Performance of a soybean–maize off-season double crop system in response to potassium fertilization strategies in a Brazilian Cerrado oxisolABSTRACT
Soybean–maize cropping system is widely used in the Brazilian Cerrado region. A field experiment was performed in a Cerrado oxisol to evaluate potassium (K) fertilization strategies on the performance of a soybean–maize cropping system. Five fertilization treatments were investigated, including control (unfertilized), KCl, polyhalite, KCl + polyhalite (72/28, % based on K), and KCl + lime + gypsum. In all K fertilization strategies, a rate of 66.5 kg K·ha-1 was applied only at the time of soybean sowing. Soybean and maize grain yields were not significantly influenced by K fertilization management, but the cumulative grain yield of the cropping system (soybean + maize) was 21% higher by using polyhalite than KCl. Exclusive fertilization with polyhalite resulted in higher export of K by soybean grains. In addition, it was the only treatment capable of providing a positive magnesium (Mg) balance in the soybean–maize cropping system (+2.51 kg·ha-1). The calcium (Ca) and sulfur (S) balance was positive under the use of polyhalite, KCl + polyhalite, and KCl + lime + gypsum. Fertilization with polyhalite proved to be an excellent strategy to improve the performance of a soybean–maize cropping system by increasing the cumulative grain yield and providing a positive balance of Ca, Mg, and S.
Key words
Glycine max
;
Zea mays
; potassium chloride; polysulphate
INTRODUCTION
Brazil is the third largest grain producer in the world (USDA 2019), and the soybean–maize off-season double crop system represents the most important grain production systems, especially in the Cerrado region (Galvão et al. 2014, Nóia Júnior and Sentelhas 2019). In this system, maize (Zea mays L.) is cultivated in succession to soybean (Glycine max L.), and the supply of nutrients at balanced levels is a critical factor to maintain high quality and yield of this cropping system.
The Brazilian Cerrado region is characterized by acidic soils with low nutrient reserves. Besides nitrogen (N), potassium (K) is the nutrient most required by soybean and maize crops, so that its supply through fertilizers is fundamental for the sustainability of tropical agriculture (Costa et al. 2013). The supply of K by fertilization is basically performed via potassium chloride (KCl), which has in its composition ~50% of K. Polyhalite, in turn, is a sulfate-based fertilizer, which, besides K (~12%), also contains sulfur (S, 19%), calcium (Ca, 12%), and magnesium (Mg, 3.6%) (Yermiyahu et al. 2017). Recent discoveries of large reserves of polyhalite in northern United Kingdom have increased interest in the use of this mineral (Kemp et al. 2016), which emerges as an alternative to fertilizers conventionally used in Brazil (Dal Molin et al. 2019).
Some studies on the use of polyhalite in agriculture demonstrated improvements in yield and quality of potatos (Mello et al. 2018a), increase in production and nutrient concentration in tomatos (Mello et al. 2018b), higher nutrient uptake and biomass production in wheat (Yermiyahu et al. 2017), and higher dry matter yield in corn (Dal Molin et al. 2019). Despite the growing interest in polyhalite, there is a lack of field-based evidence regarding its agronomic effectiveness in double-cropping systems, such as soybean followed by off-season maize. In systems of this type, the residual effect of fertilizers has a major impact on profitability, as it can impact crop yields while providing greater operational flexibility to producers.
This study examined the effects of K fertilization strategies on the performance of a soybean–maize cropping system in a Brazilian Cerrado oxisol. Changes in soil chemical attributes and grain yield of a soybean–maize succession with the K fertilization strategies used were evaluated. We hypothesized that fertilization with polyhalite is an efficient strategy to improve the performance of a soybean–maize cropping system in a highly weathered soil.
MATERIAL AND METHODS
Site description and soil
The experiment was carried out in Rio Verde, GO, Brazil (-17.678875, -51.034513), on an oxisol (loamy Typic Hapludox) (Santos et al. 2018). The area had been under soybean–corn succession for at least four years and was selected because it represents most of soybean–corn producing areas in the region. According to Köppen-Geiger’s system (Peel et al. 2007), the climate at the site is classified as AW, tropical, with dry season in the winter and rainy summer. The annual rainfall is 1,400–1,600 mm, and the average temperature is 23–24°C (Cardoso et al. 2014). Table 1 shows the results of soil chemical analysis for different depths prior to establishment of the experiment. Specifically, in the 0–20-cm soil layer, the area showed no toxic levels of aluminum, and macronutrient levels were adequate—or even high in the case of Mg—based on interpretation criteria for the Cerrado region (Sousa and Lobato 2004).
Results of soil chemical analysis for different depths before the establishment of the experiment.
Experimental design and treatments
A randomized complete block was used, and five treatments were replicated four times. Plot size was 6 m × 5 m. The treatments consisted of a control (unfertilized) and fertilization with KCl, granulated polyhalite (Poly4® commercial product of Anglo American Crop Nutrientes – http://www.poly4.com/) KCl + polyhalite in the ratio of 72/28 (% based on K), and KCl + lime + gypsum. A standard rate of 66.5 kg K.ha-1 was used in treatments only at the time of soybean sowing, in order to represent typical system fertilization practices in the region. Maize was sown in succession to soybean without any additional K fertilization. Table 2 shows the amounts of K, Ca, Mg, and S applied in each treatment at the time of soybean sowing.
Crop management
Soybean, cultivar Brasmax Flecha IPRO, was sown on maize straw on November 4, 2017, using a mechanical seeder-fertilizer machine for direct planting, in rows spaced 0.5 m apart and with expected population of 240,000 plants.ha-1. To achieve maximum contribution of biological N2 fixation, soybean seeds were inoculated with a commercial inoculant containing Bradyrhizobium japonicum shortly before sowing. At the time of sowing, 17 kg N.ha-11 and 35 kg P.ha-1 were applied on the soil surface as monoammonium phosphate. Soybean was harvested on February 15, 2018.
Maize, hybrid P3646, was sown in succession to soybean on February 22, 2018, with a mechanical seeder-fertilizer machine for direct planting, in rows spaced 0.5 m apart and with expected population of 60,000 plants.ha-1. Maize was sown without fertilizers, and only urea was applied in top-dressing at a rate of 135 kg N.ha-1 at the V3 development stage (three fully expanded leaves). Maize was harvested on June 23, 2018.
All other production practices, including for weed and pest control, were conducted following standard recommendations practices for the region. The precipitation and maximum and minimum temperature recorded during field trials are shown in Fig. 1.
Precipitation and temperatures recorded during period of experimentation. Rio Verde, GO, Brazil.
Grain yield of soybean and maize
Soybean and maize grains were harvested from the two central rows of each plot to evaluate yield. After harvesting by hand, the soybean pods and the maize ears were threshed in a stationary threshing machine. Grain yield was expressed at 130 g.kg-1 moisture content.
Nutrient concentrations in grain of soybean and maize
Soybean and maize grain samples were dried at 60°C and subsequently ground, following harvest in each crop. Grain analysis was performed using nitric-perchloric acid digestion for K, Ca, Mg, and S (Silva 2009). Nutrient concentrations in grain were determined by flame photometry for K, atomic absorption spectrophotometry for Ca and Mg, and turbidimetry as barium sulfate for S. Nutrient export by grains of soybean and maize was calculated by multiplying the nutrient concentration in grains by grain yield.
Nutrient balance
A simplified balance of K, Ca, Mg, and S was calculated for the soybean–maize cropping system through the following expression: nutrient added via fertilization – nutrient exported by grains (soybean + maize).
Soil sampling and chemical analysis
Soil samples were taken at depths of 0–10, 10–20, 20–40, and 40–60 cm after harvesting of maize. Six soil core sample per plot were taken by means of a soil probe sampler to obtain a composite sample. Prior to the chemical analysis, soils were air-dried and ground to pass through a 2-mm sieve. The concentrations of K, Ca, Mg, and SO4–-S in the soil were determined according to methods described by Silva (2009).
Statistical analysis
Data from the soil, grain chemical analysis along with soybean and maize yields were submitted to an analysis of variance using the Sisvar software (Ferreira 2011). When there was a significant effect by the F test (p < 0.05), the means were compared by the t-test (LSD) at p = 0.05.
RESULTS AND DISCUSSION
Amendment effects on crop grain yield
Soybean and maize grain yields were not significantly influenced by the K fertilization strategies (Table 3). In our study, the topsoil (0–20 cm) had an exchangeable K+ concentration of 1.9 mmolc.dm-3 (Table 1), which was above the concentration considered limiting (1.3 mmolc.dm-3) for soybean and maize crops (Sousa and Lobato 2004). Soybean yield is normally not influenced by K fertilization in soils with medium to high exchangeable K+ concentration (Mascarenhas and Tanaka 1994, Petter et al. 2012, Korber et al. 2017, Cavalli and Lange 2018).
Influence of potassium fertilization strategies on grain yields of soybean and maize in a soybean–maize cropping system*.
Compared to the control, the application of polyhalite caused an increase in maize grain yield of 1,630 kg.ha-1, which was not significant at p < 0.05 (Table 3). In a pot study conducted with six soils from Tanzania (Africa), the addition of polyhalite in maize significantly increased grain yield, on the order of 218 and 166 kg.ha-1 compared to the use of N + P and KCl + Mg sulfate, respectively (Pavuluri et al. 2017). Another study conducted in the Corn Belt region (Iowa, United States of America) evaluated polyhalite as a sulfur source for soybean and corn across 22 site-year trials (Mahal et al. 2022). In general, sulfate-based sulfur sources, including ammonium sulfate, gypsum, and polyhalite, improved corn yield in the year of application. A residual effect was observed in only one location, where the highest corn yield occurred with elemental S and polyhalite, suggesting that polyhalite may be the sulfate source with the greatest residual effect. In the same study, no significant effects of sulfur sources on soybean yield were detected.
However, the cumulative grain yield (soybean + maize) was about 20% higher when the system was fertilized with polyhalite compared to control and KCl application (Table 3). Intermediate cumulative yields were obtained by the treatments with KCl + polyhalite and KCl + lime + gypsum. The higher cumulative grain yield with the use of polyhalite, KCl + polyhalite, and KCl + lime + gypsum can be attributed to the fact that these treatments provide other nutrients, such as Ca, Mg, and S (Table 2). The supply of these nutrients, mainly S, and the likely lower competition between chloride and sulfate anions for root absorption with the use of polyhalite could have favored the higher cumulative yields (Pavuluri et al. 2017). An advantage of using polyhalite instead of KCl could be related to its stable and long-term pattern of K release, in contrast to the rapid but decreasing availability of K after KCl application (Bernardi et al. 2018). In addition, polyhalite application reduces the movement and leaching of Ca2+, Mg2+, K+, and SO4–-S in the soil, compared to the application of sulfate salts, due to its adsorptive affinity for soil particles and slower dissolution (Yermiyahu et al. 2017).
Nutrient export by crops
Compared to the control and KCl treatments, K export by soybean grains was higher when polyhalite, polyhalite + KCl, and KCl + lime + gypsum were applied (Table 4). This effect was probably due to the slightly higher soybean yields observed in those treatments compared to KCl (Table 3). KCl treatment showed the lowest Mg export by the grains (Table 4). When only KCl was used, the lower export of Mg could have been caused by the absence of Mg in the treatment (Table 2) associated with a possible higher content of soluble K in the root environment, which may have reduced the plant Mg uptake (Mello et al. 2018b). No difference of treatments was identified for Ca and S export by the soybean grains. Nutrients were exported by soybean grains in the following order: K > Ca > Mg > S. The average amount exported per ton of soybean produced was 15.1 kg of K, 3.15 kg of Ca, 2.4 kg of Mg, and 2.05 kg of S.
There was no difference of treatments regarding nutrient export by maize grains (Table 4). Nutrients were exported by maize grains in the following order: K > Mg > S > Ca. The average amount exported per ton of maize produced was 2.21 kg of K, 0.88 kg of Mg, 0.78 kg of S, and 0.18 kg of Ca. The absence of response in the export of K, Mg, Ca, and S by maize grains could be related to the amounts of nutrients applied to soybean in the soybean–maize cropping system (Table 2). This is because of the possible residual effects of polyhalite on the supply of Ca, Mg, and S, as observed in wheat (Yermiyahu et al. 2017), when compared to other sources such as sulfate salts. However, they applied 2.5 times greater rates of polyhalita than in our study. In a study with K and S sources in the fertilization of soybean and maize, it was found that polyhalite application should be based mainly on the supply of S, because of the potential response of both crops to this nutrient (Sutradhar et al. 2016)1.
Export of potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S) by soybean and maize crops as affected by potassium fertilization strategies in a soybean–maize cropping system*.
Nutrient balance in the soybean–maize cropping system
The K balance in the soybean–maize cropping system was negative for all treatments (Fig. 2a). Thus, the exported amount of K was higher than the amount of K supplied via fertilizer. This balance was more negative in the control treatment (-77.2 kg.ha-1), in which K was not applied in the soybean–maize cropping system. Among the other treatments, the use of KCl was the one that led to the closest balance to neutrality (-6.80 kg.ha-1). The export of nutrients by harvesting can lead to a negative balance in the nutrient reserve in the soil, resulting in lower nutrient availability for plants, particularly in more intense cropping systems (Steiner et al. 2015, Dal Molin et al. 2019). In our study, however, this negative balance of K should not have impacted crop yield, since the soil had a sufficient K concentration (Table 1) and supplied this deficit, at least in this cycle of crops.
Simplified balance of (a) K, (b) Mg, (c) Ca, and (d) S as affected by potassium fertilization strategies in a soybean–maize cropping system*.
The Mg balance in the soybean–maize cropping system was only positive when polyhalite was used in the fertilization (+2.51 kg.ha-1) (Fig. 2b). The combined supply of KCl + polyhalite and KCl + lime + gypsum showed a less negative balance compared to treatments with application of KCl and control. The positive balance of Mg with the use of polyhalite in the fertilization of the soybean–maize system was due to the higher amount of Mg added (Table 2), since polyhalite contains 3.6% of Mg in its composition. Fertilization management options that contribute to maintaining adequate soil nutrient concentrations are fundamental, particularly for typical areas of Cerrado. This is of particular importance, because the options for supplying Mg via fertilization are few and/or unfeasible (in terms of costs or logistics), so the main supply of this nutrient occurs via liming. When liming is not properly performed, the exchangeable Mg concentration becomes limiting, which is a very common occurrence in several soybean and maize producing areas in the Cerrado region.
For Ca and S, the balance was positive in the treatments that received polyhalite, KCl + lime + gypsum, and KCl + polyhalite (Figs. 2c and 2d). A better balance for Ca and S was obtained with the use of polyhalite. However, after one cycle of the soybean–maize system, both the absence of fertilization and fertilization with KCl alone resulted in a negative balance of Ca and S (Figs. 2c and 2d). The use of polyhalite alone resulted in a more positive balance for Ca and S in the cropping system due to the higher amount of Ca and S added (Table 2) as a result of its composition in Ca (12.1%) and S (19%). The greater contribution of Ca and S to the soybean–maize cropping system with the use of polyhalite could be very beneficial to the Brazilian typical acid soils, increasing liming efficiency and soil structuring (Mello et al. 2018b), besides mitigating the toxic effect of Al3+ on plants (Vasconcelos et al. 2020).
Changes in soil chemical properties
After completing one cycle of a soybean–maize cropping system, the exchangeable Ca concentration at the 0–10 cm soil layer was higher with the use of polyhalite (Fig. 3a). Exchangeable Ca tends to remain close to the soil surface, since it is adsorbed in negatively charged soil particles (Corá et al. 2019)2. However, the increase in exchangeable Ca concentration at the 20–40-cm layer with the use of polyhalite possibly occurred due to the greater supply of Ca, which resulted in an increased concentration of exchangeable Ca in the soil compared to the use of KCl + lime + gypsum and KCl + polyhalite.
Exchangeable (a) Ca2+, (b) Mg2+, and (c) K+, and the extractable (d) SO4–-S concentrations in the soil profiles as affected by potassium fertilization strategies. Soils were sampled after cultivation of a soybean–maize succession*.
The exchangeable Mg concentration was influenced by treatments only in the soil surface layers (0–10 and 10–20 cm), with higher Mg concentrations in the treatments with KCl + lime + gypsum, polyhalite, and KCl + polyhalite (Fig. 3b). The higher exchangeable Mg concentrations found in the surface layers is most likely due to the entry of Mg into the system, through the use of either polyhalite and/or lime, which is a very positive point, considering that in several soybean and maize producing areas in southwestern Goiás, Brazil, Mg is the most limiting nutrient for grain yield.
Since the K balance was negative (Fig. 2a), the exchangeable K concentration found in the soil after the soybean–maize succession (Fig. 3c) was lower than that observed prior to the establishment of the experiment (Table 1). The exchangeable K concentration was influenced by treatments only in the soil surface layer (0–10 cm), with a higher K concentration being obtained in the treatment with KCl + polyhalite in comparison to the other treatments (Fig. 3c). This effect could be indicative of a lower uptake of K in the soil by the crops with the use of this treatment. The absence of difference in K concentration in the soil deeper layers is possibly due to the high concentration of K available in the soil (absorbed from the exchangeable fraction) and most likely also to non-exchangeable fractions of K, which can keep the exchangeable K concentrations of the soil stable in successive crops (Vieira et al. 2016), even in more weathered soils.
The concentration of SO4–-S in the soil profiles (0–60 cm) was not significantly influenced by the treatments (Fig. 3d), although the S balance in the production system was positive (Fig. 2d). The non-influence of treatments on the concentration of SO4–-S in the soil could be attributed, at least in part, to the low adsorption capacity of sulfate and to the high percolation of the sulfate anion to the deeper layers of tropical soils (Tiecher et al. 2012).
CONCLUSION
The cumulative grain yield (soybean + maize) of a soybean–maize cropping system was about 20% higher when the system was fertilized with polyhalite compared to the control and KCl application.
The fertilization of a soybean–maize cropping system with polyhalite increased the export of K, while fertilization with KCl decreased the export of Mg by the soybean crop.
The application of 66.5 kg K.ha-1 in a soybean–maize cropping system via polyhalite and/or KCl and KCl + lime + gypsum was not sufficient to supply the amount of K exported by grains, resulting in a negative balance of K. A better balance for Ca, Mg, and S (nutrient added via fertilization - nutrient exported by grains) was obtained with the use of polyhalite.
Overall, the more positive balance in the production system and the higher nutrient concentrations in the soil with the use of polyhalite, mainly compared to the control treatment, indicate that polyhalite may be a fertilizer with better residual effect. However, the dynamics of nutrient availability and uptake in response to polyhalite application are still poorly understood, especially in rotation systems. Therefore, further research is needed to better understand the reactions and nutrient release rates of polyhalite in Brazilian soils.
ACKNOWLEDGMENTS
The authors are grateful to Terra Forte group for its support in field trials, and to Instituto Federal de Educação, Ciência e Tecnologia Goiano for supporting this publication.
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How to cite:
Silva, F. F., Cavalcante, T. J., Albert, A. M., Caires, E. F. and Castoldi, G. (2025). Performance of a soybean–maize off-season double crop system in response to potassium fertilization strategies in a Brazilian cerrado oxisol. Bragantia, 85, e20250194. https://doi.org/10.1590/1678-4499.20250194
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FUNDING
Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorFinance code 001Anglo American Crop NutrientsGrant No.: 02/2018 (under process IF Goiano 23218.000999/2017-11)
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DECLARATION OF USE OF ARTIFICIAL INTELLIGENCE TOOLS
The authors declare that no artificial intelligence tools were used in the preparation of this manuscript.
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1
Sutradhar, A., Kaiser, D. E. and Rosen, C. J. (2016). Evaluation of polyhalite as a source of potassium and sulfur for a corn-soybean rotation in Minnesota. In Proceedings of the 46th North Central Extension-Industry Soil Fertility Conference, 32, 124-135.
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2
Corá, J., Lagarrigue, D. and Lewis, T. (2019). Evaluating the effectiveness of gypsum and polyhalite-based fertilizer poly4 on changing subsoil chemical attributes in a Brazilian oxisol. In American Society of Agronomy, ASA-CSSA-SSSA International Annual Meeting, San Antonio, Texas, USA. Available at: https://www.researchgate.net/publication/337338795_EVALUATING_THE_EFFECTIVENESS_OF_GYPSUM_AND_POLYHALITE-BASED_FERTILIZER_POLY4_ON_CHANGING_SUBSOIL_CHEMICAL_ATTRIBUTES_IN_A_BRAZILIAN_OXISOL Accessed on: Nov 12, 2025.
DATA AVAILABILITY STATEMENT
All dataset were generated or analyzed in the current study.
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Section Editor:
Gabriel Constantino Blain https://orcid.org/0000-0001-8832-7734
Balance: nutrient supplied via fertilization - nutrient exported by grains; *bars with different letters (above or below) differ from each other by the t-test (LSD) at 5% probability level.
*Horizontal bars represent the least significant difference (LSD) between the means by the t-test (LSD) at 5% probability level; NS: not significant difference.