Analysis of Long-Term Effect of Tillage Systems and Pre-Crop on Physicochemical Properties and Chemical Composition of Soil

Abstract

The aim of the present study was to analyse the physicochemical properties and chemical composition of soil after years of applying varied tillage systems and pre-crops. The field experiments were carried out in Lipnik in Poland. The experiment was conducted over 25 years, with factor I–3 tillage systems: ploughing (A), ploughless (B) and direct sowing (C), factor II-pre-crop–1–faba bean, 2–sugar beet. Simplified tillage systems were used, and increased acidity was found in both layers due to lower pH, as well as an increase in exchangeable aluminum, hydrolytic acidity and exchangeable acidity of soil. The simplification of tillage system resulted in no significant effect on the following soil parameters: sum of base cations (TEB), cation exchange capacity (CEC) and electrical conductivity (EC). In both layers, there was a marked increase in the content of total nitrogen, carbon and available magnesium in soil with ploughless (B) and direct sowing (C) tillage systems. The change of the tillage system, which implied tillage reduction, was found to be the factor which has a significant effect on the physicochemical properties and chemical composition of soil. Tillage resulted a greater effect on the physicochemical properties, whereas pre-crop was found to affect the changes in chemical composition of soil to a greater extent. The results obtained in the research indicate that the tillage systems ploughless (B) and direct sowing (C) can be applied in practice.

1. Introduction

Tillage is particular way of soil preparation and crop establishment carried out systematically and on a long-term basis. Consequently, some characteristic traits of soil and conditions for plant production develop due to the application of the specific agrotechnical tools, machines and treatments [1].

In modern practices, three tillage systems are distinguished: ploughing (conventional) tillage, ploughless tillage, and no-till with direct sowing. The main principle of the conventional tillage based on ploughing is the displacement of topsoil into the bottom of the furrow. The tool applied in this system is the plough. The ploughless tillage does not rely on the use of the plough and the soil surface is mixed (churned) instead. The no-till system, i.e., direct sowing, consists of churning the soil only to a limited extent, without preparing the soil for sowing, the seeds are planted with special direct sowing seeders, and plant residue and weed are generally destroyed with chemicals. The tools currently employed in this system are a combination of fertiliser dispensers with seeders. Agrotechnical simplifications based on a reduced number of treatments are becoming increasingly popular and constitute one of the elements of organic agriculture. Modern technology is to facilitate and accelerate the work with only minimal degradation to the environment. Also, reduced tillage systems may translate into an increase in yield and, owing to the changes in biogeochemical processes in soil, reduce nutrient loss [2].

Tillage, apart from fertilization, is a basic element of agrotechnics determining soil traits. Due to soil inversion, churning, mixing, compaction and crumbling, the physical properties of soil are changed initially, mainly the water-air relationship, soil bulk density and compaction. Consequently, the chemical and biological properties also change [3,4,5]. The type and extent of the changes resulting from varied ploughing or ploughless tillage systems, at various depths, is also determined by the plant grown as pre-crop [5].

The available literature includes a number of studies on the consequences and long-term effects of reduced tillage systems on crop quality [6,7,8]. Agriculture should not focus solely on high crop yields, but must also consider the stable relationship between agricultural human activity and natural environment quality [9]. The interest of organic farmers in adopting conservation agriculture principles, including minimal soil disturbance, permanent soil cover and crop rotation has been growing since the early 2000s, [6]. Morris et al. points out that use of non-inversion tillage can also help with soil erosion control by maintaining a higher proportion of crop residue on the soil surface than with conventional tillage [7]. Numerous authors conducted economic analyses of reduced tillage systems [10,11,12,13]. However, the effect of tillage systems on the chemical properties of soil has been much less frequently analysed despite the fact that the nutrient profile of soil plays a crucial role in tailoring agrotechnical practices. The duration of the research carried out is particularly important.

The main objective of the study of simplified tillage systems consisting in the reduction of the number of treatments is to evaluate their practical usefulness. The aim of the present study was to analyse the physicochemical properties and chemical composition of soil after years of applying varied tillage systems and pre-crops. The working hypothesis assumed that the tillage systems and pre-crops have attributes that affect the physicochemical properties and chemical composition of soil.

2. Materials and Methods

2.1. Conditions of the Conducted Experiment

The field experiments were carried out in Lipnik (53°41’ N, 14°97’ E) at the Agricultural Experimental Station belonging to the West Pomeranian University of Technology in Szczecin. The experiment was conducted for a period for 25 years. It was established in 1994 and completed in 2019. Poland is located in the temperate climate zone. The annual average air temperature is around 7.5 °C. For the region of Szczecin, the annual average of the total precipitation in the years 1991–2020 was 550 mm [14]. Samples taken after plant harvest in 2019 are the experimental material for this paper.

Soil samples were taken from two layers: at depths of 0–0.05 and 0.05–0.20 m from each plot for experimental variants and replication. Collective samples consist of 10 primary samples taken representatively from plot area. The soil belongs to light loamy sand, with weakly loamy sand underneath and, in some places, light silt. Typologically, it is characterised as brown soil [15]. It is light soil typical for the region of West Pomerania. Before starting the experiment, the soil from the arable layer (0–20) cm was characterised by the following parameters: pH_KCl = 4.7 and P_avail = 56.5; K_avail = 120.9; Mg_avail = 64.4 mg kg⁻¹. The abundance of general forms of nitrogen, carbon and sulfur was 0.064, 0.83 and 0.013%, respectively. Microelements in the soil were: iron-475, manganese-160, copper-3.37, zinc-6.65 mg kg⁻¹. The parameter-exchangeable aluminum, hydrolytic acidity (Hh) and exchangeable acidity (Hw) were, respectively, 0.22, 3.9 and 0.05 cmol kg⁻¹.

Field studies were conducted using winter wheat in a three-field crop rotation system (sugar beet–winter wheat–faba bean). The plot size was 40 m² (for harvesting 30 m²). Winter wheat “Kobra Plus” cultivar was grown in three tillage systems: ploughing (A), ploughless using cultivator and string roller (B), and direct sowing (C). For the conventional (A) and ploughless tillage (B), wheat was sown using a row drill seeder. On objects with direct sowing, a special seeder (intended for direct sowing) was used. The Kobra Plus cultivar (formerly, Kobra-1992) is a bread cultivar of cold hardiness estimated as 4° (scale 9°).

Phosphates (triple superphosphate) and potassium (potassium salt) fertilization were applied in amounts of 60 kg P₂O₅ and 90 kg K₂O per ha in the autumn before sowing the seeds each year. Nitrogen fertilization (ammonium nitrate) was applied in an amount of 150 kg N ha⁻¹. It was divided into 3 doses (50 kg each one) in the beginning of spring vegetation, at the stem extension stage and at the heading stage. After the seeds were sown, herbicide was applied, at the stem extension stage (BBCH 30) fungicide and at the heading stage (BBCH 51)–fungicide and insecticide.

The analysis compared two factors: factor I–3 tillage systems: ploughing (A), ploughless (B) and direct sowing (C), factor II-pre-crop–1–faba bean (cultivar “Martin”), 2–sugar beet (cultivar “Kutnowska”). Experimental design–split- block with 3 replications.

2.2. Chemical Analyses

The soil samples were collected using Egner soil samples from two depths: 0–0.05 and 0.05–0.20 m. The samples were dried and ground according to the requirements set out in the norm of the Polish Standard [16]. Soil pH was determined potentiometrically with the use of a pH-meter Orion Star A 211, according to the ISO standard [17]. Electrical conductivity (EC) was measured with a conductometric method (conductometer Orion 3Star) (suspension with a soil/water weight ratio 1:2.5) [18]. Hydrolytic acidity (Hh) i.e., an indicator of the saturation of the sorption complex with hydrogen and aluminium ions, was determined with Kappen’s method [19]. Exchangeable acidity and exchangeable aluminium were identified using Sokolov’s method with soil extraction with 1 M KCl [20]. The sum of base cations (TEB) was determined using Kappen’s method of soil extraction with 1M HCl and titration with 0.1 M NaOH solution [20]. Cation exchange capacity (CEC) is a sum of hydrolytic acidity and the sum of exchangeable base cations in the soil. Base saturation (V) is a percentage ratio of exchangeable base cations to cation exchange capacity (CEC).

Total content of carbon (C), nitrogen (N) and sulphur (S) was determined with the use of elemental analyser CHNS (Costech Instruments Elemental Combustion System) by ELTRA Poland. The content of available magnesium was determined with the Schachtschabel method, using the extraction with a solution of calcium chloride (0.025n CaCl₂) [21]. In the extracts obtained, the content of metals was determined with the use of Atomic Absorption Spectrometer Apparatus (Thermo Fisher Scientific iCE 3000 Series). The available forms of potassium in the soil were determined using the Egner–Riehm method based on the extraction of calcium lactate with a buffer solution characterised by a pH value of 3.55 [22]. The content of Fe, Mn, Zn and Cu forms soluble in 1M HCl was determined using Atomic Absorption Spectrometry (AAS) method [20].

2.3. Statistical Analysis

The results of the two-factor experiment were statistically processed using the analysis of variance in split- block design. The number of replications was 3. Confidence sub-intervals were calculated using Tukey’s multiple test, assuming a significance level of p < 0.05 [23]. The statistical analysis of the results obtained was carried out using the Statistica 13.3. TIBCO Software Inc., by TIBCO Statsoft Poland, the owner of the license West Pomeranian University of Technology, Szczecin, Poland.

3. Results and Discussion

3.1. Significance of Source of Variability and V% for Estimated Soil Traits

The significance of the effects of the main factors, as well as the interactions between the factors under analysis, was determined with the analysis of variance (ANOVA) and is presented in

Table 1. Significance of source of variability and V% for estimated soil traits.

Trait	Layer m	Source of Variability			V%
		Pre-Crop (F)	Tillage System (T)	Interaction FxT
pHKCl	0–0.05	*** 1)	***	ns 2)	3.72
	0.05–0.20	ns	Ns	ns	8.13
Exchangeable aluminium	0–0.05	ns	***	ns	3.72
	0.05–0.20	ns	***	ns	9.65
Hydrolytic acidity Hh	0–0.05	ns	***	ns	6.67
	0.05–0.20	***	*	ns	11.67
Exchangeable acidity Hw	0–0.05	**	**	ns	12.31
	0.05–0.20	**	*	ns	12.80
Sum of base cations TEB	0–0.05	ns	Ns	ns	11.23
	0.05–0.20	ns	Ns	ns	14.63
Cation exchange capacity CEC	0–0.05	***	Ns	**	6.56
	0.05–0.20	**	Ns	ns	11.03
Base saturation V	0–0.05	*	*	ns	17.34
	0.05–0.20	*	*	ns	18.00
Electrical conductivity EC	0–0.05	ns	Ns	ns	9.21
	0.05–0.20	***	Ns	ns	11.6
Total nitrogen	0–0.05	***	***	ns	5.36
	0.05–0.20	ns	**	ns	4.39
Total carbon	0–0.05	***	***	*	6.77
	0.05–0.20	**	**	ns	7.82
Total sulphur	0–0.05	ns	Ns	ns	5.88
	0.05–0.20	**	Ns	ns	4.32
C/N	0–0.05	*	*	ns	2.41
	0.05–0.20	***	ns	ns	3.10
Available magnesium	0–0.05	**	*	ns	12.63
	0.05–0.20	ns	ns	ns	7.80
Available potassium	0–0.05	ns	***	ns	12.43
	0.05–0.20	***	***	ns	11.66
Iron	0–0.05	***	ns	ns	5.72
	0.05–0.20	***	ns	ns	4.10
Manganese	0–0.05	***	ns	ns	7.68
	0.05–0.20	***	ns	ns	8.45
Copper	0–0.05	***	ns	ns	11.07
	0.05–0.20	*	ns	ns	12.83
Zinc	0–0.05	ns	ns	ns	9.13
	0.05–0.20	ns	ns	ns	6.72

¹⁾ significance at: 0.05—*, 0.01—**, 0.001—***, ²⁾ ns—no significance.

. The effect of pre-crop on the chemical composition of soil was found to be predominant, whereas the tillage system was found to have a stronger effect on the physicochemical properties of the soil. The interaction between the factors was found to be sporadic and identified only in two instances. The accuracy of the experiment with respect to the traits under analysis can be considered satisfactory—in most cases, the coefficient of variability (V%) was below 10% which indicates the high level of accuracy of the experiment.

3.2. Physicochemical Properties of Soil

The multiannual application of a particular tillage system permanently affects the physical properties of soil in a manner characteristic for a given tillage system [5]. The pH of the soil used in the experiment, measured as pH in, KCl, ranged from 3.92 to 5.01 (

Table 2. Physicochemical elements of soil depending on pre-crop and tillage system.

Trait	Unit	Factor	Variant	Layer
				0–0.05 m	0.05–0.20 m
pHKCl	-	Pre-crop	Sugar-beet	4.37 a ± 0.064	4.75 a ± 0.169
			Faba bean	3.92 b ± 0.105	4.82 a ± 0.065
		Tillage system	A	4.50 a ± 0.069	5.01 a ± 0.125
			B	3.97 b ± 0.112	4.78 a ± 0.177
			C	3.98 b ± 0.116	4.57 a ± 0.133
Exchangeable aluminium	cmol kg−1	Pre-crop	Sugar-beet	0.22 a ± 0.036	0.12 a ± 0.017
			Faba bean	0.26 a ± 0.029	0.15 a ± 0.043
		Tillage system	A	0.12 b ± 0.022	0.10 b ± 0.046
			B	0.37 a ± 0.028	0.15 a ± 0.043
			C	0.27 a ± 0.026	0.14 a ± 0.057
Hydrolytic acidity Hh	cmol kg−1	Pre-crop	Sugar-beet	3.96 a ± 0.110	4.69 b ± 0.175
			Faba bean	3.82 a ± 0.206	5.54 a ± 0.156
		Tillage system	A	3.23 b ± 0.164	4.73 b ± 0.280
			B	4.20 a ± 0.080	5.15 ab ± 0.236
			C	4.24 a ± 0.074	5.47 a ± 0.185
Exchangeable acidity Hw	cmol kg−1	Pre-crop	Sugar-beet	0.06 a ± 0.005	0.05 a ± 0.006
			Faba bean	0.04 b ± 0.005	0.03 b ± 0.004
		Tillage system	A	0.03 b ± 0.004	0.03 b ± 0.005
			B	0.06 a ± 0.007	0.03 a ± 0.006
			C	0.05 a ± 0.003	0.05 a ± 0.008
Sum of base cations TEB	cmol kg−1	Pre-crop	Sugar-beet	2.24 a ± 0.184	3.30 a ± 0.636
			Faba bean	2.28 a ± 0.290	3.26 a ± 0.317
		Tillage system	A	2.75 a ± 0.236	3.80 a ± 0.378
			B	1.99 b ± 0.292	3.48 a ± 0.881
			C	2.04 b ± 0.295	2.56 a ± 0.391
Cation exchange capacity CEC	cmol kg−1	Pre-crop	Sugar-beet	6.20 a ± 0.125	6.40 a ± 0.212
			Faba bean	4.06 b ± 0.113	5.30 b ± 0.112
		Tillage system	A	5.08 a ± 0.538	5.85 a ± 0.333
			B	5.04 a ± 0.341	5.76 a ± 0.243
			C	5.27 a ± 0.379	5.94 a ± 0.306
Base saturation V	%	Pre-crop	Sugar-beet	35.7 b ± 2.42	44.6 b ± 5.13
			Faba bean	56.2 a ± 7.93	61.6 a ± 6.13
		Tillage system	A	57.6 a ± 7.79	65.6 a ± 6.60
			B	39.6 b ± 7.87	50.8 b ± 7.97
			C	40.6 b ± 7.41	43.0 b ± 6.05
Electrical conductivity EC	μS cm−1	Pre-crop	Sugar-beet	46.9 a ± 2.70	91.3 a ± 7.27
			Faba bean	40.9 b ± 1.27	53.6 b ± 1.01
		Tillage system	A	40.4 b ± 2.05	72.1 a ± 8.58
			B	46.6 a ± 3.88	78.0 a ± 10.56
			C	44.7 a ± 1.68	67.3 a ± 9.27

A—ploughing; B—ploughless using cultivator and string roller; C—direct sowing. a, b—means marked by the same letter do not differ significantly at the significant level < 0.05.

). According to the adopted norm [17], the soil in the experiment is to be considered acidic and very acidic.

Reduced soil mixing resulting in an increased amount of plant residue in topsoil caused an increased in soil acidity determined in both layers. An analogous relationship differentiating soil pH depending on the tillage system was identified with pH measurements conducted on this object in 2004 [24]. When comparing the results from 2004 and 2019, the increasing acidity of the soil used in the experiment must be noted. Małecka et al. [25] observed that in ploughless tillage systems the soil is not inverted, therefore the amount of plant residue in topsoil increases. This leads to an uneven distribution of nutrients in soil profile, thus changes in the chemical properties of soil are observed. On the basis of their own studies, the authors indicated that after 11 years, the pH of topsoil was lower in the reduced tillage system by 0.41 unit, and by 0.46 unit in direct sowing, as compared with the conventional tillage system.

Also, the results obtained by Rajewski et al. [26] in an experiment with sugar beet show that conservation tillage system resulted in a decrease in pH_KCl in the springtime at the depth of 5–10 cm by, on average, 0.5 units, as compared with the traditional tillage system.

The analysis of the results of the conducted experiment does not show a significant effect of pre-crop on soil pH in the layer at a depth of 0.05–0.20 m. However, in the layer of 0–0.05 m in depth, growing faba beans as pre-crop resulted in a decrease in soil pH to 3.92, therefore the soil is to be considered very acidic (Table 2). In their analysis of the effects of long-term cereal crop rotation on selected chemical traits of soil, Smagacz et al. [27] point to the relatively little effect of the compared crop rotation on soil pH. Soil acidification is likely to be due to the increased organic matter remaining in the soil if simplified tillage systems are used.

Changes in exchangeable aluminium content in soil depend on soil pH. The results obtained in the experiment show an increase in the content of exchangeable aluminium in soil to which ploughless (B) and direct sowing (C) tillage systems were applied. However, it must be noted that a higher content of exchangeable aluminium was found in topsoil (max. 0.37 cmol kg⁻¹) (Table 2).

The hydrolytic acidity of soil describes the potential soil acidity. This parameter is the extent of saturation with hydrogen and includes total soil acidity. The results of the present experiment show a lack of change in hydrolytic acidity in topsoil depending on the pre-crop; the mean value amounted to 3.89 cmol kg⁻¹. The layer at the depth of 0.05–0.20 m was characterised by higher parameters of hydrolytic acidity and was dependent on pre-crop. Growing faba beans as pre-crop, the highest obtained value was 5.54 cmol kg⁻¹ (Table 1 and Table 2). The relationship between the changes in hydrolytic acidity of soil and the applied tillage system was analogous to that of exchangeable aluminium. There was an increase in hydrolytic acidity of soil with ploughless (B) and direct sowing (C) tillage system. The highest value of hydrolytic acidity in the soil was found for direct sowing (C), in the layer of 0.05–0.20 m–5.47 cmol kg⁻¹, (Table 2).

Exchangeable acidity is determined by H⁺ and Al³⁺ ions in soil solution and related to the sorption complex, manifested by extraction with neutral salt. Both layers of soils show lower parameters of exchangeable acidity with faba bean grown as pre-crop. The relationship between the changes in the parameters of exchangeable acidity and the adopted tillage system is analogous to that of exchangeable aluminium and hydrolytic acidity (Table 1 and Table 2). Reduced cultivation activities resulted in an increase in the parameters of exchangeable acidity of soil.

The soil sorption complex is saturated with base cations and constitutes the essential pool of nutrients for plants. A high content of the sum of base cations (TEB) in substrate is favourable for plant growth. According to [28], the mean sum of base cations in arable lands in Poland amounts to 8 cmol kg⁻¹, the highest parameters reaching 40 cmol kg⁻¹. The soil used in the experiment resulted in parameters of base cations 2.5 in the topsoil, and 3.5 cmol kg⁻¹ in the deeper layer (Table 1 and Table 2). The analysed factors did not cause changes with respect to the parameters of the sum of base cations in soil. Siebielec et al. [28], in their monitoring of the chemistry of arable soils, also stated that the content of base cations in soils taken at measuring points did not change substantially in the consecutive years of the period 2010–2012.

The cation exchange capacity (CEC) of the soil used in the experiment ranged from 4.06 to 6.40 cmol kg⁻¹ (Table 1 and Table 2). The effect of pre-crop is manifested in both layers. Sugar beet grown as pre-crop resulted in the highest parameters of CEC—the maximum of 6.49 cmol kg⁻¹ (Figure 1). A change of tillage system resulted in no influence on the parameters of the said parameter of soil. The relationships obtained are in line with the observation made by Siebielec et al. [28] that cation exchange capacity of soil is essentially a permanent trait and does not change substantially. In turn, Palm et al. [29] claim that ploughless tillage shows no effect on the parameters of cation exchange capacity of soil.

The base saturation of soil complex is expressed as a percentage share of base cations (Ca²⁺, Mg²⁺, K⁺, Na⁺, NH⁴⁺) in the cation exchange capacity of soil. The minimum base saturation required for the correct functioning of the soil system depends on the granulometric composition and it is assumed that in light soils it should not be below 40% [28]. The use of faba beans as a pre-crop resulted in a higher value of base saturation exceeding 40%. This may be connected with the uptake of the elements from the not-easily available forms of compounds and from deeper layers by the well-developed root system of faba beans which, in turn, mobilises potassium unassimilable for many plants. Soil to which ploughing tillage was applied (A) was characterised by the parameters of base saturation of 60% which is comparable to the mean determined in arable soils in Poland [28]. A reduction of cultivation activities resulted in a decrease in base saturation of soil (Table 1 and

Table 3. Macro-nutrients contents in soil depending on pre-crop and tillage system.

Trait	Unit	Factor	Variant	Layer
				0–0.05 m	0.05–0.20 m
Total nitrogen	%	Pre-crop	Sugar-beet	0.062 b ± 0.0013	0.063 a ± 0.0018
			Faba bean	0.072 a ± 0.0023	0.066 a ± 0.0013
		Tillage system	A	0.061 c ± 0.0013	0.059 b ± 0.0010
			B	0.067 b ± 0.0025	0.066 a ± 0.0015
			C	0.073 a ± 0.0026	0.068 a ± 0.0016
Total carbon		Pre-crop	Sugar-beet	0.58 b ± 0.014	0.58 b ± 0.021
			Faba bean	0.70 a ± 0.030	0.64 a ± 0.013
		Tillage system	A	0.56 c ± 0.011	0.55 b ± 0.017
			B	0.64 b ± 0.030	0.62 a ± 0.019
			C	0.72 a ± 0.035	0.65 a ± 0.022
Total sulphur		Pre-crop	Sugar-beet	0.005 a ± 0.0008	0.006 a ± 0.0006
			Faba bean	0.004 a ± 0.0006	0.003 b ± 0.0005
		Tillage system	A	0.003 a ± 0.0010	0.004 a ± 0.0008
			B	0.005 a ± 0.0009	0.004 a ± 0.0004
			C	0.005 a ± 0.0005	0.005 a ± 0.0011
C/N	-	Pre-crop	Sugar-beet	9.36 b ± 0.066	9.11 b ± 0.099
			Faba bean	9.68 ba ± 0.128	9.69 a ± 0.050
		Tillage system	A	9.30 a ± 0.082	9.32 a ± 0.151
			B	9.53 ab ± 0.135	9.44 a ± 0.145
			C	9.73 b ± 0.147	9.45 a ± 0.137
Available magnesium	mg kg−1	Pre-crop	Sugar-beet	110.1 a ± 12.58	81.5 a ± 1.73
			Faba bean	68.4 b ± 11.84	83.6 a ± 1.72
		Tillage system	A	77.9 b ± 5.68	82.8 a ± 2.35
			B	88.4 ab ± 14.56	81.0 a ± 1.45
			C	101.5 a ± 16.82	83.8 a ± 2.51
Available potassium		Pre-crop	Sugar-beet	109.5 a ± 6.34	89.2 b ± 7.46
			Faba bean	112.5 a ± 5.36	118.3 a ± 3.42
		Tillage system	A	90.7 b ± 5.90	84.1 b ± 10.01
			B	119.0 a ± 4.85	111.3 a ± 5.34
			C	123.3 a ± 3.95	115.8 a ± 6.02

A—ploughing; B—ploughless using cultivator and string roller; C—direct sowing. a, b, c—means marked by the same letter do not differ significantly at the significant level < 0.05.

).

Electrical conductivity allows the assessment of soil salinity and estimation of the practical consequences for crops. Electrical conductivity of the soil samples collected from top layers resulted in variation depending on the layer. In the layer at a depth of 0–0.05 m, mean parameters amounted to 43.9 and in the deeper layer to 72.5 μS cm⁻¹ (Table 2). The tillage systems analysed in the experiment did not differentiate the electrical conductivity of soil. However, it must be observed that the use of sugar beet as a pre-crop caused higher parameters of electrical conductivity in soil (Table 1 and Table 2).

3.3. Macro-Nutrients Contents in Soil

Among macro-nutrients, soil nitrogen is the most mobile nutrient. The analysis of the results of the experiment shows that, at the depth of 0–0.05 m, faba beans grown as a pre-crop were found to be the factor determining the increase in nitrogen content—the change was not found regarding the deeper layer. The parameters identified at the said depth were permanent 0.06% (Table 1 and Table 3). The relationships obtained can be explained by the fact that faba beans, as a leguminous plant, have the capacity to form a symbiosis with useful rhizobia and provide substantial amounts of nitrogen fixed from air to substrate.

There was a significant increase in nitrogen content in soil with ploughless (B) and direct sowing (C) tillage systems (Table 1 and Table 3). Similar results are presented by Rajewski et al. [26], who observe that the highest content of nitrogen in the whole arable layer (0–0.25 m)–on average 1.14 g kg⁻¹, was found in plots with zero tillage. The results of the studies discussed are in line with previous reports of an improvement in the nitrogen content of the soil with zero tillage, [30], which can be due to the higher nutrient uptake from loose soil, due to better root growth. In turn, this effect increases the nitrogen content in soil in no-tillage cultivation, confirmed Woźniak and Rachoń [31]. Ploughing disturbs the structure of soil and leads to a quicker breakdown of soil aggregates which, in turn, may result in a more intense release of nitrogen from the cultivated soil.

The effect of reduced tillage on the total content of nitrogen in soil is closely connected with changes in organic carbon content [12]. The content of carbon in the analysed soil was found to be 0.06% (Table 3). The use of faba beans as a pre-crop was the factor determining the higher content of carbon in soil in both layers (Figure 2). Reduced cultivation practices resulted in an increase of soil abundance in relation to carbon content. The highest content of carbon was found in the layer at the depth 0–0.05 m in the direct sowing (C) tillage system. The results by Fernández et al. [32] show that after several years of reduced tillage the content of organic carbon in soil was higher, particularly in the topsoil. Moreover, according to Żyłowski [12], an increase in organic carbon content in soil in the reduced tillage system is determined only in the surface layer of soil (0 to 5–10 cm) and not in the whole soil profile. Palm et al. [29] conclude that there is strong evidence that the content of total nitrogen and organic matter in topsoil is found to increase with reduced tillage systems. Nowadays, numerous studies have demonstrated a favourable effect of reduced tillage on the change in organic carbon content in soil [33,34,35,36]. The higher nitrogen and carbon content in soil is likely to be due to the increased organic mass remaining in the soil if simplified cultivation systems are used.

Changes in nitrogen due to the use of faba beans as a pre-crop were manifested in an increased C/N ratio in soil. There was a significant increase in the parameters of C/N ratio in soils to which the following tillage systems were applied: ploughless (B), and direct sowing (C). This points to the increased rate of change in the carbon content, as compared with nitrogen, owing to the application of different tillage systems (Table 1 and Table 3). However, Kobierski et al. [37] recorded a different relationship, namely that mean parameters of C/N ratio were comparable, which indicates a similar rate of organic matter decomposition regardless of the adopted tillage system. The authors identified the highest carbon content in soil samples collected at the depth of 0–30 cm from plots to which ploughless tillage system with the use of cultivator was applied.

Sulphur content in soil ranged from 0.003 to 0.007%. The applied tillage system, as well as the pre-crop, resulted no significant effect on the change in sulphur content in surface layer of soil. Reduced agrotechnical activities translated into an increase in soil abundance in sulphur.

On the basis of multiannual studies, Fonteyne et al. [38] found that reduced tillage had an effect on an increased organic matter content, nitrate concentration and sulphur content in topsoil (0–0.05 m), as compared with conventional tillage.

Magnesium is an element of significant physiological importance for plants as it affects the photosynthesis process. According to the applicable criteria [21], the soil used in the experiment was characterised by a high content of available magnesium. When analysing the effect of the factors under study, the variable content of magnesium in different layers of soil must be noted. The content of available magnesium in the deeper layer was found to be at the level of 80 Mg kg⁻¹ and did not change. As for topsoil, the use of sugar beet as a pre-crop caused an increase in available magnesium content to 110.1 mg kg⁻¹. The study identified a significant increase in the content of available magnesium in soil combined with the application of ploughless (B) tillage, and particularly direct sowing (C) tillage system (Table 1 and Table 3).

Both analysed layers of the soil used in the experiment were characterised by an average content of available potassium, i.e., 84.1 to 123.3 mg K kg⁻¹. When analysing the effect of the factors under study, the variable content of potassium in different layers of soil must be noted. The effect of pre-crop on the content of available potassium in soil was not identified for topsoil. As for the layer of 0.05–0.20 m and the use of sugar beet as a pre-crop, there was an increase by 32% in the content of available potassium in soil. The study identified a significant increase in available potassium in soil with the application of ploughless (B) and direct sowing (C) tillage systems (Table 1 and Table 3), which is also confirmed in studies by Żyłowski [12] and Małecka et al. [39]. According to Jaskulski, the pre-crop and tillage system resulted in no marked effect on the content of available forms of macro-nutrients (P, K and Mg) in soil, despite a slight increase due to the application of the ploughless tillage system when growing corn [5]. According to Naeem et al. [30], the addition of mung beans in the cropping system improved soil available potassium, because, compared to other crops, the cultivation of legumes is a regenerative cultivation. In the studies discussed, a higher concentration of potassium was also found after legumes pre-crop (faba beans).

Out of the methods of determining the amounts of heavy metals, the most important are the ones allowing the assessment of the content of the forms available to plants [34]. Extraction with 1 M HCl solution is widely adopted in agricultural research for the purpose of determining micronutrients bioavailability to plants.

Iron and manganese are micronutrients of every plant as they take part in the reduction and oxidation processes. The content of available iron in the soil used in the experiment was found to be low, from 469 to 792 mg Fe kg⁻¹ of soil. As for available manganese, the content was found to be higher—from 80.5 to 147.7. According to the adopted norms, the content was average [20] (

Table 4. Micronutrients contents in soil depending on pre-crop and tillage system.

Trait	Unit	Factor	Variant	Layer
				0–0.05 m	0.05–0.20 m
Iron	mg kg−1	Pre-crop	Sugar-beet	469 b ± 10.7	469 b ± 8.2
			Faba bean	766 a ± 8.8	792 a ± 7.4
		Tillage system	A	631 a ± 55.4	647 a ± 58.0
			B	606 a ± 60.4	623 a ± 59.9
			C	614 a ± 56.2	621 a ± 66.8
Manganese		Pre-crop	Sugar-beet	80.5 b ± 2.69	85.2 b ± 3.70
			Faba bean	143.8 a ± 2.73	147.7 a ± 2.16
		Tillage system	A	117.8 a ± 12.45	115.6 a ± 10.62
			B	109.2 a ± 11.79	111.7 a ± 14.00
			C	109.4 a ± 12.84	122.0 a ± 12.07
Copper		Pre-crop	Sugar-beet	1.37 a ± 0.033	1.48 a ± 0.037
			Faba bean	1.08 b ± 0.057	1.28 b ± 0.080
		Tillage system	A	1.26 a ± 0.092	1.44 a ± 0.076
			B	1.23 a ± 0.058	1.38 a ± 0.097
			C	1.18 a ± 0.084	1.33 a ± 0.080
Zinc		Pre-crop	Sugar-beet	5.16 a ± 0.152	5.46 a ± 0.126
			Faba bean	5.10 a ± 0.123	5.51 a ± 0.080
		Tillage system	A	5.32 a ± 0.190	5.37 a ± 0.102
			B	5.05 a ± 0.074	5.77 a ± 0.114
			C	5.02 a ± 0.204	5.31 a ± 0.105

A—ploughing; B—ploughless using cultivator and string roller; C—direct sowing. a, b—means marked by the same letter do not differ significantly at the significant level < 0.05.

).

The analysis of the first factor, i.e., pre-crop, shows that the use of faba beans resulted in an increase by 70% in the content of available forms of iron and manganese in the soil used in the experiment (Table 1 and Table 4).

Copper is an essential constituent of enzymes, taking part in numerous reduction and oxidation reactions in plants. The content of copper in light soil below 1.6 mg Cu kg⁻¹ is considered to be low. The soil used in the experiment was characterized by the content of available copper below the aforementioned value. Unlike for iron or manganese, the use of sugar beet as pre-crop proved to be more favourable than that of faba beans (Table 1 and Table 4). The soil collected from plots with sugar beet as a pre-crop resulted approx. 20% increase in the content of available copper.

The metabolic role of zinc for plants resides in the formation of complexes with nitrogen, oxygen and sulphur and their catalytic as well as structural role. The content of available zinc in the soil used in the experiment was very uniform—at the level of 5 mg Zn kg⁻¹ of soil. According to the applicable norm, it is to be considered average. Unlike in the case of the micronutrients discussed above, the effect of pre-crop on changes in the available zinc content in soil was not identified (Table 1).

One of the factors under analysis, i.e., tillage system, did not cause changes in the content of the analysed micronutrients in soil: available iron, manganese, copper and zinc (Table 1 and Table 4). However, opposite findings can be found in the literature on the subject. In their study on the effect of reduced tillage on chernozem, Medvedeva et al. [40] found the content of available zinc and copper to be twice as high due to ploughless tillage or direct sowing, as compared with the ploughing tillage system. A similar result was presented by Kraska, who says that in the cultivation of spring wheat grown in monoculture, the plough tillage system led to the occurrence of a higher level of copper, manganese and iron in surface layer of soil (0–20 cm) in comparison with conservation tillage [3]. Kaushik et al. presented dependencies that the availability of micronutrients zinc, manganese, and iron were found to be higher under the zero tillage system. Copper was found on par in both systems [41]. For micronutrients, the research results are very dependent on soil parameters and climatic conditions.

4. Conclusions

Depending on the analysed layer of soil, the effect of the factors under analysis was found to be variable. The use of simplified tillage systems, limiting soil mixing increased acidity in both layers due to lower pH and an increase in exchangeable aluminum, hydrolytic acidity and exchangeable acidity of soil. The simplification of the tillage system resulted in no significant effect on the following soil parameters: the sum of base cations (TEB), cation exchange capacity (CEC) and electrical conductivity (EC). In both layers, there was a marked increase in the content of total nitrogen, carbon and available magnesium in soil with: ploughless (B) and direct sowing (C) tillage systems. With respect to changes in the content of available potassium, the effect of ploughless (B) and direct sowing (C) tillage systems was found only in the topsoil where an increase was recorded. Additionally, the study identified a significant effect of pre-crop on the changes in the content of available iron, manganese and copper—in the case of available zinc the change was not observed. The adopted tillage systems had no effect on the content of the following micronutrients in soil: available iron, manganese, copper and zinc. The change of the tillage system which consisted of tillage reduction was found to be the factor which had a significant effect on the physicochemical properties and chemical composition of soil. Tillage resulted in a greater effect on the physicochemical properties, whereas pre-crop was found to affect the changes in chemical composition of soil to a greater extent. The results obtained in the research indicate that the tillage systems: ploughless (B) and direct sowing (C) can be applied in practice.