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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.
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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). ...
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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. ...
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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]. ...
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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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... 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. ...
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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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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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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.