The Impact of Swine Manure Biochar on the Physical Properties and Microbial Activity of Loamy Soils

Abstract

Biochar has been proven to influence soil hydro-physical properties, as well as the abundance and diversity of microbial communities. However, the relationship between the hydro-physical properties of soils and the diversity of microbial communities is not well studied in the context of biochar application. The soil analyzed in this study was collected from an ongoing field experiment (2019-2024) with six treatments and three replications each of biochar (B1 = 25 t·ha^-1 and B0 = no biochar) and nitrogen fertilizer (N1 = 160, N2 = 120 kg·ha^-1, and N0 = no fertilizer). The results show that biochar treatments (B1N0, B1N1, and B1N2) significantly improved the soil bulk density and total soil porosity at different depths. The B1N1 treatment substantially enhanced the volumetric water content (VMC) by 5-7% at -4 to -100 hPa suction at 5-10 cm depth. All three biochar treatments strengthened macropores by 33%, 37%, and 41%, respectively, at 5-10 cm depth and by 40%, 45%, and 54%, respectively, at 15-20 cm depth. However, biochar application significantly lowered hydraulic conductivity (HC) and enhanced carbon source utilization and soil indices at different hours. Additionally, a positive correlation was recorded among carbon sources, indices, and soil hydro-physical properties under biochar applications. We can summarize that biochar has the potential to improve soil hydro-physical properties and soil carbon source utilization; these changes tend to elevate fertility and the sustainability of Cambisol.

Keywords: biochar; carbon source utilization; soil hydraulic conductivity; soil indices; soil porosity.

Figure 1

Monthly mean temperature and precipitation at the experimental site during the period 2019–2020.

Figure 2

Effect of different treatments onsoil bulk density (B,D), (A) in May at 5–10 cm and 15–20 cm depth, (B) in August at 5–10 cm and 15–20 cm depth, and total soil porosity (C) in May at 5–10 cm and 15–20 cm depth, (D) in August at 5–10 cm and 15–20 cm depth. The letters a, b, c indicate statistically significant difference at p < 0.05.

Figure 3

Effect of different treatments on VWC (volumetric water content), FC (field capacity), and WP (plant wilting point) (A) in May at 5–10 cm depth, (B) in May at 15–20 cm depth, (C) in August at 5–10 cm depth, (D) in August at 15–20 cm depth.

Figure 4

Effect of different treatments on pore size distribution (macropores, mesopores, and micropores) (A) in May, at 5–10 cm and 15–20 cm depths, (B) in August at 5–10 cm and 15–20 cm depths for B0N0 (without biochar or N fertilization); B0N1 (without biochar and with 160 kg·ha⁻¹ N); B0N2 (without biochar and with 120 kg·ha⁻¹ N); B1N0 (biochar 25 t·ha 25 t·ha⁻¹ only); B1N1 (biochar 25 t·ha⁻¹ and 160 kg·ha⁻¹ N); and B1N2 (biochar 25 t·ha⁻¹ and 120 kg·ha⁻¹ N. The letters a–e indicate statistically significant difference at p < 0.05.

Figure 5

Effect of different treatments on soil hydraulic conductivity. B0N0 (without biochar or N fertilization); B0N1 (without biochar and with 160 kg·ha⁻¹ N); B0N2 (without biochar and with 120 kg·ha⁻¹ N); B1N0 (biochar 25 t·ha⁻¹ only); B1N1 (biochar 25 t·ha⁻¹ and 160 kg·ha⁻¹ N); and B1N2 (biochar 25 t·ha⁻¹ and 120 kg·ha⁻¹ N) at two different depths (5–10 cm and 15–20 cm) and times (May and August). The letters a, b, c indicate statistically significant difference at p < 0.05.

Figure 6

Effect of different treatments on the average mean of soil carbon sources. B0N0 (without biochar or N fertilization); B0N1 (without biochar and with 160 kg·ha⁻¹ N); B0N2 (without biochar and with 120 kg·ha⁻¹ N); B1N0 (biochar 25 t·ha⁻¹ only); B1N1 (biochar 25 t·ha⁻¹ and 160 kg·ha⁻¹ N); and B1N2 (biochar 25 t·ha⁻¹ and 120 kg·ha⁻¹ N).

Figure 7

Effect of different treatments on soil carbon sources (A) Average well color development (AWCD), (B) Richness (R), (C) Mclntosh index (U), (D) Carbohydrates, (E) Amines, (F) Miscellaneous; B0N0 (without biochar or N fertilization); B0N1 (without biochar and with 160 kg·ha⁻¹ N); B0N2 (without biochar and with 120 kg·ha⁻¹ N); B1N0 (biochar 25 t·ha⁻¹ only); B1N1 (biochar 25 t·ha⁻¹ and 160 kg·ha⁻¹ N); B1N2 (biochar 25 t·ha⁻¹ and 120 kg·ha⁻¹ N) at different times (24, 48, 72, and 96 h). The letters a, b, c, indicate statistically significant difference at p < 0.05.

Figure 8

Heatmap correlations under different treatments (A) B0N0 (without biochar and N fertilization); (B) B0N1 (Without Biochar and 160 kg·ha⁻¹ N); (C) B0N2 (Without Biochar and 120 kg·ha⁻¹ N fertilization); (D) B1N0 (Biochar 25 t·ha⁻¹ only); (E) B1N1 (Biochar 25 t·ha⁻¹ and 120 kg·ha⁻¹ N); (F) B1N2 (Biochar 25 t·ha⁻¹, 160 kg·ha⁻¹ N) for bulk density (BD), total porosity (TP), field capacity (FC), plant-available water (PAW), average well color development (AWCD), richness (R), the Shannon index (H), the Simpson index (D), the Mclntosh index (U), carbohydrates (CH), carboxylic acid (CA), miscellaneous (MS), hydraulic conductivity (HC). Note: Significant (p < 0.05) negative (red color) and positive (blue color) correlations between different soil carbon sources and soil physical properties are identified by color (−1.0 to +1.0); non-significant correlations are omitted.

Figure 9

Pearson’s correlations for bulk density (BD), total porosity (TP), field capacity (FC), plant-available water (PAW), average well color development (AWCD), richness (R), the Shannon index (H), the Simpson index (D), the Mclntosh index (U), carbohydrates (CH), carboxylic acid (CA), miscellaneous (MS), and hydraulic conductivity (HC) under different treatments, i.e., B0N0 (without biochar or N fertilization); B0N1 (without biochar and with 160 kg·ha⁻¹ N); B0N2 (without biochar and with 120 kg·ha⁻¹ N); B1N0 (biochar 25 t·ha⁻¹ only); B1N1 (biochar 25 t·ha⁻¹ and 160 kg·ha⁻¹ N); and B1N2 (biochar 25 t·ha⁻¹ and 120 kg·ha⁻¹ N).