Buffer methods for estimating potential acidity in soils of the agricultural frontier area, northeastern Brazil

ABSTRACT

The Brazilian region of Maranhão, Tocantins, Piaui, and Bahia (“Matopiba”), and more specifically the Cerrado region of Piauí, is recognized as a new Brazilian agricultural frontier. An official method for estimating soil potential acidity (H+Al) has not been defined, and determination by the calcium acetate method is costly and time-consuming. This study aimed to compare the H+Al values determined using the calcium acetate method with those obtained using two buffer methods: the Shoemaker, McLean, and Pratt (SMP) buffer and the Santa Maria (SM) buffer, considering samples from the main classes of soils cultivated in the state of Piauí. For that purpose, 57 soil samples from Cerrado were collected in the arable soil layer (0.00–0.20 m) under different agricultural systems and under native vegetation. The statistical models obtained were compared with hypothetically inadequate models used by laboratories, as calibration has not been defined for soils from the state. After laboratory analyses, paired values determined for H+Al and the corresponding equilibrium SMP and SM buffer indices were subjected to correlation and regression analyses. The SMP and SM buffer methods showed high consistency in determining potential acidity in representative Cerrado soils of Piaui, resulting in similar estimates of H+Al concentrations. The equations (i) H+Al (cmol_c dm^-3) = 33.687 – 4.5849 SMP index (I_SMP) (R² = 0.85) and (ii) H+Al (cmol_c dm^-3) = 33.863 – 4.5904 SM index (I_SM) (R² = 0.84) can be used to estimate potential acidity in soils of the Cerrado of Piaui.

Keywords
liming; Matopiba; SMP buffer; Santa Maria buffer

INTRODUCTION

In Brazil, an agricultural frontier is designated based on recent expansion of grain cropping in a given region, whether through conversion of degraded pastures or through opening of areas with native vegetation, in compliance with the Brazilian forestry protection code. The “Matopiba” region, which partially encompasses the states of Maranhão, Tocantins, Piauí, and Bahia, is characterized by the expansion of an agricultural frontier based on high-yield technologies (Miranda et al., 2014). In the Cerrado regions of Matopiba, expansion of the agricultural frontier began in the 1970s and 1980s due to the evolution of technologies and the adoption of agricultural management practices adapted to tropical conditions. Prominent among these technologies is the use of limestone and fertilization to improve soil fertility, as well as advances in breeding of grain crops for lower-latitude regions (Almeida et al., 2024).

The expansion of the agricultural frontier in the Matopiba region is an ongoing process, with some particular aspects and technological challenges, which explains the need for targeted research and, in some cases, review of established technological solutions, such as the need for lime recommendations, particularly for newly opened areas (Oliveira et al., 2024). The low natural soil fertility and the need for soil amendment, as well as drought stress caused by frequent out-of-season hot, dry periods, represent some of the main edaphoclimatic conditions inherent to the agricultural frontier regions (Evangelista et al., 2017). Therefore, the use of agricultural lime is an important technology to increase the soil volume exploited by roots and to enhance plant resilience in periods of water shortage (Lustosa Filho et al., 2021). However, the absence of specific lime recommendations for the region edaphoclimatic conditions, especially in the state of Piauí, has led producers to apply lime amounts higher than those recommended by official methods (Lustosa Filho et al., 2021; Oliveira et al., 2024).

Under the edaphoclimatic conditions of the Cerrado, the main approaches for estimating the amounts of soil acidity amendments are based on eliminating aluminum and raising the calcium and magnesium contents, as well as the Ca-Mg-K saturation method (Sousa and Lobato, 2004). In contrast, some methods for calculating lime requirements use potential acidity (H+Al), in which this property is determined using the method of 0.5 mol L^-1 calcium acetate buffered at pH 7.0 (Teixeira et al., 2017). However, this is a costly and time-consuming routine procedure. To overcome this limitation, some laboratories have used buffer methods, such as SMP (Shoemaker, McLean, and Pratt) (Shoemaker et al., 1961), to estimate H+Al values. Studies have shown the effectiveness of the SMP buffer method in several Brazilian states (Quaggio et al., 1985; Sousa et al., 1989; Pavan et al., 1996; Maeda et al., 1997; Nascimento, 2000; Silva et al., 2006; Moline et al., 2011; Gama et al., 2013; Araújo et al., 2014; Almeida Júnior et al., 2015; Prado et al., 2020). The Santa Maria (SM) buffer method has also been tested and is considered a promising alternative for Brazilian soils (Toledo et al., 2012).

Although the SMP buffer is widely used, it contains p-nitrophenol and potassium chromate, substances that are classified as hazardous. In this context, the Santa Maria buffer was developed by Toledo et al. (2012) as a free-of-toxic-substances alternative that can replicate the potentiometric response of the SMP buffer in the states of Rio Grande do Sul and Santa Catarina (RS/SC).

The SMP and Santa Maria buffer methods have shown good correlation and similarity regarding direct determination of potential acidity. However, as the Santa Maria buffer does not use toxic and environmentally hazardous reagents, such as those in the SMP buffer (Mackessy et al., 2024), it is a more suitable option for estimating soil acidity amendment requirements (Prado et al., 2020). Thus, to avoid overestimating or underestimating lime application recommendations, further calibrations are required to accurately determine the need for lime across different regional soil types (Makepeace et al., 2022).

Given the rapid expansion of agricultural frontiers and the limited scientific literature on these soils, liming is essential for crop production in low-fertility tropical soils. This study aimed to calibrate predictive equations to estimate potential acidity (H+Al) using pH readings from SMP and Santa Maria buffer solutions in soils representing the Matopiba Cerrado region. These models will improve the accuracy of soil amendment and fertility management recommendations across the region.

MATERIALS AND METHODS

This study was conducted based on analysis of soil samples that compose the database of Embrapa Meio-Norte, in the municipality of Teresina, Piauí, Brazil. The state of Piauí mainly has soils belonging to the soil classes Latossolo Amarelo (Oxisols) (41 %), Neossolo Litólico (Lithic Orthents) (24 %), Neossolo Quartzarênico (Quartzipsamments) (10 %), and Argissolo Vermelho-Amarelo (Ultisols) (5 %), which together account for 80 % of the area (Soil Survey Staff, 2014; Sagrilo et al., 2025). However, the present study considered soil classes from different municipalities of the Cerrado region of Piauí (Figure 1) that represent the agricultural frontier: Argissolo Vermelho-Amarelo, Latossolo Amarelo, and Neossolo Flúvico (Santos et al., 2025), corresponding to Ultisol, Oxisol, and Entisol (Soil Survey Staff, 2014), respectively.

Figure 1
Geographic delimitation of the municipalities where soil samples were collected in the state of Piauí.

The 0.00-0.20 m layer was sampled in 57 different areas under different types of agricultural use, such as soybean, cowpea, corn intercropped with Brachiaria grass, pasture, and crop-livestock-forest integration systems, as well as areas under Cerrado native forest. Samples from areas under agricultural use accounted for 86 %, whereas the areas under native Cerrado represented 14 % of the total samples. The samples from agricultural areas included different periods under agricultural use and different types of management; they were composed of areas of recent conversion from native forest, long-established crop areas, and areas under integrated crop/livestock systems. The aim was to consider the greatest possible diversity of soil fertility conditions and management practices.

The predominant climate in the Cerrado of Piaui, according to the Köppen-Geiger classification system, is Aw – hot, humid climate (Medeiros et al., 2020), with summer rains occurring in the south-central and southwest regions of the state from November to March. In these regions, annual rainfall ranges from 1,000 to 1,400 mm and occurs mainly from December to February, whereas the driest quarter of the year is from June to August (Fernandes et al., 2020; Lima and Andrade Júnior, 2020). In Cerrado areas farther north in the state, rains occur from January to May. The mean annual temperature is 27 °C (Fernandes et al., 2020; Lima and Andrade Júnior, 2020).

Soil chemical properties were determined after sample preparation, according to van Raij et al. (2001) and Teixeira et al. (2017). Soil pH was measured in water and in a 0.01 mol L^-1 CaCl₂ suspension (1:2.5 soil:solution, v:v). Available potassium was extracted using Mehlich-1 solution, and its concentration was determined using atomic absorption spectroscopy. Exchangeable Ca and Mg were determined using atomic absorption spectroscopy after extraction with 1 mol L^-1 KCl. Potential acidity was determined using the extraction method with 0.5 mol L^-1 calcium acetate solution and quantified by titration with 0.0125 mol L^-1 NaOH. Sum of bases (SB) was obtained by summing the cations Ca²⁺, Mg²⁺, and K⁺. Cation exchange capacity at pH 7.0 (CEC_pH7.0) was calculated as the sum of SB and potential acidity. Saturation by Ca-Mg-K (V) was calculated as the ratio between SB and CEC at pH 7.0. Soil organic matter (SOM) was determined using the method originally proposed by Walkley-Black with modifications. Clay content was measured using the Pipette Method.

Additionally, the estimation of H+Al was obtained using different buffer solutions, namely SMP (Shoemaker et al., 1961; Santanna et al., 2011) and Santa Maria (Toledo et al., 2012), with a soil:CaCl₂:buffer ratio of 10:25:5. Descriptive statistical analysis was used on the soil chemical property data.

Based on the data, correlation analysis (p<0.05) was carried out between the H+Al concentrations and the SMP index (I_SMP) and the SM index (I_SM). Regression models were fitted according to statistical significance and the coefficient of determination. Furthermore, H+Al concentrations were estimated using the SMP and SM buffers for buffer indices 5.0, 5.5, 6.0, 6.5, and 7.0 in the state of Piauí and compared with indices obtained from equations proposed for other Brazilian states.

In addition, using the equations obtained in the present study, lime application recommendations were calculated based on the Ca-Mg-K saturation method (Sousa and Lobato, 2004), considering the potential acidity values obtained by both buffer methods for the following soils: Argissolo Vermelho-Amarelo, Latossolo Amarelo, and Neossolo Flúvico in the municipality of Teresina, and Latossolo Amarelo in the municipalities of Regeneração and Bom Jesus, as follows (Equation 1):

Eq. 1 $\mathrm{Application}\mathrm{rate}(\mathrm{Mg}{\mathrm{ha}}^{-1})=\left\{\left[\right({\mathrm{V}}_2-{\mathrm{V}}_1)\times \mathrm{CEC}]/100\right\}\times \mathrm{f}$

in which: V₂ is desired Ca-Mg-K saturation (using V₂ = 80 %); V₁ is the Ca-Mg-K saturation obtained from soil analysis; and f is the correction factor used to adjust the lime application rate according to its Relative Total Neutralizing Power.

After that, the lime application recommendations obtained using I_SMP and I_SM were compared with the equations recommended for other states in Brazil (SMP and Santa Maria), namely: Amapá (Araújo et al., 2014), Goiás (Sousa et al., 1989), Mato Grosso (Prado et al., 2020), Mato Grosso do Sul (Maeda et al., 1997), Minas Gerais (Silva et al., 2006), Pará (Gama et al., 2013), Paraíba (Almeida Júnior et al., 2015), Paraná (Pavan et al., 1996), Pernambuco (Nascimento, 2000), Rondônia (Moline et al., 2011), Rio Grande do Sul/Santa Catarina (Escosteguy and Bissani, 1999), and São Paulo (Quaggio et al., 1985).

RESULTS

Low values of pH, K⁺, Ca²⁺, Mg²⁺, and V were observed. Wide variability also appeared, in the following decreasing order of variation: K⁺ > V > Clay > Ca²⁺ > Mg²⁺ > H+Al > SB > SOM > CEC > pH_CaCl2 > pH_H2O > I_SMP > I_SM (Table 1).

Table 1
Descriptive statistics for chemical properties in soil samples from the Cerrado region of Piauí collected in the 0.00–0.20 m layer

Parameter	pH(H2O)	pH(CaCl2)	ISMP		ISM
Mean	5.4	4.7	6.2		6.3
Deviation	0.7	0.6	0.5		0.5
Maximum	6.7	6.0	7.2		7.4
Minimum	4.3	3.8	5.0		5.0
CV(%)	10.7	11.7	8.1		7.9
Parameter	K+	Ca2+	Mg2+	H+Al	SB	CECpH7.0
	--- cmolc dm-3 ---
Mean	0.13	1.07	0.49	4.96	1.69	6.86
Deviation	0.10	0.55	0.25	2.43	0.76	2.30
Maximum	0.44	1.93	0.97	11.08	2.82	11.59
Minimum	0.02	0.21	0.16	1.80	0.43	2.81
CV (%)	73.1	51.3	50.0	49.1	45.1	34.5
Parameter	V		SOM		Clay
	--- % ---
Mean	26		2.7		25
Deviation	14		1.0		14
Maximum	58		5.0		61
Minimum	4		0.8		7
CV(%)	58.1		37.9		56.9

• pH(H₂O): hydrogen potential in water; pH(CaCl₂): hydrogen potential in calcium chloride; I_SMP: index in Shoemaker, Mclean, and Pratt buffer solution; I_SM: index in Santa Maria buffer solution; K⁺: potassium; Ca²⁺: calcium; Mg²⁺: magnesium; H+Al: potential acidity; SB: sum of bases; CEC _pH7.0: cation exchange capacity at pH 7.0; V: Ca-Mg-K saturation; and SOM: soil organic matter.

The relationship between the H+Al concentrations and the buffer indices exhibited inverse proportionality; that is, higher values of potential acidity were associated with lower values of both buffer indices evaluated (Figure 2).

Figure 2
Relationship between H+Al values (determined using calcium acetate) and buffer index (SMP and SM) in soils of the Cerrado region of Piauí.

In comparison to the H+Al value obtained for Piauí (10.8 cmol_c dm^-3), the SMP index of 5.0 was found to be near that reported for Amapá, Goiás, Mato Grosso, Pará, and Paraná; whereas underestimated values were observed for Paraíba, Pernambuco, Rondônia, and Rio Grande do Sul/Santa Catarina. For Mato Grosso do Sul, Minas Gerais, and São Paulo, the values were overestimated (Table 2). For the SMP index of 5.5, the H+Al concentrations were overestimated using the equation proposed for Mato Grosso do Sul; except for Paraná, the other states exhibited underestimated values compared with Piauí (8.5 cmol_c dm^-3). For the SMP index of 6.0, the H+Al concentration was underestimated by the other equations compared with the value obtained for Piauí (6.2 cmol_c dm^-3). Regarding the SMP index of 6.5, the H+Al concentration was overestimated using the equation proposed for Pará; it exhibited an H+Al value near that using the equation developed for Pernambuco. For the other states, the values were underestimated compared with the value for Piauí (3.9 cmol_c dm^-3). For the SMP index of 7.0, the H+Al concentration was overestimated using the equations proposed for Pará, Paraná, Pernambuco, and Rondônia, while the other equation proposals exhibited values near that of Piauí (1.6 cmol_c dm^-3). Considering the SM index, the H+Al values estimated for the state of Piauí were higher than the values obtained using the equation proposed for the state of Mato Grosso.

Table 2
Estimated values of potential acidity for soils of Piauí and for other states of Brazil

State	Equation	SMP index					Reference
		5.0	5.5	6.0	6.5	7.0
		H+Al
		---cmolc dm-3---
Piauí	H+Al = 33.687 - 4.5849 ISMP	10.8	8.5	6.2	3.9	1.6	Present study
Amapá	H+Al = 62.08 - 14.394 ISMP + 0.8263 I2	10.8	7.9	5.5	3.4	1.8	Araújo et al. (2014)
Goiás	ln(H+Al) = 7.719 – 1.068 ISMP	10.8	6.3	3.7	2.2	1.3	Sousa et al. (1989)
Mato Grosso	H+Al = 53.105 – 26.54 ln(ISMP)	10.4	7.9	5.6	3.4	1.5	Prado et al. (2020)
Mato Grosso do Sul	ln(H+Al) = 8.086 – 1.062 ISMP	16.1	9.4	5.6	3.3	1.9	Maeda et al. (1997)
Minas Gerais	ln(H+Al) = 8.26 – 1.124312 ISMP	14.0	8.0	4.5	2.6	1.5	Silva et al. (2006)
Pará	H+Al = 77.77 – 20.61 ISMP + 1.435 I 2	10.6	7.8	5.8	4.4	3.8	Gama et al. (2013)
Paraíba	H+Al = 57.108 -13.338 ISMP + 0.7637 I2	9.5	6.9	4.6	2.7	1.2	Almeida Júnior et al. (2015)
Paraná	ln(H+Al) = 6.0687 – 0.744 ISMP	10.7	7.4	5.1	3.5	2.4	Pavan et al. (1996)
Pernambuco	H+Al = 38.448 – 8.4855 ISMP + 0.4837 I2	8.1	6.4	4.9	3.7	2.8	Nascimento (2000)
Rondônia	H+Al = 31.22 – 8.20 ISMP + 0.59 I2	5.0	4.0	3.3	2.8	2.7	Moline et al. (2011)
Rio Grande do Sul/Santa Catarina	ln(H+Al) = 8.9832 – 0.9004 ISMP	8.8	5.6	3.6	2.3	1.5	Escosteguy and Bissani (1999)
São Paulo	ln(H+Al) = 7.76 – 1.053 ISMP	12.1	7.2	4.2	2.5	1.5	Quaggio et al. (1985)
State	Equation	SM index					Reference
		5.0	5.5	6.0	6.5	7.0
		H+Al
		---cmolc dm-3---
Piauí	H+Al = 33.863 - 4.5904 ISM	10.9	8.6	6.3	4.0	1.7	Present study
Mato Grosso	H+Al = 51.189 – 25.70 ln(ISM)	9.8	7.4	5.1	3.1	1.2	Prado et al. (2020)

When the lime application rates recommended by the Ca-Mg-K saturation method are calculated using the values obtained through the SMP index with the equations developed for other states, overestimated rates are generally found at the higher SMP index values of 7.1 for Argissolo Vermelho-Amarelo and 7.2 for Latossolo Amarelo from Teresina (Table 3). In this case, underestimated rates were found for intermediate and lower SMP index values, such as 6.2, 5.3, and 6.0 for Neossolo Flúvico from Teresina, Latossolo Amarelo from Regeneração, and Latossolo Amarelo from Bom Jesus, respectively. Regarding the lime application recommendations using the H+Al values estimated through the SM index for the state of Mato Grosso, the lime application rates for the five evaluated soils from Piauí were underestimated.

Table 3
Recommended lime application rates for soils of the Cerrado region of Piauí estimated by different regression equations (LR = lime requirement; V = 80 % desired base saturation;PRNT = relative total neutralizing power of limestone), using H+Al values obtained by the Ca-Mg-K saturation method

State	Soil Type
	Argissolo Vermelho-Amarelo (Teresina)	Latossolo Amarelo (Teresina)	Neossolo Flúvico (Teresina)	Latossolo Amarelo (Regeneração)	Latossolo Amarelo (Bom Jesus)
	SMP index
	7.1	7.2	6.2	5.3	6.0
	LR (V = 80 %; PRNT = 100 %)
	---Mg ha-1---
Piauí(1)	0.7	0.1	3.8	7.4	4.6
Amapá(2)	1.0	0.6	3.3	7.1	4.0
Goiás(3)	0.6	0.4	2.0	6.2	2.6
Mato Grosso(4)	0.6	0.2	3.4	7.0	4.1
Mato Grosso do Sul(5)	1.1	0.8	3.2	9.2	4.1
Minas Gerais(6)	0.7	0.4	2.2	6.9	2.9
Pará(7)	2.7	2.6	3.7	7.0	4.2
Paraíba(8)	0.5	0.1	2.6	6.2	3.3
Paraná(9)	1.5	1.3	3.1	6.7	3.7
Pernambuco(10)	1.8	1.5	3.2	5.5	3.6
Rondônia(11)	1.9	1.8	2.1	3.4	2.2
Rio Grande do Sul/Santa Catarina(12)	0.8	0.6	2.0	5.3	2.5
São Paulo(13)	0.8	0.5	2.4	7.0	3.0
	SM index
7.2	7.4	6.0	5.2	6.3
LR (V = 80 %; PRNT = 100 %)
	---Mg ha-1---
Piauí(1)	0.8	0.2	3.9	7.5	4.7
Mato Grosso(4)	0.4	0	3.1	6.6	3.7

• ⁽¹⁾
  Present study;
• ⁽²⁾
  Araújo et al. (2014);
• ⁽³⁾
  Sousa et al. (1989);
• ⁽⁴⁾
  Prado et al. (2020);
• ⁽⁵⁾
  Maeda et al. (1997);
• ⁽⁶⁾
  Silva et al. (2006);
• ⁽⁷⁾
  Gama et al. (2013);
• ⁽⁸⁾
  Almeida Júnior et al. (2015);
• ⁽⁹⁾
  Pavan et al. (1996);
• ⁽¹⁰⁾
  Nascimento (2000);
• ⁽¹¹⁾
  Moline et al. (2011);
• ⁽¹²⁾
  Escosteguy and Bissani (1999); and
• ⁽¹³⁾
  Quaggio et al. (1985).

The high coefficient of determination of the line relating the SMP pH values with the SM pH values shows the strong similarity between the buffer methods (Figure 3). Principal component analysis helps explain the variability of the data and shows that the SMP and SM indices are associated with the pH values (H₂O and CaCl₂), as well as Ca-Mg-K saturation. However, regarding the management practices or systems studied, a clear distinction is observed between the eucalyptus areas and the Cerrado areas, which exhibit lower pH values and higher H+Al concentrations, contributing to adequate variation among the samples used in the present study.

Figure 3
Relationship between I_SMP and I_SM values for soils of the Cerrado region of Piauí.

DISCUSSION

The variability observed in the chemical properties and clay contents of the soil samples reflects the inherent differences between cultivated areas under different acidity amendment management practices and areas with native vegetation without amendments (Figure S1). Therefore, because lime application requirements are closely related to measurable soil properties, such as texture, SOM, and CEC (Albuquerque et al., 2024), this highlights the importance of considering this variability when calibrating buffer index and potential acidity curves (Prado et al., 2020). Another relevant aspect is that the buffer index showed higher H+Al dispersion at contents higher than 8 cmol_c dm^-3, which may be associated with possible inefficiency in extracting H+Al from more buffered soils (Silva et al., 2006; Prado et al., 2020). Another limitation in the use of the SMP buffer solution is in regard to its application in acidic soils with high organic matter content (Santanna et al., 2011). However, as the soils of Piauí generally have a low concentration of this material, this type of restriction was not observed in this study.

Buffer methods, including SMP, stand out by enabling effective output from the samples analyzed (Mackessy et al., 2024), but they are also considered more versatile, due to their good accuracy over a wide range of soil buffering capacities (Predebon et al., 2018). Under specific situations, this favors extrapolation to states with similar buffering characteristics. In this context, the linear equations proposed for estimating potential acidity based on different buffer indices show similarity to those developed for other regions, such as Goiás (Sousa et al., 1989), Paraná (Pavan et al., 1996), and São Paulo (Quaggio et al., 1985). Furthermore, the similarity between the estimated potential acidity concentrations and, consequently, the lime application rates recommended by the Ca-Mg-K saturation method for the states of Goiás and Mato Grosso coincides with the areas of greater agricultural activity, concentrated in the Cerrado biome.

However, a smaller variation in the estimated concentrations of potential acidity and lime recommendation would be expected using the equation proposed for the state of Mato Grosso do Sul, which also has a high percentage of the Cerrado biome in its physiography, where soil chemical properties are similar to those of the Cerrado of Piauí, particularly regarding the soil acidity components (H⁺, Al³⁺, and H+Al). The discrepancy among Brazilian states using the SMP buffer method may also be related to a lack of effective H+Al extraction from more buffered soils, such as those with high SOM values and high clay contents, unlike the soils representing Piauí, as previously mentioned. These findings highlight the importance of regionally calibrating the methods to estimate potential acidity, as this directly affects interventions regarding lime requirements (Quispe et al., 2025). Therefore, adopting equations proposed for other states may lead to overestimation or underestimation of lime application rates, which directly impacts nutrient availability in the soil and crop yield.

Such differences are more evident when considering that the proposed value for increasing Ca-Mg-K saturation was 80 %, which is used for crops with high fertility requirements. Given that high application rates of amendments have been used more frequently, resulting in economic returns and more rapid fertility buildup throughout the soil profile (Oliveira et al., 2024; Santos et al., 2024), calibrated equations are essential to determine lime requirements more efficiently.

Another noteworthy aspect concerns the growth of agriculture into frontier regions, in soils considered marginal and with low clay contents, which require more extensive studies and specific recommendations for soil acidity amendment (Santos et al., 2024). Therefore, although the variability of soil conditions considered in this study allows optimization of potential acidity estimates in a more practical way for the soil classes that most represent the crop areas in the Cerrado regions of Piauí, some specific soil conditions in marginal areas will require additional studies to optimize the processes for estimating potential acidity and lime recommendations.

CONCLUSIONS

The SMP and Santa Maria buffer methods showed high consistency in determining potential acidity in soils representing the Cerrado of the state of Piauí, providing similar estimates of H+Al concentrations using the calcium acetate method. Lime application requirements may be overestimated or underestimated when using non-calibrated equations to estimate potential acidity for the state of Piauí. The equations (i) H+Al (cmol_c dm^-3) = 33.687 – 4.5849 I_SMP and (ii) H+Al (cmol_c dm^-3) = 33.863 – 4.5904 I_SM can be used to estimate potential acidity in Cerrado soils of the state of Piauí.

ACKNOWLEDGEMENTS

The authors gratefully acknowledge the Brazilian Agricultural Research Corporation (Embrapa Meio-Norte) for providing the materials and infrastructure required for the soil chemical analyses.

How to cite:

Souza HA, Melo FB, Andrade Júnior AS, Oliveira Júnior JOL, Leite LFC, Andrade HAF, Sousa DC, Tavares RKO, Júnior de Almeida H, Costa PM, Silva MLN, Sousa RS, Arruda FP, Sagrilo E. Buffer methods for estimating potential acidity in soils of the agricultural frontier area, northeastern Brazil. Rev Bras Cienc Solo. 2026;50:e0250163. https://doi.org/10.36783/18069657rbcs20250163

FUNDING

The authors also gratefully acknowledge the Funding Authority for Studies and Projects (FINEP), through the CT-AGRO/FNDCT program (Agreement No. 01.22.0080.00, Ref. No. 1219/21), and the National Council for Scientific and Technological Development (CNPq) (Grant No. 314920/2020-0) for their financial support.

DATA AVAILABILITY

The data will be provided upon request.

SUPPLEMENTARY MATERIALS

Supplementary data to this article can be found online at https://www.rbcsjournal.org/wp-content/uploads/articles_xml/1806-9657-rbcs-50-e0250163/1806-9657-rbcs-50-e0250163-suppl01.pdf

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*

Corresponding author: e-mail: [e-mail]

Editor:

José Miguel Reichert https://orcid.org/0000-0001-9943-2898 and Tales Tiecher https://orcid.org/0000-0001-5612-2849

Publication Dates

• Publication in this collection
  19 Oct 2026
• Date of issue
  2026

History

• Received
  20 Oct 2025
• Accepted
  13 Mar 2026