Effects of Organic, Organomineral, and Mineral Fertilization on Soil Macronutrients in Chrysanthemum Cultivar Singelo Cultivation

Abstract

The use of agro-industrial waste, such as wood ash or biomass ash, has been adopted as an alternative to synthetic fertilizers for providing nutrients to plants. This study aimed to evaluate the levels of primary and secondary macronutrients in soil cultivated with chrysanthemum under different types of fertilization management: organic, organomineral, and mineral, with and without liming. The experiment was conducted in a greenhouse for 185 days, using a randomized blocks design in a 5 × 2 factorial scheme: five fertilization types (incubated and unincubated wood ash, organomineral fertilizer, mineral fertilizer, and control) and two levels of liming (without liming and 70% base saturation) with five replicates. The soil used was Oxisol. The phosphorus, potassium, calcium, magnesium, and sulfur contents in the soil after cultivation were analyzed. There was a 77% increase in potassium in treatments with ash compared to treatments without ash. The corrected soil presented 173.2 mg dm⁻³ of potassium, compared to 153.6 mg dm⁻³ in the uncorrected soil, an increase of 11.6%. The calcium levels increased by 60% with the application of ash (incubated or not) and organomineral fertilizer, compared to soils without ash. Liming increased calcium by 1.12 cmol_c dm⁻³. Fertilizers with ash associated with liming resulted in higher magnesium levels. The sulfur content varied according to the fertilizer, with non-incubated ash showing the highest value (69.11 mg dm⁻³) compared to the control (11.08 mg dm⁻³), a difference of 83.96%. Organomineral fertilizer is an alternative for increasing the availability of macronutrients in the soil, allowing a second cropping cycle without the need to manage soil fertility, contributing to sustainable agriculture, encouraging the reuse of waste, and reducing the use of mineral fertilizers.

1. Introduction

The rise of food security when linked to production standards that seek environmental sustainability has been one of the greatest challenges of modern agriculture within the context of the Sustainable Development Goals (SDGs) [1,2].

Inevitably, the increase in agriculture worldwide generates a growing demand for fertilizers and, consequently, the depletion of natural resources. Given this premise, modern agriculture requires alternative options based on economically viable industrial byproducts in agriculture that support a circular economy within the context of sustainable agricultural production [1,2,3].

Biomass ash contains macronutrients such as phosphorus, potassium, calcium, magnesium, and sulfur, and when applied to the soil, it gradually makes these nutrients available, making it a potential alternative to fertilizer in chrysanthemum production [4,5,6].

The use of agro-industrial byproducts such as wood ash has emerged as a strategy to reduce the disposal of waste in the environment; at the same time, it constitutes an alternative fertilizer to make nutrients available to plants, in addition to promoting the neutralization of soil acidity due to the presence of alkaline compounds resulting in an increase in pH and a reduction in exchangeable acidity [5,7,8], and can reduce the costs of synthetic fertilizers. This aspect is covered by the new regulation for the use of organic waste as fertilizer that provides an amount of macronutrients in the soil, leading to a reduction of up to 30% in the use of nonrenewable mineral sources considering a second cropping cycle [9].

In this scenario, the study of the types of organic fertilizers based on wood ash, organominerals (organic + mineral), and minerals associated with liming in Oxisols is essential because Oxisols are originally poor in terms of the macronutrients available to plants [4,5]. Understanding the dynamics of these macronutrients in Oxisols is essential for the study of fertilization based on the precise amounts of nutrients that fertilizers (organic, mineral, or organomineral) can input to soils to be readily assimilated by plants [10,11].

The sustainable use of organic fertilizers, particularly the organomineral combination of wood ash and minerals, is a promising approach. Wood ash not only supplies primary and secondary nutrients but also improves soil conditioning [5,12]. In contrast, it is necessary to evaluate soil combinations with and without liming, especially in Oxisols, which are distributed in approximately 39% of the Brazilian territory and are the most representative soil class in Brazil, in addition to having the characteristics of being weathered and having high acidity [13,14].

The hypothesis was that the organic material (wood ash) and the organic combination (wood ash + mineral) would be able to replace liming with limestone and reduce the use of nonrenewable synthetic fertilizers in Oxisols, resulting in the presence of macronutrients in the soil in sufficient amounts to meet the demands of plants, which would promote sustainability in modern agriculture, food security, and the circular economy, strengthening progress towards the Sustainable Development Goals present in the 2030 agenda.

While numerous studies have investigated the properties and applications of wood ash, there is a notable paucity of research that evaluates its performance in conjunction with organomineral fertilizers within Oxisol under chrysanthemum cultivation. Thus, the objective of this study was to assess the levels of primary and secondary macronutrients in soil cultivated with chrysanthemum under different types of organic fertilization (wood ash, organomineral, and mineral fertilization) practices in the presence and absence of liming.

2. Materials and Methods

2.1. Characterization of the Study Area

The experiment was conducted under controlled conditions in a greenhouse located in the city of Rondonópolis, Mato Grosso, Brazil, at the geographical coordinates 16°27′49″ S, 54°34′46″ W, and an altitude of 290 m. According to the Köppen classification, the region’s climate is Aw.

The soil used in the experiment was collected from a native Cerrado vegetation area in the 0–0.20 m depth layer and classified as Oxisol [14,15], with a clayey texture. After collection, the soil was sieved through a 2 mm mesh for chemical and particle size characterization (

Table 1. Chemical properties of the experimental soil collected in the 0–0.20 m layer in a Cerrado vegetation area in Rondonópolis, Mato Grosso, Brazil.

pH	P	K	S	Ca	Mg	Al	H + Al	CEC	SB	OM
CaCl2	------------mg kg−1------------			--------------------------------cmolc dm−3--------------------------------						g kg−1
4.30	1.5	18.0	2.0	0.5	0.2	0.6	4.8	5.6	0.8	21.3
V	m	B	Cu	Fe	Mn	Zn		Clay	Silt	Sand
------------%------------		------------------------mg kg−1-------------------------						----------------g kg−1----------------
13.5	44.4	0.15	0.2	64.0	21.8	0.7		455	100	445

P: Phosphorus. K: Potassium. S: Sulfur. Ca: Calcium. Mg: Magnesium. Al: Aluminum. H: Hydrogen. CEC: Cation exchange capacity. SB: Sum of bases. OM: Organic matter. V: Base saturation. m: Aluminum saturation. B: Boron. Cu: Copper. Fe: Iron. Mn: Manganese. Zn: Zinc

).

The wood ash used in the experiment came from the region’s food industry. Its source material was Eucalyptus (Eucalyptus). In addition, it was characterized as a fertilizer [16] and a corrective [17] (

Table 2. Chemical characterization of wood ash as fertilizer.

pH	N	P2O5	K2O	Ca	Mg	SO4	B	Cu	Fe	Mn	Zn	CaO	MgO
CaCl2	--------------------------------------------------------------------%-------------------------------------------------------------------
10.97	0.49	0.79	3.25	4.96	4.20	0.60	0.04	0.01	0.72	0.04	0.02	9.10	6.50

N: Total nitrogen. P₂O₅: Phosphorus. K₂O: Potassium. SO₄: Sulfur. Ca: Calcium. Mg: Magnesium. B: Boron. Cu: Copper. Fe: Iron. Mn: Manganese. Zn: Zinc. CaO: Calcium oxide. MgO: Magnesium oxide.

).

2.2. Experimental Design and Treatments

The experiment was conducted in a randomized block design, in a 5 × 2 factorial scheme. The first factor included five types of fertilizers, while the second factor consisted of two liming levels. The fertilization treatments were as follows: incubated wood ash (IWA) mixed with the soil and incubated for 30 days; non-incubated wood ash (UNWA) applied directly to the soil at sowing; organomineral fertilizer (O) composed of a mixture of wood ash and mineral fertilizer; mineral fertilizer (M) composed of simple superphosphate, potassium chloride, and micronutrients; and control (no fertilizer application). The liming levels used were as follows: no liming (WL) and liming to reach 70% base saturation (L). Each treatment had 5 repetitions, resulting in 50 experimental units (2 dm³ pots). The increase in soil base saturation to 70% was based on the recommendation of Barbosa et al. (2019) [18].

2.3. Experimental Procedures and Management

2.3.1. Soil Preparation, Treatment Application, and Sowing

For treatments involving liming, lime was incorporated into the soil, with moisture adjusted to 60% of the soil’s water-holding capacity, followed by a 30-day incubation period. Wood ash was applied at a rate of 32 g dm⁻³, as recommended by [19]. The same dosage was used for the incubated and non-incubated wood ash treatments. These treatments differed in the application method: in the incubated ash treatment, the ash was mixed with the soil, moisture was adjusted to 60% of the maximum water-holding capacity, and the mixture was incubated for 30 days in plastic bags. In the non-incubated ash treatment, the ash was mixed directly into the soil at the time of sowing.

Mineral fertilizer was applied at the following rates: 360 mg dm⁻³ of P₂O₅, 240 mg dm⁻³ of K₂O, and 50 mg dm⁻³ of micronutrients [20]. The fertilizers used were single superphosphate, potassium chloride, and FTE BR12 (Fried Trace Elements—1.8% boron, 0.8% copper, 3.0% iron, 2% manganese, 0.1% molybdenum, and 9.0% zinc). The organomineral fertilizer treatment consisted of a mixture of wood ash and mineral fertilizer applied to the soil during sowing.

Nitrogen fertilization (120 mg dm⁻³ of N, using urea) [21] was split into two applications (30 and 45 days after sowing), except for the control treatment.

The cultivar used was the white-flowered Singelo chrysanthemum. Sowing was carried out in June 2021, with 10 seeds per pot. After emergence and plant growth to approximately 10 cm in height, thinning was performed, leaving only one plant per pot.

2.3.2. Irrigation Management

A subsurface self-irrigation system was used, maintaining a controlled soil water tension of 3 kPa [22] to ensure uniform soil moisture.

2.4. Analyzed Variables

The variables analyzed were phosphorus, potassium, calcium, magnesium, and sulfur in the soil. Samples were collected after the cultivation of chrysanthemum and sent to a specialized laboratory for macronutrient analysis. Phosphorus and potassium were extracted using the Mehlich⁻¹ extractant solution (0.05 N HCl and 0.025 N H₂SO₄), while calcium and magnesium were extracted with 1 N potassium chloride [23]. Calcium phosphate was used for sulfate extraction [24].

2.5. Statistical Analysis

The data were subjected to normality tests (Kolmogorov–Smirnov and Shapiro–Wilk) and homoscedasticity tests (Levene and Bartlett). Statistical analyses were performed using SISVAR version 5.8 software [25], applying the F-test for analysis of variance and, when significant, Tukey’s test at a 5% significance level. The results of the statistical tests are presented in Supplementary Table S1. In addition, Pearson’s Correlation was determined between the soil properties evaluated, as well as Principal Component Analysis (PCA) using R version 4.1.2 [26].

3. Results

The characterization and chemical classification of the Oxisol cultivated with chrysanthemum under organic and mineral fertilization with and without liming are shown in

Table 3. Macronutrient characterization of the dystrophic Oxisol as a function of the type of fertilization and liming level after chrysanthemum cultivation.

Treatments	P *	P #	K *	K #	S *	S #	Ca *	Ca ##	Mg *	Mg ##
	--------------------------------mg dm−3---------------------------------						----------------cmolc dm−3------------------
IWA (L)	63.5	Very high	255.0	Very high	38.8	High	3.6	High	1.34	High
IWA (WL)	57.3	High	235.6	Very high	47.0	High	3.0	High	1.13	High
UNWA (L)	63.0	Very high	258.0	Very high	61.7	High	3.7	High	1.35	High
UNWA (WL)	53.0	High	243.6	Very high	76.2	High	2.8	High	1.08	High
O (L)	51.2	High	211.3	High	28.2	High	3.4	High	1.26	High
O (WL)	36.9	High	183.8	High	40.7	High	2.2	Medium	0.90	Medium
M (L)	32.1	High	64.9	Medium	35.3	High	2.8	High	1.08	High
M (WL)	22.4	Medium	48.7	Low	42.5	High	1.1	Low	0.47	Medium
C (L)	5.0	Very low	76.8	Medium	8.9	Medium	2.5	High	0.98	High
C (WL)	2.5	Very low	56.3	Low	13.2	High	1.1	Low	0.48	Medium
Average pH (CaCl2) (30 DAS)				Soil acidity #		Average pH (CaCl2) (185 DAS)			Soil acidity #
6.89				Very low		5.44			Mean

*: Observed concentration. ^#: van Raij et al. (1997) [27] ^##: Ribeiro et al. (1999) [20]. IWA: incubated wood ash; UNWA: unincubated wood ash; O: organomineral; M: mineral; C: control; L: liming; WL: no liming.

. Of the ten treatments tested, the combinations of incubated ash with liming [IWA (L)]; unincubated ash without liming [IWA (WL)]; unincubated wood ash with liming [UNWA (L)]; unincubated ash without liming [UNWA (WL)]; organomineral fertilizer with liming [O (L)]; organomineral fertilizer without liming [M (WL)]; control with liming [C (L)]; and control without liming [C (WL)] showed significant variation in the attributes of phosphorus, potassium, calcium, magnesium, and soil sulfur after chrysanthemum cultivation (Table 3).

The P, K, Ca, Mg, and S compositions of the wood ash treatments were classified as very high or high, regardless of whether the soil was corrected with limestone (Table 3); this effect is possibly because wood ash is considered a soil conditioner rich in magnesium oxide and calcium oxide (Table 2).

It should also be noted that even though the soil pH decreased over the days after the application of the treatments (Table 3), the amounts of phosphorus, potassium, calcium, magnesium, and available sulfur are considered satisfactory for meeting the demands of another cropping cycle; i.e., with the management used, it is possible to produce another crop afterwards, contributing to the economy of the producer with fertilizers.

There was a significant difference according to Tukey’s test at 5% probability for the macronutrient phosphorus (P) alone for the types of fertilization (Figure 1a) and liming (Figure 1b). Phosphorus had the highest mean values in the incubated ash (IWA) and unincubated ash (UNWA) treatments (60.45 mg dm⁻³ and 58.075 mg dm⁻³, respectively). This differed from the organomineral, mineral, and control treatments (Figure 1a).

When analyzing the effect of liming on phosphorus (mg dm⁻³) in the soil after chrysanthemum cultivation, a significant effect was observed at the 5% level according to the Tukey test, with the corrected soil (L) showing the highest concentration of phosphorus, 43 mg dm⁻³, compared to the soil without correction (WL), 34.47 mg dm⁻³ (Figure 1b). This makes it clear that soil correction to reduce acidity allows for greater availability of phosphorus, which decisively contributes to the formation of plant roots, growth, and flowering.

Statistical analysis revealed that the potassium concentration (mg dm⁻³) in the soil was significantly influenced by the type of fertilizer applied during chrysanthemum cultivation. The fertilizers incubated with wood ash and unincubated wood ash had the highest mean potassium concentrations, corresponding to 245.3 and 250.8 mg dm⁻³, respectively (Figure 2a).

The organomineral, mineral, and control fertilizers differed significantly at the 5% probability level according to Tukey’s test when analyzing the potassium present in the soil after chrysanthemum cultivation (Figure 2a). The mineral fertilizer and the control had the lowest potassium values, 56.8 and 66.5 mg dm⁻³, respectively. The reduction in potassium dynamics was 77% when comparing fertilizers with ash in their constitution to those without, reinforcing the importance of wood ash as a conditioner and fertilizer for the soil.

Liming significantly influenced the soil potassium content after chrysanthemum cultivation, and the highest potassium values were obtained in the corrected soil (173.2 mg dm⁻³) versus the uncorrected soil (153.6 mg dm⁻³), representing a decrease of 11.6% (Figure 2b). It is also possible to observe that the wood ash fertilizers obtained individual values higher than those of the treatment with correction using limestone, which shows the better structure and composition of wood ash as a conditioner and alternative fertilizer to commercial products.

A significant effect was observed at the 5% level by Tukey’s test for the fertilization and liming factors alone (Figure 3). For the soil calcium content after chrysanthemum cultivation, the treatments with wood ash had the highest absolute values, which significantly differed from those of the treatments with mineral-only fertilizers and the control (Figure 3a).

Compared with those in soils without ash, the amounts of calcium (cmol_c dm⁻³) in soils incubated with wood ash, unincubated wood ash, and organomineral fertilizers increased by 60% after chrysanthemum cultivation (Figure 3a). High amounts of calcium in the soil contribute to greater pH stability, providing greater availability of other essential nutrients for plants.

Statistically, the amount of calcium (cmol_c dm⁻³) in the soil subjected to liming with lime was significantly different from that in the soil without lime (Figure 3b). There was an increase of 1.12 cmol_c dm⁻³ in calcium in the soil when liming was performed, which highlights the need for soil correction for greater availability of the nutrient to the soil so that it is readily assimilated by plants.

There was an interaction effect between fertilizer type and liming on magnesium in the Oxisol after chrysanthemum cultivation (Figure 4). The treatments with vegetal ash in their composition when associated with liming had greater amounts of magnesium in the soil. However, it should be noted that there was no difference between the Oxisol fertilized with ash combined with liming and the Oxisol fertilized with combined ash without liming (Figure 4). Hydroxides, carbonates, and other minerals confer a characteristic similar to the limestone used in liming, which provides soil conditioning and, consequently, its correction.

According to the Tukey test for magnesium in the Oxisol after chrysanthemum cultivation, the levels of the organomineral and mineral fertilizers and the control did not differ significantly at the 5% level after correction with limestone; however, their values were classified as average. Although there was no statistically significant difference between treatments, there was a reduction of 56% and 50% when comparing the mineral fertilizer treatment and the control with liming and without liming, respectively (Figure 4).

The macronutrient sulfur was significantly influenced by the fertilizer type (Figure 5). Sulfur varies considerably depending on the type of fertilizer applied to the soil, and unincubated wood ash was the fertilizer that provided the highest value (69.11 mg dm⁻³) compared to the control treatment. At 11.08 mg dm⁻³, there was a relative decrease of 83.96%, indicating that wood ash supplied a nutrient source to the soils even after the chrysanthemum crop cycle had been completed. It is a viable option for correction and fertilization to adequately meet the nutritional needs of the plant, and sufficient nutrients remain for a later cycle.

All fertilization treatments, with the exception of the control with liming treatment, corroborated the high sulfur content in the soil. Based on the data, fertilizers with wood ash did not require the application of limestone to increase the availability of sulfur in the soil. The organomineral without liming is an alternative fertilizer because, in addition to having a high sulfur content in the soil, it decreases the volume of wood ash and mineral fertilizer used in soils that require liming and fertilization, in addition to not being necessary for the application of liming. The ash constituents of the organomineral fertilizer corrected the soil acidity.

The Ca/Mg ratio was significantly different between the fertilization and liming treatments alone at the 5% level according to Tukey’s test (Figure 6). In terms of the relationship as a function of fertilization, a greater value was observed in the treatments with incubated wood ash (2.68), unincubated wood ash (2.71), and organomineral (2.61) (Figure 6a), and fertilizers containing ash increased soil Ca and Mg.

The decrease in the Ca/Mg ratio as a function of the fertilization type in the treatments with wood ash was in the order of 9.22% compared with that in the treatments without ash (Figure 6a). This emphasizes wood ash as a constituent of fertilizers that favor the increase of nutrients such as calcium and magnesium in the soil, decisively reflecting the reduction of costs with soil conditioners and synthetic fertilizers contributing to an improvement in the circular economy as well as for agricultural production that is sustainable and economically viable.

When observing the Ca/Mg ratio as a function of liming (Figure 6b) in a dystrophic Oxisol after chrysanthemum cultivation, it was observed that the liming of the soil with limestone differed significantly at the 5% level according to the Tukey test of the soil without liming. The observed decrease in the Ca/Mg ratio in the corrected soil compared to that in the uncorrected soil was in the order of 6%.

Pearson’s analysis indicated significant correlations between phosphorus (P) and potassium (K), as well as correlations with calcium (Ca), magnesium (Mg), and the Ca/Mg ratio (Figure 7a). Potassium significantly correlated with Ca, Mg, and the Ca/Mg ratio. There was also a significant correlation between Ca and Mg. Sulfur (S) was significantly correlated with P and K, but with less association (Figure 7a).

Regarding principal component analysis (PCA), the first two components together explained 94.99% of the total variance in the data, with 78.4% attributed to the first component (PC1) and 16.6% to the second (PC2) (Figure 7b).

PC1 showed the strongest associations with the variables P, K, Ca, and Mg. The distribution of treatments in the biplot revealed that UNWA-L, UNWA-WL, IWA-L, and IWA-WL showed the highest values along CP1, indicating greater accumulation of nutrients in the soil under these conditions. These treatments are possibly correlated with the presence of phosphorus, potassium, calcium, and magnesium. In addition, the UNWA-WL treatment also showed a higher value in CP2, suggesting a greater contribution from sulfur.

In contrast, the M-L and O-WL treatments had the lowest values along CP1, indicating a low contribution to the chemical elements evaluated. These treatments may be associated with the lower chemical composition of the soil, as evidenced by their distribution in relation to the arrows representing the variables.

4. Discussion

Fertilization with wood ash has a long neutralizing effect on soil pH when analyzed in the organic layer [10,28]. In this sense, ash is considered an alternative source of macronutrients, as well as a liming material, whose main constituents are metal oxides, hydroxides, carbonates, salts, and soil minerals [29]. This fact justifies the stabilization of pH, enriching the soil with phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S) after cultivation with chrysanthemum.

In view of this result, it can be emphasized that the recycling of wood ash can replace the use of liming with limestone and reduce the use of nonrenewable synthetic fertilizers in soils, demonstrating the presence of sufficient quantities of macronutrients in the soil to meet the demands of plants in more cycles, which provides an environmentally acceptable solution to residue problems.

The application of wood ash promotes the neutralization of soil acidity due to the presence of alkaline compounds such as Ca and Mg oxides, hydroxides, and carbonates [7,30]. These components react with hydrogen (H⁺) and aluminum (Al³⁺) ions in the soil solution, resulting in an increase in pH and a reduction in exchangeable acidity [8,31]. The precipitation of Al³⁺ as insoluble hydroxides also reduces plant toxicity. In addition, carbonates and hydroxides act as buffering agents, reacting with the H⁺ released by biogeochemical processes and stabilizing the soil pH [6,32].

The increase in soil pH intensifies the dissociation of acid functional groups in the mineral fraction and organic matter colloids, releasing negative charges that increase the CEC [30]. This increase in CEC favors the retention of cations such as K⁺, Ca²⁺, and Mg²⁺, reducing leaching losses and improving the availability of these nutrients for plants. In this way, wood ash acts as an acidity corrector and source of macronutrients, representing an alternative to commercial agricultural lime [33].

The phosphorus content (mg dm⁻³) in the soil after chrysanthemum cultivation was classified as very high or high in treatments containing wood ash, showing that in addition to its neutralizing effect on soil acidity, the use of wood ash as fertilizer is essentially a direct source of phosphorus to the soil, which contributes to the establishment of crops. The treatments with incubated wood ash, unincubated wood ash, and organomineral fertilizer alone resulted in a high phosphorus content in the soil; thus, there was no need for liming when using these types of fertilization.

Phosphorus is the macronutrient responsible for rooting and flowering, in addition to being important in the vegetative development of chrysanthemum [34]. Thus, the supply of wood ash significantly contributes to increasing soil phosphorus levels [35,36], which explains the higher concentrations found in treatments with ash in the soil.

P fixation is a limitation in highly weathered Oxisols due to the high concentration of Fe and Al oxides with a high adsorption capacity. In acidic conditions, soluble P reacts with A^l3+ and Fe³⁺ ions to form insoluble phosphates [37]. In these soils, P is mainly adsorbed or precipitated. P can be adsorbed onto inorganic colloids (silicate clays). Wood ash’s application raises the soil’s pH, promoting the precipitation of Al³⁺ and the partial neutralization of reactive Fe, which reduces the number of active sites for P sorption.

Phosphorus (P) is one of the nutrients affected by several soil attributes, especially pH, which influences the adsorption dynamics of this macronutrient.

Fertilizers containing wood ash directly influence soil chemistry and biology in intricate ways, primarily through effects like elevated pH and nutrient enrichment, as well as secondary effects involving nutrient availability dynamics and interactions with biological processes. These factors justify the use of wood ash as a fertilizer under economically viable conditions for sustainable agricultural practices [38].

It should be noted that the replacement of limestone as a soil improver is due, in particular, to the fact that this correction is not always an ideal choice since it requires mining, a factor that has contributed to unsustainable agricultural production over the years [39].

Soils fertilized with wood ash after one year of cultivation with pine increased the amount of K in the soil by two to six times compared to that in the control plots, depending on the dose of wood ash used [28]. These results are consistent with those obtained in the present study, as the ash compound fertilizers resulted in the highest potassium levels after chrysanthemum cultivation.

Because wood ash has the smallest particle characteristics, it contributes to a rapid pH change compared to that of the commercial limestone used for soil correction, and it can also provide substantial amounts of macronutrients to soils [8].

The amount and availability of Mg in soils are influenced by several factors, including soil texture, organic matter (OM), and cation exchange capacity (CEC) [10]. In this context, the hydrogenic potential of the soil (pH) is considered one of the main factors influencing the availability of Mg, so a reduction in soil pH is closely linked to symptoms of a deficiency in exchangeable Mg in the soil [40]. There have been reports that a soil pH below 4–4.5 hinders the growth of the root system of several plants due to H+ toxicity, leading to drastic reductions in agricultural production [41]. Given this context, soil management practices such as liming using limestone have been adopted as effective mitigating measures to adjust soil acidity.

When analyzing soil sulfur, it should be noted that it is considered the fourth macronutrient absorbed by plants; in addition, its composition in the soil decisively influences the absorption of other nutrients, such as nitrogen. When absorbed by plants, it constitutes a basic component of amino acids that serve as the basis for constructing proteins, affecting the metabolism and activity of Rubisco, the key catalytic enzyme for producing carbohydrates in plants [34]. It should also be noted that the effect of fertilization on the calcium and magnesium contents of the soil is more robust than the effect of liming, which is consistent with the finding that the use of wood ash as a component of fertilizers is more economically viable and more effective at remediating soil and providing nutrients to plants.

Fertilizers containing wood ash used as fertilizer and soil conditioners resulted in significant changes in the soil chemical properties in all the treatments, and the magnitude of the response to the treatments differed among the suggested fertilizer types. It is important to conduct a chemical analysis of the ash before using it to assess the quality of this waste, including the concentrations of heavy metals and salts, which may be part of the composition of the ash depending on how it was burned.

The correlations observed indicate an interdependence between the macronutrients calcium, magnesium, and potassium, suggesting that the management practices adopted in this study may have influenced the joint supply of these elements. Phosphorus also showed a good association with these variables, although sulfur showed weaker correlations, suggesting that its behavior may be more independent or controlled by other factors.

In general, the results of the PCA indicated that the ash treatments, regardless of whether incubation and liming were carried out, could improve the dynamics of macronutrients in the residual soil, promoting greater nutrient availability. This pattern suggests that management strategies involving wood ash can effectively improve the chemical attributes of the soil in agricultural systems, contributing to sustainability and strengthening the 2030 agenda, as indicated by other research such as that by Johan et al. (2021) [35] and Baloch et al. (2024) [42].

5. Conclusions

• Soil fertilized with fertilizers containing wood ash provided high levels of primary and secondary macronutrients;
• Organomineral fertilizer is an alternative fertilizer for reducing the volume of synthetic fertilizer and wood ash used, in addition to providing high levels of macronutrients in the Oxisol, allowing a second cropping cycle without the need to maintain soil fertility, contributing to sustainable agriculture and the circular economy;
• There is no need for liming when using fertilizers containing wood ash;
• The application form of incorporated wood ash showed better results in relation to the content of primary and secondary macronutrients in Oxisol;
• Future studies are needed to investigate the long-term impacts on crop yields and soil nutrient availability, and field-scale validations are needed to assess the practical applications of these organomineral fertilizers in various agricultural environments.