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Article

Fertilisation Potential of Combined Use of Wood Biomass Ash and Digestate in Maize Cultivation

by
Elżbieta Rolka
,
Mirosław Wyszkowski
*,
Anna Skorwider-Namiotko
and
Radosław Szostek
Department of Agricultural and Environmental Chemistry, Faculty of Agriculture and Forestry, University of Warmia and Mazury in Olsztyn, Łódzki 4 Sq., 10-727 Olsztyn, Poland
*
Author to whom correspondence should be addressed.
Agronomy 2025, 15(8), 1968; https://doi.org/10.3390/agronomy15081968
Submission received: 10 July 2025 / Revised: 8 August 2025 / Accepted: 13 August 2025 / Published: 15 August 2025
(This article belongs to the Special Issue New Advances in Sustainable Fertilization: Efficiency and Environmental Challenges)
Browse Figures
Versions Notes

Abstract

In recent years, there has been growing interest in using wood biomass for energy production, which has led to an increase in post-processing waste in the form of wood biomass ash (WBA). Due to the rich composition of WBA, its fertilising potential should be considered. In the conducted studies, WBA was used both alone and in combination with digestate (DG). The WBA was obtained from the Municipal Heat Energy Company and the DG from the Agricultural Biogas Plant in the form of unseparated liquid digestate (ULD), separated solid digestate (SSD) and separated liquid digestate (SLD). The studies included four series: (1) WBA, (2) WBA + ULD, (3) WBA + SSD and (4) WBA + SLD. In each series, WBA was introduced in three increasing doses (0.5, 1.0 and 1.5, expressed in hydrolytic acidity units (HACs) and determined based on the general alkalinity of the material). The digestates (DGs) were applied in fixed doses, which were balanced with respect to the nitrogen introduced into the soil. The test plant was the maize (Zea mays L.) variety Garantio, which was grown in a vegetation hall. The obtained results indicate that the combined use of WBA and DGs (especially ULD and SLD) had a positive effect on the plant height, leaf greenness index (SPAD), and thus, maize yield and dry matter content. In the series with DG addition, the maize yield ranged from 615.5 g (WBA + SSD) to 729.6 g pot−1 (WBA + SLD), which was 28–52% higher than in the series with WBA alone. In turn, the application of increasing doses of WBA alone did not significantly affect the biomass yield but significantly increased the content of N (34%), K (60%), Mg (56%), Ca (60%) and Na (4%). In the series with WBA and DGs, the increase in the content of the above-mentioned macronutrients depended on the type of DG and the dose of WBA. The exception among the macronutrients was P, whose content generally decreased (by 4–23%) with an increasing WBA dose, regardless of the test series. The most favourable results in terms of the chemical composition, excluding the P content, were observed following the combined application of WBA and liquid forms of DG (ULD and SLD).

1. Introduction

This research was undertaken in response to the recent development of bioheat plants using biomass for heating or energy purposes, as well as agricultural biogas plants processing various biodegradable wastes. The biomass combustion process aims to reduce emissions of toxic substances into the environment compared to traditional solid and liquid energy sources [1,2]. This is one of the fundamental principles of the programme “Energy Policy of Poland until 2040” [1]. It is estimated that by 2050, 33–50% of global energy resources could be covered by biomass combustion. In Poland, the main source of biomass is wood chips generated as waste in forestry production. This process inextricably produces a by-product—wood biomass ash (WBA) [3]. In turn, the main goal of agricultural biogas plants is to produce biogas through anaerobic fermentation processes. While this process utilises biodegradable waste, including animal excrement and corn silage, it also produces large quantities of digestate (DG). In Poland, the situation regarding DG from agricultural biogas plants has already been resolved, with recommendations for its use recorded in legal acts [4,5,6]. However, a rational solution for WBA is still pending. WBA generated as a by-product in bioheating plants is still treated as waste in Polish conditions, classified under code 10 01 03 [7]. This waste has a high fertilising potential, which is widely described in the literature [8]. WBA generally has a high content of Ca, K, P and S [9], as well as of Mn, Zn and Cu, which suggests its suitability for agricultural use [10]. However, the target composition of WBA depends on various factors, including the type of biomass [1,2,3,11,12] and the species of trees from which the wood chips intended for the combustion process originate. The treatment of biomass prior to combustion [2], or the combustion process itself [1,3], can often have a strong impact on the chemical composition of WBA, resulting in a higher content of not only nutrients and toxic elements (including Pb and Cd).
Application of WBA to the soil increases the content of organic carbon and essential nutrients for plants, including Mg, K, P, Ca, Na and S [13,14,15,16,17], particularly the available forms of the macroelements P, K and Mg [16], as well as the microelements Zn, Fe, Cu, Mn and B [13,14,16,18]. Due to its high K content [17] and pH-raising properties [16,17], WBA has potential as an alternative potassium fertiliser, especially for acidic soils and those with low K content [17]. By improving the soil properties [19,20], WBA contributes to an increase in the yield of cultivated plants [17,21,22,23,24,25,26,27], and the observed effects may persist in subsequent years [24,28]. The application of WBA to soil can positively affect the maize yield [27], reducing its sensitivity to drought and improving the growth of plants shoots and roots [29]. Adding WBA increases the content of macroelements (N, K, Mg, Ca and Na) in the maize yield and modifies the leaf greenness index (SPAD) during cultivation [27]. However, the low nitrogen (N) concentrations in WBA may reduce its potential positive effect on plant growth [24]. In addition, the adverse effects associated with soil application of WBA include reduced bioavailability of some nutrients at high pH levels and soil salinisation, which can result from long-term use [30,31]. WBA application affects the mobility of nutrients in the soil [32], including microelements (Ni and Co) as well as xenobiotics (Pb and Cd) [16].
Therefore, a potential problem in the natural management of WBA is not only the risk of soil contamination by xenobiotics, its alkalisation or its salinisation but also the very low N content of WBA [13,33,34] and the possibility of spontaneous combustion due to the high proportion of unburned organic matter. One solution could be to combine WBA with other fertiliser materials [13,34]. To supplement the N deficiencies of WBA, the addition of mineral fertilisers has been proposed as an agronomic solution that is profitable in maize cultivation [29]. The beneficial effects of using WBA can be maximised when used in combination with other organic and inorganic additives [25,35]. In the literature, there are attempts to combine WBA with poultry manure [36], sewage sludge [37] or digestate [38,39]. However, these studies typically focus on the liquid fraction of DG. There is still a lack of information on the selection of DG fractions for combining with WBA. The use of DG from an agricultural biogas plant as a fertilising material is proposed in the conducted studies. DG is a material rich in N, including N easily absorbed by plants. Due to its liquid consistency, it can also prevent the self-heating of WBA. DG from agricultural biogas plants is a material free from excessive contents of undesirable toxic compounds, including heavy metals [40]. Due to this feature, DG would be a good material to supplement the N deficiencies of WBA without posing additional threats. Increasing the water removal from DG means that biogas plants offer DG in the form of unseparated liquid digestate (ULD) and, after drying, as separated solid digestate (SSD) and separated liquid digestate (SLD). The content of individual macro- and microelements in each DG form usually differs [40]. The liquid fractions (ULD and SLD) are usually rich in N and K compounds, while the solid fraction (SSD) is characterised by a higher content of P and organic matter [41]. The division of DG into fractions affects their salinity level and ultimately affects the changes in soil properties [40] and may consequently affect the amount and quality of crops. To verify the most desirable form of DG to supplement the N content of WBA, the combined use of these materials in maize cultivation is proposed.
The research undertaken involved the formulation of a hypothesis assuming a positive effect on the yield, leaf greenness (SPAD) and macroelement content (N, P, K, Mg, Ca and Na) of maize biomass through the simultaneous application of various forms of DG (ULD, SSD and SLD) from an agricultural biogas plant and soil application of WBA. Confirmation of this hypothesis would enable the rational management of WBA as a raw material rather than a waste, and it would also promote sustainable development in line with the principles of the circular economy. The aim of this research was to verify the put forward hypothesis based on maize cultivation in the conditions of a pot experiment and to identify the most beneficial DG fraction for use in combination with WBA.

2. Materials and Methods

2.1. Characteristics of the Experiment

This research was based on a pot experiment conducted in a vegetation hall at the University of Warmia and Mazury in Olsztyn (Poland), between 10 May 2024 and 11 July 2024. In order to verify the research hypothesis, four series were distinguished: (1) with wood biomass ash (WBA), (2) with WBA and unseparated liquid digestate (WBA + ULD), (3) with WBA and separated solid digestate (WBA + SSD) and (4) with WBA and separated liquid digestate (WBA + SLD) (Figure 1). The WBA in each series was introduced in three increasing doses (0.5, 1.0 and 1.5 of hydrolytic acidity—HAC), determined based on the total alkalinity of this material. The alkalinity of WBA was compared with the alkalising capacity of calcium oxide. The WBA doses (9 kg of soil per pot) were 2.436, 4.872 and 7.308 g of kg−1 of soil. Digestate was applied in constant doses, which were balanced with respect to the nitrogen (N) introduced into the soil. In the studies, constant NPK fertilisation was used. Whereas N in series 1 (WBA) was introduced only in the form of urea solution (CO(NH2)2), in series 2, 3 and 4, N introduced with digestate constituted 50.6% of the full dose applied per pot. The remaining N (49.4%) was applied with urea (CO(NH2)2). The nitrogen rates applied with digestate were based on standard agricultural practices that limit N introduced with organic fertilisers [4,5]. The established doses of phosphorus (P) and potassium (K) were introduced as potassium phosphate (KH2 PO4) and potassium sulphate (K2 SO4). The total doses of N, P and K calculated per pot were 0.112 g, 0.067 g and 0.134 g, respectively. All the additives (WBA, ULD, SSD, SLD and NPK) were introduced into the soil according to the adopted scheme. They were thoroughly mixed with the soil and placed in polyethylene (PE) pots. As indicated in Figure 1, in each series of the experiment, a control object without WBA and digestates was also included. The experiment included 16 objects, carried out in 3 replications.
The test plant was the maize (Zea mays L.) variety Garantio, which was grown for 62 days in the amount of 8 pcs. per pot. The plants were harvested at the BBCH53 stage (beginning of panicle eruption). During the cultivation, the greenness of the leaves (SPAD) was measured four times, taking the first measurement on the 3rd leaf (BBCH15—fifth leaf stage), the second on the 5th (BBCH17—seventh leaf stage), the third on the 7th (BBCH19—ninth leaf stage) and the fourth on the 9th leaf (BBCH21—eleventh leaf stage). The measurements were taken in accordance with the previously described and used methodology [27], using a SPAD–502 Plus chlorophyll meter. After harvest, the length of the plants was measured and then their mass was weighed.

2.2. Characteristics of the Soil

The soil used in the experiment was collected from the top layer (1–30 cm) and sieved to separate unwanted impurities and to unify the composition. Based on the content of the sand fraction (2.00–0.05 mm—71.00%), dust fraction (0.05–0.002 mm—28.00%) and clay fraction (<0.002 mm—1.00%), the soil was defined as loamy sand. The soil was characterised by acidic reaction (pHKCl—3.96), low salinity (EC—49.10 µS cm−1) and quite poor sorption complex: hydrolytic acidity (HAC)—28.25 mmol(+) kg−1, sum of basic cations (SBC)—45.33 mmol(+) kg−1, cation exchange capacity (CEC)—73.58 mmol(+) kg−1, and base saturation (BS)—61.60%. The following components were found in 1 kg of soil: total nitrogen (Ntot)—0.541 g, total carbon (TC)—4.087 g, available forms: phosphorus (Pav)—68.93 mg, potassium (Kav)—97.69 mg and magnesium (Mgav)—31.00 mg. The C/N ratio was 7.55.

2.3. Characteristics of the Materials (WBA, ULD, SSD, SLD)

Ash (WBA) was obtained from the Municipal Heat Energy Company in Olsztyn (MHEC Olsztyn, Poland). This material is a by-product of the combustion process. It is exclusively made from wood chips from the Kortowo-Bio bio-combustion plant. The burned wood chips are dominated by pine. The by-product is currently classified as waste and disposed of in a landfill [16]. The digestates were obtained from the Agricultural Biogas Plant in Łęguty (MINEX KOGENERACJA Sp. z o.o., Łęguty, Poland). This plant primarily processes corn silage, haylage, green waste and agricultural produce, manure, and slurry. It also processes waste from food, dairy, fruit and vegetable, and animal processing plants, primarily whey, and sludge or flotation from on-site wastewater treatment plants. It effectively separates domestic and municipal wastewater, as well as waste from the fruit and vegetable industry, such as fruit and vegetable parts, pomace, bran, and distillery residues [42,43,44]. The plant produces unseparated liquid digestate (ULD), separated solid digestate (SSD) and separated liquid digestate (SLD), which under the decision issued by the Minister of Agriculture and Rural Development [42,43,44] obtained the status of organic fertilisers. SSD (solid fraction) and SLD (liquid fraction) digestate are products after the dehydration of unseparated liquid digestate (ULD). The basic properties of the materials used (WBA, ULD, SSD and SLD) are shown in Table 1. All the materials were characterised by an alkaline pH (Table 1). WBA was additionally distinguished by a high calcium content (168.9 g Ca kg−1) and potassium (33.41 g K kg−1). The high Ca content in WBA led to its significant alkalinity (26.93% CaO), which was crucial for determining the WBA doses. Among the used digestates, the richest composition was noted in SSD, which was related to the drying of this material and thus the concentration of components. SSD contained significantly more TC, Ntot, Ptot and Mgtot in relation to ULD and SLD. The exception was the content of Ktot, higher amounts of which were noted in ULD and SLD.

2.4. Analytical Analyses

In order to conduct chemical analyses, the plant material, WBA, ULD, SSD and SLD were dried at 60 °C (FED dryer model 700). The plant material was finely ground (SM 200 cutting mill) and the WBA, ULD, SSD and SLD were ground in a porcelain mortar. The soil was dried in the open air and sieved through a sieve with a mesh diameter of 2 mm. Some of the WBA, ULD, SSD and SLD samples in the fresh state were flooded with H2 SO4 to determine their macronutrients. Chemical analyses were performed according to well-established methodologies [45,46,47,48,49,50]. The chemical analyses are described in Table S1.
The CEC and BS were calculated using the formulae published in previous papers [16,27]. In addition, the uptake of macronutrients from the soil by the above-ground mass of maize was calculated according to the previously used formula [27].

2.5. Statistical Analyses

The statistical analysis of the obtained results was conducted using the Pearson correlation coefficient (r), standard deviation (SD), and analysis of variance. Microsoft Excel® (version 2206) (Microsoft, Redmond, WA, USA) was used to calculate the r and SD [51]. Statistical tables [52] were used to determine the significance of the values (r). Values were considered significant at p ≤ 0.05 and highly significant at p ≤ 0.01. The effect of the WBA, ULD, SSD and SLD applications on the studied features was assessed using the LSD test using a two-way ANOVA. The increasing WBA doses were treated as the first factor, and the applied DG fractions as the second factor. The Duncan test at p ≤ 0.05 was used to assess homogenous groups. For this purpose, the Statistica® program (version 13.3 PL) (TIBCO Software Inc., Palo Alto, CA, USA) was used [53].

3. Results

Soil application of WBA alone, as well as its combined application with selected forms of DG (ULD, SSD and SLD), affected all the considered maize traits, including the plant height, greenness index (SPAD), fresh mass yield, and content of dry mass and macroelements (N, P, K, Mg, Ca and Na).

3.1. Yield, Plant Height and Leaf Greenness (SPAD) of Maize

The yield of fresh maize mass depended on the experimental series and ranged from 481.1 g in series 1 (WBA) to 729.6 g pot−1 in series 4 (WBA + SLD) (Table 2). The applied WBA doses had no significant effect on the amount of obtained fresh maize mass. However, the combined application of DG and WBA, as included Table 2, regardless of the form of DG, significantly influenced the increase in the maize yield. In the series with the addition of DG, the yield was higher by 28–52% in relation to the series with WBA. The most beneficial effect on the maize yield was exerted by the liquid forms of DG (SLD and ULD).
The height of the maize plants in each series of experiments is presented in Figure 2. The average height of the maize plants collected from all the treatments was 163.0 cm (Figure 2c). The adopted WBA doses did not significantly affect this trait (Figure 2b). However, the application of DGs had a significant and positive effect (Figure 2c). In the series with DGs, the average height of the maize plants ranged from 160.8 cm (WBA + SSD) to 174.8 cm (WBA + ULD). Compared to the control series (WBA), this represented a difference of between 11.6 and 25.6 cm.
The leaf greenness index (SPAD), which was determined four times during plant growth, is presented in Figure 3. The average SPAD value from all four measurements was 32.3 (Figure 3(e3)). The average SPAD value obtained for the doses (Figure 3(e2)) did not have a significant effect on the tested feature. However, the averages from the individual series (Figure 3(e3)) revealed a positive and significant effect of the applied DGs on the leaf greenness. The analysis of the SPAD values from individual dates showed a consistent decline during maize growth and development. The average SPAD values from the first, second, third and fourth measurements were 44.32; 38.29; 25.73 and 20.87, respectively. The difference between the first and fourth measurements was 53%. The LSD analysis showed a significant and positive effect of the combined use of WBA and DGs. The most long-lasting positive effect was noted when using WBA and liquid forms of DG (ULD and SLD) (Figure 3(a3,b3,c3,d3)). Conversely, WBA alone had a significant and positive effect on the SPAD value during the first measurement only (Figure 3(a1)).

3.2. Dry Matter (DM) Content of Maize

The average dry matter (DM) content of the maize biomass was 20.43% (Table 3). A significantly higher DM content was noted in the series with DGs added compared to the control series (WBA). The average DM content in these treatments was 1.79–2.86% higher than in the control series (WBA). The LSD test showed that the adopted WBA doses did not significantly affect the DM content, as can be seen in the series in which WBA was used together with DGs. The exception to this was series 1, where application of WBA resulted in a decrease in the DM content, as indicated by the results in Table 3. A significant effect was noted at WBA doses equal to 1.0 and 1.5 HAC, where the DM content was lower by 2.40–2.75% compared to the control.

3.3. Content and Uptake of Macronutrients (N, P, K, Mg, Ca and Na) by Maize Biomass

The chemical composition of the maize biomass in terms of the macronutrient content, which is presented in Table 4, was characterised by the highest K content. The average K concentration for all the treatments was 21.02 g kg−1 DM. Lower contents were noted for N and P in the maize biomass, with the lowest average content observed for Na, Mg and Ca, which was 5.577 g, 3.753 g, 0.881 g, 0.798 g and 0.763 g kg−1 DM, respectively. The content of P, K, Mg and Ca showed a significant dependence on the adopted WBA doses. The correlation was positive (0.537 ** ≤ r ≤ 0.700 **) in the case of K, Mg and Ca, and negative (r = −0.402 **) in the case of P. The increase in the K, Mg and Ca content against the background of increasing WBA doses was 30%, 20% and 33%, respectively, and the decrease in P content—14%. Furthermore, the LSD test showed a positive effect of the third dose of WBA (1.5 HAC) on the N content of the maize biomass. This positive effect of WBA application on the N content was particularly evident in series 1 (WBA), where the difference in the N content between the control treatment and the treatment with the highest WBA dose was 34%, and r = 0.789 **. However, no significant relationship was observed between increasing WBA doses and changes in the Na content (r = −0.040 n.s.) of the maize biomass.
Taking into account the control objects of the individual series of the experiment, the addition of ULD influenced an increase in the content of N, K, Mg, Ca and Na in the biomass of maize. The addition of SSD influenced the increase in the content of Mg, while the application of SLD influenced the increase in the content of K, Mg, Ca and Na (Table 4). It should also be noted that the application of SSD influenced a decrease in the content of N and Na. The changes observed in the control objects in the series with DGs were most often maintained after the joint application of DGs and WBA. Considering the value of the correlation coefficient in the individual series of the experiment, it can be concluded that the combined use of WBA and DGs (all forms) had a positive effect on the content of K (0.728 ** ≤ r ≤ 0.810 **) and Ca (0.652 * ≤ r ≤ 0.708 **), while the combined use of WBA and SSD positively affected the content of Na (r = 0.816 **). However, the LSD test showed a significantly positive effect of the combined use of WBA and ULD on the content of K, Mg and Na, and of the combined application of WBA and SLD on the content of K and Na. Based on the average contents of the individual series, it is indicated that the content of K, Mg and Na in series 2 (WBA + ULD) was, respectively, 3%, 2% and 12% higher in relation to the content of those elements recorded in series 1 (WBA). On the other hand, the content of K and Na in series 4 (WBA + SLD) was higher by 9% and 18% in relation to their content recorded in series 1 (WBA). In addition, the combined application of WBA and SSD resulted in a significant reduction in the content of N, K, Ca and Na, respectively, by 19%, 14%, 8% and 20% in relation to series 1 (WBA). The combined application of WBA and SLD also had a negative effect on the N and P content of the maize biomass, reducing their content by 14% and 11% in comparison to the series with WBA.
The calculated correlations between the contents of the analysed macroelements in the above-ground mass of maize (Table 5) showed a highly significant relationship between the contents of N and K, as well as Mg and Ca (0.388 ** ≤ r ≤ 0.672 **), and a significant relationship between N and Na (r = 0.308 *). Moreover, highly significant relationships were also observed in terms of the contents of K and Mg, Ca and Na (0.532 ** ≤ r ≤ 0.759 **) and between the contents of Mg and Ca (r = 0.647 **).
As shown in Table S2, the uptake of macroelements by maize biomass depended on the factors considered in the experiment in a similar way to their content in the biomass. The highest mean uptake was recorded for K (0.428 g), followed by N (0.114 g) and P (0.077 g). The lowest uptake was recorded for Na (0.18 g), Mg (0.016 g), and Ca (0.014 g per pot). The adopted WBA doses had a significant effect on the uptake of P, K, Mg and Ca by maize. For P, the effect was negative (r = −0.482 **), whereas for K, Mg and Ca, the effect was positive (0.467 ** < r < 0.698 **). However, the K uptake increased significantly up to the highest WBA dose (1.5 HAC), the Mg uptake increased after application of the first WBA dose (0.5 HAC) and the Ca uptake increased after the highest dose (1.5 HAC). However, no significant effect of the applied WBA doses was noted in the case of the N and Na intake. Conversely, the combined use of WBA and ULD significantly increased the intake of N, K, Mg and Na, while the combination of WBA and SLD significantly increased the intake of K and Na. In series 3 (WBA + SSD), no higher intake of macronutrients was observed than in series 1 (WBA). However, it should be noted that the intake of K and Ca increased against the background of increasing WBA doses (0.792 ** < r <0.939 **). Series 3 (WBA + SSD) also showed significantly reduced P uptake (r = −0.638 *) against the background of increasing WBA doses. Series 4 (WBA + SLD) showed significantly reduced Na uptake (r = −0.667 *).

4. Discussion

Reusing WBA in agriculture is important for nutrient cycling and reducing the use of mineral fertilisers [54]. According to some studies [55], about 40% of the world’s soil resources are significantly impacted by anthropogenic activity, reducing their production capacity dependent on the use of fertilisers. Given the growing demand for mineral fertilisers and the depletion of the raw materials used to produce them, we should pay more attention to mineral waste that has significant fertilising potential. One such waste is WBA, characterised by an alkaline reaction and a fairly rich chemical composition with a predominance of alkaline elements (Table 1). The positive effects on the soil quality [16], maize yield, leaf greenness and macronutrient content [27] suggest the possibility of using this material in the cultivation of this plant. Other researchers have also highlighted the positive role of WBA in relation to the plant yield [17,21,22,23,24,25,26]. In the currently presented studies, the independent application of WBA did not significantly affect the height of the plants (Figure 2) or the change in the fresh mass of the maize yield (Table 2). The independent application of WBA positively corrected the SPAD value, but only up to the BBCH15 phase (Figure 3(a1)). SPAD measurements taken at later dates showed a systematic decrease in this parameter (Figure 3), which is quite consistent with earlier observations [27]. It should be noted that the WBA doses in the current studies were determined based on its alkalinity, which was significant due to the high proportion of Ca present (Table 1). The high alkalinity of the WBA reduced the total amount of WBA introduced into the soil, which ranged from 2.437 to 7.309 g kg−1 of soil. However, in earlier studies, the WBA doses used were in a much wider range (from 1.667 to 10.000 g kg−1 of soil) and the WBA itself contained almost 21% more N [27], which could have had a positive effect on the increase in the maize yield observed at that time. In the currently presented research, the reason for the decrease in the SPAD value with plant growth could be due to the lack of N. As stated in the methodology, N was applied once before sowing the plants to better clarify the effect of the used materials. Despite the lack of effect of the adopted WBA doses on the maize yield in the current study, the self-application of WBA (Table 4) increased the content of most macronutrients (N, K, Mg, Ca and Na) in the harvested biomass, with the exception of P. These results confirm previous research findings [27]. The increase in the macronutrient content of the maize yield is the result of the high levels of these nutrients in the material (Table 1), as well as the increase in the content of available forms of these nutrients in the soil observed after WBA was applied to the soil, as observed in previous studies [16]. On the other hand, the decrease in the P content may be due to the insufficient supply of this element in the soil. Previous studies [27] and the current study indicate a quite significant decrease in the SPAD index value during maize growth. Since fertilisation was only applied before sowing in both experiments, this suggests a lack of top dressing in the cultivation of this plant. This could explain the decrease in the SPAD index value and the lack of yield increase in the current studies. Another possible issue is the form of the supplied N, which in the previous experiment [27] and in series 1 (WBA) of the current studies was supplemented only by the addition of urea solution.
The different results regarding the maize yield obtained in the compared experiments may be due to the variability in the WBA composition reported in the literature [1,2,3,11,12], which is associated here with the heating period. This could be due to the wood chips being obtained from different locations, a different composition of wood species used to prepare wood biomass or the combustion process itself. The physical and chemical properties of WBA depend largely on the type of furnace. The rational management of WBA requires knowledge of its quantity and properties [56]. The variable composition of WBA and the potential content of toxic compounds in it are significant problems in terms of developing rational management of this waste. However, the results of the current research indicate that higher doses of DG or the use of fertilisation treatments to supplement the macro- and microelement reserves in the later stages of plant growth should be considered. Another problem with the natural management of WBA is the risk of spontaneous combustion due to the high proportion of unburned organic matter. This poses a real danger during the long-term storage, warehousing or transportation of WBA. One solution to this could be to combine WBA with other fertilising materials [13,34], especially in liquid form, to prevent spontaneous combustion. Based on previous results [27], the current research introduced nitrogen fertilisation in three forms of DG (ULD, SSD and SLD). DGs contain large amounts of N and other nutrients necessary for plants [57,58,59] in a form that is easily available and mineralises quickly in the soil [57,58]. There are many arguments in favour of using DG, especially ULD and SLD. These include the liquid form, which could prevent of spontaneous combustion of WBA, and the N content, which would be a good complement to the deficiencies of this macroelement in WBA. DG has already been proven to have a positive effect on the yield and quality of cucumber fruit [60], ryegrass and barley [59] and winter rapeseed yield, as well as its fat, protein and macronutrient content [61]. DG fertilisation enables the abandonment of mineral N fertilisation, without negatively impacting on the quality or chemical composition of triticale and maize used as biogas substrates [62]. Due to their rich composition, DGs can be used as an alternative to conventional fertilisers [63,64]. Using DG for fertilisation purposes also solves the problem of retaining this material in tanks or lagoons where it is stored. The accumulation and storage of DG for too long carries environmental threats, including unpleasant odours and leakage into groundwater [60]. Additionally, DG from agricultural biogas plants fuelled by typical household waste can be used in agricultural production without fear of introducing excessive amounts of heavy metals into the environment [57]. The problem with using liquid forms of DG in agriculture is usually associated with the excess water that must be introduced into the soil when using this fertiliser. However, in the current study, the water content of the liquid forms of DG is advantageous because it can be used for post-process quenching of WBA.
As indicated in the literature, a mixture of WBA and DG enables plants to grow without the need for mineral fertilisers [58]. Some studies indicate that a mixture of DG and biochar improves plant growth. This mixture increases the content of organic carbon and reduces the bioavailability of heavy metals [65]. Some researchers argue that biochar coated with fermentate can act as a slow-release fertiliser, ensuring better growth and yield of the fresh mass of ornamental plants [66]. According to some, the mixture of WBA with DG may also be a slow-release fertiliser [67]. In addition, scientific studies [35] prove the positive role of combining DG and WBA as an optimal mixture for fertilising deciduous trees in forestry, improving the photosynthesis parameters and shortening the growth period. This solution could be used in cases of excessive content of heavy metals in WBA or DGs. The mixture of WBA and DG can be considered an alternative fertiliser for maize cultivation, enabling the production of high-quality green biomass [68]. In the presented studies, the combined use of the adopted doses of WBA and DGs had a significant and positive effect on the following: plant height (Figure 2c), leaf greenness (SPAD) (Figure 3(a3–e3)), maize biomass yield (Table 2) and DM content (Table 3). The maize biomass yield increased by between 28% and 52%, with the most favourable effect being observed with the liquid forms—ULD and SLD. Regardless of the form of DG used during maize growth, a systematic decrease in the SPAD values was similarly observed as in the series with WBA alone (Figure 3). On average, the difference between the BBCH15 (Figure 3(a3)) and BBCH21 (Figure 3(d3)) phases was 53%. The liquid forms of DGs used (ULD and SLD) usually increased the uptake (Table S2) and the content of macroelements in maize (Table 2). Combined use of WBA and ULD increased in the content of K, Mg and Na by 2–12%, while combined application of WBA and SLD increased the content of K by 9% and Na by 18%. The combined application of WBA and SSD had a negative effect on the content of most macroelements (N, K, Ca and Na) in the maize mass. In contrast, the interaction of WBA and SLD adversely affected the content of N and P, resulting in an 8–20% decrease compared to the series without DGs. The adverse effect of combining WBA and SSD was likely due to the short duration of the experiment. As our own research results indicate, SSD was characterised by a significantly lower C/N ratio than ULD or SLD. This could have influenced the availability of nutrients contained in this material. Previous studies [40] conducted with two forms of DG (liquid, unseparated LD and solid, separated SD) indicated that these forms had a less favourable effect on the soil properties. SD enriched the soil with N to a lesser extent, thus lowering the C/N ratio. Therefore, it can be assumed that the currently selected DG fractions have a similar effect, which may affect the availability of nutrients and explain the results of the studies. In our own research, the combined treatments (WBA + DG), regardless of the DG fraction, produced a significantly higher dry matter content (Table 3). This beneficial effect is due to the potential for later use of the crop for silage [39]. In summary, the most beneficial results were obtained after the use of WBA and ULD. These results are all the more satisfactory given that ULD is the initial form of DG—unseparated and burdened with the lowest acquisition costs. The increased content of these macronutrients suggests that using WBA alone, or a mixture of WBA and liquid DG fractions (ULD and SLD), introduces readily available nutrients into the soil [57]. The presence of significant amounts of elements in the soil solution leads to rapid plant growth. The so-called dilution effect is observed. This is related to the fact that higher crop yields contain lower concentrations of elements, while lower yields contain smaller accumulations of components. However, the results obtained indicate the need to refine the doses of nutrients and the dates of their application. However, as the results of the current research indicate (no biomass increase in the series with DGs compared to increasing WBA doses—Table 2), the use of higher doses of DG should be considered. Due to the decrease in the SPAD index value observed independently of the experiment series (Figure 3), supplementary fertilisation could be considered in subsequent studies to address the nutrient deficiencies during the intensive growth phases of maize. Some studies [63] also suggest that DG can work even more effectively with a small addition of selected nutrients (P, S and/or B). Although satisfactory results were obtained from the combined use of WBA and DG, one important issue remains: the process of obtaining such a mixture. The problem with obtaining the finished product from WBA and DG is the mixing process. Loss of N through the volatilisation of ammonia (NH4) and loss of C through the emission of carbon dioxide (CO2) can be expected during this process. However, both of these unwanted processes can be minimised or controlled. An increase in the alkalinity of the mixture could slow down the CO2 emissions, and the volatile NH4 could be recovered by capturing it with sulfuric acid (H2SO4) [67]. From the perspective of circular economy principles, using WBA alone or in combination with other by-products or waste materials to fertilise plants is a very reasonable approach. However, reasonable does not mean easy. It is reasonable because it allows for the aforementioned improvement of the soil conditions and the achievement of higher yields with a richer chemical composition. This is a challenging area because WBA is characterised by a variable composition and is often contaminated with undesirable ingredients or is excessively saline. However, the promising research results provide a basis for further, more detailed work aimed at developing a productive mixture, adapted to the nutritional needs of cultivated plants and enabling rational and safe management of WBA.

5. Conclusions

The application of WBA alone had no significant effect on the height of the plants and thus did not affect the change in the fresh mass of the maize yield, only slightly reducing the DM content. The application of WBA positively corrected the SPAD value, but only up to the BBCH15 phase. Regardless of the WBA dose and the additives used, a systematic decrease in the SPAD values was observed during maize growth, where the difference between the BBCH15 and BBCH21 phases was 53%. On the other hand, the combined use of the adopted WBA and DGs doses significantly and positively affected the plant height, leaf greenness (SPAD) and yield, increasing them by 28–52%, as well as increasing the DM content. The most beneficial effects were achieved using liquid forms (ULD and SLD).
Among the macroelements, the dominant component of the maize biomass was K (21.02 g kg−1 DM). Significantly lower contents were noted for N (5.577 g), P (3.753 g), Na (0.881 g), Mg (0.798 g) and Ca (0.763 g kg−1 DM). Increasing doses of WBA alone increased the content of most macronutrients (N, K, Mg, Ca and Na). The LSD test showed that the adopted doses of WBA significantly and positively influenced the content of K (30%), Mg (20%) and Ca (33%), while having a negative influence on the content of P (14%) compared to the control (without WBA). The applied DGs usually improved the chemical composition of the maize (increasing the content of macroelements), and liquid forms of DG (ULD and SLD) had the most favourable effect in this respect. Combined application of WBA and ULD increased the content of K, Mg and Na, while combined application of WBA and SLD increased the content of K and Na. However, the combined application of WBA and SSD negatively affected the content of most macroelements (N, K, Ca and Na) in the maize biomass. Conversely, the interaction of WBA and SLD negatively affected the content of N and P, resulting in an 8–20% decrease in these elements compared to the series without DGs.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/agronomy15081968/s1, Table S1: Analytical methods. Table S2. Uptake of macronutrients (N, P, K, Mg, Ca and Na) from the soil by the above-ground mass of maize (g pot−1 DM).

Author Contributions

Conceptualisation, E.R.; methodology, E.R.; software, E.R.; validation, E.R.; formal analysis, E.R.; investigation, E.R., A.S.-N. and R.S.; resources, E.R.; data curation, E.R., A.S.-N. and R.S.; writing—original draft preparation, E.R.; writing—review and editing, E.R., M.W., A.S.-N. and R.S.; visualisation, E.R.; supervision, M.W.; project administration, E.R.; funding acquisition, E.R. and M.W. All authors have read and agreed to the published version of the manuscript.

Funding

Funded by the Minister of Science under “the Regional Initiative of Excellence Program”. This research was financed by the Department of Agricultural and Environmental Chemistry, Faculty of Agriculture and Forestry, University of Warmia and Mazury in Olsztyn, Poland (grant no. 30.610.004–110).

Data Availability Statement

Data are contained within the article.

Acknowledgments

The authors would like to thank the Municipal Heat Energy Company in Olsztyn (MHAC Olsztyn, Poland) and the Agricultural Biogas Plant in Łęguty (MINEX KOGENERACJA Sp. z o.o., Łęguty, Poland) for providing the samples of wood biomass ash and digestates used in this study.

Conflicts of Interest

The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

Abbreviations

The following abbreviations are used in this manuscript:
WBAwood biomass ash
DGdigestate
DGsdigestates
ULDunseparated liquid digestate
SSDseparated solid digestate
SLDseparated liquid digestate
DMdry matter

References

  1. Energy Policy of Poland Until 2040; Ministry of Climate and Environment: Warsaw, Poland, 2021; pp. 1–102. Available online: https://www.gov.pl/attachment/b1febd0c-e544-412d-a0d7-f6bff01707c1 (accessed on 28 July 2025).
  2. Pazalja, M.; Salihović, M.; Sulejmanović, J.; Smajović, A.; Begić, S.; Špirtović-Halilović, S.; Sher, F. Heavy metals content in ashes of wood pellets and the health risk assessment related to their presence in the environment. Sci. Rep. 2021, 11, 17952. [Google Scholar] [CrossRef] [PubMed]
  3. Odzijewicz, J.I.; Wołejko, E.; Wydro, U.; Wasil, M.; Jabłońska-Trypuć, A. Utilization of ashes from biomass combustion. Energies 2022, 15, 9653. [Google Scholar] [CrossRef]
  4. Ministry of Agriculture and Rural Development. Act on Fertilisers and Fertilisation of 10 July 2007. J. Laws 2007, 147, 1–45. [Google Scholar]
  5. Ministry of Agriculture and Rural Development. Regulation of the Minister of Agriculture and Rural Development of 18 June 2008 on the implementation of certain provisions of the Act on fertilisers and fertilisation. J. Laws 2008, 119, 1–6. [Google Scholar]
  6. Ministry of Agriculture and Rural Development. Regulation of the Minister of Agriculture and Rural Development of 12 October 2023 on a detailed list of substrates that can be used in agricultural biogas plants. J. Laws 2023, 2230, 1–3. [Google Scholar]
  7. Ministry of Climate and Environment. Regulation of the Minister of Climate of 18 January 2020 on the waste catalogue. J. Laws 2020, 10, 1–48. [Google Scholar]
  8. Munawar, M.A.; Khoja, A.H.; Naqvi, S.R.; Mehran, M.T.; Hassan, M.; Liaquat, R.; Dawood, U.F. Challenges and opportunities in biomass ash management and its utilization in novel applications. Renew. Sustain. Energy Rev. 2021, 150, 111451. [Google Scholar] [CrossRef]
  9. Zając, G.; Szyszlak-Bargłowicz, J.; Gołębiowski, W.; Szczepanik, M. Chemical characteristics of biomass ashes. Energies 2018, 11, 2885. [Google Scholar] [CrossRef]
  10. Smol, M.; Szołdrowska, D. An analysis of the fertilizing potential of selected waste streams–municipial, industrial and agricultural. Miner. Resour. Manag. 2021, 37, 75–100. [Google Scholar] [CrossRef]
  11. Zając, G.; Szyszlak-Bargłowicz, J.; Szczepaniak, M. Influence of biomass incineration temperature on the content of selected heavy metals in the ash used for fertilizing purposes. Appl. Sci. 2019, 9, 1790. [Google Scholar] [CrossRef]
  12. Smołka-Danielowska, D.; Jabłońska, M. Chemical and mineral composition of ashes from wood biomass combustion in domestic wood fired furnaces. Int. J. Environ. Sci. Technol. 2022, 19, 5359–5372. [Google Scholar] [CrossRef]
  13. Demeyer, A.; Voundi Nkana, J.C.; Verloo, M.G. Characteristics of wood ash and influence on soil properties and nutrient uptake: An overview. Bioresour. Technol. 2001, 77, 287–295. [Google Scholar] [CrossRef]
  14. Füzesi, I.; Heil, B.; Kovács, G. Effects of wood ash on the chemical properties of soil and crop vitality in small plot experiments. Acta Silv. Lignaria Hung. 2015, 11, 55–64. [Google Scholar] [CrossRef]
  15. Varshney, A.; Dahiya, P.; Sharma, A.; Pandey, R.; Mohan, S. Fly ash application in soil for sustainable agriculture: An Indian overview. Energy Ecol. Environ. 2022, 7, 340–357. [Google Scholar] [CrossRef]
  16. Rolka, E.; Żołnowski, A.C.; Wyszkowski, M.; Zych, W.; Skorwider-Namiotko, A. Wood biomass ash (WBA) from the heat production process as a mineral amendment for improving selected soil properties. Energies 2023, 16, 5110. [Google Scholar] [CrossRef]
  17. Jian, C.; Hamamoto, T.; Inoue, C.; Chien, M.-F.; Naganuma, H.; Mori, T.; Sawada, A.; Hidaka, M.; Setoyama, H.; Makino, T. Effects of wood ash fertilizer on element dynamics in soil solution and crop uptake. Agronomy 2025, 15, 1097. [Google Scholar] [CrossRef]
  18. Kishor, P.; Ghosh, A.K.; Kumar, D. Use of fly ash in agriculture: A way to improve soil fertility and its productivity. Asian J. Agric. Res. 2010, 4, 1–14. [Google Scholar] [CrossRef]
  19. Basu, M.; Pande, M.; Bhadoria, P.B.S.; Mahapatra, S.C. Potential fly–ash utilization in agriculture: A global review. Prog. Nat. Sci. 2009, 19, 1173–1186. [Google Scholar] [CrossRef]
  20. Gill, K.S.; Malhi, S.S.; Lupwayi, N.Z. Wood ash improved soil properties and crop yield for nine years and saved fertilizer. J. Agric. Sci. 2015, 7, 72–83. [Google Scholar] [CrossRef]
  21. Ajala, R.; Awodun, M.; Oladele, S. Effects of wood ash biomass application on growth indices and chlorophyll content of maize and lima bean intercrop. Turk. JAF Sci. Technol. 2017, 5, 614–621. [Google Scholar] [CrossRef]
  22. Arshad, S.; Iqbal, M.Z.; Shafiq, M.; Athar, M.; Kabir, M.; Farooqui, Z.R. Azadirachta indica A. Juss: Wood ash affects seedling growth of mung bean Vigna radiata L. Eur. J. Agric. Food Sci. 2020, 2, 1–5. [Google Scholar] [CrossRef]
  23. Arshad, S.; Iqbal, M.Z.; Shafiq, M.; Kabir, M.; Farooqui, Z.R. The effects of wood ash on seed germination and seedling growth of pulse crop Vigna radiata (L.) R. Wilczek. Biosci. Res. 2020, 17, 221–227. [Google Scholar]
  24. Johansen, J.L.; Nielsen, M.L.; Vestergård, M.; Mortensen, L.H.; Cruz-Paredes, C.; Rønn, R.; Kjøller, R.; Hovmand, M.; Christensen, S.; Ekelund, F. The complexity of wood ash fertilization disentangled: Effects on soil pH, nutrient status, plant growth and cadmium accumulation. Environ. Exp. Bot. 2021, 185, 104424. [Google Scholar] [CrossRef]
  25. Romdhane, L.; Ebinezer, L.B.; Panozzo, A.; Barion, G.; Cortivo, C.D.; Radhouane, L.; Vamerali, T. Effects of soil amendment with wood ash on transpiration, growth, and metal uptake in two contrasting maize (Zea mays L.) hybrids to drought tolerance. Front. Plant Sci. 2021, 12, 661909. [Google Scholar] [CrossRef]
  26. Adeyemo, A.J.; Daramola, A.R.; Adejoro, S.A.; Ojeniyi, S.O. Application of urea and wood ssh on soil nutrient composition, growth and yield of okra under degraded humid tropical alfisol of South Western Nigeria. J. Hortic. Sci. Crop Res. 2022, 2, 101. [Google Scholar]
  27. Rolka, E.; Żołnowski, A.C.; Wyszkowski, M.; Skorwider-Namiotko, A. Determination of the possibilities of using woody biomass ash from thermal power plants in corn cultivation. Energies 2024, 17, 2783. [Google Scholar] [CrossRef]
  28. Couch, R.L.; Luckai, N.; Morris, D.; Diochon, A. Short–term effects of wood ash application on soil properties, growth, and foliar nutrition of Picea mariana and Picea glauca seedlings in a plantation trial. Can. J. Soil Sci. 2021, 101, 203–215. [Google Scholar] [CrossRef]
  29. Adekayode, F.O.; Olojugba, M.R. The utilization of wood ash as manure to reduce the use of mineral fertilizer for improved performance of maize (Zea mays L.) as measured in the chlorophyll content and grain yield. J. Soil Sci. Environ. 2010, 1, 40–45. [Google Scholar]
  30. Pandey, V.C.; Singh, N. Impact of fly ash incorporation in soil systems. Agric. Ecosyst. Environ. 2010, 136, 16–27. [Google Scholar] [CrossRef]
  31. Szostek, M.; Szpunar-Krok, E.; Ilek, A. Chemical speciation of trace elements in soil fertilized with biomass combustion ash and their accumulation in winter oilseed rape plants. Agronomy 2023, 13, 942. [Google Scholar] [CrossRef]
  32. James, A.K.; Thring, R.W.; Helle, S.; Ghuman, H.S. Ash management review–applications of biomass bottom ash. Energies 2012, 5, 3856–3873. [Google Scholar] [CrossRef]
  33. Park, B.B.; Yanai, R.D.; Sahm, J.M.; Lee, D.K.; Abrahamson, L.P. Wood ash effects on plant and soil in a willow bioenergy plantation. Biomass Bioenergy 2005, 28, 355–365. [Google Scholar] [CrossRef]
  34. Iderawumi, A.M. Effects of ash on soil properties and yield of crops. Agric. Obs. 2020, 1, 61–66. [Google Scholar]
  35. Zuševica, A.; Adamovics, A.; Duminš, K.; Vendina, V.; Žigure, S.; Lazdina, D. Soil fertility improvement with mixtures of wood ash and biogas digestates enhances leaf photosynthesis and extends the growth period for deciduous trees. Plants 2023, 12, 1152. [Google Scholar] [CrossRef]
  36. Emma-Okafor, L.C.; Obijuru, E.E.; Nwokeji, I.M.; Echereobia, C.O.; Okoli, N.A. Effect of poultry manure and wood ash on the growth and yield of cucumber (Cucumis sativum L.) in Owerri Southeastern Nigeria. Net. J. Agric. Sci. 2022, 10, 49–53. [Google Scholar] [CrossRef]
  37. Simon, L.; Makadi, M.; Uri, Z.; Vigh, S.; Irinyine-Olah, K.; Vincze, G.; Toth, C. Phytoextraction of toxic elements and chlorophyll fluorescence in the leaves of energy willow (Salix sp.), treated with wastewater solids and wood ash. Agrochem. Soil Sci. 2022, 71, 77–99. [Google Scholar] [CrossRef]
  38. Abelenda, A.M.; Aiouache, F. Wood ash based treatment of anaerobic digestate: State–of–the–art and possibilities. Processes 2022, 10, 147. [Google Scholar] [CrossRef]
  39. Adamovics, A.; Poiša, L. The effect of digestate and wood ash mixtures on the productivity and yield quality of maize. Environ. Technol. Resour. 2024, 1, 15–18. [Google Scholar] [CrossRef]
  40. Rolka, E.; Wyszkowski, M.; Żołnowski, A.C.; Skorwider–Namiotko, A.; Szostek, R.; Wyżlic, K.; Borowski, M. Digestate from an agricultural biogas plant as a factor shaping soil properties. Agronomy 2024, 14, 1528. [Google Scholar] [CrossRef]
  41. Van Midden, C.; Harris, J.; Shaw, L.; Sizmur, T.; Pawlet, M. The impact of anaerobic digestate on soil life: A review. Appl. Soil Ecol. 2023, 191, 105066–105078. [Google Scholar] [CrossRef]
  42. Decision of the Minister of Agriculture and Rural Development No. 730/22 of 2 September 2022; Case number: DHR.ns.8100.42.2022.168; Ministry of Agriculture and Rural Development: Warsaw, Poland, 2022.
  43. Decision of the Minister of Agriculture and Rural Development No. 728/22 of 5 September 2022; Case number: DHR.ns.8100.46.2022.169; Ministry of Agriculture and Rural Development: Warsaw, Poland, 2022.
  44. Decision of the Minister of Agriculture and Rural Development No. 729/22 of 5 September 2022; Case number: DHR.ns.8100.43.2022.170; Ministry of Agriculture and Rural Development: Warsaw, Poland, 2022.
  45. Panalytical Malvern. Mastersizer 3000. Brochure. Available online: https://www.malvernpanalytical.com/en/assets/mastersizer%203000%20brochure%20(en)_tcm50-58994.pdf (accessed on 14 April 2023).
  46. Karczewska, A.; Kabała, C. Methodology of Laboratory Analyzes of Soils and Plants; University of Life Sciences: Wrocław, Poland, 2008. [Google Scholar]
  47. Bremner, J.M. Nitrogen–Total. Methods of Soil Analysis. Part 3. In Chemical Methods; Sparks, D.L., Page, A.L., Helmke, P.A., Loeppert, R.H., Soltanpour, P.N., Tabatabai, M.A., Johnston, C.T., Sumner, M.E., Eds.; Soil Science Society of America: Madison, WI, USA, 1996; pp. 1087–1123. [Google Scholar]
  48. Ostrowska, A.; Gawliński, S.; Szczubiałka, Z. Methods of Analysis and Assessment of Soil and Plants Properties, 1st ed.; Institute of Environmental Protection: Warsaw, Poland, 1991. [Google Scholar]
  49. Egner, H.; Riehm, H.; Domingo, W.R. Untersuchungen Uber Die Chemische Bodenanalyse Als Grundlage Fur Die Beurteilung Des Nahrstoffzustandes Der Boden. II. Chemische Extraktionsmethoden Zur Phosphorund Kaliumbestimmung. K. Lantbrukshogskolans Ann. 1960, 26, 199–215. [Google Scholar]
  50. Panak, H. Methodological Guide for Agricultural Chemistry Exercises; Agricultural and Technical University in Olsztyn: Olsztyn, Poland, 1995. [Google Scholar]
  51. Microsoft. MS Excel® for Microsoft 365 MSO; Microsoft Corporation: Albuquerque, NM, USA, 2021. [Google Scholar]
  52. Burdzy, J. Statistical Tables; Lublin University of Technology Publishing House: Lublin, Poland, 1999. [Google Scholar]
  53. Tibco. Statistica Data Analysis Software System; Tibco Software Inc.: Palo Alto, CA, USA, 2021. [Google Scholar]
  54. Schiemenz, K.; Eichler-Löbermann, B. Biomass ashes and their phosphorus fertilizing effect on different crops. Nutr. Cycl. Agroecosyst. 2010, 87, 471–482. [Google Scholar] [CrossRef]
  55. De la Rosa, J.M.; Pérez-Dalí, S.M.; Campos, P.; Sánchez-Martín, Á.; González-Pérez, J.A.; Miller, A.Z. Suitability of volcanic ash, rice husk ash, green compost and biochar as amendments for a mediterranean alkaline soil. Agronomy 2023, 13, 1097. [Google Scholar] [CrossRef]
  56. Ike, M.; Kawagoe, H.; Oshita, K.; Takaoka, M. Detailed estimation of generated woody biomass ash for use as fertilizer material. Waste Manag. 2025, 195, 275–283. [Google Scholar] [CrossRef]
  57. Kovacevic, D.; Manojlovic, M.; Cabilovski, R.; Ilic, Z.S.; Petkovic, K.; Štrbac, M.; Vijuk, M. Digestate and manure use in Kohlrabi production: Impact on plant–available nutrients and heavy metals in soil, yield, and mineral composition. Agronomy 2022, 12, 871. [Google Scholar] [CrossRef]
  58. Adamovics, A.; Poiša, L. The effect of an innovative fertilizer of digestate and wood ash mixtures on winter garlic productivity. Environ. Technol. Resour. 2023, 1, 12–16. [Google Scholar] [CrossRef]
  59. Tymchuk, I.; Malovanyy, M.; Zhuk, V.; Kochubei, V.; Yatsukh, K.; Luchyt, L. Towards increasing the utilization of anaerobic digestate from biogas production in agrotechnologies. Ecol. Quest. 2023, 34, 1–18. [Google Scholar] [CrossRef]
  60. Çalik, B.; Sönmez, İ. The effects of liquid biogas digestate on yield and mineral nutrition of cucumber growing in greenhouse. HortiS 2024, 41, 28–35. [Google Scholar] [CrossRef]
  61. Koszel, M.; Parafiniuk, S.; Szparaga, A.; Bochniak, A.; Kocira, S.; Atanasov, A.Z.; Kovalyshyn, S. Impact of digestate application as a fertilizer on the yield and quality of winter rape seed. Agronomy 2020, 10, 878. [Google Scholar] [CrossRef]
  62. Witorożec-Piechnik, A.; Matyka, M.; Woźniak, M.; Oleszek, M. The effect of fertilization with the digestate on the quality and chemical composition of selected plants intended for biogas production. Pol. J. Agron. 2022, 48, 28–36. [Google Scholar] [CrossRef]
  63. Weimers, K.; Bergstrand, K.-J.; Hultberg, M.; Asp, H. Liquid anaerobic digestate as sole nutrient source in soilless horticulture–or spiked with mineral nutrients for improved plant growth. Front. Plant Sci. 2022, 13, 770179. [Google Scholar] [CrossRef]
  64. Szwed, M.; Koszel, M.; Przywara, A.; Kachel-Górecka, M. Impact of digestate fertilization on crop production–a comprehensive review. Adv. Sci. Technol. Res. J. 2024, 18, 347–353. [Google Scholar] [CrossRef]
  65. Kujawska, J.; Cel, W.; Kwiatkowski, C.A.; Harasim, E.; Zamorska, J. The effect of digestate from biogas plants alone and with the addition of biochar and zeolite on soil properties and sorghum yield. Bioresources 2025, 20, 5765–5789. [Google Scholar] [CrossRef]
  66. Yan, M.; Tian, H.; Song, S.; Tan, H.T.W.; Lee, J.T.E.; Zhang, J.; Sharma, P.; Tiong, Y.W.; Tong, Y.W. Effects of digestate–encapsulated biochar on plant growth, soil microbiome and nitrogen leaching. J. Environ. Manag. 2023, 334, 117481. [Google Scholar] [CrossRef] [PubMed]
  67. Abelenda, A.M.; Semple, K.T.; Lag-Brotons, A.J.; Herbert, B.M.J.; Aggidis, G.; Aiouache, F. Effects of wood ash-based alkaline treatment on nitrogen, carbon, and phosphorus availability in food waste and agro–industrial waste digestates. Waste Biomass Valorization 2021, 12, 3355–3370. [Google Scholar] [CrossRef]
  68. Adamovičs, A.; Poiša, L. The effects of digestate and wood ash mixtures on the productivity and yield quality of winter wheat. Environ. Technol. Resour. 2025, 1, 17–21. [Google Scholar] [CrossRef]
Agronomy 15 01968 g001
Figure 1. Maize plants just before harvest (BBCH53 phase—the beginning of panicle eruption). WBA—wood biomass ash; ULD—unseparated liquid digestate; SSD—separated solid digestate; SLD—separated liquid digestate.
Figure 1. Maize plants just before harvest (BBCH53 phase—the beginning of panicle eruption). WBA—wood biomass ash; ULD—unseparated liquid digestate; SSD—separated solid digestate; SLD—separated liquid digestate.
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Agronomy 15 01968 g002
Figure 2. Plant height (in cm): (a) mean for objects; (b) mean for doses; (c) mean for series. WBA—wood biomass ash; ULD—unseparated liquid digestate; SSD—separated solid digestate; SLD—separated liquid digestate; 0, 0.5, 1.0 and 1.5 HAC—doses of WBA; different lowercase and uppercase letters indicate significant differences at p ≤ 0.05; n = 3; various lowercase letters (a–d) next to the given values indicate the significant influence of the interaction of the doses of WBA and the DG fraction on the examined feature; capital letters (A–C) indicate the significant influence of the WBA dose (mean for all series) or DG fraction (mean for all doses); the same letters indicate the lack of significance of the factors considered.
Figure 2. Plant height (in cm): (a) mean for objects; (b) mean for doses; (c) mean for series. WBA—wood biomass ash; ULD—unseparated liquid digestate; SSD—separated solid digestate; SLD—separated liquid digestate; 0, 0.5, 1.0 and 1.5 HAC—doses of WBA; different lowercase and uppercase letters indicate significant differences at p ≤ 0.05; n = 3; various lowercase letters (a–d) next to the given values indicate the significant influence of the interaction of the doses of WBA and the DG fraction on the examined feature; capital letters (A–C) indicate the significant influence of the WBA dose (mean for all series) or DG fraction (mean for all doses); the same letters indicate the lack of significance of the factors considered.
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Agronomy 15 01968 g003
Figure 3. Leaf greenness index (SPAD) of maize: (a1–a3) 1st measurement date; (b1–b3) 2nd measurement date; (c1–c3) 3rd measurement date; (d1–d3) 4 th measurement date; (e1–e3) mean SPAD for all objects; 1—mean for objects; 2—mean for doses; 3—mean for series; WBA—wood biomass ash; ULD—unseparated liquid digestate; SSD—separated solid digestate; SLD—separated liquid digestate; different lowercase letters indicate significant differences at p ≤ 0.05; n = 3; various lowercase letters (a–f) next to the given values indicate the significant influence of the interaction of the doses of WBA and the DG fraction on the examined feature; capital letters (A–C) indicate the significant influence of the WBA dose (mean for all series) or DG fraction (mean for all doses); the same letters indicate the lack of significance of the factors considered.
Figure 3. Leaf greenness index (SPAD) of maize: (a1–a3) 1st measurement date; (b1–b3) 2nd measurement date; (c1–c3) 3rd measurement date; (d1–d3) 4 th measurement date; (e1–e3) mean SPAD for all objects; 1—mean for objects; 2—mean for doses; 3—mean for series; WBA—wood biomass ash; ULD—unseparated liquid digestate; SSD—separated solid digestate; SLD—separated liquid digestate; different lowercase letters indicate significant differences at p ≤ 0.05; n = 3; various lowercase letters (a–f) next to the given values indicate the significant influence of the interaction of the doses of WBA and the DG fraction on the examined feature; capital letters (A–C) indicate the significant influence of the WBA dose (mean for all series) or DG fraction (mean for all doses); the same letters indicate the lack of significance of the factors considered.
Agronomy 15 01968 g003
Table 1. Basic parameters of the materials (WBA, ULD, SSD, SLD) used in the experiment.
Table 1. Basic parameters of the materials (WBA, ULD, SSD, SLD) used in the experiment.
ParameterUnitWBAULDSSDSLD
Dry mas%60.28 ± 0.6465.509 ± 0.23924.56 ± 0.6195.238 ± 0.044
Soil reaction (pHKCl)−log10(H+)11.97 ± 0.0907.477 ± 0.0349.527 ± 0.0257.487 ± 0.026
Electrical conductivity (EC)mS cm−110.49 ± 0.22529.13 ± 1.04025.15 ± 1.10528.87 ± 0.943
Hydrolytic acidity (HAC)mmol kg−1600.0 ± 4.082285.0 ± 8.500116.3 ± 3.750300.0 ± 5.000
Total carbon (TC)g kg−1231.7 ± 8.33320.95 ± 0.11939.05 ± 1.33819.51 ± 0.579
Total nitrogen (Ntot)g kg−13.550 ± 0.3302.800 ± 0.1145.833 ± 0.1752.473 ± 0.175
C/Nratio65.27 ± 7.1757.496 ± 0.3496.700 ± 0.3067.943 ± 0.781
Phosphorus (Ptot)g kg−110.51 ± 0.3272.108 ± 0.16413.36 ± 0.4882.053 ± 0.073
Potassium (Ktot)g kg−133.41 ± 0.1278.558 ± 0.0627.722 ± 0.2098.359 ± 0.129
Magnesium (Mgtot)g kg−110.31 ± 0.0510.384 ± 0.0020.482 ± 0.0020.368 ± 0.005
Calcium (Catot)g kg−1168.9 ± 0.5142.368 ± 0.1024.772 ± 0.0222.138 ± 0.228
Sodium (Natot)g kg−12.180 ± 0.0243.409 ± 0.0713.245 ± 0.0963.507 ± 0.120
Alkalinity (%CaO)(%CaO)26.93 ± 0.876---
WBA—wood biomass ash; ULD—unseparated liquid digestate; SSD—separated solid digestate; SLD—separated liquid digestate; -: not marked.
Table 2. Yield of maize above ground mass (g FM pot−1).
Table 2. Yield of maize above ground mass (g FM pot−1).
WBA Doses of HACWBAWBA + ULDWBA + SSDWBA + SLDMean for Doses
0498.2 ± 25.60 a716.8 ± 26.49 c604.9 ± 16.00 b719.6 ± 8.79 cd634.9 ± 93.76 A
0.5478.7 ± 14.03 a694.5 ± 46.06 c607.7 ± 24.87 b706.8 ± 3.87 c621.9 ± 95.07 A
1.0469.0 ± 11.03 a691.8 ± 15.31 c617.5 ± 9.75 b757.8 ± 13.15 d634.0 ± 108.2 A
1.5478.7 ± 11.67 a700.7 ± 18.25 c631.9 ± 3.27 b734.0 ± 5.45 cd636.3 ± 98.84 A
Mean for series481.1 ± 19.75 A701.0 ± 30.69 C615.5 ± 18.89 B729.6 ± 20.78 D631.8 ± 99.28
r−0.386 n.s.−0.185 n.s.0.537 n.s.0.506 n.s.0.000 n.s.
WBA—wood biomass ash; ULD—unseparated liquid digestate; SSD—separated solid digestate; SLD—separated liquid digestate; different lowercase and uppercase letters indicate significant differences at p ≤ 0.05; n = 3; r—correlation coefficient; n.s.—not significant; various lowercase letters (a–d) next to the given values indicate the significant influence of the interaction of the doses of WBA and the DG fraction on the examined feature; capital letters (A–D) indicate the significant influence of the WBA dose (mean for all series) or DG fraction (mean for all doses); the same letters indicate the lack of significance of the factors considered.
Table 3. Dry matter (DM) content (%) of maize.
Table 3. Dry matter (DM) content (%) of maize.
WBA Doses of HACWBAWBA + ULDWBA + SSDWBA + SLDMean for Doses
020.44 ± 0.619 c20.61 ± 0.936 c21.06 ± 0.891 c20.60 ± 0.642 c20.68 ± 0.818 A
0.519.58 ± 0.846 bc21.27 ± 1.243 c20.80 ± 1.340 c21.44 ± 0.244 c20.77 ± 1.249 A
1.017.69 ± 1.150 a21.03 ± 0.150 c20.93 ± 0.809 c20.22 ± 0.718 c19.97 ± 1.569 A
1.518.04 ± 0.715 ab21.43 ± 0.473 c21.09 ± 0.461 c20.68 ± 0.242 c20.31 ± 1.428 A
Mean for series18.94 ± 1.411 B21.08 ± 0.873 A20.97 ± 0.937 A20.73 ± 0.675 A20.43 ± 1.335
r−0.720 **0.286 n.s.0.027 n.s.−0.157 n.s.0.000 n.s.
WBA—wood biomass ash; ULD—unseparated liquid digestate; SSD—separated solid digestate; SLD—separated liquid digestate; different lowercase and uppercase letters indicate significant differences at p ≤ 0.05; n = 3; r—correlation coefficient; **—significant at p ≤ 0.01; n.s.—not significant; various lowercase letters (a–c) next to the given values indicate the significant influence of the interaction of the doses of WBA and the DG fraction on the examined feature; capital letters (A, B) indicate the significant influence of the WBA dose (mean for all series) or DG fraction (mean for all doses); the same letters indicate the lack of significance of the factors considered.
Table 4. Content of macronutrients (N, P, K, Mg, Ca and Na) of maize (g kg−1 DM).
Table 4. Content of macronutrients (N, P, K, Mg, Ca and Na) of maize (g kg−1 DM).
WBA Doses of HACWBAWBA + ULDWBA + SSDWBA + SLDMean for Doses
Nitrogen (N)
05.413 ± 0.476 abcd6.160 ± 0.229 de4.947 ± 0.132 ab5.040 ± 0.457 ab5.390 ± 0.595 A
0.55.507 ± 0.660 abcd6.067 ± 0.476 de5.133 ± 0.132 ab5.693 ± 0.264 bcde5.600 ± 0.548 AB
1.06.067 ± 0.132 de5.880 ± 0.229 cde4.853 ± 0.132 a5.227 ± 0.132 abc5.507 ± 0.515 AB
1.57.280 ± 0.396 f6.347 ± 0.264 e4.760 ± 0.229 a4.853 ± 0.132 a5.810 ± 1.091 B
Mean for series6.067 ± 0.873 B6.113 ± 0.358 B4.923 ± 0.213 A5.203 ± 0.419 A5.577 ± 0.743
r0.789 **0.116 n.s.−0.442 n.s.−0.274 n.s.0.176 n.s.
Phosphorus (P)
04.225 ± 0.116 c4.133 ± 0.448 c4.217 ± 0.242 c3.622 ± 0.315 abc4.049 ± 0.394 C
0.53.702 ± 0.238 abc3.869 ± 0.127 abc3.616 ± 0.125 abc3.538 ± 0.420 abc3.681 ± 0.285 AB
1.03.794 ± 0.214 abc4.125 ± 0.536 c3.793 ± 0.568 abc3.535 ± 0.357 abc3.812 ± 0.489 BC
1.54.039 ± 0.360 bc3.189 ± 0.121 a3.362 ± 0.123 ab3.282 ± 0.007 a3.468 ± 0.390 A
Mean for series3.940 ± 0.322 B3.829 ± 0.526 AB3.747 ± 0.447 AB3.494 ± 0.342 A3.753 ± 0.449
r−0.161 n.s.−0.547 n.s.−0.597 n.s.−0.334 n.s.−0.402 **
Potassium (K)
016.00 ± 0.633 a18.83 ± 0.821 bcd16.39 ± 1.337 ab20.97 ± 1.323 defg18.05 ± 2.277 B
0.519.89 ± 0.327 cde20.88 ± 1.762 defg17.22 ± 1.379 abc22.51 ± 1.417 efgh20.12 ± 2.338 C
1.023.01 ± 2.070 fghi24.12 ± 1.399 hi18.98 ± 0.873 bcd23.78 ± 1.018 ghi22.48 ± 2.497 A
1.525.56 ± 1.298 i23.41 ± 1.680 ghi20.26 ± 0.294 def24.57 ± 1.231 hi23.45 ± 2.345 A
Mean for series21.11 ± 3.791 A21.81 ± 2.561 AB18.21 ± 1.846 C22.96 ± 1.852 B21.02 ± 3.164
r0.938 **0.742 **0.810 **0.728 **0.656 **
Magnesium (Mg)
00.627 ± 0.088 a0.809 ± 0.029 bcde0.718 ± 0.028 abc0.716 ± 0.037 ab0.718 ± 0.083 C
0.50.767 ± 0.110 bcde0.834 ± 0.024 bcde0.807 ± 0.064 bcde0.788 ± 0.030 bcde0.799 ± 0.071 A
1.00.882 ± 0.013 ef0.840 ± 0.015 bcde0.750 ± 0.038 bcd0.794 ± 0.012 bcde0.817 ± 0.054 AB
1.50.979 ± 0.064 f0.851 ± 0.047 de0.769 ± 0.014 bcde0.845 ± 0.088 cde0.861 ± 0.096 B
Mean for series0.814 ± 0.153 AB0.833 ± 0.035 B0.761 ± 0.051 A0.786 ± 0.068 AB0.798 ± 0.093
r0.857 **0.427 n.s.0.209 n.s.0.643 *0.537 **
Calcium (Ca)
00.591 ± 0.013 ab0.641 ± 0.034 abcd0.577 ± 0.010 a0.632 ± 0.026 abc0.610 ± 0.035 A
0.50.674 ± 0.018 abcde0.694 ± 0.006 bcdef0.593 ± 0.018 ab0.680 ± 0.060 abcde0.660 ± 0.051 B
1.00.725 ± 0.021 cdef0.709 ± 0.077 cdef0.694 ± 0.021 bcdef0.743 ± 0.057 def0.718 ± 0.054 C
1.50.944 ± 0.070 g0.790 ± 0.044 f0.745 ± 0.073 def0.776 ± 0.064 ef0.814 ± 0.100 D
Mean for series0.847 ± 0.136 A0.742 ± 0.072 A0.775 ± 0.080 B0.686 ± 0.078 A0.763 ± 0.100
r0.734 **0.708 **0.652 *0.707 **0.700 **
Sodium (Na)
00.847 ± 0.008 c0.986 ± 0.030 d0.656 ± 0.002 a1.055 ± 0.042 e0.886 ± 0.155 A
0.50.851 ± 0.015 c0.982 ± 0.030 d0.657 ± 0.022 a1.067 ± 0.027 e0.889 ± 0.156 A
1.00.855 ± 0.006 c0.954 ± 0.007 d0.712 ± 0.014 b0.976 ± 0.007 d0.874 ± 0.105 A
1.50.878 ± 0.016 c0.946 ± 0.025 d0.713 ± 0.006 b0.964 ± 0.022 d0.875 ± 0.101 A
Mean for series0.858 ± 0.017 B0.967 ± 0.030 C0.684 ± 0.031 A1.015 ± 0.054 D0.881 ±0.132
r0.636 *−0.540 n.s.0.816 **−0.762 **−0.040 n.s.
WBA—wood biomass ash; ULD—unseparated liquid digestate; SSD—separated solid digestate; SLD—separated liquid digestate; different lowercase and uppercase letters indicate significant differences at p ≤ 0.05; n = 3; r—correlation coefficient; **—significant at p ≤ 0.01; *—significant at p ≤ 0.05; n.s.—not significant; various lowercase letters (a–i) next to the given values indicate the significant influence of the interaction of the doses of WBA and the DG fraction on the examined feature; capital letters (A–D) indicate the significant influence of the WBA dose (mean for all series) or DG fraction (mean for all doses); the same letters indicate the lack of significance of the factors considered.
Table 5. Correlation coefficient (r) between the content of macronutrients (N, P, K, Mg, Ca and Na) of maize.
Table 5. Correlation coefficient (r) between the content of macronutrients (N, P, K, Mg, Ca and Na) of maize.
ElementsNitrogen (N)Phosphorus (P)Potassium (K)Magnesium (Mg)Calcium (Ca)
Phosphorus (P)0.235 n.s.
Potassium (K)0.388 **−0.276 n.s.
Magnesium (Mg)0.672 **−0.086 n.s.0.595 **
Calcium (Ca)0.494 **−0.246 n.s.0.759 **0.647 **
Sodium (Na)0.308 *−0.120 n.s. 0.532 **0.143 n.s.0.206 n.s.
r—correlation coefficient; **- significant at p ≤ 0.01; *—significant at p ≤ 0.05; n.s.—not significant.
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Rolka, E.; Wyszkowski, M.; Skorwider-Namiotko, A.; Szostek, R. Fertilisation Potential of Combined Use of Wood Biomass Ash and Digestate in Maize Cultivation. Agronomy 2025, 15, 1968. https://doi.org/10.3390/agronomy15081968

AMA Style

Rolka E, Wyszkowski M, Skorwider-Namiotko A, Szostek R. Fertilisation Potential of Combined Use of Wood Biomass Ash and Digestate in Maize Cultivation. Agronomy. 2025; 15(8):1968. https://doi.org/10.3390/agronomy15081968

Chicago/Turabian Style

Rolka, Elżbieta, Mirosław Wyszkowski, Anna Skorwider-Namiotko, and Radosław Szostek. 2025. "Fertilisation Potential of Combined Use of Wood Biomass Ash and Digestate in Maize Cultivation" Agronomy 15, no. 8: 1968. https://doi.org/10.3390/agronomy15081968

APA Style

Rolka, E., Wyszkowski, M., Skorwider-Namiotko, A., & Szostek, R. (2025). Fertilisation Potential of Combined Use of Wood Biomass Ash and Digestate in Maize Cultivation. Agronomy, 15(8), 1968. https://doi.org/10.3390/agronomy15081968

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