Total Soil Organic Carbon Content Research Articles

Shining a Light on How Soil Organic Carbon Behaves at Fine Scales under Long-Term Elevated CO2: An 8 Year Free-Air Carbon Dioxide Enrichment Study.

Building and protecting soil organic carbon (SOC) are critical to agricultural productivity, soil health, and climate change mitigation. We aim to understand how mechanisms at the organo-mineral interfaces influence SOC persistence in three contrasting soils (Luvisol, Vertisol, and Calcisol) under long-term free air CO2 enrichment conditions. A continuous wheat-field pea-canola rotation was maintained. For the first time, we provided evidence to a novel notion that persistent SOC is molecularly simple even under elevated CO2 conditions. We found that the elevated CO2 condition did not change the total SOC content or C forms compared with the soils under ambient CO2 as identified by synchrotron-based soft X-ray analyses. Furthermore, synchrotron-based infrared microspectroscopy confirmed a two-dimensional microscale distribution of similar and less diverse C forms in intact microaggregates under long-term elevated CO2 conditions. Strong correlations between the distribution of C forms and O-H groups of clays can explain the steady state of the total SOC content. However, the correlations between C forms and clay minerals were weakened in the coarse-textured Calcisol under long-term elevated CO2. Our findings suggested that we should emphasize identifying management practices that increase the physical protection of SOC instead of increasing complexity of C. Such information is valuable in developing more accurate C prediction models under elevated CO2 conditions and shift our thinking in developing management practices for maintaining and building SOC for better soil fertility and future environmental sustainability.

High levels of soil calcium and clay facilitate the recovery and stability of organic carbon: Insights from different land uses in the karst of China.

Soil organic carbon (SOC) is a crucial medium of the global carbon cycle and is profoundly affected by multiple factors, such as climate and management practices. However, interactions between different SOC fractions and land-use change have remained largely unexplored in karst ecosystems with widespread rock outcrops. Owing to the inherent heterogeneity and divergent response of SOC to land-use change, soil samples with close depth were collected from four typical land-use types (cropland, grassland, shrubland, and forestland) in the karst rocky desertification area of China. The aim of this study was to explore the responses of SOC dynamics to land-use types and underlying mechanism. The results showed that land-use type significantly affected SOC contents and its fractions. Compared with cropland, the other three land uses increased the total organic carbon (TOC), microbial biomass carbon (MBC), and non-labile organic carbon (NLOC) contents by 6.11-129.44%, 32.58-173.73%, and 90.98-347.00%, respectively; this demonstrated that a decrease in both labile and recalcitrant carbon resulted in SOC depletion under agricultural land use. Readily oxidized organic carbon (ROC) ranged from 42 to 69%, accounting for almost half of the TOC in the 0-40-cm soil layer. Cropland soil showed significantly higher ROC:TOC ratios than other land-use types. These results indicated that long-term vegetation restoration decreased SOC activity and improved SOC stability. Greater levels of soil exchangeable calcium (ECa) and clay contents were likely responsible for higher stabilization and then accumulation of SOC after vegetation restoration. The carbon pool index (CPI) rather than the carbon pool management index (CPMI) exhibited consistent variation trend with soil TOC contents among land-use types. Thus, further study is needed to validate the CPMI in evaluating land use effects on soil quality in karst ecosystems. Our findings suggest that land-use patterns characterized by grass or forest could be an effective approach for SOC-sequestration potential and ensure the sustainable use of soil resources in the karst area.

A Properly Chosen Rate of NPK Fertilizers Has a Positive Effect on C Sequestration in Sandy Soils in the Conditions of a Changing Climate

Abstract Soil organic carbon (SOC) plays a significant role in climate change. Its content can be modified by soil management practices, however, the effect of mineral fertilization on SOC is not clear. For this reason, a long-term effect of gradually increasing rates of NPK fertilizers on changes in soil organic carbon (SOC) in bulk soil and in water-stable aggregates (WSA) in soils with sandy loam and loamy sand texture at two experimental sites (Skierniewice, Poland, and Dražovce, Slovakia) was quantified. In both sites, soil samples were collected from the following treatments: NF – no fertilization, NPK1 and NPK2 – 1st level and 2nd level of NPK fertilization, respectively. The results showed that 100-year long application of NPK1 increased total carbon (TC) and SOC content by 24%, while NPK2 decreased it by 5% compared to NF at the Skierniewice site. The content of water-stable macroaggregates (WSAma) increased because of NPK application. In NPK1, the content of WSAma was higher and the content of water-stable microaggregates (WSAmi) was lower than in NPK2 or NF. However, as a result of NPK application, the content of agronomically favorable WSAma in size fraction 0.5–3 mm was reduced by 8 and 24% in NPK1 and NPK2, respectively, compared to NF. Overall, SOC in WSAma was lower than in bulk soil. The SOC in WSAma in NF, NPK1 and NPK2 treatments was 6.51, 7.77 and 5.89 g.kg−1, respectively. Similar tendency of SOC in WSAma 0.5–3 mm was observed (NF: 6.12 g.kg−1, NPK1: 7.35 g.kg−1, and NPK2: 6.88 g.kg−1). The SOC in WSAmi in NF, NPK1 and NPK2 was 8.33, 7.39 and 7.24 g.kg−1, respectively. At Dražovce site, TC content decreased significantly due to the graded rates of NPK, not because of SOC mineralization but as a result of carbonate dissolution for a period of 14 years. The carbonate content decreased from 20 g.kg−1 in NF to 6.5 g.kg-1 in NPK1 and 3.0 g.kg-1 in NPK2, while SOC did not change significantly: (NF: 23.8 g.kg−1, NPK1: 25.9 g.kg−1, and NPK2: 23.4 g.kg−1). In NPK1, the WSAma content was reduced significantly when compared to NPK2 and NF treatments. No significant difference was observed between NF and NPK2. On the contrary, the content of WSAma 0.5–3 mm significantly increased when compared to NF and NPK1. No difference was observed between NF and NPK1. Lower SOC content was found in WSA than in the bulk soil. Overall, higher SOC content was observed in WSAma when compared with WSAmi. The application of NPK1 and NPK2 increased SOC in WSAma as well as in WSAma 0.5–3 mm. The effect was more significant in NPK1 than NPK2 treatments when compared to NF.

Enhanced Soil Carbon Stability through Alterations in Components of Particulate and Mineral-Associated Organic Matter in Reclaimed Saline–Alkali Drainage Ditches

Soil carbon content and stability are primarily influenced by the stabilization of particulate organic matter (POM) and mineral-associated organic matter (MAOM). Despite extensive research on the stabilization processes of POM and MAOM carbon components under various land-use types, the investigation into stabilization processes of soil carbon remains limited in saline–alkali soils. Therefore, we collected soil samples from different positions of saline–alkali drainage ditches at four reclamation times (the first, seventh, fifteenth, and thirtieth year) to determine their carbon content and physicochemical properties. Moreover, POM and MAOM fractions were separated from soil samples, and Fourier transform infrared spectra (FTIR) were used to investigate changes in their chemical composition. The results showed that with increasing reclamation time, the soil total carbon and soil organic carbon (SOC) contents significantly increased from 14 to 15 and 2.9 to 5.5 g kg−1, respectively. In contrast, soil inorganic carbon content significantly decreased from 11 to 9.6 g kg−1. Notably, the changes in soil carbon components following the increasing reclamation time were primarily observed in the furrow sole at a depth of 20–40 cm. While the SOC content of the POM fraction (SOCPOM) decreased significantly, the SOC content of the MAOM fraction (SOCMAOM) increased significantly. These alterations were largely dominated by drainage processes after reclamation instead of a possible conversion from SOCPOM to SOCMAOM. FTIR results revealed that MAOM was greatly influenced by the reclamation time more than POM was, but the change in both POM and MAOM contributed to an increase in soil carbon stability. Our findings will deepen the comprehension of soil carbon stabilization processes in saline–alkali drainage ditches after reclamation and offer a research framework to investigate the stability processes of soil carbon components via alterations in POM and MAOM fractions.

Mitigating methane emissions and global warming potential while increasing rice yield using biochar derived from leftover rice straw in a tropical paddy soil

The sustainable management of leftover rice straw through biochar production to mitigate CH4 emissions and enhance rice yield remains uncertain and undefined. Therefore, we evaluated the effects of using biochar derived from rice straw left on fields after harvest on greenhouse gas emissions, global warming potential (GWP), and rice yield in the paddy field. The experiment included three treatments: chemical fertilizer (CF), rice straw (RS, 10 t ha−1) + CF, and rice straw-derived biochar (BC, 3 t ha−1 based on the amount of product remaining after pyrolysis) + CF. Compared with CF, BC + CF significantly reduced cumulative CH4 and CO2 emissions, net GWP, and greenhouse gas emission intensity by 42.9%, 37.4%, 39.5%, and 67.8%, respectively. In contrast, RS + CF significantly increased cumulative CH4 emissions and net GWP by 119.3% and 13.8%, respectively. The reduced CH4 emissions were mainly caused by the addition of BC + CF, which did not increase the levels of dissolved organic carbon and microbial biomass carbon, consequently resulting in reduced archaeal abundance, unlike those observed in RS + CF. The BC + CF also enhanced soil total organic carbon content and rice grain yield. This study indicated that using biochar derived from leftover rice straw mitigates greenhouse gas emissions and improves rice productivity in tropical paddy soil.

Warming persistently stimulates respiration from an arable soil over a decade, regardless of reduced summer precipitation

Climate change factors alter soil microbial biomass and respiration, which represent two key parameters of carbon (C) cycling in soils. While these interrelations are increasingly well described for soils in natural ecosystems, long-term studies conducted in temperate agricultural ecosystems do rarely exist. Here we used the ‘Hohenheim Climate Change Experiment (HoCC)’ to describe the response of microbial biomass and respiration to interacting effects of climate change factors. We were interested in whether effects would be season specific, and if ultimately, climate change factors would affect the total soil organic carbon (SOC) content in the arable soil. The HoCC experiment is an agroecosystem where soils were permanently warmed for one decade, and summer precipitation amount and frequency were reduced. We found that soil respiration was not affected by reduced summer precipitation, but strongly increased by warming. This increase was not season specific and persisted over the years. Further, warming continuously enhanced labile C availability, while microbial biomass did not differ between warmed and ambient temperature soils. Therefore, soil respiration stimulated by warming was independent of microbial biomass, and accordingly, we found an increase of the metabolic quotient. Despite the warming induced increase in soil respiration, no indications for a loss in SOC content of the arable soil was detected. These results suggest that in an arable soil with overall low SOC content, the persisting stimulation of respiration due to warming is driven by an agroecosystem specific labile C pool dynamic.

Temporal and depth‐dependent variations in soil aggregate‐associated organic carbon in reclaimed coastal poplar plantations

AbstractCoastal reclamation alters the ecological environment of wetlands and influences global carbon cycles. However, variations in soil organic carbon fractions and stability in the soil profile during reclamation, particularly in the subsoil, remain unclear. In this study, soil aggregate‐associated organic carbon and its stability were investigated in soil profiles (0–100 cm) at different reclamation times (0, 24, 44, and 64 years) in coastal poplar plantations in East China. Total soil organic carbon concentrations in the topsoil (0–40 cm) increased with increasing reclamation time but varied little in the subsoil (40–100 cm). In the topsoil, the soil organic carbon concentrations in different aggregate fractions tended to increase with increasing reclamation time, which was enhanced mainly by particulate organic carbon within macro‐aggregates. In the subsoil, soil organic carbon concentrations increased in the micro‐aggregate fraction and decreased in the silt and clay fraction with increasing reclamation time, whereas the opposite changes led to smaller variations in total soil organic carbon. This relative balance was regulated by micro‐aggregate formation via new organic matter input (e.g., root litter) and old mineral‐associated organic carbon depletion. Regardless of the soil horizon, soil aggregate stability increased with reclamation time, whereas the total particulate organic carbon/mineral‐associated organic carbon ratio increased with increasing reclamation time, implying that the soil organic carbon stability decreased, which may be attributed to an increase in the vulnerability of soil organic matter to mineralization as the reclamation progresses. These findings indicate that long‐term plantation development influences aggregate‐associated organic carbon accrual throughout the soil profile in reclaimed coastal land. Thus, effective management is required to improve soil organic carbon accrual in coastal woodland subsoil, which is crucial for increasing soil carbon sequestration.

Residual Effect of Compost and Biochar Amendment on Soil Chemical, Biological, and Physical Properties and Durum Wheat Response

The residual effect of compost and biochar amendment on soil properties and durum wheat response was evaluated under field conditions in a Mediterranean environment. The treatments compared in a randomized complete block experimental design with three replications were: mineral fertilizer (100 kg N ha−1), compost applied at the rate of 25 Mg ha−1, biochar applied at the rates of 10 and 30 Mg ha−1, unfertilized control. Wheat was the second crop included in a sorghum–wheat cropping system and did not receive fertilizer supply. A hierarchical statistical analysis was carried out to investigate how different treatments could impact the cropping system performance. The findings highlight the significant influence of soil properties, particularly total N, WEOC, and TOC, on wheat and protein yield. One year after the amendment and fertilizer application, compost and biochar significantly increased soil total organic carbon content. The highest soil water extractable organic carbon was found with the compost application (76.9 mg kg−1), whereas the lowest value (50 mg kg−1) was with the highest rate of biochar. Soil respiration rates and hydraulic properties were not affected by the investigated treatments. This behavior is probably related to the short experimental duration and to the silty clayey soil texture. Significant correlations were observed between bulk density and water content at pressure heads in the −20 and −100 cm range; this range accounts for the effect of soil macro and mesopores. Multiple linear regression analysis revealed strong predictive power for grain (R2_adj = 0.78; p < 0.001) and protein yield (R2_adj = 0.77; p < 0.001). The highest grain yield (3.36 Mg ha−1) was observed with compost, and the lowest (2.18 Mg ha−1) with biochar at a rate of 30 Mg ha−1. These findings lay the basis for understanding how different soil amendment management may impact soil quality and wheat performance, even in consideration of climate change.

Optimizing the rate of straw returning to balance trade-offs between carbon emission budget and rice yield in China

Rice paddies are a prominent contributor to greenhouse gases (GHGs) emissions, accounting for 22 % of the overall agricultural methane (CH4) emissions. Although returning rice straw to the field can increase yield and soil organic carbon (SOC), the significant GHGs released during this process often negate these positive effects. Thus, understanding the impact of straw returning on the relationship between rice yield and GHGs is crucial for farming adaptation and climate change mitigation. This study aims to investigate the effects of varying straw returning rates on rice yield and GHGs in China and identify the optimal rates on a provincial scale. This study utilized county-level meteorological, soil, and field management data. The Dynamic Nitrogen and Carbon Model (DNDC) model was used to simulate the impacts on rice yield, GHGs, and SOC changes under different straw returning rates in China from 2010 to 2022, including no straw, 1/3, 2/3, and full straw returning. The results showed that 1/3, 2/3, and full straw incorporation increased rice yield per unit area by 1.07 %, 2.25 %, and 3.26 % for single rice cropping, 1.10 %, 2.24 %, and 3.52 % for early rice, and 1.92 %, 3.91 %, and 5.95 % for late rice, respectively. Compared with no straw returning, the total SOC content (0–50 cm) increased by 3.88 % (78.07 Tg), 7.75 % (156.09 Tg), and 11.65 % (234.62 Tg) under 1/3, 2/3, and full straw returning, respectively. However, the total GHGs were increased by 23.32 %, 43.50 %, and 61.48 % for 1/3, 2/3, and full straw incorporation compared to no straw returning. While the overall benefits of straw returning varied across regions, in certain areas like northeastern China, Xinjiang, and Yunnan, an increase in straw returning rates leads to a significant increase in yield with a relatively smaller increase in GHGs. This can be attributed to factors such as lower temperatures, decreased SOC, and lower soil pH, restricting CH4 production. Conversely, in regions with higher soil pH, such as north China and the Sichuan Basin, as well as in warmer southern areas, the increase in GHGs is quite pronounced. In summary, implementing straw returning significantly increases rice production and SOC but simultaneously increases GHGs. In China, the most widespread utilization of rice straw remains straw returning. We have summarized the average impact of straw returning on yield, SOC, and GHGs, and proposed straw returning rates tailored to the comprehensive benefits in different regions, to enhance the carbon sequestration and emission reduction rate of rice straw returning.

Effects of Water-Level Fluctuation on Soil Aggregates and Aggregate-Associated Organic Carbon in the Water-Level Fluctuation Zone of the Three Gorges Reservoir, China

Water-level fluctuation (WLF) can destroy soil aggregates and induce soil organic carbon (SOC) loss, potentially triggering impacts on the concentration of atmospheric carbon dioxide. However, responses of soil aggregate content and aggregate-associated organic carbon to WLF have not been well studied, especially in the water-level fluctuation zone (WLFZ) of the Three Gorges Reservoir (TGR). Therefore, samples from different elevations (145 m, 155 m and 165 m) in the WLFZ of the TGR were collected for experiments. The wet sieving method was used to divide soil into silt and clay (<0.053 mm), micro-aggregate (0.053–0.25 mm) and macro-aggregate (>0.25 mm). The K2Cr2O7-H2SO4 oxidation method was used to measure total SOC content in different soil aggregates. A modified Walkley and Black method was used to measure labile carbon in different soil aggregates. Results showed that macro-aggregate content substantially decreased, while micro-aggregate content remained stable and silt and clay fraction accumulated with a decrease in water-level elevations. Moreover, total SOC content and labile carbon in macro-aggregate were obviously higher than those in the micro-aggregate and the silt and clay fraction. Macro-aggregate contributed the most to SOC sequestration, while micro-aggregate contributed the least, and the contribution of macro-aggregate increased with a decrease in water-level elevations. We concluded that the macro-aggregate was the most active participant in the SOC sequestration process, and preferentially increasing the macro-aggregate content of the lowest water-level elevation was conducive to an improvement in soil carbon sequestration potential and would mitigate climate change.

Legacy effects of long‐term autumn leaf litter removal slow decomposition rates and reduce soil carbon in suburban yards

Societal Impact StatementAs cities grow, it is essential to understand how landscape management decisions in urban spaces alter ecosystem function. This study demonstrates that the ubiquitous practice of long‐term leaf litter removal in suburbs, even in relatively small patches of a yard, reduces the soil's ability to cycle nutrients in plant litter and results in lower amounts of carbon stored in the soil. Even two years of retaining leaves where they previously were removed is insufficient to restore decomposition rates or carbon pools. This research is an important step in creating best practices for litter management to maintain essential ecosystem functions, like carbon sequestration, water holding capacity, and soil fertility.Summary Seasonal senesced leaf litter removal eliminates considerable organic material from suburban soils annually. We test if this disturbance alters decomposition and carbon cycles and depletes soils of organic matter over time, creating persistent legacy effects. We used a factorial experimental design to implement 1–2 years of current leaf litter manipulations (remove or retain fallen leaves) within historically raked and unraked areas in suburban Maryland yards. We then compared total organic soil carbon and decomposition using a standardized substrate decomposition methodology (Tea Bag Index) across treatment plots. Long‐term litter removal in suburban yards reduced decomposition rates by 17% and total soil organic carbon concentration by up to 24% compared to areas where leaf litter was retained in situ. In contrast, short‐term management changes (1–2 years) did not significantly impact decomposition rates or total organic soil carbon concentrations. Our findings suggest that long‐term suburban litter raking creates legacy effects that alter decomposition and carbon storage process trajectories that are not easily reversed. This is important in understanding urban ecosystem function and sustainable management.

Evaluation of food and fodder based cropping systems for sustaining productivity, resource use efficiency and profitability in western plain zone of Uttar Pradesh

A field experiment was conducted during 2015–16 to 2018–19 at the research farm of ICAR-Indian Institute of Farming Systems Research, Modipuram, Uttar Pradesh to assess the potential yield (PY), sustainability and resource use efficiency (RUE) of 7 cropping systems (CS), viz. maize + blackgram–pea–sorghum; cluster beanwheat-teosinte; stylo-berseem-maize + cowpea; clitoria-mustard–greengram; rice–chickpea–okra; rice–wheat and sugarcane–wheat system. The experiment was laid out in randomized block design (RBD) with 3 replications. Among the different cropping systems, rice (Oryza sativa L.)–chickpea (Cicer arietinum L.)–okra (Abelmoschus esculentus L.) was found to be most superior in terms of wheat equivalent yield (WEY) (19.77 t/ha/year) and sustainable yield index (SYI=0.894). The highest land use efficiency (LUE) was recorded with cluster bean (Cyamopsis tetragonoloba L.)–wheat (Triticum aestivum L.)–teosinte (Zea spp.) cropping system (95.16%) with 347 days of ground cover. Production efficiency was registered maximum with maize (Zea mays L.) + blackgram [Vigna mungo (L.) Hepper]–pea (Pisum sativum L.)–sorghum [Sorghum bicolor (L.) Moench] system (66.91 kg/ha/ day), followed by rice–chickpea–okra system (62.25 kg/ha/day). Nevertheless, the highest net return (` 300.8×103 / year) was realized with rice–chickpea–okra system. Total soil organic carbon (SOC) content was highest (1.34%) under stylo-berseem- maize + cowpea [Vigna unguiculata (L.) Walp.] cropping system in comparison to other cropping systems. Thus, it can be concluded that rice–chickpea–okra system proved more productive, remunerative (` 824/ha/day) and sustainable cropping system than the existing sugarcane (Saccharum officinarum L.)–wheat/ rice–wheat cropping system in the western plain zone of Uttar Pradesh, India.

Spatial differentiation of soil nutrients and their ecological chemometrics based on geographic detector in National Agricultural Park of Tangchang, Southwest China.

In order to analyze the spatial variability of soil nutrients and their ecological chemometrics in Tangchang Town, National Agricultural Park, 20 influencing factors were selected: soil pH, Cd, Hg, As, Cu, Pb, Cr, Zn, Ni, Se, elevation, slope, aspect, land use type, distance from industrial land, distance from commercial land, distance from railway, distance from residential area, distance from highway and distance from river. The effects of various influencing factors on the spatial variability of total organic carbon (TOC), total nitrogen (N), total phosphorus (P), total potassium (K) and ecological stoichiometry were analyzed by means of geographic detector. The results showed that average contents of soil TOC, N, P and K in the study area are 10.24 g kg-1, 1.33 g kg-1, 1.14 g kg-1 and 23.60 g kg-1, respectively, and there were significant differences in the spatial distribution of soil nutrients and their eco-stoichiometry in the study area, and TOC, N, P, K, C/N, C/P, C/K, N/P, N/K and P/K has a significant correlation with each other and most correlation coefficients are above 0.5 or below -0.5. Factor detection showed that soil properties, distance from railway and distance from residential area had the most significant explanatory power to the spatial heterogeneity of soil nutrients and eco-stoichiometry. Interaction detection showed that the interaction between soil properties with other factors was the most important factor affecting the spatial differentiation of soil nutrients and their ecological chemometrics, and elevation, distance from railway and distance from residential area were also important factors. Risk detection showed that the differences of soil nutrients and their ecological stoichiometry were most significant in the subregions of soil properties (pH, Cd, Hg, As, Cu, Pb, Cr, Zn, Ni and Se).

Substituting readily available nitrogen fertilizer with controlled-release nitrogen fertilizer improves crop yield and nitrogen uptake while mitigating environmental risks: A global meta-analysis

ContextControlled-release nitrogen fertilizer (CRN) is considered as an efficient tool for improving crop total uptake of N (TUN) and crop yield by providing better synchronization of crop N demand, but its effects on crop productivity, greenhouse gases (GHG) emissions and N loss are variable across agroecosystems. Objective and methodsHere, we conducted a meta-analysis by synthesizing 8874 observations from 240 published studies to address the effects of substituting CRN for readily available N fertilizer on crop yield, TUN, profit, GHG emissions, and N loss in rice, maize, wheat, soybean, and rape, with focus on cereals. ResultsOverall, CRN could increase crop productivity (crop yield, 5.1 %; profit, 8.2 %; TUN, 7.1 %) and reduce environmental pollution (GHG emissions, −3.6 % to − 18.6 %; N loss, −32.6 % to −49.1 %). These efficacies varied among crops but showed similar trends in general. The effect of CRN on crop yield was modulated by the N rate and the ratio of CRN. The optimal N rate and CRN ratio to obtain higher crop yields and profits also varied with crops. The CRN efficacies for decreasing GHG emissions and N loss depended on the mean growing season temperature, mean growing season precipitation, background soil total organic carbon content and pH values, the regions, and the CRN ratio and coating materials. A synergy of CRN with other crop management practices, such as mulching and efficient irrigation, was an effective strategy for increasing both crop productivity and environmental benefits. ConclusionsSubstituting readily available nitrogen fertilizer with CRN could produce more food and obtain higher profits with less environmental risk in crops, especially in cereals. ImplicationsThis study provides new insights into the effect of plant-soil-climate-management systems on crop productivity and environmental benefits for Sustainable Development Goals.

Tree size diversity is the major driver of aboveground carbon storage in dryland agroforestry parklands

Despite the importance of agroforestry parkland systems for ecosystem and livelihood benefits, evidence on determinants of carbon storage in parklands remains scarce. Here, we assessed the direct and indirect influence of human management (selective harvesting of trees), abiotic factors (climate, topography, and soil) and multiple attributes of species diversity (taxonomic, functional, and structural) on aboveground carbon (AGC) stocks in 51 parklands in drylands of Benin. We used linear mixed-effects regressions and structural equation modeling to test the relative effects of these predictors on AGC stocks. We found that structural diversity (tree size diversity, HDBH) had the strongest (effect size β = 0.59, R2 = 54%) relationship with AGC stocks, followed by community-weighted mean of maximum height (CWMMAXH). Taxonomic diversity had no significant direct relationship with AGC stocks but influenced the latter indirectly through its negative effect on CWMMAXH, reflecting the impact of species selection by farmers. Elevation and soil total organic carbon content positively influenced AGC stocks both directly and indirectly via HDBH. No significant association was found between AGC stocks and tree harvesting factor. Our results suggest the mass ratio, niche complementarity and environmental favorability as underlying mechanisms of AGC storage in the parklands. Our findings also highlight the potential role of human-driven filtering of local species pool in regulating the effect of biodiversity on AGC storage in the parklands. We conclude that the promotion of AGC stocks in parklands is dependent on protecting tree regeneration in addition to enhancing tree size diversity and managing tall-stature trees.

Soil and litter properties from a riparian to non-riparian zone in a tropical dry forest

Riparian zones of dry tropical forests are important due to their effect on nutrient cycling and carbon dynamics. It’s important to evaluate the changes that occur when these areas are altered, in order to ascertain the magnitude of nutrient gains or losses. This work evaluates chemical changes in soil and litter transitioning from a riparian to a non-riparian zone. Plots were established for soil and litter sampling in riparian and non-riparian zones. For chemical analysis, litter and soil surface sampling were performed at depths of 0.0 to 0.10 m and 0.10 to 0.20 m. The descriptive and principal component analysis assessed chemical attribute sets' soil and litter characteristics. We observed higher P, K, and Ca content at both depths in soils of the non-riparian zone. The total soil organic carbon content in the non-riparian zones was 1.28 and 1.51 times greater at 0-10 and 10-20 cm depths, respectively than in the riparian zones. This study revealed that despite the chemical and organic inputs in the non-riparian zones, no significant differences were observed regarding the chemical properties of the soils of riparian areas as opposed to the soils of non-riparian areas since the litter of the riparian zones was richer in nutrients. Additionally, this study suggests that the humic acid and humin fractions are responsible for maintaining fertility in riparian areas due to strong correlations with soil nutrients.

The QuantiSlakeTest, measuring soil structural stability by dynamic weighing of undisturbed samples immersed in water

Abstract. We evaluated the performance of a new, simple test to evaluate soil structural stability. The QuantiSlakeTest (QST) consists in a quantitative approach of the slake test, a dynamic weighing of a dried structured soil sample once immersed in water. The objective of this work was threefold: we aimed to (i) derive indicators from QST curves to evaluate soil structural stability, (ii) establish the relationship between soil properties and QST indicators, and (iii) assess how QST indicators respond to contrasting soil management practices. To reach these goals, we sampled the soil of 35 plots from three long-term field trials in the silt loam region of Belgium dealing respectively with contrasting organic matter inputs, tillage and P–K fertilisation. For each plot, indicators calculated from QST curves (e.g. total relative mass loss, disaggregation speed and time to meet a threshold values of mass loss) were compared to the results of the three tests of Le Bissonnais (1996), used as a reference method for the measurement of soil aggregate stability. Shortly after immersion in water, soil mass increases due to the rapid replacement of air by water in soil porosity. Then soil mass reaches a maximum before decreasing, once mass loss by disaggregation exceeds mass gain by air loss. Our results confirmed that the early mass loss under water is mainly related to slaking, whereas after a longer time period, clay dispersion and differential swelling become the dominant processes of soil disaggregation. The overall soil structural stability was positively correlated to the soil organic carbon (SOC) content and negatively correlated to the clay content of soil. Consequently, the SOC : clay ratio was closely related to QST indicators. Nevertheless, for a similar mean annual carbon (C) input, green manure and crop residues were more efficient in decreasing clay dispersivity and differential swelling, whereas farmyard manure promoted SOC storage and was more efficient against slaking. QST curves had a strong discriminating power between reduced tillage and ploughing regardless of the indicator, as reduced tillage increases both total SOC content and root biomass in the topsoil. The QST has several advantages. It (i) is rapid to run, (ii) does not require expensive equipment or consumables, and (iii) provides a high density of information on both specific mechanisms of soil disaggregation and the overall soil structural stability. As an open-access programme for QST data management is currently under development, the test has a strong potential for adoption by a widespread community of end users.

Impact of agro-geotextiles on soil aggregation and organic carbon sequestration under a conservation-tilled maize-based cropping system in the Indian Himalayas

Although agro-geotextile (AGT) emplacement shows potential to mitigate soil loss and, thus, increase carbon sequestration, comprehensive information is scanty on the impact of using agro-geotextiles on soil organic carbon (SOC) sequestration, aggregate-associated C, and soil loss in the foothills of the Indian Himalayan Region. We evaluated the impacts of Arundo donax AGT in different configurations on SOC sequestration, aggregate stability, and carbon management index (CMI) since 2017 under maize-based cropping systems on a 4% land slope, where eight treatment procedures were adopted. The results revealed that A. donax placement at 0.5-m vertical-interval pea–wheat (M + AD10G0.5-P-W) treatment had ∼23% increase in SOC stock (27.87 Mg·ha−1) compared to the maize–wheat (M-W) system in the 0–30-cm soil layer. M + AD10G0.5-P-W and maize–pea–wheat treatments under bench terracing (M-P-W)BT had similar impacts on SOC stocks in that layer after 5 years of cropping. The total SOC values in bulk soils, macroaggregates, and microaggregates were ∼24, 20, and 31% higher, respectively, in plots under M + AD10G0.5-P-W treatment than M-W in the topsoil (0–5 cm). The inclusion of post-rainy season vegetable pea in the maize–wheat cropping system, along with AGT application and crop residue management, generated additional biomass and enhanced CMI by ∼60% in the plots under M + AD10G0.5-P-W treatment over M-W, although M + AD10G0.5-P-W and (M-P-W)BT had similar effects in the topsoil. In the 5–15-cm layer, there was no significant effect of soil conservation practices on CMI values. Under the M + AD10G0.5-P-W treatment, the annual mean soil loss decreased by ∼92% over M-W treatment. We observed that CMI, proportion of macroaggregates, aggregate-associated C, labile C, total SOC concentration (thus, SOC accumulation rate), and mean annual C input were strongly correlated with the mean annual soil loss from 2017 to 2021. The study revealed that the emplacement of an A. donax mat and incorporation of a legume in a cropping system (M-W), conservation tillage, and crop residue retention not only prevented soil loss but also enhanced C sequestration compared to farmers’ practice (M-W) in the Indian Himalayas. The significance of this study is soil conservation, recycling of residues and weeds, and climate change adaptation and mitigation, as well as increasing farmers’ income.

The Responses of N2O, CO2 Emissions, and Bacterial Communities to Nitrogen Addition in Saline–Alkaline Wetlands of Northeast China

The Zhalong Wetland is impacted by elevated atmospheric nitrogen (N) deposition and N inputs from agricultural fertilization, which in turn affect greenhouse gas (GHG) emissions. It is unclear how N addition affects nitrous oxide (N2O) and carbon dioxide (CO2) emissions in this wetland. Therefore, we conducted a short-term experiment, collecting soil samples from three representative points with different water levels, and five N addition levels (N0 = 0 mg N kg−1, N10 = 10 mg N kg−1, N30 = 30 mg N kg−1, N50 = 50 mg N kg−1, N100 = 100 mg N kg−1) were used to simulate N input. Overall, N2O emissions were significantly increased by N addition. Differently, N addition had a significant suppressive effect on CO2 emissions in high-flooded soils, whereas the highest CO2 emissions were regarded under the N30 treatment in middle-flooded and dry soils. Through Pearson’s correlation analysis, we found a significant positive correlation between N2O emissions and ammonium (NH4+), and CO2 emission was significantly positively correlated with pH and total organic carbon (TOC). Meanwhile, the bacterial community of the soil was analyzed via high-throughput sequencing. The results revealed that N addition was not significantly affecting soil bacterial community structure, while the three points were significantly different. Among them, the relative abundance of the dominant genera of Trichoderma and Pseudomonas were significantly enhanced after N addition. Furthermore, the bacterial communities were found to be significantly correlated with soil pH, TOC, NH4+, and nitrate contents, which affected N2O and CO2 emissions.

Prediction of perfluoroalkyl acids (PFAAs) in homegrown eggs: Insights into abiotic and biotic factors affecting bioavailability and derivation of potential remediation measures

Homegrown eggs from free-ranging laying hens often contain elevated concentrations of perfluoroalkyl acids (PFAAs). However, it is unclear which factors contribute to these relatively large exposure risk scenarios. Moreover, existing bioavailability and modeling concepts of conventional organic pollutants cannot be generalized to PFAAs due to their different physicochemical soil interactions. Therefore, there is an urgent need for empirical models, based on real-world data, to provide insights into how (a)biotic factors affect the bioavailability to eggs. To this end, 17 targeted analytes were analyzed in abiotic (i.e. rainwater, soil; both N = 101) matrices and homegrown eggs (N = 101), which were sampled in 101 private gardens across Flanders (Belgium) in 2019, 2021 and 2022. Various soil characteristics were measured to evaluate their role in affecting PFAA bioavailability to the eggs. Finally, PFAAs were measured in potential feed sources (i.e. homegrown vegetable and earthworm pools; respectively N = 49 and N = 34) of the laying hens to evaluate their contribution to the egg burden. Modeling suggested that soil was a major exposure source to laying hens, accounting for 16–55% of the total variation in egg concentrations for dominant PFAAs. Moreover, concentrations in vegetables and earthworms for PFBA and PFOS, respectively, were significantly positively related with corresponding egg concentrations. Predictive models based on soil concentrations, total organic carbon (TOC), pH, clay content and exchangeable cations were successfully developed for major PFAAs, providing possibilities for time- and cost-effective risk assessment of PFAAs in homegrown eggs. Among other soil characteristics, TOC and clay content were related with lower and higher egg concentrations for most PFAAs, respectively. This suggests that bioavailability of PFAAs to the eggs is driven by complex physicochemical interactions of PFAAs with TOC and clay. Finally, remediation measures were formulated that are readily applicable to lower PFAA exposure via homegrown eggs.