Ameliorating Effects of Biochar, Sheep Manure and Chicken Manure on Acidified Purple Soil

Abstract

The proportion of acidic purple soils has increased. Consequently, an effective method for amelioration of acidic purple soils is urgently needed. A 40 day incubation experiment using apple tree biochar, fermented sheep manure and chicken manure was conducted to assess the effects of organic materials on the acidity and fertility of acidic purple soil. The results showed that application of organic materials increased soil pH and decreased soil-exchangeable acidity. All of the treatments increased soil-exchangeable and water-soluble base cations after incubation. Specifically, biochar increased soil pH and reduced exchangeable acidity more than the other two fermented manures, because biochar was rich in carbonates and other alkaline substances. The concentration of soil available K was significantly higher under biochar than manure addition, while the opposite was true for soil available P and N, with a higher increase in soil available P in the manure treatments. By evaluating the soil fertility using a fuzzy comprehensive method, it was found that the fermented livestock manure enhanced soil fertility more strongly than biochar. Considering the effectiveness of soil amendments and production cost, applying a large amount of fermented organic fertilizer is an effective approach to the amelioration of acidified purple soil.

1. Introduction

Purple soils belonging to Cambosols and Primosols are mainly distributed in the southwest hilly regions of China, covering an area of 160,000 km², and comprise the most important agricultural soil type in the Sichuan basin of China [1]. Due to the rapid physical weathering process, the parent rocks, sedimentary mudstone and sandstone of the Triassic to Cretaceous system, have a profound influence on the properties of purple soils [2,3,4]. In the Chinese Soil Genetic Classification, purple soils are classified into three subgroups, which are acidic purple soil (pH < 6.5), neutral purple soil (pH 6.5–7.5) and calcareous purple soil (pH > 7.5) [5]. In recent decades, the proportion of acidic purple soil increased owing to the overuse of chemical fertilizers [1,6,7]. Our previous studies have reported that purple soils face higher risks of acidification than Alfisol and Oxisol [8], limiting crop growth and lowering crop yield. Consequently, it is essential to pay more attention to the ongoing acidification of these type of soils, and especially to the amelioration of acidified purple soils.

Recently, during our field investigation, we found that two agriculture facilities (Figure 1a,b) located in Jiulongpo district of Chongqing have been used continuously for vegetable cultivation for 10 years. The soils at both of these sites developed from the purple rocks of the Jurassic Shaximiao Formation (J₂s). Soil A (Figure 1a) (29.49325° N, 106.32608° E) is slightly alkaline, with a pH value of 7.86 (Figure 1c). Differently, the pH value of soil B (Figure 1b) (29.28213° N, 106.34826° E) is 4.50 (Figure 1d). The acidified soil shows the phenomenon of soil compaction and moss on the soil surface (Figure 1f). Additionally, the soil acidification induced the abnormal growth of coriander (Figure 1h). This discrepancy in acidity characteristics (e.g., pH, exchangeable acidity, and base saturation) between two purple soils can be attributed to the application of organic materials. Long-term and heavy application of chemical fertilizers (compound fertilizer, urea, and calcium superphosphate, with amounts of around 6000 kg/ha per year) induced the acidification of soil B. Soil A was also severely acidified. In the last 3 years, organic materials (e.g., decomposed fungus residue) in amounts of around 45 tons/ha per year were used in soil A (Figure 1e). Compared to soil B, large-scale application of organic materials ameliorated the acidity and increased the SOM content in soil A obviously (Figure 1g,h). So, organic materials have been shown to have ameliorating effects on acidic purple soils in field practice.

Organic materials, such as biochar, livestock manure and crop straw, have been widely used to ameliorate acidified soils. Biochar, a kind of carbon-rich solid substance, is produced through the thermal treatment of organic waste in the absence or limited supply of oxygen (pyrolysis) [9], and is very effective in ameliorating soil acidity [10,11,12,13]. The properties of biochar are affected by the type of raw material, pyrolysis temperature, and reaction residence time. Higher pyrolysis temperatures enhance the aromatic structure of biochar, significantly increasing specific surface area, pore volume, and alkaline groups [14]. Therefore, biochar produced by high-temperature anaerobic combustion is very effective in ameliorating soil acidity [14,15,16,17]. Composting organic matter is a process of degrading organic matter into inorganic matter and humus by controlling conditions such as water content, pH, C/N, and temperature [18]. The growth and reproduction process of microorganisms can degrade organic substances such as amino acids and proteins, resulting in deamination, and thus increasing the pH of mature fertilizers and neutralizing soil acidity [19]. It has been demonstrated that organic materials (straw, wood ash, sheep manure and mixed fermented organic fertilizer) have a similar pH-increasing effect on latosol relative to inorganic materials (lime and silicon calcium magnesium potassium fertilizer) [20]. Similarly, Li [21] reported that 37 years of manure-based fertilization significantly increased the pH of acidic paddy soil by a unit of 0.30 compared to control.

Little attention was paid to the amelioration of acidic purple soil, which is the most important agricultural soil in the Sichuan basin of southwestern China [1]. In field practice, organic materials have been shown to ameliorate acidic purple soil. However, systematic and quantitative characterization of the ameliorating effects of organic materials on acidified purple soil is urgently needed. Therefore, a lab incubation experiment was conducted to investigate the effects of three kinds of organic materials (biochar, chicken manure and sheep manure) on the acidity and fertility of acidified purple soil. The aim of this study was to explore the effects of biochar, sheep manure, and chicken manure on the acidity and fertility of purple soil through short-term cultivation. The results obtained in the study will provide useful references for amelioration of acid purple soils.

2. Materials and Methods

2.1. Collection and Analysis of Soil and Amendments

Acidified purple soil was collected from a farmland located in Jiangjin (29.07386° N, 106.19650° E), Chongqing. The parent rock of this soil was purple sandstone of the Jurassic Shaximiao Formation (J₂s). Topsoil (0–20 cm) was sampled, air-dried and then ground to pass a 2 mm sieve for incubation. Biochar as well as fermented chicken and sheep manure were chosen as the amendments. Biochar was produced by anaerobic pyrolysis of apple tree branches at 550℃ for 5 h. Chicken manure and sheep manure were air-dried after fermentation. These organic materials were also ground to pass a 2 mm sieve. Basic properties of soil and organic materials (

Table 1. Basic properties of the acidic purple soil.

Utilization	pH	SOM	Available Nutrients			Exchangeable Acidity	Exchangeable Base Cations				ECEC	BS
			N	P	K		K+	Na+	Ca2+	Mg2+
		g·kg−1	mg·kg−1			cmol·kg−1
Farmland	4.91	16.0	119	3.25	196	3.05	0.54	0.26	19.1	2.71	25.7	88.1%

Note: SOM: soil organic matter; ECEC: effective cation exchange capacity; BS: base saturation.

and

Table 2. Basic properties of these organic materials.

Organic Materials	pH	Total Elements						Water-Soluble Base Cations
		C	N	P	K	Ca	Mg	K+	Na+	Ca2+	Mg2+
		g·kg−1						mg·kg−1
Chicken manure	7.1	209	12.4	4.59	10.4	46.2	3.45	6450	1800	3505	174
Sheep manure	7.3	139	11.0	3.51	11.4	47.5	3.22	6875	2450	4343	74
Biochar	10.7	426	16.2	2.48	87.9	66.6	3.00	80,000	900	469	115

) were measured [22]. The pH of both soil and organic materials were measured in a 1:2.5 solid:water suspension by pH meter (DDS-307, Fangzhou, China). The soil organic matter (SOM) was determined by the K₂Cr₂O₇-H₂SO₄ method. The soil available nitrogen (N) was measured by the alkali hydrolysis and diffusion method. Soil available phosphorus (P) was extracted by 0.5 M NaHCO₃ and measured by molybdenum-blue colorimetry. Soil available potassium (K) was measured by flame photometry (AP1401, Aopu, China) after extraction by 1.0 M NH₄OAc. Soil exchangeable acidity (H⁺ and Al³⁺) was extracted with 1.0 M KCl and then titrated by 0.01 M NaOH. Soil exchangeable base cations (K⁺, Na⁺, Ca²⁺, Mg²⁺) were extracted with 1.0 M NH₄OAc. The water-soluble base cations (K⁺, Na⁺, Ca²⁺, Mg²⁺) in organic materials were extracted by deionized water. After pretreatments, Ca²⁺ and Mg²⁺ in these extractants were measured by atomic absorption spectrometry (Z-5000, Hitachi, Japan), and K⁺ and Na⁺ by flame photometry. The total carbon (C) and total N of organic materials were measured by elemental analyzer (Vario Micro, Elementar, Germany). The total K, calcium (Ca) and magnesium (Mg) in three organic materials were measured after digestion with aqua regia. The total P in organic materials was measured via vanadium molybdenum-yellow colorimetry after digestion of H₂SO₄ and H₂O₂. X-ray diffraction (XRD, XD-3, Persee, China) patterns of three organic materials were used to identify the mineral composition. The functional groups of organic materials were identified using Fourier transform infrared spectroscopy (FTIR) (L1280018, PerkinElmer, Waltham, MA, USA).

2.2. Incubation Experiment

Organic materials were incorporated into 200 g of air-dried soil with three levels—0 (control), 1%, 3%, and 5%—and then placed into 500 mL plastic beakers. Deionized water (40 mL) was supplied to the soil to bring the soil water content to the field water-holding capacity. The experiment was conducted in an incubator at a constant temperature of 25 °C for 40 days. Plastic film with small holes was used to cover the beakers to reduce moisture loss and allow air exchange. Three replicates were performed for each treatment. During the incubation, deionized water was added every 3 days after weighing each plastic beaker to maintain constant weight.

After incubation, the soil samples were air-dried and sieved for further analysis. Soil pH, soil organic matter (SOM), available nutrients (N, P, and K), soil exchangeable acidity (including exchangeable H⁺ and exchangeable Al³⁺), and exchangeable and water-soluble base cations (K⁺, Na⁺, Ca²⁺ and Mg²⁺) were measured.

2.3. Statistical Analysis

The Origin 2021 and SPSS 26.0 software packages were used for data analysis. A one-way analysis of variance (ANOVA) with least significant difference (LSD) test was used to test significant differences among the treatments. Data are expressed as the mean ± standard error in all tables and figures.

To compare the effects of organic amendments on soil fertility, the integrated soil fertility was evaluated by fuzzy comprehensive method with the fertility indexes of SOM, available N, available P, and available K. First, the membership value (N_ik) was calculated by S-shaped functions according to the influence of nutrient indexes on crop growth. The formula for calculation of N_ik is shown in Formula (1).

$$N_{\mathrm{i}\mathrm{k}}=\left\{\begin{array}{ccc}1& & x\ge x_2\\ \frac{0.9(x-x_1)}{x_2-x_1}+0.1& & x_1<x<x_2\\ 0.1& & x\le x_1\end{array}\right.$$

(1)

The turning points in the membership function curve of each indicator were finally determined as shown in

Table 3. Turning points of curve in the S-type function.

	SOM	Available N	Available P	Available K
x1	10	120	5	200
x2	30	180	20	300

[23,24].

Second, according to the contribution of each nutrient index, each factor was given a certain weight coefficient (M_ik). The absolute values of the correlation coefficients of each index were averaged. The ratio of the obtained average value to the sum of average values of correlation coefficients of all nutrient indexes is the M_ik of this nutrient index.

Finally, the fertility comprehensive index (INI) of each treatment was obtained by multiplying N_ik and M_ik (Formula (2)). The integrated soil fertility of each treatment can be characterized by the value of INI. The higher the INI value, the higher the soil fertility.

$$INI=\sum N_{\mathrm{i}\mathrm{k}}\times M_{\mathrm{i}\mathrm{k}}$$

(2)

3. Results and Discussion

3.1. Properties of Soil and Organic Materials

Basic properties of the acidified purple soil are summarized in Table 1. The pH value of the acidic purple soil was 4.91, and the content of soil exchangeable acidity was 3.25 cmol·kg⁻¹. The soil was seriously acidified and had an Al³⁺ toxicity risk for crops. It is worth noting that the acidified purple soil was rich in base cations, with base saturation of 88.1%. The pH value of biochar was 10.7, which was much higher than that of chicken manure (7.1) and sheep manure (7.3) (Table 2). Compared to chicken manure and sheep manure, biochar had the highest contents of total C and N, but the lowest content of total P. Among the three organic materials, the chicken manure had the highest contents of total P and water soluble Mg²⁺, and the sheep manure had the highest content of water soluble Ca²⁺. The content of K⁺ in biochar was much larger than that in chicken manure and sheep manure. This is because biochar contained a considerable amount of KCl (Figure 2a). The main crystalline substances in the three organic materials were quartz, KCl, CaCO₃, and K₂SO₄ (Figure 2a). Based on X-ray diffraction spectra, the peak of CaCO₃ in biochar was much stronger than that of manure, indicating that the biochar was rich in CaCO₃ (Figure 2a).

The FTIR spectra of the three organic materials are shown in Figure 2b. Generally, the peaks in the range of 3200–3650 cm⁻¹ were used to confirm the presence of alcohol, phenol and acids. The peak at 3286 cm⁻¹ (-OH functional group) was stronger in biochar than that in manure. The peak in all materials around 1110 cm⁻¹ caused by carbonate in-plane flexural vibration modes indicated the presence of carbonate, which is consistent with the XRD spectrum [25]. The peak around 1620 cm⁻¹ could be due to C = C for aromatic ring or C = O vibrations; the strong peak around 1404 cm⁻¹ present in biochar might be attributed to carboxyl group vibrations [26]. Negatively charged groups such as --O⁻ and -COO⁻ can buffer the acid addition and contribute to the alkalinity of organic material through association of these groups with H⁺ [27].

3.2. Effect of Organic Materials on Soil Acidity

Compared to the control, all materials increased the soil pH significantly after incubation (Figure 3), and the effect increased with the application rate. For example, following the addition of chicken manure, the soil pH values at 0%, 1%, 3%, and 5% rates were 4.69, 4.84, 5.12, and 5.47, respectively. Biochar worked best on soil pH even at minimal addition rate. A high concentration of Al³⁺ in the acidic soil easily prevents the growth of plant roots and reduces crop yields [28,29]. Therefore, one of the most urgent concerns is to reduce the Al³⁺ concentration in the soil, which is controlled by soil pH. As the pH increases, there is a transformation of exchangeable Al³⁺ to hydroxyl-aluminum polymerization and precipitation of Al hydroxides through hydrolysis reactions [12]. In this work, the material additions significantly reduced soil exchangeable acidity, especially exchangeable Al³⁺ (

Table 4. Effects of chicken manure, sheep manure and biochar on exchangeable acidity, exchangeable H⁺ and exchangeable Al³⁺ of acidic purple soil.

Treatment		Exchangeable Acidity	Exchangeable H+	Exchangeable Al3+
		cmol·kg−1
Control	-	3.21 ± 0.18a	0.47 ± 0.03a	2.74 ± 0.20a
Chicken manure	1%	2.21 ± 0.08b	0.37 ± 0.03ab	1.83 ± 0.06b
	3%	1.04 ± 0.10c	0.28 ± 0.05bc	0.52 ± 0.37c
	5%	0.60 ± 0.06de	0.26 ± 0.03bc	0.34 ± 0.09d
Sheep manure	1%	2.37 ± 0.26b	0.49 ± 0.17a	1.88 ± 0.12b
	3%	0.79 ± 0.12d	0.49 ± 0.25a	0.31 ± 0.29d
	5%	0.42 ± 0.03e	0.37 ± 0.03ab	0.05 ± 0.05e
Biochar	1%	0.44 ± 0.17e	0.23 ± 0.07bc	0.21 ± 0.24de
	3%	0.18 ± 0.05f	0.18 ± 0.05c	0
	5%	0	0	0

Note: Different letters within a column indicate significant differences among treatments (p < 0.05).

).

The contents of soil exchangeable and water-soluble base cations after incubation are listed in

Table 5. Effects of chicken manure, sheep manure and biochar on exchangeable base cations and ECEC of purple soil.

Treatment		Exchangeable Base Cations				ECEC
		K+	Na+	Ca2+	Mg2+
		cmol·kg−1
Control	-	0.60 ± 0.03g	0.27 ± 0.02f	19.5 ± 0.82h	2.74 ± 0.10f	26.3 ± 0.77f
Chicken manure	1%	0.82 ± 0.02g	0.32 ± 0.02ef	20.3 ± 0.58gh	2.90 ± 0.10ef	26.6 ± 0.53f
	3%	1.27 ± 0.03f	0.52 ± 0.00cd	24.7 ± 0.41e	3.50 ± 0.05cd	31.0 ± 0.36d
	5%	1.64 ± 0.02e	0.68 ± 0.02b	28.1 ± 1.40bc	3.85 ± 0.15bc	34.9 ± 1.59c
Sheep manure	1%	0.84 ± 0.04g	0.45 ± 0.11de	21.9 ± 0.90fg	3.12 ± 0.09e	28.7 ± 1.24e
	3%	1.26 ± 0.02f	0.62 ± 0.03bc	26.0 ± 1.27de	3.74 ± 0.19bd	32.4 ± 1.48d
	5%	2.13 ± 0.07d	0.90 ± 0.09a	31.1 ± 1.15a	4.42 ± 0.15a	39.0 ± 1.16b
Biochar	1%	3.64 ± 0.07c	0.28 ± 0.15f	22.8 ± 0.59f	3.26 ± 0.10e	30.4 ± 0.78de
	3%	9.29 ± 0.14b	0.32 ± 0.12ef	27.1 ± 0.24cd	3.69 ± 0.11bd	40.7 ± 0.40b
	5%	14.65 ± 0.42a	0.64 ± 0.02bc	29.6 ± 1.28ab	4.02 ± 0.11b	48.9 ± 1.46a

Note: Different letters within a column indicate significant differences among treatments (p < 0.05).

and

Table 6. Effects of chicken manure, sheep manure and biochar on water-soluble base cations of purple soil.

Treatment		Water-Soluble Base Cations
		K+	Na+	Ca2+	Mg2+
		mg·kg−1
Control		17.2 ± 0.58h	11.8 ± 0.76i	117 ± 3.00h	13.5 ± 0.44h
Chicken manure	1%	34.2 ± 0.58g	28.5 ± 1.00f	185 ± 13.1g	21.7 ± 0.92g
	3%	79.2 ± 1.44f	51.2 ± 0.29d	367 ± 15.5e	36.1 ± 0.85d
	5%	120 ± 2.52e	89.2 ± 1.44b	426 ± 42.6d	40.2 ± 1.57b
Sheep manure	1%	36.2 ± 1.04g	32.2 ± 1.26e	240 ± 7.51f	26.5 ± 0.55e
	3%	84.2 ± 1.44f	80.8 ± 2.89c	556 ± 23.2b	42.8 ± 0.31a
	5%	139 ± 1.15d	119 ± 1.15a	847 ± 10.0a	42.2 ± 0.06a
Biochar	1%	192 ± 2.89c	18.2 ± 2.08h	221 ± 5.13f	23.8 ± 0.40f
	3%	668 ± 17.6b	24.2 ± 0.29g	438 ± 5.69d	37.7 ± 0.17c
	5%	1095 ± 22.9a	29.5 ± 0.50f	485 ± 17.6c	40.4 ± 0.53b

Note: Different letters within a column indicate significant differences among treatments (p < 0.05).

. Similarly to the results for pH and exchangeable acidity, the contents of exchangeable and water-soluble base cations in the soil with the amendments were generally higher than the control and increased with the application rate. The exchangeable and water-soluble K⁺ in the soil with biochar addition were increased, and were 8.9 and 9.1 times higher than with chicken manure and 6.8 and 7.8 times higher than with sheep manure, respectively, at the addition rate of 5%. This discrepancy can be attributed to the total amount and solubility of potassium in the three organic materials (Table 2). A great deal of K⁺ dissolved from biochar can markedly increase the content of soil water-soluble K⁺ and promote more K⁺ adsorption on the soil surface. The contents of water-soluble Ca²⁺ among the three organic materials followed the order of sheep manure > chicken manure > biochar (Table 2), which induced the high content of water-soluble Ca²⁺ in the sheep manure-amended soil. In general, the effect of organic materials increasing base cations followed this order: biochar > sheep manure > chicken manure. The type of organic material significantly altered the concentration of exchangeable and water-soluble base cations (K⁺, Na⁺, Ca²⁺, Mg²⁺) and ECEC, and the application rate of organic materials also impacted the concentration of exchangeable and water-soluble base cations (K⁺, Na⁺, Ca²⁺, Mg²⁺) and ECEC significantly (Table 5).

The organic materials ameliorated soil acidity mainly with their alkali calcium carbonate, organic functional groups, and base cations. The calcium carbonate was confirmed in XRD spectra (Figure 2a), and the associated hydrolysis could release a large amount of OH⁻ to neutralize the soil acidity. There were abundant, weakly acidic functional groups (e.g., -COOH and -OH) on the surface of the three organic materials (Figure 2b). The protonation of the dissociated organic anions consumed H⁺ in soil solution and thus increased soil pH [30]. In addition, after incorporating incubation with organic materials, the negative surface charges (e.g., ECEC) and base cations of acidified purple soil increased (Table 5). This means that, to maintain the balance of charges, more base cations would be adsorbed on the soil surface with the depletion of exchangeable H⁺ and Al³⁺. Among these materials, biochar performed better than the other two organic fertilizers in improving soil pH, exchangeable acidity, exchangeable base cations, and ECEC. Therefore, the ameliorating effect of biochar in this study on soil acidity was much better than that of the animal manures.

3.3. Effects of Organic Materials on SOM and Soil Available N, P, K

SOM plays a key role in promoting the formation of soil aggregates and maintaining good soil structure. Compared with the control, the application of organic materials significantly increased the SOM concentration (Figure 4a), with the effect following the order of biochar > chicken manure > sheep manure. This is consistent with the C content in these organic materials (Figure 4a and Table 2).

With the increasing application rate of chicken manure and sheep manure, soil available N increased significantly. However, biochar hardly affected soil available N, even though it contained a higher nitrogen concentration than the livestock manure (Figure 5b and Table 2). This discrepancy between livestock manure and biochar in soil available N can be attributed to the microbial activity and carbon/nitrogen ratio (C/N) of organic materials [31]. After high pyrolysis treatment, the carbon in biochar is mainly in the form of inert aromatic moieties and graphitized ordered structures, which are very hard to be utilized by microbes. Generally, the microbial activity in fermented livestock manure was higher than that in biochar [32]. Additionally, the C/N of livestock manure is lower than that of biochar. Thus, livestock manure can stimulate nitrogen mineralization more strongly than biochar [9]. Especially, since the application of biochar markedly increased the contents of soil exchangeable and water-soluble K⁺, the content of soil available K after incubation with biochar was much higher than that with livestock manure (Figure 4c). In contrast to soil available K, the ameliorating effect of the three organic materials on increasing soil available P followed the order: chicken manure > sheep manure > biochar (Figure 4d and Table 2). The inorganic and organic phosphorus in organic materials can be released into the soil directly or after mineralization by microorganisms, which increases the content of soil available P [33,34]. Both chicken manure and sheep manure improved the soil fertility by evenly increasing the contents of SOM and available NPK. Biochar significantly increased soil available K content, but had little effect on soil available N and P.

With four fertility indexes (SOM and soil available N, P, K), a fuzzy comprehensive method was used to evaluate the integrated soil fertility of purple soil after incubation. The correlation coefficients of each nutrient index are listed in

Table 7. Correlation coefficients among soil properties.

	SOM	Available P	Available K
Available P	0.488 **
Available K	0.709 **	−0.010 NS
Available N	0.097 NS	0.842 **	−0.466 **

Note: ** in the table means statistically significant correlation at p < 0.01, NS: not significant.

. After averaging the absolute correlation coefficients of each index, M_ik of this nutrient index, the ratio of the obtained average value to the sum of the average values of the correlation coefficients of all nutrient indexes, was calculated (

Table 8. The averaged correlation coefficient and the weight coefficient of each nutrient index.

Index	Averaged Correlation Coefficient	Weight Coefficient
SOM	0.431	0.2394
Available P	0.477	0.2647
Available K	0.425	0.2360
Available N	0.468	0.2599

).

Figure 5 showed the INI value calculated by Formula (2) for every treatment in this study. Compared to control, the application of organic materials significantly increased the soil fertility. Chicken and sheep manure improved the fertility of the acidified purple soil more than biochar. Although biochar showed a greater ameliorating effect on soil acidity than the two fermented manures, its production cost is higher. Taken together, our findings indicate that applying a large amount of fermented organic fertilizer is an effective choice for the amelioration of acidified purple soil.

4. Conclusions

The incubation experiment found that the large-scale application of biochar, sheep manure and chicken manure ameliorated the acidity of purple soil, which decreased soil pH and exchangeable acidity (H⁺ and Al³⁺) and increased the content of soil base cations. Since biochar is rich in alkalis (e.g., carbonate, base cations, and carboxyl groups), it showed a better ameliorating effect on soil acidity than fermented chicken manure and sheep manure. However, the fermented animal manures can improve soil fertility more strongly than biochar by evenly increasing the contents of SOM and soil available N, P, and K. In agricultural practice, the cost of biochar is much higher than that of fermented organic fertilizer. Therefore, we propose that the cost-effective choice for ameliorating the acidity and improving the fertility of acidic purple soil is to apply a large amount of fermented organic fertilizer (e.g., livestock manure).