Annual estimates of CO.sub.2 and dissolved carbon concentrations in the soil profile provide valuable insight into the dynamics of organic matter in soil and the effect of changes to vegetation ...cover. The aim of this study was to observe the spatial influence of litter decomposition in the first few centimeters of the soil for CO.sub.2 fluxes and to describe the processing of soil organic matter throughout the soil profile by comparing three small tropical watersheds. Data were collected biweekly for six months, from December 2015 to May 2016. CO.sub.2 was measured using an infrared gas analyzer in fixed chambers and the dissolved carbon of soil solution was analyzed in a TOC analyzer. No differences were found in the total soil CO.sub.2 fluxes (control flux treatments) between the three study areas. In both cacao agroforestry systems (managed and unmanaged), total CO.sub.2 fluxes were influenced by the decomposition of litter. CO.sub.2 emissions in the soil profile of the cacao agroforestry systems were highly variable, compared to the preserved forest, and highly dependent on the soil characteristics attributed to the type of vegetation cover. Although a definite pattern between the temperature and soil moisture was not identified, these parameters showed a strong relationship in controlling the release of CO.sub.2 between treatments. The organic and inorganic dissolved carbon patterns in the soil solution of the three areas revealed different responses of soil organic matter processing related to soil characteristics and vegetation. The results confirm the hypothesis that the top of soils (total CO.sub.2 fluxes) of both cacao agroforestry systems (managed and unmanaged) emits fluxes of CO.sub.2, which do not differ statistically from the preserved forest. However, depending on the soil characteristics, the cacao agroforestry system can result in an accumulation of CO.sub.2 and dissolved inorganic carbon in the soil profile that is prone to being transported by hydrological routes to groundwater and stream water.
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•Hydrochars are rich in carbon, nutrients, and reactive functional groups.•Hydrochar characteristics are determined by HTC conditions and feedstock types.•Hydrochars improve the ...physical, chemical, and biological property of degraded soil.•Hydrochars containing abundant nutrients could be used as slow release fertilizers.•Hydrochar remediates water and soil pollutions due to its high adsorption capacity.
With the rapid global population growth and industrial development, the promotion of sustainable agricultural production and environmental conservation has attracted great public and research interests. Application of carbonaceous materials (e.g., activated carbon, biochar, and hydrochar) for soil improvement and environmental remediation is highly recommended because of their economic viability and applicability. Hydrochars, carbonaceous solid materials with unique physicochemical properties and produced by hydrothermal carbonization (HTC) of biomass, have received wide attention due to their increasing applications as soil amendments, slow-release fertilizers, adsorbents, and energy sources. This review highlights the production of hydrochars from dry and wet feedstocks and summarizes the physicochemical properties including surface structure, porosity, nutrient content, and stability. Applications of hydrochars for soil improvement and environmental remediation are systematically analyzed and reviewed on the aspects of improving soil physicochemical and biological properties, affecting greenhouse gas emission, and remediating heavy metals and organic pollutants in water and soil environments. Finally, the knowledge gaps in the production, characterization, and application of hydrochars are addressed and the future research directions toward the development of hydrochar technology are proposed.
Soil, a non-renewable resource, sustains life on Earth by supporting around 95% of global food production and providing ecosystem services such as biomass production, filtration of contaminants and ...transfer of mass and energy between spheres. Unsustainable management practices and climate change are threatening the natural capital of soils, particularly in the Mediterranean region, where increasing population, rapid land-use changes, associated socio-economic activities and climate change are imposing high pressures on the region's shallow soils. Despite evidence of high soil susceptibility to degradation and desertification, the true extent of soil degradation in the region is unknown. This paper reviews and summarises the scientific literature and relevant official reports, with the aim to advance this knowledge by synthesizing, mapping, and identifying gaps regarding the status, causes, and consequences of soil degradation processes in the European Mediterranean region. This is needed as scientific underpinning of efforts to counteract soil degradation in the region. Three main degradation categories are then considered: physical (soil sealing, compaction, erosion), chemical (soil organic matter, contamination, salinisation), and biological. We find some degradation processes to be relatively well-documented (e.g. soil erosion), while others, such as loss of biodiversity, remain poorly addressed, with limited data availability. We suggest establishment of a continuous, harmonised soil monitoring system at national and regional scale in the Mediterranean region to provide comparable datasets and chart the spatial extent and temporal changes in soil degradation, and corresponding economic implications. This is critical to support decision-making and fulfilment of related sustainable development goals.
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•The Mediterranean is the most susceptible region in Europe to soil degradation and desertification.•Multiple forms of physical, chemical and biological degradation affect the Mediterranean soils.•Some Mediterranean soils are reaching critical limits for its ability to provide ecosystem services.•A continuous and harmonised soil assessment is required to evaluate trends in soil degradation.
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•Long-term drought affects the soil ecosystem and can initiate desertification.•SAH improves the soil-pore structure and water retention characteristics.•Plant growth and survival ...time increases with increasing SAH concentration.•Soil texture, salinity and application rate influence the performance of SAH.•SAH amendment can protect plant-soil ecosystem from drought stress.
Drought is one of the worst natural disasters that affect the economic, social, and environmental status of any country. The long-term drought affects the soil ecosystem and can initiate desertification and deterioration of soil health. This leads to severe water distress, which is further aggravated by improper water management, poor irrigation practice, degradation of soil quality, and low water holding capacity of soil. Effective land management is the most feasible solution during drought. It is established that the utilization of superabsorbent hydrogel (SAH) as a soil amendment can improve soil structure, water-holding capacity, and plant available water content because of its hydrophilic three-dimensional network. However, there are contrasting observations in the existing literature related to the absorption capacity of SAH under different conditions, which may have an impact on drought management. This study purports to critically review the findings reported in the literature to reveal the influence of SAH addition for solving water stress conditions. The influence of SAH application on the physical properties of soil, such as water retention capacity, plant available water content, hydraulic conductivity, and infiltration, was investigated. This study brings out the discrepancies associated with the influence of SAH application in different textured soil, presence of salinity, and biodegradation of synthetic SAH. It was found that the application of SAH can reduce the evaporation loss and deep percolation, thereby increasing the plant growth and survival time in drought despite some reduction in swelling capacity under saline condition. The need for further studies for the development of biodegradable SAH and its performance evaluation under various environmental conditions has been summarized.
•Biochar studies were assessed relating to experiment and crop types, biochar and soil condition.•Despite most studies in developed countries soils are less impaired than in developing ...countries.•Wood and municipal wastes were major biochar sources compared to crop residues and manures.•Averaged across many scientific studies, biochar increases crop yields ∼20% with about 10tha−1.•Strong collaboration is required globally to advance the research and adoption of biochar.
Multiple nutrient deficiencies related to severe soil fertility depletion have emerged as the major constraint to the sustainability of agriculture on a global scale. Use of biochar and biochar-compost mixtures from different alternative organic sources have been proposed as an option for improving soil fertility, restoring degraded land, and mitigating the emissions of greenhouse gasses associated with agriculture. We review the findings of 634 publications in the last decade on biochar and biochar-compost mixtures as soil amendments in order to identify the potential gaps in our understanding of the role of these amendments in agriculture. We found that: i) the majority of published studies have been carried out in developed countries where soils are less impaired in terms of food production capacity than in many developing countries; ii) studies on biochar produced in small kilns are more common than biochars produced at commercial scale in developed countries, whereas biochars produced using traditional techniques are more commonly used than biochars produced in modern pyrolysis units in developing countries; iii) laboratory and greenhouse studies are more common than field studies; and iv) wood and municipal wastes were the major feedstock for the preparation of biochar compared to crop residues and manures. Although, biochar-compost application proved to be more generally effective in improving soil properties and crop yields (field crops and horticulture crops) than biochar alone, along with desired soil properties, could be a feasible alternative to remediate the degraded soils and improve their productivity potential in the long-term. Overall, a lack of long-term, well-designed field studies on the efficacy of biochar and biochar-compost mixtures on different soil types and agro-climatic zones are limiting our current understanding of biochar's potential to enhance crop production and mitigate climate change. We further suggest that greater collaboration between researchers, biochar producers, and policy makers is required to advance the research and uptake of this important technology at a global scale.
Biochar can sequestrate carbon (C) in soils and affect native soil organic carbon (SOC) mineralization via priming effects. However, the roles of soil aggregation and microbial regulation in priming ...effects of biochars on SOC in coastal wetland soils are poorly understood. Thus, a coastal wetland soil (δ13C −22‰) was separated into macro-micro aggregates (53–2000μm, MA) and silt-clay fractions (<53μm, SF) to investigate the priming effect using two 13C enriched biochars produced from corn straw (δ13C −11.58‰) at 350 and 550°C. The two biochars induced negative priming effect on the native SOC mineralization in the both soil aggregate size fractions, attributed to the enhanced stability of the soil aggregates resulting from the intimate physico-chemical associations between the soil minerals and biochar particles. Additionally, biochar amendments increased soil microbial biomass C and resulted in a lower metabolic quotient, suggesting that microbes in biochar amended aggregates could likely incorporate biomass C rather than mineralize it. Moreover, the biochar amendments induced obvious shifts of the bacterial community towards low C turnover bacteria taxa (e.g., Actinobacteria and Deltaproteobacteria) and the bacteria taxa responsible for stabilizing soil aggregates (e.g., Actinobacteria and Acidobacteria), which also accounted for the negative priming effect. Overall, these results suggested that biochar had considerable merit for stabilizing SOC in the coastal soil and thus has potential to restore and/or enhance “blue C” sink in the degraded coastal wetland ecosystem.
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•Biochar had negative priming effect in macro-micro aggregates and silt-clay fractions.•Enhanced stability of soil aggregate fractions was due to associations of minerals and biochars.•Biochar increased microbial biomass C and C use efficiency.•Biochar shifted bacterial community towards to low C turnover bacteria taxa.•Biochar promisingly enhanced “blue C” sink in the degraded coastal wetland.
Soil erosion is a major global soil degradation threat to land, freshwater, and oceans. Wind and water are the major drivers, with water erosion over land being the focus of this work; excluding ...gullying and river bank erosion. Improving knowledge of the probable future rates of soil erosion, accelerated by human activity, is important both for policy makers engaged in land use decision-making and for earth-system modelers seeking to reduce uncertainty on global predictions. Here we predict future rates of erosion by modeling change in potential global soil erosion by water using three alternative (2.6, 4.5, and 8.5) Shared Socioeconomic Pathway and Representative Concentration Pathway (SSP-RCP) scenarios. Global predictions rely on a high spatial resolution Revised Universal Soil Loss Equation (RUSLE)-based semiempirical modeling approach (GloSEM). The baseline model (2015) predicts global potential soil erosion rates of
43
−
7
+
9.2
Pg yr−1, with current conservation agriculture (CA) practices estimated to reduce this by ∼5%. Our future scenarios suggest that socioeconomic developments impacting land use will either decrease (SSP1-RCP2.6–10%) or increase (SSP2-RCP4.5 +2%, SSP5-RCP8.5 +10%) water erosion by 2070. Climate projections, for all global dynamics scenarios, indicate a trend, moving toward a more vigorous hydrological cycle, which could increase global water erosion (+30 to +66%). Accepting some degrees of uncertainty, our findings provide insights into how possible future socioeconomic development will affect soil erosion by water using a globally consistent approach. This preliminary evidence seeks to inform efforts such as those of the United Nations to assess global soil erosion and inform decision makers developing national strategies for soil conservation.
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