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Article

Forest Logging Residue Valorization into Valuable Products According to Circular Bioeconomy

by
Sarmite Janceva
1,
Agrita Svarta
2,
Vizma Nikolajeva
3,
Natalija Zaharova
1,
Gints Rieksts
1 and
Anna Andersone
1,4,*
1
Laboratory of Lignin Chemistry, Latvian State Institute of Wood Chemistry, Dzerbenes Street 27, LV-1006 Riga, Latvia
2
Faculty of Agriculture, Latvia University of Life Sciences and Technologies, 2 Liela Str., LV-3001 Jelgava, Latvia
3
Microbial Strain Collection of Latvia, Faculty of Medicine and Life Sciences, University of Latvia, Jelgavas Street 1, LV-1004 Riga, Latvia
4
Ekokompozit Ltd., Dzerbenes 27, LV-1006 Riga, Latvia
*
Author to whom correspondence should be addressed.
Forests 2025, 16(9), 1418; https://doi.org/10.3390/f16091418
Submission received: 30 June 2025 / Revised: 21 August 2025 / Accepted: 22 August 2025 / Published: 4 September 2025
(This article belongs to the Section Wood Science and Forest Products)
Browse Figures
Versions Notes

Abstract

The manuscript explores the valorization of forest logging residues, collected during forest management operations between summer 2023 and spring 2025 in mixed deciduous and coniferous forests, as a raw material for producing valuable bioactive products. These products offer a sustainable alternative to synthetic pesticides and fertilizers. Seven batches of biomass, comprising understory trees and branches from deciduous (mainly aspen, birch, and grey alder) and coniferous (mainly Scots pine) species, were collected during different seasons, crushed, and extracted using an ethanol–water solution. The yield of hydrophilic extracts containing proanthocyanidins (PACs) ranged from 18 to 25% per dry biomass. The highest PACs concentration (42% of extract dry mass) was found in small branches with a high bark content. The extracts and PACs at concentrations of 6.25–12.50 mg mL−1 showed fungicidal activity against several pathogenic fungi, including Botrytis cinerea Pers., Mycosphaerella sp. Johanson, Heterobasidion annosum (Fr.) Bref., and Heterobasidion parviporum Niemelä & Korhonen. Residual biomass after extraction, enriched with sea buckthorn berry pomace and a siliceous complex, was characterized and evaluated for its impact on the growth of Scots pine seedlings and selected agricultural crops. Results from forest and agricultural field trials in 2023–2025 confirmed a positive effect of the fertilizer on crop yield and quality at a low application rate (40 kg ha−1 per crop). Fertilizer increased the yield of radish, dill, potatoes, and wheat by up to 44% (highest for potatoes and dill) compared to the reference, confirming its agronomic value.

Graphical Abstract

1. Introduction

Currently, forest logging residues, including deciduous and coniferous tree branches generated during stem delimbing, small-diameter trees harvested during thinning or deforestation, debarking biomass, stumps, and similar materials, are primarily utilized as a renewable energy source [1,2,3]. However, their potential for conversion to high-value bioproducts remains largely underexploited.
The efficient and rational use of local logging residues is a priority within the European Union’s circular and cascading bioeconomy strategy. Latvia ranks fifth in Europe in terms of forest coverage relative to the total area [4], which provides a strong foundation for the proposed study. This approach contributes to reducing reliance on external resources and ensuring consistent, residue-free application of forest biomass in industrial processes.
Forest biomass, particularly bark, is rich in biologically active compounds, with extractives comprising up to 25% of its dry mass (DM), depending on the tree species [5]. These extractives include a complex mixture of phenolic compounds, many of which exhibit antimicrobial and antioxidant properties [6]. Among them, proanthocyanidins (PACs)—oligomers and polymers of flavan-3-ols such as catechin and epicatechin—are of particular interest due to their high reactivity and broad biological activity [7,8]. PACs possess strong antifungal and antibacterial properties and are capable of forming complexes with proteins and metal ions [9,10], which make them promising candidates for sustainable plant protection in agriculture and forestry, helping to reduce the use of chemically synthesized pesticides, lessen the risk of development of the pathogens’ resistance to pesticides, and minimize the environmental impact of fungicidal agents. In addition, residues after the forest logging biomass extraction can serve as a base for organo-mineral fertilizers. These fertilizers help to restore organic matter in the soil and improve both soil structure and fertility, all essential for maintaining the proper functioning of the soil biotic complex. Authors’ previous studies have shown that lignin- and silicon (Si)-based fertilizers promote plant growth and development and increase soil nitrogen (N) and organic matter levels [11,12].
According to literature data, lignocellulosic biomass residues typically contain 5–15 kg of N, 1–3 kg of phosphorus (P), and 5–10 kg of potassium (K) per tonne (t) of dry biomass (DB), depending on tree species and processing methods [13,14,15,16,17,18,19,20]. Although these residues contain lower levels of immediately available nutrients than synthetic fertilizers, they contribute to long-term soil fertility and structural stability. An effective fertilizer should provide macro- and micronutrients, e.g., N, P, K, calcium (Ca), magnesium (Mg), sulphur (S), iron (Fe), and zinc (Zn); support beneficial microbial activity in soil; and enhance nutrient retention [21]. To meet these criteria, the residual forest logging biomass after PACs extraction could be enriched with other components, like siliceous complexes, or the other agricultural processing waste, for example, sea buckthorn pomace.
Such biomass-based fertilizer has the potential to partially replace traditional organic fertilizers such as compost and peat-based soil amendments, as well as mineral fertilizers, particularly in organic or low-input farming systems.
This cascading use of biomass, with extracting high-value compounds first, followed by the application of residues as soil amendments, exemplifies the principles of the circular bioeconomy. Sea buckthorn pomace is a nutrient-rich bioproduct containing significant amounts of nitrogen, phosphorus, potassium, and various micronutrients [22]. Si is an abundant element in soils, but not all forms of Si are bioavailable for plants. Si enhances plant resistance to environmental stress, diseases, and toxicity from heavy metals [23,24], and, thus, Si-based additives can correct deficiencies and support plant growth and development [23,24,25].
Currently, the demand for ecologically friendly plant development stimulants, which increase agricultural crop production yield, improve their quality, and increase stress tolerance without harming the environment, is constantly growing. Such products are particularly valuable in organic agriculture, where input options are limited while quality expectations remain high.
The aim of this study was the evaluation of forest logging residues, obtained at forest cleaning operations and after timber harvesting, as raw materials for the production of value-added bioactive products, specifically, fungicidal PACs extracts and organo-mineral fertilizers, for use in forestry and agriculture as sustainable alternatives to chemically synthesized agrochemicals.
The hypothesis of this study was that forest logging residues, when subjected to ethanol–water extraction and combined with organic and siliceous additives, could yield:
(a) Bioactive extracts or individual compounds with fungicidal properties.
(b) A multifunctional fertilizer capable of increasing the yield and quality of agricultural crops and forest tree seedlings, even at low application rates.

2. Materials and Methods

2.1. Material Collection and Preparation

The forest logging residues (S1–S7) originated from forest cleaning operations conducted in the period from summer 2023 until spring 2025 in mixed deciduous and coniferous forest stands, aged up to 60 years, located in Olaine Parish, Olaine District, Latvia. The dominant tree species included grey alder (Alnus incana (L.) Moench), black alder (Alnus glutinosa (L.) Gaertn.), aspen (Populus tremula L.), birch (Betula pendula Roth), Scots pine (Pinus sylvestris L.), and Norway spruce (Picea abies (L.) H.Karst.). The collected biomass comprised understory trees with a diameter of up to 10 cm and branches pruned from mature trees. Trees, branches, and pine bark (obtained by debarking pine trees) were chipped directly at the harvesting sites using a mobile chipper (Figure 1).
The chips were transported to a storage site, where an average samples were prepared by combining 10 subsamples (10 kg each) collected from different parts of the chip pile. As a result, seven biomass batches (S1–S7) were obtained, each with an initial moisture content >70% (Table 1).
Deciduous and conifer species’ chip fraction size did not exceed 5 cm and included bark. Before further analysis, the samples were dried at 40 °C and milled using a Retsch SM100 rotor mill (RETSCH, Haan, Germany) and sieved. The resulting ground material, hereafter referred to as biomass, was stored at −8 °C.

2.2. Biomass Extraction

The extraction conditions were optimized in our previous studies [26]. For extraction, milled and sieved biomass fractions (S1–S7), in the amount of 20 g per one flask, with a moisture content of 8.6%–9.2% and particle size of ≤1 mm were used. Biomass was extracted using an ethanol–water solution (8:2, v/v). The ratio of dry biomass (DB) to solvent was 1:8 (w:v). Extraction was carried out in a flask for 1 h using heating and stirring with a magnetic stirrer while maintaining a temperature of 60–70 °C. After the extraction, the ethanol was removed by vacuum distillation at 60 °C. The resulting aqueous extracts were cooled to 25 ± 2 °C and subsequently deep frozen at −30 °C. The frozen samples were then transferred to a lyophilization chamber, where, under vacuum (1.2–1.5 hPa) and −50 °C temperature, the frozen solvent was removed via sublimation (Heto PowerDry PL 300, Thermo Scientific, Waltham, MA, USA). This process yielded a dry, homogeneous, powder-like extract that retained its structural integrity and biological activity, thereby significantly extending its shelf life. The yield of extracts and PACs was determined using gravimetric analysis and expressed as a percentage of the DB.

2.3. Determination of PACs Content in Extract

The total content of PACs in the hydrophilic extracts was measured using the butanol-HCl assay, with procyanidin dimer B2 as a reference compound, as described by Andersone et al. [27].

2.4. PACs Isolation

The isolation of PACs from extracts was performed by column chromatography, using Sephadex LH-20 (2.5 cm × 120 cm column), eluted successively with ethanol (96%, v/v) and aqueous acetone (70%, v/v) at room temperature. Each sample was lyophilized as described in Section 2.2 [28].

2.5. Fungicidal Activity Determination

The fungicidal activity tests of the samples were carried out at the Faculty of Biology, University of Latvia. The tested fungi included Botrytis cinerea Pers., Mycosphaerella sp. Johanson, Heterobasidion annosum (Fr.) Bref., and Heterobasidion parviporum Niemelä & Korhonen, obtained from the Microbial Strain Collection of Latvia (MSCL), University of Latvia. Fungi colonies were grown in 9.5 cm Petri dishes. The broth medium (reference sample) was malt extract agar. The deciduous tree extracts were mixed into malt extract medium at concentration of 2%. A 7 mm diameter piece of fungus was placed in the middle of each Petri dish. The minimum inhibitory concentration (MIC) was defined as the lowest concentration of the sample that prevented visible fungal growth on solid medium. The minimum fungicidal concentration (MFC) was defined as the lowest concentration of the tested sample that resulted in ≥99.9% reduction in colony-forming units (CFUs) compared to the reference sample, indicating complete fungicidal effect. The reference sample in the tests consisted of fungal cultures treated with sterile distilled water [29].

2.6. Biomass Residue Modification

The biomass after extraction was hydrolysed using a dilute alkaline solution [30]. After alkaline hydrolysis, the substrate was washed with distilled water to a neutral pH value and enriched with sea buckthorn berry residue and a Si-containing composition in mass ratios (8:1:1, w/w/w). The fertilizer preparation took 30 days, during which the pH and temperature stabilized, indicating the completion of the microbial and chemical transformation processes within the biomass mixture. The preparation was carried out under aerobic conditions at ambient temperature (approximately 22 ± 2 °C) with manual agitation every 48 h to ensure homogeneity and oxygen availability. The stabilization of pH (ranging from 8.5 to 8.7) and temperature fluctuations (<2 °C over the last 5 days) was used as an indicator that the composting-like process had reached maturity.

2.7. Raw Materials, Fertilizer, and Soil Characterization

2.7.1. Wet Chemistry Analysis

The chemical characterization of the fertilizer and soil was performed in accordance with the European standards listed in Table 2.
Each sample was analysed in triplicate. The confidence interval (CI) was 0.2% for moisture and dry matter content, 6.9% for organic matter content, and 2.0 for the Klason method, at α = 0.05.

2.7.2. FTIR Analysis

For recording the FTIR spectra, the samples (1.6 mg) were added to KBr (weight 200 mg including the sample), milled in an agate mortar by an agate pestle to make a fine mixture and even distribution of the sample, and pressed to make a pellet. The Nicolet iS50 FT-IR spectrometer (Thermo Scientific, Waltham, MA, USA) was used for recording the spectra as described in Andersone et al. [27]. Detection range was 4400–400 cm−1. Room temperature was 22 °C, and before each measure, a background spectrum was recorded to avoid influence of changes in humidity and temperature. Then, 32 scans were performed automatically, at a resolution of 4 cm−1. Program The Spectrum v5.0.1 was applied for the spectrum processing.

2.7.3. Elemental Analysis

The N content was analysed by the Vario MACRO CHNS elemental analysis equipment with a thermal conduction detector (Elementar Analysensysteme GmbH, Langenselbold, Germany) [35]. The prepared sample and combustion catalyst mixture was tableted and put in the automatic sample feeder. The data were processed using VARIOEL V5.16.10 software, and the N content was expressed as a percentage of DM. Each sample was analysed in triplicate. The CI was 0.2% at α = 0.05 [36].

2.7.4. ICP-MS Analysis

The contents of the P and K (in soil and fertilizer) and heavy metals, namely, arsenic (As), cadmium (Cd), lead (Pb), and mercury (Hg), were detected by ICP-MS analysis using Thermo Fisher Scientific iCAP TQe equipment (Bremen, Germany, as described in Naccarato et al. [37]. A peristaltic pump and an autosampler ASX-560 (Thermo Fisher Scientific, GmbH, Bremen, Germany) were used to pump the solutions from the tubes. Before analysis, the ICP-MS system was stabilized for 20–30 min. Equipment tuning was performed using a dedicated tuning solution to optimize signal strength and minimize interference. High-purity argon (0.8 mL min−1 in auxiliary flow) and helium (5.3 mL min−1 in the nebulizer flow) gases (99.99%) were used. Sample digestion was performed using 65% nitric acid (HNO3, Suprapur®, Supelco, Bellefonte, PA, USA) and 30% hydrogen peroxide (H2O2). Calibration curves for quantitative analysis were prepared by serial dilution of standard multielement solutions: K, P, Cd, As, and Pb, 10 mg L−1, and Hg, 1000 mg L−1, (Merck, Darmstadt, Germany). Each analytical batch included calibration standards, procedural blanks, and the test samples. Sample weight was 100 mg, and all analyses were performed in triplicate. The CI was 3.2% at α = 0.05.

2.7.5. Determination of Humic Substances in the Fertilizer

The determination of the humic substances was performed according to the standard procedures for agricultural chemical analysis. A 10 g of dry fertilizer sample was weighed, and 200 mL of 0.5 M sodium hydroxide (NaOH) was added to the sample. The mixture was shaken for 24 h. For separation of the insoluble humin, centrifugation was used, and the entire supernatant was transferred to a clean centrifuge tube. Then, for adjustment of the pH to 2.0, 6 M hydrochloric acid (HCl) was added to the supernatant, followed by centrifugation to precipitate the humic acids. The CI was 0.5 at α = 0.05 [38].

2.7.6. Evaluation of the Porous Structure of Fertilizer

The porous structure (specific surface area and total pore volume) was evaluated based on the nitrogen adsorption-desorption isotherm at 77 K using Nova 4200e equipment (Quantachrome, Boynton Beach, FL, USA) [39].

2.8. Field Experiments

Field experiments with wheat, dill, radish, and potatoes were carried out during the 2023/2024 growing season at a certified organic farm (N 56° 69.275′, E 25° 14.173′). Potatoes, wheat, dill, and radish were selected as test plants because they are among the most cultivated crops in Latvia. The soil composition was determined using the methods described in Section 2.7.3 and Section 2.7.4 Weather data, including air temperature and rainfall, were tracked throughout the season and compared to long-term averages. Data were obtained from the Skriveri Observation Station of the Latvian Environment, Geology, and Meteorology Centre. The samples and plot sizes are listed in Table 3.
Standard agronomic planting norms for Latvia were applied dill, 1–2 g m−2, radish 6–8 kg ha−1.
Fertilizer trials were performed on two plots: F0—reference plot without fertilizer; F1—plot with fertilizer applied at 40 kg ha−1. The field trials were arranged in four replicates. Soil samples were collected in accordance with the regulations of the Environmental Plant Protection Service.

2.8.1. Wheat Cultivation and Characterization

The varieties used in the field trials were winter wheat “Edvin” and spring wheat “Robijs”. After harvest, grain yield, grain purity, and moisture content were measured. Yield-forming components were assessed at wheat growth stages (GS) 87–89. Plant samples were collected at each plot at two random locations (each 0.5 m2). The following parameters were recorded: number of productive tillers per 1 m2; number of grains per spike (calculated as the total number of grains divided by the number of productive tillers). The weight of 1000 grains was measured according to the EN ISO 520:2010 standard “Cereals and Pulses” [41], using a Cantador seed counter (Pfeuffer GmbH, Kitzingen, Germany) and an electronic balance. Total protein content, wet gluten content, Zeleny’s sedimentation index, starch content, and bulk density were determined by near-infrared reflectance spectroscopy (NIRS) [42] using the OmegAnalyzer Grain equipment (Bruins Instruments, Puchheim, Germany) and InfratecTM NOVA (FOSS, Hilleroed, Denmark). The falling number for winter wheat was measured using the Hagberg-Perten method (ISO 3093:2009) [43].

2.8.2. Radish Cultivation and Characterization

Field trials with the autumn radish variety “Rosso Tondo” were carried out in 2023. The following parameters were measured: total yield, standard yield (roots that are healthy, have a uniform pulp, and are free from cracks, hollow or woody areas, undeveloped zones, insect damage, or microbial contamination), the proportion of standard yield in the total yield, and average root weight. To assess the impact of fertilizer treatment on radish yield, a one-way ANOVA analysis was performed.

2.8.3. Dill Cultivation, Characterization, and Extraction

Field trials with the dill cultivar “Thalia” were carried out in 2023. The dill green mass was collected on the 63rd day of growing, in accordance with Cabinet of Ministers Regulation No. 461, “Requirements for Food Quality Schemes, Their Implementation, Operation, Monitoring and Control Procedure” [34], and its total yield was measured in kg m−2. The effect of the fertilizer on dill quality was assessed by isolating hydrophilic extracts from dill green mass and quantifying biologically active compounds in the extracts’ composition.
Extraction of hydrophilic compounds from dill green mass was performed by ethanol–water solution (1:1, v/v) at 50 °C for 30 min. Following extraction, ethanol was evaporated from the ethanol-containing extracts, and the remaining aqueous extracts were freeze-dried. The yield of the dry extract (DE) was expressed as a percentage of the dill DM. The CI was ≤3% at α = 0.05.
The total polyphenol content of the dill extracts was determined using the Folin–Ciocalteu method as described in Andersone et al. [44], calculated from a standard curve in milligrams of gallic acid equivalents (mg GAE) per gram of dry extract. The CI ≤3% at α = 0.05.
Determination of total flavonoid content in dill extracts was performed according to Shay et al. [45] with slight modifications. Then, 10 mg of the dry sample was dissolved in 25 mL of 50% ethanol–water solution (1:1, v/v). After that, 0.4 mL of the sample solution was added to a 10 mL tube with 2 mL of distilled water. Subsequently, 0.12 mL of 5% sodium nitrite solution was added to the solution, and the mixture stayed for 5 min at room temperature. This was followed by the addition of 0.24 mL of 10% aluminium nitrate solution. In 6 min, 1 mol L−1 sodium hydroxide in the amount of 0.8 mL was added. The absorbance was measured at 420 nm using a UV/VIS spectrometer (Lambda 650, Perkin Elmer, Inc., Waltham, MA, USA) against a blank containing 1 mL of the extraction solvent. A calibration curve with a rutin standard was performed. The results were expressed as milligrams of rutin equivalents (mg RU) per gram of dry extract. CI was ≤3% at α = 0.05.
The PAC content in the dill extracts was determined according to the method described by Andersone et al. [27].

2.8.4. Potato Cultivation and Characterization

Field trials were performed with potato cultivar “Imanta”. It was planted on May 15 and harvested on 3 September 2024. After harvesting, potato tubers were sorted into three size fractions: small (<35 mm), medium (35–55 mm), and large (>55 mm) tubers. Each size fraction was weighed separately with an accuracy of 0.1 kg. Tubers with visible external defects, including rot, cracks, or disease symptoms, were collected, separately weighed with the same accuracy, and included in the substandard yield (classified under the small tubers fraction). Mechanically damaged tubers were assigned to their corresponding size fraction. The total yield was calculated as the sum of all size categories and expressed in t ha−1. Commercial yield was determined by combining the weights of medium and large tubers. Tuber yield was calculated using the following formula:
R = (S + N)/L × 10,
where (at the end of the growing season): R—yield of tubers (t ha–1), S—mass of commercial tubers (kg), N—mass of small tubers (kg), and L—area of the plot (m2).

2.9. Field Experiments with Pine Seedlings

Pine seedlings were grown in a forest plantation with fertilizer applied individually to each seedling (40 kg ha−1). Growth dynamics were assessed by measuring the length of the aboveground part.

2.10. Statistical Analyses

Field Experiments
The Bonferroni test was applied for multiple comparisons of means at a significance level of p < 0.05. Statistical analysis was carried out using the open-source software “R,” version 4.0.2. Analysis of variance (ANOVA) was performed using RStudio version 4.4.3 to analyse the experimental data, including yield-forming components and yield. Values that were significantly different were labelled with different superscript letters (a,b). If the effect of the studied factor was not significant (p > 0.05), the symbol “n” was used.
All measurements were performed in triplicate. The results are the mean value ± standard deviation (SD). Statistical analyses were performed in Microsoft Excel 2018. Confidence intervals (CI) for a mean using Student’s T distribution were calculated at a significance level of α = 0.05.

3. Results and Discussion

3.1. Assessment of Biomass as a Potential Source for PAC-Rich Extract Isolation

To evaluate the potential of forest waste as a raw material for PAC extraction, branches were collected during forest felling, chopped into chips, and subsequently crushed to a size of 1–2 mm. Due to its high selectivity towards polyphenolic compounds, ethanol–water solution was used as the extractant. The extract yield from all studied biomass batches was in the range of 18%–25%/DM. The content of the extract’s main target compound, PACs, was not lower than 28%/DM in six samples, except for one (sample S7) with PACs content of 16%/DM. The highest PACs content (41.8%/DM) was found in pine bark collected in autumn of the year 2024. (Figure 2).
Lower content of PAC in the sample S7 could be linked to the low bark proportion in this sample’s biomass. Numerous authors have shown that bark contains the highest PACs levels, which are associated with their accumulation under various stress conditions, such as low temperature, drought, injury, high light intensity, and pathogen attack [46]. Several studies have reported that the bark of Pinus caribaea Morelet, Alnus glutinosa (L.) Gaertn., Alnus incana (L.) Moench, Quercus robur L., and Pinus sylvestris L. is a valuable raw material for producing PAC-rich extracts [47,48,49].
Based on the obtained data, a comparative analysis of the seven biomass batches (S1–S7) indicates that approximately 220 kg of PACs-rich extract, or about 70 kg of isolated PACs, can be obtained from 1 t of forest logging residues. This highlights the significant potential of forest by-products as a sustainable source of valuable bioactive compounds for use in agricultural and industrial applications.

3.2. Fungicidal Activity of the Extracts

Our previous studies indicate that PACs are powerful antioxidants. In addition, PACs exhibit antimicrobial effect properties, inhibiting bacteria (E. coli, B. cereus, S. aureus, etc.) and fungi (C. albicans) [27,44], as well as demonstrating anti-inflammatory properties. Potential antitumor effects have also been reported [50]. However, despite their fungicidal properties, PACs do not always inhibit all fungal growth, which could be associated with the presence of polyphenolic glucosides. To evaluate the potential of PACs-rich extracts isolated from forest waste biomass as antifungal agents, studies were conducted on their inhibitory effects against phytopathogenic fungi: Botrytis cinerea, Mycosphaerella sp., Heterobasidion annosum, and Heterobasidion parviporum.
Botrytis cinerea can infect more than 200 plant species; it causes grey mould characterized by a fuzzy grey mycelium. It is one of the most destructive plant pathogens globally, leading to estimated economic losses of USD 10 to 100 billion annually [51]. Our results demonstrated that only PACs-rich extracts (from S1 biomass) exhibited fungicidal activity against B. cinerea. The PACs-free fraction showed no significant effect compared to the control. At a 2% concentration, the PAC-rich extract reduced the fungal colony formation by 1.9 times within three days. (Figure 3).
Similar studies have reported that PACs, particularly those from grape seeds, effectively inhibit B. cinerea with an IC50 ranging from 11.2 to 12.2 mg mL−1 [51]
Septoria tritici leaf blotch, caused by Mycospharella spp., is a widespread wheat disease worldwide, leading to yield losses of up to 50% annually in affected regions [52]. All samples containing oligomeric and low-molecular-weight polyphenols and their glycosides showed antifungal activity against Mycospharella spp., reducing fungal colony development by 1.2 to 1.5 times over six days at a 2% concentration.
Heterobasidion annosum, a basidiomycete responsible for conifer root and butt rot, poses a major threat to commercial forestry, particularly in Scandinavia, where it affects Norway spruce (Picea abies) in up to 25% of forest stands and causes hundreds of millions of euros in losses each year [53]. Both extract types showed fungicidal effects, with the PACs-containing samples being more effective. Similar activity was observed against Heterobasidion parviporum, which causes white rot and significantly reduces timber quality [54].
The MIC and MFC were studied for three samples: (1) isolated PACs from the extract; (2) extract containing 36% PACs/DM; (3) the fraction remaining after PACs isolation, consisting predominantly of polyphenols with low molecular weight. The results, summarized in Table 4, showed that all samples exhibited fungicidal activity. Compared to the isolated PACs, the PACs-rich extract was more effective against Botrytis cinerea, Heterobasidion annosum, and Heterobasidion parviporum. The enhanced activity is likely due to the synergetic effects of PACs with other polyphenols, such as flavonoids, present in the extract. In contrast, the PACs-free fraction exhibited lower activity, highlighting the significant role of PACs in the overall antifungal efficacy of the extracts.
Compared to commercial preparations, the obtained extract and the released PACs are more effective and can be used for plant protection (Table 5).

3.3. Raw Material and Fertilizer Composition Characteristics

An analysis of raw materials was conducted to prepare the fertilizer. The elemental analysis showed that the biomass is rich in carbon (56%–59% per DM) and low in nitrogen (1%–3% per DM). Sea buckthorn pomace is high in vitamins and micro- and macro-elements, containing 2.4% of N, 1.1% of P, and 2.2% of K (all per DM). It also contains organic matter (89% per DM), making it a valuable organo-mineral component for natural fertilizers. Although precise statistical data on sea buckthorn pomace quantities in Latvia are unavailable, estimates suggest an annual volume of 1440 to 1920 tonnes, representing a significant resource for agriculture and industry. Sapropel was used as a humic-containing component, with an organic matter content of about 94%, including 26% of humic acids and 8% of fulvic acids. Latvia’s sapropel reserves are estimated at approximately 190 million tonnes. This is an organic-rich sediment that is notable for its high nutrient levels. The final fertilizer product, based on the S1 biomass residue, was characterized using FTIR (Figure 4).
The FTIR spectrum of the fertilizer shows complex functional groups characteristic of lignocellulosic and mineral-organic matrices. A broad band between 3200 and 3600 cm−1 indicates the presence of hydroxyl groups; peaks at 2920 cm−1 and 2850 cm−1 correspond to C-H stretching vibrations. A band near 1700 cm−1 indicates the presence of C=O groups, while signals in the 1600–1650 cm−1 region indicate aromatic C=C bonds or phenolic OH groups. Absorption around 1000–1100 cm−1 corresponds to C-O-C and Si-O vibrations, confirming Si incorporation. Additional signals in the 800–500 cm−1 range are associated with Si-O deformation and aromatic ring bending. Overall, the FTIR analysis confirms that the fertilizer has a complex structure comprising organic and inorganic components, which support soil stabilization and nutrient retention.
The fertilizer has a low moisture content (6.4 ± 0.1%), ensuring good storage stability. The dry matter content was 94.0 ± 0.1%, with a high organic matter content of 92.8 ± 1.4%. The lignin was present at 38.5 ± 0.5%, contributing to structural stability and long-term improvement in soil texture. Lignin’s slow biodegradation contributes to carbon sequestration and supports microbial activity, which plays a key role in organic matter turnover and soil health [60]. Furthermore, lignin fragments can indirectly stimulate root proliferation by modifying soil porosity and water-holding capacity.
Humic acids accounted for 4.3 ± 0.1%, which is agronomically significant. These substances enhance soil fertility by increasing cation exchange capacity, buffering pH, and improving nutrient uptake, particularly of N and P. Additionally, humic acids have been shown to stimulate root elongation and plant growth by acting as natural bio-stimulants with auxin-like effects [61]. Their presence may also increase drought tolerance by improving water retention in the rhizosphere.
The fertilizer contained 2.35 ± 0.02% total N, an essential nutrient for plant growth. However, levels of P (0.6 ± 0.1%) and K (0.4 ± 0.1%) were relatively low, suggesting that the product may primarily function as an organic soil amendment or be used in combination with mineral P and K sources for balanced fertilization strategies.
Heavy metal analysis indicated low contamination: Hg was below the detection limit (<0.2 mg kg−1), As was 0.17 ± 0.02 mg kg−1, and Cd was 1.13 ± 0.09 mg kg−1, all within the regulatory limits defined by Cabinet of Ministers Regulation No. 506. No lead (Pb) was detected. The pH was moderately alkaline at 8.7, which is beneficial for neutralizing acidic soils, improving nutrient availability in such conditions, and suppressing certain soil-borne pathogens.
Si has known benefits in improving plant resistance to abiotic and biotic stresses, enhancing mechanical strength, and reducing susceptibility to diseases [23]. Its incorporation in organic fertilizers contributes to improved crop performance, especially in stress-prone environments.
BET surface area was 0.87 m2 g−1 with a pore volume of 2.48 mm3 g−1 (Figure 5), indicating a moderately porous structure that supports moisture retention and aeration, aiding root growth and microbial activity. These properties facilitate nutrient release and improve fertilizer efficiency in the field.
Although the measured BET surface area is relatively low compared to highly porous materials, such as activated biochar (typically > 100 m2 g−1), it is comparable to or even higher than values reported for many composts and organic soil amendments, which often range from 0.5 to 5 m2 g−1 [62]. For organic-based fertilizers, BET values in this range are considered adequate to ensure beneficial physical properties such as water-holding capacity and slow nutrient release. Thus, the obtained value is consistent with the expected functionality of organo-mineral fertilizers derived from natural raw materials.

3.4. Field Experiments with Raddish, Dill and Potato

The soil agrochemical properties were as follows: pH 5.2–6.0, organic matter content of 2.2%–2.7% per DM, plant-available P of 51–58 mg kg−1 (classified as low), and plant-available K of 67–72 mg kg−1 (also classified as low). The total N content was relatively low, ranging between 0.09% and 0.12%, which may limit crop productivity, as optimal nitrogen levels for most agricultural soils typically fall within the range of 0.15%–0.30% [63]. According to commonly accepted agronomic standards [64], the measured P and K concentrations are considered low for optimal crop production, where ideal values typically exceed 100 mg kg−1 for P and 150 mg kg−1 for K, depending on the crop species and soil type. The slightly acidic pH is within a suitable range for most field crops but may still affect nutrient availability and microbial dynamics. The moderate organic matter content supports basic microbial activity but may not be sufficient to sustain long-term soil fertility without amendment. These conditions highlight the need for soil fertility improvement measures, including the application of organic amendments rich in N, Si, and humic substances.
Based on data obtained from the Skriveri Observation Station of the Latvian Environment, Geology, and Meteorology Centre, the meteorological conditions during the growing seasons (2023–2025) were consistent with the crop’s requirements.

3.4.1. Impact of Fertilizer on Radish Growth

Radish was harvested 36 days after sowing. The yield ranged from 1.99 to 2.67 kg m−2 and was significantly influenced by the seed treatment (Table 6).
The seed treated with the fertilizer produced higher yields compared to untreated controls, indicating improved early growth and nutrient uptake. This suggests that the fertilizer not only enhanced germination but also promoted more vigorous root development and biomass accumulation during the short growing period.

3.4.2. Impact of Fertilizer on Dill Growth

The dill green mass yield ranged from 0.90 to 1.32 kg m−2 (Table 7). In comparison with the control (untreated soil), the yield increased significantly only after soil treatment with fertilizer (RS0.05 = 0.27 kg m−2). This suggests that the fertilizer had a clear positive effect on dill biomass production. The increased yield of dill observed may be due to improved soil structure, increased availability of macro-elements and organic matter, and better moisture retention, which are especially important for fast-growing herbs like dill. Similar findings have been reported by Rostaei et al. (2018) [65], who noted a significant rise in dill yield and essential oil content following the application of organic fertilizers enriched with humic substances. Another study by Golubkina et al. (2019) [66] showed that supplementing with silicon and humic acid enhanced stress tolerance in leafy vegetables, including dill.
The chemical characterization of dill throws, including extraction and determination of bioactive compounds, revealed that fertilizer application increased the polyphenol content in dill extract and, consequently, in the plant material itself.
The total polyphenol content in 50% ethanol (EtOH) extracts from dill obtained from the F0 plot was 60.1 mg GAE g−1 of dry extract (DE). At the same time, in the F1 plot it reached 65.0 mg GAE g−1 of DE. The total flavonoid content in the same extracts was 42.7 mg RU g−1 and 46.8 mg RU g−1 of DE, respectively. The presence of PACs in the extracts was not detected. As polyphenols are known for their antioxidant activity, the observed increase in their content in the extract, and consequently in dill biomass, demonstrates that fertilizer application not only improves yield but also enhances the quality of dill, as it is a potential natural source of antioxidants.

3.4.3. Impact of Fertilizer on Potato Growth

The total potato yield ranged from 13.93 to 20.01 t ha−1, which is considered average under local agroclimatic conditions. The proportion of commercial tubers was high (84.9%–88.5%). Pre-treatment of seed potatoes with the fertilizer increased both the total yield and the proportion of commercial-grade tubers (Table 8).
The heaviest commercial tubers averaged 76.8 g, indicating improved tuber size. These results suggest that the use of fertilizer can enhance the economic return of potato cultivation by increasing the high-quality produce.
Similar findings have been reported in studies by other authors. Composts and fertilizers derived from lignocellulosic biomass were shown to improve soil structure. Microbial activity and nutrient availability were also enhanced, which resulted in higher potato yields [67]. Research by Gao et al. (2019) [68] showed that applying straw-derived compost enhanced tuber growth and improved nitrogen use efficiency in Solanum tuberosum. Additionally, studies by Wang et al. (2023) [69] found that the incorporation of humic-rich organic fertilizers boosted tuber quality, increased the share of marketable yield, and improved soil organic carbon content. These results support the potential of lignocellulosic fertilizers as sustainable tools for improving potato productivity in diverse growing conditions.
The experience of other authors shows that the use of Si-containing fertilizers can reduce lodging by 63%, increase total potato yield by 14.3%, and enhance the proportion of marketable tubers by 15.8%. Our previous studies have shown that lignin and Si-based fertilizer sequentially increase potato yield and its quality [70].

3.5. Impact of Fertilizer on Wheat Growth

Spring wheat yield ranged from 2.82 to 3.85 t ha−1, considered average. Seed treatment with fertilizer increased yield. Hot and dry weather also affected grain quality. Despite the high protein (12.4%–13.5%) and gluten (23.1%–26.4%) content, the bulk density of the harvested grain was low (<730 g L−1) (Table 9).
Similar results were also described by other authors, who indicated that the use of Si improves the yield of spring wheat, especially under drought conditions [71].
By comparing the effect of the fertilizer across all tested crops, it was observed that the most pronounced effect occurred in the potato and dill treatment, where the yield increased by 44% and 42%, respectively. The differences between crops may be related to species-specific nutrient requirements, growth rates, and root system characteristics, which influence how efficiently each plant utilizes the applied fertilizer.

3.6. Impact of Fertilizer on Pine Seedling Growth

The influence of the fertilizer on Scots pine seedlings’ (PS) growth was evaluated over 18 months after planting one-year-old PS in a forest plantation. The average biometric measurements of PS during this study are shown in Table 10.
At the start of the experiment, PS with an aboveground part (AGP) length of 12 ± 4 cm and root length of 15 ± 3 cm were selected for both the control and fertilizer treatment groups. More noticeable differences between the groups appeared after 6 months. In fertilized PS, root length increased to 29 ± 5 cm, compared to 26 ± 3 cm in the control. From month 9 onward, especially at months 12 and 18, clear growth differences became evident. At 12 months, root length in the fertilized group reached 52 ± 7 cm, while in the control, it was only 36 ± 3 cm. By month 18, AGP length in the fertilized group was also significantly greater, measuring 43 ± 6 cm versus 34 ± 6 cm in the control. The results suggest that a single initial application can sustainably promote the growth of perennial plants like conifers without requiring repeated yearly fertilization.

4. Conclusions

This study shows that forest logging residues from mixed deciduous and coniferous stands are a valuable feedstock for producing PACs-rich extracts with strong antifungal properties. Pine bark yielded the highest PACs content and showed the most pronounced antifungal activity against Botrytis cinerea, Mycosphaerella sp., Heterobasidion annosum, and Heterobasidion parviporum, offering a potential alternative to synthetic fungicides considering rising antimicrobial resistance and environmental restrictions. The post-extraction biomass was combined with sea buckthorn berry residues and Si-containing complex to produce an organic fertilizer with favourable porosity and nutrient retention properties. Fertilizer increased the yield of radish, dill, potatoes, and wheat by up to 44% (highest for potatoes and dill) compared to the reference, confirming its agronomic value. The innovation lies in the integrated approach, extracting bioactive PACs and valorizing the remaining biomass into fertilizer, enabling full utilization of forest logging residue. Future research should focus on process scaling, long-term validation, and assessment of industrial applicability.

Author Contributions

Conceptualization, S.J. and A.A.; methodology, S.J., A.A., V.N., and A.S.; software, A.S.; validation, S.J., A.A., V.N., and A.S.; formal analysis, S.J., A.A., V.N., and A.S.; investigation, S.J., A.A., V.N., N.Z., A.S., and G.R.; resources, S.J., A.A., and G.R.; data curation, S.J., A.A., V.N., and A.S.; writing—original draft preparation, S.J.; writing—review and editing, S.J., A.A., and N.Z.; visualization, S.J., A.A., and N.Z.; supervision, S.J. and A.A.; project administration, A.A. and G.R.; funding acquisition, S.J., A.A., and G.R. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Rural Support Service of the Republic of Latvia, the European Agricultural Fund for Rural Development (EAFRD), Measure “Cooperation”, project No. 23-00-A01612-000008 “Wasteless application of residual logging biomass for obtaining environmentally friendly plant protection products and soil additives”.

Data Availability Statement

The data described in this study are available on request from the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest. Anna Andersone is employed by Ekokompozit Ltd.; her employer’s company is involved in this study only in the frames of the above-mentioned acknowledged project (Rural Support Service of the Republic of Latvia, European Agricultural Fund for Rural Development (EAFRD), Measure “Cooperation”, project No. 23-00-A01612-000008), which is a non-commercial project, not connected to the business of Ekokompozit Ltd., and there is no relevance between this research and the company.

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Forests 16 01418 g001
Figure 1. Biomass collected and chipped in the Olaine Parish.
Figure 1. Biomass collected and chipped in the Olaine Parish.
Forests 16 01418 g001
Forests 16 01418 g002
Figure 2. Biomass characterization as PAC and extract source. For yield of extract CI ≤ 0.5%, and for other experiments CI ≤ 0.1%, at α = 0.05.
Figure 2. Biomass characterization as PAC and extract source. For yield of extract CI ≤ 0.5%, and for other experiments CI ≤ 0.1%, at α = 0.05.
Forests 16 01418 g002
Forests 16 01418 g003
Figure 3. Fungicidal activity of extract samples.
Figure 3. Fungicidal activity of extract samples.
Forests 16 01418 g003
Forests 16 01418 g004
Figure 4. FTIR spectrum of fertilizer.
Figure 4. FTIR spectrum of fertilizer.
Forests 16 01418 g004
Forests 16 01418 g005
Figure 5. Total pore volume data of fertilizer. In red—BET (Brunauer–Emmett–Teller) adsorption isotherm, in blue—BET desorption isotherm.
Figure 5. Total pore volume data of fertilizer. In red—BET (Brunauer–Emmett–Teller) adsorption isotherm, in blue—BET desorption isotherm.
Forests 16 01418 g005
Table 1. Abbreviation of biomass samples.
Table 1. Abbreviation of biomass samples.
Sample AbbreviationMaterial TypeDominant SpeciesTrees or Branches Diameters, cmCollection Year, Month Period
S1Understory treesGrey alder, aspenUp to 102023, July–September
S2Branches Pruned from mature treesGrey alder, black alderUp to 52023, October–December
S3Understory treesBirch, grey alderUp to 82024, January–March
S4Understory treesGrey alder, black alderUp to 102024, April–June
S5Understory treesBaltic pine, Norway spruceUp to 52024, July–September
S6Pine barkBaltic pine-2024, October–December
S7Understory treesAspen and grey alderUp to 102025, January–March
Table 2. The list of applied testing standards relevant for chemical characterization of the samples.
Table 2. The list of applied testing standards relevant for chemical characterization of the samples.
CharacteristicsStandard
Humidity, %LVS EN 13040:2008 [31]
Dry matter (DM), %LVS EN 13040:2008 [31]
Organic matter content, %LVS EN 13039:2012 [32]
pHLVS ISO 10390:2006 [33]
Lignin content in sample, %/DM (Klason method) *ISO 21436:2020 [34]
* The analysis was carried out only for fertilizer.
Table 3. The samples for the field trials, fertilizer dose 40 kg ha−1, 4 replicates.
Table 3. The samples for the field trials, fertilizer dose 40 kg ha−1, 4 replicates.
Culture and SpeciesVarietyVegetation PeriodRemarks *Experimental Field
(Coordinates)		Plot Size
Winter wheat (Triticum aestivum L.)Edvins27 September 2024–15 March 2025A56°69.275′ Z, E 25°14.173′0.9 m2; 2 × 0.45 m (3 rows)
Spring wheat (Triticum aestivum L.)Robijs2 May 2025–25 July 2025B56°69.275′ Z, E 25°14.173′13.5 m2; 1.5 m × 9 m (3 rows)
Potatoes (Solanum tuberosum L.)Monta20 May 2024–27 August 2024C56°69.275′ Z, E 25°14.173′12.6 m2 (1.4 m × 9 m)
Dill (Anethum graveolens L.)Thalia7 September 2023–3 October 2023D56°69.275′ Z, E 25°14.173′0.9 m2 (2.0 m × 0.45 m)
Radish (Raphanus sativus L.)Rosso Tondo2 August 2023–7 September 2023E56°69.275′ Z, E 25°14.173′0.9 m2 (2.0 m × 0.45 m)
Pine (Pinus Sylvestris)-1 September 2023–-56°44′27.4″ N, 23°45′01.7″ E0.5 ha
* A—Late autumn (27.09–31.10.24): mild to cool temperature (~8–12 °C daytime, ~0 °C nighttime) generally favourable for winter wheat establishment; precipitation conditions near seasonal norms. Winter (01.11.24–28.02.25): prolonged period of sub-zero daytime temperature (−1 to −3 °C) and colder nighttime minima (down to −10 °C); likely snow cover providing protective insulation. Early spring (March 2025): gradual warming; mean temperature ~1.2 °C; total precipitation in March ~74 mm; daylight length increasing above 12 h. These conditions—stable cold but not extreme winter, followed by sufficient soil moisture and temperature rise in spring—were generally conducive to winter wheat overwintering and early growth. B—From 2 May to 25 July 2025, the daily maximum temperature ranged between approximately 18–24 °C, and the minimum between 11 and 15 °C, consistent with typical summer patterns. Monthly precipitation was in the range of ~48 mm in May, ~68 mm in June, and ~63 mm in July, corresponding to 6–10 rainy days per month. These conditions were generally favourable for early-to-mid-season crop growth. Standard agronomic planting norms for Latvia were applied to ensure comparability of the fertilizer effect across different plant species: spring or summer wheat 450–550 seeds m−2; winter wheat 350–500 seeds m−2. C—The growing season was hotter and drier than average, with mean daily highs around 20–25 °C, nighttime lows ~12–16 °C, and below-average rainfall—a combination that reduced the favourability for potato development. The potato planting norm was considered the standard rate (25 kg ha−1) obtained in the absence of fertilizer application. D—Temperatures ranged between 14–20 °C by day and 8–16 °C at night; precipitation likely matched period norms (70–130 mm over ~9 rainy days), creating generally favourable conditions for dill and radish growth. E—Early September (01.09.23–07.09.23): morning temperatures decreased (~7–8 °C), daytime average around ~17 °C, with moderate precipitation (<~15 days per month)—overall still suitable for radish growth, particularly supporting the desired cold tolerance [40].
Table 4. Minimum inhibitory and fungicidal concentration of samples.
Table 4. Minimum inhibitory and fungicidal concentration of samples.
SampleBotrytis cinereaMycosphaerella sp.Heterobasidion annosumHeterobasidion parviporum
MIC/MFC, mg/mL
PACs25/5025/5012.5/12.512.5/12.5
Extract containing 36% PACs12.5/2525/506.25/12.56.25/12.5
PACs-free fraction12.5/2525/5025/5025/50
Table 5. Comparison of the commercial preparations and extract application doses.
Table 5. Comparison of the commercial preparations and extract application doses.
Active CompoundCommercial NamePreparation ConcentrationApplication DosePathogenic FungiPreparation Type
FenhexamidTeldor 500 SC [55]500 g L−10.8–1.5 L ha−1Botrytis cinerea; Mycosphaerella sp.Synthetic fungicidal agent
AzoxystrobinAmistar 250 SC [56]250 g L−10.8–1.5 L ha−1Botrytis cinerea; Mycosphaerella sp.Synthetic fungicidal agent
EpoxiconazoleOpus 125 SC [57]125 g L−10.4–0.8
L ha−1		Botrytis cinerea; Mycosphaerella sp.Synthetic fungicidal agent
Cyprodinil + FludioxonilSwitch 62.5 WD [58]375
g kg−1 + 250 g kg−1		0.8–1.0
kg ha−1		Botrytis cinerea; Mycosphaerella sp.Synthetic fungicidal agent
AzoxystrobinAmistar 250 SC [59]250 g L−10.8–1.5 L ha−1Botrytis cinerea; Mycosphaerella sp.Synthetic fungicidal agent
PACs-12.5 g L−1-Heterobasidion annosum, H. parviporumBiological fungicide agent
PACs-50 g L−1-Botrytis cinerea; Mycosphaerella sp.Biological fungicide agent
Extract containing 36% PACs-12.5 g L−1-Heterobasidion annosum, H. parviporumBiological fungicide agent
Extract containing 36% PACs-25 g L−1-Botrytis cinereaBiological fungicide agent
Extract containing 36% PACs-50 g L−1-Mycosphaerella sp.Biological fungicide agent
Table 6. Fertilizer effect on radish crop.
Table 6. Fertilizer effect on radish crop.
Plot VariantTotal Yield of
Radish, kg m−2		Standard
Yield of
Radish, kg m−2		Standard
Yield, % of
Total Radish Yield		Average Weight of Radish, g
F0 *1.99 a1.62 a81 a10.6 a
F1 **2.67 b2.25 b84 b13.4 b
* F0—reference plot without fertilizer; ** F1—plot with fertilizer applied at 40 kg ha−1; a and b—group labels in ANOVA analysis, significantly different values.
Table 7. Fertilizer effect on dill green mass yield.
Table 7. Fertilizer effect on dill green mass yield.
Plot VariantTotal Yield of Dill Green Mass, kg m−2The Above-Ground
Part of the Dill Green Mass from the Total Mass of the Plant, %
F0 *0.9386.3
F1 **1.32 a88.2
* F0—reference plot without fertilizer; ** F1—plot with fertilizer applied at 40 kg ha−1; a and b—group labels in ANOVA analysis, significantly different values.
Table 8. Fertilizer effect on potato yield and quality.
Table 8. Fertilizer effect on potato yield and quality.
Plot VariantTotal Yield, t ha−1Commercial ProductionFraction Yield, t ha−1
t ha−1%Tubers, d * < 35 mm Tubers, d * = 35–55 mm Tubers, d * > 55 mm
F0 **13.93 b11.83 b84.92.1010.241.59
F1 ***20.01 a17.20 a86.02.8113.603.60
* d—diameter; ** F0—reference plot without fertilizer; *** F1—plot with fertilizer applied at 40 kg ha−1; a and b—group labels in ANOVA analysis, significantly different values.
Table 9. Fertilizer effect on spring wheat yield and quality.
Table 9. Fertilizer effect on spring wheat yield and quality.
Plot VariantYield of Wheat,
t ha−1		Protein Content in Grain,
%		Gluten Content, %Starch Content, %Zeleny Index, mLVolume Weight,
g L−1		Falling Number, s
F0 *2.82 b13.525.765.951.86726.6300
F1 **3.43 a12.423.167.043.11729.0292
* F0—reference plot without fertilizer; ** F1—plot with fertilizer applied at 40 kg ha−1; a and b—group labels in ANOVA analysis, significantly different values.
Table 10. Fertilizer effect on PS growth: F0—forest plot without fertilizer; F1—forest plot with fertilizer.
Table 10. Fertilizer effect on PS growth: F0—forest plot without fertilizer; F1—forest plot with fertilizer.
Duration of Growth in the PlantationLength of the AGP * of PS, cmRoot Length, cmLength of the AGP of PS **, cmRoot Length, cm
ControlFertilizer 40 kg ha−1
Parameters of initial PS **12 ± 415 ± 312 ± 415 ± 3
3 month14 ± 4-16 ± 5-
6 month22 ± 326 ± 324 ± 529 ± 5
9 month26 ± 329 ± 632 ± 333 ± 4
12 month32 ± 436 ± 339 ± 352 ± 7
15 month33 ± 8-41 ± 3-
18 month34 ± 635 ± 743 ± 661 ± 5
* AGP—aboveground part, ** PS—Scots pine seedlings.
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Janceva, S.; Svarta, A.; Nikolajeva, V.; Zaharova, N.; Rieksts, G.; Andersone, A. Forest Logging Residue Valorization into Valuable Products According to Circular Bioeconomy. Forests 2025, 16, 1418. https://doi.org/10.3390/f16091418

AMA Style

Janceva S, Svarta A, Nikolajeva V, Zaharova N, Rieksts G, Andersone A. Forest Logging Residue Valorization into Valuable Products According to Circular Bioeconomy. Forests. 2025; 16(9):1418. https://doi.org/10.3390/f16091418

Chicago/Turabian Style

Janceva, Sarmite, Agrita Svarta, Vizma Nikolajeva, Natalija Zaharova, Gints Rieksts, and Anna Andersone. 2025. "Forest Logging Residue Valorization into Valuable Products According to Circular Bioeconomy" Forests 16, no. 9: 1418. https://doi.org/10.3390/f16091418

APA Style

Janceva, S., Svarta, A., Nikolajeva, V., Zaharova, N., Rieksts, G., & Andersone, A. (2025). Forest Logging Residue Valorization into Valuable Products According to Circular Bioeconomy. Forests, 16(9), 1418. https://doi.org/10.3390/f16091418

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