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Introduction: Plastic film mulching has been widely used to enhance soil hydrothermal conditions and increase crop yields in cool, semi-arid areas. However, its impact on soil microbial carbon metabolic activity and functional diversity during plant growth remains unclear despite their important roles in nutrient cycling and soil quality evaluation. Methods: This study used the Biolog EcoPlate technique to investigate the dynamics and driving factors of soil microbial carbon metabolic activity and functional diversity at different maize growth stages following plastic film mulching. Results and discussion: The results revealed that film mulching significantly increased microbial carbon metabolic activities [represented by average well color development (AWCD)] by 300% at the seedling stage and by 26.8% at maturity but decreased it by 47.4% at the flowering stage compared to the control (without mulching). A similar trend was observed for the microbial functional diversity index. Redundancy analysis identified soil moisture (SM), soil temperature (ST), dissolved organic carbon (DOC), microbial biomass carbon (MBC), and bacteria amounts as the primary factors influencing changes in soil microbial carbon source utilization. The mulch treatment significantly increased SM at all growth stages, while its warming effect disappeared at the flowering stage. Soil DOC, MBC, and bacterial populations were notably higher under mulching at the seedling and maturity stages but lower at the flowering stage. Pearson correlation analysis showed that changes in SM, ST, DOC, MBC, and bacterial populations positively correlated with the utilization of all carbon source classes, AWCD, and functional diversity indexes after film mulching. Furthermore, maize grain yield and water use efficiency increased by 142 and 129%, respectively, following film mulching. In conclusion, plastic film mulching enhanced soil microbial carbon metabolic activity and functional diversity at the seedling and maturity stages, improving crop yields in cool, semi-arid areas. Furthermore, the decrease in soil carbon metabolic capacity at flowering stage highlights that supplementing soil carbon sources should be considered after continuous film mulching to sustain or enhance farmland productivity and soil quality. [ABSTRACT FROM AUTHOR]

Fibrous and pioneer roots are essential in the uptake and transport of water and nutrients from the soil. Their dynamic may be influenced by the changing of soil physicochemical properties due to the addition of biochar, which, in turn, has been shown to improve plant growth and productivity in the short term. However, the long-term effects of biochar application on root dynamics are still widely unknown. In this study, we aimed to investigate the long-term effects of biochar application on grapevine fibrous and pioneer root dynamics and morphological traits in relation to soil characteristics. To this aim, grapevine plants amended in 2009 and 2010 respectively with one and two doses of biochar, were analyzed in their fibrous and pioneer root production and turnover rate, standing biomass, length, and specific root length, over two growing seasons. Our findings demonstrate that in the long term, biochar application significantly increased soil pH, nutrient availability, and water-holding capacity causing a decrease in the production of fibrous and pioneer roots which is reflected in a reduction of the root web characterized though by a higher turnover rate. Furthermore, we observed that these root morpho-dynamical changes were of higher magnitude in the upper soil layers (0-20 cm) and, at least in the long term, with no significant difference between the two doses. These results suggest that in the long term, biochar can be a powerful tool for improving soil quality, which in turn lowers carbon-cost investment toward the root production and maintenance of a reduced root web that might be directed into grapevine growth and productivity. Such effects shed some light on the root plastic and functional adaptation to modified soil conditions facilitated by the long-term application of biochar, which can be used for implementing adaptive agricultural practices to face the current climate change in a frame of sustainable agricultural policies. [ABSTRACT FROM AUTHOR]

IntroductionPlastic film mulching has been widely used to enhance soil hydrothermal conditions and increase crop yields in cool, semi-arid areas. However, its impact on soil microbial carbon metabolic activity and functional diversity during plant growth remains unclear despite their important roles in nutrient cycling and soil quality evaluation.MethodsThis study used the Biolog EcoPlate technique to investigate the dynamics and driving factors of soil microbial carbon metabolic activity and functional diversity at different maize growth stages following plastic film mulching.Results and discussionThe results revealed that film mulching significantly increased microbial carbon metabolic activities [represented by average well color development (AWCD)] by 300% at the seedling stage and by 26.8% at maturity but decreased it by 47.4% at the flowering stage compared to the control (without mulching). A similar trend was observed for the microbial functional diversity index. Redundancy analysis identified soil moisture (SM), soil temperature (ST), dissolved organic carbon (DOC), microbial biomass carbon (MBC), and bacteria amounts as the primary factors influencing changes in soil microbial carbon source utilization. The mulch treatment significantly increased SM at all growth stages, while its warming effect disappeared at the flowering stage. Soil DOC, MBC, and bacterial populations were notably higher under mulching at the seedling and maturity stages but lower at the flowering stage. Pearson correlation analysis showed that changes in SM, ST, DOC, MBC, and bacterial populations positively correlated with the utilization of all carbon source classes, AWCD, and functional diversity indexes after film mulching. Furthermore, maize grain yield and water use efficiency increased by 142 and 129%, respectively, following film mulching. In conclusion, plastic film mulching enhanced soil microbial carbon metabolic activity and functional diversity at the seedling and maturity stages, improving crop yields in cool, semi-arid areas. Furthermore, the decrease in soil carbon metabolic capacity at flowering stage highlights that supplementing soil carbon sources should be considered after continuous film mulching to sustain or enhance farmland productivity and soil quality.

Fibrous and pioneer roots are essential in the uptake and transport of water and nutrients from the soil. Their dynamic may be influenced by the changing of soil physicochemical properties due to the addition of biochar, which, in turn, has been shown to improve plant growth and productivity in the short term. However, the long-term effects of biochar application on root dynamics are still widely unknown. In this study, we aimed to investigate the long-term effects of biochar application on grapevine fibrous and pioneer root dynamics and morphological traits in relation to soil characteristics. To this aim, grapevine plants amended in 2009 and 2010 respectively with one and two doses of biochar, were analyzed in their fibrous and pioneer root production and turnover rate, standing biomass, length, and specific root length, over two growing seasons. Our findings demonstrate that in the long term, biochar application significantly increased soil pH, nutrient availability, and water-holding capacity causing a decrease in the production of fibrous and pioneer roots which is reflected in a reduction of the root web characterized though by a higher turnover rate. Furthermore, we observed that these root morpho-dynamical changes were of higher magnitude in the upper soil layers (0-20 cm) and, at least in the long term, with no significant difference between the two doses. These results suggest that in the long term, biochar can be a powerful tool for improving soil quality, which in turn lowers carbon-cost investment toward the root production and maintenance of a reduced root web that might be directed into grapevine growth and productivity. Such effects shed some light on the root plastic and functional adaptation to modified soil conditions facilitated by the long-term application of biochar, which can be used for implementing adaptive agricultural practices to face the current climate change in a frame of sustainable agricultural policies.

Gravel mulch is an agricultural water conservation practice that has been widely used in the semi-arid region of northwest China, but its effectiveness is now lessening due to soil degradation caused by long-term gravel mulching. In this study, we report on a 6-year-long gravel mulch experiment conducted in the northwestern Loess Plateau to evaluate the impact of gravel mulch on soil physicochemical properties and microbial communities, with the objective of clarifying the causes of long-term gravel mulching-induced land degradation. After 6 years mulching, we found that gravel mulched soil contained significantly higher concentrations of total carbon and total organic carbon than non-mulched soil (control). Long-term gravel mulching significantly changed the soil microbial diversity and abundance distribution of bacterial and fungal communities. Notably, the relative abundance of Acidobacteria was significantly higher under gravel mulching than the control (no mulching), being significantly greater in the AG treatment (small-sized gravel, 2-5 mm) than all other treatments. Conversely, the relative abundance of Actinobacteria was significantly lower under gravel mulching than the control, being the lowest in the BG treatment (large-sized gravel, 40-60 mm). At the same time, the relative abundance of Bacteroidetes was significantly lower in AG yet higher in BG vis-à-vis the other treatments. Of the various factors examined, on a 6-year scale, the capture of dust by gravel mulch and altered carbon and nitrogen components in soil play major contributing roles in the compositional change of soil microorganisms. These results suggest that modified soil material input from gravel mulching may be the key factor leading to soil degradation. More long-term experimental studies at different sites are now needed to elucidate the mechanisms responsible for soil degradation under gravel mulching. [ABSTRACT FROM AUTHOR]

Secondary tropical forests are increasingly important for their role in the global carbon (C) balance as they can rapidly accumulate aboveground biomass C during regrowth. Substantial amounts of plant-derived carbon are also incorporated into the soil through decomposition processes, but our understanding of soil C dynamics during forest regrowth is limited. Secondary succession is characterised by a shift in tree functional groups from light-demanding to shade-tolerant species over time, which can influence rates of C turnover via differences in litter quality and by modifying the decomposition environment. Changes in decomposition processes in turn affect the amount of organic C stored in the soil or released to the atmosphere as CO2. Consequently, understanding how tree functional composition influences C turnover during decomposition could help us predict soil C storage during tropical forest regrowth. We experimentally explored the relationship between tree functional groups and soil C dynamics (decomposition and respiration) by conducting a litter decomposition experiment across a successional gradient of naturally regenerating tropical forest. We created litter mixtures representing tree communities differing in their shade tolerance, as well as a functionally diverse litter mixture, and observed litter mass loss and soil respiration as measures of C turnover over a 6 month period. Litter from light-demanding species decomposed faster than litter from shade-tolerant species, which was reflected in the pattern of soil respiration. There were no clear patterns of increasing or decreasing rates of litter decay or soil respiration with increasing forest age, but there was an interaction between stand age and litter type which influenced both decomposition and soil respiration rates. Interestingly, soil respiration from the functionally diverse litter mixture was significantly higher in the younger than older forest stands, and the functionally diverse litter mixture decayed more rapidly than expected in one of the younger stands. Our findings highlight the potential importance of functionally diverse plant inputs, as well as the interaction between local environmental attributes and litter type, for soil C dynamics in tropical forests.

The advent of “natural climate solutions” and “climate smart agriculture” has increased interest in managing agricultural lands to sequester soil carbon and mitigate climate change. This has led to enormous opportunities for soil scientists and growers alike, as new soil carbon initiatives are created by public, private, and philanthropic entities. It has also led to confusion over what is possible or practical to achieve through agricultural management, as soil carbon formation and storage is complex, and its response to management is context-dependent. This can pose challenges to decision makers tasked with creating defensible, science-informed policies and programs for building and protecting soil carbon. Here we summarize the science concerning the potential for agricultural soils to serve as a natural climate solution, in order to frame a discussion of current approaches in United States (US) policy and practice. We examine existing strategies such as soil health initiatives and direct incentive payments, as well as emerging schemes such as carbon markets and crop insurance reform. We suggest future directions for each strategy, and make recommendations for synthesizing approaches into a cohesive US policy portfolio. Guiding principles for this discussion include the notions that (i) climate change adaptation must be prioritized alongside climate change mitigation; (ii) soil carbon sequestration must be paired with greenhouse gas emission reductions; (iii) structural issues and barriers to adoption must be addressed as part of all policies and programs; (iv) practice- and place-specific programs must be administered in lieu of one-size-fits-all prescriptions; and (v) soil carbon science is not yet sufficiently advanced for the accounting and contractual frameworks proposed in cap-and-trade or regulatory approaches.

IntroductionLucerne (Medicago sativa L.) is a crucial component in agricultural rotation systems due to its ability to enhance soil carbon (C) and nitrogen (N) contents. In China, conventional tillage (CT) is commonly used for lucerne termination, leading to soil structure degradation and C and N losses. While herbicide application has been suggested for lucerne termination in the United States and EU, its impact on lucerne growth suppression and soil C and N contents in China remains uncertain.MethodsIn this study, we examined the effects of herbicide type [glyphosate and 2,4-D (G + 2), glyphosate and dicamba (G + D), 2,4-D and dicamba (2 + D), with water (W) and CT as controls] and concentration (100, 200, 300%) on various lucerne and soil properties.Results and DiscussionOur findings revealed that G + 2 and 2 + D treatments significantly reduced the regreening rate, and the recommended herbicide concentration (100%) was sufficient for lucerne termination. CT and W treatments resulted in a higher soil pH compared to herbicide treatments. Moreover, herbicide treatments exhibited higher soil organic C (SOC) and total N (TN) levels than the CT treatment. The 2 + D treatment demonstrated a higher SOC content compared to the G + 2 treatment, while the 200 and 300% herbicide concentrations reduced SOC and TN levels. The G + 2 treatment had the highest soil ammonium nitrogen content (7.94 ± 1.45 mg kg−1), while the CT treatment showed the lowest (6.46 ± 1.54 mg kg−1). In conclusion, our study suggests that applying the recommended herbicide dosage (100%) effectively terminates lucerne grassland on the Loess Plateau of China without negatively impacting soil C and N storage. Finally, it is important to acknowledge that one-year trials at a single site have inherent limitations, and the findings should be considered cautiously when informing policy decisions.

Introduction: Crops influence both soil microbial communities and soil organic carbon (SOC) cycling through rhizosphere processes, yet their responses to nitrogen (N) fertilization have not been well investigated under continuous monoculture. Methods: In this study, rhizosphere soil microbial communities from a 5-year continuous mono-cropped peanut land were examined using Illumina HighSeq sequencing, with an N fertilization gradient that included 0 (N0), 60 (N60), 120 (N120) and 180 (N180) kg hm-2. Soil respirationrate (Rs) and its temperature sensitivity (Q10) were determined, with soil carbon-acquiring enzyme activities assayed. Results and discussion: The obtained results showed that with N fertilization, soil mineral N (Nmin) was highly increased and the soil C/N ratio was decreased; yields were unchanged, but root biomass was stimulated only at N120. The activities of b-1,4-glucosidase and polyphenol oxidase were reduced across application rates, but that of b-1,4-cellobiohydrolase was increased only at N120. Bacterial alpha diversity was unchanged, but fungal richness and diversity were increased at N60 and N120. For bacterial groups, the relative abundance of Acidobacteria was reduced, while those of Alphaproteobacteria and Gammaproteobacteria were increased at N60 and N120. For fungalmembers, the pathogenic Sordariomycetes was inhibited, but the saprotrophic Agaricomycetes was promoted, regardless of N fertilization rates. RDA identified different factors driving the variations in bacterial (root biomass) and fungal (Nmin) community composition. N fertilization increased Rs slightly at N60 and significantly at N120, mainly through the promotion of cellulose-related microbes, and decreased Rs slightly at N180, likely due to carbon limitation. N fertilization reduced microbial biomass carbon (MBC) at N60, N120 and N180, decreased SOC at N120 and N180, and suppressed dissolved organic carbon (DOC) at N180. In addition, the unchanged Q10 may be a joint result of several mechanisms that counteracted each other. These results are of critical importance for assessing the sustainability of continuously monocultured ecosystems, especially when confronting global climate change. [ABSTRACT FROM AUTHOR]

Introduction: The contrasting soil management in flooded-transplanted rice (Oryza sativa) and dry-tilled wheat (Triticum aestivum) poses a challenge for improving low nitrogen use efficiency (NUE) of the rice-wheat system. Integration of organics in nutrient management can bring in changes favoring efficient N uptake via changes in growing conditions and soil responses. Materials and methods: This study reported the results of a 15-year-long experiment on integrated nutrient management (INM) systems for rice-wheat cropping. The INM included substituting ~50% of chemical fertilizers via (i) including a legume crop (Vigna radiata) in the sequence and its biomass incorporation (LE), (ii) green manuring with Sesbania aculeata (GM), (iii) farmyard manure application (FYM), (iv) 1/3 wheat stubble in situ retention (WS), and (v) 1/3 rice stubble in situ retention. Results and Discussion: The INM strategies resulted in improved NUE compared to 100% chemical fertilizers (F). The INM had significantly higher net N mineralization and improved biological activity aligning with the NUE trends. The reductions in redox potential (Eh) and pH during rice season improved NUE under integrated management. Highly reduced conditions favored N mineralization and plant availability in form of NH+4 - N resulting in enhanced uptake efficiency, in rice crop. The soil organic carbon (C) significantly increased in INM, and an effect of the active C fractions was evident on the NUE of the wheat crop. Conclusion: The results showed that these INM strategies can immensely benefit the rice-wheat system via improvement in biological health along with electrochemical changes for flooded rice, and labile-C-assisted improvement in soil conditions for wheat. [ABSTRACT FROM AUTHOR]

IntroductionThe contrasting soil management in flooded-transplanted rice (Oryza sativa) and dry-tilled wheat (Triticum aestivum) poses a challenge for improving low nitrogen use efficiency (NUE) of the rice-wheat system. Integration of organics in nutrient management can bring in changes favoring efficient N uptake via changes in growing conditions and soil responses.Materials and methodsThis study reported the results of a 15-year-long experiment on integrated nutrient management (INM) systems for rice-wheat cropping. The INM included substituting ~50% of chemical fertilizers via (i) including a legume crop (Vigna radiata) in the sequence and its biomass incorporation (LE), (ii) green manuring with Sesbania aculeata (GM), (iii) farmyard manure application (FYM), (iv) 1/3 wheat stubble in situ retention (WS), and (v) 1/3 rice stubble in situ retention.Results and DiscussionThe INM strategies resulted in improved NUE compared to 100% chemical fertilizers (F). The INM had significantly higher net N mineralization and improved biological activity aligning with the NUE trends. The reductions in redox potential (Eh) and pH during rice season improved NUE under integrated management. Highly reduced conditions favored N mineralization and plant availability in form of NH4+−N resulting in enhanced uptake efficiency, in rice crop. The soil organic carbon (C) significantly increased in INM, and an effect of the active C fractions was evident on the NUE of the wheat crop.ConclusionThe results showed that these INM strategies can immensely benefit the rice-wheat system via improvement in biological health along with electrochemical changes for flooded rice, and labile-C-assisted improvement in soil conditions for wheat.

The formation and turnover of soil organic carbon (C), the largest terrestrial C pool, is strongly impacted by the ultimate source of that C: leaves, wood, roots, and root exudates. The quantity and quality of these inputs is determined by the identity of the plants involved. Yet substantial uncertainty surrounds the complex relationships among plant traits and soil C, precluding efforts to maximize whole-ecosystem C uptake in nature-based climate mitigation scenarios. In this study, we leveraged a biodiversity-ecosystem function experiment with trees (IDENT) to explore the effects of interspecific variation in plant traits on soil C dynamics in the very early stages of stand development (9 years since planting). Mineral soil C stocks to 5 cm depth were quantified in monospecific plots of 19 tree species planted on a former agricultural field, and analyzed in relation to tree growth and functional traits. We found that tree species identity affected soil bulk density and, to a lesser extent, the carbon content of the topsoil, and thereby total C pools. Among species and across plots, mineral soil C stocks were positively correlated with rates of tree growth and were significantly larger beneath broadleaf trees with “fast” functional traits vs. conifers with more conservative leaf traits, when comparisons were made over equivalent soil depth increments. Thus, plant functional traits mediate interspecific differences in productivity, which in turn influence the magnitude of belowground C stocks. These results highlight important linkages between above- and belowground carbon cycles in the earliest stages of afforestation.

Endpoint impacts related to the transformation of land—including that related to energy infrastructure—have yet to be fully quantified and understood in life cycle assessment (LCA). Concentrated solar power (CSP) which generates electricity by using mirrors to concentrate incoming shortwave radiation onto a receiver, may serve as an alternate source of reliable baseload power in the coming years. As of 2019 (baseline year of the study), the United States (U.S.) had 1.7 GW of installed capacity across a total of eight CSP sites. In this study, we (1) develop an empirical, spatially explicit methodology to categorize physical elements embodied in energy infrastructure using a LCA approach and manual image annotation, (2) use this categorization scheme to quantify land- and ecosystem service-related endpoint impacts, notably potential losses in soil carbon, owing to energy infrastructure development and as a function of electricity generated (i.e., megawatt-hour, MWh); and (3) validate and apply this method to CSP power plants within the U.S. In the Western U.S., CSP projects are sited in Arizona, California, and Nevada. Project infrastructure can be disaggregated into the following physical elements: mirrors (“heliostats”), generators, internal roads, external roads, substations, and water bodies. Of these elements, results reveal that mirrors are the most land intensive element of CSP infrastructure (>90%). Median land transformation and capacity-based land-use efficiency are 0.4 (range of 0.3–6.8) m2/MWh and 40 (range of 11–48) W/m2, respectively. Soil grading and other site preparation disturbances may result in the release of both organic and inorganic carbon—the latter representing the majority stocks in deeper caliche layers—thus leading to potentially significant losses of stored carbon. We estimate three scenarios of soil carbon loss into the atmosphere across 30 years, based on land transformation in m2 per megawatt-hour (m2/MWh) and carbon stock in kilograms of carbon per megawatt-hour (kg C/MWh). Results reveal that potential belowground CO2 released may range from 7 to 137% of total life cycle CO2 emissions. While this study takes a simplistic approach to estimating loss of carbon, the broad methodology provides a valuable baseline for improving comparative analyses of land-related endpoint impacts across energy technologies and other product systems.

Microbial-derived soil organic matter (SOM), or necromass, is an important source of SOM and is sensitive to climate warming. Soil classification systems consider soil physicochemical properties that influence SOM, hinting at the potential utility of incorporating classification systems in soil carbon (C) projections. Currently, there is no consensus on climate warming effects on necromass and if these responses vary across reference soil groups. To estimate the vulnerability of necromass to climate warming, we performed a meta-analysis of publications examining in situ experimental soil warming effects on microbial necromass via amino sugar analysis. We built generalized linear models (GLM) to explore if soil groups and warming methodologies can be used to predict necromass stocks. Our results showed that warming effect sizes on necromass were not uniform across reference soil groups. Specifically, warming effect sizes were generally positive in permafrost soils but negative in calcic soils. However, warming did not significantly change average necromass. Our GLMs detected significant differences in necromass across soil groups with similar texture and clay percentage. Thus, we advocate for further research to define what predictors of necromass are captured in soil group but not in soil texture. We also show warming methodology is a significant predictor of necromass, depending on the necromass biomarker. Future research efforts should uncover the mechanistic reason behind how passive versus active warming methodology influences necromass responses. Our study highlights the need for more in situ soil warming experiments measuring microbial necromass as this will improve predictions of SOM feedback under future climate scenarios. [ABSTRACT FROM AUTHOR]

Livestock are an important source of livelihoods in agricultural systems in sub-Saharan Africa (SSA), while also being the largest source of national greenhouse gas (GHG) emissions in most African countries. As a consequence, there is a critical need for data on livestock GHG sources and sinks to develop national inventories, as well as conduct baseline measurements and intervention testing to mitigate GHG emissions and meet ambitious national climate goals. Our objective was to review studies on GHG emissions from livestock systems in SSA, as well as soil carbon storage in livestock-dominated systems (i.e., grasslands and rangelands), to evaluate best current data and suggest future research priorities. To this end, we compiled studies from SSA that determined emission factors (EFs) for enteric methane and manure emissions, along with studies on soil organic carbon (SOC) stocks in SSA. We found that there has been limited research on livestock GHG emissions and SOC relative to national ambitions for climate change mitigation in SSA. Enteric methane emission factors (EFs) in low productivity cattle systems may be lower than IPCC Tier 1 default EFs, whereas small ruminants (i.e. sheep and goats) had higher EFs compared to IPCC Tier 1 EFs. Manure EFs were equal to or lower than IPCC Tier 1 EFs for deposited manure (while grazing), manure applied as fertilizer, and manure management. SOC stocks for grasslands and rangelands in SSA show broad agreement with IPCC estimates, but there was a strong geographic bias and many studies did not report soil type, bulk density, or SOC stocks at >30 cm depth. In general, the largest data gaps included information for manure (quantity, quality, management), small ruminants, agropastoral/pastoralist systems, and in general from West Africa. Future research should focus on filling major data gaps on locally appropriate mitigation interventions and improving livestock activity data for developing Tier 2 GHG inventories in SSA. At the science-policy interface, all parties would benefit from enhanced coordination within the research community and between researchers and African governments to improve Tier 2 inventories and harmonize measurement for mitigation in livestock systems in SSA. [ABSTRACT FROM AUTHOR]

Enhanced weathering is a proposed carbon dioxide removal (CDR) strategy to accelerate natural carbon sequestration in soils via the amendment of silicate rocks to agricultural soils. Among the suitable silicates (such as basalt and olivine), the fast-weathering mineral wollastonite (CaSiO3) stands out. Not only does the use of wollastonite lead to rapid pedogenic carbonate formation in soils, it can be readily detected for verification of carbon sequestration, but its weathering within weeks to months influences soil chemistry and plant growth within the same crop cycle of its application. This enables a variety of short-term experimental agronomic studies to be conducted to demonstrate in an accelerated manner what could take years to be observed with more abundant but slower weathering silicates. This study presents the results of three studies that were conducted to investigate three distinct aspects of wollastonite skarn weathering in soils in the context of both agricultural and horticultural plants. The first study investigated the effect of a wide range of wollastonite skarn dosages in soil (1.5-10 wt.%) on the growth of green beans. The second study provides insights on the role of silicon (Si) release during silicate weathering on plant growth (soybeans and lettuce). The third study investigated the effect of wollastonite skarn on the growth of spring rye when added to soil alongside a nitrogen-based coated fertilizer. The results of these three studies provide further evidence that amending soil with crushed silicate rocks leads to climate-smart farming, resulting in inorganic carbon sequestration, as well as better plant growth in agricultural (soybean and spring rye) and horticultural (green bean and lettuce) crops. They also demonstrate the value of working with wollastonite skarn as a fast-weathering silicate rock to accelerate our understanding of the mineral-soil-plant-nutrient synergism of enhanced weathering. [ABSTRACT FROM AUTHOR]

Our study measured heterotrophic carbon dioxide (CO2) emissions in a drained peatland under potato cultivation in south-western Uganda. Soil carbon losses have not previously been reported for this land use, and our study set out to capture the range and temporal variation in emissions, as well as investigate relationships with key environmental variables. Soil chamber-based emission measurements were taken over five days at four points in time over the year to capture daily and monthly variability, including day and night sampling to capture any diurnal variations in temperatures and soil flux. Differences in soil microtopography from mounding of soils for potato beds and drainage trenches had a significant effect on the rate of soil flux. Diurnal sampling showed no significant difference in emissions or soil temperatures in the raised potato beds between day and night. More significant effects on soil flux from environmental drivers, such as water table depth, were observed between months, rather than hours and days. There were significant differences in the relationships between environmental variables and soil flux, depending on if soils had been recently disturbed or not. Area-weighted emissions based on microtopography gave a mean annual emissions factor of 98.79 ± 1.7 t CO2 ha-1 y-1 (± standard error) from this peatland use. [ABSTRACT FROM AUTHOR]

Soil carbon (C) is a major driver of soil health, yet little Is known regarding how sensitive measures of soil C shift temporally within a single growing season in response to short- term weather perturbations. Our study aimed to i) Examine how long-term management impacts soil C cycling and stability across a management intensity and plant biodiversity gradient and ii) Assess how sensitive soil health indicators change temporally over the course of a single growing season in response to recent weather patterns. Here we quantify a variety of sensitive soil C measures at four time points across the 2021 growing season at the W.K. Kellogg Biological Station's Long Term Ecological Research Trial (LTER) located in southwest Michigan, USA. The eight systems sampled included four annual soybean (Glycine max) systems that ranged in management intensity (conventional, no-till, reduced input, and biologically-based), two perennial biofuel cropping systems (switchgrass (Panicum virgatum) and hybrid poplars (Populus nigra x P.maximowiczii)), and two unmanaged systems (early successional system and a mown but never tilled grassland). We found that unmanaged systems with increased perenniality enhanced mineralizable C (Min C) and permanganate oxidizable C (POXC) values. Additionally, all soil health indicators were found to be sensitive to changes in short- term weather perturbations over the course of the growing season. The implications of this study are threefold. First, this study assess indicators of labile and stable C pools over the course of the growing season and reflects the stability of soil C in different systems. Second, POXC, Min C, and β-glucosidase (GLU) activity are sensitive soil health indicators that fluctuate temporally, which means that these soil health indicators could help elucidate the impact that weather patterns have on soil C dynamics. Lastly, for effective monitoring of soil C, sampling time and frequency should be considered for a comprehensive understanding of soil C cycling within a system. [ABSTRACT FROM AUTHOR]

Microbial-derived soil organic matter (SOM), or necromass, is an important source of SOM and is sensitive to climate warming. Soil classification systems consider soil physicochemical properties that influence SOM, hinting at the potential utility of incorporating classification systems in soil carbon (C) projections. Currently, there is no consensus on climate warming effects on necromass and if these responses vary across reference soil groups. To estimate the vulnerability of necromass to climate warming, we performed a meta-analysis of publications examining in situ experimental soil warming effects on microbial necromass via amino sugar analysis. We built generalized linear models (GLM) to explore if soil groups and warming methodologies can be used to predict necromass stocks. Our results showed that warming effect sizes on necromass were not uniform across reference soil groups. Specifically, warming effect sizes were generally positive in permafrost soils but negative in calcic soils. However, warming did not significantly change average necromass. Our GLMs detected significant differences in necromass across soil groups with similar texture and clay percentage. Thus, we advocate for further research to define what predictors of necromass are captured in soil group but not in soil texture. We also show warming methodology is a significant predictor of necromass, depending on the necromass biomarker. Future research efforts should uncover the mechanistic reason behind how passive versus active warming methodology influences necromass responses. Our study highlights the need for more in situ soil warming experiments measuring microbial necromass as this will improve predictions of SOM feedback under future climate scenarios.

Livestock are an important source of livelihoods in agricultural systems in sub-Saharan Africa (SSA), while also being the largest source of national greenhouse gas (GHG) emissions in most African countries. As a consequence, there is a critical need for data on livestock GHG sources and sinks to develop national inventories, as well as conduct baseline measurements and intervention testing to mitigate GHG emissions and meet ambitious national climate goals. Our objective was to review studies on GHG emissions from livestock systems in SSA, as well as soil carbon storage in livestock-dominated systems (i.e., grasslands and rangelands), to evaluate best current data and suggest future research priorities. To this end, we compiled studies from SSA that determined emission factors (EFs) for enteric methane and manure emissions, along with studies on soil organic carbon (SOC) stocks in SSA. We found that there has been limited research on livestock GHG emissions and SOC relative to national ambitions for climate change mitigation in SSA. Enteric methane emission factors (EFs) in low productivity cattle systems may be lower than IPCC Tier 1 default EFs, whereas small ruminants (i.e. sheep and goats) had higher EFs compared to IPCC Tier 1 EFs. Manure EFs were equal to or lower than IPCC Tier 1 EFs for deposited manure (while grazing), manure applied as fertilizer, and manure management. SOC stocks for grasslands and rangelands in SSA show broad agreement with IPCC estimates, but there was a strong geographic bias and many studies did not report soil type, bulk density, or SOC stocks at >30 cm depth. In general, the largest data gaps included information for manure (quantity, quality, management), small ruminants, agropastoral/pastoralist systems, and in general from West Africa. Future research should focus on filling major data gaps on locally appropriate mitigation interventions and improving livestock activity data for developing Tier 2 GHG inventories in SSA. At the science-policy interface, all parties would benefit from enhanced coordination within the research community and between researchers and African governments to improve Tier 2 inventories and harmonize measurement for mitigation in livestock systems in SSA.

Enhanced weathering is a proposed carbon dioxide removal (CDR) strategy to accelerate natural carbon sequestration in soils via the amendment of silicate rocks to agricultural soils. Among the suitable silicates (such as basalt and olivine), the fast-weathering mineral wollastonite (CaSiO3) stands out. Not only does the use of wollastonite lead to rapid pedogenic carbonate formation in soils, it can be readily detected for verification of carbon sequestration, but its weathering within weeks to months influences soil chemistry and plant growth within the same crop cycle of its application. This enables a variety of short-term experimental agronomic studies to be conducted to demonstrate in an accelerated manner what could take years to be observed with more abundant but slower weathering silicates. This study presents the results of three studies that were conducted to investigate three distinct aspects of wollastonite skarn weathering in soils in the context of both agricultural and horticultural plants. The first study investigated the effect of a wide range of wollastonite skarn dosages in soil (1.5–10 wt.%) on the growth of green beans. The second study provides insights on the role of silicon (Si) release during silicate weathering on plant growth (soybeans and lettuce). The third study investigated the effect of wollastonite skarn on the growth of spring rye when added to soil alongside a nitrogen-based coated fertilizer. The results of these three studies provide further evidence that amending soil with crushed silicate rocks leads to climate-smart farming, resulting in inorganic carbon sequestration, as well as better plant growth in agricultural (soybean and spring rye) and horticultural (green bean and lettuce) crops. They also demonstrate the value of working with wollastonite skarn as a fast-weathering silicate rock to accelerate our understanding of the mineral–soil–plant–nutrient synergism of enhanced weathering.

Soil carbon (C) is a major driver of soil health, yet little is known regarding how sensitive measures of soil C shift temporally within a single growing season in response to short-term weather perturbations. Our study aimed to i) Examine how long-term management impacts soil C cycling and stability across a management intensity and plant biodiversity gradient and ii) Assess how sensitive soil health indicators change temporally over the course of a single growing season in response to recent weather patterns. Here we quantify a variety of sensitive soil C measures at four time points across the 2021 growing season at the W.K. Kellogg Biological Station’s Long Term Ecological Research Trial (LTER) located in southwest Michigan, USA. The eight systems sampled included four annual soybean (Glycine max) systems that ranged in management intensity (conventional, no-till, reduced input, and biologically-based), two perennial biofuel cropping systems (switchgrass (Panicum virgatum) and hybrid poplars (Populus nigra x P.maximowiczii)), and two unmanaged systems (early successional system and a mown but never tilled grassland). We found that unmanaged systems with increased perenniality enhanced mineralizable C (Min C) and permanganate oxidizable C (POXC) values. Additionally, all soil health indicators were found to be sensitive to changes in short-term weather perturbations over the course of the growing season. The implications of this study are threefold. First, this study assess indicators of labile and stable C pools over the course of the growing season and reflects the stability of soil C in different systems. Second, POXC, Min C, and ß-glucosidase (GLU) activity are sensitive soil health indicators that fluctuate temporally, which means that these soil health indicators could help elucidate the impact that weather patterns have on soil C dynamics. Lastly, for effective monitoring of soil C, sampling time and frequency should be considered for a comprehensive understanding of soil C cycling within a system.

Our study measured heterotrophic carbon dioxide (CO2) emissions in a drained peatland under potato cultivation in south-western Uganda. Soil carbon losses have not previously been reported for this land use, and our study set out to capture the range and temporal variation in emissions, as well as investigate relationships with key environmental variables. Soil chamber-based emission measurements were taken over five days at four points in time over the year to capture daily and monthly variability, including day and night sampling to capture any diurnal variations in temperatures and soil flux. Differences in soil microtopography from mounding of soils for potato beds and drainage trenches had a significant effect on the rate of soil flux. Diurnal sampling showed no significant difference in emissions or soil temperatures in the raised potato beds between day and night. More significant effects on soil flux from environmental drivers, such as water table depth, were observed between months, rather than hours and days. There were significant differences in the relationships between environmental variables and soil flux, depending on if soils had been recently disturbed or not. Area-weighted emissions based on microtopography gave a mean annual emissions factor of 98.79 ± 1.7 t CO2 ha-1 y-1 (± standard error) from this peatland use.

Large quantities of semiconductor minerals on soil surfaces have a sensitive photoelectric response. These semiconductor minerals generate photo-electrons and photo-hole pairs that can stimulate soil oxidation–reduction reactions when exposed to sunlight. We speculated that the photocatalysis of semiconductor minerals would affect soil carbon cycles. As the main component of the carbon cycle, soil respiration from paddy soil is often ignored. Five rice cropping areas in China were chosen for soil sampling. Semiconductor minerals were measured, and three main semiconductor minerals including hematile, rutile, and manganosite were identified in the paddy soils. The identified semiconductor minerals consisted of iron, manganese, and titanium oxides. Content of Fe2O3, TiO2, and MnO in the sampled soil was between 4.21–14%, 0.91–2.72%, and 0.02–0.22%, respectively. Most abundant semiconductor mineral was found in the DBDJ rice cropping area in Jilin province, with the highest content of Fe2O3 of 14%. Soils from the five main rice cropping areas were also identified as having strong photoelectric response characteristics. The highest photoelectric response was found in the DBDJ rice cropping area in Jilin province with a maximum photocurrent density of 0.48 μA/cm2. Soil respiration was monitored under both dark and light (3,000 lux light density) conditions. Soil respiration rates in the five regions were (from highest to lowest): DBDJ > XNDJ > XBDJ > HZSJ > HNSJ. Soil respiration was positively correlated with semiconductor mineral content, and soil respiration was higher under the light treatment than the dark treatment in every rice cropping area. This result suggested that soil respiration was stimulated by semiconductor mineral photocatalysis. This analysis provided indirect evidence of the effect semiconductor mineral photocatalysis has on the carbon cycle within paddy soils, while exploring carbon conversion mechanisms that could provide a new perspective on the soil carbon cycle. [ABSTRACT FROM AUTHOR]

Determining the mechanisms, traits, and pathways that regulate microbial transformation of natural organic matter (NOM) is critical to informing our understanding of the microbial impacts on the global carbon cycle. The capillary fringe of subsurface soils is a highly dynamic environment that remains poorly understood. Characterization of organo-mineral chemistry combined with a nuanced understanding of microbial community composition and function is necessary to understand microbial impacts on NOM speciation in the capillary fringe. We present a critical review of the popular analytical and omics techniques used for characterizing complex carbon transformation by microbial communities and focus on how complementary information obtained from the different techniques enable us to connect chemical signatures with microbial genes and pathways. This holistic approach offers a way forward for the comprehensive characterization of the formation, transformation, and mineralization of terrestrial NOM as influenced by microbial communities. [ABSTRACT FROM AUTHOR]

Climate change is one of the greatest threats to high-latitude permafrost and leads to serious permafrost degradation. However, few attention has been paid to whether peat soil carbon or nitrogen is sensitive to permafrost degradation. This study has selected three typical sample areas (MoHe-continuous permafrost, TaHe-Island-shaped melting permafrost, Jagdaqi-Island-shaped melting permafrost) as research object to compare the response rate and degree of peat soil carbon and nitrogen under permafrost degradation. The results show that soil organic carbon and nitrogen contents are the highest in 0–10 cm soil and permafrost regions show obvious surface aggregation. The carbon content of different types of frozen soil decreases with the depth of soil layer, and the differences are significant (p < 0.01). The distribution pattern of total nitrogen content in each soil layer among different permafrost types is Mohe < Tahe < Jagedaqi. And when it is getting vertically deeper than the surface layer, there is no significant difference between the soil layers in soil profile. The study also focuses on the variations of carbon and nitrogen content in different soil layers of peatland in typical permafrost regions. The results show that soil carbon responds faster to the degradation of frozen soil than soil nitrogen. Moreover, the accumulation degree of soil carbon is also significantly higher than soil nitrogen. Under climate change and for better permafrost conservation, it is necessary to study how the peatland’s soil carbon and the nitrogen are influenced by the permafrost degradation in high latitude.

Large quantities of semiconductor minerals on soil surfaces have a sensitive photoelectric response. These semiconductor minerals generate photo-electrons and photo-hole pairs that can stimulate soil oxidation–reduction reactions when exposed to sunlight. We speculated that the photocatalysis of semiconductor minerals would affect soil carbon cycles. As the main component of the carbon cycle, soil respiration from paddy soil is often ignored. Five rice cropping areas in China were chosen for soil sampling. Semiconductor minerals were measured, and three main semiconductor minerals including hematile, rutile, and manganosite were identified in the paddy soils. The identified semiconductor minerals consisted of iron, manganese, and titanium oxides. Content of Fe2O3, TiO2, and MnO in the sampled soil was between 4.21–14%, 0.91–2.72%, and 0.02–0.22%, respectively. Most abundant semiconductor mineral was found in the DBDJ rice cropping area in Jilin province, with the highest content of Fe2O3 of 14%. Soils from the five main rice cropping areas were also identified as having strong photoelectric response characteristics. The highest photoelectric response was found in the DBDJ rice cropping area in Jilin province with a maximum photocurrent density of 0.48 μA/cm2. Soil respiration was monitored under both dark and light (3,000 lux light density) conditions. Soil respiration rates in the five regions were (from highest to lowest): DBDJ > XNDJ > XBDJ > HZSJ > HNSJ. Soil respiration was positively correlated with semiconductor mineral content, and soil respiration was higher under the light treatment than the dark treatment in every rice cropping area. This result suggested that soil respiration was stimulated by semiconductor mineral photocatalysis. This analysis provided indirect evidence of the effect semiconductor mineral photocatalysis has on the carbon cycle within paddy soils, while exploring carbon conversion mechanisms that could provide a new perspective on the soil carbon cycle.

Determining the mechanisms, traits, and pathways that regulate microbial transformation of natural organic matter (NOM) is critical to informing our understanding of the microbial impacts on the global carbon cycle. The capillary fringe of subsurface soils is a highly dynamic environment that remains poorly understood. Characterization of organo-mineral chemistry combined with a nuanced understanding of microbial community composition and function is necessary to understand microbial impacts on NOM speciation in the capillary fringe. We present a critical review of the popular analytical and omics techniques used for characterizing complex carbon transformation by microbial communities and focus on how complementary information obtained from the different techniques enable us to connect chemical signatures with microbial genes and pathways. This holistic approach offers a way forward for the comprehensive characterization of the formation, transformation, and mineralization of terrestrial NOM as influenced by microbial communities.

Sustainable aviation fuel (SAF) production from lipids is a technologically mature approach for replacing conventional fossil fuel use in the aviation sector, and there is increasing demand for such feedstocks. The oilseed Brassica carinata (known as Ethiopian mustard or simply carinata) is a promising SAF feedstock that can be grown as a supplemental cash crop over the winter fallow season of various annual crop rotations in the Southeast US, avoiding land use changes and potentially achieving some of the soil carbon sequestration and ecosystem service benefits of winter cover crops. However, carinata may require more intensive management than traditional cover crops, potentially leading to additional soil greenhouse gas (GHG) emissions through increased carbon losses from soil tillage and nitrous oxide (N2O) emissions from nitrogen fertilizer application. In this work, the 2017 version of the process-based DayCent ecosystem model was used to establish initial expectations for the total regional SAF production potential and associated soil GHG emissions when carinata is integrated as a winter crop into the existing crop rotations across its current suitability range in southern Alabama, southern Georgia, and northern Florida. Using data from academic and industry carinata field trials in the region, DayCent was calibrated to reproduce carinata yield, nitrogen response, harvest index, and biomass carbon-to-nitrogen ratio. The resulting model was then used to simulate the integration of carinata every third winter across all 2.1 Mha of actively cultivated cropland in the study area. The model predicted regional average yields of 2.9–3.0 Mg carinata seed per hectare depending on crop management assumptions. That results in the production of more than two million Mg of carinata seed annually across the study area, enough to supply approximately one billion liters of SAF. Conventional management of carinata led to only modest increases in soil carbon storage that were largely offset by additional N2O emissions. Climate-smart management via adopting no-till carinata establishment or using poultry litter as a nitrogen source resulted in a substantial net soil GHG sink (0.23–0.31 Mg CO2e ha−1 y−1, or 0.24–0.32 Mg CO2e per Mg of seed produced) at the farms where carinata is cultivated.

To successfully reduce atmospheric CO2 by sequestering additional soil carbon, it is essential to understand the potential of a given soil to store carbon in a stable form. Carbon that has formed organo-mineral complexes with silt and clay particles is believed to be less susceptible to decay than non-complexed, or particulate, organic carbon. Using direct measurements of mineral associated organic matter (MAOC) on a subset of samples, and an approach developed previously for primarily allophanic soils, we took a modeling approach to estimate MAOC for 537 samples of much coarser and younger soils from 99 non-cultivated and agricultural sites in the Okanagan Valley, British Columbia, Canada. Using specific surface area (SSA) or soil texture as indicators of the mineral surface area available for sorption of organic matter, we used both Random Forest (RF) and Stepwise Multiple Regression with Akaike Information Criterion (SMR) to determine a best fit model for predicting MAOC. Random Forest modeling using SSA in addition to total SOC, exchangeable calcium, exchangeable potassium, and soil pH performed better than SMR for determining MAOC in these soils (R²: 0.790 for RF; R²: 0.713 for SMR). To determine if a MAOC deficit existed for these soils, we then applied a quantile regression approach wherein the predicted 90th quantile of MAOC represents the MAOC formation capacity. We determined that MAOC deficits were present in all soils and increased with depth. Moreover, clay rich soils had greater MAOC deficits (1.62 g kg-1 for 0-15 cm, 4.01 g kg-1 for 15-30 cm, and 5.80 g kg-1 for 30-60 cm), than sandier soils (1.01 g kg-1 for 0-15 cm, 2.72 g kg-1 for 15-30 cm, and 3.69 g kg-1 for 30-60 cm). Furthermore, the upper 30 cm of these soils have the potential to increase MAOC stocks by 29% (48.0 million kg of MAOC over 8,501 ha) before they reach formation capacity. This study highlights the variability in MAOC formation capacity of soils with different physicochemical properties and provides a framework for estimating MAOC concentrations and deficits for soils with a wide range of physicochemical properties. [ABSTRACT FROM AUTHOR]

To successfully reduce atmospheric CO2 by sequestering additional soil carbon, it is essential to understand the potential of a given soil to store carbon in a stable form. Carbon that has formed organo-mineral complexes with silt and clay particles is believed to be less susceptible to decay than non-complexed, or particulate, organic carbon. Using direct measurements of mineral associated organic matter (MAOC) on a subset of samples, and an approach developed previously for primarily allophanic soils, we took a modeling approach to estimate MAOC for 537 samples of much coarser and younger soils from 99 non-cultivated and agricultural sites in the Okanagan Valley, British Columbia, Canada. Using specific surface area (SSA) or soil texture as indicators of the mineral surface area available for sorption of organic matter, we used both Random Forest (RF) and Stepwise Multiple Regression with Akaike Information Criterion (SMR) to determine a best fit model for predicting MAOC. Random Forest modeling using SSA in addition to total SOC, exchangeable calcium, exchangeable potassium, and soil pH performed better than SMR for determining MAOC in these soils (R2: 0.790 for RF; R2: 0.713 for SMR). To determine if a MAOC deficit existed for these soils, we then applied a quantile regression approach wherein the predicted 90th quantile of MAOC represents the MAOC formation capacity. We determined that MAOC deficits were present in all soils and increased with depth. Moreover, clay rich soils had greater MAOC deficits (1.62 g kg−1 for 0–15 cm, 4.01 g kg−1 for 15–30 cm, and 5.80 g kg−1 for 30–60 cm), than sandier soils (1.01 g kg−1 for 0–15 cm, 2.72 g kg−1 for 15–30 cm, and 3.69 g kg−1 for 30–60 cm). Furthermore, the upper 30 cm of these soils have the potential to increase MAOC stocks by 29% (48.0 million kg of MAOC over 8,501 ha) before they reach formation capacity. This study highlights the variability in MAOC formation capacity of soils with different physicochemical properties and provides a framework for estimating MAOC concentrations and deficits for soils with a wide range of physicochemical properties.

Mangroves are important sinks of organic carbon (C) and there is significant interest in their use for greenhouse gas emissions mitigation. Adverse impacts on organic carbon storage potential from future climate change and deforestation would devalue such ambitions, thus global projections of future change remains a priority research area. We modeled the effects of climate change on future C stocks and soil sequestration rates (CSR) under two climate scenarios (“business as usual”: SSP245 and high-emissions: SSP585). Model results were contrasted with CO2 equivalents (CO2e) emissions from past, present and future rates of deforestation on a country specific scale. For C stocks, we found climate change will increase global stocks by ∼7% under both climate scenarios and that this gain will exceed losses from deforestation by the end of the twenty-first century, largely due to shifts in rainfall. Major mangrove-holding countries Indonesia, Malaysia, Cuba, and Nigeria will increase national C stocks by > 10%. Under the high-end scenario, while a net global increase is still expected, elevated temperatures and wider temperature ranges are likely increase the risk of countries’ C stocks diminishing. For CSR, there will likely be a global reduction under both climate change scenarios: 12 of the top 20 mangrove-rich countries will see a drop in CSR. Modeling of published country level mangrove deforestation rates showed emissions have decreased from 141.4 to 6.4% of annual CSR since the 1980’s. Projecting current mangrove deforestation rates into the future resulted in a total of 678.50 ± 151.32 Tg CO2e emitted from 2012 to 2095. Reducing mangrove deforestation rates further would elevate the carbon benefit from climate change by 55–61%, to make the proposition of offsetting emissions through mangrove protection and restoration more attractive. These results demonstrate the positive benefits of mangrove conservation on national carbon budgets, and we identify the nations where incorporating mangrove conservation into their Nationally Defined Contributions offers a particularly rewarding route toward meeting their Glasgow Agreement commitments.

Ecological sanitation (EcoSan) systems capture and sanitize human excreta and generate organic nutrient resources that can support more sustainable nutrient management in agricultural ecosystems. An emerging EcoSan system that is implemented in Haiti and several other contexts globally couples container-based household toilets with aerobic, thermophilic composting. This closed loop sanitation system generates organic nutrient resources that can be used as part of an ecological approach to soil nutrient management and thus has the potential to contribute to Sustainable Development Goals 2 (zero hunger), 6 (clean water and sanitation for all), and 13 (climate change solutions). However, the role of organic nutrient resources derived from human excreta in food production is poorly studied. We conducted a greenhouse experiment comparing the impact of feces-derived compost on crop production, soil nutrient cycling, and nutrient losses with two amendments produced from wastewater treatment (pelletized biosolids and biofertilizer), urea, and an unfertilized control. Excreta-derived amendments increased crop yields 2.5 times more than urea, but had differing carry-over effects. After a one-time application of compost, crop production remained elevated throughout all six crop cycles. In contrast, the carry-over of crop response lasted two and four crop cycles for biosolids and biofertilizer, respectively, and was absent for urea. Soil carbon concentration in the compost amended soils increased linearly through time from 2.0 to 2.5%, an effect not seen with other treatments. Soil nitrous oxide emissions factors ranged from 0.3% (compost) to 4.6% (biosolids), while nitrogen leaching losses were lowest for biosolids and highest for urea. These results indicate that excreta-derived compost provides plant available nutrients, while improving soil health through the addition of soil organic carbon. It also improved biogeochemical functions, indicating the potential of excreta-derived compost to close nutrient loops if implemented at larger scales. If captured and safely treated through EcoSan, human feces produced in Haiti can meet up to 13, 22, and 11% of major crop needs of nitrogen, phosphorus, and potassium, respectively.

A continuously growing pressure to increase food, fiber, and fuel production to meet worldwide demand and achieve zero hunger has put severe pressure on soil resources. Abandoned, degraded, and marginal lands with significant agricultural constraints—many still used for agricultural production—result from inappropriately intensive management, insufficient attention to soil conservation, and climate change. Continued use for agricultural production will often require ever more external inputs such as fertilizers and herbicides, further exacerbating soil degradation and impeding nutrient recycling and retention. Growing evidence suggests that degraded lands have a large potential for restoration, perhaps most effectively via perennial cropping systems that can simultaneously provide additional ecosystem services. Here we synthesize the advantages of and potentials for using perennial vegetation to restore soil fertility on degraded croplands, by summarizing the principal mechanisms underpinning soil carbon stabilization and nitrogen and phosphorus availability and retention. We illustrate restoration potentials with example systems that deliver climate mitigation (cellulosic bioenergy), animal production (intensive rotational grazing), and biodiversity conservation (natural ecological succession). Perennialization has substantial promise for restoring fertility to degraded croplands, helping to meet future food security needs.

Restoration aimed at rewetting the valley floor has the potential to increase organic carbon stock in the form of floodplain soil carbon, downed wood, and riparian vegetation. The primary goal of stream restoration is typically to restore habitat or maintain balance between natural ecosystem function and human land use. Although many benefits result from stream restoration, the carbon sequestration potential of different restoration approaches in diverse geographic settings has not yet been quantified. We investigate the carbon storage potential of restored stream segments (known as treatment segments) relative to otherwise analogous degraded and reference segments. We develop a conceptual framework to identify the conditions that maximize carbon storage in relation to characteristics of the river corridor and specific restoration practices and propose response surfaces for carbon storage. We illustrate application and quantification of the conceptual framework using data from a pilot study of treatment, degraded, and reference stream segments along two streams in Oregon, United States. The conceptual model is designed to help managers identify levels of hydrologic connectivity, channel and floodplain dynamics, floodplain vegetation, and other variables that may optimize carbon storage at a treatment site.

Large-scale quantification of soil organic carbon (C) and nitrogen (N) stocks and their distribution between particulate (POM) and mineral-associated (MAOM) organic matter is deemed necessary to develop land management strategies to mitigate climate change and sustain food production. To this end, diffuse reflectance mid-infrared spectroscopy (MIR) coupled with partial least square (PLS) analysis has been proposed as a promising method because of its low labor and cost, high throughput and the potential to estimate multiple soil attributes. In this paper, we applied MIR spectroscopy to predict C and N content in bulk soils, and in POM and MAOM, as well as soil properties influencing soil C storage. A heterogeneous dataset including 349 topsoil samples were collected under different soil types, land use and climate conditions across the European Union and the United Kingdom. The samples were analyzed for various soil properties to determine the feasibility of developing MIR-based predictive calibrations. We obtained accurate predictions for total soil C and N content, MAOM C and N content, pH, clay, and sand (R2> 0.7; RPD>1.8). In contrast, POM C and N content were predicted with lower accuracies due to non-linear dependencies, suggesting the need for additional calibration across similar soils. Furthermore, the information provided by MIR spectroscopy was able to differentiate spectral bands and patterns across different C pools. The strength of the correlation between C pools, minerals, and C functional groups was land use-dependent, suggesting that the use of this approach for long-term soil C monitoring programs should use land-use specific calibrations.

Protecting existing soil carbon (C) and harnessing the C sequestration potential of soils require an improved understanding of the processes through which soil organic matter accumulates in natural systems. Currently, competing hypotheses exist regarding the dominant mechanisms for soil C stabilization. Many long-standing hypotheses revolve around an assumed positive relationship between the quantity of organic inputs and soil C accumulation, while more recent hypotheses have shifted attention toward the complex controls of microbial processing and organo-mineral complexation. Here, we present the observed findings of soil response to 20 years of detrital manipulations in the wet, temperate forest of the H.J. Andrews Experimental Station. Annual additions of low-quality (high C:N content) wood litter to the soil surface led to a greater positive effect on observed mean soil C concentration relative to additions of higher-quality (low C:N content) needle litter over the 20-year study period. However, high variability in measurements of soil C led to a statistically non-significant difference in C concentration between the two treatments and the control soil. The observed soil C responses to these two addition treatments demonstrates the long timescale and potential magnitude of soil C responses to management or disturbance led changes in forest litter input composition. Detrital input reduction treatments, including cutting off live root activity and the aboveground removal of surface litter, led to relatively small, non-significant effects on soil C concentrations over the 20-year study period. Far greater negative effects on mean soil C concentrations were observed for the combined removal of both aboveground litter and belowground root activity, which led to an observed, yet also non-significant, 20% decline in soil C stocks. The substantial proportion of remaining soil C following these dramatic, long-term reductions in above- and belowground detrital inputs suggests that losses of C in these forest soils are not readily achieved over a few decades of reductions in detrital input and may require far greater periods of time or further perturbations to the environment. Further, the observed soil C responses to detrital manipulations support recent hypotheses regarding soil C stabilization, which emphasize litter quality and mineral stabilization as relevant controls over forest soil C.

Enhancing soil organic matter in agricultural soils has potential to contribute to climate mitigation while also promoting soil health and resilience. However, soil carbon (C) sequestration projects are rare in C markets. One concern surrounding soil C is uncertainty regarding the permanence of newly sequestered soil C. This scientific uncertainty is exacerbated by differences in terminology used by scientists and policymakers, which impedes the integration of new scientific findings regarding soil carbon longevity into evidence-based policies. Here, we review the evolution of understanding of soil C lifespan and the language used to describe it in both scientific and policy sectors. We find that recent scientific findings that have bearing on soil C lifespan are not part of discussions surrounding C policy, and conversely, policymaker concerns are not clearly addressed by scientific research. From a policy perspective, soil C is generally assumed to be a vulnerable pool at risk of being quickly lost via microbial degradation or other avenues of physical loss if soil C building practices are not maintained indefinitely. This assumption has been challenged by recent scientific advances demonstrating that microbial consumption and transformation of plant-derived C actually necessary for the long-term storage of soil organic matter. Here, we argue that soil C longevity can best be understood as resulting from continual movement and transformation of organic compounds throughout the soil matrix, and show that this definition is directly at odds with how soil C longevity is represented in current policies. Given current interest in new policies to promote soil C sequestration activities, resolving these definitions is critical. We further identify priority areas for future research in order to answer key policymaker questions about soil C lifespan, and to help develop new tools and benchmarks necessary to assess efficacy of agricultural soil C sequestration efforts.

Management of the temperate, grazed grasslands in New Zealand for more than a century has led to swards dominated by ryegrass/clover, which, with inputs of inorganic fertilizers, are highly productive for grazing animals. In the last 20 years the widespread introduction of irrigation to dryland areas on flat land has increased productivity further. However, these intensive practices decrease soil carbon stocks. In contrast, there is limited evidence that improved management of dryland, grazed, hill country grasslands can lead to increases in soil carbon stocks. To address global needs for food security and climate change mitigation, priority actions to increase soil carbon stocks need to focus on improved management practices to increase carbon inputs and retention in soils identified as having high potential for increasing carbon storage. While there are limited data from New Zealand studies, international observations suggest that soil carbon stocks can be increased by enhancing below-ground carbon inputs from plants with deep roots, using swards with diverse species, and moderate grazing rather than harvesting biomass. However, there is less certainty about the processes regulating the formation and decomposition of soil organic matter and their dependence on soil physical properties and microbial access. Scaling findings from plot studies to forecast long-term changes in soil carbon stocks at the landscape scale can be done using models but new approaches are required to integrate the impacts of multiple concurrent practices associated with grazing management.

Soils contain a large and dynamic fraction of global terrestrial carbon stocks. The distribution of soil carbon (SC) with depth varies among ecosystems and land uses and is an important factor in calculating SC stocks and their vulnerabilities. Systematic analysis of SC depth distributions across databases of SC profiles has been challenging due to the heterogeneity of soil profile measurements, which vary in depth sampling. Here, we fit over 40,000 SC depth profiles to an exponential decline relationship with depth to determine SC concentration at the top of the mineral soil, minimum SC concentration at depth, and the characteristic “length” of SC concentration decline with depth. Fitting these parameters allowed profile characteristics to be analyzed across a large and heterogeneous dataset. We then assessed the differences in these depth parameters across soil orders and land cover types and between soil profiles with or without a history of tillage, as represented by the presence of an Ap horizon. We found that historically tilled soils had more gradual decreases of SC with depth (greater e-folding depth or Z∗), deeper SC profiles, lower SC concentrations at the top of the mineral soil, and lower total SC stocks integrated to 30 cm. The large database of profiles allowed these results to be confirmed across different land cover types and spatial areas within the Continental United States, providing robust evidence for systematic impacts of historical tillage on SC stocks and depth distributions.

To develop more accurate global carbon (C) budgets and to better inform management of human activities in the ocean, we need high-resolution estimates of marine C stocks. Here we quantify global marine sedimentary C stocks at a 1-km resolution, and find that marine sediments store ∼ 3117 (3006–3209) Pg C in the top 1 m (more than twice that of terrestrial soils). Sediments in abyss/basin zones account for 75% of the global marine sediment C stock, and 52% of that stock is within the 200-mile Exclusive Economic Zones of countries. Currently, only ∼2% of sediment C stocks are located in highly to fully protected areas that prevent the disturbance of the seafloor. Our results show that marine sediments represent a large and globally important C sink. However, the lack of protection for marine C stocks makes them highly vulnerable to human disturbances that can lead to their remineralization to CO2, further aggravating climate change impacts.

In the Mediterranean, long-term impact of typical land uses on soil fertility have not been quantified yet on replicated mixed crop-livestock farms and considering the variability of soil texture. Here, we report the effects, after 15 years of practice, of two legume-winter cereal rotations, olive orchards and vineyards on microbiological and chemical indicators of soil fertility and the communities of arbuscular mycorrhizal fungi (AMF). We compare the changes among these four agricultural land-use types to woodland reference sites. Root colonization by AMF of English ryegrass (Lolium perenne L.), a grass that occurred under all land use types, was only half as heavy in biannual berseem clover (Trifolium alexandrinum L.)-winter cereal rotations than in 4-year alfalfa (Medicago sativa L.)-winter cereal rotations. In olive (Olea europaea L.) orchards and vineyards (Vitis vinifera L.), where weeds are controlled by frequent surface tillage, the AMF root colonization of ryegrass was again much lower than in the legume-cereal rotations and at the woodland reference sites. All the microbial parameters and soil organic carbon correlated most strongly with differences in occurrence and relative abundance (β-diversity) of AMF genera in soil. The soil pH and mineral nutrients in soil strongly correlated with differences in AMF root colonization and AMF genus richness (α-diversity) in soil. Diversity of AMF was much less affected by soil texture than land use, while the opposite was true for microbial and chemical soil fertility indicators. Land uses that guaranteed a continuous ground cover of herbaceous plants and that involved only infrequent tillage, such as multiyear alfalfa-winter cereal rotation, allowed members of the AMF genus Scutellospora to persist and remain abundant. On the contrary, under land uses accompanied by frequent tillage and hence discontinuous presence of herbaceous plants, such as tilled olive orchard and vineyard, members of the genus Funneliformis dominated. These results suggest that multiyear alfalfa-winter cereal rotation with active plant growth throughout the year is the least detrimental agricultural land use in soil carbon and AMF abundance and diversity, relative to the woodland reference.

In the Mediterranean, long-term impact of typical land uses on soil fertility have not been quantified yet on replicated mixed crop-livestock farms and considering the variability of soil texture. Here, we report the effects, after 15 years of practice, of two legume-winter cereal rotations, olive orchards and vineyards on microbiological and chemical indicators of soil fertility and the communities of arbuscular mycorrhizal fungi (AMF). We compare the changes among these four agricultural land-use types to woodland reference sites. Root colonization by AMF of English ryegrass (Lolium perenne L.), a grass that occurred under all land use types, was only half as heavy in biannual berseem clover (Trifolium alexandrinum L.)-winter cereal rotations than in 4-year alfalfa (Medicago sativa L.)-winter cereal rotations. In olive (Olea europaea L.) orchards and vineyards (Vitis vinifera L.), where weeds are controlled by frequent surface tillage, the AMF root colonization of ryegrass was again much lower than in the legume-cereal rotations and at the woodland reference sites. All the microbial parameters and soil organic carbon correlated most strongly with differences in occurrence and relative abundance (β-diversity) of AMF genera in soil. The soil pH and mineral nutrients in soil strongly correlated with differences in AMF root colonization and AMF genus richness (α-diversity) in soil. Diversity of AMF was much less affected by soil texture than land use, while the opposite was true for microbial and chemical soil fertility indicators. Land uses that guaranteed a continuous ground cover of herbaceous plants and that involved only infrequent tillage, such as multiyear alfalfa-winter cereal rotation, allowed members of the AMF genus Scutellospora to persist and remain abundant. On the contrary, under land uses accompanied by frequent tillage and hence discontinuous presence of herbaceous plants, such as tilled olive orchard and vineyard, members of the genus Funneliformis dominated. These results suggest that multiyear alfalfa-winter cereal rotation with active plant growth throughout the year is the least detrimental agricultural land use in soil carbon and AMF abundance and diversity, relative to the woodland reference. [ABSTRACT FROM AUTHOR]

Forest soils harbor diverse microbial communities responsible for the cycling of elements including carbon (C), nitrogen (N), and phosphorus (P). Conversely, anthropogenic N deposition can negatively feed back on soil microbes and reduce soil organic matter (SOM) decomposition. Mechanistically, this can include reductions of decomposer biomass, especially fungi, and decreases in activities of lignin-modifying enzyme (LMEs). Moreover, N inputs can lower resource C:N and thus decrease the C:N imbalance between microbial decomposers and their resources. As a result, microbially-mediated decomposition might slow down, resulting in larger SOM pools with consequences for ecosystem nutrition and climate regulation. Here, we studied the long-term impact of experimental N addition on soil microbes and microbially-mediated decomposition in two coniferous forests in Switzerland and Denmark. We measured microbial biomass C and N, phospholipid fatty acid (PLFA) biomarkers and potential enzyme activities related to C, N, and P acquisition along the topsoil profile (0–30 cm). In particular, we investigated shifts in microbial C:N homeostasis and relative C:N:P limitation. Contrary to prevailing theory, microbial biomass and community composition were remarkably resistant against two decades of 750 and 1,280 kg ha−1 of cumulative N inputs at the Swiss and Danish site, respectively. While N reduced fungal-specific PLFAs and lowered fungi-to-bacteria (F:B) ratios in some (mainly organic) horizons where soil organic carbon (SOC) has accumulated, it increased F:B ratios in other (mainly mineral) horizons where SOC has declined. We did not find a consistent reduction of LME activities in response to N. Rather, relationships between LME activities and SOC concentrations were largely unaffected by N addition. This questions prevalent theories of lignin decomposition and SOC storage under elevated N inputs. By using C:N stoichiometry, we further show that microbial communities responded in part non-homeostatically to decreasing resource C:N, in addition to a likely increase in their carbon use efficiency and a decrease in nitrogen use efficiency. While the expected increased allocation to C- and decreased allocation to N-acquiring enzymes was not found, microbial investment in P acquisition (acid phosphatase activity) increased in the nutrient-poor Podzol (but not in the nutrient-rich Gleysol). Enzyme vector analysis showed decreasing C but increasing P limitation of soil microbial communities at both sites. We conclude that simulated N deposition led to physiological adaptations of soil microbial communities across the topsoil profile in two independent experiments, with long-term implications for tree nutrition and SOC sequestration. However, we expect that microbial adaptations are not endless and may reach a tipping point when ecosystems experience nitrogen saturation.

Variability of CO2 concentrations within the Earth system occurs over a wide range of time and spatial scales. Resolving this variability and its drivers in terrestrial and aquatic environments ultimately requires high-resolution spatial and temporal monitoring; however, relatively high-cost gas analyzers and data loggers can present barriers in terms of cost and functionality. To overcome these barriers, we developed a low-cost Arduino monitoring platform (CO2-LAMP) for recording CO2 variability in electronically harsh conditions: humid air, soil, and aquatic environments. A relatively inexpensive CO2 gas analyzer was waterproofed using a semi-permeable, expanded polytetrafluoroethylene membrane. Using first principles, we derived a formulation of the theoretical operation and measurement of PCO2(aq) by infrared gas analyzers submerged in aquatic environments. This analysis revealed that an IRGA should be able to measure PCO2(aq) independent of corrections for hydrostatic pressure. CO2-LAMP theoretical operation and measurement were also verified by accompanying laboratory assessment measuring PCO2(aq) at multiple water depths. The monitoring platform was also deployed at two sites within the Springfield Plateau province in northwest Arkansas, USA: Blowing Springs Cave and the Savoy Experimental Watershed. At Blowing Springs Cave, the CO2-LAMP operated alongside a relatively greater-cost CO2 monitoring platform. Over the monitoring period, measured values between the two systems covaried linearly (r2 = 0.97 and 0.99 for cave air and cave stream dissolved CO2, respectively). At the Savoy Experimental Watershed, measured soil CO2 variability capturing sub-daily variation was consistent with previously documented studies in humid, temperate soils. Daily median values varied linearly with soil moisture content (r2 = 0.84). Overall, the CO2-LAMP captured sub-daily variability of CO2 in humid air, soil, and aquatic environments that, while out of the scope of the study, highlight both cyclical and complex CO2 behavior. At present, long-term assessment of platform design is ongoing. Considering cost-savings, CO2-LAMP presents a working base design for continuous, accurate, low-power, and low-cost CO2 monitoring for remote locations.

To promote food security and sustainability, ecologically intensive farming systems should reliably produce adequate yields of high-quality food, enhance the environment, be profitable, and promote social wellbeing. Yet, while many studies address the mean effects of ecologically intensive farming systems on sustainability metrics, few have considered variability. This represents a knowledge gap because producers depend on reliable provisioning of yields, profits, and environmental services to enhance the sustainability of their production systems over time. Further, stable crop yields are necessary to ensure reliable access to nutritious foods. Here we address this by conducting a global meta-analysis to assess the average magnitude and variability of seven sustainability metrics in organic compared to conventional systems. Specifically, we explored the effects of these systems on (i) biotic abundance, (ii) biotic richness, (iii) soil organic carbon, (iv) soil carbon stocks, (v) crop yield, (vi) total production costs, and (vii) profitability. Organic farms promoted biotic abundance, biotic richness, soil carbon, and profitability, but conventional farms produced higher yields. Compared to conventional farms, organic farms had lower variability in abundance and richness but greater yield variability. Organic farms thus provided a “win-win” (high means and low variability) for environmental sustainability, while conventional farms provided a “win-win” for production by promoting high crop yields with low variability. Despite lower yields, and greater yield variability, organic systems had similar costs to conventional systems and were more profitable due to organic premiums. Our results suggest certification guidelines for organic farms successfully promote reliable environmental benefits, but greater reliance on ecological processes may reduce predictability of crop production.