The Response of Retisol’s Carbon Storage Potential to Various Organic Matter Inputs

Abstract

Organic carbon sequestration and its quality in soil is a crucial aspect in maintaining the productivity of the soil and the whole ecosystem. The study examined the changes in soil organic carbon (SOC), its sequestration potential, and the mean effect size under various long-term organic matter inputs in acid soil (Dystric Retisol). Cattle manure (CM 60 t ha⁻¹) and various plant residues were used for the fertilization of acid and limed soil. The following treatments were included in the experimental design: (1) natural Retisol; (2) natural Retisol + CM; (3) natural Retisol + various plant residues; (4) calcium carbonate (CaCO₃) at a 1.0 rate every five years); (5) CaCO₃ + CM; (6) CaCO₃ + various plant residues. The data demonstrated that the treatments including the use of organic material (CM and various plant residues) showed a greater SOC content accumulation with a storage of up to 0.2–0.6% more carbon in the topsoil. Alternative organic fertilizers had a detrimental impact when applied to unlimed soil, with a loss of 0.59 g kg⁻¹ C per year. All the fertilization treatments significantly increased the SOC level with the mean effect size of 0.02–0.28, and the increase varied from 1.89% to 32.89%. This result suggested that liming, together with organic fertilizers, proved to be a relatively efficient approach to improving the soil’s health and quality.

1. Introduction

The primary source of carbon in natural ecosystems is soil organic carbon (SOC), and its preservation is crucial for controlling the climate, controlling the rate of erosive processes, and ensuring the availability of nutrients [1,2]. It is a significant “sink” of greenhouse gases as well as a “source” of such gases [3]. For the abovementioned reasons, SOC preservation has become a primary objective of current research and a key subject in soil science. As soils are the largest carbon sink in the world [4], even small changes can substantially alter the cycle of carbon [5,6].

Worldwide, human activities and global warming have significantly deteriorated the soil, particularly through SOC loss. Organic matter plays a very important role in assessing soil health and its vitality, and it is also an important aspect of determining soil ecosystem services. Regarding its importance for crop growth, mitigating climate change, and ensuring the sustainability of agriculture, the maintenance of the SOC content in arable soils is of the highest priority. The SOC quantity and quality in the soil is adversely affected by environmental and edaphic conditions and human-caused activities as well [7]. Furthermore, crop residue management and fertilization, both organic and inorganic, have a significant impact on the soil fertility and crop yield [8,9,10]. The scientific concern about soil preservation strategies such as minimal/no-till agricultural activities and the insertion of organic and inorganic origin substances as well as plant aboveground biomass incorporation with the aim to improve SOC storage and natural soil productivity has risen over the past ten years [11,12,13,14]. Appropriate strategies for soil management, particularly sustainable fertilization, are urgently required to increase and maintain acid soils’ ability to store carbon, to improve the soil quality, and to mitigate climate change.

It has been determined by many scientists that fertilization is the most dependable method for raising the carbon storage potential, soil quality, crop grain, and biomass yields in intensively managed agricultural areas. The amount of carbon that can be stored depends on the type of fertilization [15,16,17]. Long-term scientific research has proven that organic fertilization is one of the main factors determining a higher concentration of SOC, while inorganic fertilization can result in unexpected outcomes [8,18,19]. Applications of mineral and organic fertilizers differ in their ability to improve the SOC: (i) considering that organic manure contains a high amount of organic matter, carbon could be incorporated directly; (ii) various organic matter inputs could improve the soil’s physical and chemical properties, which may increase the crop biomass and facilitate the addition of SOC through plant residues. Crop residues, green manure, and cattle manure are examples of organic resources that can be added to soil to improve its physiochemical status in a number of ways in addition to providing nutrients, by increasing the ion exchange capacity, the soil structure, the water storage capacity, the drainage, and the aeration [11,20,21,22]. One of the most important aspects is the selection of appropriate agricultural practices [23]; thus, agricultural land is capable of storing approximately 0.25–1.0 Mg C/ha yr⁻¹ [7]. Particularly in areas with a prevalence of acid soil characterized by low SOC content and low productivity, the choice of fertilizing type needs to be thoughtfully considered as it is one of the key barriers to efficient agricultural productivity. In such a scenario, combining organic–inorganic material, like farmyard manure with liming, can be a successful way to increase the availability of nutrients that limit the soil’s productivity and simultaneously enhance the soil structure and carbon storage. According to earlier research, different organic matter inputs ensure optimal soil aggregate properties and soil carbon pools’ characters, indicating its significance for enhancing SOC storage and resilience, simultaneously addressing the problems of emissions of greenhouse gases and soil deterioration [24,25].

The study hypothesizes that in naturally acidic soils, the content of the SOC decreases, and the carbon storage potential and chemical parameters’ status deteriorate. It is likely that incorporation of organic material and CaCO₃ affects the carbon accumulation and determines its transformation processes in the soil, determining the greater effect size and response to applied management systems. The following goals were accomplished by the current research: (1) analysis of the alterations in the SOC caused by the various organic matter inputs in Retisol; (2) estimation and comparison of the effect size of different organic inputs on the carbon storage potential and other chemical parameters in acid soil; (3) identification of an appropriate fertilization type that aids in SOC sequestration.

2. Materials and Methods

2.1. Experimental Site Characterization

The field experiment was executed at the Vezaiciai Branch, Institute of Agriculture, LAMMC (Figure 1). The study lasted for 9 years from 2011 to 2019. The experimental area was situated in western Lithuania. Cold and wet climatic conditions are typical for the experimental area, where the long-term mean of the annual air temperature is 11.4 °C and the long-term mean of the precipitation is 493.5 mm, which is always higher than the long-term mean of the evapotranspiration. The maritime climate has a significant impact on this area, while anthropogenic activities continuously promote the natural process of soil acidity. The study site’s soil was Bathygleyic Dystric Glossic Retisol according to the international soil classification system WRB 2015. When the experiment was first started (in 1959), the soil’s arable layer was 19–22 cm thick, and its pH _KCl ranged from 4.2 to 4.4. The soil was characterized by a moderate humus concentration (2.6–2.9%), a very low content of nutrients, a plant available phosphorus content of 0.05–0.06 g kg⁻¹, a plant available potassium of 0.13–0.18 g kg⁻¹, and carbonates had been identified at least two meters below the surface of the soil

2.2. Study Treatments

Cattle manure (CM) (60 t ha⁻¹) and various plant residues were used as organic amendments, incorporated naturally and limed with calcium carbonate (CaCO₃) Retisol with the intention of evaluating the impact of different organic amendments’ incorporation on the organic carbon storage and its sequestration potential. The research scheme consisted of the following treatments: (1) natural Retisol; (2) natural Retisol + CM; (3) natural Retisol + various plant residues; (4) calcium carbonate (CaCO₃) at a 1.0 rate every 5 years); (5) CaCO₃ + CM; (6) CaCO₃ + various plant residues. Each treatment underwent 3 replications in a randomized block design (4.25 m × 6 m plot).

In 1959 and 2005, two equally divided CM applications (80 and 120 t ha⁻¹) were implemented. After the experiment’s reconstruction in 2005, the applied CM dose was changed, and 60 t ha⁻¹ of cattle manure was added in a separate application, although the manure was not used in the treatments where the various plant residues were applied. The solid cattle manure used for fertilization was characterized by the following characteristics: dry matter—14.5%, organic matter—17.8%, N_total—0.4%, P₂O₅—0.3% K₂O—0.7%, Ca—2668 mg kg⁻¹, Mg—692 mg kg⁻¹, pH_KCl 8.5. Every year, with the exception of the year when spring barley with undersowing was cultivated, various plant residues as an organic amendment were used. Depending on the crops cultivated in the rotation, winter wheat straw, green masses of lupine–oats mixture, oilseed rape stubble, and perennial grasses were employed as alternatives to fertilizers. The average annual amount of plant residues added to the natural and calcium carbonate fertilized soil varied from wheat straw—3.13 and 3.45 t ha⁻¹ dry mass, green mass of lupine and oats—9.26 and 9.44 t ha⁻¹ dry mass, rape stubble and straw—3.85 and 4.82 t ha⁻¹ dry mass, to perennial grasses—6.08 and 7.18 t ha⁻¹ dry mass.

Calcium carbonate (CaCO₃) was incorporated in natural Retisol at a 1.0 rate (3.65 t ha⁻¹) every 5 years to keep the optimum pH_KCl (5.7–6.1). Mineral fertilizers were applied in a single dose to all treatments (background fertilization). When necessary, fungicides and insecticides were exploited; herbicides were not applied. The traditional tillage technique was employed. For 60 years, the natural Retisol was continuously enriched with various organic and inorganic amendments.

2.3. Chemical Analysis of Soil Samples

Every year from 2011 to 2019, in September, after the vegetation period, Retisol samples from different treatments were collected for conducting chemical analysis. A steel auger was used to collect the soil samples (n = 243) from three replicates of the 0–20 cm layer. After air-drying each sample, the visible plant remains and roots were physically excluded. Then, the soil was squashed and sifted through a 2 mm diameter sieve and homogeneously intermingled. For determination of the SOC content, the samples were sieved through a smaller diameter sieve than for general chemical properties and heated at a temperature of 105 °C to a constant weight for 16 h.

The chemical soil characteristics were determined at the Chemical Research Laboratory of LAMMC. The following methods were applied for the determination of the soil chemical characteristics: soil pH—ISO 10390:2005; SOC—ISO 10694:1995; soil total nitrogen (N_total)—Kjeldahl method; mobile aluminum—ISO 14254:2018, and plant-available phosphorus (P₂O₅), as well as potassium (K₂O)—Egner–Riehm–Domingo (A-L) method.

2.4. Data Analysis

The calculation of the annual change in the organic carbon amount (AC) during the investigation under various organic matter inputs was conducted using the formula below:

$$AC=\frac{{SOC}_t-{SOC}_0}{t},$$

(1)

where SOC₀ and SOC_t are the initial and final SOC amounts determined in the first and last years of the study, respectively; t is the length of investigation.

The relative annual change in the SOC content (RAC) was quantified by subtracting the annual change of the SOC amount in natural Retisol (CK) from that under different organic amendments’ application (TR) during the investigation period to ascertain the precise impacts of the various organic matter inputs on the carbon accumulation.

$$RAC=\frac{{\left({SOC}_t-{SOC}_0\right)}_{\mathit{TR}}-{\left({SOC}_t-{SOC}_0\right)}_{\mathit{CK}}}{t}$$

(2)

The average relative annual change rate of the SOC (Y) based on various organic matter inputs was computed, applying the following formula:

$$Y=\frac{{\left({SOC}_t-{SOC}_0\right)}_{\mathrm{TR}}-{\left({SOC}_t-{SOC}_0\right)}_{\mathrm{CK}}}{{\left({SOC}_0\right)}_{\mathrm{TR}}\times t}\times 100\%.$$

(3)

When evaluating the potential for carbon sequestration under various soil management techniques, the length of time of the carbon storage and sequestration could serve as an indicator:

SP = density × RAC × depth × 0.1.

(4)

We estimated the response ratio (RR) in the attempt to assess the effect size as a consequence of the applied agricultural practices on the organic carbon amount and other general physicochemical characteristics. A favorable effect is indicated by an RR > 0 and a negative effect by an RR 0. The natural log of RR was employed for estimating the effect size [26]:

$$RR=\mathrm{l}\mathrm{n}\left(\frac{Y_t}{Y_c}\right),$$

(5)

where Yt is the average amount of SOC or other soil characteristics after the incorporation of various organic amendments, and Yc is the average amount of organic carbon or other soil parameters for the natural Retisol.

For simplicity, RR was converted to the percent change:

$$Percent change=\left(e^{RR}-1\right)\times 100\%.$$

(6)

2.5. Statistical Analysis

The SAS Enterprise package’s ANOVA computer program was used to perform the statistical investigation. A one-way analysis of variance was used to estimate the differences in the tested parameters among the treatments and reported as the mean ± standard error of the mean. The least significant difference method (LSD) at the 5% probability levels was used to test the significance of the differences between treatment means.

3. Results and Discussion

3.1. Changes in the Retisol Chemical Characteristics under Various Organic Matter Inputs

The main chemical constraint on the soil’s fertility and agricultural productivity is soil acidity. Due to nutrient deficiencies, a lack of essential elements, and the toxicity of aluminum and manganese, plants growing in natural Retisol characterized by high acidity are ingested. Because of the weak roots’ low water and nutrient uptake, crops grown in natural Retisol have restricted access to water and nutrients, which reduces the plants’ development and production. In this case, the evaluation of the soil’s chemical characteristics and acid soil conditions under different fertilization techniques is very important.

In this study, the tendency of the soil acidity to decline was identified after the incorporation of CM and alternative organic fertilizers (

Table 1. Effect of the various organic matter inputs on the Retisol chemical characteristics (mean ± standard deviation), 2011–2019 data.

Treatments	Natural Retisol	Natural Retisol + CM	Natural Retisol + PR	CaCO3 at 1.0 Rate	CaCO3 + CM	CaCO3 + PR
pHKCl	4.02 ± 0.021 a	4.38 ± 0.004 c	4.17 ± 0.110 b	5.61 ± 0.003 d	5.73 ± 0.015 e	5.68 ± 0.036 e
Al3+, mg kg−1	80.48 ± 2.451 c	13.25 ± 3.698 a	45.36 ± 1.758 c	0 d	0 d	0 d
P2O4, mg kg−1	182.4 ± 8.96 ab	222.5 ± 9.01 c	196.6 ± 10.36 a	157.4 ± 7.45 d	229.7 ± 12.04 c	180.8 ± 8.89 b
K2O, mg kg−1	111.4 ± 2.58 b	117.8 ± 1.46 d	120.9 ± 2.25 b	78.7 ± 7.28 c	114.8 ± 6.36 bd	90.4 ± 4.58 a
Ntotal, %	0.129 ± 0.2674 a	0.151 ± 0.0458 d	0.141 ± 0.1598 c	0.137 ± 0.0389 b	0.149 ± 0.3663 e	0.141 ± 0.1452 c
Exchangeable Ca, mg kg−1	172 ± 14.5 c	649 ± 22.7 a	460 ± 36.7 e	1213 ± 33.9 b	1313 ± 26.7 d	1347 ± 12.8 f
Exchangeable Mg, mg kg−1	67.7 ± 0.58 b	68.3 ± 0.69 b	62.3 ± 1.45 a	88.0 ± 2.45 d	107 ± 3.36 e	113 ± 1.14 c

Note: CM—cattle manure (60 t ha ⁻¹), PR—incorporated plant residues. Letters a–f indicate data that differ significantly at the 5% probability level.

). Incorporating organic fertilizer into the soil had a noticeable effect in all study treatments and increased the soil pH_KCl. In comparison to the unlimed soil, the application of CM and other organic fertilizers to limed soil showed the greatest decrease in acidity (the soil acidity decreased by 2.02 and 1.97 pH units, accordingly). It is proven that spreading CM causes a significant rise in the total quantity of compounds made up of organic matter, enhances the base saturation, and improves the soil structure, which may be an explanation for the change in the soil pH. The content of Al³⁺ in the natural Retisol was 80.48 mg kg¹. The concentration of mobile aluminum decreased in conjunction with the reduction in soil acidity from 4.02 to 5.73. The incorporation of organic fertilizers could supply more nutrients for crops as well as carbon, and the effects of adding manure could persist for years while providing crops with the nutrients that are required for optimal growth [27]. Based on the consequences of various organic matter material inputs and changes in the nutritional demands of plants, plant available phosphorus and potassium significantly increased only in the treatments where CM was applied. This may have occurred as a result of the deposition of undissolved Ca₃(PO₄)₂, which may reduce the availability of P and K in the soil with an increase in the pH and a decrease in the Al³⁺ levels. The amount of total nitrogen also significantly increased after organic fertilizers were applied to the acid and limed soil. These findings are in accordance with Wasak and Drewnik’s [28] findings, which stated that the use of organic fertilizers enhanced the nutrient bioavailability to plants and microorganisms.

The amounts of exchangeable calcium and magnesium differed substantially between the treatments, which were supplied with organic amendments and those that were not. As stated by scientists [29,30,31], organic matter incorporation into the soil enhances the exchangeable Ca and Mg amount. In the opinion of these scientists, applying fertilizer to acid soils increases the content of the exchangeable bases while decreasing some micronutrients (Fe, Zn). These statements are in accordance with our data, where the content of exchangeable Ca and Mg in treatments fertilized with organic matter increased approximately six times compared to natural Retisol.

3.2. Effect of Various Organic Matter Inputs on the SOC Changes

Carbon sequestration has been acknowledged as a crucial study area in order to prevent emitting greenhouse gases and reduce the impact on the environment. Various organic matter inputs unequally affect the SOC storage in soil, and mineral and organic fertilization have varying degrees of carbon storage. The increase in soil carbon is caused by a variety of processes, involving improved litter restitution caused by rhizodeposition and enhanced grass productivity, a decrease in carbon loss due to mineralization and respiration, and the direct input of carbon via organic fertilization. Thus, it is crucial to comprehend the mechanisms underlying the carbon dynamics across a variety of applied techniques in order to assess the global biosphere’s carbon pool, reduce the impact of human activities, and enhance future climatic scenarios more accurately [17,32].

The data displayed in Figure 2 illustrate how different organic matter inputs influence the SOC content in naturally acidic Retisol. The lowest amount of SOC was determined in naturally acidic Retisol. This may most probably be explained by the absence of organic substrates triggering the activity of the microbial communities due to the lack of energy and nutrients. As expected, the continuous incorporation of organic origin amendments significantly affected the carbon storage in acid Retisol. The treatments where CM and various plant residues in natural Retisol were applied showed a significant increase in SOC content, but the highest storage potential of carbon was determined to be in the treatment where CaCO₃ and CM were incorporated compared to the naturally acidic Retisol (SOC—1.57%), which allowed storing up to 0.2–0.6% more carbon in the topsoil.

According to Fujisaki et al. [16], the primary driver of the SOC content is the direct C input into the soil. These statements are in line with our findings, where the highest SOC content was determined to be in the fertilized treatments. However, as reported by Chen et al. [33], the total SOC content remained constant after the incorporation of organic fertilizers. These findings suggest that a number of variables, including the period of the experiment and the type of soil, tillage, and fertilizer used, could influence how the SOC responds to management. A significant increase in the SOC content by the application of organic matter inputs in combination with calcium carbonate (CaCO₃) has already been reported by other researchers [34,35,36]. Comparing the mineral fertilizers with applying manure, the total SOC increased at the maximum rate. Only the calcium carbonate application into the soil speeded up the breakdown of the organic molecules and boosted the soil microbiological activity and nitrogen release. The elevated soil pH in the soils treated with the CaCO₃ could increase the soil microbial community, which might have led to changes in the type of the soil enzymes responsible for soil organic matter breakdown, thus leading to a loss of SOC. In this study, the significant SOC content increase was quantified in Retisol where the application of calcium carbonate (CaCO₃) at a 1.0 rate was applied. Other researchers also pointed out this regularity; however, in-depth investigation revealed that the accumulated SOC was composed of easily degradable SOC compounds [37,38].

The results of our study displayed an overall increase in carbon storage after nine years of fertilization (Figure 3). The carbon content in the natural Retisol was enhanced from its baseline value of 0.9% in 1959 to 2.17% after 60 years of fertilization. After incorporating plant residues in combination with CaCO₃, exactly the same levels of carbon (1.93%) were identified.

The SOC increased in all the investigated organic matter inputs’ approaches, excluding the natural Retisol, where the SOC content decreased by 0.03% after nine years of the experiment. These results show that the incorporation of calcium carbonate (CaCO₃) at a 1.0 rate raised the soil pH, thus facilitating the bacterial mineralization of both the fresh and old organic matter. According to Dumale et al. [39], adding CaCO₃ to light clay soils with less than 20% clay concentration can enhance the SOC mineralization. On the other hand, these results show how important it is to consider all the soil parameters without isolating specific properties when trying to model the soil carbon cycle.

The greatest storage potential of carbon was determined in the CM-fertilized treatments. In these treatments, the SOC increased by 0.13% and 0.3%, respectively. Other authors [40,41], who reported that manure applications could improve the SOC and soil nutrients over long-term fertilization, support these findings. Manure application might provide additional nutrients in addition to carbon for crop absorption. After many years, the manure application’s residual effect may become apparent, increasing the SOC and nutrient availability. For soils with a low SOC content, as prevalent in Lithuania, straw as an alternative organic fertilizer could be an appropriate measure for increasing the SOC accumulation and improving the soil quality [42]. Our findings indicated that the incorporation of plant residues generally had a less significant impact on the carbon storage in Retisol. The amount of carbon after the incorporation of plant residues increased by 0.09–0.15% during the period from 2011 to 2019 (Figure 3), and this increase was two times lower than the CM application. The reason for this is that plant residues are mainly formed from nitrogen-containing compounds that might accelerate the decomposition processes, contrary to the CM application [42,43].

3.3. Estimation of the Effects of Various Organic Matter Inputs on the Carbon Transformation Processes

To determine the efficacy of various organic matter inputs in order to select a highly efficient combination to increase the SOC storage in natural Retisol, meta-analysis is a useful statistical approach. According to the analysis of the relative annual change (RAC), continuously different organic amendments’ incorporation in natural Retisol demonstrated a significant ability to sequester SOC (Figure 4).

The RAC in the SOC ranged from a decrease of 0.59 g kg⁻¹ of carbon to an increase of 0.83 g kg⁻¹ of carbon each year. The results obtained by our research were also confirmed by studies conducted by other foreign scientists, who also investigated the effect of various origin amendments incorporation on SOC transformation processes [44,45]. The results that were achieved can be clarified through the following facts: the input of various types of organic matter promoted the fixation of particulate organic carbon in newly formed microaggregates, which were characterized by greater stability [46]. The results obtained from the long-term experiment indicated that the application of plant residues to the natural Retisol had a detrimental effect (−0.59 g kg⁻¹ loss of C every year). This negative balance of organic carbon accumulation could be influenced by the chemical structure of the employed plant residues, most of which consist of nitrogenous compounds. These compounds are quickly mineralized in the soil, as a result of which humus accumulates more slowly. The negative balance of organic carbon accumulation could also be caused by the lack of nutrients in this study treatment, which led to the mineralization of organic matter.

The same trends were found in the evaluation of the mean difference carbon sequestration rate (Figure 5).

The mean difference in the SOC change rate values was not calculated for natural Retisol, as no agro-techniques were applied. The positive values of the mean difference in the carbon sequestration rate indicate an increase in the amount of organic carbon after the applied agricultural measures, and negative values indicate a decrease in the amount of organic carbon. The lowest amount of carbon was accumulated in the natural Retisol, where plant residues were incorporated. In this treatment, negative values of the mean difference in the SOC change rate were obtained. This means that approximately 0.08 g kg⁻¹ C per year was lost in this study treatment. These results might be explained by an enhanced breakdown of organic compounds after the inclusion of organic material that is quickly decomposable to soil [47]. The largest content of SOC was accumulated in the soil after the incorporation of calcium carbonate and cattle manure (0.14 g kg⁻¹ C per year). This finding could be clarified through a higher input of organic matter with a higher amount of lignin during CM fertilization, which would lead to a higher accumulation rate per unit of C input.

It is important to note that the application of CM encouraged a considerable increase in the sequestrated carbon. For particular applied agro-techniques, the duration of carbon sequestration can be used as an indicator to calculate the C sequestration potential (g kg⁻¹). Most of the research conducted abroad has shown that the highest carbon sequestration potential can be achieved by adding organic fertilizers into the soil. These measures not only increase the SOC content but also promote carbon sequestration from the atmosphere [48,49]. The data obtained in our study support these findings (Figure 6). The highest C sequestration potential (0.42 g kg⁻¹) was determined in Retisol after the incorporation of CaCO₃ in combination with CM. Similar results have been obtained by other scientists, where the organic carbon sequestration potential varied between 0.32 and 0.41 g kg⁻¹ when adding manure to the soil [50,51]. These data can be explained through the possibility that applying CM along with calcium carbonate might change the soil’s aggregate structure, in the same way as the composition of the SOC.

Negative values of the carbon sequestration potential (−0.19 g kg⁻¹) were obtained in natural Retisol with the addition of plant residues. Similar results were revealed by other authors, who found that incorporation of plant residues could slow down the carbon sequestration by accelerating the carbon decomposition and lowering the carbon retention effectiveness [52,53,54]. This may be due to the fact that the low-nutrient treatment had a lower microbial biomass, which in turn encouraged SOC decomposers [53].

3.4. Response Ratio of the Soil Properties to the Different Organic Matter Inputs

The storage of the SOC depends on a number of elements, including anthropogenic activity, geography, weather, and other environmental variables. Anthropogenic activities are under human control, which could be adopted by appropriate land-use approaches, such as different organic matter inputs to mitigate the impact of the environment. Human-caused soil management could cause the intensive SOC storage processes; however, more research is required to determine the type of fertilization that will most effectively encourage the development of sustainable soils.

The most widely used management technique for preserving or enhancing soil quality and SOC content is the use of organic amendments. According to our study, all the selected organic matter inputs significantly increased the SOC content with the mean effect size of 0.02–0.28, and the increase varied from 1.89% to 32.89% (Figure 7,

Table 2. Effect of the different organic matter inputs on the percent change of the mean effect size (RR) in Retisol, where: CM—cattle manure (60 t ha⁻¹), PR—incorporated plant residues.

Treatments	Natural Retisol + CM	Natural Retisol + PR	CaCO3 at 1.0 Rate	CaCO3 + CM	CaCO3 + PR
pHKCl	8.96	3.73	39.55	42.59	41.29
Al3+	−33.24	−23.92	−44.42	−47.13	−44.42
P2O4	21.98	7.79	−13.71	25.93	−0.88
K2O	5.75	8.53	−29.35	3.05	−18.85
Ntotal	17.05	9.30	6.20	15.50	9.30
Corg	24.94	1.89	10.09	32.89	5.26

). The highest increase in the SOC content was observed in the CM-fertilized treatment in both soil backgrounds, where the SOC increased by 24.94% in the natural Retisol and by 32.89% in the CaCO₃-applied soil.

Applied different organic matter inputs significantly increased the soil pH, N_total, and plant available phosphorus and potassium content, as compared to the initial values, and decreased the mobile aluminum content in all the study treatments. The decreasing tendency of the plant available phosphorus and potassium content was observed in Retisol, where the CaCO₃ was applied at a 1.0 rate, and in Retisol, where CaCO₃ in combination with plant residues were applied. In these treatments, the plant available phosphorus content decreased by 13.71% and 0.88%, respectively, and the plant available potassium decreased by 29.35% and 18.85%, respectively. This imbalance of nutrients in the soil is most likely caused by the absence of the C input in these treatments; it results in soil nutrients that are not adequately supplied being absorbed. The same tendencies were determined by calculating the mean effect size of these soil parameters.

The mean effect size of the SOC and the other investigated soil parameters was largest under the CM-fertilized soil in combination with calcium carbonate. This result showed that combining the addition of CaCO₃ with organic fertilizers into naturally acidic Retisol was a reasonably effective way to enhance the soil quality. This observation might certainly provide an explanation for how anthropogenic soil management, especially different organic matter inputs, changes the carbon storage and other soil characteristics in Retisol. In natural Retisol, where plant residues were added, the lowest mean size effect meanings were found of all the variables that were evaluated. This was probably due to the fact that plant residues cannot significantly raise the SOC levels without returning crop residue, as these actions may change the soil microbial activity, the microbial biomass C levels, and therefore the SOC content [55,56].

4. Conclusions

The outcome of this investigation revealed that the continuous application of organic matter as a soil amendment might elevate the SOC content in Lithuania’s acid soils and that organic fertilization in combination with the use of calcium carbonate can accumulate more SOC under long-term fertilization than only organic fertilization. Among the five fertilization treatments, the relative annual change in the SOC content under the cattle manure-fertilized soil in combination with the CaCO₃ was the most efficient. It was the most appropriate practice for Lithuanian acidic Retisol considering the SOC sequestration potential. The mean effect size of the SOC and the other investigated soil parameters was largest under the CM and calcium carbonate applied soil treatment. The obtained results showed that combining the use of calcium carbonate with organic matter inputs was a reasonably successful approach to enhance the soil quality. Overall, the analysis provided an in-depth quantitative evaluation of the impact of organic matter application as a soil amendment on carbon storage and other parameters, which could help to further understand the manner in which the SOC is affected by agricultural management practices and provide evidence in the direction of maintaining acid soil. Consequently, an appropriate use of organic fertilizers and liming is necessary for the sustained development of western Lithuania’s agriculture and a more beneficial path for the long-term sequestration of carbon in soil.