the third to fourth year after biochar addition, and resulted in a significant increase in total N of 2.4 kg N ha ⁻¹ in 2019 in C 3 NPK treatment. During the entire experiment, the ¹⁵ N recovery rates of 74–80% were observed highest in the C 2 NPK and C 3 NPK treatments, resulting in an annual increase in yields significantly. The lowest subsoil δ ¹⁵ N values ranged from 66‰ to 107‰, and the ¹⁵ N residual rate would take 70 years for a complete decay to 0.001% in the C 3 NPK. Our findings suggest that biochar compound fertilizers can increase C stability and N retention in soil and improve N uptake by maize, while the loss of N was minimized. Biochars, therefore, may have an important potential for improving the agroecosystem and ecological balance. Graphic abstract
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Synthesis modified biochar-based slow-release nitrogen fertilizer increases nitrogen use efficiency and corn (Zea mays L.) growth
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Full-text available
  • Nov 2020
Nitrogen use efficiency enhancement is an important approach to obtain sustainable agriculture. Engineered biochar is considered as a super carrier to produce high-quality slow-release fertilizer. The purpose of this study was to compare nitrate and ammonium release using three treatments (i.e., MgCl2-modified biochar-based slow-release fertilizer (MBSRF), enriched modified biochar (EMBC), and chemical fertilizer (ammonium nitrate: AN)) and to analyze their effects on water retention, nitrogen use efficiency, and Zea mays L. growth. The treatments were prepared, and nitrate and ammonium release were determined. A pot experiment was performed with four treatments (control, MBSRF, EMBC, and AN), and the treatments’ impacts on selected parameters were investigated. Soils treated with EMBC and MBSRF retained more water than those treated with AN and the control treatment. The nitrate and ammonium release of MBSRF was slower and about 2.5 and 1.5 times lower than that of AN. MBSRF effectively increased plant height (20.1, 11.7, 37.1 %), shoot dry weight (24.2, 23.3, 44.0 %), root dry weight (29.9, 24.1, 48.8 %), chlorophyll content (9.43, 8.01, 13.6 %), and leaf area (24.8, 21.0, 30.4 %) in comparison to the AN, EMBC, and control treatments, respectively. Furthermore, the highest soil and plant nitrogen content and nitrogen use efficiency were associated with the MBSRF treatment. In conclusion, the use of MgCl2-modified biochar is promising in the synthesis of nitrogen slow-release fertilizer, and MBSRF can be used as a novel nitrogen slow-release fertilizer for increasing nitrogen use efficiency and improving corn growth.
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Feedstock choice, pyrolysis temperature and type influence biochar characteristics: a comprehensive meta-data analysis review
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Full-text available
  • Sep 2020
Various studies have established that feedstock choice, pyrolysis temperature, and pyrolysis type influence final biochar physicochemical characteristics. However, overarching analyses of pre-biochar creation choices and correlations to biochar characteristics are severely lacking. Thus, the objective of this work was to help researchers, biochar-stakeholders, and practitioners make more well-informed choices in terms of how these three major parameters influence the final biochar product. Utilizing approximately 5400 peer-reviewed journal articles and over 50,800 individual data points, herein we elucidate the selections that influence final biochar physical and chemical properties, total nutrient content, and perhaps more importantly tools one can use to predict biochar's nutrient availability. Based on the large dataset collected, it appears that pyrolysis type (fast or slow) plays a minor role in biochar physico-(inorganic) chemical characteristics; few differences were evident between production styles. Pyrolysis temperature, however, affects biochar's longevity, with pyrolysis temperatures > 500 °C generally leading to longer-term (i.e., > 1000 years) half-lives. Greater pyrolysis temperatures also led to biochars containing greater overall C and specific surface area (SSA), which could promote soil physico-chemical improvements. However, based on the collected data, it appears that feedstock selection has the largest influence on biochar properties. Specific surface area is greatest in wood-based biochars, which in combination with pyrolysis temperature could likely promote greater changes in soil physical characteristics over other feedstock-based biochars. Crop-and other grass-based biochars appear to have cation exchange capacities greater than other biochars, which in combination with pyrolysis temperature could potentially lead to longer-term changes in soil nutrient retention. The collected data also suggest that one can reasonably predict the availability of various biochar nutrients (e.g., N, P, K, Ca, Mg, Fe, and Cu) based on feedstock choice and total nutrient content. Results can be used to create designer biochars to help solve environmental issues and supply a variety of plant-available nutrients for crop growth.
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Effects of biochar-based controlled release nitrogen fertilizer on nitrogen-use efficiency of oilseed rape (Brassica napus L.)
Article
Full-text available
  • Jul 2020
Biochar-based controlled release nitrogen fertilizers (BCRNFs) have received increasing attention due to their ability to improve nitrogen-use efficiency (NUE) and increase crop yields. We previously developed a novel BCRNF, but its effects on soil microbes, NUE, and crop yields have not been reported. Therefore, we designed a pot experiment with five randomised treatments: CK (without urea and biochar), B (addition biochar without urea), B + U (biochar mixed urea), Urea (addition urea without biochar), and BCRNF (addition BCRNF), to investigate the effects of BCRNF on nitrifiers and denitrifiers, and how these impact nitrogen supply and NUE. Results of high-throughput sequencing revealed bacterial community groups with higher nutrient metabolic cycling ability under BCRNF treatment during harvest stage. Compared to Urea treatment, BCRNF treatment stimulated nitrification by increasing the copy number of the bacterial amoA gene and reducing nitrous oxide emission by limiting the abundance of nirS and nirK. Eventually, BCRNF successfully enhanced the yield (~ 16.6%) and NUE (~ 58.79%) of rape by slowly releasing N and modulating the abundance of functional microbes through increased soil nitrification and reduced denitrification, as compared with Urea treatment. BCRNF significantly improved soil NO3−, leading to an increase in N uptake by rape and NUE, thereby promoting rape growth and increasing grain yield.
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Phosphorus recovery using magnesium-enriched biochar and its potential use as fertilizer
Article
Full-text available
  • May 2020
Phosphorus (P) recovery from wastewater using biochar is an alternative to P recycle and reuse. However, the impregnation of cations for biochar production is needed to enhance P removal. We aimed at studying the P adsorption and release capacity of biochar enriched with magnesium (Mg²⁺) and its potential use as fertilizer. Biochars were produced from poultry litter (PLB), pig manure (PMB), and sewage sludge (SSB) impregnated with MgCl2. Characterization comprised pH, Electrical conductivity, total nutrient content, moisture and ash contents, FTIR, XRD, Raman, and SEM-EDX. Phosphorus adsorption isotherms by biochars were obtained and P desorption was also studied. A pot experiment with maize in an Oxisol was performed with the P-loaded biochars, triple superphosphate - TSP (positive control) and no P application (negative control). PMB showed the highest P adsorption (68.0 mg g⁻¹). The main mechanisms of P removal were through precipitation with cations, ligand exchange reactions and electrostatic attraction on the biochar surface. The P-loaded biochars promoted plant growth and accumulation of P in maize, which was similar or greater than TSP. In conclusion, Mg-impregnated biochar is a sustainable option to add value to organic residues and to recycle P to be reused as enhanced efficiency fertilizer.
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Encapsulated biochar-based sustained release fertilizer for precision agriculture: A review
Article
  • Apr 2021
  • J CLEAN PROD
The excessive use of conventional fertilizers leads to environmental issues associated with the loss of nutrient through leaching, volatilization, denitrification and surface run-off. Biochar-based fertilizer has gained much research interest as it can be used as a slow release fertilizer. Biochar-based fertilizer can alleviate the properties of soil to slow down the nutrient release rate. However, the sustained release mechanism of biochar-based fertilizer is still facing limitations. As a solution to mitigate this issue, the integration of encapsulating technology and biochar-based fertilizer has been introduced to improve the sustained release mechanism. This paper presents an extensive overview on the various formulations of biochar-based fertilizer and encapsulated biochar-based fertilizer. Additionally, the influence of the inorganic mineral, polymer and hydrogel-based fertilizers on the nutrient release behaviour are also critically discussed. The various methods used to synthesize the fertilizers and their effects on soil amendment are also discussed in detail. This paper could be used as a good source of information on the current advances and future perspectives of encapsulated biochar-based sustained release fertilizer for precision agriculture.
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Participation of urea-N absorbed on biochar granules among soil and tobacco plant (Nicotiana tabacumL.) and its potential environmental impact
Article
  • Jun 2021
  • AGR ECOSYST ENVIRON
Over use of nitrogen (N) fertilizers, most commonly as urea, is a major source for severe environmental impacts in agricultural field. Application of biochar-based N fertilisers is a promising strategy to enhance N retention and use efficiency (NUE) of crops, and alleviate environmental impact. In this study, granular biochar-urea fertilisers were prepared through adsorbed urea on biochar pellets. Low-rate biochar-enriched N fertiliser (BN), straw-powders-coated BN fertiliser (BNM), straw-powders-blended N fertiliser (MN), and a conventional N fertiliser were applied to tobacco root-zone soils in two fields at Linquan and Heishi, China. The ¹⁵N isotopic trace technique was used to track the applied N among soil N pools and tobacco plant organs. BN treatment increased the middle leaf yield by 43% and 14% in Linquan and Heishi, respectively. The yield increased by 28% and 39% when BNM was used compared to that of the soils were applied with N fertiliser. The addition of BN fertiliser decreased the NUE of tobacco but increased root-zone liable N (KEN) retention at the time of harvest, leading to a 3–10% increase in soil KEN accumulation. Such an effect could be enhanced by straw powder coating in Heishi, mainly to increase supplied urea-N retention in the root-zone. ¹⁵N fertiliser tracing revealed that application of small amounts of granular biochar-based N fertilisers increased the uptake of intrinsic soil N by plants compared to that with only N fertiliser application. Thus, biochar could be blending with urea to obtain granular biochar-based N fertilisers to replace mineral urea, thereby reducing N application rate. Further studies at multiple sites are required to determine the effects of biochar plus urea on N processes in soil–plant systems.
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A novel maize biochar-based compound fertilizer for immobilizing cadmium and improving soil quality and maize growth
Article
  • Feb 2021
  • ENVIRON POLLUT
In this study, a novel biochar-based compound fertilizer (BCF) was synthesized with maize straw biomass, diatomite, triple superphosphate and urea at different temperatures (300 °C, 450 °C, 600 °C) and mixture proportions (5:1:1:x and 10:1:1:x). An investigation was conducted into the effects of BCF at low application rates on the immobilization of available cadmium, soil fertility and maize growth. The lab incubation experiments showed that the low doses of BCF (B5PNx and B10PNx) contributed to a significant reduction of the Cd availability in soil, with the highest reduction rate of available Cd up to 44.13 %. Field experiments demonstrated that the low doses (<0.1 %) of BCF（especially for B5PN600）led to the improvement of soil fertility and maize growth (including maize yield) and the significant reduction of Cd contents in maize grains. The increase of pyrolysis temperature could enhance the biochar adsorption capacity for Cd²⁺ by increasing both specific surface areas and total pore volume. The modification of urea, diatomite and triple superphosphate played a vital role on cadmium immobilization, soil improvement and maize growth by forming porous adsorption, precipitates or complexation with the increase of functional groups, as well as supplementation of N, P, Si nutrients. This study suggested that the biochar-based compound fertilizer (BCF with a mixture ratio of 5:1:1:x) produced at 600 °C could be served as a promising and eco-friendly remediation agent for the arable soils polluted with Cd, with reduction of chemical fertilizers.
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Re-use of sugarcane residue as a novel biochar fertiliser - Increased phosphorus use efficiency and plant yield
Article
  • Apr 2020
  • J CLEAN PROD
With the advent of mechanized sugarcane harvesting in Brazil around 70 Mt of straw each year is left on the field, and ∼70% of its carbon (C) is decomposed and returned to the atmosphere on the same timeframe. The adoption of a stabilised C product such as biochar as a vehicle for nutrient delivery might address two ends of a problem: to increase nutrient use efficiency by plants while creating a viable and efficient strategy to increase stable C in soil. This study proposed a production route for a biochar fertiliser (BF) from sugarcane straw biochar (SSB), by activation of SSB with KOH and subsequent neutralisation with H3PO4. The phosphorus (P) content of BF (8.6% P) was superior to SSB. It was also noticed that structure of SSB matrix was altered, creating increased sorption capacity, with the fertiliser bound to the biochar rather than physically mixed. The BF was tested in a controlled condition experiment with sugarcane for 120 days using three low P soils with different clay contents (147, 326 and 528 g kg−1). BF led to higher biomass yield (15%) and P use efficiency (PUE) (∼10%) compared to standard P source (triple superphosphate – TSP) in the most clayey soil. The adoption of a fertiliser based on a nutrient enriched biochar can increase the effectiveness of crop production. Enhanced delivery of crop nutrients increases the attractiveness of increased soil C.
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