Biochar-based slow-release of fertilizers for sustainable agriculture: A mini review

Abstract

Increasing global population and decreasing arable land pose tremendous pressures to agricultural production. The application of conventional chemical fertilizers improves agricultural production, but causes serious environmental problems and significant economic burdens. Biochar gains increasing interest as a soil amendment. Recently, more and more attentions have been paid to biochar-based slow-release of fertilizers (SRFs) due to the unique properties of biochar. This review summarizes recent advances in the development, synthesis, application, and tentative mechanism of biochar-based SRFs. The development mainly undergoes three stages: (i) soil amendment using biochar, (ii) interactions between nutrients and biochar, and (iii) biochar-based SRFs. Various methods are proposed to improve the fertilizer efficiency of biochar, majorly including in-situ pyrolysis, co-pyrolysis, impregnation, encapsulation, and granulation. Considering the distinct features of different methods, the integrated methods are promising for fabricating effective biochar-based SRFs. The in-depth understanding of the mechanism of nutrient loading and slow release is discussed based on current knowledge. Additionally, the perspectives and challenges of the potential application of biochar-based SRFs are described. Knowledge surveyed from this review indicates that applying biochar-based SRFs is a viable way of promoting sustainable agriculture.

Keywords: Agricultural production; Biochar; Slow-release fertilizer; Soil amendment; Sustainability.

Graphical abstract

Fig. 1

Schematic of the research evolution of biochar-based SRFs.

Fig. 2

Various methods for the synthesis of biochar-based SRFs.

Fig. 3

a. Schematic of BSRFs synthesis via co-pyrolysis; b. microwave-assisted heating behavior; c. SEM image, and d. EDX analysis; e-g. XPS P 2p spectra; h. FTIR spectra; i. XRD spectra; j. P leaching loss and the utilization efficiency. Reprinted (adapted) with permission from [66]. Copyright 2020 American Chemical Society.

Fig. 4

a. Schematic of CSRFs preparation via integrating co-pyrolysis and encapsulation; b., d. SEM images; c. AFM image; e., f. TEM images; g. elemental mapping of P; h. degradation behavior of BSRFs and CSRFs; i. fresh weight and dry weight of plant, and j. P leaching loss and utilization efficiency. Reprinted (adapted) with permission from [125]. Copyright 2021 Elsevier.

Fig. 5

a. Schematic of the synthesis of urea-infused biochar; b. FTIR of the slow-release fertilizers; c. XRD patterns of slow-release fertilizers prepared from H₃PO₄ activated biochar; d. SEM image of slow-release fertilizer; e. urea release, f. NH₄⁺-N availability, and g. cumulative N leaching. Reprinted (adapted) with permission from [70]. Copyright 2021 American Chemical Society.

Fig. 6

a. Schematic of the synthesis of biofilm coated biochar-based SRFs; b. SEM images; c. P leaching, d. cumulative P release loss; e. fresh weight, f. dry weight, and g. pictures of maize growth. Reprinted (adapted) with permission from [71]. Copyright 2021 Elsevier.

Fig. 7

The advantages and disadvantages of method for fabricating biochar-based SRFs.

Fig. 8

a. Phosphate adsorption on various biochar materials. Adapted with permission from [135]. Copyright 2018 Elsevier. b. Schematic of nutrient attachment onto biochar-based SRFs. Adapted with permission from [50]. Copyright 2021 Elsevier.