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Article

Unveiling the Transformative Effects of Forest Restoration on the Soil Chemistry and Biology of Sandy Soils in Southern Nyírség, Hungary

by
István Attila Kocsis
1,2,3,*,
Magdolna Tállai
1,
Ágnes Zsuposné Oláh
1,
Zoltán László
1,3,
Béla Mokos
1,3,
Ida Kincses
1,
Evelin Kármen Juhász
1,
Daniel A. Lowy
4 and
Zsolt Sándor
1
1
Institute of Agricultural Chemistry and Soil Science, Faculty of Agricultural and Food Sciences and Environmental Management, University of Debrecen, H-4032 Debrecen, Hungary
2
Nyírerdő Nyírségi Erdészeti Zrt, H-4400 Nyíregyháza, Hungary
3
Kálmán Kerpely Doctoral School, University of Debrecen, H-4032 Debrecen, Hungary
4
Department of Economics, Finance and Accounting, Keleti Károly Faculty for Business and Management, Óbuda University, H-1084 Budapest, Hungary
*
Author to whom correspondence should be addressed.
Agriculture 2025, 15(10), 1030; https://doi.org/10.3390/agriculture15101030
Submission received: 4 March 2025 / Revised: 6 May 2025 / Accepted: 8 May 2025 / Published: 9 May 2025
(This article belongs to the Special Issue New Challenges and Trends in Agri-Environmental Management: Accomplishment of Sustainable Development Goals)
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Versions Notes

Abstract

:
Protecting humankind’s natural resources and soils, including forestry, represents a top priority in agriculture. Addressing climate change should prioritize preserving and enhancing organic carbon, specifically humus, in soils. In this paper, we examine the impact of soil preparation on soil humus and microbial life during the reforestation of Southern Nyírség, Hungary. We determined soil plasticity, pH in distilled water solution, the quantity and quality of humus content, the total number of bacteria and microbial fungi, as well as CO2 production. In addition to stump removal and plowing, the wealthiest layer of organic matter was detached from the surface. A significant decrease in humus content (HU%) was observed at the five experimental sites (loss of 19.20–40.14 HU% at 0–30 cm depth). Soil organic matter is concentrated in the stump depositions. According to the results, the quantity of humus content is strongly correlated with the measured parameters of soil life, specifically with the number of microbial fungi (r = 0.806 **) and the total number of bacteria (r = 0.648 **). Another correlation (r = 0.607 **) was assessed between the humus content and CO2 production. This study helps to understand the importance of the no-tillage methods used in reforestation.

1. Introduction

There are about 900 million hectares of sandy soil on Earth, mostly in arid and semi-arid regions. Sandy soils can be found on all continents and, according to WRB, are referred to as arenosols [1]. About 51% of the world’s arenosols are located in Africa, 21% in Australia, 10% in Asia, 14% in South and Central America, and a total of 4% in North America and Europe [2]. Nyírség is the second-largest sand ridge in Hungary, occupying a territory of 510,600 hectares, over 20.8% of which is covered by forests [3].
The afforestation of lowland sandy soils in Hungary was conducted in the first half of the 19th and 20th centuries to reduce wind erosion [4]. Deforestation amplified from the 1980s to the 2000s and started to decline after 2007. Subsequently, Hungary experienced the most significant net increase in forest area in Eastern Europe, at 27%, partly because of land conversion [5].
Economical forestlands are increasing worldwide, also due to the growing human population and the resulting increase in demand for wood products, resulting in the continuous transformation of primary forests into secondary forests [6].
In the Mediterranean, many native forests have been converted into agroforestry systems, while abandoned agricultural lands have also been reforested. These land use changes have reduced soil degradation, such as soil erosion. Reforestation on these soils can increase the soil organic carbon (SOC) storage capacity [7].
While carbon sequestration occurs more slowly in soils than in biomass, C stored in soils is more resistant than C stored in biomass [8]. It should be remembered that, globally, soil C storage is decreasing [9]. Soil organic matter concentrations and stocks can be increased through increased organic matter inputs and reduced soil disturbance [7], which we investigated in this paper. The amount of C stored in forest soils is a significant fraction of the world’s total C stock. One estimates that SOC stored in forest soil is more than 70% of the global SOC [10]. Other research estimates this value to be just over 40% [11]. Forest conversion and changing human impacts on forests are likely to affect forest biomass and soil C stocks [12]. In forest soils, trees modify microclimatic conditions (especially soil moisture and temperature), increase organic matter (OM) uptake, and improve soil quality [13]. In addition, the absence of tillage in these systems improves soil microbial and faunal communities and the formation of stable aggregates [14], protecting against OM degradation [15]; C/N ratios of afforested soils are more similar to those of arable [16] and horticultural [17] crops than to native forest soils [18]. Forest soils have been recognized as important reservoirs of stable carbon (C) in the biosphere and thus play a key role in the global carbon cycle [19].
Forests are essential for biodiversity conservation and climate change mitigation [20]. According to forestry research, models show a high similarity with the drying and warming weather in the sand ridge area between the Danube and the Tisza rivers (Hungary) [21]. Quicksand and humus sandy soils were formed here [22]. In these soils, proper management practices are required for effective plant production [23]. Kong and co-workers examined the environmental consequences of soil management, comparing the results obtained for Hungarian and Japanese soils. According to their research, land use significantly impacts the cumulative production of N2O and CO2 in soil [24]. Ecological management positively affects the quality and fertility of the sandy soils in the Nyírség region by improving the chemical soil parameters and increasing the community size and activity of microbes [25].
The dominant and characteristic element of the forest ecosystem is the woody vegetation [26]. The open surface is less resistant to weather events; in sandy areas, in particular, sand erosion, deflation, and surface warming may be a problem for the survival of young trees. Seedlings try to establish an extended cover as soon as possible; this explains why black locusts (Robinia pseudoacacia, L.) show intensive height growth at 1–5 years of age [27]. To initiate forest regeneration growth, it may be advisable to intervene actively in soil improvement, mainly where the topsoil is very shallow, i.e., only a few cm thick, and its humus content is less than 1.0–1.5%, as we found in many cases after tillage in our study.
Deforestation is the most critical factor in soil degradation, as it changes the soil environment, the availability of nutrients, and the carbon cycle [28,29]. With changes in land use, the natural ecosystem deteriorates, and soil erosion may occur [30].
Forest management practices can positively and negatively affect forest soil, greenhouse gases, and carbon balance [12,31]. Clear-cutting is the most common and impactful deforestation practice worldwide. It usually negatively affects soil organic C content, resulting in a 10% reduction in soil OM in the overall soil profile [32]. Coniferous forest floor C stocks decreased 30 years after clear-cutting: when at its lowest stock level, Picea and Pinus forest floor C stocks were reduced relative to the initial stock levels by 23% and 14%, respectively [33].
Post-cutting reforestation promotes the rapid establishment of new stands. Nevertheless, reforestation causes additional soil disturbance (rotation), affecting soil temperature and moisture, potentially impacting soil biological activity and respiration [34].
Following tree harvesting in the study area, forest exploitation primarily involves the removal of stumps using rotary excavators. The stumps are then sorted into depositions. This operation also removes the wealthiest layer of organic matter, specifically the top 0–5 cm. The relocation of organic matter is assumed to be highly detrimental to soil life and, therefore, to the subsequent development of forest regeneration. One should protect the soil from erosion and deflation damage. Soil organic carbon and total nitrogen content were reduced. In contrast, soil pH, electrical conductivity, and soil nutrients (available P, K, and Ca) were increased for at least 2 years after field burning in fallow years [35]. Dissolved organic carbon (DOC) and soil organic carbon (SOC) react differently on sloping lands with water erosion, where plant age and density may cause variances in nutrient loss [36]. Their physical properties and topsoil thickness mainly determine the water-holding capacity of soils [37].
Humus is a complex variable material consisting of several high-molecular-weight compounds with roughly the same basic structure [38]. Seasonal fluctuations in biological activity are more pronounced in soils with low humus content than in soils with higher humus content [39,40]. Based on this finding, it is essential to investigate the impact of soil cultivation on humus content and preserve the soil’s organic matter stock.
The sample plots were selected in the Nyírerdő Ltd. (Nyíregyháza, Hungary) areas with forest end-use. Our research focused on investigating the properties of different soil types at the sites of the planned forest renewal (afforestation). After the end-use tree harvesting, various operations were conducted, including stump extraction, landscaping, and deep plowing. As the sampling posed severe difficulties and was time-consuming, the authors had to limit their investigation to collecting and processing 60 samples, which were needed for statistical evaluation. The results presented here were obtained by exploring five different soil profiles. On each sample, we performed 8 types of tests, so that 480 data points were processed in the study. We examined the changes in properties across different soil layers using physical, chemical, and microbiological methods. We aim to identify correlations between the measured chemical and microbial parameters of soils with varying physical and chemical properties, demonstrating the adverse effects of complete tillage on reforestation efforts.

2. Materials and Methods

2.1. Overview of the Sampling Sites

Soil profiles were excavated after the end-use harvesting of trees at several villages in the Hosszúpályi and Debrecen areas. Five soil profiles were explored in the examined regions after tree harvesting at four locations. Soil samples were collected in unplowed areas before stump removal (Figure 1).
The maximum humus content was found in the top 0–30 cm layer. At depths below 30 cm, we determined a humus content of less than 0.1% in each soil profile before plowing. After plowing (Figure 2), samples were extracted from depths of 0–30 cm and 30–70 cm, as well as from the rows where the stumps were deposited.
During planting, roots are placed in the 0–30 cm layer, crucial for saplings to access water and nutrients. Table 1 lists the extracted tree species and species for afforestation.
Table 2 is a summary table indicating the sampling locations, their GPS coordinates, cultivation methods, sampling depths, and the number of collected samples. The forests in the study were unmixed plantations unaffected by extraordinary events, such as storm damage. They were at the age recommended for end-use cutting according to Hungarian regulations.
Sampling locations are shown on the map (Figure 3). These forest restorations coincided.

2.2. Soil Sampling and Analyses

In the five selected forest sections, soil profile excavations were performed according to simple random sampling [41]. Samples were taken from 3 locations within each examined layer to characterize the profiles. We performed physical, chemical, and microbiological analyses for the collected soil samples to evaluate soil fertility quality. We determined the following soil properties: soil plasticity, pH in distilled water solution, and humus content quantity and quality. We measured the total number of bacteria, microbial fungi, and CO2 production among the microbiological properties. A key objective of the study was to establish correlations among humus content, microscopic fungi, soil bacteria, CO2 production, soil pH, and humus stability parameters.
Soil samples were measured at the soil chemistry and biology laboratories of the Institute of Agricultural Chemistry and Soil Science at the DE MÉK in Debrecen, Hungary, during the 2022 growing season. Among the physical properties measured, the Arany-type plasticity index (KA) was determined [42].
The humus content of the soil (HU%) was measured using the Székely colorimetric method, according to the Hungarian standard procedure [43,44]. This method is based on the ability of soil organic matter to be oxidized with K2Cr2O7, where the reaction proceeds with a change in solution color from orange to green. To determine the organic carbon content of the samples, the measurement was performed at a 580 nm wavelength using a Philips Unicam PU 8600 UV spectrophotometer. The CO2 production was evaluated via NaOH trapping after 10 days of incubation [45].
The “Hargitai two-solvent” method was utilized to determine the humus quality [46,47]. The samples were treated with aqueous NaOH (0.5 wt.%) and NaF (1.0 wt.%) solutions, respectively, and the stability of the humic substances was estimated from the light absorption (extinction, E NaOH, E NaF) of the two extracts. Measurements were performed by colorimetry with a Philips UPU 8600 UV spectrophotometer at the wavelengths of 480 nm (Q4), 540 nm (Q5), and 670 nm (Q6), respectively. The stability value Q of the humus was calculated according to Equation (1).
Q = E NaF/E NaOH.
While its mean value is given by Equation (2).
Qaverage = (Q4 + Q5 + Q6)/3.
The stability coefficient (K) per unit humus content was calculated according to Equation (3).
K = E Na/(E NaOH × HU%).
The higher the value of the coefficient K, the more stable the quality of the humus is. Soil pH was measured by adding 1.0 part soil to 2.5 parts distilled water, pH (H2O) solution (according to the Hungarian standard [48]). The pH was measured with a Jenway 570 pH Meter digital instrument [49].
Two microbiological parameters, the total number of bacteria, ×106 (g soil)−1 (colony-forming units, CFUs), and the number of microscopic fungi, ×103 (g soil)−1, were determined by plate dilution on a bouillon plate and peptone–glucose agar, respectively [50]. To evaluate the total bacteria, incubation was conducted at 30 ± 1 °C for 48 h. For the microscopic fungi, incubation was 72 h at 25 ± 1 °C. After incubation, colony counting was performed on a Leica-type colony counter. The CO2 production was evaluated by NaOH trapping from fresh soil samples after 10 days of incubation at 25 °C [45,51,52].

2.3. Statistical Methods

The effect of soil preparation technologies on the soil’s physical, chemical, and biological properties was assessed by one-way ANOVA (p < 0.05) analysis. The cultivation methods at each sampling site were compared with the Tukey post hoc test. All measurements were conducted in triplicate, and data analysis was performed using Microsoft Excel 2016 and IBM SPSS (version 29.0.0.0) to process and evaluate the results. Pearson’s correlation was applied to explore the relationships between the examined parameters.

3. Results

The soil profile of the Hosszúpályi (HP) 7 H forest is displayed in Table 3; the measurements acquired in the study are listed in Table 4.
Our measurements found an extremely low humus content (HU% = 0.36) in the upper soil underlying the harvested pine (Pinus sylvestris, L.) forest. In contrast, the soil’s pH was strongly acidic, with a pH (H2O) of 4.59. Fungal activity of 31.5 × 103 (g soil)−1 was considerable. After deep plowing, the organic matter content of the upper soil layer decreased to 0.22 HU%; however, according to our measurements, more stable humus materials from the deeper layers moved toward the surface (K = 7.06). After plowing, 0.10 HU% was measured at a depth of 30–70 cm, while a considerable quantity of organic matter (4.20 wt.%) accumulated in the stump row. The stability coefficient (K) was very low (K = 0.07), indicating poor humus quality. As a result of the stump removal, the upper soil layer containing the humus was concentrated in the stump row, having weakly decomposed plant remains. As a result of the large amount of accumulated organic matter, the number of microbial fungi in the stump row increased significantly to 121.5 × 103 (g soil)−1.
Table 5 displays the soil profile of the Hosszúpályi (HP) 8 M forest area, while Table 6 includes the measurements performed.
The Hosszúpályi 8 M forest profile was diverse in terms of micro-topography. Soil plasticity was loam in the upper soil layer and sand in the deeper layer. The soil profile of the area located at a higher elevation is displayed in Table 5, while the results are shown in Table 6. Historically, the area was home to poplar trees (Populus spp.). The soil layer near the surface contained 2.84 wt.% humus with a stability coefficient of K = 0.46. After deep plowing, these values changed to HU% = 1.70 and K = 0.99, respectively; thus, the organic matter content decreased due to plowing. Nonetheless, the deeper soil layer’s humus materials of better quality were repeatedly brought closer to the soil surface. The soil was mildly acidic with high fungal activity, peaking at 151.75 × 103 g−1 soil before plowing. The stump row’s humus content and quality were like the plowed soil layers.
Table 7 displays the second explored soil profile of the Hosszúpályi 8 M forest section.
Table 7 reveals an intense glaciation in depth. During deep plowing, the ironstone located at 40 to 60 cm depths was loosened. These test results are listed in Table 8. The humus accumulated extensively (4.01 HU%) in the upper layer, where a dark-colored layer is visible to the naked eye. The pH was slightly alkaline (pH 7.79), and the bacterial activity of the soil was substantial, equal to 10.73 × 106 (g soil)−1, which was found to be the highest value among the samples in our study. After soil cultivation, we determined the HU% to be 3.24 in the upper soil layer, almost identical to the accumulated humus in the stump row (HU% = 3.11). Meanwhile, the humus content at a 30–70 cm depth was 1.03% HU. We found high-quality humus materials within this depth range with a K value of 2.33.
In the past, the area was home to black locust (Robinia pseudoacacia, L.) trees. The upper layer consists of sandy loam, and sand is in the deeper layers (see Table 9). Before tillage, the soil’s humus content was only 0.26 wt.%, which decreased after deep plowing to 0.17 wt.% in the upper 0–30 cm layer. Nevertheless, close to the surface, the small organic matter content exhibited high stability (K = 1.55), which increased in part with depth in the 30–70 cm range after deep plowing (K = 1.87). Such an increase may be favorable to the later development of the tree seedlings. The pH of the soil was strongly acidic (pH 4.15), resulting in a low total bacterial count. By contrast, the number of fungi increased considerably.
Table 10 lists the results of examining the physical, chemical, and biological properties of the Hosszúpályi forest (HP) 4 L sample site. Standard deviations are also provided.
The Debrecen 369 A forest area (Table 11) is characterized by an old pine (Pinus sylvestris, L.) forest, which results in a highly acidic soil pH.
The soil plasticity was sand in all layers of the profile. A high organic matter accumulation was found close to the surface (HU% = 4.33, Table 12). Nevertheless, it mainly consisted of raw humus with clearly recognizable remains of plant parts. Therefore, the stability coefficient was very low (K = 0.07). As a result of the extremely high content of organic matter, we found a vast number of fungi, 430.5 × 103 (g soil)−1, which indicated a high rate of decomposition by microscopic fungi. The pH of the soil was strongly acidic (pH 4.08), and the pH did not increase significantly after cultivation (pH 4.63). The humus content decreased, however, in the 0–30 cm depth range (HU% = 2.82). A significant amount of organic matter (HU% = 3.11) appeared on the established stump row. High CO2 production was measured in all soil samples because of the large quantity of organic matter.
The loss of humus content in each area is illustrated (Figure 4). The humus content of each sample area was marked with a dark color, while the data relating to the new soil condition measured after the soil preparation at the same depth (0–30 cm) was marked with a light color.
The diagram reveals that the amount of organic matter decreased at all planting depths, with no exception. The organic matter accumulated in the row of tree stumps.
In the Hosszúpályi 7 H forest unit, a loss of 38.89 HU% was ascertained in the 0–30 cm planting soil depth. In the high-altitude part of the Hosszúpályi 8 M forest unit, one assessed 40.14 HU% loss, while in the low-altitude part of the area, only 19.20 HU% loss was found. The loss determined in the Hosszúpályi 4 L forest unit was 34.62 HU%, while in the Debrecen 369 A forest unit, the loss was equal to 34.87 HU%. The average amount of organic matter loss caused by the tillage practices in the study areas was 33.54% (see Table 13).
Table 14 lists the results of a correlation analysis among the parameters studied. This analysis enabled us to understand the relationships between the variables. The correlation values highlighted medium and close correlations. The correlation table includes all the sections and their tested parameters.
The humus content strongly correlates with the number of microscopic fungi (r = 0.806). The decomposition of organic matter can explain this. Nonetheless, the humus content also correlates positively with the number of bacteria (r = 0.648) and at a medium level with the CO2 production (r = 0.607). Hence, as expected, the organic matter content is related to the number of soil microbes.
The decrease in organic matter content assessed in the upper layer of the deep-plowed soil layer is particularly hazardous in sandy soils because it results in lower colloid content of the soil, along with decreased amounts of nutrients and water. When the afforestation of these areas is completed, professionals must pay special attention to the new young plants and provide thorough care for soil preparation.

4. Discussion

Extreme weather events resulting from global climate change necessitate developing measures to mitigate these changes. The growth of forest cover can help reduce atmospheric CO2 concentrations [53]. Land use change from arable land [54] or orchards [55] to forest can lead to differences in soil nutrient and organic matter content. The reforestation efforts motivated us to research the soil profiles in this territory and investigate the organic matter stocks and the distribution of humus materials within the soil profile. With this goal, we measured several physical, chemical, and microbiological properties of soil samples where reforestation is planned. Deep plowing was carried out before planting the new nursery stock to loosen the compacted topsoil and reduce weed competition. This mixing of soil layers caused a relocation of the organic matter content. The tillage of reforestation soil layers significantly affected soil organic carbon and microbial community, as found in other studies [56,57]. Results show a significant reduction in humus content in every planting area (in 0–30 cm layers), with an average decrease of 33.54%. At a 30–70 cm depth, low humus content (<0.10 HU%) did not increase with soil preparation; we can still find a low humus content after deep plowing. HP 4 L has the highest humus content (0.41 HU%) in the deeper layer, where fallow land deep plowing probably happened earlier before afforestation, as we can guess from its soil profile. The chances of survival of future seedlings were reduced. Stump depositions presented one of the highest values in microscopic fungi and soil bacteria, except for the HP 8 M higher sample site, where, after tillage, the upper 0–30 cm layer had the highest number of microscopic fungi (28.00 × 103 (g soil)−1), with most of the humus content concentrated in this layer. This sample site probably offered the best conditions (HU%, pH, KA) for microbial activity in the study area.
Our study has demonstrated, however, that a more significant accumulation of humus content does not always imply a high quality of the organic matter [58,59]. A low stability coefficient (e.g., stump row in HP 7H, K = 0.07) can still have a high microbial number (microscopic fungi and bacteria), suggesting that this factor alone does not fully explain the biological activity. For example, Debrecen 369 A had the highest HU% (4.33) with the lowest stability coefficient (K = 0.07) and pH (H2O) = 4.59, whereas the Hosszúpályi 8 M deeper sample site had 4.01 HU% with K = 2.11 and pH (H2O) = 7.79. The main difference between the compared forest sites is the soil pH. This outcome indicates that the content of organic matter is closely related to the abundance of soil microbes. A similar result was reported by Hicks et al. [60], who found that soil organic matter content improves nutrient cycling, soil microorganism dynamics, abundance, and activity [46,61,62,63]. Samples with high HU% (e.g., DB 369 A unplowed 0–30 cm layer with 4.33 HU% or stump row in HP 7H with 4.20 HU%) indicate higher microbial presence and CO2 emissions. Higher organic matter content may result from more active soil life [64]. With low humus content, we found low microbial counts (e.g., Sample 19—0.10 HU%, 22.50 thousand microscopic fungi g−1, 0.78 million soil bacteria g−1) at a depth of 30–70 cm in the sample sites. Our statistical evaluation demonstrated that the humus content is strongly correlated with the number of microscopic fungi and positively correlated with the number of bacteria. At the same time, there is a significant correlation level with CO2 production. The highest emissions (e.g., Sample 20—17.81 mg) align with high microbial abundance, elevated HU% and KA, and moderate pH. Depending on the soil pH, the number of microbial fungi (in acidic medium, e.g., Sample 17—430.50 thousand microscopic fungi g−1) or soil bacteria (in neutral to alkaline medium, e.g., Sample 12—7.12 million soil bacteria g−1) increased, similar to the results reported by Anderson [65] and Buckeridge and colleagues [66].
Reforestation can also play other frequently overlooked but essential roles in helping society and ecosystems adapt to climate variability and change [67]. Over time, the rapid and drastic changes in climatic conditions suggest that regular soil monitoring, particularly in less favorable areas, is becoming increasingly meaningful in the examined region.

5. Conclusions

Deep plowing, which inverts, covers, or mixes the soil’s organic layer (forest floor) and surface mineral A horizon into the mineral subsoil, burying the upper soil horizon in deeper layers and disrupting pedogenic processes, is a debatable topic in forest plantation management [68]. Traditional technologies of forest soil preparation by dump plowing are outdated and do not allow for a radical increase in labor productivity [69]. The outcome of our study is evidence that the targeted interventions to maintain and improve soil fertility are highly justified in the examined area of sandy soils. The organic and inorganic colloid content of sandy soils is very low, so nutrient and water management are essential [23], as well as the availability of humus content for the plants’ early growth. As our results indicate, in the study site, after deep plowing, only a lower amount of humus was turned into the 0–30 cm layers and much less into the deeper (30–70 cm) layers. We found an adverse effect of soil preparation before reforestation because a large amount of humus was concentrated in the stump depositions. Well-thought-out soil preparation will become increasingly important for all professionals to reduce abiotic stress and facilitate successful reforestation. The study documents the significant organic matter-reducing effect of complete soil preparation on forest regeneration in the seedlings’ root depth. Consequently, we expect the role of partial soil preparation (no stump removal) to increase, primarily to mitigate the unfavorable effects of climate change and ensure proper seedling development.

Author Contributions

Conceptualization, I.A.K. and Z.S.; methodology, I.A.K. and I.K.; software, I.A.K., M.T. and E.K.J.; formal analysis, M.T.; investigation, I.A.K., Z.L., I.K., B.M. and Z.S.; resources, Z.S.; data curation, I.A.K., M.T., Z.L. and I.K.; writing—original draft preparation, I.A.K. and Á.Z.O.; writing—review, editing, proofreading, and style improvement, D.A.L.; visualization, I.A.K.; supervision, Z.S.; project administration, Z.S. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the University of Debrecen Program for Scientific Publication.

Institutional Review Board Statement

Not applicable, as this study did not involve humans or animals.

Data Availability Statement

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

Acknowledgments

The authors express special thanks to the Institute of Agricultural Chemistry and Soil Science at the Faculty of Agricultural and Food Sciences and Environmental Management, University of Debrecen, for accommodating the authors in its laboratory, and to Nyírerdő Nyírségi Erdészeti, Ltd., (Nyíregyháza, Hungary), where the samples were collected for this investigation.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
HPHosszúpályi
DBDebrecen
Kstability coefficient
KAArany-type plasticity index
HU%humus content of the soil
SOCsoil organic carbon
OMorganic matter
DOCdissolved organic carbon

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Figure 1. Stump depositing is in progress (HP 7 H)—original photograph taken by the author István Attila Kocsis.
Figure 1. Stump depositing is in progress (HP 7 H)—original photograph taken by the author István Attila Kocsis.
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Figure 2. Deep plowing is in progress (HP 4 L)—original photograph taken by the author István Attila Kocsis.
Figure 2. Deep plowing is in progress (HP 4 L)—original photograph taken by the author István Attila Kocsis.
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Figure 3. Sampling locations in the Southern Nyírség (Hungary).
Figure 3. Sampling locations in the Southern Nyírség (Hungary).
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Figure 4. Change in the humus content in the upper 0–30 cm layer of the total sample areas (summary diagram) (n = 3).
Figure 4. Change in the humus content in the upper 0–30 cm layer of the total sample areas (summary diagram) (n = 3).
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Table 1. The location of the examined forest areas, the deforested areas, and planned tree species for afforestation.
Table 1. The location of the examined forest areas, the deforested areas, and planned tree species for afforestation.
Location of the Forest Extracted Tree SpeciesTree Species for Afforestation
Hosszúpályi 7 HScotch pine (Pinus sylvestris, L.)Black locust (Robinia pseudoacacia, L.)
Hosszúpályi 8 MCotton wood (Populus x)Black locust (Robinia pseudoacacia, L.)
Hosszúpályi 8 MCotton wood (Populus x)Cottonwood (Populus x)
Hosszúpályi 4 LBlack locust (Robinia pseudoacacia, L.)Scotch pine (Pinus sylvestris, L.)
Debrecen 369 AScotch pine (Pinus sylvestris, L.)Black locust (Robinia pseudoacacia, L.)
Table 2. The sites of soil sampling and the applied cultivation methods.
Table 2. The sites of soil sampling and the applied cultivation methods.
Sampling Sites with GPS Coordinates (GPSWGS84)Cultivation MethodsDepth (cm)Sample No.
Forest I.
Hosszúpályi 7 H
47.431, 21.730		* HP 7 H: unplowed0–301
HP 7 H: deep plowed upper layer0–302
HP 7 H: deep plowed lower layer30–703
HP 7 H: row of tree stumps with soil content0–154
Forest II.
(high-altitude area)
Hosszúpályi 8 M
47.424, 21.734		HP 8 M: unplowed0–305
HP 8 M: deep plowed upper layer0–306
HP 8 M: deep plowed lower layer30–707
HP 8 M: row of tree stumps with soil content0–158
Forest II.
(deep-altitude area)
Hosszúpályi 8 M
47.427, 21.733		HP 8 M: unplowed0–309
HP 8 M: deep plowed upper layer0–3010
HP 8 M: deep plowed lower layer30–7011
HP 8 M: row of tree stumps with soil content0–1512
Forest III.
Hosszúpályi 4 L
47.407, 21.702		HP 4 L: unplowed0–3013
HP 4 L: deep plowed upper layer0–3014
HP 4 L: deep plowed lower layer30–7015
HP 4 L: row of trees stumps with soil content0–1516
Forest IV.
Debrecen 369 A
47.503, 21.811		DB 369 A: unplowed0–3017
** DB 369 A: deep plowed upper layer0–3018
DB 369 A: deep plowed lower layer30–7019
DB 369 A: row of tree stumps with soil content0–1520
* Hosszúpályi (HP). ** Debrecen (DB).
Table 3. The soil profile of the Hosszúpályi 7 H sampling area of the forest (humous sand; WRB Arenosols). Original photograph taken by the author István Attila Kocsis.
Table 3. The soil profile of the Hosszúpályi 7 H sampling area of the forest (humous sand; WRB Arenosols). Original photograph taken by the author István Attila Kocsis.
Agriculture 15 01030 i001Horizon
Designation		Horizon Depth (cm)Description of the Soil Layer
Ah0–5Reddish gray (2.5YR 5/1) color, single-grain sand, slightly humic level
AC5–50Light reddish gray (2.5YR 7/1) color, single-grain sand, slightly humus-like, roots interspersed
Bw50–110Light red (2.5YR 7/6) color, single-grain sand, sparsely rooted
Cl/Bt110–140Reddish brown (2.5YR 5/4) color, single-grain sand
Cl/Bt140–170Pinkish gray (7.5YR 6/2) color, single-grain sand
Clr170–Gray (7.5YR 6/1) color, single-grain sand with reductive features
Table 4. The examined physical, chemical, and biological properties of the Hosszúpályi forest (HP) 7 H sample site.
Table 4. The examined physical, chemical, and biological properties of the Hosszúpályi forest (HP) 7 H sample site.
SampleKAHU%Stability Coefficient (K)pH (H2O)Microscopic Fungi × 103 g−1Soil Bacteria × 106 g−1mg CO2 × 100 g−1 Soilmg CO2 × 100 g−1 × 10 Day−1
119.80 ± 0.79 ab0.36 ± 0.28 a1.26 ± 0.14 a4.59 ± 0.20 a31.50 ± 5.27 ab0.95 ± 0.27 a12.97 ± 1.85 a13.67 ± 2.46 a
218.20 ± 1.42 a0.22 ± 0.13 a7.06 ± 1.40 b5.41 ± 0.23 b51.50 ± 4.36 b0.41 ± 0.09 a12.47 ± 1.38 a13.27 ± 1.17 a
318.40 ± 1.64 a0.10 ± 0.04 a0.53 ± 0.13 a5.22 ± 0.22 b10.50 ± 1.50 a0.68 ± 0.24 a13.45 ± 0.47 a16.78 ± 1.22 ab
421.70 ± 0.70 b4.20 ± 0.53 b0.07 ± 0.03 a4.69 ± 0.12 a121.50 ± 21.78 c7.68 ± 0.64 b17.88 ± 1.14 b17.86 ± 1.11 c
Data marked with the same letter in the columns is not significantly different at p ≤ 0.05.
Table 5. The soil profile of the Hosszúpályi 8 M higher-lying area is brown forest soil with alternating thin layers of clay substance (WRB Arenosols). Original photograph taken by the author István Attila Kocsis.
Table 5. The soil profile of the Hosszúpályi 8 M higher-lying area is brown forest soil with alternating thin layers of clay substance (WRB Arenosols). Original photograph taken by the author István Attila Kocsis.
Agriculture 15 01030 i002Horizon DesignationHorizon Depth (cm)Description of the Soil Layer
Ah0–10Dark gray (2.5Y 4/1) color, sandy loam, strong humus level, interwoven with roots
E110–15Grayish white (2.5Y 8/1) color, single-grain sand, slightly humus level, interwoven with roots
A/E15–45Gray (2.5Y 6/2) color, single-grain sand, interspersed with roots, traces of soil mixing
E245–50Light gray (2.5Y 7/1) color, single-grain sand, root interspersed
Bw50–55Gray (7.5YR 6/1) color, single-grain sand, interspersed with roots, organic matter accumulation
C55–85Pinkish gray (7.5YR 7/2) color, more compacted, single-grain sandy loam
C/Bt85–140Dark reddish brown (2.5YR 3/3) color, compacted loam layer
Clr140–150Grayish brown (2.5Y 5/2) color, rootless sand
Clr150–Gray (2.5Y 5/1) color single-grain sand with reductive features
Table 6. The examined physical, chemical, and biological properties of the Hosszúpályi forest (HP) 8 M higher sample site.
Table 6. The examined physical, chemical, and biological properties of the Hosszúpályi forest (HP) 8 M higher sample site.
SampleKAHU %Stability Coefficient (K)pH (H2O)Microscopic Fungi × 103 g−1Soil Bacteria × 106 g−1mg CO2 × 100 g−1 Soilmg CO2 × 100 g−1 × 10 Day−1
536.20 ± 1.49 c2.84 ± 0.24 b0.46 ± 0.14 a6.68 ± 0.27 b151.75 ± 36.52 b0.70 ± 0.21 a14.70 ± 2.39 a15.13 ± 2.05 ab
622.00 ± 2.12 a1.70 ± 0.32 a0.99 ± 0.31 b5.66 ± 0.32 a28.00 ± 7.37 a1.55 ± 0.34 b12.56 ± 1.23 a13.36 ± 0.94 a
728.60 ± 1.39 b1.27 ± 0.26 a0.38 ± 0.05 a6.31 ± 0.24 ab12.50 ± 4.92 a1.06 ± 0.26 ab12.05 ± 1.54 a17.51 ± 1.07 b
831.50 ± 0.92 b1.41 ± 0.16 a1.39 ± 0.17 b7.23 ± 0.56 b15.00 ± 2.18 a5.55 ± 0.34 c13.08 ± 1.14 a16.47 ± 1.42 ab
Data marked with the same letter in the columns is not significantly different at p ≤ 0.05.
Table 7. The soil profile of the Hosszúpályi 8 M deep-lying area (meadow soil; WRB Chernic Gleysoil). Original photograph taken by the author István Attila Kocsis.
Table 7. The soil profile of the Hosszúpályi 8 M deep-lying area (meadow soil; WRB Chernic Gleysoil). Original photograph taken by the author István Attila Kocsis.
Agriculture 15 01030 i003Horizon DesignationHorizon Depth (cm)Description of the Soil Layer
Ah10–10Very dark gray (10YR 3/1) color, subangular blocky structure, clay loam, heavily humic level, heavily rooted.
Ah210–35Dark grayish brown (10YR 4/21) color, subangular blocky structure, loamy loam, highly humic level, heavily rooted, slightly calcareous
Blo35–55Red (2.5YR 4/6) color, single-grain structure loam, sparsely rooted
Ab55–80Dark reddish gray (2.5YR 4/1) color, grain structure loam, less rooted
C80–120Grayish white (2.5Y 8/1) color, single-grain sand
Clo120–160Olive gray (2.5Y 5/2) color, single-grain sand
Clr160–Bluish-gray color (GLEY2 5/5B) loam
Table 8. The examined physical, chemical, and biological properties of the Hosszúpályi forest (HP) 8 M deeper sample site.
Table 8. The examined physical, chemical, and biological properties of the Hosszúpályi forest (HP) 8 M deeper sample site.
SampleKAHU %Stability Coefficient (K)pH (H2O)Microscopic Fungi × 103 g−1Soil bacteria × 106 g−1mg CO2 × 100 g−1 Soilmg CO2 × 100 g−1 × 10 Day−1
942.60 ± 1.59 c4.01 ± 0.16 b2.11 ± 0.22 a7.79 ± 0.36 a37.00 ± 5.41 bc10.73 ± 1.22 c14.54 ± 0.72 a15.81 ± 1.41 a
1030.60 ± 1.99 a3.24 ± 0.36 b2.26 ± 0.18 a7.52 ± 0.33 a24.00 ± 6.61 ab6.45 ± 0.28 b13.69 ± 1.28 a14.34 ± 1.33 a
1134.10 ± 1.04 ab1.03 ± 0.48 a2.33 ± 0.21 a7.92 ± 0.27 a11.50 ± 2.65 a0.73 ± 0.10 a15.69 ± 1.45 a17.88 ± 1.98 a
1238.40 ± 2.38 bc3.11 ± 1.03 b2.07 ± 0.13 a7.84 ± 0.28 a43.50 ± 8.35 c7.12 ± 0.35 b14.26 ± 1.01 a15.39 ± 0.92 a
Data marked with the same letter in the columns is not significantly different at p ≤ 0.05.
Table 9. The soil profile of the Hosszúpályi 4 L forest section (Blownsand; WRB: Arenosols). Original photograph taken by the author István Attila Kocsis.
Table 9. The soil profile of the Hosszúpályi 4 L forest section (Blownsand; WRB: Arenosols). Original photograph taken by the author István Attila Kocsis.
Agriculture 15 01030 i004Horizon DesignationHorizon Depth (cm)Description of the Soil Layer
Ah0–20Brown (7.5YR 5/2) color, single-grain sand, slightly humus-like, rooted
A/C20–40Brown (7.5YR 4/4) color, single-grain sand, buried in a lightly humic layer, interspersed with roots. The shape of layer boundaries is irregular
C40–90Light Brown (7.5YR 6/4) color, single-grain sand, sparsely rooted
C/Bt90–180Brown (7.5YR 4/4) color, single-grain sand
Cl180–Gray (7.5YR 6/1) color, single-grain sand
Table 10. The examined physical, chemical, and biological properties of the Hosszúpályi forest (HP) 4 L sample site.
Table 10. The examined physical, chemical, and biological properties of the Hosszúpályi forest (HP) 4 L sample site.
SampleKAHU%Stability Coefficient (K)pH (H2O)Microscopic Fungi × 103 g−1Soil Bacteria × 106 g−1mg CO2 × 100 g−1 Soilmg CO2 × 100 g−1 × 10 Day−1
1326.70 ± 1.39 c0.26 ± 0.09 a1.55 ± 0.38 b4.15 ± 0.12 a39.50 ± 8.35 b0.73 ± 0.18 a10.76 ± 0.44 a16.30 ± 1.21 b
1418.10 ± 1.25 a0.17 ± 0.07 a0.48 ± 0.10 a4.25 ± 0.22 a16.50 ± 2.50 a1.24 ± 0.26 a11.17 ± 2.50 a12.73 ± 1.39 a
1521.80 ± 1.14 b0.41 ± 0.10 a1.87 ± 0.18 b5.63 ± 0.34 b4.50 ± 1.00 a0.87 ± 0.19 a12.68 ± 1.57 a15.22 ± 0.75 ab
1628.90 ± 1.14 c0.96 ± 0.32 b0.32 ± 0.15 a5.02 ± 0.54 ab73.50 ± 13.43 c3.46 ± 0.17 b13.82 ± 0.49 a14.02 ± 0.27 ab
Data marked with the same letter in the columns is not significantly different at p ≤ 0.05.
Table 11. The soil profile of the Debrecen 369 A forest section (humous sand; WRB: Arenosols)—Original photograph taken by the author István Attila Kocsis.
Table 11. The soil profile of the Debrecen 369 A forest section (humous sand; WRB: Arenosols)—Original photograph taken by the author István Attila Kocsis.
Agriculture 15 01030 i005Horizon DesignationHorizon Depth (cm)Description of the Soil Layer
Ah0–3Gray (7.5YR 5/1) color, single-grain sand, slightly humus-like level, rooted
E3–20Light gray (7.5YR 7/1) color, single-grain sand, slightly humus-like level, rooted
Bw20–55Dark brown (7.5YR 3/3) color, single-grain sand, heavily rooted
C55–90Reddish yellow (7.5YR 6/6) color, single-grain sand, lightly rooted
Clr90–160Dark gray (7.5YR 4/1) color, single-grain sand
Table 12. The physical, chemical, and biological properties of the Debrecen Forest (DB) 369 A sample site were examined.
Table 12. The physical, chemical, and biological properties of the Debrecen Forest (DB) 369 A sample site were examined.
SampleKAHU %Stability Coefficient (K)pH (H2O)Microscopic Fungi × 103 g−1Soil Bacteria × 106 g−1mg CO2 × 100 g−1 Soilmg CO2 × 100 g−1 × 10 Day−1
1719.70 ± 0.62 ab4.33 ± 0.28 c0.07 ± 0.03 a4.08 ± 0.19 a430.50 ± 30.43 d7.77 ± 1.60 c16.68 ± 3.98 a17.19 ± 2.25 a
1817.60 ± 1.73 a2.82 ± 0.22 b0.16 ± 0.07 a4.63 ± 0.29 b124.50 ± 17.68 b2.70 ± 0.63 ab12.54 ± 2.05 a15.72 ± 1.35 a
1917.90 ± 0.69 ab1.03 ± 0.33 a0.32 ± 0.25 a5.42 ± 0.22 c22.50 ± 4.58 a0.78 ± 0.28 a15.85 ± 5.19 a17.63 ± 1.73 a
2020.40 ± 082 b3.11 ± 0.48 b0.09 ± 0.03 a4.61 ± 0.10 ab184.50 ± 23.11 c4.11 ± 0.16 b17.62 ± 1.18 a17.81 ± 1.36 a
Data marked with the same letter in the columns is not significantly different at p ≤ 0.05.
Table 13. Losses of humus content of the sample areas in the upper 0–30 cm layer.
Table 13. Losses of humus content of the sample areas in the upper 0–30 cm layer.
ForestSampleHU (%)HU (%) Loss
HP 7 H: unplowed10.3638.89
HP 7 H: deep plowed20.22
HP 8 M: upper lying unplowed52.8440.14
HP 8 M: upper lying deep plowed61.70
HP 8 M: deep-lying area unplowed94.0119.20
HP 8 M: deep-lying area deep plowed103.24
HP 4 L: unplowed130.2634.62
HP 4 L: deep plowed140.17
DB 369 A: unplowed174.3334.87
DB 369 A: deep plowed182.82
Average: 33.54%
Table 14. Pearson-type correlation table (n = 24).
Table 14. Pearson-type correlation table (n = 24).
Pearson Correlations
HU%K-CoefficientpH (H2O)Microscopic FungiTotal No. of BacteriaCO2 Production
HU%1
K coefficient−0.3301
pH (H2O)0.0170.0551
Microscopic fungi0.806 **−0.254−0.3601
Total no. of bacteria0.648 **−0.248−0.1550.469 *1
CO2 production0.607 **−0.3640.1220.2380.2231
** Correlation is significant at the 0.01 level (one-tailed). * The correlation is significant at the 0.05 level (one-tailed).
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MDPI and ACS Style

Kocsis, I.A.; Tállai, M.; Zsuposné Oláh, Á.; László, Z.; Mokos, B.; Kincses, I.; Juhász, E.K.; Lowy, D.A.; Sándor, Z. Unveiling the Transformative Effects of Forest Restoration on the Soil Chemistry and Biology of Sandy Soils in Southern Nyírség, Hungary. Agriculture 2025, 15, 1030. https://doi.org/10.3390/agriculture15101030

AMA Style

Kocsis IA, Tállai M, Zsuposné Oláh Á, László Z, Mokos B, Kincses I, Juhász EK, Lowy DA, Sándor Z. Unveiling the Transformative Effects of Forest Restoration on the Soil Chemistry and Biology of Sandy Soils in Southern Nyírség, Hungary. Agriculture. 2025; 15(10):1030. https://doi.org/10.3390/agriculture15101030

Chicago/Turabian Style

Kocsis, István Attila, Magdolna Tállai, Ágnes Zsuposné Oláh, Zoltán László, Béla Mokos, Ida Kincses, Evelin Kármen Juhász, Daniel A. Lowy, and Zsolt Sándor. 2025. "Unveiling the Transformative Effects of Forest Restoration on the Soil Chemistry and Biology of Sandy Soils in Southern Nyírség, Hungary" Agriculture 15, no. 10: 1030. https://doi.org/10.3390/agriculture15101030

APA Style

Kocsis, I. A., Tállai, M., Zsuposné Oláh, Á., László, Z., Mokos, B., Kincses, I., Juhász, E. K., Lowy, D. A., & Sándor, Z. (2025). Unveiling the Transformative Effects of Forest Restoration on the Soil Chemistry and Biology of Sandy Soils in Southern Nyírség, Hungary. Agriculture, 15(10), 1030. https://doi.org/10.3390/agriculture15101030

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