*Article* **The Effect of Pelletized Lime Kiln Dust Combined with Biomass Combustion Ash on Soil Properties and Plant Yield in a Three-Year Field Study**

**Donata Drapanauskaite˙ 1,2, Kristina Buneviˇciene˙ 1, Regina Repšiene˙ 1, Danute Karˇ ˙ causkiene˙ 1, Romas Mažeika <sup>1</sup> and Jonas Baltrusaitis 2,\***


**Abstract:** Extensive application of mineral fertilizers resulted in high soil acidity, which is one of the major problems for crop production and soil degradation. Industrial solid waste, such as lime kiln dust and wood ash, can be used as alternative liming materials to benefit sustainable agricultural development. In this work, pelletized lime kiln dust with and without wood ash was utilized as liming material and the results of the three-year field study were compared with conventional mineralbased liming materials. It was determined that pelletized lime kiln dust satisfies the requirements posed by the recent European Union regulations to qualify as liming materials. The application of 2000 kg/ha Ca equivalent pelletized lime kiln dust increased soil pHKCl by ~0.55 pH units. Moreover, pelletized lime kiln dust significantly increased spring wheat grain yields ranging from 33.6% to 40.4%, depending on the pellet size. The usage of these liming materials not only increased crop yield but also decreased heavy metal concentration in soil. Due to high alkalinity, carbonate content, easy handling, and the transportation of pelletized lime kiln dust with and without wood ash, the materials have the potential to be used in agriculture as liming materials to reduce soil acidification and increase crop productivity or be used as soil amendments.

**Keywords:** lime kiln dust; pellets; soil chemical properties

#### **1. Introduction**

High soil acidity is a significant problem impeding crop production and is associated with soil degradation globally. The total area of topsoils affected by soil acidity range from 3.78 to 3.95 billion ha [1]. While soil acidification is a natural process, it can be exacerbated by human factors, such as acid rain, leaching of nutrients, and human activities such as using acidic fertilizers or harvesting plant materials without returning them to the soil. The emerging cause of soil acidification due to nitrogen (N) fertilizers has been of increasing concern worldwide [2,3]. Ammonium salts strongly acidify soils through their nitrification [4]. In particular, acidification takes place when ammonia is converted to nitrites followed by nitrates that are then leached [5]. For example, in Chinese farmland areas, soil pH decreased by 0.3 pH units from 1981 to 2012 due to increased mineral fertilizer application, while a critical N fertilizer application amount of 200 kg/ha per year was also reached [6]. Soil acidification changes biodiversity and increases nutrient losses, such as potassium (K), sodium (Na), calcium (Ca), and magnesium (Mg), via leaching, thus reducing plant productivity and increasing greenhouse gas emissions [7]. Decreasing soil pH harms the productivity of many crops (barley, rapeseeds, clover, and sugar beet). For

**Citation:** Drapanauskaite, D.; ˙ Buneviˇciene, K.; Repšien ˙ e, R.; ˙ Karˇcauskiene, D.; Mažeika, R.; ˙ Baltrusaitis, J. The Effect of Pelletized Lime Kiln Dust Combined with Biomass Combustion Ash on Soil Properties and Plant Yield in a Three-Year Field Study. *Land* **2022**, *11*, 521. https://doi.org/10.3390/ land11040521

Academic Editors: Chiara Piccini, Rosa Francaviglia and Richard Cruse

Received: 14 February 2022 Accepted: 1 April 2022 Published: 4 April 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

most plants, the optimum soil pH ranges from 5.5 to 7.0. Additionally, soil pH affects the availability of nutrients and enhances the solubility of toxic metals causing nutrition imbalance in plants. Soil acidification was behind increased cadmium (Cd), lead (Pb), and zinc (Zn) levels, while manganese (Mn) and aluminum (Al) solubility can often reach a toxic level with decreasing soil pH [4]. Soil acidification not only affects the availability of nutrients but also soil physical properties.

Various bioclimatic zones are associated with certain soil formation pathways resulting from the decomposition of primary minerals and secondary mineral formation, as well as the formation of secondary complex organomineral compounds followed by their accumulation and transport [8]. Water-soluble Ca and Mg cations in the upper layers of these minerals can leach out into the watershed, resulting in overall soil acidification. In this manner, Ca- and Mg-rich soils across the globe in localities associated with high precipitation amounts become more acidic. These soils with a higher propensity to acidify are chiefly Retisols and Luvisols comprising carbonates within the 2-meter depth; hence, it is intrinsically prone to acidification due to temporal and environmental factors. Liming has been shown as one of the most economical methods of decreasing soil acidity. Liming improves soil structure, oxygen infiltration, and aeration [9,10]. It also enhances biological N fixation and the mineralization of phosphorus (P) and sulfur (S) [11–13]. Several studies have shown that liming remarkably decreased Cd mobility in soil and accumulation in plants [14,15]. The application of liming materials not only reduces the solubility of heavy metals but also enhances the availability of phosphorus to the plants [16,17]. Finally, increasing soil pH has a direct effect on N-related greenhouse gas emissions. Khaliq et al. showed that the application of dolomite and lime can reduce N2O emissions from the soil by 44% and 37%, respectively, in upland and 52% and 44%, respectively, in paddy soils [18]. Additionally, previous studies demonstrated that liming decreased N2O production under some conditions in fluvial soils [19]. To mitigate the acidification processes in soil, limestone and dolomite (CaMg(CO3)2)—widely available natural minerals—are often applied and utilized for the dual purpose of acidity neutralization as well as soil fertilization [20]. Furthermore, other liming materials include those comprised of Ca- and Mg-containing oxides, hydroxides, carbonates, and even silicates [21,22]. Lime industry processing waste, such as lime kiln dust (LKD), has recently been proposed as a potential liming material to improve acid soil quality since it contains large amounts of calcium (Ca) and magnesium (Mg) [23]. Much less work has been carried out on comparing actual soil property enhancement when utilizing LKD in field experiments in comparison with different types of natural minerals on spring barley or spring wheat growth properties. This is particularly important since the granulation of powders is critical in economically and efficiently converting and transporting them into usable and recyclable raw materials [24–26]. Pelletization provides the benefits of slower nutrient release and the ease of handling these bulk materials. In particular, pelletization alleviates various problems associated with dust handling during transport and field applications. In particular, there are very few examples of compacted, granulated, and pelletized lime kiln dust [27] and biomass ash [28–30]. Sell and Fischbach described the pelletization of the cement kiln dust with the resulting pellets returned to the clinker-making process [31]. Yliniemi et al. granulated peat-wood ash using potassium silicate and sodium aluminate to produce lightweight aggregates suitable to use in civil engineering or lightweight concrete [32]. Other researchers granulated bioenergy production waste (fly ash and biochar) with organic-rich lake sediments for the sustainable reuse of waste materials and the possibility to use granules in agriculture [33].

Understanding whether the benefits of traditional soil liming materials, as well as those from industrial waste, originate due to the improvement in soil pH, increased Ca availability, or enhancement in soil structure is of great concern. Since approximately 51.0% of Eastern Lithuanian and 66.0% of Western Lithuanian agricultural land have soil pH values less than or equal to 5.5, fertilizer use in these acid soils is inefficient. The purpose of this study was to investigate the effects of recovered waste from lime processing plants as soil liming materials on soil properties and crop yield. In particular, pelletized LKD with and without biomass ash were utilized and their liming properties were compared to those of natural minerals, such as ground chalk and crushed dolomite.

#### **2. Materials and Methods**

#### *2.1. Materials and Reagents*

Liming materials after anthropogenic processing were obtained from industrial manufacturers in Lithuania. Specifically, ground chalk was obtained from *JSC Baltijos Klintis*, Lithuania while crushed dolomite from *SC Dolomitas*, Lithuania. LKD was obtained from *JSC Naujasis Kalcitas*, Naujoji Akmene, Lithuania, while the pelletization of LKD powders into several fractions (namely 0.1–2, 2–5, and 5–8 mm) was performed by *JSC Mortar Akmene*. PLKDWA was also obtained from *JSC Mortar Akmene* using lime kiln dust (LKD) and wood ash (WA), and pellet sizes vary from 2 to 5 mm.

These samples were stored in plastic containers. All chemicals for chemical analysis were obtained of reagent grade from Fischer Sci and used as received. Double distilled water was used in all experiments. All liming materials are summarized in Table 1.


**Table 1.** Sample description.

An evaluation of the chemical composition of the liming materials was performed. The samples were ground, and the elements were extracted using aqua regia and analyzed with Perkin Elmer Optima 2100 DV ICP-OES spectrometer. Atomic Absorption Spectroscopy (AAS) was used to find the concentration of Al, Fe, Ca, and Mg. The amount of Si was found using a gravimetric method.

The neutralizing value of liming materials was determined by treating a sample with 0.5 N HCl heated for 10 min and later potentiometrically titrated with 0.25 N NaOH u pH reached 7.0 for 1 min. The neutralizing value was estimated as follows:

$$N\_V = \frac{0.014 \times (V\_1 - 0.5 \times V\_2) \times 100}{m} \tag{1}$$

where *NV*—Neutralizing value (%);

*V*1—the volume HCl (mL);

*V*2—the volume NaOH (mL);

*m*—sample mass (g).

Reactivity was determined by treating the sample with water and quickly potentiometrically titrating with 5.0 N HCl until pH reached 2.0, and titration was finished after 10 min keeping pH 2.0. The reactivity was estimated as follows:

$$
\tau\_{ac} = \frac{c\_{HCl} \times 14.02 \times 100}{m \times N\_V} \tag{2}
$$

where *rac*—reactivity (%);

*CHCl*—the volume of 5.0 N HCl (mL);

*NV*—neutralizing value of liming material (%);

*m*—sample mass (g).

Water content was determined gravimetrically according to the standard LST EN 12048:2003.

#### *2.2. Field Experiments*

Field experiments were conducted from 2017 to 2019 at the Lithuanian Research Centre for Agriculture and Forestry Vezaiciai Branch, West Lithuania, on naturally acidic moraine loamy soil (*Bathygleyic Distric Glossic Retisol*) [34]. The agrochemical characteristics of the upper soil layer were as follows: pHKCl—5.06 ± 0.541; soluble Ca—899 ± 30.0 mg/kg; soluble Mg—127 ± 3.9 mg/kg; soluble K2O—199 ± 4.6 mg/kg; soluble P2O5—164 ± 7.1 mg/kg; soluble Al—24.4 ± 14.07 mg/kg.

The field trial was set up in a randomized design with four replicates. The following experimental design was used. Namely, (1) control (without liming material), (2) 2000 kg Ca/ha ground chalk, (3) 2000 kg Ca/ha crushed dolomite, (4) 2000 kg Ca/ha pelletized lime kiln dust outer diameter (OD) 0.1–2 mm, (5) 2000 kg Ca/ha pelletized lime kiln dust OD 2–5 mm, and (6) 2000 kg Ca/ha pelletized lime kiln dust-wood ash OD 2–5 mm. The experimental plot size was 48 m<sup>2</sup> (12 × 4 m). The experimental site was limed (except for the control treatment) with liming materials in May 2017 before planting the seeds. The liming rate (2000 kg Ca/ha) was calculated using the amount of active element Ca in liming materials. Mineral fertilizers were added every year before sowing. The mineral fertilizer application rate for spring barley and spring wheat was 60 kg/ha N, 60 kg/ha P2O5, and 60 kg/ha K2O before sowing and 60 kg/ha N at the bushing stage of spring barley and wheat. The mineral fertilizer application rate for pea was 20 kg/ha N, 40 kg/ha P2O5, and 60 kg/ha K2O. On the day of sowing, the pea seeds were coated with bacterial product Rizogen and sown immediately. Liming materials and fertilizers were applied manually, e.g., spread by hand on the soil's surface and incorporated into the soil by the cultivator. Spring barley cv. *'Louke A'* was grown in 2017, spring wheat cv. *'Granary'* was grown in 2018, and peas cv. *'Respect'* was grown in 2019.

#### *2.3. Soil and Plant Sampling and Chemical Analyses*

Soil samples for agrochemical analysis (pHKCl, soluble P2O5, soluble K2O, soluble Ca, soluble Mg, soluble Al, and total heavy metals) were collected from 0 to 20 cm depth of the topsoil layer. The sample for chemical analyses was collected from 10 to 15 spots via a "W" shaped pattern across the sampling area. Soil samples were taken from four replicates of each treatment every year during the spring and fall after harvest. Soil soluble K2O, P2O5, Ca, and Mg were determined according to the Egner–Riehm–Domingo (A-L) method [35]. Soil soluble K2O, P2O5, Ca, and Mg were extracted using a 1:20 (wt/vol) soil suspension of ammonium lactate–acetic acid extractant (pH = 3.7). The suspension was shaken for 4 h. Soluble P2O5 was determined in the extract using ammonium molybdate via the spectrometric method with a Shimadzu UV 1800 spectrophotometer, while soluble K2O was determined using flame emission spectroscopy with a JENWAY PFP7 flame photometer; soluble Ca and soluble Mg were determined using atomic absorption spectrometer AAnalyst 200. Soil soluble Al was determined by the Sokolov method [36] via extraction from 1:2.5 (wt/vol) soil suspension in the 1 M KCl, shaken for 1 h, and later measured using the titrimetric method.

The determination of soil pH was performed using a 1:5 (vol/vol) soil suspension in the 1 M KCl. The mixture was shaken for 60 min and left to sit for 1 h. The pH of the suspension was measured at 20 ± 2 ◦C stirring with a pH meter.

The heavy metal (Cd, Cr, Ni, and Pb) content in soil was determined by extraction in aqua regia and analyzed with a Perkin Elmer Optima 2100 DV ICP-OES spectrometer and AAnalyst 200 AAS spectrometer. Heavy metals in soil were determined according to ISO 11466:1995, ISO 11047:1998, and ISO 22036:2008: Soil pH-ISO 10390:2005.

The crops were harvested at full maturity. Barley, wheat grain, and peas seeds properties were determined as follows: grain/seed yield (t/ha, calculated on a 14% grain/seeds moisture basis), grain/seeds number per spike/pod, and 1000 grain/seed weight (g). The thousand grain/seed weight was determined using an automatic seed counter.

#### *2.4. Meteorological Conditions*

The data presented in Figure 1 for the study period from 2017 to 2019 suggest differences in weather conditions relative to the standard climate norm (SCN). Averaged across the growing seasons, the air temperature was higher in the 2018 and 2019 years of the study compared to SCN (4.0 ◦C in May 2018 1.8 ◦C in June 2018, 2.1 ◦C in July 2018, 2.6 ◦C in August 2018 and 4.6 ◦C in June 2019, and 1.2 ◦C in August 2019). However, total precipitation during the plant growing seasons showed significant variations, especially during May 2017, when a 41.9 mm decrease in total precipitation compared to SCN was reported, and during the May 2019 growing season, when the total precipitation increased by 30.0 mm compared to the standard climate norm. In summary, for temperature and precipitation regimes, the weather conditions in 2017 were cool and wet; in 2018 and 2019, the conditions were warm and dry.

**Figure 1.** Mean monthly air temperature (◦C) and precipitation (mm), according to the meteorological data from the Lithuanian Hydrometeorological Service under the Ministry of Environmental.

#### *2.5. Statistical Analysis*

A one-way analysis of variance was used to compare the soil characteristics and crop yield before and after soil liming. Means were compared using Fisher's least significant difference test at *p* ≤ 0.05 and *p* ≤ 0.01 and Duncan's multiple range test at *p* ≤ 0.01. The statistical software package SAS [37] was used for analysis.

#### **3. Results and Discussion**

#### *3.1. Chemical Composition of Liming Materials*

Table 2 shows the physical properties of liming materials used in these field studies. Pelletized lime kiln dust (PLKD) alone and with wood ash was of highly alkaline pH (12.8– 12.9) when compared to natural liming materials (GC and CD), which were less alkaline with a pH of 8.9 and 9.3, respectively. The water content in PLKD and PLKDWA varied from 11.9% to 6.36%, while in natural liming materials CD and GC, it varied from 9.3% to 8.9%. Water in the pelletization process was used as a binder, while pellets were dried afterward at 25 ◦C for 48 h. The neutralizing value measures the ability of the liming materials to reduce acidity, while reactivity indicates the rate of liming material to reduce the acidity of the soil. Ho¸sten and Gülsün showed that particle size and the dolomite content in the limestones were the most influential parameters in the reactivity of limestones [38]. According to

EU Regulation 2019/1009 for liming materials [39], the minimum reactivity (based on the hydrochloric acid test) cannot be less than 10% or neutralizing value (equivalent CaO) less than 15. As observed in Table 2, pelletized lime kiln dust (PLKD 0.1–2, PLKD 2–5, and PLKDWA 2–5) meets these requirements. The pellet strength may have a strong effect on the reactivity of granulated liming materials. PLKDWA 2–5 pellets were the hardest (51 ± 13.1 N/pellet), while PLKD 0.1–2 pellets were the weakest (18 ± 7.5 N/pellet). Effectively, pelletized liming materials can be hypothesized to contain different liming properties due to the more controlled release of nutrients, as opposed to CD, GC, LKD, and WA, which were applied as powders.


**Table 2.** Physical properties of liming materials and pelletized LKD.

Note: Colored columns for the table represent parent materials, which were used for pelletized liming materials.

LKD chemical composition typically varies and depends on the source and the process of lime being processed [40]. The typical composition of LKD varies from 31 to 55% CaO, 0–26% of free lime, 1.7–9.9% SiO2, 0.7–4.1% Al2O3, 0.03–0.22% K2O, and 0.5–25% MgO [41]. Figure 2a shows the chemical composition of the main nutrients present as well as alumosilicates measured in liming materials. The liming materials chiefly comprised Ca-containing compounds, with Ca accounting for 20% to 41% by weight of the measured nutrients. Other major plant nutrients, such as Mg and K, did not contribute significantly to the overall composition in CD reaching up to ~10%. Fe is an important micronutrient in small amounts needed to sustain plant growth and reproduction [42]. Alkaline soil, however, binds Fe and causes plant iron deficiency as it is immobilized and unavailable for plants [43]. The concentration of heavy metals in liming materials is shown in Figure 2b. Low levels of Cd were obtained in GC, CD, and PLKD without WA. In PLKDWA, the amount of Cd was 2.63 ± 0.120 mg/kg, and it slightly exceeded the allowable limit of 2 mg/kg according to EU Regulation 2019/1009. The higher Cd content in PLKDWA was due to the high concentration of 5.21 ± 0.134 mg/kg Cd in wood ash. The highest concentration of Pb (25.8 ± 0.21 mg/kg) compared to other liming materials was found in CD but did not exceed the 120 mg/kg allowable limit. Ni and Cr contents in liming materials also did not exceed allowable limits. Summarily, this work showed that most of the heavy metals measured were detected within concentrations lower than those defined in the regulatory documents describing fertilizers as well as liming materials for soil use. Hence PLKD and PLKDWA can be utilized as a source of liming material.

**Figure 2.** (**a**) Main nutrients and alumosilicates measured comprising liming materials. (**b**) Heavy metal concentration in liming materials.

#### *3.2. Measured Soil Chemical Composition after the Liming Material Application*

Liming has been widely recommended to manage soil acidification and improve plant yield and soil agrochemical parameters. The available reports suggest that crop yield can be increased using liming due to the improvement in the resulting soil's physical, chemical, and biological properties [44–46]. The soil pHKCl in all experiments was ~5 before liming. The optimal soil pHKCl range needed for plant growth is provided in Figure 3 and is between 5.5 and 7 [47,48]. Table 3 shows the pHKCl values after liming.

**Figure 3.** Measured soil pH values of different liming material treatments.


**Table 3.** pHKCl values after 27 months of liming.

Note: different lowercase letters indicate a significant difference according to Duncan's multiple range test (DMRT *p* ≤ 0.05).

Our results shown in Figure 3 suggest that different liming materials did not have the same effect on the neutralization of soil pHKCl. The fastest and the highest increase in soil pHKCl was with applied ground chalk (GC). GC increased soil pHKCl from 5.08 to 6.15 after 4 months when applied at 2000 kg Ca/ha. However, after 27 months the pHKCl decreased to 5.75, possibly due to the leaching of Ca2+ ions from the soil due to the high amount of rainfall in 2017, as shown in Figure 1. In agreement, long-term research in soil sorption complex of forest soils showed that soil pHKCl decrease is related to H<sup>+</sup> increase and Ca2+ and Mg2+ ion decrease in soil sorption complex [49]. This is also supported by a strong positive correlation shown in Figure 5a (vide infra) between soluble Ca content in soil and soil pHKCl (r = 0.875). In general, the fastest soil pHKCl increase was observed when the milled GC was applied; the slowest was observed when the crushed CD was applied, while pelletized liming materials (PLKD 0.1–2; 2–5, PLKDWA 2–5) exhibited liming properties that were in between. Pelletized lime kiln dust (PLKD) 0.1–2 and pelletized lime kiln dust with wood ash (PLKDWA) 2–5 increased soil pH by ~0.5 after 3 years of liming. This corroborates the earlier studies on using ash as a liming material to increase soil pH [50,51]. Liming with 2000 kg Ca/ha of CD resulted in a very slightly statistically not significant increase in soil pHKCl. This can be explained by the much faster removal of calcium compounds present in GC than those in dolomite due to the increased reaction kinetics and complex surface-limited reactions [52]. The hydrated calcium compounds in LKD can release calcium faster when in contact with the soil when compared to limestone and result in an efficient pH change of the soil [53]. de Vargas in a long-term field experimental study determined calcitic lime exhibits much more facile soil neutralization properties when compared to dolomite [54].

Soluble Ca concentration in soil was measured four times during the three years. Soluble Ca content in soil was ~900 mg/kg in all treatments before liming. The concentration of soluble Ca in soil depends on carbonating layer depression depth, which is rich in Ca- and Mg-carbonates. In Western Lithuania, this layer is at 1.5–3.0 m depth. Liming significantly (*p* ≤ 0.01) increased soluble Ca content in the soil, as shown in Figure 4a. The application of PLKD 0.1–2 corresponding to 2000 kg Ca/ha increased soluble Ca concentration ~2.5 times more when compared to control after 4 months of liming. This is possible since the hydroxide amount in pelletized liming materials is higher, rendering it more reactive than calcium carbonate [55]. Moreover, PLKD 2–5 showed a statistically significant effect on soluble Ca content in the soil, but it was less than GC or PLKD 0.1–2. Liming with CD showed a statistically significant (*p* ≤ 0.01) increase in soluble Ca in the soil, but the increase was the smallest of all tested materials. After 3 years of liming, the highest content of soluble Ca in the soil of 1500 mg/kg was measured after liming with PLKDWA 2–5. Importantly, when comparing liming performance among the materials after 3 years of liming, PLKD 0.1–2, 2–5 and PLKDWA2–5 had a statistically significant (*p* ≤ 0.01) effect on soluble Ca, which was higher than that of CD. Ultimately, soluble Ca level was assessed as low before liming and after three years, different liming materials increased this from low to average [56]. To this extent, the results presented here for Lithuanian Retisol are in agreement with previous work where various liming material powders of natural and industrial origin, including

lime mud, carbide lime, wood ash, cement kiln dust, and natural calcitic and dolomitic lime, increased soil exchangeable Ca amount and enhanced microbial activity in soil [57,58]. Annually, soluble Ca from the soil is leached at about a rate of 200–300 kg/ha, which depends on the amount of rainfall, soil texture, the amount of CO2 produced from plant roots, and other factors [59]. Due to the high precipitation from September 2017 to February 2018 shown in Figure 1, a large decrease in soluble Ca was observed after 15 months of liming compared to 4 months after liming (Figure 4a). This suggests that the addition of Ca ions in acid soils with liming was necessary.

**Figure 4.** (**a**) Soluble Ca, (**b**) soluble Mg, (**c**) soluble P2O5, and (**d**) soluble K2O in the soil during the 3-year liming experiment. *Soluble* is defined as being available for plants. Lowercase letters indicate a significant difference according to Duncan's multiple range test (DMRT *p* ≤ 0.01).

Before liming, soluble Mg content in soil was low at around 130 mg/kg, as shown in Figure 4b. The largest increase in soluble Mg in the soil after liming was found with applied CD because it has the highest Mg content of 10.3%. However, liming with PLKD 0.1–2 and PLKDWA 2–5 also resulted in a statistically significant (*p* ≤ 0.01) increase in soluble Mg in the soil after 4 months and significant (*p* ≤ 0.01) after 15 months. Similar to Ca, after 27 months of liming with PLKD and PLKDWA 2–5, a statistically significant (*p* ≤ 0.01) increase in soluble Mg was observed when compared to GC. Notably, soluble Mg is best absorbed by plants when the ratio of soluble Ca and soluble Mg is 1:5–8. When CD was applied, this ratio was 1:6 and was suitable for plants to absorb the soluble Mg. For other liming materials, the ratio was higher than 1:8 and the absorption of soluble Mg was blocked by Ca ions due to the antagonistic competition between Ca2+ and Mg2+ ions for cation exchange sites [60].

In acidic soil where there is an abundance of soluble Al and Fe, any P forms insoluble Al and Fe orthophosphates [61]. Before the field experiments, the soluble P2O5 concentration in soil was ~165 mg/kg. The further analysis of soluble P2O5 in soil showed that without liming, the amount of soluble P2O5 decreased throughout the experiment, as shown in Figure 4c. Only the application of 2000 kg Ca/ha with CD did not have a significant effect on soil soluble P2O5 concentration. Liming with PLKDWA 2–5 and PLKD 2–5 significantly (*p* ≤ 0.01) increased soluble P2O5 content in soil compared to the control by 85 mg/kg and 71 mg/kg, respectively, after 4 months of application. Moreover, this soluble P2O5 increase was statistically significant (*p* ≤ 0.01) when compared to GC and CD, not only to the control. Comparing PLKD with natural liming materials (GC, CD) after 3 years of application, PLKD 2–5 and PLKDWA 2–5 had a statistically significant (*p* ≤ 0.01) effect on soluble P2O5 increase. An increase in soluble or available phosphorus amounts in acid soils after the application of liming materials was obtained in some other studies [44,62].

Measured soluble K2O in the soil is shown in Figure 4d. Soil soluble K2O varied from 194 mg/kg to 236 mg/kg before liming. After 4 months of liming with 2000 kg Ca/ha of PLKD 0.1–2 and PLKDWA 2–5, soil soluble K2O content increased statistically and significantly (*p* ≤ 0.01) by 26 mg/kg and 28 mg/kg, respectively. Additionally, application with PLKD 2–5, GC, and CD changed soil soluble K2O statistically and insignificantly. After 27 months of liming, the overall highest soluble K2O increase was observed in treatments with PLKD 0.1–2 and PLKDWA 2–5. For PLKDWA 2–5, these results may be related to the relatively high K2O concentration of 2.9%. K in wood ash may be soluble and available to plants, and previous studies showed that the application of wood ash can increase K content in the soil [50,63].

Soluble Al concentration in the soil before the liming experiments was high or very high and varied in a wide range from 17.1 mg/kg to 52.14 mg/kg. The average soluble Al concentration before the application of liming materials was 24.4 ± 14.07 mg/kg. For the control treatment with no liming, the soluble Al content in the soil after 27 months increased from 24.4 ± 14.07 mg/kg to 37.2 ± 18.97 mg/kg. After liming in treatments where pHKCl changed to 5.0 or higher, no soluble Al in soil was detected. Hence, liming reduced soluble Al content in the soil. Soluble Al concentrations were strongly affected by liming and exhibited a high negative nonlinear (polynomial) correlation with soil pHKCl, as shown in Figure 5b. Soluble Al has a toxic effect on plant roots. The roots become poorly developed and weak. When there is an excess of soluble Al in the soil, plants hardly absorb P, Ca, S, and other elements. The relationship between soluble P2O5 and soluble Al was also found in this work to be described with a negative polynomial curve (r = 0.836) (Figure 5c). Similarly for other soils, Mrvi´c et al. observed a strong negative (r = 0.952) non-linear correlation between exchangeable Al and soil pH values in Stagnosols [64]. Moreover, Moir and Moot's research showed similar results to the relationship between exchangeable plant-available Al and soil pH in Brown soils [65].

**Figure 5.** (**a**) Relationship between soluble Ca and pHKCl, (**b**) between soluble Al and pHKCl, and (**c**) between soluble P2O5 and soluble Al.

#### *3.3. Grain Yield and Yield-Related Parameters*

The effects of liming on grain yield improvement of crops in rotation are shown in Figure 6. In the first year, a statistically significant yield improvement was observed for spring barley in treatments with GC, PLKD 2–5, and PLKDWA 2–5. The biggest yield improvement of 10.4% and 9.9%, when compared to control, was obtained when liming with GC and PLKD 2–5, respectively. The highest statistically significant (*p* < 0.01) 1000th-grain mass of 54.4 ± 0.95 g was observed in the PLKD 2–5 treatment. However, liming with PLKD 0.1–2 did not improve spring barley yield. Grain yield was likely limited by the lower content of soil soluble P2O5 (Figure 4c) and pHKCl in PLKD 0.1–2 treatment, although soil soluble P2O5 content was very similar to that obtained with GC.

**Figure 6.** (**a**) The yield of spring barley, spring wheat and peas; (**b**) 1000-grain weight of spring barley, spring wheat and 1000-seed weight of peas. \* and \*\* indicate significant differences according to Fisher's least significant difference test. Statistically significant at \* *p* < 0.05 and \*\* *p* < 0.01 level.

The water deficit in 2017, shown in Figure 1, that occurred during barley booting could have influenced the number of grains per spike and spring barley grain yield. After 15 months of liming, a statistically significant (*p* < 0.01) spring wheat yield improvement, when compared to the control, was obtained in all treatments. However, the lowest statistically significant (*p* < 0.01) yield improvement of 21.9% of spring wheat was obtained in the treatment with CD while the smallest 1000th grain mass 42.9 ± 0.39 g was observed for the same treatment. The highest increase in spring wheat grain yield of 40.4% was obtained after liming with LKDWA. This result may be related to pH, which increases the availability of nutrients in the soil. Patterson et al. found that a 6 t/ha application of wood ash with nitrogen fertilizer increased barley and canola grain yield when compared to the control [66]. Moreover, other studies have shown an increase in oat biomass using pelletized wood ash [50] and an increase in oilseed productivity but a decrease in the quality of seed production [67]. In the third year of crop rotation, when the peas were grown, the liming increased yield for all treatments by about 4.5% compared to the control but the increase was not statistically significant. However, liming with CD was statistically significant (*p* < 0.01) for the reduced peas' 1000th seed mass.

Different crops exhibit significantly different tolerance to soil acidity and sensitivity to soil pH [20], as exhibited by various resulting properties such as plant height, plant density, germination, and reproductive performance [68,69]. The results of the number of plants per square meter are shown in Figure 7a. In 2017, when liming materials were applied, spring barley plants per square meter positively responded with CD (296 no. per m2) and PLKD 0.1–2 (299 no. per m2) compared to the control (283 no. per m2) treatment. The second-year after liming spring wheat plants per square meter negatively responded to all treatments compared with the control. The lowest number of wheat plants per m<sup>2</sup> were obtained in treatments with CD and PLKD 2–5. It may be due to the higher than usual amount of precipitation in 2017 Fall and Winter, which caused high nutrient losses from soil. Additionally, a lower amount of rainfall and higher air temperature compared to SCN in 2018 may have an influence. After three years of liming, in 2019, liming had a positive effect on pea plants per square meter. It may be related to the pH increase and soluble

Al decrease in the soil after liming, which favors root proliferation. In agreement, other researchers reported a positive response of wheat plants per square meter with other liming material applications [70,71].

**Figure 7.** (**a**) The number of plants per square meter of spring barley, spring wheat, and peas; (**b**) the spike length of spring barley, spring wheat, and plant length of peas; (**c**) the number of grains per spike of spring barley, spring wheat, and the number of seeds per pod and number of pods per plant of peas. \* and \*\* indicate significant differences according to Fisher's least significant difference test. Statistically significant at \* *p* < 0.05 and \*\* *p* < 0.01 level.

The corresponding data for the pea plant height, spring barley, and wheat spike length are shown in Figure 7b. Plant height can potentially be improved due to the effect of liming. Liming increases soil pH, which affects root proliferation and increases nutrient availability, which can contribute to plant height. The application of 2000 kg Ca/ha of GC and PLKDWA 2–5 had a statistically significant effect on pea plant height when compared to control. In particular, pea plants limed with GC and PLKDWA 2–5 were 5.2 cm and 3.6 cm higher, when compared to the control. Moges et al. also showed that the application of 4 and 6 t/ha of lime significantly increased plant height [72]. However, the application of CD and PLKD 0.1–2 reduced plant height by 3.8 cm and 4.7 cm when compared to the control. Spring barley spike length and the number of grains per spike (Figure 7c) were greater with GC and PLKD 2–5 treatments compared to the control. The application of PLKD 2–5 also increases spike length and the number of grains per spike for spring wheat. Spike length and number of grains per spike were only affected by various environmental factors to a small degree since they strongly depend on the genotype [73].

#### *3.4. Heavy Metals in the Soil*

Changes in heavy metal (Cd, Cr, Ni, and Pb) concentrations in the soil during the liming period are shown in Figure 8. The total Cd content in the soil before liming was 1.95 ± 0.140 mg/kg (Figure 8a). According to The EU Commission Council Directive 86/278/EEC [74], the Cd content in the soil before liming does not reach the maximum allowable limit. After 15 months of application of liming materials, the total Cd content in soil was reduced 3 times from 0.45 ± 0.140 mg/kg to 0.14 ± 0.013 mg/kg. Cd concentration in the control treatment (unlimed) increased 1.3 times in 27 months, from 0.43 ± 0.035 mg/kg to 0.55 ± 0.040 mg/kg. Cd content after liming decreased because liming neutralized H+ ions and reduced Cd bioavailability. Additionally, pH change can increase negative surface charge, which in turn could result in Cd adsorption and precipitation as Cd carbonates, reactions to Cd(OH)2, and the reduction of Cd2+ to Cd0. Cd content in unlimed soil–control increased due to the pH decrease, which may increase the enhanced solubility and mobility of cadmium in soil. Ramtahal et al. field and laboratory studies showed that liming reduced bioavailable Cd in soil and Cacoa beans [75]. Shaheen and Rinklebe used different low-cost alternative amendments to show that the application of cement kiln dust decreased soluble and exchangeable Cd content in the soil [76]. Total Cr content before the application of liming materials ranged from 9.77 mg/kg to 10.4 mg/kg and averaged at 10.1 ± 0.26 mg/kg (Figure 8b). The application of natural liming materials (GC and CD) slightly reduced Cr amounts in the soil while PLKD 0.1–2, PLKD 2–5, and PLKDWA 2–5 increased Cr content. In general, the amount of Cr in the soil can vary depending on the heterogeneity of soil and fertilization, and mineral fertilizers (especially phosphorus) can increase it. After 27 months of liming, the amount of Cr in soil increased 55% in the control treatment and 52% in the limed treatment with PLKDWA 2–5, while the smallest increase was obtained when limed with PLKD 0.1–2. This is due to H<sup>+</sup> competition for binding sites enhancing metal release from the soil matrix.

For GC and CD, the Cr content reduced after 4 months, while after 27 months, the amount increased by 31% and 36%, which is consistent with the change in soil pH values shown in Figure 3. Liming had a significant effect on reducing total lead (Pb) and total nickel (Ni) concentrations in soil (Figure 8c,d). The application of liming materials after 27 months reduced total Ni and total Pb amounts in soil by 1.5 as well as 1.3 times compared to untreated soil. Ni availability in the soil was reduced by increasing base-cation saturation, which consequently raises the soil's pH. Moreover, Ni solubility decreases when soil pH increases. Shaheen et al. showed that cement kiln dust and limestone decreased the watersoluble and soluble contents with exchangeable Ni concentration in the soil as a result of an increase in the sorbed and bound carbonate fraction [77]. Total heavy metal concentration in soil depends on the nature of the soil, its organic matter concentration, texture, and depth. As a consequence of adsorption of soil organic matter or atmospheric deposition, the highest concentration of some elements, such as Cd and Pb, are found on the soil's surface; for other elements (Ni, Fe, and V) that are associated with clays and hydrous oxides, they are concentrated in lower soil depths [78]. Liming changes not only the chemical properties of soil but also the morphological features, thus altering the size distribution of clay and silt with the soil's profile. Soil pH also has a direct effect on the availability of heavy metals

by affecting their solubility and capacity to form chelates. An increase in soil pH after liming causes an increase in cation adsorption onto soil particles [79]. Tlustoš et al. pot and Rhizobox experimental results also showed that liming reduces 50% Cd, 20% Pb, and 80% of Zn and is effective for the immobilization of Cd, Pb, and Zn [80]. The efficiency of PLKD and PLKDWA in decreasing the mobilization of heavy metals may be explained by their high alkalinity and carbonate content, surface area, and oxide contents. The metals might decrease due to sorption and precipitation reactions.

**Figure 8.** (**a**) Total Cd, (**b**) Cr, (**c**) Pb, and (**d**) Ni concentrations in the soil during the liming experiment. Regulatory limit values according to the EU Commission [74] standards are also shown.

#### **4. Conclusions**


**Author Contributions:** Conceptualization, K.B., R.R., D.K. and D.D.; methodology, R.M. and R.R., investigation, D.D.; data Curation, R.M., D.D. and D.K.; writing—original draft preparation, D.D. and. J.B.; writing—review and editing, D.D. and J.B.; visualization, D.D. and K.B.; supervision, J.B. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work is supported by Engineering for Agricultural Production Systems program, grant no. 2020-67022-31144 from the USDA National Institute of Food and Agriculture, and by the long-term research program 'Productivity and sustainability of agricultural and forest soils' supported by the Lithuanian Research Centre for Agriculture and Forestry.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Data are contained within the article.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**

