Chemical characterization of soybean stover shows potential to mitigate soil acidity in Brazil

ABSTRACT

Soybean is the primary legume cultivated worldwide, but knowledge regarding soybean stover chemical composition is sparse. The objectives of this study were to characterize soybean stover from two production regions in Brazil and to evaluate the potential for mitigating Oxisol acidity. Samples of soybean stover were collected in Paraná and Rio Grande do Sul, states of southern Brazil, and in Bahia, state of northeast Brazil. Samples were analyzed for C, N, Ca, Mg, K, Na, S, P, Cu, Mn, Zn, V, Ni, Ba, pH, and available alkalinity. Potential acidity mitigation was assessed by incubating soybean stover in an acid Oxisol and analyzing pH CaCl₂ and Al³⁺ after a 30-day incubation period. Stover from Bahia (BA) had higher levels of Mg, K, and P, while stover from Paraná (PR) and Rio Grande do Sul (RS) had higher C, N, S, Al, Cu, Mn, V, Ni, and Ba. After incubation, soil pH increased and Al³⁺ decreased with no difference between regions, but soil pH was correlated with available alkalinity (r = -0.68; PR+RS stover) and with sum of cations (r = -0.74; BA stover). Although the chemical quality of soybean stover varied due to regional fertilization and liming practices, addition of stover to soil (regardless of composition) can be beneficial for acidity reduction.

Key words
plant residue; acidic soils; Brazilian cerrado; Oxisol

INTRODUCTION

Worldwide, soybean [Glycine max (L.) Merrill] is a crop of great economic importance and a major source of protein and vegetable oil (OECD/FAO 2023). Brazil is the largest producer, representing 39% of the 316.7 million tons produced in 2023/2024 (CONAB 2023, USDA 2024b). Cultivated areas in Brazil expanded from 30.1 million ha to 45.6 million ha between 2013/2014 to 2023/2024, and the expectation is that they grow 0.8% per year over the next decade (OECD/FAO 2023, USDA 2024a). In Brazil, the states of Mato Grosso (26%), Paraná (15%), Rio Grande do Sul (14%), Goiás (10%), Mato Grosso do Sul (8%), Minas Gerais (5%), and Bahia (5%) are the primary producers (USDA 2024a).

Brazilian cultivation of soybeans began in 1931 in the southern states of Rio Grande do Sul, Santa Catarina, and Paraná since the regional characteristics are very similar to the characteristics of the largest production regions of the United States of America (Sowa and Busch 1998). In the 1960s and 1970s, production expanded into Mato Grosso, Mato Grosso do Sul, Goiás, Tocantins, Maranhão, Minas Gerais, and Bahia (Sowa and Busch 1998). During the last decade, the area known as MATOPIBA (Maranhão, Tocantins, Piauí, and Bahia states) became a significant soybean production region (Rausch et al. 2019).

As soybean production expanded into different regions of Brazil, there was an increase in the scope of different climatic conditions, native vegetation, geology, and soil type. In southern states, soybean was grown under subtropical conditions without a defined dry season. Previous vegetation consisted of forest and subtropical grassland on soils formed from igneous rock (basic — basalt, and acidic — rhyodacite) and small areas of sedimentary rock (sandstone) (Magri et al. 2022). This resulted in variation in soil fertility depending on the soil weathering. The northeastern state of Bahia is characterized by savanna (Cerrado) under tropical conditions with a dry season of five or six months (April/May to September) and highly weathered soil (predominantly from sedimentary rock) with very low fertility (Lopes and Guilherme 2016), sandy composition, and low levels of organic matter (Fontana and Oliveira 2015).

In Brazil, soybean-based cultivation areas primarily adopted no-till conservation practices in terms of soil preparation, crop rotations, and soil cover maintenance (Fuentes-Llanillo et al. 2021). Maintaining crop residues promotes soil protection, as well as helping supply resources to subsequent crops through nutrient cycling (Maluf et al. 2015). Covering the soil with crop residue is known to be beneficial for regulating surface temperature, aiding water infiltration, reducing evaporative losses, and increasing organic matter (Heckler et al. 1998, Maria et al. 2019, Possamai et al. 2022).

In addition to soil protection and nutrient cycling, the decomposition of organic residues by microorganisms results in organic acids with dissociation constants (pK_a) that are either higher or lower than the soil pH, which reduces (higher pK_a; Berg and McClaugherty 2003, Brady and Weil 2013) or increases soil acidity (lower pK_a; Rukshana et al. 2012). Other characteristics of plant residue that could change soil pH are decarboxylation of organic anions and ammonification (Sakala et al. 2004, Sousa et al. 2007, Tang and Yu 1999), which increases soil pH and cation levels (Ca²⁺, Mg²⁺, K⁺, and Na⁺) (Vanzolini et al. 2017).

Since soybean cultivation occupies diverse areas in Brazil and legumes constitute an important source of soil nutrients (Fuentes-Llanillo et al. 2021, Possamai et al. 2022), knowing the nutrient content and quality of soybean stover from different regions is very important. Our hypothesis was that residues produced under subtropical environments are richer in nutrients and available alkalinity than those from tropical environments due to better soil conditions. The objectives of this study were to characterize the chemical composition of soybean stover from two important Brazilian production areas with contrasting climatic and soil conditions. This included determining available alkalinity (OH^-), characterizing regional differences, and evaluating the potential of these soybean stovers to mitigate soil acidity.

MATERIAL AND METHODS

Collection and characterization of soybean stover

Soybean stover material was collected manually (minimizing the collection of both soil and residues from previous crops) from commercial farms located in five municipalities of the state of Paraná (PR) and one municipality of Rio Grande do Sul (RS), in southern Brazil (n = 51), as well as in four municipalities of Bahia (BA), in northeast Brazil (n = 47) (Table 1). In Paraná, the soybean cultivars that produced stover residues were NS 6906 IPRO, HO PIRAPÓ IPRO, NEO 610 IPRO, BMX ZEUS, Nidera NA5909, DONMARIO DM57i52, DONMARIO DM53I54 IPRO, and Nidera NS5505i2X. In Rio Grande do Sul, the variety was DONMARIO DM59I58, and in Bahia, the varieties collected were Domínio IPRO, M8349 IPRO, GH1687 IPRO, 58B28 IPRO, HO Juruena IPRO, and Extrema IPRO (Albuquerque et al. 2025). Collected material consisted of aboveground portions of soybeans (primarily leaves, branches, stems, and some remaining pods) that were deposited on the soil surface after grain harvests in the months of February to April 2023 (2022/2023 crop season). Stover was collected using a 0.25-m² frame, stored in paper bags, oven dried (65°C for 48 h), and weighed to determine dry matter. Samples were then homogenized, ground, and sieved (< 1 mm) prior to characterization.

Table 1
Soybean stover collection locations, soil parent material, climate according to Koppen’s classification, number of samples from each location, dry matter (g), and dry matter per ha.

Municipality	Parent material	Climate	Number of samples	Dry matter* g	Dry matter kg·ha-1
Lidianópolis-PR	Basalt	Cfa	9	147.8	5,911.5
Turvo-PR	Basalt	Cfb	3	251.6	10,065.3
Luiziana-PR	Basalt	Cfb	3	249.1	9,962.7
Lapa-PR	Sandstone	Cfb	9	129.4	5,177.8
Fernandes Pinheiro-PR	Sandstone	Cfb	21	182.9	7,316.6
Erechim-RS	Basalt	Cfa	6	116.4	4,655.8
Luís Eduardo Magalhães-BA	Sandstone	Aw	2	76.0	3,040.8
Formosa do Rio Preto-BA	Sandstone	Aw	3	162.8	6,513.3
Barreiras-BA	Sandstone	Aw	18	106.3	4,251.7
Riachão das Neves-BA	Sandstone	Aw	24	169.2	6,987.4

• Cfa: temperate, humid, hot summer; Cfb: temperate, humid, cool summer; Aw: rainy tropical, dry winter; *average of dry matter (from 0.25-m² areas) of all soybean stover samples collected from respective locations of each municipality.

Levels of Ca, Mg, P, S, Cu, Mn, Zn, Ni, Ba, and V were determined by inductively coupled plasma optical emission spectroscopy (ICP-OES, Varian 720-ES) and K and Na by flame photometer. Extractions were made by digesting 200 mg of ground dried stover residue with 4 mL of HNO₃ 65% P.A., 1 mL of H₂O₂, and 3 mL of Milli-Q water in a microwave (Mars Xpress 6, CEM) with heating ramp at 1,300 W for 20 min, followed by 15 min at a maximum temperature of 180°C. Extracts were filtered through slow filter paper into a 25-mL flask and brought to volume with ultrapure Milli-Q water. Total C and N were determined with an elemental analyzer (ELEMENTAR Vario EL III), and pH was determined using reverse osmosis H₂O in a ratio of 1:10 (m/v) (Teixeira et al. 2017).

To determine available alkalinity of the stover, 25 mL of a 0.015 mol.L^-1 CaCl₂ solution was added to 0.5 g of each ground dried stover and shaken for 15 min. The pH of each residue solution was determined, and solutions were titrated with H₂SO₄ 5 mmo.L^-1 until pH 4 was attained (Sakala et al. 2004).

Incubation of soybean stover mixed with soil

Air-dried soil (150 g) was weighed into plastic bags and mixed with amounts of soybean stover equivalent to 48 t.ha^-1 to simulate a soil layer of 0–0.2 m. This high rate was used to simulate cumulative effects over several years or the interface between soil and residue. The mixture of soil and stover was homogenized, and the water content of the mixture was adjusted to 80% of field capacity by adding reverse osmosis water. All bags were closed using an elastic band; a plastic aeration tube was used to maintain aerobic conditions throughout the experimental period. Incubation was conducted in a greenhouse at ~25°C for 30 days.

Soil used in the incubation

The A horizon of an Oxisol (Latossolo, according to the Brazilian soil classification) was collected from the Campos Gerais region, Paraná. Soil was air-dried, sieved (< 2 mm), and analyzed for pH CaCl₂ 0.01 mol.L^-1 (1:2.5 m/v); Ca, Mg, and Al extracted with KCl 1 mol.L^-1, followed by Ca and Mg determination by flame atomic absorption spectroscopy and Al determination by titration with 0.025 mol.L^-1 NaOH using a bromothymol blue indicator; and P and K extracted with Mehlich-I and determined by colorimetry and flame photometry, respectively. Particle size analysis to determine sand, silt, and clay fractions was done by the pipette method, and total C and N were determined using an elemental analyzer (ELEMENTAR Vario EL III) (Teixeira et al. 2017). Results of chemical analyses were: pH CaCl₂ = 3.76; Al³⁺ = 1.37 cmol_c.kg^-1; H+Al = 9 cmol_c.kg^-1; Ca²⁺ = 0.66 cmol_c.kg^-1; Mg²⁺ = 0.28 cmol_c.kg^-1; K⁺ = 0.08 cmol_c.kg^-1; P = mg.kg^-1; C = 19.82 g.kg^-1, and N = 1.2 g.kg^-1. Results of particle size analysis were: sand = 600 g.kg^-1, silt = 50 g.kg^-1, and clay = 350 g.kg^-1.

Chemical analysis of soil used in the incubation

After the 30-day incubation, the soil stover mixture was oven dried (40°C) and sieved (< 2 mm) prior to determining pH (1:2.5 m/v, CaCl₂ 0.01 mo.L^-1) and Al³⁺ (KCl 1 mol.L^-1). Measurements of pH used a pH meter table equipped with a glass electrode, and available Al³⁺ was determined by titration with 0.025 mol.L^-1 NaOH in the presence of bromothymol blue indicator using a digital burette (Teixeira et al. 2017).

Experimental design and statistical analysis

Chemical composition results (macro and micronutrients and trace elements), pH, C, N, and alkalinity of soybean stover were evaluated by separating them by Paraná and Rio Grande do Sul states (PR+RS) and Bahia state (BA) using the Mann-Whitney’s test at a 5% significance level; boxplots made using OriginLab software were used to represent medians and data distribution. Correlations (Spearman) were evaluated between pH, available alkalinity, and soybean stover nutrients for both regions.

The soil incubation experiment with soybean stover was conducted using a completely randomized experimental design (98 experimental units) that considered each stover sample as one replication and was separated into two groups: PR+RS (n = 51) and BA (n = 47). Results of pH CaCl₂ and Al³⁺ were subjected to the Shapiro-Wilk’s normality test at a 5% significance level. Obtaining normality, analysis of variance (ANOVA) and Tukey’s test were performed to evaluate differences between the control treatment (without stover addition) and the stover treatments (PR+RS and BA). Correlations (Pearson) were evaluated between the main chemical attributes of soybean stover alkalinity (pH, available alkalinity, and sum of cations) and pH CaCl₂ and Al³⁺ of the soil incubated with stover. All statistics were conducted using R statistical software through the RStudio interface.

RESULTS AND DISCUSSION

Chemical characterization of soybean stover

Macronutrient levels in soybean stover followed the order of C > N > Ca > K > Mg > P > S, while the highest micronutrient levels followed the order of Mn > Cu > Zn > Ni (Figs. 1 and 2). Among trace elements, Ba was the most abundant in both regions, followed by V. Levels of N, P, K, and S in soybean stover were lower than those noted by Kurihara et al. (2013), while Ca, Mg, Mn, and Zn levels were equivalent, and Cu was higher. Compared to findings by Zobiole et al. (2012), levels of N, P, K, S, Zn, and Mn in our study were lower, Ca and Mg were equivalent, and Cu was higher. Differences between our findings and the literature are probably due to the initial decomposition and nutrient release that occurred before stover was collected.

There was a significant difference (p < 0.05) between Mg, K, Na, P, S, available alkalinity, Cu, Mn, Ba, V, Ni, C, and N (Figs. 1 and 2) for soybean stover from PR+RS and BA. Soybean stover from BA had significantly higher medians (p < 0.05) of Mg, K, Na, and P than stover from PR+RS. In PR+RS, stover had higher S levels (Figs. 1a and 1b). Available alkalinity, C, and N values were higher in stover collected from PR+RS (Figs. 2b, 2c, and 2d). Soybean stover from PR+RS also showed higher levels of Cu, Mn, Ba, V, and Ni (Fig. 1c).

Figure 1
Boxplots of (a) Ca, Mg, and K cations (Ca+Mg+K+Na contents), (b) P, S, and Na, and (c) Ba, Cu, Mn, Ni, V, and Zn in soybean stover collected in PR+RS (green) and BA states (blue). Values with the same letters do not differ from each other according to the Mann-Whitney’s test at 5% significance level (p > 0.05).

Figure 2
Boxplots of (a) pH, (b) available alkalinity (OH^-), (c) C, and (d) N in the soybean stover collected from PR+RS (green) and BA (blue). Values with the same letters do not differ from each other according to the Mann-Whitney’s test at 5% significance level (p > 0.05).

In general, the large difference in soil properties (Albuquerque et al. 2025), as well as Ca, Mg, K, and cations between the two regions, was not observed in stover residue (Fig. 1a). It is well known that more Ca and Mg reach roots by mass flow in rich soils than the crop is capable of absorbing (Vargas et al. 1983). Thus, crop root selectivity plays an important role for these nutrients. While uptake by soybean seems to be higher for Ca compared to Mg, similar exportation to seeds results in higher concentrations of Ca in residue (Esper Neto et al. 2021). This information supported observations in our study. The low mobility and low translocation of Ca to grain (low harvest rate) result in high concentrations in stems, leaves, and petioles (Marschner 2012, Zanon et al. 2022). With legumes such as soybeans, Ca is very important in biological N fixation, especially when plants and rhizobia interact during nodule formation. For this reason, N₂-fixing plants demand more Ca (Sousa et al. 2007). Since Ca is in plant cell walls, this macronutrient has the lowest rate of mineralization through decomposition, which possibly helps explain equivalent levels at both locations (Fig. 1a; Maluf et al. 2015, Padovan et al. 2006).

Potassium can exhibit luxury consumption and availability under optimum water availability and be a major factor influencing diffusion and absorption (Fernández et al. 2011). Thus, higher K concentration in BA region (despite lower K availability) could be related to better soil moisture conditions. Soybean uptake for K is generally more than three times than that of Ca and Mg (Pauletti and Motta 2019), but stover K concentration was between the levels of Ca and Mg. This could be explained by higher translocation to seeds (greater than 50% of K uptake; Pauletti 2004) and K leached from plant tissue by rain and irrigation (Padovan et al. 2006, Fernández et al. 2011). This could have primarily affected N and K due to their short half-life of release. However, strong climatic influences such as rainfall distribution could accelerate this process (Padovan et al. 2006).

Similar to K, tissue concentrations of P were higher in BA than in PR+RS, but unlike K, the higher concentration makes sense given that soil concentration was higher in BA than in PR+RS. This could be a result of farmer efforts to enhance P by supplying ample P fertilizer in the Cerrado region (Zancanaro et al. 2023) combined with low P retention due to low clay content (Barbosa et al. 2022) that drove increased P absorption (Freitas et al. 2014). Both K and P are highly mobile within plants (Marschner 2012, Zanon et al. 2022) and are highly exported by seeds (Pauletti 2004).

The concentrations of S and N were higher in stover from PR+RS than from BA (Figs. 1b and 2d). Sulfur can be supplied by fertilizers like mono calcium phosphate and calcium sulphate or by soil organic matter (Zancanaro et al. 2023, Zanon et al. 2022). Since soil from PR+RS had higher values of soil organic matter than the one from BA, this could justify the higher concentration of S (Albuquerque et al. 2025). Soil organic matter can also act on N supply since biological N fixation is responsible for 60% of assimilated N in soybeans (Zancanaro et al. 2023). Again, higher soil organic matter may be the reason for higher N and S found in PR+RS than in BA.

The soybean stover from PR+RS had higher concentrations of Ba, Cu, Ni, Mn, and V and a similar concentration for Zn compared to BA. Since Ba and V are not recognized as nutrients and there are no manual recommendations for Ni (Pauletti and Motta 2019), it is likely that soil availability is responsible for their abundance in stover. Mn, Cu, and Zn can be applied directly to soil or foliar applied to very poor soils in the Cerrado region (Sousa and Lobato 2004), where BA is located. This is especially true for Zn, which is recommended at large rates upon initial soil use and afterwards during seedling establishment to ensure adequate soil Zn supply. This helps explain the similar Zn levels in stover residue found in our study.

In contrast, the highest levels of Fe, V, Mn, Cu, Co, Zn, and Ni were found in soils formed from basic igneous rock (such as basalt) with a clayey texture compared to those sandy texture soils formed from sandstone (Magri et al. 2022, Motta et al. 2020, Suppi et al. 2022). This is the basis for high levels in southern soybean stover, as noted by Marques et al. (2004) and by this study. The importance of soil parent material can be seen in Figs. 3a and 3b. The micronutrients Zn, Mn, and Cu are naturally deficient in the Brazilian Cerrado region (Lopes and Cox 1977) due to the combination of low levels in parent material and the high degree of weathering. Holmgren et al. (1993) did a large soil survey in the United States of America and found inverse relationships for Zn, Cu, and Ni, with soil weathering and an opposite pattern for cation exchange capacity (CEC). The low CEC can be seen in soil from BA (Albuquerque et al. 2025).

When analyzing the levels of Zn, Cu, Mn, Ba, V, and Ni in PR+RS soybean stover and separating by soil parent material, significantly higher levels of Zn, Cu, Mn, Ba, and V were observed in stover cultivated on soils derived from basalt relative to sandstone (Figs. 3a and 3b), and Ni was the only micronutrient more prevalent in plants grown in sedimentary derived soils. While there is no technical recommendation for Ni fertilization management in Brazil, Ni is an essential micronutrient that participates in plant N metabolism (Macedo et al. 2016).

Nutrient and alkalinity characterization of stover showed a high Spearman correlation (ρ > 0.6, p < 0.01) between available alkalinity and plant cations, regardless of the region where it was grown. When plants absorb cations, H⁺ is extruded into the rhizosphere to maintain chemical balance (Sousa et al. 2007). Depending on the legume, 37 to 49 mg H⁺ are released per gram of N fixed, increasing plant alkalinity in relation to other crops (Cooper and Scherer 2012).

Figure 3
Boxplots of (a) Ni, V, Cu, and Zn and (b) Ba and Mn for soybean stover collected in PR+RS from soils developed from basalt (green) and sandstone (sedimentary rock—blue). Values with the same letters do not differ from each other according to the Mann-Whitney’s test at 5% significance level (p > 0.05).

Available alkalinity of soybeans in this study (362.8 mmol_c.kg^-1 in PR+RS and 293.4 mmol_c.kg^-1 in BA) was lower than the one of the soybean reported by Sakala et al. (2004) (577 mmol_c.kg^-1). However, our study stover was collected after grain harvest, meaning that there was more time for absorption of P and S to occur, which reduced alkalinity through extrusion of OH^- to the rhizosphere. The available alkalinity value was significantly higher in stover from the south (Fig. 2b), possibly due to the higher P in Cerrado stover (Fig. 1b), causing high extrusion of OH^-, which impacted available alkalinity of soybean residue from this region.

pH CaCl₂ and Al³⁺ of soil incubated with soybean stover

Incubation with soybean stover increased the pH CaCl₂ of the natural soil (pHcontrol = 3.74) by approximately 0.30 units (Fig. 4a). Soil exchangeable Al (Al³⁺_control = 1.19 cmol_c.kg^-1) decreased by approximately 0.40 cmol_c.kg^-1 when incubated with soybean stover for 30 days (Fig. 4b). There was no significant effect on soil pH and exchangeable Al after incubation with stover from different regions of the country (p > 0.05) (Fig. 4). Stover decomposition was beneficial for alleviating soil acidity regardless of chemical attributes of plant residue.

Figure 4
Soil pH and Al³⁺ variation after 30 days of incubation with and without stover. (a) Average pH CaCl₂ and (b) Al³⁺ of soil in the control treatment (without stover—gray), with PR+RS soybean stover (green) and with BA stover (blue) after incubation for 30 days. Treatments with the same letters do not differ from each other according to the Tukey’s test at 5% significance level.

The pH (r = 0.68) and exchangeable Al (r = -0.59) of soil incubated with PR+RS stover (Fig. 5a) had a higher correlation with available alkalinity than the soil incubated with BA stover (r = 0.62 and r = -0.52, respectively) (Fig. 5b). This can be attributed to the significantly higher (p < 0.05) available alkalinity in PR+RS stover (Fig. 2b). Release of available alkalinity directly affects soil pH since it decreases H⁺ activity in the soil solution and attenuates Al³⁺ activity by hydrolysis, which forms Al(OH)₃ that is unavailable to plants (Abdulaha-Al Baquy et al. 2017).

Figure 5
Representation of Pearson correlation coefficients (r) between pH (stover pH), available alkalinity (stover OH^-), and cations (stover cations - ∑ = Ca, Mg, K, and Na) from soybean stover from (a) PR+RS and (b) BA with the pH CaCl₂ (Soil pH) and Al³⁺ (Soil Al) of soil incubated for 30 days with respective stovers.

Attributes of soybean stover from PR+RS (Fig. 5a) that correlated with the pH CaCl₂ of incubated soil were available alkalinity (r = 0.68, p < 0.01) and sum of cations (r = 0.51, p < 0.01). The Al³⁺ of the incubated soil correlated with stover available alkalinity (r = -0.59, p < 0.01) and the pH CaCl₂ resulting from incubation (r = -0.80, p < 0.01) (Fig. 5a).

Available alkalinity of BA stover (Fig. 5b) also correlated with the pH CaCl₂ of incubated soil (r = 0.62, p < 0.01). Sum of cations in stover influenced final soil pH (r = 0.74, p < 0.01). Soil exchangeable Al resulting from incubation with stover was influenced by available alkalinity (r = -0.52, p < 0.01), pH CaCl₂ of soil (r = -0.69, p < 0.01), and sum of cations from soybean stover (r = -0.62, p < 0.01) (Fig. 5b).

Sum of cations in stover from Bahia (Fig. 5b) had a more relevant impact on soil pH, with a much higher correlation (r = 0.74) than with southern stover (r = 0.51) (Fig. 5a). The correlation of soil Al (r = -0.62) with sum of cations for BA stover (Fig. 5b) was not observed with PR+RS stover (p > 0.05) (Fig. 5a). Release of cations from decomposed organic material increases base saturation and alleviates soil acidity by replacing H⁺ and Al³⁺ in exchange complexes (Marschner and Noble 2000).

These incubation results demonstrated that available alkalinity of PR+RS stover contributed more significantly to increased pH, as well as decreased Al³⁺ in soil, while sum of cations in BA stover was more important. However, pH and final exchangeable Al of incubated soil did not differ depending on the residue origin.

In a study of nutrient export by soybean in the state of Paraná, Barth et al. (2018) reported that for 0.015 mg.kg^-1 of Ca in biomass, only 0.003 mg.kg^-1 of Ca was removed from the system in the form of grain; this represents 19% of the Ca absorbed by the plant. The Ca that was not exported by grain remained in the system, thereby mitigating acidification caused by Ca absorption. Most of the absorbed Mg was also returned to the system (64%). Replacement occurs by plant residue decomposition, that returns nutrients to the system (Pereira et al. 2017). The present study showed that, in addition to the replacement of cations such as Ca²⁺, Mg²⁺, and K⁺, crop residues covering the soil can provide great contributions to alkalinity (in the form of OH^-) that help alleviate the effects of soil acidification.

CONCLUSION

It was seen that the soybean stover from two regions effectively reduced soil acidity of Oxisol. This is very significant, since in Brazil soybean occupies the most cropped area and Oxisol is the most abundant soil. However, changes were observed after the application of large amounts of residue. Based on our results, the interphase soil stover under no till can be affected by stover decay reducing soil acidity. Also, how residue impacts seasonal variation in soil acidity needs to be considered. Not every stover has the same potential, since available alkalinity, measured in laboratory, showed variation between regions. Also, the potential of stover to correct soil acidity can be estimated by laboratory measures of stover cations levels or available alkalinity. Except for Ca and Zn, stover elemental composition varies between regions, and some difference could be related to soil organic matter for N and S, soil parent material for Mn, Cu, Ba and Ni, soil P availability, and other abiotic conditions influencing Mg and K availability. Knowledge of residue composition and its effect on soil acidity can be a useful tool in soil management. Nevertheless, it is important to know that soybean residue reduces the long-term acidity potential of the soil, but it is not sufficient to completely mitigate the soil acidification process. In addition, it is necessary to monitor the chemical analysis of the soil to determine each time the soil analysis indicates.

ACKNOWLEDGMENTS

The authors would like to thank Eduardo Ferreira, Felipe Sokulski, Guilherme Paraboni, Nicolas Trentin, Albert Melinski, and Marcelo Trybek for the soybean stover collection.

• How to cite:
  Albuquerque, C. G., Motta, A. C. V., Lammel, D. R., Barbosa, J. Z., Gavelaki, F., Prior, S. A. and Dieckow, J. (2026). Chemical characterization of soybean stover shows potential to mitigate soil acidity in Brazil. Bragantia, 85, e20240110. https://doi.org/10.1590/1678-4499.20240110
• FUNDING
  Not applicable.

DATA AVAILABILITY STATEMENT

Data are available in https://zenodo.org/records/17477880.

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• Albuquerque, C. G., Motta, A. C. V., Lammel, D. R., Barbosa, J. Z., Gavelaki, F., Prior, S. A., Dieckow, J. (2025). Data from: Chemical characterization of soybean stover shows potential to mitigate soil acidity in Brazil. Available at: https://zenodo.org/records/17477880 Accessed on: Oct. 30, 2025.
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Edited by

• Section Editor:
  Osvaldo Guedes Filho https://orcid.org/0000-0001-8550-8505

Publication Dates

• Publication in this collection
  09 Jan 2026
• Date of issue
  2026

History

• Received
  24 May 2025
• Accepted
  16 Sept 2025