Preliminary Studies on the Effect of Soil Conditioner (AMP) Application on the Chemical and Microbiological Properties of Soil under Winter Oilseed Rape Cultivation

Abstract

This study analyzed the effect of the application of a soil conditioner under the trade name of the Agro Mineral Product (AMP) in the winter rapeseed cultivation on the bacterial and fungal abundance, ion concentrations, and electrolytic conductivity of the soil solution. It was demonstrated that the AMP influenced changes in the total abundance of the culturable fractions of the soil bacteria and fungi at each of the tested time points. A stimulatory effect of the preparation on the growth of the soil bacteria and an inhibitory effect on the development of the fungi was observed, particularly at doses of 4 and 8 t·ha⁻¹. A dose of 12 t·ha⁻¹ proved to be the least effective in relation to the development of the soil microbiome. Increasing the AMP fertilization dose above 4 t·ha⁻¹ caused changes in the chemistry of the soil solution (pH, EC, HCO₃⁻, K⁺, and PO₄-P). It is worth noting that this primarily resulted in decreases in the amounts of mobile forms of potassium (from 40.4 mg·dm⁻³ in the control to 26.7 mg·dm⁻³ at the 8 t·ha⁻¹ dose) and orthophosphate as phosphorus (from −6.00 mg·dm⁻³ in the control to 3.75 mg·dm⁻³ at the 8 t·ha⁻¹ dose) in the soil solution, which resulted in a reduction in the yield of the winter rapeseed (from 4.76 t·ha⁻¹ in the control to 4.61 t·ha⁻¹ at the 8 t·ha⁻¹ and 4.43 t·ha⁻¹ at the 12 t·ha⁻¹ AMP dose).

1. Introduction

Throughout the growing season, plants are accompanied by a significant number of microorganisms that exhibit a high biodiversity. This diversity leads to the formation of an interaction network between microorganisms and plants, which assumes various direct, indirect, and positive or negative relationships [1]. The rhizosphere is intriguingly complex and dynamic, and understanding its ecology and evolution is key to enhancing plant productivity and ecosystem functioning. Novel insights into key factors and evolutionary processes shaping the rhizosphere microbiome will greatly benefit from integrating reductionist and systems-based approaches in both agricultural and natural ecosystems [1]. The process of germination and root growth is a period of intense production of organic matter in the form of root exudates and dead cells, which promotes the development of microbial communities associated with the root and the zone around it, known as the rhizosphere [2]. The structure of the root system itself (morphology, respiratory activity, root exudates) plays an extremely important role in the processes occurring in the rhizosphere, both from the perspective of microorganisms and plants. These properties can be highly significant in the context of interactions with other soil organisms, including bacteria and fungi [3]. Rhizodeposition can be influenced by the plant species, its age, and the physicochemical properties of the soil. Many of the released organic compounds serve as chemoattractants, drawing specific groups of microorganisms into the direct proximity of the roots [4].

Soil acidity is an important factor influencing plant growth. This process is caused by the release of carbonic acid from the respiratory processes occurring in root cells and microorganisms, the secretion of organic acids, and organic matter decomposition. Acidification can also occur through the disruption of the balance between cations and anions [5]. The accumulation of nutrients and trace elements in the root zone of plants promotes an increase in the number of microorganisms and their activity. However, plants can directly influence the abundance of bacterial and fungal populations by selectively stimulating or inhibiting the growth of specific groups or even species [6]. The soil microbiome can also have a beneficial effect on plant development. A number of microorganisms demonstrate the ability to produce plant hormones, including indole-3-acetic acid (IAA), gibberellins, and cytokinins. Among these microorganisms, two groups can be distinguished: endophytic PGPB (plant growth-promoting bacteria) and rhizospheric PGPR (plant growth-promoting rhizobacteria) [7]. Another mechanism supporting plant growth is the ability of rhizospheric microorganisms to inhibit the growth and development of pathogens [8]. According to many authors, the soil solution is the most dynamic part of the three-phase soil system, it is there that the majority of the chemical reactions take place. It plays a major role in plant nutrition, elemental circulation, and ecosystem contamination. The composition of the soil solution is particularly important in soils that are subject to a strong influence of anthropo-pressure, and are frequently contaminated [9]. Despite many years of research, the relationships between microorganisms, plants, and soil still remain poorly understood. The presence of root secretions, as well as the physical and chemical parameters of the soil, such as reactions, humidity, and the organic matter content, may be factors shaping the rhizosphere microorganism communities [10]. The relationships between these parameters and their impact on the biodiversity of microbial communities require further research, as pointed out by other authors [11]. The research hypothesis was whether the use of the Agro Mineral Product (AMP) could improve the soil properties, microbiological life, and seed yield of the winter rapeseed.

The research objectives have been specified on the basis of the current knowledge regarding the effects of lime fertilizers and soil conditioners on soil microbiology and chemical properties: (i) Can the application of the Agro Mineral Product (AMP) modify the soil microbial life? (ii) Can it (AMP) shape the content of the (non-composition) cations in the soil solution? (iii) Can the application of the (AMP) modify the seed yield?

2. Materials and Methods

2.1. Experimental Field Characteristics

According to the World Reference Base for Soil Resources (WRB) [2022], the analyzed soils were classified as Haplic Luvisol (Anoarenic, Endoloamic, Aric, Cutanic, Ochric). According to the current Polish Soil Classification system [2019], the soils were classified as two-part Luvisol (deeply calcareous). The analyzed soils belonged to quality class IVa, i.e., a very good rye complex. In terms of the soil texture, the surface layers of the soils under study were classified as loamy sands, with a clay fraction content of 4%, a silt content of 14%, and a sand fraction content of 82%. The eluvial horizon contained slightly less clay and silt fractions. The enrichment (B) and bedrock levels were definitely more compact. The bulk density of the analyzed soil samples was 1.48 g·cm⁻³. The pH measured in the water extract was approximately 6.8, while in the KCl solution, it was approximately 6.3, falling within the upper slightly acidic range. The organic carbon content was approximately 1%, which accounted to 1.7% humus. The total nitrogen content was 0.086%, and the C:N ratio was approximately 12:1. The sorption capacity was at a fairly high level, approximately 8 cmol(+)·kg⁻¹, with the sorption complex characterized by a very high saturation with basic cations (almost 90%). Calcium predominated among the cations in the sorption complex, accounting for over 75%, while the other elements were present in significantly smaller quantities: Mg—8.5%, K—2.7%, and Na at approximately 1%. Plant available P and K in the soil were analyzed using the method of Egner–Riehm (DL) and CAL. In the first case, the bioavailable K and P were extracted with Ca lactate at a pH of 3.6 with a soil-to-extracting ratio of 1:50. The mean content of the available potassium was 120.1 mg K·kg⁻¹ and the mean content of the available phosphorus was 75.1 mg P·kg⁻¹ in the analyzed soil samples. The content of available magnesium was tested using the Schachtschabel method (0.0125 M CaCl₂) and the mean content of the available forms of magnesium was 25.0 mg Mg·kg⁻¹ in the analyzed soil samples. The experiment involved sowing the winter oilseed rape cultivar Harry (Brassica napus), and spring wheat (Triticum aestivum L.) as a preceding crop. The winter oilseed rape was sown on 24 August 2023, at 3 kg·ha⁻¹, with the emergence recorded on 1 September 2023. The sowing depth was 1 cm, with a row spacing of 24 cm. After the spring wheat harvesting, the crop residues were shredded and plowed in shallowly. Then the seed plowing was carried out. Then, the AMP was applied on the surface according to the experimental scheme (0, 4, 8, 12 t·ha⁻¹). Before sowing the winter rapeseed, the experimental field was prepared and seasoned for sowing. The cultivation of the experimental field was the same throughout the entire area, only the AMP dose was varied. The NPK mineral fertilization of the winter rapeseed in autumn (before sowing) was at the following level: 15 kg N·ha⁻¹, 50 kg P₂O₅·ha⁻¹, 75 kg K₂O·ha⁻¹(Polifoska 6). In spring, a total of 140 kg N·ha⁻¹(ammonium nitrate) was applied in two periods of 70 kg N·ha⁻¹ (29 February 2024, and 22 March 2024). The winter rapeseed was harvested with a plot combine harvester on 3 July 2024.

2.2. Microbiological Analysis

The soil samples for the microbiological analysis were collected using a Pürckhauer auger from 15 points in each experimental plot (Złotniki village, 52°28′59.006″ N 16°49′55.027″ E), from which a pooled sample was created. The counts of the microorganism were determined using solid media. Ten grams of soil were suspended in 90 mL of sterile saline solution (0.85% NaCl) and shaken for 40 min at 130 rpm. The samples were immediately stored in refrigerators. Subsequently, a series of dilutions was made from the soil suspension, and 0.1 mL was plated using the pour plate method onto the appropriate media. The plates were incubated for 5–7 days at 28 °C, after which the grown colonies were counted. The plating was performed in five replicates for each soil sample. The results are presented as lg CFU per 1 g d.m. soil. The total count of the culturable bacterial fraction was determined on 10% tryptone soy broth agar (TSBA, Merck, Rahway, NJ, USA) with nystatin. The total count of the culturable fungal fraction was determined on potato dextrose agar (PDA, Merck, Rahway, NJ, USA) with the addition of streptomycin and rose Bengal. The medium was sterilized at 121 °C for 20 min. Microbiological samples from the experimental plot were collected at 2, 4, 8, and 12 weeks after sowing the winter oilseed rape (August to November). The sampling frequency (such an interval) was conditioned by the fact that the last sampling date was still in autumn. At the beginning, the interval was shorter, due to the evaluation of the AMP in terms of the speed of action, while the last one was within three months of the application of the preparation in the soil. The four soil sampling intervals and the control facility provided an improved picture of the soil changes. Additionally soil microbiological analysis was performed before sowing the winter oilseed rape. In the soil samples, the total bacterial count was determined to be lg 3.7 CFU g⁻¹ dry soil, while the fungal count was lg 2.75 CFU g⁻¹ dry soil.

2.3. Soil Analyses

The surface soil samples were collected from a depth of 0–20 cm and dried in the laboratory at 50 °C. Subsequently, they were pulverized in a porcelain mortar and sieved through a 2 mm mesh sieve. The soil pH of the air-dried samples was determined in water and KCl extract at a ratio of 1:2.5. The soil solution was obtained by mixing the soil with deionized water at a ratio of 1:1. After mixing, the solution was centrifuged, and then filtered into falcon tubes.

The obtained soil extracts were analyzed using the methods described by Spychalski et al. [12] to determine the following:

• Concentrations of nitrate nitrogen (NO₃-N), orthophosphate as phosphorus (PO₄-P), and ammonium nitrogen (NH₄-N) were determined colorimetrically;
• Concentrations of calcium ions (Ca²⁺), sodium ions (Na⁺), potassium ions (K⁺), and magnesium ions (Mg²⁺) were determined using atomic absorption spectrometry (AAS) using a Varian SpectrAA 220 FS instrument;
• Electrolytic conductivity (EC) was measured using an Orion conductivity meter;
• Concentration of chloride ions (Cl⁻) was determined using titration with AgNO₃ using potassium chromate as an indicator;
• Concentration of bicarbonate ions (HCO₃⁻) was determined using HCl titration.

The soil samples for chemical analyses were collected 6 months after the date of the winter oilseed rape sowing.

2.4. Thermal and Moisture Conditions during the Field Trial Were as Follows

The thermal and moisture conditions during the period of the field trials are included in

Table 1. Average daily air temperature and total precipitation (location—Złotniki, Poland).

Month	Average Daily Air Temperature [°C]	Total Precipitation [mm]
August (2023)	19.3	128.0
September (2023)	18.1	3.0
October (2023)	10.4	67.2
November (2023)	4.0	74.2
December (2023)	2.2	57.4
January (2024)	0.4	49.8
February (2024)	6.8	71.7
March (2024)	8.2	34.1
April (2024)	11.1	37.8
May (2024)	17.2	66.5
June (2024)	17.9	68.9

. In general, it should be stated that the air temperature as well as the amount of precipitation were favorable for the growth and development of the winter oilseed rape.

2.5. Characteristics of the Agro Mineral Product (AMP)

The Agro Mineral Product (AMP) was manufactured at the sewage treatment plant of the Municipal and Housing Management Company in Krotoszyn (

Table 2. Chemical composition of the Agro Mineral Product (AMP).

Chemical Elements	Moist Matter (g·kg−1)	Dry Matter (g·kg−1)
K	0.55 ± 0.01	0.72 ± 0.02
Na	0.32 ± 0.05	0.42 ± 0.06
Mg	2.10 ± 0.39	2.76 ± 0.52
Ca	164.7 ± 25.7	216.2 ± 33.7
P	2.28 ± 0.06	2.99 ± 0.08
Zn	0.10 ± 0.002	0.13 ± 0.002
Mn	0.14 ± 0.004	0.19 ± 0.005
Fe	5.59 ± 0.67	7.34 ± 0.88
Chemical Elements	Moist Matter (mg·kg−1)	Dry Matter (mg·kg−1)
Cu	16.4 ± 2.69	21.5 ± 3.54
Ni	7.56 ± 0.81	9.90 ± 1.07
Cd	0.27 ± 0.04	0.30 ± 0.04
Cr	10.0 ± 2.04	13.2 ± 2.69
Pb	1.10 ± 0.19	1.40 ± 0.25

Values in columns are mean ± standard deviation (n = 2).

). The treatment plant is located in the western part of Krotoszyn, approximately 2 km from the city center. It has a nominal capacity of 8000 m³ per day. It employs a mechanical–biological sewage treatment technology with chemical phosphorus removal support using the PIX coagulant. The product is made using the granulation process of sewage sludge with slaked lime. The process involves mixing the chemical reagent—lime—with the sewage sludge produced at the treatment plant. The thermal process of the physical and chemical transformation of sewage sludge results in a hydrophobic product with a granular composition. The product significantly reduces the organic matter, provides complete sanitation, and eliminates the pathogenic bacteria of the genus Salmonella, as well as the viable eggs of intestinal parasites. After the hygienization and granulation process, the product undergoes a resting period to lower the temperature to an ambient level before being dispatched by road transport. Consequently, a sterilized granulate suitable for soil fertilization is obtained in accordance with the current regulations. The chemical composition of the AMP fertilizer is included in Table 2 and

Table 3. Chemical composition of the Agro Mineral Product (AMP) cont.

Content (% Dry Matter)				−		%	−
N	TC	TOC	S	C:N	N:S	CaCO3	pH KCl
1.077	14.35	9.25	0.061	8.60	17.7	42.89	12.52

. The ions’ contents in the AMP were determined according to the ISO (11466) procedure at the Department of Soil Science and Microbiology, University of Life Sciences in Poznan (Poland). The material for analysis was prepared in Aqua Regia and the ions were determined using atomic absorption spectrometry (AAS) using a Varian SpectrAA 220 FS.

2.6. Statistical Analysis

A one-way analysis of variance (ANOVA) was used to determine the presence of statistically significant differences between the means of the traits under study. If a significant effect of fertilization on these traits was observed, the Tukey HSD procedure was applied. In addition, correlation coefficients were used to measure the strength of the statistical relationships between the tested characteristics [13].

All the calculations were carried out using the STATISTICA 13.3 software package (2017). The statistical significance was taken as a p-value < 0.05.

3. Results

Time point I (2 weeks from the sowing date) (Figure 1 and Figure 2). In the control combination, the total population counts of the bacteria and fungi were at levels of 3.14 and 2.89, respectively. The applied doses of the Agro Mineral Product (AMP) (4, 8, 12 t·ha⁻¹) increased the total abundance of bacteria and decreased the abundance of fungi compared with the control. Doses of 4, 8, and 12 t·ha⁻¹ resulted in a relative increase in the bacterial abundance of approximately 44.0%, 39.5%, and 15.0%, respectively, and a decrease in the fungal count of 18.0%, 37.4%, and 51.2%, respectively.

Time point II (4 weeks from the sowing date) (Figure 1 and Figure 2). In the control combination, the counts of the bacteria and fungi were at levels of 2.80 and 2.35, respectively. The applied Agro Mineral Product (AMP) at doses of 4 and 8 t·ha⁻¹ increased the bacterial counts by 56.4% and 41.4%, respectively, and decreased the fungal abundance by 10.5% and 21.9%, respectively, compared with the control. The Agro Mineral Product (AMP) applied at a dose of 12 t·ha⁻¹ exerted inhibitory effects on both the bacteria and fungi, with their abundance decreasing relative to the control by 61.1% and 82.8%, respectively.

Time point III (8 weeks from the sowing date) (Figure 1 and Figure 2). In the control combination, the bacterial and fungal counts were determined at 1.90 and 1.93, respectively. Doses of 4 and 8 t·ha⁻¹ resulted in a relative increase in the bacterial abundance of approximately 52.6% and 37.4%, respectively, and a decrease in the fungal counts of 17.1%, 37.4%, and 28.5%, respectively. After applying a dose of 12 t·ha⁻¹, the numbers of bacteria and fungi were reduced by relatively 84.2% and 94.8% compared with the control.

Time point IV (12 weeks from the sowing date) (Figure 1 and Figure 2). In the control combination, the total counts of the bacteria and fungi were determined at levels of 1.66 and 1.42, respectively. Doses of 4 and 8 t·ha⁻¹ resulted in an increase in the bacterial abundance by approximately 45.2% and 50.0%, respectively, and a decrease in fungal count by 70.0% and 11.3%, respectively, compared with the control. After applying a dose of 12 t·ha⁻¹, the numbers of bacteria and fungi were reduced by relatively 88.0% and 93.0% compared with the control.

It should be noted that the total counts of the bacteria and fungi decreased with each successive sampling time point (duration of the experiment) compared with time point I. The highest abundance of bacteria and fungi was observed in the samples treated with the AMP at doses of 4 and 8 t·ha⁻¹ on each of the test dates. Analyzing time point I as the period with the highest abundance of bacteria and fungi, it should be noted that in time point IV, these counts were at the lowest level. The bacterial and fungal abundance in the control sample (0 t·ha⁻¹) decreased by 47.1% and 50.9%, respectively; in the 4 t·ha⁻¹ sample, by 46.7% and 44.3%, respectively; in the 8 t·ha⁻¹ sample, by 43.2% and 30.4%, respectively; and in the 12 t·ha⁻¹ sample, a decrease of 94.5% and 92.9%, respectively, was recorded.

Table 4. Concentrations of cations in the soil solution (mg·dm⁻³).

Factor	The Levels of Factor	K+	Na+	Mg2+	Ca2+
		mg·dm−3
Fertilization	Control	40.4 ± 1.70 a	1.50 ± 0.13 a	1.00 ± 0.07 a	13.8 ± 0.20 a
	4 t	36.4 ± 1.30 a	1.37 ± 0.05 a	0.96 ± 0.01 a	13.4 ± 0.10 a
	8 t	26.7 ± 0.10 b	1.02 ± 0.01 a	1.30 ± 0.18 a	14.6 ± 1.10 a
	12 t	23.3 ± 0.20 b	1.86 ± 0.56 a	1.22 ± 0.37 a	21.3 ± 1.70 a

Values in columns are mean ± standard deviation. Means in columns marked with at least the same letter do not differ significantly.

and

Table 5. pH values, electrical conductivity (EC), and concentrations of anions in the soil solution (mg·dm⁻³).

Factor	The Levels of Factor	pH		(EC)	PO4-P	NH4-N	NO3-N	Cl−	HCO3−
		H2O	KCl	μS·cm−1	mg·dm−3
Fertilization	Control	6.71 ± 0.28 b	6.09 ± 0.18 b	141.8 ± 8.60 ab	6.00 ± 0.13 a	2.86 ± 0.10 ab	12.7 ± 2.07 a	4.59 ± 0.05 a	5.00 ± 0.17 c
	4 t	7.21 ± 0.23 ab	6.46 ± 0.12 ab	122.1 ± 0.80 b	5.64 ± 1.01 a	2.64 ± 0.02 b	11.7 ± 1.33 a	5.76 ± 0.64 a	7.02 ± 1.22 bc
	8 t	7.30 ± 0.17 ab	6.68 ± 0.01 a	167.7 ± 12.2 a	3.75 ± 1.00 b	2.48 ± 0.20 b	9.83 ± 0.87 a	5.67 ± 0.63 a	10.58 ± 1.8 ab
	12 t	7.66 ± 0.15 a	6.88 ± 0.05 a	145.8 ± 7.90 ab	3.10 ± 0.27 b	3.37 ± 0.17 a	9.06 ± 1.62 a	4.78 ± 0.76 a	15.73 ± 1.53 a

Values in columns are mean ± standard deviation. Means in columns marked with at least the same letter do not differ significantly.

summarize the chemical composition analyses of the aqueous solutions obtained from the soil samples collected from the experiment involving the winter oilseed rape cultivation and the AMP application, and the control. The Agro Mineral Product applied in the experiment had a statistically significant effect on parameters such as the soil pH and electrolytic conductivity, as well as potassium, orthophosphate as phosphorus (PO₄-P), ammonium nitrogen (NH₄-N), and the bicarbonate ion content.

The pH values of the analyzed soils determined in the water extract ranged from 6.71 to 7.66, while those determined in the KCl extract ranged from 6.09 to 6.88 (Table 5). The pH values in the control plots and those fertilized with doses of 4 and 8 t·ha⁻¹ did not differ significantly, and similar statistical values were obtained. The application of the 12 t·ha⁻¹ dose was the only treatment that resulted in a statistically significant increase in the pH values. With respect to the pH value determined in the potassium chloride extract, the application of the 4 t·ha⁻¹ dose did not statistically significantly contribute to an increase in this parameter compared with the control, while increasing the dose to 8 t·ha⁻¹ resulted in a significant increase in the pH value. Further increases in the dose of the AMP did not cause a statistically significant increase in the value of this parameter. Electrical conductivity (EC) is dependent on the concentrations of ions in the water extract. In the present experiment, the lowest electrical conductivity of 122.1 μS·cm⁻¹ was observed in the plots where the AMP with a dose of 4 t·ha⁻¹ was applied (Table 5). This value differed significantly from those obtained for the soil samples collected from the plots where the AMP was applied at a rate of 8 t·ha⁻¹.

The application of the AMP at a dose of 4 t·ha⁻¹ did not result in statistically significant changes in the concentrations of potassium and orthophosphate as phosphorus (PO₄-P) compared with the control. The samples collected from the control plots and those fertilized with 4 t·ha⁻¹ of the AMP contained similar concentrations of potassium ions (Table 4 and Table 5). Increasing the dose to 8 t·ha⁻¹ resulted in a statistically significant decrease in the concentration of this component in the soil solution. A further increase in the rate of AMP to 12 t·ha⁻¹ resulted in a decrease in water-soluble potassium, but this change was not statistically confirmed.

The application of the AMP also significantly increased the concentration of bicarbonate ions. The application of the 8 t·ha⁻¹ dose led to a statistically significant increase in the concentration of bicarbonate ions compared with the control plots. A further increase in the AMP dose did not result in statistically significant changes in the concentration of this component in the soil. The level of ammonium nitrogen (NH₄-N) was highest (3.37 mg NH₄-N·dm⁻³) in the plots where liming was applied at a dose of 12 t·ha⁻¹. This content was significantly higher compared with the plots where the AMP was applied at doses of 4 and 8 t·ha⁻¹, but the concentration did not differ significantly from that observed in the control plot (Table 5). The individual fertilization combinations applied did not result in statistically significant differences in the content of sodium, magnesium, calcium, nitrate nitrogen, and chloride ions (Table 4 and Table 5).

Our own research showed no significant effect of the AMP dose on the moisture content of the winter rapeseed seeds during harvest (

Table 6. Average values of the grain moisture and its yield for fertilization.

Factor	The Levels of Factor	Seeds Moisture [%]	Seeds Yield [t⋅ha−1]
Fertilization	Control	8.50 ± 0.23 a	4.76 ± 0.51 ab
	4 t	8.75 ± 0.41 a	5.29 ± 0.53 a
	8 t	8.48 ± 0.15 a	4.61 ± 0.52 ab
	12 t	9.05 ± 0.06 a	4.43 ± 0.54 b

Values in columns are mean ± standard deviation. Means in columns marked with at least the same letter do not differ significantly.

). In the case of seed yield, the AMP dose significantly modified the value of this feature. Significantly, the highest yield of the winter rapeseed seeds was obtained at a dose of 4 t·ha⁻¹, while the lowest was obtained at a dose of 12 t·ha⁻¹ (Table 6).

Moreover, the power of the relationships of the tested characteristics was determined. The results are given in

Table 7. Pearson correlation coefficients for the tested characteristics.

		pH		(EC)	K+	Na+	Mg2+	Ca2+	PO4-P	NH4-N	NO3-N	HCO3−
		H2O	KCl
pH	H2O	1.00	0.95 **	0.18	−0.82 *	0.31	0.46	0.55	−0.81 *	0.34	−0.65	0.85 **
	KCl	0.95 **	1.00	0.34	−0.92 **	0.13	0.48	0.42	−0.91 **	0.29	−0.69	0.90 **
(EC)		0.18	0.34	1.00	−0.51	−0.19	0.78 *	0.26	−0.60	−0.06	−0.42	0.41
K+		−0.82 *	−0.92 **	−0.51	1.00	−0.10	−0.59	−0.49	0.98 **	−0.36	0.85 **	−0.93 **
Na+		0.31	0.13	−0.19	−0.10	1.00	0.26	0.81 *	−0.16	0.85 **	−0.21	0.41
Mg2+		0.46	0.48	0.78 *	−0.59	0.26	1.00	0.74 *	−0.67	0.23	−0.69	0.63
Ca2+		0.55	0.42	0.26	−0.49	0.81 *	0.74 *	1.00	−0.54	0.69	−0.64	0.69
PO4-P		−0.81 *	−0.91 **	−0.60	0.98 **	−0.16	−0.67	−0.54	1.00	−0.41	0.84 **	−0.95 **
NH4-N		0.34	0.29	−0.06	−0.36	0.85 **	0.23	0.69	−0.41	1.00	−0.42	0.62
NO3-N		−0.65	−0.69	−0.42	0.85 **	−0.21	−0.69	−0.64	0.84 **	−0.42	1.00	−0.84 **
HCO3−		0.85 **	0.90 **	0.41	−0.93 **	0.41	0.63	0.69	−0.95 **	0.62	−0.84 **	1.00

**—significant at p-value < 0.01; *—significant at p-value < 0.05.

. Statistically significant positive correlations were observed between, e.g., the pH (in the water extract and KCl) and the concentration of bicarbonate ions; the concentration of potassium ions and the concentrations of orthophosphate as phosphorus (PO₄-P) and nitrate nitrogen (NO₃-N); the concentration of orthophosphate as phosphorus (PO₄-P) and the concentration of nitrate nitrogen (NO₃-N). Furthermore, statistically significant negative correlations were found between, e.g., the pH (in the water extract and KCl) and the concentrations of potassium and phosphate ions; the concentrations of potassium, phosphate, and nitrate ions and the concentration of bicarbonate ions.

No statistically significant linear correlations were observed between the yield and the remaining characteristics, as well as between the concentration of chloride ions and the remaining characteristics. As a result, these two traits were not included in Table 7.

4. Discussion

Gaining a comprehensive understanding of the relationships between the soil microbiome and the biological, physical, and chemical factors requires the application of diverse methods, including those related to the culturable fraction of microorganisms [14]. The soil microbiome shows significant potential to increase its abundance and activity depending on changes in the soil environment, including nutrient availability [15,16]. Liming of the soil can have multifaceted effects on its functioning, e.g., structure, plant nutrition, the microbiome, and consequently, soil-borne diseases [17]. High levels of calcium and neutral pH in soils generally lead to an increase in bacterial populations, as indicated by the present results. Chandrakar et al. [18] reported a 28% increase in the bacterial population (70.62 × 10⁶ CFU) after soil liming under maize cultivation compared with the control samples (55.25 × 10⁶ CFU). The latter authors observed less abundant fungal populations compared with bacterial populations. They were at the level of 40.54 × 10⁴ CFU in the control samples and increased by 61% to 65.45 × 10⁴ CFU after liming. These findings were not confirmed in the current study, as we observed a decrease in the fungal populations as a result of the conditioner application. As reported by Ning et al. [19], fungi can tolerate a wider range of pH values and environmental temperatures compared with bacteria. A high soil acidity inhibits the development of bacteria in favor of more resistant fungi. On the other hand, liming, which raises the soil pH, usually improves the conditions for bacterial growth [20]. It is also important to note that changes in the microbial abundance are not necessarily equivalent to their biomass.

An important aspect of soil liming is the effect of this treatment on the development of both beneficial and pathogenic microbiomes. According to Holland et al. [21], the highest activity of mycorrhizal fungi could be recorded in soils with a pH of 5–6, while this activity begins to decrease with increasing alkalinization. Changes in the soil pH can also affect the activity of nitrogen-fixing bacteria. In highly acidic environments, the process of root colonization by bacteria such as Rhizobium may be reduced [22]. Not all groups of soil microorganisms respond similarly to liming. This treatment primarily increases the number of bacteria that are intolerant to acidic environments and those that thrive in alkaline conditions. Ding et al. [23] found in their study that liming at doses of ≤11.5 t·ha⁻¹ improved the diversity and increased the abundance of the soil bacteria, while doses of >11.5 t·ha⁻¹ inhibited microbial growth and activity, and reduced the biomass and diversity of the soil microorganisms, as well as suppressed interspecific interactions among them. The application of the 12 t·ha⁻¹ dose at time points I-IV resulted in a decrease in the abundance of the studied groups of microorganisms. According to Jadczyszyn and Lipinski [24], a rapid increase in the pH in strongly acidic soils, in each agronomic category, may disrupt the uptake of mineral nutrients by plants and disturb the functioning of the soil microorganisms. Guo et al. [25] applied CaCO₃ at doses of 2.25, 4.5, and 7.7 t·ha⁻¹, and observed the highest diversity of soil bacteria after the minimum and moderate doses. Swędrzyńska et al. [26] used a soil bioconditioner at doses of 0, 300, and 600 kg·ha⁻¹ (containing 32% CaCO₃) and recorded a significant increase in the bacterial abundance and a decrease in the fungal abundance at the 300 kg·ha⁻¹ dose. It should be remembered that during the entire development process, plants are accompanied by a significant number of microorganisms with a high biodiversity. Thanks to this diversity, the network of interactions between microorganisms and plants takes on various forms, including direct, indirect, and positive or negative relationships. During the germination and root growth process, organic matter is already released into the soil in the form of root secretions and dead cells, which promotes the development of microorganism communities associated with the root and the zone around it. In this way, plants create a specific ecological niche, with a greater number and activity of microorganisms than in the extra-root soil. This phenomenon is called the rhizosphere effect. This rhizosphere effect can also be modified by adding an Agro Mineral Product (AMP) to the soil.

The primary purpose of liming is to reduce the soil acidity [27], while the soil pH affects the availability of plant nutrients, thereby indirectly influencing crop growth. In the present work, similarly to the studies of other authors [28,29,30], liming caused an increase in the soil pH values (Table 3). On the other hand, the decrease in the water-soluble potassium content with the increasing fertilization rate can be attributed to the blockage of the sorption complex and the displacement of potassium cations [31] by an excess of calcium cations. Additionally, Adamczyk et al. [32] have reported that potassium ions (K⁺) are quite mobile in the soil and can be easily leached, especially in sandy soils. Łabętowicz et al. [33] and Tkaczyk [34] observed in their studies that the application of lime could significantly reduce the availability of phosphorus in the soil. Additionally, the decrease in the content of labile forms of phosphorus with increasing doses of the AMP can be explained by its increased chemical sorption, which may lead to the binding of phosphates by calcium, resulting in the formation of insoluble compounds of calcium phosphates and apatites [35,36,37]. Additionally, Yang et al. [38] reported that the application of some fertilizers could make plants resistant to wilting under water deficits and possible salinity stress, which could become an important subject of future research on the AMP.

5. Conclusions

Responding to research objectives, the applied soil improver Agro Mineral Product (AMP) affected changes in the total abundance of the culturable fraction of the soil bacteria and fungi at all the experimental time points. The stimulating effect of the formulation on the growth of the soil bacteria and the inhibition of fungal development was recorded, particularly for doses of 4 and 8 t·ha⁻¹. The dose of 12 t·ha⁻¹ was the least effective in relation to the development of the soil microbiome. Each subsequent analysis period was characterized by lower microbial counts. At time points III and IV, after applying a dose of 12 t·ha⁻¹, the lowest numbers of the bacteria (0.30 lg CFU g⁻¹ d.m. at time point III and 0.20 lg CFU g⁻¹ d.m. at time point IV) and fungi (0.10 lg CFU g⁻¹ d.m. at time points III and IV) were detected in the tested samples.

The most optimal results following the application of the soil conditioner AMP were achieved with the 4 t·ha⁻¹ fertilizer dose. Increasing the AMP fertilization rate above 4 tons primarily resulted in a decrease in the quantity of mobile forms of potassium (from 40.4 mg·dm⁻³ in the control to 26.7 mg·dm⁻³ at the 8 t·ha⁻¹ dose) and orthophosphate as phosphorus (PO₄-P) (from 6.00 mg·dm⁻³ in the control to 3.75 mg·dm⁻³ at the 8 t·ha⁻¹ dose) in the soil solution. The Agro Mineral Product used affected the yield of the winter rapeseed seeds. Significantly, the highest seed yield (5.29 t·ha⁻¹) was observed with the dose of 4 t·ha⁻¹, while the lowest (4.43 t·ha⁻¹) was observed with the dose of 12 t·ha⁻¹. The dose of the Agro Mineral Product had no significant effect on the seed moisture.

The product can be used in field crops that are not intended for direct human consumption or for feed production, on soils requiring deacidification. It can be used at specific intervals, with the dosing depending on the type of soil.

Analyzing the results of the initial studies, it can be stated that they do not provide a full view of the effect of the preparation used on the activity of the soil microorganism consortium on the plant and the physicochemical properties of soils. It is necessary to continue these studies on a broader spectrum aimed at a clear explanation of the effect of the AMP preparation on the enzymatic activity of the soil, the yield formation, and selected indicator microorganisms, e.g., PGPB (Rhizobium sp. and Azotobacter sp.) isolated from the rhizosphere zone of a specific crop plant.