Soil Health and Properties in a Changing Environment

1. Introduction

Healthy soil is the foundation of sustainable and productive agroecosystems. Soil must perform various agronomic and ecosystem functions, maintain biological productivity, support environmental quality, and promote plant and animal health [1,2].

Soil is home to numerous biological, chemical, and physical processes that directly affect plant growth, productivity, and environmental protection. A sustainable agroecosystem cannot exist without good soil conditions, as it is the soil that provides plants with the nutrients they need for growth and development, regulates water circulation, prevents erosion and the effects of droughts or floods, stores carbon reserves, helps to combat climate change, and promotes biodiversity, as it is home to a multitude of microorganisms, fungi, and invertebrates that perform important biological functions [3,4].

In addition, healthy soil helps to avoid excessive dependence on chemical fertilizers and pesticides, as it naturally supports plant resistance to diseases and pests. Therefore, in order to develop sustainable agricultural practices and ensure a long-term food supply, it is necessary to take care of soil health, which is a long-term investment in the well-being of people, the environment, and the economy [5].

The main goal of this Special Issue was to invite scientists and researchers to publish their research results to help fill in gaps in knowledge and allow for a broader understanding of the problem as a whole and its solutions. The publication contains fifteen original scientific articles, reviews, and opinions on soil properties under changing environmental conditions. They include not only analyses of the chemical, physical, and biological indicators of soil but also studies that can reveal how we can better analyze, model, and reevaluate various indicators of soil health.

2. Soil Property Assessment and Modeling

The article by G. Almendra and co-authors describes how the use of MIR spectroscopy in combination with chemometric models can be used to efficiently and non-invasively assess many important soil properties, both chemical and biological, using a single analysis. Such a methodology is particularly useful for monitoring and assessing soils in the semi-arid Mediterranean region with low organic carbon concentrations. Although PLS models are useful, the authors emphasize that other algorithms can also be useful for specific indicators, but PLS here provided evidence-based predictions with a clear chemometric basis.

Another group of researchers describe the discrete element method (DEM) with stratification, i.e., modeling the soil in three different depth zones (0–6 cm, 6–15 cm, and 15–21 cm), in order to improve the accuracy of soil–machine interaction models. It was found that the inclusion of stratification and the combined model of JKR + Bonding provide a better description of the interaction between soil mechanics and machinery than a single layer. A fast, efficient parameter extraction methodology is proposed, which can help optimize the design of agricultural machinery and soil management practices.

It is noted that the model has so far only been calibrated for a specific sandy loam soil of the Inner Mongolia region—verification in other regions and soil types is needed [6].

3. Soil Biological Properties

Soil macrofauna, including nematodes, are key components of soil micro-nutrient networks that support ecosystem functions by regulating organic matter decomposition, nutrient mineralization, and energy transfer [7]. Research conducted by Y. Hu and co-authors allows us to assess the impact of precipitation entering the soil on the structure and functions of these microbiological indicator organisms and on the overall health of the ecosystem. The precipitation gradient strongly determines the structure and functions of nematode communities, ranging from a simpler structure dominated by r-strategists in dry areas to greater diversity and fungal decomposition in regions of moderate humidity.

In addition to macrofauna, microfauna also play an important role in soil. Soil microorganisms play a key role in ecosystems, being the main drivers of nutrient cycling, organic matter decomposition, and plant growth. Microorganisms help maintain soil fertility, facilitate nutrient cycling, and increase plant productivity [8]. A paper by L. He and co-authors show that the cultivation of both cereals and legumes in the Mu Us desert can significantly improve soil chemical properties and promote the abundance and diversity of bacterial communities. Such practices, particularly the inclusion of cereals (Setaria italica), can help transform degraded sandy soils into more productive and ecologically sound agroecosystems. The scientific evidence supports sustainable agricultural strategies in drylands.

4. Effects of Organic Fertilizers and Crop Residues on Soil Chemistry

Cover crop residues are known to promote nitrogen availability and broader aspects of soil health, including reducing weed and disease control and soil erosion, while increasing soil organic matter [9]. Three articles on this topic are included in this Special Issue. In one of them, authors Ray and Zhao review studies that evaluate how various organic fertilizers, cover crop residues, and composts affect soil health indicators in sandy soils after an organic celery (Apium graveolens var. dulce) growing cycle. This study demonstrates that an integrated strategy is necessary when developing organic soil improvement plans for sandy soils, combining appropriate organic fertilizers, composts, and cover crops, and taking into account seasonal changes and long-term effects.

In two other articles, U. Mecione/Stulpinaite and her co-authors write about how different application technologies—application time (season), soil cultivation methods, and application method (incorporation into the soil or leaving as mulch)—affect the rate of mineralization of hemp residues and the main chemical properties of the soil. These studies emphasize that optimal hemp residue management—especially incorporation in the fall—allows for more effective promotion of mineralization and increased soil carbon enrichment without fear of large pH fluctuations or nitrogen deficiency. Advanced residue management combined with nitrogen supplementation can help unlock the potential of hemp as a sustainable soil improvement practice. All hemp residue management technologies contribute to increasing soil carbon content, but timing and tillage are important for maximizing yield.

5. The Role of Organic Carbon in Soil

Soil is the largest carbon reservoir in terrestrial ecosystems. Even small changes can have large feedback effects on carbon stocks and climate change. Therefore, studying soil carbon changes and their determinants is essential for developing effective soil management strategies and addressing climate change issues [10]. Numerous studies have shown that various soil-forming factors, such as climate, biology, parent material, and topography, can directly change the ratio and amount of organic carbon (OC) and inorganic carbon (IC). Therefore, to dynamically adjust soil C reservoir strategies, it is necessary to understand the evolutionary rates and trajectories of different C components in soil along developmental gradients.

There are two articles on this topic in this collection. B. Su and co-authors examine how soil development stages and land use patterns affect organic and inorganic carbon concentrations in alluvial soils in the Lower Yangtze River region. The results of this study show that organic carbon (OC) accumulates in the surface layers as the soil matures, while inorganic carbon (IC) decreases significantly. Rice fields with dry–wet season rotation help to accumulate OC more efficiently than dry fields, while maintaining stable IC levels. These results highlight that sustainable land use and soil maturity management are important factors in maintaining or even increasing soil carbon stocks and contributing to climate change mitigation.

R. Wang and co-authors present soil organic carbon maps with predicted regional patterns of change, allowing for more accurate management of soil quality and ecosystem carbon sequestration (for these indicators in climate change and clean agriculture strategies). SEM analysis revealed that climatic conditions, soil properties, and terrain directly or indirectly affect SOC supply and its temporal changes. This helps to identify priority areas for sustainable agricultural management and soil carbon storage.

6. Improving the Use of Nitrogen Fertilizers for Soil Fertilization

Nitrogen is one of the main elements that increases plant productivity. Although progress has been made in the field of nitrogen management, there remains an urgent need to properly incorporate soil health indicators into fertilization models. Indeed, despite significant advances in fertilization technologies, current nitrogen recommendation models often do not take into account the impact of soil health on crop response to fertilization [11].

This is discussed in the article by J. Bontemps and co-authors. They present an innovative method that combines an extended extreme learning machine (A-ELM) and particle swarm optimization to efficiently select significant features and accurately predict nitrogen use efficiency and corn yield. This integrated approach allows for data reduction while maintaining high prediction accuracy, thereby contributing to more accurate decisions in agriculture. This study demonstrates that advanced machine learning and optimization technologies can be effectively applied to manage sustainable nitrogen use, increasing agricultural productivity and reducing environmental pollution.

7. Soil Hydraulic and Other Physical Properties

The ability of a soil to retain its optimum moisture content is the physical property that controls the movement and storage of water, as well as the uptake of nutrients and water by plants. Therefore, these properties are vital for predicting plant–water relationships, irrigation, drainage, nutrient leaching, runoff, watershed management, and overall soil health [12]. Three articles on soil hydraulic property assessment are included in this Special Issue.

In his article, Mzezewa J. presents the results of research on how the transformation of natural grasslands into arable land or avocado orchards affected soil hydraulic properties in various soil layers. The collected research data show that land use changes irreversibly alter soil structure and hydraulic properties, which can affect plant water consumption, aeration, soil health, and, in the long term, the sustainability of farming and the environment.

Moisture problems in dry soils are also discussed in an article by Selmy S.A.H. and co-authors. In their research, land suitability and water requirements of different crops are assessed in the arid desert zone of Western Egypt near the city of El-Dabaa. The soil capacities and suitability for the cultivation of twenty crops are analyzed, and their water requirements based on evapotranspiration are calculated. This work provides a comprehensive site analysis and planning tool—land capacity, suitability maps, and crop water requirements—for the effective use of arid regions. The results support sustainable farming strategies, providing a basis for investment decisions and agronomic advice in arid zones.

The fact that soil moisture is a very important link between precipitation, surface water, and groundwater is presented in the article by Zhang Y. and co-authors. Their results show that the 40 cm deep smash-ridging plowing option is optimal for sugarcane fields in the arid conditions of the Guangxi region: it ensures high average moisture, the most effective response to precipitation, intensive vertical moisture exchange, better water retention, and lower moisture fluctuations. This analysis provides a basis for agronomists to recommend the 40 cm plowing depth for the smash-ridging technique in sugarcane in the Guangxi region, especially in the absence of an irrigation system.

8. Soil Health and Quality Assessment

In assessing soil quality, the focus is on the impact of human management and the internal properties of the soil. Unlike air and water, soil often responds slowly to changes in land use and management, making it difficult to detect changes in soil quality before irreversible damage occurs. Therefore, it is crucial to identify sensitive soil properties that can serve as indicators of soil quality [13,14].

On this topic, a review by R.A. El Behairy and co-authors analyses how soil quality can be assessed in a targeted and effective manner: definition, selection of indicators, assessment methods, and practical case studies. The importance of soil quality for sustainable agricultural development and food security is highlighted, and a comprehensive overview of modern methods for rapid and accurate assessment of soil quality is provided. The authors review traditional laboratory tests, advanced remote sensing technologies, sensor systems, and data analysis tools (e.g., GIS and artificial intelligence), concluding that the most accurate results are achieved by integrating several methods, combining physical, chemical and biological indicators. They also emphasize that automatic and remote technologies can significantly accelerate the assessment processes, while maintaining high reliability. Finally, the authors highlight the need to create standardized, accessible, and practically applicable systems that would allow for effective monitoring of soil quality for both scientific research and sustainable agriculture.

Finally, I. Krahl and co-authors propose an innovative method for assessing soil health using thermogravimetric analysis (TGA). TGA allows researchers to monitor how different organic components in the soil decompose with increasing temperature, which helps to assess the quality and stability of organic matter. Using this method, researchers can accurately and quickly determine qualitative differences in soil organic matter, which are often not observed by traditional assessment methods. This requires the inclusion of near-natural soils and possibly also the consideration of homogenized sample preparation concerning bound water.