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Article

The Synergistic Effects of Rice Straw-Pyrolyzed Biochar and Compost on Acidity Mitigation and Carbon Sequestration in Acidic Soils: A Comparative Study

by
Xiaoying Pan
1,2,3,
Tianchu Shu
1,2,
Renyong Shi
4,*,
Xiaoxia Mao
5,
Jiuyu Li
4,6,7,
Jackson Nkoh Nkoh
8 and
Renkou Xu
4,6,7
1
College of Resources and Environment, Zhongkai University of Agriculture and Engineering, Guangzhou 510225, China
2
Engineering and Technology Research Center for Agricultural Land Pollution Integrated Prevention and Control, Guangdong Higher Education Institutes, Guangzhou 510225, China
3
La Trobe Institute for Sustainable Agriculture and Food, Department of Animal, Plant and Soil Sciences, La Trobe University, Bundoora, VIC 3086, Australia
4
State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China
5
Key Laboratory of Intelligent Quality Monitoring and Soil Fertility Improvement for Farmland, Anqing Normal University, Anqing 246011, China
6
University of Chinese Academy of Sciences, Beijing 100049, China
7
Nanjing College, University of Chinese Academy of Sciences, Nanjing 211135, China
8
Guangdong Provincial Key Laboratory for Plant Epigenetics, Guangdong Engineering Research Center for Marine Algal Biotechnology, College of Life Science and Oceanography, Shenzhen University, Shenzhen 518060, China
*
Author to whom correspondence should be addressed.
Sustainability 2025, 17(10), 4408; https://doi.org/10.3390/su17104408
Submission received: 1 April 2025 / Revised: 4 May 2025 / Accepted: 8 May 2025 / Published: 13 May 2025
(This article belongs to the Special Issue Soil Ecology and Carbon Cycle)
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Abstract

:
Straw biochar and compost can mitigate soil acidity and enhance carbon sequestration in acidic soils. However, their differential synergistic effects and underlying mechanisms remain poorly understood. To address this gap, an incubation experiment was conducted in which rice straw biochar (BC) and compost (DC) were incorporated into an Ultisol at rates of 1% and 3%. BC outperformed DC in elevating the soil pH (0.39 vs. 0.28 units), reducing the exchangeable acidity (69% vs. 62%), and decreasing the potential active aluminum pool (35.1% vs. 25.2%) due to its higher alkalinity. Additionally, BC enhanced the soil organic carbon more effectively than DC (83.7% vs. 64.0%). While 3% BC treatment reduced the readily oxidizable and dissolved organic carbon in the soil, DC increased these parameters. This contrasting effect is attributed to BC’s lower carbon reactivity, higher alkalinity, and greater C/N ratio compared to DC. Compared with the control, BC and DC also increased the soil exchangeable K+ (14.0-fold vs. 12.3-fold), Ca2+ (5.4-fold vs. 4.9-fold), and Mg2+ (3.7-fold vs. 5.2-fold). Overall, BC demonstrated superiority in mitigating acidity and sequestering carbon, while DC showed greater potential for improving fertility in acidic soils. Elucidating the distinct benefits of biochar versus compost provides valuable insights into the sustainable amelioration of acidic soils.

Graphical Abstract

1. Introduction

Acidic soils cover approximately 3.95 billion hectares globally, and are primarily located in tropical and subtropical regions. In China, the total area of acidic soil (pH < 5.5) is approximately 448,000 km2, with 75.0% of these areas located in the southern regions [1]. The high temperatures and abundant rainfall in these regions have facilitated soil mineral weathering and the leaching of base cations, resulting in a decrease in soil pH and the mobilization of aluminum (Al) [1]. When the concentration of Al in a soil solution reaches 10 μmol L−1, it compromises the integrity of the plasma membranes of the root tip cells, thereby inhibiting root growth [2]. Additionally, the warm and humid conditions have accelerated the turnover of the soil organic carbon, resulting in a diminished soil organic carbon content. For example, the average organic carbon content in cropland in southern China is only about 11.38 g kg−1 [3]. It has been reported that crop yields increase with rising soil organic carbon levels up to a specific threshold. In southern China, the yields of major crops, such as maize, wheat, and rice, can increase by 0.19 to 0.60 t ha−1 for each 1.0 g kg−1 rise in the soil organic carbon [4]. Therefore, multiple constraints, including low soil pH, aluminum toxicity, and insufficient organic matter, significantly limit agricultural productivity and sustainability in acidic soils.
Liming is a traditional method for ameliorating acidic soils and improving crop yields [5]. As lime is a non-renewable mineral resource, its large-scale application is unsustainable. Moreover, soil organic carbon mineralization is accelerated after applying the lime, which reduces the organic carbon content in acidic soils [6,7]. Returning straw to fields is regarded as a key practice in promoting the sustainable development of agriculture [8,9]. However, the effect of direct straw return on the reduction in soil acidity exhibits significant uncertainty in some cases [10]. Previous studies have shown that applying straw biochar (produced via carbonization) or decomposed straw (e.g., compost) to acidic soils not only consistently mitigates the soil acidity, but also enhances carbon sequestration [11,12]. For example, Yuan et al. [13] found that the soil pH values in treatments with 2% biochar were 0.11–1.09 pH units higher than those in direct straw return treatments. The results from a field experiment in northeastern China (Mollisols) showed that the soil organic carbon contents in treatments with maize straw biochar and maize straw compost were 352% and 93% higher, respectively, than that in a direct straw return treatment [11]. Therefore, the application of biochar and compost derived from straw presents better synergistic effects on the acidity reduction and carbon sequestration in acidic soils compared with direct straw return.
These beneficial effects of biochar and compost on acidic soils are determined by their compositions and physicochemical characteristics [12,14]. The liming effects of these organic amendments depend primarily on their inherent alkalinity contents [14]. The toxicity of the Al in acidic soils can be mitigated by straw-derived amendments through dual mechanisms: (i) the alkaline components drive the hydrolysis and precipitation of reactive Al species, and (ii) oxygen-containing surface functional groups (-COOH, -OH) adsorb Al3+ via complexation [15,16]. The carbon sequestration potential and fertility-enhancing effects of biochar and compost are closely associated with their carbon speciation and nutrient element composition [17]. For example, Shao et al. [18] found that corn straw compost is characterized by a higher proportion of aliphatic carbon, while its biochar counterpart exhibits a greater prevalence of aromatic carbon structures. Consequently, biochar application enhanced the molecular condensation and aromaticity of the humic acid in the Mollisols compared to compost, thereby promoting the stabilization of the soil organic carbon [18]. In addition to the carbon structures, the alkalinity, surface functionality, and abundance of nutrient elements can be influenced by the distinct conversion pathways of straw (anaerobic pyrolysis for biochar versus aerobic decomposition for compost) [17]. Therefore, it can be deduced that biochar and compost derived from the same straw would exert different effects on the acidity mitigation, carbon sequestration, and fertility enhancement in acidic soils. However, there is a paucity of research focusing on the differences between biochar and compost derived from identical agricultural residues with regard to the amelioration of acidic soils and the underlying mechanisms [17]. This knowledge gap is a significant impediment to achieving the maximum sustainable potential of straw return in acidic soils.
In this study, rice straw was used as the raw material for biochar (BC) and compost (DC). The BC was prepared through anaerobic pyrolysis at 400 °C, while the compost (DC) was produced by decomposition using an Effective Microorganisms (EM) inoculant. Subsequently, a laboratory incubation experiment was conducted by adding 1% and 3% of these straw derivates into an acidic soil. The objectives of this study were as follows: (i) to compare the differences between the straw-derived biochar and compost in their effects on acidity reduction and aluminum immobilization; (ii) to investigate the impacts of the straw-derived biochar and compost on the soil carbon fractions and fertility improvement; and (iii) to analyze the mechanisms underlying their distinct synergistic effects on acid mitigation and carbon sequestration. The findings of this study could provide a scientific basis and technical support for optimizing crop residue utilization to enhance the sustainable development of acidic soils.

2. Materials and Methods

2.1. Preparation and Basic Properties of Soil and Straw Derivates

The soil used in this experiment is an Ultisol developed from red sandstone and conglomerate. A soil sample was collected from the surface layer (0–20 cm) of cropland in Shaoguan, Guangdong Province, China (24°8′ N, 113°6′ E). After removing the stones and residual roots, the soil sample was air-dried and ground to pass through a 2 mm sieve and a 0.25 mm sieve. The 2 mm-sieved sample was used in the incubation experiment, while the 0.25 mm-sieved sample was used to determine the soil’s basic physicochemical properties. The soil pH was 4.25. The soil organic matter content was 10.70 g kg−1. The soil cation exchange capacity (CEC) was 9.74 cmol(+) kg−1. The contents of exchangeable H+ and Al3+ in the soil were 0.33 cmol kg−1 and 10.80 cmol(+) kg−1, respectively. The contents of exchangeable K+, Ca2+,, and Mg2+ in the soil were 0.50, 0.33, and 0.35 cmol(+) kg−1, respectively.
Both the biochar and the compost used in this study were derived from rice straw. The rice straw was collected from paddy fields in Shaoguan, Guangdong Province, China (24°8′ N, 113°6′ E). After washing with water, the straw was air-dried and then ground through a 0.43 mm sieve. The straw sample was carbonized in a muffle furnace under anaerobic conditions, with the pyrolysis process heated at a rate of 20 °C min−1 and maintained at 400 °C for 3 h. After cooling to room temperature, the carbonized product was collected and ground through a 0.25 mm sieve to obtain the rice straw biochar (BC) [19].
The rice straw compost (DC) was produced by decomposing the straw sample under aerobic conditions. First, the C/N ratio of the rice straw was adjusted to 25 with urea, and then, 2% EM microbial inoculant was added and thoroughly mixed. The mixture was moistened with deionized water to a 65% water content and incubated at 30 °C for 150 days. The pile was rehydrated every 3 days to maintain the moisture. After 30 days, the water content was reduced to 40% to ensure normal microbial activity. During the initial stage of the incubation, the pile was turned every 3 d. This interval was extended to once every 7 days after one week, and turning ceased after 45 days. After decomposition, the composted straw was dried at 60 °C and ground to pass through a 0.25 mm sieve [20]. The yields of the BC and DC were 35.39% and 26.61%, respectively. The basic properties of the BC and DC are shown in Table 1.

2.2. The Soil Incubation Experiment

When biochar or compost are used as amendments, their medium and high application rates of 20 and >40 t ha−1 have been reported in the literature [21]. Here, the BC and DC were mixed with the soil samples at addition rates of 1% and 3%, resulting in field application rates in the topsoil equivalent to approximately 20 and 60 t ha−1. These mixed samples were labeled as 1% BC, 3% BC, 1% DC, and 3% DC. In addition, the soil sample without the addition of BC or DC was used as a control (CK). Three replicates were established for each treatment. The mixtures were placed in plastic cups and moistened with deionized water to 70% of the soil’s field water-holding capacity (approximately 20% w/w). The plastic cups were covered with a perforated plastic film to allow for gas exchange while minimizing the moisture loss. All samples were incubated in a Percival incubator (Percival 136NL, Percival Scientific, Perry, IA, USA) at 25 °C for 60 d in the dark. During the incubation period, they were weighed and rehydrated every 3 days to maintain the moisture levels. After incubation, the soil samples were air-dried, ground, and passed through a 0.25 mm sieve. The following parameters were measured to investigate the effects of the BC and the DC on the soil acidity amelioration: soil pH, exchangeable acidity, soluble aluminum (Al), and solid-phase Al speciation, which included exchangeable Al (Ex-Al), organically bound Al (Org-Al), hydroxyl-bound Al (Hyd-Al), and amorphous Al (Amo-Al). The soil exchangeable base cations and organic carbon fractions—including the total organic carbon (SOC), readily oxidizable organic carbon (ROC), and dissolved organic carbon (DOC)—were analyzed to evaluate the effects of the BC and the DC on carbon sequestration and soil fertility improvement in the acidic soil.

2.3. Analytical Methods

The pH of the straw derivatives was determined using an Orion pH meter (Thermo Scientific Orion Star A211, Waltham, MA, USA) at a solid-to-liquid ratio of 1:20. The ash alkalinity of the straw derivatives was measured using a modified titration method [13]. The contents of carbonates in the straw derivatives were measured through the volumetric analysis of CO2. The contents of soluble base cations (Na+, K+, Mg2+, Ca2+), exchangeable base cations (K+, Ca2+, and Mg2+), and the CEC of the straw derivatives were determined by a modified ammonium acetate substitution method [13]. The total carbon and nitrogen contents of the straw derivatives were determined using an elemental analyzer (Multi N/C 3100 TOC/TN, Analytik Jena, Jena, Germany).
The soil pH was measured in 0.01 M CaCl2 at a ratio of 1:2.5 w/v using an Orion pH meter (Thermo Scientific Orion Star A211) and a combined pH electrode. The soil CEC was measured with the ammonium acetate method at a pH of 7.0, and the extracted solution was then used to measure the soil exchangeable base cations (Ca2+, Mg2+, K+,, and Na+). The Ca2+ and Mg2+ were measured by atomic absorption spectrophotometry (novAA350, Analytik Jena AG, Jena, Germany), and the K+ and Na+ were measured using flame photometry (Sherwood M410, Sherwood Scientific Ltd., Cambridge, UK) [22]. The soil exchangeable acidity (H+ and Al3+) was extracted with 1.0 M KCl and titrated with 0.01 M NaOH [22]. The soil soluble Al was determined by inductively coupled plasma mass spectrometry (ICP-MS 7700x, Agilent, CA, USA) after extraction with 1 mM KCl. The soil solid-phase Al speciation was analyzed after sequential extraction. The soil exchangeable Al was extracted with 1 M KCl solution, the organically bound Al with a solution containing 0.1 M CuCl2 and 0.5 M KCl, the hydroxyl-bound Al with 1 M NH4OAc solution, and the amorphous Al with 1 M (NH4)2C2O4 solution. The Al contents in these extracts were measured by inductively coupled plasma atomic emission spectrometry (ICP-AES VISTA MPX, Varian, CA, USA) [23]. The SOC contents were determined by the wet oxidation titration method [22]. The ROC in the soil and the derivatives was determined using the KMnO4 oxidation method [24]. The contents of DOC in the soil and the derivatives were determined using a carbon and nitrogen analyzer (Multi N/C 3100 TOC/TN, Analytik Jena, Jena, Germany) after extraction with deionized water [24].

2.4. Statistical Analysis

SPSS 26.0 (SPSS Inc., Chicago, IL, USA) was used for the statistical analysis of the data obtained. A one-way analysis of variance (ANOVA) was used to test for significant differences among the different treatments. The means were compared using the least significant differences (LSDs) with Duncan’s multiple range test at p < 0.05, following the one-way ANOVA. Pearson correlation analyses were performed to assess the relationships between (i) the exchangeable aluminum (Al) and soil pH, (ii) the solubilized Al and soil pH, and (iii) the solubilized Al and DOC.

3. Results and Discussion

3.1. Effects of BC and DC on Soil Acidity

As shown in Figure 1, the BC and DC significantly increased the soil pH, and the magnitude of the increase was proportional to their application rates. The soil pH increased by 0.39 and 0.28 pH units after applying the 3% BC and DC, respectively. Correspondingly, the application of BC and DC significantly reduced the exchangeable acidity of the soil (Figure 1B), especially that of the soil exchangeable Al3+. The exchangeable acidity in the 3%BC and 3%DC treatments was reduced by 69% and 62%, respectively. The Pearson correlation analyses showed that the increase in soil pH was significantly correlated with a decrease in soil exchangeable acidity (R2 = 0.96, p < 0.05). This indicates that the increase in the soil pH following the application of BC and DC promoted the hydrolysis of exchangeable Al3+, thereby reducing the exchangeable acidity in the soil.
Compared with the DC, the BC presented a superior effect in ameliorating the soil acidity (Figure 1). It has been widely accepted that the contents of alkaline substances, characterized by ash alkalinity, in organic amendments determines their liming effects on acidic soils [25]. Here, the liming effects of the DC and BC were also consistent with their inherent alkalinities. The ash alkalinities in the BC and the DC were 148.51 cmol kg−1 and 115.73 cmol kg−1, respectively (Table 1). Field et al. [25] quantified alkaline substances in biochar into four categories, including organic surface conjugate acids (such as -COO-, 5 ≤ pKa ≤ 6.4), soluble organic alkalinity, carbonates (HCO3− and CO32+), and other inorganic alkalinities (non-carbonate, such as metal oxides). These alkaline substances can consume the protons in acidic soils, thereby increasing the soil pH. Additionally, the decarboxylation of the active organic anions in BC and DC can also contribute to the increase in soil pH by releasing OH− [26].
Both the carbonization and decomposition of straw can enrich alkaline substances due to the loss of carbon elements [25]. Therefore, the application of straw biochar and compost shows a more stable liming effect over time than the direct addition of straw to acidic soils [12]. It is noteworthy that both the yield and ash alkalinity of the BC were higher than those of the DC (yield: 35.39% vs. 26.61%). This indicates that the anaerobic pyrolysis of the rice straw at 400 °C was more favorable for alkaline enrichment than the aerobic decomposition of the straw at room temperature. The content of alkaline substances in biochar is significantly influenced by both pyrolysis temperature and straw type. Therefore, further research is warranted to more precisely evaluate the differences in liming effects between biochars derived from various feedstocks pyrolyzed at different temperatures and their corresponding straw composts.

3.2. Changes in Soil Al Speciation After Applying BC and DC

The concentration of soil soluble Al decreased with increasing BC application rates.
The 3% DC application also decreased the soluble Al concentration in the soil, whereas the 1% DC application increased it (Figure 2). Compared with the control, the application of 1% BC, 3% BC, and 3% DC reduced the soil soluble Al concentration by 16.6%, 37.7%, and 21.2%, respectively, while the 1% DC significantly increased the soil soluble Al concentration by 43.8%. The reduction in the soil soluble Al concentration was negatively correlated with the increase in the soil pH (R2 = 0.52, p < 0.01). This indicates that the soil pH elevation after the BC and DC addition was the main contributor to the substantial decrease in the soil soluble Al concentration. A higher soil pH would facilitate the hydrolysis and subsequent precipitation of Al3+ in the soil solution [27]. In addition to the soil pH, the DOC content also influenced the concentration of soil soluble Al. The soil pH was not significantly increased in the 1% DC treatment (p > 0.05), whereas the DOC content increased by 18.6% after the 1% DC application. These soluble organic molecules can complex with Al3+ to form Al-DOC complexes, which enhance the dissolution of solid-phase Al in soil [28]. Soil soluble Al decreases exponentially with a rising soil pH, but increases linearly with the DOC concentration [15]. Therefore, the influence of the BC and DC on the soil soluble Al depended on the balance between their liming effects and DOC-enhancing effects. The BC exhibited greater liming effects, but a weaker DOC-enhancing capacity than the DC, resulting in a more pronounced reduction in the soil soluble Al.
The potentially active Al (Ex-Al, Org-Al, Hyd-Al) and amorphous Al (Amo-Al) in the soil solid phase were significantly affected by BC and DC application (Figure 3). The soil exchangeable Al decreased with increasing BC and DC applications, with the BC treatments showing greater reduction compared to the DC treatments. The 3% BC and 3% DC applications decreased the soil exchangeable Al by 74.0% and 66.0%, respectively (Figure 3A). Conversely, both the Hyd-Al and Org-Al contents increased with BC and DC application. While the Hyd-Al showed greater enhancement in the BC treatments than in DC treatments, the opposite trend was observed for the Org-Al. Specifically, the 3% BC and 3% DC applications increased the Hyd-Al content by 40.0% and 29.0%, and the Org-Al content by 30.0% and 116.0% (Figure 3B,C). The total pool of potentially active Al in the soil gradually decreased with increasing application rates of both BC and DC, with the BC demonstrating greater reduction effectiveness than the DC. The application of 3% BC and 3% DC reduced the total potentially active Al pool by 35.1% and 25.2%, respectively. Correspondingly, the soil Amo-Al content significantly increased with the application of BC and DC (Figure 3D). It should be noted that when amended soils undergo reacidification, these potentially active Al fractions could be rapidly mobilized into the soil solution [28]. The observed reduction in the soil’s potentially active Al pool suggests a decreased risk of Al activation during soil reacidification, with the BC demonstrating more pronounced mitigation effects compared to the DC.
The mechanisms by which the BC and DC immobilized the soil reactive Al can be quantified by calculating the proportions of the increments of Org-Al, Hyd-Al, and Amo-Al to the decreases in Ex-Al following the addition of BC and DC. The decrease in the soil Ex-Al following the application of BC and DC exceeded the cumulative increase in the soil Org-Al, Hyd-Al, and Amo-Al. This discrepancy means that some of the Ex-Al was transformed into crystalline minerals through hydrolytic precipitation. Its contribution ranged from 49.1% to 62.4% in the BC and DC treatments, and increased with their application rates. Additionally, the hydrolytic precipitation of the Ex-Al also formed amorphous Al, accounting for 3.3%~25.8% of the decrease in the Ex-Al after the DC and BC applications, and this contribution decreased with increasing amendment rates. This can be attributed to the enhanced transformation of amorphous Al into crystalline Al at high soil pH levels [29]. Furthermore, hydrolytic precipitation constitutes the primary mechanism for the BC and DC’s immobilization of the soil active Al, accounting for over 58.4% of the reduction in the soil Ex-Al in the BC and DC treatments. The precipitation’s contributions in the BC treatments exceeded those in the DC treatments, owing to BC’s superior liming effect. Additionally, surface complexation adsorption also contributed to the decrease in the soil Ex-Al, as evidenced by the increases in the soil Org-Al and Hyd-Al. Specifically, organic complexation and hydroxyl-Al adsorption accounted for 23.9% and 17.6% in the 3% DC treatment and 5.4% and 21.8% in the 3% BC treatment, respectively. These results suggest that the Al adsorption on the DC surfaces was mainly mediated by organic complexation, whereas it was dominated by hydroxyl-Al adsorption on the surface of the BC. The stronger liming effect of the BC facilitated the hydrolysis of the exchangeable Al to Al(OH)2+ and Al(OH)2+, which were subsequently adsorbed onto the 2:1 mineral surface to form Hyd-Al. In contrast, the DC surface exhibited more oxygen-containing functional groups (e.g., -COOH and -OH), which are the primary sites of Al complexation [16], compared to the BC (158.0 vs. 108.0 cmol kg−1). Consequently, the DC demonstrated greater efficacy in forming Org-Al compared to the BC. The pathways and contributions of DC and BC in immobilizing soil active Al are closely related to their alkalinity and surface properties. Due to its higher alkalinity, BC incorporation significantly enhanced the transformation of the exchangeable Al into more stable forms (including the amorphous and crystalline phases) compared to the DC, thereby improving Al stability in the acidic soils.

3.3. Response of Soil Organic Carbon to BC and DC Application

The application of organic materials is recognized as a crucial strategy for improving soil fertility and enhancing carbon sequestration capacity. As illustrated in Figure 4A, both the BC and DC treatments significantly increased the total organic carbon in the soil. The magnitude of the SOC enhancement increased with the amounts of BC and DC applied. The SOC contents in the BC treatments were significantly higher than those in the DC treatments. The 3% BC and 3% DC applications increased the SOC content by 83.7% and 64.0%, respectively. ROC and DOC are widely recognized as sensitive indicators of organic matter decomposition and nutrient release potential [30]. The ROC contents in the soil were increased by 28.9% and 47.8% in the 1% BC and 1% DC treatments, respectively. However, the 3% BC treatment decreased the ROC content by 27.6% compared to the control (Figure 4B). The changing trend in the DOC content after BC application was opposite to that after DC application. BC application led to its reduction (34.17% and 24.02% decreases for the 1% and 3% applications, respectively), while DC addition resulted in substantial increases (18.61% and 93.76% for the 1% and 3% treatments, respectively) (Figure 4C). These findings indicate that the BC was more effective in promoting long-term carbon retention, whereas the DC demonstrated greater potential to enhance the soil fertility. These observations are consistent with a previous field experiment investigating the incorporation of maize straw biochar and compost into a neutral Mollisol (pH = 6.2) [11].
The response of the soil carbon fractions to exogenous organic materials is fundamentally governed by the carbon compositional characteristics of the amendments and the dynamics of the soil carbon turnover processes [31,32]. As shown in Table 1, the total carbon content of the BC was 1.99 times that of the DC, with recalcitrant organic carbon accounting for 93.81% of its composition. Therefore, the carbon sequestration potential of the BC was superior to that of the DC (Figure 4A). The ROC and DOC in derivatives and soils are highly susceptible to microbial decomposition, resulting in their inherent instability. Three primary mechanisms can explain the relatively weaker enhancement effects of the BC on the soil ROC and DOC contents compared to the DC (Figure 5). First, the BC inherently contained lower concentrations of ROC and DOC than the DC, with its ROC content being only 28.3% of that of the DC (Table 1). Second, the superior liming effect of BC significantly stimulates microbial activity, thereby accelerating the decomposition of ROC and DOC in soils [33]. This was also the reason why the soil ROC contents were lower in the treatments with higher rates of BC and DC compared to those with lower rates (Figure 3). Third, the higher C/N ratio of the BC compared to the DC may induce a stronger positive priming effect, enhancing the decomposition of the native soil organic matter. This phenomenon has been well documented in previous studies. For example, Xu et al. [34] reported that materials with high C/N ratios increased the soil priming effect by 148–288%. Zhou et al. [35] demonstrated that the positive priming effects of biochar incorporation can be mitigated by the addition of nitrogen. As a result, the ROC and DOC contents in the BC treatments were lower than those in the DC treatments, and even lower than those in the control.
These results highlight the complex interplay between the characteristics of straw derivatives and the soil carbon dynamics in determining the fates of different carbon fractions in amended acidic soils. Considering the temporal susceptibility of ROC and DOC to environmental conditions, it is essential to evaluate the longevity of the beneficial effects of DC on the soil ROC and DOC through long-term field experiments. High-temperature and humid environments may accelerate the degradation of ROC and DOC, while heavy rainfall may exacerbate leaching losses of DOC [32]. Consequently, the effective duration of the soil ROC and DOC enhancement induced by DC may decrease with rising environmental temperatures and precipitation. This study could provide critical insights for determining the optimal dosage and frequency of the application of decomposed straw to enhance the fertility and sustainability of acidic soils.

3.4. Influences of BC and DC on Soil Exchangeable Base Cations

The application of BC and DC significantly increased the contents of exchangeable K+, Ca2+, and Mg2+ in the soil (Table 2). Compared to the control, applying the 3% BC and DC increased the contents of soil exchangeable K+, Ca2+, and Mg2+ by 14.00, 5.44, and 3.65 times and 12.26, 4.85, and 5.23 times, respectively. This indicates that the BC performed better in increasing the soil exchangeable K+ and Ca2+, while the DC had a greater effect on enhancing the soil exchangeable Mg2+. These observed differences can be attributed to the differences in the contents of soluble and exchangeable K+ and Mg2+ in the BC and DC (Table 1). These cations were released into the soil solution and competed with the exchangeable H+ and Al3+ on the soil surface through ion exchange, thereby increasing the content of soil exchangeable base cations and reducing the soil exchangeable acidity [36]. In addition, the BC treatments showed higher soil exchangeable Ca2+ than the DC treatments, although the contents of soluble and exchangeable Ca2+ were lower in the BC than in the DC. This can be attributed to the higher content of insoluble calcium carbonate in the BC (73.99 g kg−1) compared to the DC (73.17 g kg−1). These insoluble calcium salts can neutralize soil acidic substances, releasing Ca2+, which is then adsorbed onto the soil exchange sites [37].
In addition to the soil exchangeable base cations, the soil effective cation exchange capacity (ECEC) also increased following the application of the BC and DC. As shown in Table 2, the application of the 3% BC and 3% DC resulted in 11.82% and 15.20% increases in the soil ECEC, respectively. On one hand, the addition of the BC and DC increased the soil pH, thereby promoting the dissociation of variable charge sites and enhancing the negative charge on the soil surface [12]. On the other hand, both the BC and the DC contained abundant oxygen-containing functional group anions (e.g., -COO−), which contributed substantial numbers of negative charge sites on their surfaces [20,38]. Notably, although the soil pH and intrinsic CEC under the DC treatments were lower than those under the BC treatments, the soil ECEC under the DC treatments was still slightly higher than that under the BC treatments. This suggests that the interactions between the straw derivatives and the soil components influenced the distribution of negative charge sites on the soil surfaces. For instance, the BC promoted the conversion of soil exchangeable Al into soil hydroxyl-bound Al (Figure 3B), which is typically adsorbed as a flocculent colloidal film on the surfaces or edges of clay minerals, thereby shielding some of the negatively charged sites on the soil surface [39]. The surface of aluminum hydroxide is generally positively charged. The overlap of electric double layers between these positively charged colloidal particles and negatively charged particles such as kaolinite would also contribute to a decrease in the soil ECEC [40].
These exchangeable base cations were adsorbed onto the soil surface by electrostatic interaction. They were available to the plant roots, and were not susceptible to leaching. The BC could supply more K+ and Ca2+ than the DC, while the DC could supply more Mg2+ to plants than the BC. The increased ECEC indicated that the capacity to retain nutrients was improved by the application of BC and DC. The increased ECEC was mainly attributed to the abundant oxygen-containing functional groups, such as carboxyl groups (-COO−). It has been reported that the -COO− group content on the surface of biochar increases with field aging time [41]. Therefore, the positive effects of the BC and DC on the soil’s nutrient retention capacity may persist over time. In addition, the increased ECEC also implies an increase in the soil pH buffering capacity [37]. When protons are added into soils amended with BC or DC, carboxyl groups on the surfaces of the DC and the BC can consume the protons through protonation, thus inhibiting soil reacidification. This is also the reason why BC and DC present longer-term liming effects than lime in acidic soils.

3.5. Implications

The widespread application of lime in vast acidic soils is unsustainable due to the consumption of lime resources. The application of lime can increase the soil pH, which accelerates the decomposition of soil organic matter by stimulating microbial activity and ultimately reduces the carbon sequestration potential of acidic soils [6]. Returning straw to the field after carbonization and decomposition is a promising sustainable practice that can reduce soil acidity and Al toxicity, while increasing the soil organic carbon content and soil carbon sequestration potential [9]. However, the differences in the synergistic effects on acidity mitigation and carbon sequestration between straw biochar and compost were still unclear. The results of the present study revealed that the application of BC to acidic soils produced a more pronounced synergistic effect in mitigating the soil acidity and enhancing carbon sequestration compared to DC. This can be attributed to the higher alkalinity and total carbon content of the BC, with recalcitrant carbon being the dominant carbon fraction. On the other hand, the ROC and DOC contents were lower in the BC than in the DC. Furthermore, the BC’s higher alkalinity and C/N ratio induced a more pronounced positive priming effect on the soil organic carbon compared to the DC. Consequently, the soil ROC and DOC levels in the BC treatments were lower than those in the DC treatments, and even lower than those in the control. Moreover, the effects of the DC treatments in increasing the soil exchangeable Mg2+ and soil ECEC were more significant than those of the BC. Therefore, compared to the BC, applying the DC presented a greater positive effect on the soil fertility in the acidic soils. Considering these characteristics of the BC and DC, BC application preferentially ameliorated strongly acidic soils (pH < 4.5) with high acidity and Al toxicity constraints, whereas DC incorporation proved more effective in enhancing weakly acidic soils (such as the sandstone-derived Ultisols, 4.5 < pH < 5.5) limited by inherent nutrient deficiencies.
Given the limitations of the short-term incubation experiment in the present study, more attention should be given in future research to the beneficial effects and mechanisms of straw biochar and compost for the sustainable management of acidic soils under long-term field conditions. First, the dynamics of the liming effects and carbon fraction after straw biochar and compost addition should be monitored to reveal their durability and optimal frequency of application. Second, microbial activity plays a crucial role in soil health and significantly influences the cycling of carbon and nitrogen in acidic soils. The microbial communities and functional diversity in response to DC and BC application should also be investigated to reveal the microbial mechanisms underlying their influence on the carbon sequestration and nutrient cycling processes in acidic soils. Third, carbon dioxide is released into the atmosphere during both the processes of straw carbonization and decomposition [42,43]. Therefore, future research endeavors should adopt a comprehensive life cycle assessment framework to systematically evaluate both the agroecological efficacy of crop residue derivatives in acidic soil remediation and their carbon offset potential. Notably, the properties of straw-derived biochar and compost are influenced by both the type of crop straw used and the preparation conditions (e.g., pyrolysis temperature and microbial inoculant) [21,44]. Further research is needed to investigate the synergistic effects of biochar and compost derived from different crop residues under various preparation conditions for ameliorating acidic soils. These studies will provide more specific guidance for the effective utilization of crop residue resources in ameliorating acidic soils, while establishing a scientific foundation for optimizing their dual functions in sustainable agriculture and climate change mitigation strategies.

4. Conclusions

This study evaluated the synergistic effects of rice straw biochar (BC) and compost (DC) on alleviating soil acidity, enhancing carbon sequestration, and improving fertility in acidic soils. The BC showed superior performance in soil acidity amelioration and carbon sequestration due to its significantly higher alkalinity and recalcitrant carbon content compared to DC. The excellent liming effect of the BC also facilitated Al immobilization through the enhanced hydrolysis of active Al3+ in the acidic soils, promoting the formation of amorphous and crystalline Al phases. This transformation reduced the potentially active Al pool and improved the Al stability in the BC-amended soils. Conversely, the soil ROC and DOC contents in the BC treatments were lower than those in the DC treatments, and even lower than those in the control. This phenomenon is associated with the lower ROC and DOC contents, higher alkalinity, and higher C/N ratio in the BC compared to the DC. Additionally, the BC was less effective in increasing the soil exchangeable Mg2+ and soil ECEC. Overall, BC was more effective than DC in reducing the soil acidity, immobilizing the active Al, and enhancing the soil carbon sequestration, but less effective in improving the soil fertility. The trade-off analysis revealed distinct application thresholds: BC demonstrated optimal efficacy on highly acidic soils (pH < 4.5), whereas DC was more suitable for weakly acidic soils with fertility constraints (such as sandstone-derived Ultisols, 4.5 < pH < 5.5). Future research should focus on the life cycle assessment of different crop residue return pathways at the field scale to maximize the sustainability of agricultural production.

Author Contributions

Conceptualization, X.P.; methodology, T.S.; writing—original draft preparation, R.S.; writing—review, X.M.; supervision, J.L.; writing—review and editing, J.N.N.; supervision, R.X. All authors have read and agreed to the published version of the manuscript.

Funding

This research was supported by the Guangdong Province Key Field Research and Development Program, 2023B0202010027; the Strategic Pilot S&T Special Project of the Chinese Academy of Sciences, XDA0440201; the National Key Research and Development of China, 2022YFD1900604; the National Natural Science Foundation of China, 41877102; the Anhui Province high-end talent promotion action youth top talent young scholars project; and the Distinguished Young Scholars of Anhui Provincial Department of Education Research Plan, 2022AH020068.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data are contained within the article.

Acknowledgments

The support from the China Scholarship Council (CSC) during a visit of Pan Xiaoying to La Trobe University is acknowledged (CSC NO.202308440462).

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Zhao, X.Q.; Pan, X.Z.; Ma, H.Y.; Dong, X.Y.; Che, J.; Wang, C.; Shi, Y.; Liu, K.L.; Shen, R.F. Scientific Issues and Strategies of Acid Soil Use in China. Acta Pedol. Sin. 2023, 60, 1248–1263. (In Chinese) [Google Scholar] [CrossRef]
  2. Kocjan, A.; Kwasniewska, J.; Szurman-Zubrzycka, M. Understanding Plant Tolerance to Aluminum: Exploring Mechanisms and Perspectives. Plant Soil 2024, 507, 195–219. [Google Scholar] [CrossRef]
  3. Zhao, Y.C.; Wang, M.Y.; Hu, S.J.; Zhang, X.D.; Ouyang, Z.; Zhang, G.L.; Huang, B.A.; Zhao, S.W.; Wu, J.S.; Xie, D.T.; et al. Economics- and Policy-Driven Organic Carbon Input Enhancement Dominates Soil Organic Carbon Accumulation in Chinese Croplands. Proc. Natl. Acad. Sci. USA 2018, 115, 4045. [Google Scholar] [CrossRef]
  4. Ma, Y.; Woolf, D.; Fan, M.; Qiao, L.; Li, R.; Lehmann, J. Global Crop Production Increase by Soil Organic Carbon. Nat. Geosci. 2023, 16, 1159–1165. [Google Scholar] [CrossRef]
  5. Zhang, S.; Zhu, Q.; de Vries, W.; Ros, G.H.; Chen, X.; Muneer, M.A.; Zhang, F.; Wu, L. Effects of Soil Amendments on Soil Acidity and Crop Yields in Acidic Soils: A World-wide Meta-analysis. Environ. Manag. 2023, 345, 118531. [Google Scholar] [CrossRef]
  6. Shen, Z.; Han, T.F.; Huang, J.; Li, J.W.; Daba, N.A.; Gilbert, N.; Khan, M.N.; Shah, A.; Zhang, H.M. Soil Organic Carbon Regulation by pH in Acidic Red Soil Subjected to Long-Term Liming and Straw Incorporation. Environ. Manag. 2024, 367, 122063. [Google Scholar] [CrossRef]
  7. Moran-Rodas, V.E.; Joergensen, R.G.; Wachendorf, C. Does Liming Improve Microbial Carbon Use Efficiency after Maize Litter Addition in A Tropical Acidic Soil? Biol. Fertil. Soils 2023, 59, 619–627. [Google Scholar] [CrossRef]
  8. Liu, J.; Fang, L.C.; Qiu, T.Y.; Chen, J.; Wang, H.; Liu, M.X.; Zhang, H.L.; Wang, C.; Sardans, J.; Chen, L.; et al. Crop Residue Return Achieves Environmental Mitigation and Enhances Grain Yield: A Global Meta-Analysis. Agron. Sustain. Dev. 2023, 43, 78. [Google Scholar] [CrossRef]
  9. Paradelo, R.; Navarro-Pedreño, J.; Glaser, B.; Grobelak, A.; Kowalska, A.; Singh, B.R. Potential and Constraints of Use of Organic Amendments from Agricultural Residues for Improvement of Soil Properties. Sustainability 2023, 16, 158. [Google Scholar] [CrossRef]
  10. Liang, F.; Li, B.; Vogt, R.D.; Mulder, J.; Song, H.; Chen, J.; Guo, J. Straw Return Exacerbates Soil Acidification in Major Chinese Croplands. Resour. Conserv. Recycl. 2023, 198, 107176. [Google Scholar] [CrossRef]
  11. Liang, Y.; Al-Kaisi, M.; Yuan, J.C.; Liu, J.Z.; Zhang, H.X.; Wang, L.C.; Cai, H.G.; Ren, J. Effect of Chemical Fertilizer and Straw-Derived Organic Amendments on Continuous Maize Yield, Soil Carbon Sequestration and Soil Quality in A Chinese Mollisol. Agric. Ecosyst. Environ. 2021, 314, 107403. [Google Scholar] [CrossRef]
  12. Nkoh, J.N.; Baquy, M.A.A.; Mia, S.; Shi, R.Y.; Kamran, M.A.; Mehmood, K.; Xu, R.K. A Critical-Systematic Review of the Interactions of Biochar with Soils and the Observable Outcomes. Sustainability 2021, 13, 13726. [Google Scholar] [CrossRef]
  13. Yuan, J.H.; Xu, R.K.; Qian, W.; Wang, R.H. Comparison of the Ameliorating Effects on an Acidic Ultisol between Four Crop Straws and Their Biochars. J. Soils Sediments 2011, 11, 741–750. [Google Scholar] [CrossRef]
  14. Tusar, H.M.; Uddin, M.K.; Mia, S.; Suhi, A.A.; Wahid, S.B.A.; Kasim, S.; Sairi, N.A.; Alam, Z.; Anwar, F. Biochar-acid soil interactions—A review. Sustainability 2023, 15, 13366. [Google Scholar] [CrossRef]
  15. Shetty, R.; Vidya, C.S.N.; Prakash, N.B.; Lux, A.; Vaculík, M. Aluminum Toxicity in Plants and its Possible Mitigation in Acid Soils by Biochar: A Review. Sci. Total Environ. 2021, 765, 142744. [Google Scholar] [CrossRef]
  16. Qian, L.; Chen, B. Dual Role of Biochars as Adsorbents for Aluminum: The Effects of Oxygen-Containing Organic Components and The Scattering of Silicate Particles. Environ. Sci. Technol. 2013, 47, 8759–8768. [Google Scholar] [CrossRef]
  17. Siedt, M.; Schäffer, A.; Smith, K.E.; Nabel, M.; Roß-Nickoll, M.; Van Dongen, J.T. Comparing Straw, Compost, and Biochar Regarding Their Suitability as Agricultural Soil Amendments to Affect Soil Structure, Nutrient Leaching, Microbial Communities, and the Fate of Pesticides. Sci. Total Environ. 2021, 751, 141607. [Google Scholar] [CrossRef]
  18. Shao, M.J.; Dou, S.; Xie, Z.B. Effects of Corn Straw and its Humified and Carbonized Materials Applying to the Black Soil with an Equal Mass of Carbon on Soil Humus. J. Agro-Environ. Sci. 2018, 37, 2202–2209. (In Chinese) [Google Scholar] [CrossRef]
  19. Biswas, B.; Balla, P.; Krishna, B.B.; Adhikari, S.; Bhaskar, T. Physiochemical Characteristics of Biochar Derived from Pyrolysis of Rice Straw under Different Temperatures. Biomass Convers. Bior. 2024, 14, 12775–12783. [Google Scholar] [CrossRef]
  20. Pan, X.Y.; Shi, R.Y.; Hong, Z.N.; Jiang, J.; He, X.; Xu, R.K.; Qian, W. Characteristics of Crop Straw-Decayed Products and Their Ameliorating Effects on an Acidic Ultisol. Arch. Agron. Soil Sci. 2021, 12, 1708–1721. [Google Scholar] [CrossRef]
  21. Zhang, N.; Xing, J.; Wei, L.; Liu, C.; Zhao, W.; Liu, Z.; Wang, Y.; Liu, E.; Ren, X.; Jia, Z.; et al. The Potential of Biochar to Mitigate Soil Acidification: A Global Meta-analysis. Biochar 2025, 7, 49. [Google Scholar] [CrossRef]
  22. Pansu, D.M.; Gautheyrou, J. Handbook of Soil Analysis; Springer: Berlin/Heidelberg, Germany, 2006. [Google Scholar]
  23. Soon, Y.K. Fractionation of extractable aluminum in acid soils: A review and a proposed procedure. Commun. Soil Sci. Plant Anal. 1993, 24, 1683–1708. [Google Scholar] [CrossRef]
  24. Chen, X.M.; Zhang, D.Q.; Liang, G.H.; Qiu, Q.Y.; Liu, J.X.; Zhou, G.Y.; Liu, S.Z.; Chu, G.W.; Yan, J.H. Effects of Precipitation on Soil Organic Carbon Fractions in Three Subtropical Forests in Southern China. J. Plant Ecol. 2016, 1, 10–19. [Google Scholar] [CrossRef]
  25. Fidel, R.B.; Laird, D.A.; Thompson, M.L.; Lawrinenko, M. Characterization and Quantification of Biochar Alkalinity. Chemosphere 2017, 167, 367–373. [Google Scholar] [CrossRef]
  26. Cai, Z.; Xu, M.; Zhang, L.; Yang, Y.; Wang, B.; Wen, S.; Misselbrook, T.H.; Carswell, A.M.; Duan, Y.; Gao, S. Decarboxylation of Organic Anions to Alleviate Acidification of Red Soils from Urea Application. J. Soils Sediments 2020, 20, 3124–3135. [Google Scholar] [CrossRef]
  27. Yu, W.J.; Ren, T.S.; Duan, Y.H.; Huai, S.C.; Zhang, Q.Y.; Cai, Z.J.; Lu, C.A. Mechanism of Al Toxicity Alleviation in Acidic Red Soil by Rice-Straw Hydrochar Application and Comparison with Pyrochar. Sci. Total Environ. 2023, 877, 162849. [Google Scholar] [CrossRef]
  28. Shi, R.Y.; Ni, N.; Nkoh, J.N.; Dong, Y.; Zhao, W.R.; Pan, X.Y.; Li, J.Y.; Xu, R.K.; Qian, W. Biochar Retards Al Toxicity to Maize (Zea mays L. ) During Soil. Acidification: The Effects and Mechanisms. Sci. Total Environ. 2020, 719, 137448. [Google Scholar] [CrossRef]
  29. Du, X.; Wang, Y.; Su, X.; Li, J. Influences of pH Value on The Microstructure and Phase Transformation of Aluminum Hydroxide. Powder Technol. 2009, 192, 40–46. [Google Scholar] [CrossRef]
  30. Mandal, M.; Kamp, P.; Singh, M. Effect of Long Term Manuring on Carbon Sequestration Potential and Dynamics of Soil Organic Carbon Labile Pool Under Tropical Rice-Rice Agro-Ecosystem. Commun. Soil. Sci. Plant 2020, 51, 468–480. [Google Scholar] [CrossRef]
  31. Wu, B.; Zhang, M.; Zhai, Z.; Dai, H.; Yang, M.; Zhang, Y.; Liang, T. Soil Organic Carbon, Carbon Fractions, and Microbial Community under Various Organic Amendments. Sci. Rep. 2024, 14, 25431. [Google Scholar] [CrossRef]
  32. Chen, L.; Zhou, S.; Zhang, Q.; Zou, M.; Yin, Q.; Qiu, Y.; Qin, W. Effect of Organic Material Addition on Active Soil Organic Carbon and Microbial Diversity: A Meta-Analysis. Soil. Till. Res. 2024, 241, 106128. [Google Scholar] [CrossRef]
  33. Wang, C.; Kuzyakov, Y. Soil Organic Matter Priming: The pH Effects. Glob. Change Biol. 2024, 30, e17349. [Google Scholar] [CrossRef] [PubMed]
  34. Xu, Q.; Yao, Z.Y.; Chen, Y.P.; Liu, N.; Teng, Z.R.; Huang, D.L.; Cao, W.D.; Kuzyakov, Y.; Shah, Y.H.; Zhao, N.; et al. Priming and Balance of Soil Organic Carbon Differ with Additive C: N Ratios and Long-Term Green Manuring. Appl. Soil. Ecol. 2024, 201, 105495. [Google Scholar] [CrossRef]
  35. Zhou, X.H.; Feng, Z.Q.; Yao, Y.X.; Liu, R.Q.; Shao, J.J.; Jia, S.X.; Gao, Y.N.; Xue, K.; Chen, H.Y.; Fu, Y.L.; et al. Nitrogen Input Alleviates the Priming Effects of Biochar Addition on Soil Organic Carbon Decomposition. Soil Biol. Biochem. 2025, 202, 109689. [Google Scholar] [CrossRef]
  36. Yuan, J.H.; E, S.Z.; Che, Z.X. Base Cation-Enhancing Role of Corn Straw Biochar in an Acidic Soil. Soil Use Manag. 2022, 38, 1322–1336. [Google Scholar] [CrossRef]
  37. Shi, R.Y.; Hong, Z.N.; Li, J.Y.; Jiang, J.; Baquy, M.A.A.; Xu, R.K.; Qian, W. Mechanisms for Increasing the pH Buffering Capacity of an Acidic Ultisol by Crop Residue-Derived Biochars. J. Agric. Food Chem. 2017, 65, 8111–8119. [Google Scholar] [CrossRef]
  38. Wang, H.F.; Yang, Y.; Wang, M.P.; Yuan, R.J.; Song, W.Y.; Wang, L.; Liang, N.; Shi, J.Y.; Li, J. Insights into the Roles of Surface Functional Groups and Micropores in the Sorption of Ofloxacin on Banana Pseudo-Stem Biochars. Sustainability 2024, 16, 2629. [Google Scholar] [CrossRef]
  39. Dietel, J.; Ufer, K.; Kaufhold, S.; Dohrmann, R. Crystal Structure Model Development for Soil Clay Minerals–II. Quantification and Characterization of Hydroxy-Interlayered Smectite (HIS) Using the Rietveld Refinement Technique. Geoderma 2019, 347, 1–12. [Google Scholar] [CrossRef]
  40. Li, J.Y.; Xu, R.K. Inhibition of Acidification of Kaolinite and an Alfisol by Aluminum Oxides through Electrical Double-Layer Interaction and Coating. Eur. J. Soil Sci. 2013, 64, 110–120. [Google Scholar] [CrossRef]
  41. Apostolović, T.; Gross, A.; Rodríguez, Á.F.G.; de la Rosa, J.M.; Glaser, B.; Knicker, H.; Maletić, S. Impact of Biochar Aging on Soil Physicochemical Properties. Agronomy 2024, 14, 3007. [Google Scholar] [CrossRef]
  42. Lehmann, J.; Cowie, A.; Masiello, C.A.; Kammann, C.; Woolf, D.; Amonette, J.E.; Cayuela, M.L.; Camps-Arbestain, M.; Whitman, T. Biochar in Climate Change Mitigation. Nat. Geosci. 2021, 14, 883–892. [Google Scholar] [CrossRef]
  43. Lee, J.H.; Lee, J.G.; Jeong, S.T.; Gwon, H.S.; Kim, P.J.; Kim, G.W. Straw Recycling in Rice Paddy: Trade-off Between Greenhouse Gas Emission and Soil Carbon Stock Increase. Soil. Till. Res. 2020, 199, 104598. [Google Scholar] [CrossRef]
  44. Chen, Q.; Li, Y.; Wang, C.; Wang, Y. Comparison of the Effect of NaOH Pretreatment and Microbial Agents on Rice Straw Decomposition. Agronomy 2023, 13, 816. [Google Scholar] [CrossRef]
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Figure 1. Effects of rice straw biochar (BC) and rice straw decayed product (DC) on soil pH (A) and soil exchangeable acidity (B). Bars indicate standard errors of means (n = 3), and different letters on squares indicate significant differences among treatments (p < 0.05).
Figure 1. Effects of rice straw biochar (BC) and rice straw decayed product (DC) on soil pH (A) and soil exchangeable acidity (B). Bars indicate standard errors of means (n = 3), and different letters on squares indicate significant differences among treatments (p < 0.05).
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Figure 2. Effects of rice straw biochar (BC) and rice straw decayed product (DC) on soluble aluminum in soil. Bars indicate standard errors of means (n = 3), and different letters on squares indicate significant differences among treatments (p < 0.05).
Figure 2. Effects of rice straw biochar (BC) and rice straw decayed product (DC) on soluble aluminum in soil. Bars indicate standard errors of means (n = 3), and different letters on squares indicate significant differences among treatments (p < 0.05).
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Figure 3. Effects of rice straw biochar (BC) and rice straw decayed product (DC) on soil exchangeable Al (A), organically bound Al (B), hydroxyl-bound Al (C), and their proportions (D). Bars indicate standard errors of means (n = 3), and different letters on squares indicate significant differences among treatments (p < 0.05).
Figure 3. Effects of rice straw biochar (BC) and rice straw decayed product (DC) on soil exchangeable Al (A), organically bound Al (B), hydroxyl-bound Al (C), and their proportions (D). Bars indicate standard errors of means (n = 3), and different letters on squares indicate significant differences among treatments (p < 0.05).
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Figure 4. The effects of the rice straw biochar (BC) and rice straw decayed product (DC) on the total organic carbon (A), readily oxidized organic carbon (B), and dissolved organic carbon (C) in the soils. The bars indicate the standard errors of the means (n = 3), and the different letters on the squares indicate significant differences among the treatments (p < 0.05).
Figure 4. The effects of the rice straw biochar (BC) and rice straw decayed product (DC) on the total organic carbon (A), readily oxidized organic carbon (B), and dissolved organic carbon (C) in the soils. The bars indicate the standard errors of the means (n = 3), and the different letters on the squares indicate significant differences among the treatments (p < 0.05).
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Figure 5. The mechanisms of the differences in the effects of the BC and DC on the soil ROC and DOC.
Figure 5. The mechanisms of the differences in the effects of the BC and DC on the soil ROC and DOC.
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Table 1. Characteristics of rice straw biochar (BC) and rice straw decayed product (DC).
Table 1. Characteristics of rice straw biochar (BC) and rice straw decayed product (DC).
Straw
Derivates		pHECTotal CTotal NCarbonateROCDOCSoluble Base CationsExchangeable Base CationsCECAsh
Alkalinity		BET
Surface Area
K+Na+Ca2+Mg2+K+Ca2+Mg2+
ms cm−1--------%-------------------g kg−1---------------------------------------------------------- (cmol(+) kg−1) -------------------------------------m2 g−1
BC9.4111.1751.351.0873.9931.2113.38108.6546.461.441.3739.8149.0419.11138.73148.513.57
DC9.2014.0726.213.0673.13110.2314.28118.17223.647.305.9311.8451.0227.8474.97115.733.20
ROC—eadily oxidized organic carbon; DOC—dissolved organic carbon; EC—electrical conductivity.
Table 2. Exchangeable base cations in acidic soil after applying rice straw biochar (BC) and rice straw decayed product (DC) (mean ± se, n = 3).
Table 2. Exchangeable base cations in acidic soil after applying rice straw biochar (BC) and rice straw decayed product (DC) (mean ± se, n = 3).
TreatmentsSoil Exchangeable Base CationsECEC
K+Na+Ca2+Mg2+
mmol(+) kg−1
CK2.48 ± 0.00 e3.79 ± 1.30 ab2.87 ± 0.37 d2.14 ± 0.04 e85.16 ± 1.06 b
1%BC14.31 ± 0.14 c4.37 ± 0.00 ab8.39 ± 0.95 c4.85 ± 0.12 d87.48 ± 0.78 b
3%BC37.2 ± 0.85 a4.94 ± 0.42 a18.49 ± 0.30 a9.95 ± 0.15 b95.23 ± 1.72 a
1%DC11.24 ± 0.64 d2.29 ± 0.20 b8.54 ± 1.37 c5.87 ± 0.18 c86.91 ± 2.88 b
3%DC32.94 ± 0.73 b5.06 ± 0.35 a16.82 ± 0.22 b13.33 ± 0.10 a98.10 ± 0.69 a
Mean values with different lowercase letters indicate that they are statistically significant different among treatments (p < 0.05). ECEC—effective cation exchange capacity.
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Pan, X.; Shu, T.; Shi, R.; Mao, X.; Li, J.; Nkoh, J.N.; Xu, R. The Synergistic Effects of Rice Straw-Pyrolyzed Biochar and Compost on Acidity Mitigation and Carbon Sequestration in Acidic Soils: A Comparative Study. Sustainability 2025, 17, 4408. https://doi.org/10.3390/su17104408

AMA Style

Pan X, Shu T, Shi R, Mao X, Li J, Nkoh JN, Xu R. The Synergistic Effects of Rice Straw-Pyrolyzed Biochar and Compost on Acidity Mitigation and Carbon Sequestration in Acidic Soils: A Comparative Study. Sustainability. 2025; 17(10):4408. https://doi.org/10.3390/su17104408

Chicago/Turabian Style

Pan, Xiaoying, Tianchu Shu, Renyong Shi, Xiaoxia Mao, Jiuyu Li, Jackson Nkoh Nkoh, and Renkou Xu. 2025. "The Synergistic Effects of Rice Straw-Pyrolyzed Biochar and Compost on Acidity Mitigation and Carbon Sequestration in Acidic Soils: A Comparative Study" Sustainability 17, no. 10: 4408. https://doi.org/10.3390/su17104408

APA Style

Pan, X., Shu, T., Shi, R., Mao, X., Li, J., Nkoh, J. N., & Xu, R. (2025). The Synergistic Effects of Rice Straw-Pyrolyzed Biochar and Compost on Acidity Mitigation and Carbon Sequestration in Acidic Soils: A Comparative Study. Sustainability, 17(10), 4408. https://doi.org/10.3390/su17104408

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