It is well known that biopores are crucial for soil functioning. However, their dynamics is rarely studied and their origin with regards to the soil organisms involved is still hard to determine. In this study we investigated the diversity of biopores and their regeneration rates in situ in various pedoclimatic conditions. Our approach involved field incubation of repacked soil cores with lateral openings across nine study sites in five countries (France, Vietnam, India, Laos and Thailand). After 12 months, biopores were characterized by X-ray computed tomography and grouped according to their diameter, length and sphericity index using principal component analysis followed by K-means clustering. The regeneration dynamics of biopores was assessed by comparing those created after one year of incubation to the biopores determined in soil cores taken from the surrounding soils (assuming the latter are in a steady-state). Additionally, we examined the relationships between newly formed biopores and soil macrofauna taxa. Our results evidenced significant variability in biopore diameter (0.90 to 15.84 mm), length (1 to 1600 mm) and sphericity index (0.03 to 0.93). We propose 10 biopore groups allowing to distinguish most of the study sites. Complete regeneration of biopores after 12 months was achieved in seven out of nine sites. Three groups of biopores showed a positive relation with earthworm abundance (r values ranged from 0.69 to 0.90), whereas the other groups of biopores showed no association with any macrofauna taxa. We conclude that biopore formation can be assessed under field conditions with repacked soil cores, regardless the pedoclimatic conditions. However, the involvement of macrofauna other than earthworms in biopore formation still remains to be unraveled. To capture their contribution to biopore formation, improvements of the repacked soil core approach and complementary laboratory experiments were suggested.

Soil physical structure, a key indicator of soil health and biomass production potential, can be altered by agricultural practices. In South Africa, the intensive and long-term sugarcane (Saccharum officinarum L.) monoculture is known to degrade soil characteristics. The objective of this study was to evaluate the effect of crop residue management practices (mulching, burning with residues scattered or removed) and mineral fertilization (with or without) on soil physical structure and to investigate possible link with soil microbial communities. To this aim, we analyzed soil aggregation and shrinkage curves (SSCs) in a long-term sugarcane trial established in 1939. The SSC provides descriptive structural soil data by differentiating and characterizing two pore systems (plasma and structural pores). We also quantified soil microbial communities’ abundance by qPCR as well as exopolysaccharides (EPS). Residue management and fertilization practices were found to have significant effects both on physical and microbial properties. Partial redundancy analysis showed that residue management practices had a slightly higher effect (19% of total variance) on hydrostructural variables compared with fertilization (12%). Total soil shrinkage, specific volume, and swelling capacity of the plasma were higher in mulched and/or unfertilized plots, indicating that soil was less compact, and shrinkage was more intense, including at the plasma level. The stronger structural dynamics and aggregate stability of the soil were explained by the behavior of the primary aggregates (peds), which were more porous and reactive during the drying process. In addition, swelling capacity of the plasma and the mean weight diameter of aggregates were both correlated to the amount of microbial EPS and the fungal abundance. This study highlights the importance of mulching and limited fertilization to maintain soil structure over the long term through the action of microbial communities.

The hydrological cycle is strongly affected by climate changes causing extreme weather events with long drought periods and heavy rainfall events. To predict the hydrological functioning of Tunisian catchments, modelling is an essential tool to estimate the consequences on water resources and to test the sustainability of the different land uses. Soil physical properties describing water flow are essential to feed the models and must therefore be determined all over the watershed. A simple but robust ring infiltration method combined with particle size distribution (PSD) analysis (BEST method) was used to evaluate and derive the retention properties and the hydraulic conductivities. Physically based and statistical pedotransfer functions based on PSD were compared to test their potential use for different types of Tunisian soils. The functional sensitivity of these parameters was assessed by employing the Hydrus-1D software (PC Progress, Prague, Czech Republic) for water balance computations. This evaluation process involved testing the responsiveness and accuracy of the parameters in simulating various water balance components within the model. The evaluation of soil hydraulic parameters across the three used models highlighted significant variations, demonstrating distinct characteristics in each model. While notable differences were evident overall, intriguing similarities emerged, particularly regarding saturated hydraulic conductivity between BEST and Rosetta, and the shape parameter (n) between Arya–Paris and Rosetta. These parallels indicate shared hydraulic properties among the models, underscoring areas of agreement amid their diverse results. Significant differences were shown for scale parameter α for the various methods employed. Marginal differences in evaporation and drainage were observed between the BEST and Arya–Paris methods, with Rosetta distinctly highlighting a disparity between physically based models and statistical models.

Soil degradation is a short or long ongoing process that limits ecosystem services. Intensive land use, water scarcity, land disturbance, and global climate change have reduced the quality of soils worldwide. This degradation directly threatens most of the land in the Middle East and North Africa, while the remaining areas are at high risk of further desertification. Rehabilitation and control of these damaged environments are essential to avoid negative effects on human well-being (e.g., poverty, food insecurity, wars, etc.). Here we review constructed soils involving the use of waste materials as a solution to soil degradation and present approaches to address erosion, organic matter oxidation, water scarcity and salinization. Our analysis showed a high potential for using constructed soil as a complimentary reclamation solution in addition to traditional ones. Constructed soils could have the ability to overcome the limitations of existing solutions to tackle land degradation while contributing to the solution of waste management problems. These soils facilitate the provision of multiple ecosystem services and have the potential to address particularly challenging land degradation problems in semi and dry climates.

Spring mounds are specific geomorphological landforms in arid or semi-arid environments associated with playas and artesian springs. Spring mounds are found worldwide, especially in the great Artesian Basin of Australia and in North American and Egyptian deserts. They result from an exceptional succession of climatic, geomorphological and hydrogeological conditions, with processes that follow each other in a specific order. In Tunisia, in the arid zone, ca. 126 spring mounds have been identified in Nefzaoua province alone, especially in the oasis east of Chott el Jerid. They have a conical shape that ranges from 200 to more than 2000 m in diameter and 3-30 m tall, and their centre is hollowed out by an artesian spring of fresh water. Palm groves (Phoenix dactylifera) spread out at the foot of each mound. The springs have dried up because of the proliferation of borehole wells. Because of the low electric conductivity (EC) of the sediments (<1 mS cm-1) at their base, spring mounds have been excavated and used as a soil amendment to expand new palm plantations. This excavation allows for analysis of their internal structure, which has never been observed well. In the present study, fine analysis of sediment layers in four sections of two representative mounds showed that vegetation had trapped sediment at their base. Fine strata of variable texture alternating with variable calcium carbonate, gypsum or organic carbon contents suggest a clear limnic origin. Many redoximorphic features, sometimes associated with the presence of old roots, suggest variation in the water level in the centre of the mound. The mounds are capped by a thick layer of indurated gypsum, which helps them resist hydric and aeolian erosion. The origin of the sediment components is discussed.

Cambodia plans to expand its rice sector and become a prominent rice exporter. A key concern is that soil fertility is a crucial factor affecting rice production, and nutrient leaching into the environment can lead to reduced nutrient uptake and lower rice yield. Carbonized waste biochar has gained recognition not only as a potential soil fertility enhancer but also as a significant nutrient leaching reducer. It is currently being introduced in many regions. The study was to evaluate how a combination of chemical fertilizers and rice husk biochar affects nutrient leaching into the topsoil layer and plow sole of soil columns during direct seeding with continuous flooding, and to assess their combined effects on rice growth and yield. In the leachate from these two soil layers, except for ortho-phosphate (PO 4 3− ), the combination of CHEM + BIO2 or + BIO4 treatment (chemical fertilizers + biochar at a rate of 2t ha −1 or + biochar at a rate of 4t ha −1 ) significantly decreased ammonium (NH 4 + ) and nitrate (NO 3 − ) levels more than CHEM alone, particularly in the plow sole, suggesting that their combination and biochar sorption capacity are beneficial for nitrogen use by plants. CHEM + BIO2 had varying effects, whereas CHEM + BIO4 led to a significant increase in rice yield, plant biomass, tiller number, panicle length, grains per panicle, and grain weight per panicle. These findings suggest that incorporating biochar amendments in rice production can reduce N leaching. However, there is no evidence to support its effectiveness in reducing P leaching. Therefore, further studies are needed to determine the usefulness of this approach.

Abstract Context Farmland on steep slopes is increasingly abandoned because it is unsuitable for most forms of modern agriculture. Succession back to forest is often slow or inexistent due to over-exploitation. Observations and measurements in Dong Cao catchment 47.9 ha Vietnam, started under farming and continued after abandonment: 20 years of uninterrupted monitoring of soil, water, land use and vegetation were integrated in this study.Objective Our aim is to identify the specific combination of soil features and agricultural practices that are responsible for fast, slow or blocked succession. We differentiate between the recovery of forest structure, relatively easy, and recovery of the original species composition, more difficult.Methods Multivariate analysis of vegetation data produced plant communities in a gradient of complexity. Using classic statistics, we sought relationships between environmental variables, land use and vegetation.Results Forest recovery failed the first 10 years, then part of the catchment developed forest. Land use explained best the distribution of plant communities over the catchment, slope and soil features were less related. Cassava cropping seriously slowed down the succession to closed forest. During abandonment soil carbon stocks (0–15 cm depth) increased with about 3% per year.Conclusion Starting from weedy thickets (2002) we distinguished two successional pathways: a positive pathway towards increased resemblance with the original Lowland forest via broken forest to closed deciduous to closed evergreen forest; a negative pathway away from the original forest species composition to degraded shrub land and low grass. Livestock was related to the negative pathway.

In southern Tunisia, in an arid environment subjected to climate change, the olive-production sector is important for the local Economy. With low local biomass production a multi sourced compost composed of olive waste byproducts and seaweed was tested on an Arenic Calcisol. The application at the subsurface of 180 kg (0.5 m3) of compost per tree in a rainfed olive tree (Olea europaea L.) grove with declining productivity showed a significant increase in total C, N, K, P, and respiration rate in amended horizons. Surprisingly the soil volumic water content (Vw%) at the subsurface (0-20 cm) below amended (7.5% +/- 2.3) was not significantly different below non amended trees (6.9% +/- 3.3). It increased slightly under non-amended trees, from 6.6% (+/- 4.3) at a depth of 5 cm-8.1% (+/- 1.5) at 65 cm depth, while below the amended olive trees the Vw% increased from 6.7% (+/- 3.4) in the composted horizon at 5 cm depth to 13.5% (+/- 1.1) at 70 cm depth. The main positive effect of composting on soils was decreasing the water loss due to capillary rise, since the compost developed clear hydrophobic properties. Two years after applying the compost, olive tree branches were 15% longer and olives were 40% heavier on amended trees.

In Cambodia, termite mounds are commonly used by farmers as amendments to increase the fertility of their paddy fields. However, despite their utilization, their chemical and physical properties have not been described yet. Therefore, the aim of this study was to analyze the chemical and physical properties of two termite constructions commonly found in paddy fields: (a) termitaria built and occupied by the fungus-growing termite Macrotermes gilvus and (b) lenticular mounds that are initially built by termites but host a large diversity of other invertebrates and plants. This study shows that these biogenic structures have very specific properties. Termitaria were characterized by higher clay, phosphorus and electrical conductivity than the surrounding soil. However, their effect on carbon dynamics was limited to a modification of the interactions between soil organic matter and minerals and to the presence of carbonates. At the same time, lenticular mounds appeared as patches of nutrients in paddy fields because they were always enriched in carbon, nitrogen, and phosphorus in comparison with the surrounding cultivated soil. Lenticular mounds were also enriched in clay, although this effect was only measured when the sand content in the surrounding environment was >60%. Together with these changes, lenticular mounds were characterized by a lower bulk density, higher saturated hydraulic conductivity (Ksat), and higher water holding capacity. In conclusion, this study shows that termite constructions can be considered fertility and biogeochemical hotspots in paddy fields, thus explaining their use by farmers for improving the fertility of their lands.

In the high altitude (>3000 m asl) grasslands of northern Ecuador, the P ' aramo ecosystem, soils generally formed on recent volcanic ashes being <10,000 years old in the northern and central part of the cordilleras. With time these soils evolved in to non-allophanic Andisols with hydric properties such as evidenced in profiles from the Cajas massif located in the western central Cordillera. However soils at the Fierro Urcu massif and at the On similar to a plateau at the eastern Cordillera formed on a non pyroclastic indurated parent material. Compared to non-allophanic Andisols from the Cajas massif, they present similar morphological properties with a dark 50 cm thick carbon-rich (80-120 g kg-1) topsoil with a very low bulk density (<0.65 g cm-3) and high water retention. These top soils appear to have originated from fall-out, derived from close and still active volcanoes of Sangay and/or Tungurahua, both located in a distance of 200-250 km NNE of the On similar to a Massif, respectively. Geochemical determinations of trace and rare earth elements, however, confirm the lack of volcanic ash contribution in the Saraguro and On similar to a samples based on Eu/Eu* and Ce/Ce* anomalies relative to the lack of such anomalies in the Cajas samples. The On similar to a and Saraguro soils appear to be the result of a long-lasting double pedogenic process. The basement of the Saraguro soil is a Ferralsol with gibbsite and kaolinite and the On similar to a soil is a 5 m thick kaolinitic Ferralsol. The upper part of these profiles are the result of a major climatic change with increasing colder conditions, generating an increase in organic matter content and a very acidic environment leading to the instability of kaolinite and gibbsite, thereby liberating large amounts of free aluminium and iron oxides. The evolution of these very highly evolved Ferralsols into soils with Andic properties is proposed to be the result of rapid tectonic uplift calculated at a rate exceeding 0.6 mm/year in the region leading to a general decrease in temperature limiting carbon mineralization and favouring the formation of organo-metallic complexes. The soils studied here reveal compelling new evidence and information about the uplift of a part of the Ecuadorean Andes.

Termites are key soil bioturbators in tropical ecosystems. Apart from mound nests constructed by some advanced lineages, most of the species use their faeces, oral secretions, debris, or soil aggregates to protect themselves from predators and desiccation when they go out to forage. Although this soil 'sheeting' is considered to play a key role in soil functioning, the properties of this termite-made material has been poorly studied. The few available data showed that sheeting properties are highly variable with positive, neutral or negative impacts on soil C and clay content, and consequently on soil aggregate stability. Therefore, the objective of this study was to determine the factors controlling the physical (particle size fractions and structural stability) and chemical (pH, electrical conductivity and carbon content) properties of soil sheeting produced by termite species encompassing all feeding and building categories using a dataset representative of an important diversity of biotopes coming from 21 countries from all continents colonized by termites. We showed that sheeting properties were explained by the properties of their environment, and especially by those of the bulk soil (linear relationships), followed in a lesser extent by the mean annual precipitation and biotope. Classic hypotheses related to termite feeding and building strategies were not hold by our analysis. However, the distinction of termites into fungus-growing and non-fungus growing species was useful when differentiating the impact of termites on soil electrical conductivity, C content, and structural stability. The large variability observed suggests the need to redefine termite functional groups based on their impacts on soil properties using a trait-based approach from morphological, anatomical and/or physiological traits.

The oases in the arid the Nefzaoua region in central-western Tunisia are associated with spring mounds. Spring mounds result from an exceptional succession of geomorphological, hydrogeological and climatic conditions and processes that follow each other in a specific order. They look like small volcanoes that range from 200 m to more than 2000 m in diameter and 3-30 m in height, which centres were once occupied by a pond fed by an artesian spring. They are at the origin of each oasis's irrigation system, which radiates from the mound's foot. Due to intense irrigation of intensive date palm plantations (Phoenix dactylifera) in recent decades, all artesian springs dried out. We established a complete inventory and typology (i.e. location, dimension, and types of degradation) of all spring mounds in the Nefzaoua region. Overall, in an area of 3000 km2, 126 spring mounds of 7 types were identified, of which 112 (89%) were degraded. Due to the low salt content in spring mound sediments, they are excavated and used as a soil amendment to expand new palm plantations. Only 14 mounds (11%) are presently preserved. Their qualification as a geomorphosite could preserve them from complete destruction.

Soil fertilization is one of the top rice crop production issues. Nutrient leaching in rice crop production, leading to lower plant uptake and low yield, poses a challenge for Cambodian farmers and is becoming a key concern for the environment. Carbonized organic waste, called biochar, is known as a potentially valuable input to enhance soil properties. It has been introduced in many regions. A soil column-based experiment was conducted to evaluate the effect of biochar on the leaching of N and P and rice growth in link with soil structure. Two types of columns were built, using disturbed and undisturbed soil. Four rates of nutrient input including chemical fertilizer, chemical fertilizer + 2 t/ha of biochar, chemical fertilizer + 4 t/ha of biochar, and control were applied to the plantation of rice cultivar (locally named Sen-Pidor) in both conditions. Leachate (NH4-N, NO3-N, and PO43−) and rice growth were collected at 7-day intervals, while the grain yield and biomass of plant were collected at the mature stage. Our primary results showed that the leachate and rice growth were not significantly different between both conditions. However, the leaching of NH4-N and NO3-N in the column with chemical fertilizer + 4 t/ha of biochar was lower than the column with chemical fertilizer, while PO43− leaching was the same measured from both rates. Remarkably, the plant height was the highest under the disturbed condition with chemical fertilizer + 2 t/ha of biochar, whereas under the undisturbed condition it was the highest with chemical fertilizer + 4 t/ha. In addition, biochar amendment at the rate of 4 t/ha enhanced rice yield by 32.17% in comparison with the column using chemical fertilizer, and by 52.77% in comparison with the control. Additionally, biochar amendment at the rate of 4 t/ha had a great impact on the biomass of plants compared to the column without biochar contact. Our results indicate that biochar amendment has the potential to minimize N leaching, but not P leaching, while enhancing rice yield and biomass of plant.

The graphical abstract below summarizes the sequence of human interventions observed in the study area when tropical forest is cleared for cultivation. The key practices responsible for destroying forest residuals and reducing plant diversity are represented. With each downward step, the cumulative disturbance is such that regeneration towards the original forest becomes more and more difficult. Also shown is the resilience of the environment to human damage, for instance long-cycle shifting cultivation with a single burning allows the preservation of most of the primary forest species. [Graphical abstract here]The study area, Dong Cao catchment (49.7 ha), northern Vietnam, is a scientific observatory for vegetation, soil, water and land use studies. The study was diachronic, from 2000 to 2019. Deforestation in 1975 was followed by cultivation of a variety of crops leading to a treeless landscape of herbs and thickets. Forest recovery failed the first 10 years. Only after 10-15 years the vegetation started to differentiate as part of the catchment developed forest while part did not.The ordination of a two-way species by sample matrix (Braun-Blanquet method) produced six plant communities in a complexity gradient. Soil, land form and agricultural data, analysed independently, confirmed the floristic analysis. Long-term cultivation of cassava seriously slowed down the succession to closed forest. Livestock was linked to the development of open and drier vegetation. During abandonment soil carbon stocks increased greatly with about 3% per year, at an average rate of 1.09 tC ha -1 year -1 in the top 15 cm. Soil carbon varied significantly with plant communities.

Abstract The utilization of termite mounds for the improvement of soil fertility is a worldwide practice and usually explained by the specific properties of this biogenic material. In Cambodia, farmers also use termite mound soils as amendments with the aim to improve the fertility of paddy fields. The first objective of this study was, therefore, to describe the physical and chemical properties of this material and, consequently, to determine its potential for improving soil fertility. A second objective was to consider farmer’s perception and to quantify the diversity of services provided by termite mounds. We confirmed the specific soil properties of termite mounds but showed that their positive influence on soil chemical fertility and water retention are only significant in very sandy soil (>80% sand) while they remain limited in less sandy soil (~40 and 60% of sand). However, termite mounds are considered useful by farmers independently of the soil condition, mostly because this soil material is considered to positively increase soil fertility but also because they host a specific biodiversity which can be used for medicinal purposes or because consumed, then increasing population livelihood. Our work shows the discrepancy between the perception of farmers and the real impact of termite mounds on soil fertility as well as the diversity of services delivered by biodiversity in paddy fields.

Sugarcane (Saccharum officinarum L.), an intensive, long-term, monoculture, economical crop in South Africa, is known to degrade soil characteristics. Soil structure, a key indicator of soil health and biomass production potential, is manageable by agricultural practices. This study aims to evaluate the effect of crop residue management practices (mulching, burning with residues scattered or removed) and mineral fertilization (with or without) on soil structure by analyzing soil shrinkage curves (SSCs) and other soil physical and chemical properties in a long-term sugarcane trial established in 1939. The SSC provides descriptive structural soil data by differentiating and characterizing two pore systems (plasma and structural pores). By analyzing the SSC of 24 plots (four replicates each treatment), residue management and fertilization practices were found to have statistically and physically significant effects on hydrostructural variables. Partial redundancy analysis showed that residue management practices had a slightly higher effect (19% of total variance) on hydrostructural variables compared with fertilization (12%). The main hydrostructural variables representing the management effect were total soil shrinkage, specific volume, and swelling capacity of the plasma, which were higher in mulched and/or unfertilized plots, indicating that soil was less compact, and shrinkage was more intense, including at the plasma level. The stronger structural dynamics and aggregate stability of the soil were explained by the behavior of the primary aggregates (peds), which were more porous and reactive during the drying process. This study highlights the importance of mulching and limited fertilization to maintain soil structure in the long term while still ensuring yield production.

Les paysages des tertres oasiens du Nefzaoua sont disposés à l’est du Chott el Jerid en Tunisie aride. Les palmeraies s’étalent au pied des tertres, monticules de forme conique creusés au centre par une source artésienne d’eau douce. Ils ont été aménagés et ont été à la base du développement des oasis. Aujourd’hui, les sources sont taries par la prolifération des forages et les tertres, fruits d’une conjonction de conditions géomorphologiques, hydrogéologiques et climatiques sont à l’abandon, voire détruits pour étendre les plantations de palmiers dattiers. Ces édifices peuvent être considérés à la fois comme un géopatrimoine et un patrimoine culturel en péril et certains mériteraient d’être préservés.

This dataset has been collected thanks to the long-term partnership with National Park, Wildlife and Plant Conservation Department (DNP), Thailande, which granted the permission for field access, and to the financial, scientific, technical, and/or logistical support of the M-TROPICS CZO. The soil samples were taken under different vegetation cover at the long term observatory catchment Huay Ma Nai in northern Thailand in 2017. This dataset holds some chemical and physical soils properties. Dry combustion analysis (CHN) was used to assess Carbon (C) and Nitrogen (N) concentrations. Fourier-transform infrared (FTIR) spectroscopy was used to measure the signature of the samples in the medium infrared region. Soil analyses has been carried out at the Pole d’experimentation et d’analyse des sols et sediments tropicaux (ALYSES).

Wind erosion is a major threat to the sustainability of arid and semi-arid ecosystems. In these environments, biological soil crusts positively impact soil resistance to erosion. Less is known, however, on the impact of soil bioturbation by animals. In Southern Tunisia, bioturbation is mainly carried out by termites, ants and rodents which deposit mineral and organic components on the soil surface in the form of soil sheetings for termites or as soil heaps for ants and rodents. We here question the properties of these soils and measure their resistance to wind erosion. We showed that soil sheetings are made of sand grains linked together by bridges of organic matter, clay particles and other small size minerals such as carbonates and gypsum. The stability of these aggregates is comparable to that of biological soil crusts, despite their very different organizations. Conversely, the soil excavated by ants and rodents mainly consists in individual sand grains, which are impoverished in organic carbon and prone to wind erosion. In conclusion, this study highlights the importance of termites, as key soil bioturbator, on the dynamics of soil aggregates in Southern Tunisia. It also shows that they have an opposite effect than that of ants and rodents on the resistance of soil to erosion.