Role of Soil Health in Mitigating Climate Change

Abstract

Soil health plays an important role in mitigating climate change, soils being the main reservoir for sequestering carbon and reducing greenhouse gas emissions in the atmosphere. In poorly managed soils or cultivated with unsustainable practices, carbon can be released in the form of CO₂ into the atmosphere, contributing to climate change. The conversion of forests and pastures into agricultural land has led to large losses of carbon from the soil. The restoration of degraded soils and the use of conservation practices will determine the reduction of greenhouse gas emissions, increase of carbon storage capacity and ensure resilience to climate change. This chapter will present the principles of sustainable management of soil fertility with the aim of reducing greenhouse gas emissions and sequestering carbon in the soil, as well as the effective use of fertilizers to ensure soil health and reduce the impact of climate change.

1. Introduction

Soil health has been defined as “the continued capacity of soils to support ecosystem services, in line with the Sustainable Development Goals and the Green Deal” (EU Mission Soil). Despite this undeniable ecological, economic and social role, holistic understanding and practice-oriented recommendations to maintain soil health are still limited. Climate change, land exploitation and controversial discussions about sustainable land management present great challenges in all industrial sectors. The vital role of soil is not only about the production of safe food, but also about healthy ecosystems and human well-being.

Soil health, as its continued ability to function as a living and vital ecosystem, supporting all living organisms, is maintained through the interconnection of agricultural science with policy, stakeholder needs and sustainable supply chain management. Although soil health was focused on crop production, it is also found in water quality, human health and the intensity of climate change. However, the quantification of soil health is still dominated by chemical indicators, despite the growing appreciation of the importance of soil biodiversity (Figure 1).

Figure 1.

Soil health diagram.

Soil degradation in Europe, but also worldwide, as a result of inadequate and unsustainable management practices, industrial contamination, soil compaction, air pollution and climate change, is linked to environmental impacts [1]. Around 60–70% of soils in the EU are unhealthy, with various forms of degradation. In agriculture, the inappropriate use of chemical fertilizers and pesticides along with unbalanced crop rotations and intensive mechanization cause soil degradation [2]. These factors affect the various properties of the soil and cannot replace its functions in organic matter cycling, nutrient cycles, aggregate formation and combating pathogens and pests. The irrational use of chemicals in agriculture contributes majorly to the pollution of environmental factors (soil, water, air) and to the reduction of biodiversity by harming non-target plants, insects, birds, mammals and amphibians [3]. Soil erosion, compaction, pollution, salinity and climate change are exacerbating soil health problems in Europe and around the world [4]. It is estimated that climate change will have an overwhelming impact on agriculture through direct and indirect effects on the evolution of agricultural production, soil quality, animal breeding and diseases.

Because of its direct and significant influence on agricultural productivity, the increasing need for fertilizer and amendment applications, and the profound influence of soil chemical properties on changing its biological and physical health, soil chemical and physical health is receiving more attention from both researchers, as well as the interested parties and will be discussed in this chapter.

2. Soil chemical health management for climate change mitigation

The increasing degradation of soils as a result of climate change can be reduced by maintaining the chemical health of the soil, especially by reducing nutrient deficiencies and the accumulation of pesticide residues in the soil, but also by sequestering carbon, because the organic carbon of the soil is one of the most important criteria for evaluating his health.

2.1 Soil organic carbon

Although natural climate changes are a slow process involving relatively small changes in temperature and precipitation patterns, amplified by anthropogenic factors, they have an overwhelming impact on soil fertility. The effects of climate change are expected to influence soil moisture conditions with effects on soil temperature and CO₂ levels. Agriculture, through plant cultivation and animal husbandry, besides carbon dioxide (CO₂) and methane CH₄), is an important source of nitrous oxide (N₂O). It is estimated that agricultural systems produce about one quarter of global N₂O emissions [5].

The organic carbon (OC) content of the soil is influenced by climatic factors, the biotic activity of plants and microbial communities, as well as the physic-chemical properties of the soil, all of which control its dynamics. Soil organic carbon (SOC) is an important component of the terrestrial carbon pool and plays a crucial role both in maintaining the functioning of ecosystems and in the global carbon cycle [6]. The amount of organic carbon in the soil is the result of a long-term balance process, between losses and accumulations [7]. The physical and chemical stability of terrestrial carbon deposits under the action of climate change is unclear. The uncertainty regarding the size and stability of the soil organic carbon reserve is due to the lack of knowledge of both the distribution and the cycle times of organic carbon from the depth, because the amount and age of C stored below 30 cm depth and especially below 1 meter is not very well known [8]. To estimate the impact of climate change on the carbon cycle, studies have been carried out on organic carbon in particles in rivers, which show that increased precipitation and increased temperature destabilize organic carbon stores. On the other hand, the increase in CO₂ content in the atmosphere has the effect of intensifying the photosynthesis process, increasing the efficiency of water use, obtaining high harvests, increasing the amount of plant residues and, as a result, increasing the content of organic matter in the soil. It also increases the availability of C for microorganisms and accelerates the nutrient cycle.

The increase in CO₂ content in the soil causes a change in the C/N ratio, resulting in an intensification of microbial activity manifested by an increase in the partial pressure of CO₂ in the gaseous phase and its concentration in the liquid phase of the soil, with a negative effect on the accumulation of organic C in the soil. Soil C deposits, which act both as a source of C and as a reserve for atmospheric CO₂, are massively influenced by climate change and soil water content. Global warming can directly or indirectly influence the organic carbon content of the soil, by acting on microbial and enzymatic activity [9, 10].

The response of soil organic matter decomposition to increasing temperature is an important aspect of ecosystem response to climate change. The impact of climate warming on the dynamics of soil organic matter decomposition has not been determined, due to the existence of the second fraction of C: a labile one, with a short cycle and high sensitivity to temperature increase, and a fraction with reduced sensitivity to temperature change, with a long cycle for decades or even centuries, which makes up the majority of soil C deposits [11, 12]. The existence of these two types of fractions limits the ability to forecast the influence of temperature changes on the organic C content of the soil [13, 14]. Even a small change in soil organic carbon content can substantially affect the stability of ecosystems,

Soil organic carbon has two important functions for drought resistance: it can store up to 10 times its weight in water, and it is used as a food source for soil microorganisms (bacteria, fungi, and other soil life) that build soil structure. This also creates a habitat for macrofauna, such as earthworms, which make wider pores in the soil for water to drain into the soil profile rather than the surface causing soil erosion.

The primary sources of organic carbon, of a biogenic nature (emissions of volatile organic compounds from vegetation, biological particles - pollen, plant debris, soil, dust, bacteria and viruses, forest fires, volcanic emanations, plankton activity), anthropogenic (burning and fossil fuel and ethanol production, biomass burning, household heating and cooking, solvent use), emissions from agriculture (such as pesticides) and natural gas exploration, are released into the atmosphere as gases and particles. Gases from the soil are in a permanent exchange with the atmosphere, the lack of this exchange leading to the creation of unfavorable conditions for microbiological activity and mobilization of nutrients in assimilable forms. Following the exchange with the atmosphere, the soil receives oxygen as it is consumed and eliminates CO₂ due to its higher concentration in the soil. CO₂ release from soil can be considered as an indicator of microbial activity and soil fertility. Thus, fertile soils release more than 60 mg CO₂/kg/day, and poorly fertile ones less than 30 mg CO₂/kg/day [15]. The intensity of gas exchange depends to a high extent on the air permeability of the soil; it is maximum in sandy soils and minimum in clayey, more compact soils. On average, annually, in the temperate zone, precipitation contains 0.82–2 mg organic C/L [16], inorganic C being generally lower. Dissolved organic carbon from precipitation infiltrates into the soil, being leached onto the soil profile.

Soil clay percentage is often used to determine variations in SOC stability and to model SOC turnover [17]. In principle, clay content determines the stabilization of soil organic matter both by favoring the adsorption process of organic molecules on the surface of minerals with dimensions 2 μm, and by their occlusion in aggregates [18, 19]. Fine-textured soils contain higher amounts of protected SOC compared to coarser-textured soils [20]. In areas with similar pedoclimatic conditions, soil organic carbon content tends to increase in direct proportion to clay content. Due to the interactions between SOC and mineral particles, montmorillonite clays reduce the accessibility of OC to degradation, thus controlling the susceptibility to mineralization; and implicitly the release of CO₂ into the atmosphere [21]. Fine soil mineral particles and soil aggregate structures control organic carbon content by adsorption of organic matter to mineral surfaces and occlusion in aggregates, protecting organic matter from further degradation [22]. The interaction between the soil organic carbon content and the percentage of colloidal particles, such as clay and loam, are used to approximate the capacity of soils to store organic matter and to model the organic carbon cycle in the soil. Climatic conditions were found to affect the relationship between OC stocks and clay content [23]. Correlations between clay content and environmental factors and between environmental factors, as well as the various interrelations between them, can confound the effects of fine particles in OC storage. By controlling these site factors, the analysis of the assessment of the influence of fine mineral particles on OM storage can be more precise [24].

One of the most important and distinct properties of the soil is the total cation exchange capacity, as it can represent a direct measure of the adsorption of the organic carbon content on the mineral surfaces of the soil under the existing pH conditions. A series of researchers have shown that polyvalent metal cations (Ca, Al) have an important role in SOC stabilization by forming metal bonds and exchangeable bridges between the surface of minerals and organic compounds [19, 20]. It has been suggested that the strength of the bond between the metal cation largely depends on the size of the hydrating shell and the valence of the cation. The formation of complexes through ionic bonds between organic molecules and metal cations present on the surface of minerals depends mainly on the displacement of the hydrating shell of the cations, as well as on the type of organic molecule from the soil solution [25]. In soils with acid pH, it was observed that Al³⁺ plays an important role in the formation of complexes between organic molecules and mineral surfaces. The divalent calcium ion Ca²⁺, weekly polarizable, has a tendency to form ionic bonds with O-containing ligands, such as carboxylic acids, thus forming complexes with organic substrates [26]. The monovalent cation Na⁺ does not form ionic bonds with organic ligands, and K⁺ only participates in these complexes in the interlayers of certain phyllosilicates. The physical protection of SOM, produced by aggregation, is due to the ability of the metal ions on the surface of the minerals to form organo-metallic compounds by binding several organic compounds [27].

2.2 Modification of soil mineral nutrient status

Climate change may alter the annual and seasonal availability and cycling of nutrients. These climate changes, together with the modification of soil properties and the distribution of nutrients in the soil result in a complicated scenario that influences the microbial activity of the soil and therefore the availability of nutrients to the plant. Variations in temperature or precipitation caused by climate change alter nutrient cycles and, as a result, plant nutrient availability [28]. The research carried out by various researchers [29] show that increasing CO₂, increasing temperatures and water stress are the main factors that could change the demand and availability of nutrients.

The influence of climate change on plant nutrition is highly complicated because climate factors influence all phases of plant growth, including plant development, metabolism, physiology, and production [30]. Agroecosystems capture water, light, CO₂ and nutrients and use them in metabolic processes to form proteins, carbohydrates and starch (Table 1).

Reservoir	Carbon (×10^12 kg)	Nitrogen (×10^12 kg)	Sulfur (×10^12 kg)
Atmosphere	700 (CO2)	3,800,000 (N2)	4
Surface ocean (to the depth of 50 m)	800	1 (organic)	0,1 (organic)
Living biomass	500	14 (organic)	2 (organic)
Soils, to 1 m depth	1800 (organic)	180 (organic)	20 (organic)

Table 1.

Distribution of carbon, nitrogen and sulfur at the earth’s surface [25].

Nutrient imbalances in the soil occur due to the differential absorption of nutrients and the addition of fertilizers, without taking into account the plant’s specific consumption of nutrients corresponding to a certain period of their vegetation. Multi-nutrient deficiency of the soil was increased due to the application of only primary nutrients (especially N and P), with complete dependence on soil nutrient reserves for other nutrients.

Soil is an important part of the natural carbon, nitrogen and sulfur cycle. In the nitrogen cycle, nitrate and ammonium ions from rainwater are retained in the soil, absorbed by plant roots and microorganisms and transformed into amino acids or molecular nitrogen N₂ and nitrous oxide N₂O which are then released into the atmosphere. Under natural conditions, losses of gaseous nitrogen from the soil are approximately equal to the N₂ retained in the soil and converted to amino acids by symbiotic microorganisms.

Nitrogen supply is essential for maintaining soil fertility and increasing crop yield. However, nitrogen that is not absorbed by plant roots can be converted into nitrous oxide (N₂O), a greenhouse gas that has 298 times the warming potential of CO₂ [31]. Various studies have shown that the application of mineral nitrogen fertilizers tends to produce a higher intensity of N₂O emissions even when applied at half the rate of nitrogen application as organic fertilizer [32]. The amount of nitrous oxide released into the atmosphere depends on pedoclimatic conditions, prolonged wet weather can increase N₂O emissions due to anaerobic soil conditions [33].

N₂O dynamics is affected by labile carbon content, as it can create anaerobic conditions in the soil and thus increase N₂O emissions. N₂O emissions are also influenced by soil mineralization-immobilization and nitrification processes [34] as well as clay content [35]. The ideal C/N ratio in soil is 12. When this ratio is changed by applying nitrogen fertilizers, nitrogen uptake by plants, addition of low-carbon organic matter such as straw or wood, soil microorganisms will restore the C/N balance through carbon oxidation, nitrogen fixation or denitrification.

Soil nitrogen content can fluctuate with fertilizer application, including the cultivation of leguminous or non-leguminous plants. Only about half of the applied dose of nitrogen fertilizer is used by plants, the rest being subjected to denitrification or leaching. Fertilization tends to increase the N₂O/N₂ gas emission ratio during denitrification. Water, organic matter in the soil, such as sewage sludge, manure can load the soil with larger amounts of nitrogen than the plants can consume. When these organic matters are oxidized, they will release CO₂, N₂ and N₂O into the atmosphere. However, the amount of gases released by the oxidation of organic matter in normal beds is relatively low, increasing as nitrogen fertilizers are applied. Soil microorganisms can reduce the nitrate ion NO₃⁻ resulting from the application of mineral fertilizers, increasing the N₂O/N₂ ratio as the amount of nitrate ions increases. Nitrate ion reduction is an important pathway of N₂O and N₂ emissions to the atmosphere. To counteract these effects, researchers are developing a variety of strategies, for example, urease inhibition and capping technologies have been tried to reduce N₂O emissions from soil, with varying levels of success [36].

Although mineral nitrogen fertilization increases biomass production and input of plant residues to soil, as well as organic carbon (OC) accumulation, it can enhance the microbial oxidation of soil organic carbon, leading to loss of organic matter and total soil nitrogen. Acceleration of soil organic carbon mineralization induced by N fertilizer application occurs only when N fertilizer is applied at excessive rates [37].

Soil nitrogen is the most difficult element to characterize: it appears in inorganic and organic form (both anion and cation), in the soil solution and in gaseous form. Plants absorb it only in its inorganic form. The forms of nitrogen contained in organic and mineral fertilizers are: ammonia, urea and ammonium and nitrate ions. Ammonia NH₃ reacts quickly with soil water forming the ammonium cation NH₄⁺. Urea (NH₂)₂CO is quickly converted, by urease, to ammonia. When urea or fresh manure is applied to the soil surface, nitrogen is lost as ammonia, especially in dry soils with high temperature and pH. After incorporation and decomposition in the soil, urea quickly passes into the form of ammonia and then ammonium. The ammonium cation, as a result of the positive charge, is retained by the negative charges of the colloidal complex. This prevents the loss of nitrogen through leaching, except for soils with low cation exchange capacity.

Phosphorus is a major nutrient macronutrient required for many physiological and biochemical functions of plants. Climate change creates challenges in phosphorus management, affecting overall crop production The availability and absorption of phosphorus in plants, as well as its mobility in the soil, depend on temperature variations, soil reaction, soil humidity and the increase in CO₂ concentration. P absorption and translocation are reduced at very low or high temperature values. At alkaline pH, phosphorus can be retained in the soil in the form of tertiary calcium phosphates, insoluble compounds, from which phosphorus is not accessible to plants. Acid values of the soil reaction will reduce the intensity of soil microbial activity, but also the rate of transpiration, absorption and use of P. High concentrations of CO₂ in the soil will reduce the absorption of phosphorus by plants [38].

Potassium, calcium, magnesium, manganese, zinc, iron and copper appear in the soil in cationic form. Apart from potassium and ammonium, which have a positive charge (K⁺ and NH₄⁺), the rest of the elements possess two or more positive charges. The greater the charge of the cation, the stronger it will be retained by the negative charge of the colloidal complex. When the sum of cation charges exceeds the soil’s ability to retain nutrients, potassium and ammonium will be released before cations with two or more positive charges, being made available to plants. K⁺ leaching generally occurs on sandy soils with low cation exchange capacity. As a result of the high positive charges, micronutrients form in the soil compounds with very strong bonds (coordinative bonds). They cannot be leached under normal conditions.

Numerous studies show that increasing CO₂ levels reduced the levels of some nutrients (such as Ca, K, Mg and P) in the edible parts of plants when they are found in lower amounts than N concentrations. It has also been shown, that high CO₂ levels reduce the concentrations of Co, Fe, Mg, Mn, Ni, S and Zn in plants [39].

In areas with short growing seasons, increasing temperatures can improve crop yields. However, sudden increases in temperature will have a negative impact on growth, photosynthesis, respiration, reproduction and the water regime of plants. In addition, increased temperature can shorten the growth and grain filling periods of the crop. In addition, different crop varieties may show diverse responses to future climate change due to the length of different seasons [40]. Arndal et al. [41] states that the increase in temperature determines the extension of the vegetation period and the increase in the intensity of the mineralization rate of organic matter, increasing the availability of nutrients and their absorption. The increase in soil temperature, which occurs faster in high areas as a result of climate change, leads to the intensification of microbial activity in the soil, influencing its physiology. As a result, there is an acceleration of the organic matter decomposition process, increasing the amount of mineral nitrogen in the soil. This could result in soil nutrient release and availability and decreased nutrient limitation. This happens more in warmer temperatures than in colder ones [42].

2.3 Soil reaction

The reaction of the soil directly influences its health, neutral pH values being suitable for most crops and different soil properties; while sudden changes in soil reaction affect its chemical health. Modification of soil pH due to anthropogenic activities are observed at a very slow rate due to the buffering capacity of the soil. Environmental factors that cause changes in soil reaction include:

• meteorological factors, mainly rainfall and temperature, which cause alkalization and erosion phenomena in the soil;

• climatic factors that intensify the alteration of parent soil materials;

• topographical factors, such as: the topography of the land and the presence or absence of vegetation on the surface of the soil.

Most cultivated plants cannot support a pH < 4.5 or pH > 8.3, nor large variations thereof. Most plants grow well on neutral (pH = 6.8–7.2) or slightly acidic (pH = 6.3–6.8) soils. As a rule, plants tolerate an acidic environment better than an alkaline one. The maximum sensitivity to acidity, respectively to alkalinity, manifests itself at the beginning of the vegetation period, in the first phases, and especially at the seedling stage. The sensitivity of plants to extreme pH conditions increases, in principle, under conditions of water and nutrient stress.

Low values of the soil reaction, pH < 5.8, cause its acidification. If on strongly acid soils, numerous plant species develop weakly or die, this is not only due to the presence of a large amount of H+ ions, but to the entire soil complex, especially Al³⁺ and Mn²⁺ mobile in the soil solution above certain limits, to the deficiency of some nutritional elements, as well as the imbalances produced by acidity in their accessibility for plants. The causes of soil acidification are application of fertilizers with acidic physiological reaction, organic matter mineralization, root absorption of nutrients, root secretions, nitrogen fixation by leguminous plants and acidic rain [43]. Acidification negatively affects soil health by reducing plant nutrient availability and soil microbial activity. Toxicity phenomena for plants may also occur due to increased concentrations of one or more mineral elements.

The high values of the soil reaction, pH > 8.2, determine its alkalinization. This phenomenon is the opposite of soil acidification, as soil pH is increased by the predominance of sodium carbonates and bicarbonates. For plants that are extremely sensitive to the presence of sodium, a content of ≥5% exchangeable sodium causes sodium to accumulate in toxic amounts in plant tissues. A high sodium content in soils leads to Mg and Ca deficiency. The high pH of saline soils can accentuate the deficiency of several microelements (Fe, Cu, Zn or Mn). Also, high pH values lead to an increase in the amount of soluble aluminum. The accumulation of soluble salts in soils inhibits plant growth. They induce the phenomenon of plasmolysis, by which water is removed from the plant, being passed into the soil solution.

The source of nitrogen for plants is organic matter, its decomposition being reduced at pH values lower than 7. At pH values below 5.5, the nitrification process predominates. Ammonium ions will accumulate in acidic forest soils because microorganisms participating in the decomposition of organic matter are less dependent on pH than those participating in the nitrification process. Ammonium ion fixation between layers of clay minerals with an expandable structure decreases with increasing soil pH.

Phosphorus has greater mobility in soils with pH = 5.5–7.0. At pH < 5.5, the formation of insoluble iron and aluminum phosphates occurs, from which phosphorus is inaccessible to plants. At pH values >7.0 and up to 8.5, secondary and tertiary calcium phosphates are formed, hardly soluble, from which plants cannot use phosphorus. At pH > 8.5, sodium phosphates are formed, easily soluble and accessible to plants.

On acid soils, potassium is easily leached, in contrast to neutral and alkaline soils, and following calcium amendment, its mobility decreases. Ca2+ ions cause an accentuated desorption of K+ from the colloidal complex, and have an antagonistic effect on its absorption by plants.

Calcium and magnesium are more soluble at pH values higher than 6.0. Iron, copper and zinc have reduced mobility at pH > 7.5. Boron is very mobile at low pH, and molybdenum at neutral pH (6.7–7). Molybdenum is less accessible to plants at low pH values.

In acidic soils, aluminum partially passes into soluble forms, the high concentrations of Al³⁺ in the nutrient solution having harmful effects on the roots, which undergo morphological changes, turn black, and changes in the capacity to absorb and retain cations occur. Al³⁺ occupies the exchange positions of the root hairs, preventing the absorption of other nutrients: K⁺, Ca²⁺, Mg²⁺, Fe²⁺, etc. In the presence of Al3+, the phosphorus introduced into the soil through fertilizers is inaccessible to plants due to the formation of AlPO₄, insoluble and inaccessible to plants. As a result, on strong soils acidic, with a lot of aluminum, it is necessary to apply high amounts of phosphate fertilizers, in order to prevent on the one hand the lack of phosphorus, and on the other hand the harmful effect of aluminum through its precipitation in the form of tertiary phosphate. The negative effect of aluminum starts from 15 to 50 ppm exchangeable Al, and from 0.3 me/100 g soil (27 ppm Al) calcium amendment is required.

Along with aluminum, manganese also produces toxic effects at very varied concentrations, depending on the plants’ sensitivity to this element. Thus, while some plants show important disturbances at concentrations of 1–4 ppm Mn, corn can tolerate concentrations above 15 ppm Mn, without growth retarding effects. Mn accumulates more in the aerial part of the plant, which causes disturbances in protein metabolism. Common symptoms of toxicity are the appearance of brown spots on the leaves. The excess of Mn in the soil solution sometimes causes symptoms that indicate a false lack of iron.

3. Soil physical health

The physical health of soils, manifested by the phenomenon of erosion or compaction, is determined either by intensification of meteorological factors (precipitation and wind), the aerobic-anaerobic cycles of the state of soil moisture, or by human activities, such as: increased intensity of soil work, intensive grain-based cropping systems (rice-wheat cropping system; [44]), reduction of soil organic matter content as a result of non-application of organic fertilizers and lack of vegetation.

3.1 Soil erosion

The intensity of water erosion is determined by the following factors: rainfall characteristics (intensity, distribution and frequency), soil erodibility, slope and slope length, cultivation practices and erosion control measures. Erosion due to wind manifests itself especially on loose, dry soils not covered by vegetation and is subject to the action of strong winds. These conditions are mainly found in arid areas, erosion being accelerated by poor land management. Wind erosion of agricultural lands results in the removal of topsoil, biologically active soil particles, rich in organic matter and nutrients, affecting the water retention capacity, chemical fertility and biological activity of the soil. Wind erosion of agricultural lands results in the removal of topsoil, biologically active soil particles, rich in organic matter and nutrients, affecting the water retention capacity, chemical fertility and biological activity of the soil [45, 46].

Soil erosion due to precipitation and wind contributes to the contamination of the environment with dust particles, microplastics, heavy metals and pesticides, which reach the soil after fertilization with sewage sludge, compost and plastic film mulching, chemical fertilizers, pesticides [47, 48].

The high temperatures associated with climate change cause the intensification of soil degradation processes. Increased evaporation rates lead to excessive drying of the soil, reducing its fertility and making it more prone to erosion [49, 50].

Climate change has a direct impact on crops, requiring the choice of new species of plants to be cultivated, changes in crop rotation, the vegetation period and increasing susceptibility to pests and diseases. Soil cover with vegetation plays a crucial role in preventing erosion. When the soil surface is adequately covered, it acts as a natural barrier against erosion by reducing the impact of raindrops, slowing water runoff and decreasing wind speed near the ground. Ground cover helps maintain soil structure, stability and fertility, as well as preventing the loss of valuable topsoil. Vegetation, such as grasses, shrubs or trees, is one of the most effective forms of ground cover. Plant roots bind soil particles together, making them less susceptible to erosion. The aerial parts of plants, such as leaves and stems, intercept raindrops and reduce their erosive force. Plant cover also helps to improve water infiltration into the soil, allowing it to be absorbed and reducing surface runoff [51].

Modern agricultural practices aim at changing the cultivation calendar, sowing period and techniques, soil preparation and conservation practices, changing the periods of agricultural activities, adopting crops resistant to climate change. Modern practices may also include choosing crops and species better adapted to the growing season and available water, adapting crops with the help of existing genetic diversity and new opportunities offered by biotechnology. The productivity of vulnerable soils, especially those on slopes, must also be protected against water erosion (the effects of rainfall runoff) through the use of good agricultural and environmental practices, including contour plowing.

3.2 Soil compaction

When the soil surface is subjected to pressure, soil compaction occurs, leading to changes in soil permeability and porosity. Gases and water circulation through the soil it is prevented by the interruption of the pores, determining the existence of a reduced amount of water and oxygen. Root growth is hampered.

Soil is removed by erosion much faster than it can be replaced by the process of soil formation. The loss of the surface layer results in reduced fertility, causing lower productivity.

Soil compaction can cause or accelerate other soil degradation processes, such as erosion or landslides. Compaction reduces the degree of infiltration, which leads to the intensification of spreading on inclined surfaces. Due to the presence of a layer with low permeability, the upper layer of the soil will be more prone to water saturation and therefore heavier, presenting the risk of landslides. In the sixth zone, compaction can cause water supersaturation, determining the destruction of aggregates and causing crust formation.

The structure of the soil is improved with organic matter, reducing its predisposition to compaction, erosion and landslides.

4. Conclusions

Healthy soils are essential for increasing resilience to climate change by maintaining or increasing their carbon content and reducing greenhouse gas emissions. The release of carbon from the soil into the atmosphere results in land degradation, also contributing to climate change. Sustainable management and maintenance of soil health are key factors in increasing resilience to extreme weather events such as hurricanes, floods and droughts.

Soil degradation in Europe and around the world is the result of inadequate and unsustainable management practices in agriculture and forestry, industrial contamination, soil sealing, air pollution, having a major impact on climate change. The pressure to meet the growing demand for food and unsustainable agricultural practices, such as: the use of intensive tillage techniques, the abandonment and neglect of agricultural land, the cultivation of monocultures, the application of chemicals in the form of fertilizers, amendments and pesticides, have an impact on soils health, causing their compaction, degradation or pollution, reduction of microbial activity, reduction of bioavailability of nutrients or their loss through leaching or volatilization. One of the main factors of sustainable agriculture is the soil quality, which is determined by the influence of climatic and anthropogenic factors on its physical, chemical and biological properties. Degradation of soil quality is the result of current agricultural land management practices, but sustainable soil management can significantly contribute to achieving climate neutrality by eliminating anthropogenic emissions from organic soils and by increasing the amount of carbon stored in mineral soils. The use of fertilizers in excess can create nutritional imbalances, resulting in water and air pollution with negative effects on the environment and human health. However, the application of insufficient amounts of nutrients in the soil can have a negative impact on the microbial activity, reducing the organic matter content of the soil and its fertility. In order to maintain a healthy soil ecosystem, a sustainable soil management is required, namely: increasing the organic matter content of the soil, maintaining vegetation on the soil surface, rational use of fertilizers, applying crop rotation, eliminating plowing after harvesting. Concerned with these challenges, the Green Deal, especially the Circular Economy Action Plan, the Farm to Fork and the Bioeconomy strategies of the European Union set ambitious goals for the ecological transformation and sustainable adaptation of agriculture to the challenges of climate change. By 2030, the use of fertilizers is to be reduced by 20% and the use of chemical pesticides by 50%. At the same time, nutrient losses are to be reduced by 50%, while ensuring that soil fertility is not impaired.

Acknowledgments

This paper is published from the project 6PFE of the University of Life Sciences “King Mihai I” from Timisoara and Research Institute for Biosecurity and Bioengineering from Timisoara.

Conflict of interest

The authors declare no conflict of interest.

Acronyms and abbreviations

SOC	Soil organic carbon.
OC	Organic carbon.
OM	Organic matter.