Increase Soil Organic Carbon Levels Research Articles

Effects of soil pH and organic carbon content on in vitro Cr bioaccessibility in Ultisol, Alfisol, and Inceptisol

Hexavalent chromium (Cr(VI)) is a toxic heavy metal and its mobility and bioaccessibility in soils are influenced by soil properties. In this study, the soil pH and organic carbon contents of Ultisol, Alfisol, and Inceptisol were adjusted before they were polluted with 230 mg kg−1 Cr(VI). Alkaline digestion, sequential extraction, and an in vitro experiment were conducted to study the valence state, species, and bioaccessibility of Cr in the soils. The results showed that a high soil pH was not favorable for reduction of Cr(VI); therefore the Cr(VI) and exchangeable Cr contents were positively related to soil pH. Soil organic carbon promoted the reduction of Cr(VI). Almost all Cr(VI) was reduced to Cr(III) when the soil organic carbon content reached 10 g kg−1. Chromium bioaccessibility in simulated gastric and intestinal phase solutions was influenced by Cr(VI) and Cr(III) adsorption/desorption, dissolution/precipitation, and redox reactions. Chromium bioaccessibility differences between the gastric and intestinal phases were associated with the Cr(VI)/Cr(III) ratio. Acidic conditions and a high organic carbon content promoted the conversion of Cr(VI) to Cr(III). When soil pH was increased from 4.01 to 5.85, Cr(VI) in Alfisol without the addition of humic acid increased from 96.38 to 174.78 mg kg−1, the exchangeable Cr proportion increased from 9.7% to 22.6%, and Cr bioaccessibility increased from 41.29% to 49.14% in the gastric phase and from 41.32% to 48.24% in the intestinal phase. When the organic carbon content increased from 3.95 to 9.28 g kg−1 in Alfisol, Cr(VI) content decreased from 167.66 to 20.52 mg kg−1, which led to a decrease in Cr bioaccessibility from 49.15% to 13.8% in the gastric phase and from 45.85% to 7.67% in the intestinal phase. Therefore, acidic conditions and increasing soil organic carbon levels can reduce the health risk posed by Cr in soils.

Effects of tillage management on cbbL-carrying bacteria and soil organic carbon dynamics across aggregate size classes in the farmland of North China Plain

Calvin-Benson-Bassham cycle (cbbL)-carrying bacteria in soil are essential to renew and circulate organic matter. However, the relation between cbbL-carrying bacteria and soil carbon dynamics under tillage managements, especially across the aggregate size remains unclear. Thus, in our study, soil organic carbon (SOC) storages, mineralization, and the cbbL-carrying bacterial community across five soil aggregate sizes were thoroughly investigated under four tillage treatments: conventional rotary tillage (CT), deep plowing (DP), subsoiling (SS), no-tillage (NT). We found macroaggregates (>2 mm) contributed most with regard to SOC stocks, whereas microaggregates (<0.25 mm) contributed the least among all the tillage managements (NT, DP, SS and CT). Macroaggregates (>1 mm) with the highest cumulative SOC mineralization were found in subsoiling, whereas microaggregates had the lowest cumulative mineralization under no-tillage. By physically protecting, no-tillage specifically inhibited carbon dioxide (CO2) emissions in macroaggregates (>1 mm), whereas increased SOC levels and encouraged CO2 releases across microaggregates. Shifts in the co-occurrence network demonstrated that subsoiling promoted the joint symbiotic function between cbbL-carrying bacteria, the efficiency of matter and energy, and information transfer. And the keystone species, the enhanced cooperation and stochastic processes of autotrophic microorganisms under subsoiling lead to increased carbon fixation and reduced CO2 emissions in microaggregates with limited oxygen and nutrients. Overall, our work verified physical protection of large aggregates under no-tillage and improvement of microbial interaction efficiency under subsoiling. This may offer a theoretical foundation for the choice of tillage practices in fluvo-aquic soil regions.

Negative responses of terrestrial nitrogen fixation to nitrogen addition weaken across increased soil organic carbon levels

The traditional view holds that biological nitrogen (N) fixation is energetically expensive and thus, facultative N fixers reduce N fixation rates while obligate N fixers are excluded by non-N fixers as soil N becomes rich. This view, however, contradicts the phenomenon that N fixation does not decline in many terrestrial ecosystems under N enrichment. To address this paradoxical phenomenon, we conducted a meta-analysis of N fixation and diazotroph (N-fixing microorganism) community structure in response to N addition across terrestrial ecosystems. N addition inhibited N fixation, but the inhibitory effect weakened across increased soil organic carbon (SOC) concentrations. The response ratios of N fixation (including free-living, plant-associated, and symbiotic types) to N addition were lower in the ecosystems with low SOC concentrations (<10 mg/g) than in those with medium or high SOC concentrations (10–20 and > 20 mg/g, respectively). The negative N-addition effects on diazotroph abundance and diversity also weakened across increased SOC levels. Among the climatic and soil factors, SOC was the most important predictor regarding the responses of N fixation and diazotroph community structure to N addition. Overall, our study reveals the role of SOC in affecting the responses of N fixation to N addition, which helps understand the relationships of biological N fixation and N enrichment as well as the mechanisms of terrestrial C and N coupling.

Carbon farming: Are soil carbon certificates a suitable tool for climate change mitigation?

Increasing soil organic carbon (SOC) stocks in agricultural soils removes carbon dioxide from the atmosphere and contributes towards achieving carbon neutrality. For farmers, higher SOC levels have multiple benefits, including increased soil fertility and resilience against drought-related yield losses. However, increasing SOC levels requires agricultural management changes that are associated with costs. Private soil carbon certificates could compensate for these costs. In these schemes, farmers register their fields with commercial certificate providers who certify SOC increases. Certificates are then sold as voluntary emission offsets on the carbon market.In this paper, we assess the suitability of these certificates as an instrument for climate change mitigation. From a soils' perspective, we address processes of SOC enrichment, their potentials and limits, and options for cost-effective measurement and monitoring. From a farmers’ perspective, we assess management options likely to increase SOC, and discuss their synergies and trade-offs with economic, environmental and social targets. From a governance perspective, we address requirements to guarantee additionality and permanence while preventing leakage effects. Furthermore, we address questions of legitimacy and accountability.While increasing SOC is a cornerstone for more sustainable cropping systems, private carbon certificates fall short of expectations for climate change mitigation as permanence of SOC sequestration cannot be guaranteed. Governance challenges include lack of long-term monitoring, problems to ensure additionality, problems to safeguard against leakage effects, and lack of long-term accountability if stored SOC is re-emitted. We conclude that soil-based private carbon certificates are unlikely to deliver the emission offset attributed to them and that their benefit for climate change mitigation is uncertain. Additional research is needed to develop standards for SOC change metrics and monitoring, and to better understand the impact of short term, non-permanent carbon removals on peaks in atmospheric greenhouse gas concentrations and on the probability of exceeding climatic tipping points.

Biological soil quality and soil organic carbon change in biodynamic, organic, and conventional farming systems after 42 years

Soils are the basis of life on land and the ways in which we manage them for crop production, impact their role, functions and quality. Conventional farming uses industrial inputs to a level that is economically justified, whilst organic farming systems avoid mineral fertilizers and synthetic chemical pesticides. This study investigates the long-term effect of organic and conventional farming systems on soil quality. The DOK trial (bioDynamic, bioOrganic, Konventionell (German for conventional)) running since 1978 in Therwil (CH), compares bioorganic (BIOORG), biodynamic (BIODYN), and conventional (CONFYM) farming systems at two farmyard manure intensities corresponding to 0.7 and 1.4 livestock units per hectare with a purely mineral fertilized system (CONMIN) and an unfertilized control (NOFERT). The treatments in the DOK trial vary in plant protection and receive system-specific organic matter inputs differing in rate and quality. With this work, we revisit the soil organic carbon (SOC) dynamics across 42 years and redefine the previous perception of mainly declining SOC contents after 21 years of organic and conventional management (Fliessbach et al. 2007). After 42 years, we found SOC contents to be increased in BIODYN 1.4 and to a lesser extent also in BIOORG 1.4. CONFYM 1.4 showed stable SOC contents, while systems fertilized with manure of 0.7 livestock units and CONMIN lost SOC. SOC loss was highest in NOFERT. Enhanced biological soil quality under organic and particularly biodynamic management highlights the close link between soil biology and SOC changes. The impact of farming systems on SOC was detectable after 2 decades of continuous management. We conclude that recycling manure at a level of 1.4 livestock units per hectare permits maintenance of SOC levels and that composting manure, as performed in BIODYN 1.4, helps to further increase SOC levels and improve biological soil quality.

Contribution of Fine Roots to Soil Organic Carbon Accumulation in Different Desert Communities in the Sangong River Basin.

This study explored the relationship between soil organic carbon (SOC) and root distribution, with the aim of evaluating the carbon stocks and sequestration potential under five plant communities (Alhagi sparsifolia, Tamarix ramosissima, Reaumuria soongorica, Haloxylon ammodendron, and Phragmites communis) in an arid region, the Sangong River watershed desert ecosystem. Root biomass, ecological factors, and SOC in different layers of a 0–100 cm soil profile were investigated. The results demonstrated that almost all living fine root biomass (11.78–34.41 g/m2) and dead fine root biomass (5.64–15.45 g/m2) levels were highest in the 10–20 cm layer, except for the P. communis community, which showed the highest living and dead fine root biomass at a depth of 60–70 cm. Fine root biomass showed strong seasonal dynamics in the five communities from June to October. The biomass levels of the A. sparsifolia (138.31 g/m2) and H. ammodendron (229.73 g/m2) communities were highest in August, whereas those of the T. ramosissima (87.76 g/m2), R. soongorica (66.29 g/m2), and P. communis (148.31 g/m2) communities were highest in September. The SOC of the five communities displayed strong changes with increasing soil depth. The mean SOC value across all five communities was 77.36% at 0–30 cm. The highest SOC values of the A. sparsifolia (3.08 g/kg), T. ramosissima (2.35 g/kg), and R. soongorica (2.34 g/kg) communities were found in June, and the highest value of the H. ammodendron (2.25 and 2.31 g/kg, p > 0.05) community was found in June and September. The highest SOC values of the P. communis (1.88 g/kg) community were found in July. Fine root production and turnover rate were 50.67–486.92 g/m2/year and 1.25–1.98 times per year. The relationships among SOC, fine root biomass, and ecological factors (soil water content and soil bulk density) were significant for all five communities. Based on the results, higher soil water content and soil conductivity favored the decomposition of root litter and increased fine root turnover, thereby facilitating SOC formation. Higher pH and bulk density levels are not conducive to soil biological activity and SOC mineralization, leading to increased SOC levels in desert regions.

Effect of shifting cultivation and fallow on soil quality index in Mokokchung district, Nagaland, India

BackgroundShifting cultivation is a major agriculture practice in the Nagaland state of India. This study examines the effect of shifting cultivation and the length of the fallow period on soil quality index (SQI). Four sites were selected for the study, viz., a shifting cultivation site (SCS), a 3-year-old fallow land (FL-3), a 7-year-old fallow land (FL-7), and a 12-year-old fallow land (FL-12). Soil parameters were recorded seasonally and SQI was calculated from the minimum data set.ResultsWith the increase in the fallow period, the values of conductivity, soil organic carbon, available nitrogen, available phosphorus, exchangeable potassium, moisture, clay, and cation exchange capacity of soil increased. Meanwhile, soil pH and bulk density decreased with fallow duration. The additive SQIa values were in the order SCS < FL-3 < FL-12 < FL-7; meanwhile, the weighted SQIw values were in the order SCS < FL-3 < FL-7 < FL-12. It is also observed that the SQI value decreases with the increase in soil depth under both the weighted and additive indexes. SCS with the lowest SQI value reflects the reduced soil organic carbon (SOC) and macronutrients. Increased SOC levels in site FL-12 (2.88–3.94%) may be one reason for its higher SQI value.ConclusionsOur study highlights that unsustainable practices of shifting cultivation and reduction in the fallow period negatively affect soil quality. Furthermore, the study also recommends the use of the weighted method of SQI as it agrees with the reports of land use causing alteration in the soil quality. Our findings may be utilized to quickly access and disseminate information to the stakeholders and aid in constructing local soil quality index maps of the region. There is an urgent need for a rapid, cost and resource-efficient soil quality assessment and SQI may be one tool that achieves this goal.

Conservation agriculture practices drive maize yield by regulating soil nutrient availability, arbuscular mycorrhizas, and plant nutrient uptake

Conservation agriculture (CA) can sustainably increase crop productivity through improved soil chemical, physical, and biological properties, among others. However, the implementation of all its three main components (i.e., no-tillage, organic soil cover/mulch, and crop diversification) in southern Africa is often challenging, resulting in variable yield responses. Disentangling the contributions of CA practices is necessary to understand the drivers of maize grain yield within the region. Here we analysed two 6-year long component omission experiments, one at a sandy soil location and the other at a clay soil location. In these two experiments, soil chemical parameters, total plant nutrient uptake, rate of crop residue decomposition, and arbuscular mycorrhizal fungi (AMF) colonization of maize roots were assessed. Soil chemical properties only differed across systems at the sandy soil location with the mulched systems under no-tillage (NT) resulting in increased soil organic carbon levels, total nitrogen, and soil available phosphorus as compared to conventional tillage with no mulch or rotation (CT). Conventional tillage-based systems resulted in fastest decomposition of maize residues, while systems with NT and rotation resulted in highest AM fungal root colonization rate of maize at the clay soil location. Total plant N uptake was almost 2-fold higher in tilled and no-tilled systems with both mulch (M) and rotations (R) (i.e., NT+M+R and CT+M+R) as compared to CT. Structural equation modeling was used to disentangle the links between cropping systems, soil chemical and biological properties, plant nutrient uptake, and maize grain yield. Cropping systems had direct and indirect influences on yield at both locations. At both locations, cropping systems influenced yield via plant N uptake, with the NT+M+R and CT+M+R systems having more beneficial effects compared to other systems, as shown by their higher path coefficients. In conclusion, we recommend a more holistic approach to cropping system assessment that includes a higher number of abiotic and biotic determinants. This would allow for a more rigorous evaluation of the drivers of yield and increase our understanding of the effects and performance of practices under the prevailing agro-ecological conditions. • Mulching under no-tillage increase soil organic carbon (SOC) and total nitrogen (N) • No-tillage plus rotation improve symbiosis of arbuscular mycorrhizal fungi & maize • Conventional tillage enhances stover decomposition but reduces SOC and N build-up • Conservation agriculture influences maize yield positively via nitrogen uptake

Soil organic carbon stock in arid and semi-arid steppe rangelands of North Africa

The assessment of soil organic carbon stock (SOCS) in degraded and rehabilitated soils in steppelands and rangelands of North Africa is crucial for the adoption of adequate management strategies that respond to sustainable development. This study aimed to estimate the SOCS in the surface layer of soils rehabilitated by prickly pear plantations (PPP) and analyze the effects of edaphic factors controlling the variation of SOCS in old PPP (OPPP), young PPP (YPPP) and control plots (unplanted plots). Under arid and semi-arid climates, three steppe sites were sampled in which three plots with OPPP (age = 10–20 years), YPPP (age < 5 years) and controls plots were considered. In each plot, five quadrats were delimited and within each quadrat, two pedological profiles were dug to collect soil samples. The determined parameters were soil organic carbon (SOC), bulk density (BD), pH, electrical conductivity (EC) and total calcium carbonate. The averages of SOCS varied between 14.51 ± 11.03 t/ha (min–max: 0.09–35.88 t/ha) under arid climate and 17.32 ± 9.05 t/ha (range: 0.26–41.84 t/ha) under semi-arid climate. The variations of SOCS were significant (P = 0.002) between the type of steppe managements but not significant (P > 0.05) among climate zones. Generally, the control plots and OPPP stored more carbon (14–19 t/ha) than steppes with YPPP (11–14 t/ha). SOCS varied significantly with changes in soil depths, it reached 27 t/ha at 15 cm and dropped to 10–18 t/ha at 20 cm. Regardless of the type of climate and rangeland management, SOCS evolved with BD and soil organic matter. This study estimated for the first time the SOCS in soils of degraded steppe rangelands in North Africa. Even if the SOCS remains low degraded steppes rangelands, it is necessary to avoid the loss of SOC in these ecosystems. The adoption of conservation agricultural practices, e.g. organic matter addition and reduced tillage techniques can increase SOC levels in these ecosystems.

EFFECT OF KITCHEN WASTE COMPOST ON TOMATO YIELD AND CARBON ACCUMULATION IN SOIL

Two years field study was conducted on the effect of kitchen waste compost on tomato yield and carbon accumulation in soil at Regional Agricultural Research Station (RARS), Jamalpur, Bangladesh under Old Brahmaputra Floodplain (AEZ 9) during rabi season of 2020-2021 and 2021-2022. The objectives were to determine whether composted kitchen waste would increase soil organic carbon levels and tomato yield. The BARI tomato-21 was utilized as the test crop, and the experiment was set up using a randomized complete block design (RCBD) with three replications. There were seven treatments comprising T1 = 100 % RDCF (control), T2=100 % RDCF + Kitchen Waste Compost @ 2.5 t ha-1, T3 = 100 % RDCF + Kitchen Waste Compost @ 5 t ha-1, T4 = 85% RDCF + Kitchen Waste Compost @ 2.5 t ha-1, T5 = 85% RDCF + Kitchen Waste Compost @ 5 t ha-1, T6 =70% RDCF + Kitchen Waste Compost @ 2.5 t ha-1 and T7 = 70% RDCF + Kitchen Waste Compost @ 5 t ha-1. Data revealed that, combined application of kitchen waste compost and chemical fertilizer increased tomato production as compared to sole application of chemical fertilizers. The highest average tomato fruit yield (68.46 t ha-1) was found in T3 treatment (100 % RDCF + Kitchen Waste Compost @ 5 t ha-1). T1 treatment (100 % RDCF) yielded 55.82 t ha-1 of tomatoes, indicating that plants could not receive enough nutrients from a single application of chemical fertilizer. On the other hand, as chemical fertilizers were reduced, tomato yield gradually declined. The T6 treatment (70 % RD + kitchen waste compost @ 2.5 t ha-1) had the lowest average tomato output, 52.73 t ha-1. The T3 treatment (100 % RDCF + kitchen waste compost @ 5 t ha-1) performed better after the second cycle was finished in terms of total nutrient content in post-harvest soil. In comparison to previous treatments, this treatment also increased soil carbon accumulation. As a result, it is practicable to apply the full dose of chemical fertilizer with 5 t ha-1 kitchen waste compost, which will boost tomato yields, bring about economic benefits and prevent soil and environmental contamination.

Challenges and Potentials for Soil Organic Carbon Sequestration in Forage and Grazing Systems

Forage and grazing (FG) systems can store a substantial amount of soil organic carbon (SOC) under appropriate land use management and reduce atmospheric CO2 concentrations. Increasing SOC levels along with many interlinked ecosystem services are essential for increased productivity and sustainability of FG lands (FGLs). Although adoption of improved management practices (MPs) that support SOC sequestration (SOCq) is necessary, clear understandings of challenges and opportunities which are sometimes unique to individual FGLs, are also important for implementation of MPs. The objective of this forum paper is to explore the latest scientific knowledge on opportunities to address major challenges for increasing SOCq in FGLs. In intensively managed FGLs where the goal is often to maximize yields, lands are heavily fertilized and thus, usually drive towards SOC loss. Diversifications of both forage and grazing species along with strategic grazing plans have been proven as effective MPs for increasing SOCq. However, challenge of maintaining productivity levels still remains. Implementing improved grazing for nutrient cycling and integrating forage diversification for increased biodiversity are found to improve soil health attributes, which are critical for SOCq. However, to achieve this, we also need to consider site- and soil- specific factors. Extreme climatic events often lead to a decline in soil fertility status, SOCq and overall productivity of FGL systems. To address these challenges, uses of models to simulate the FGL systems and have definite choices of suitable MPs are helpful. However, we must be able to access a wide range of datasets to develop system-level adaption strategies that are effective in mitigating these adverse effects. Ultimately, participatory research with novel views and improved perceptions based on the value of SOCq and long-term benefits of the implementation of the best MPs and developing education and outreach materials to enrich the producers’ knowledge gaps are helpful for climate-resilient FGL systems.

Impacts of climate variability and adaptation strategies on crop yields and soil organic carbon in the US Midwest.

Climate change is likely to increase the frequency of drought and more extreme precipitation events. The objectives of this study were i) to assess the impact of extended drought followed by heavy precipitation events on yield and soil organic carbon (SOC) under historical and future climate, and ii) to evaluate the effectiveness of climate adaptation strategies (no-tillage and new cultivars) in mitigating impacts of increased frequencies of extreme events and warming. We used the validated SALUS crop model to simulate long-term maize and wheat yield and SOC changes of maize-soybean-wheat rotation cropping systems in the northern Midwest USA under conventional tillage and no-till for three climate change scenarios (one historical and two projected climates under the Representative Concentration Path (RCP) 4.5 and RCP6) and two precipitation changes (extreme precipitation occurring early or late season). Extended drought events caused additional yield reduction when they occurred later in the season (10–22% for maize and 5–13% for wheat) rather than in early season (5–17% for maize and 2–18% for wheat). We found maize grain yield declined under the projected climates, whereas wheat grain yield increased. No-tillage is able to reduce yield loss compared to conventional tillage and increased SOC levels (1.4–2.0 t/ha under the three climates), but could not reverse the adverse impact of climate change, unless early and new improved maize cultivars are introduced to increase yield and SOC under climate change. This study demonstrated the need to consider extreme weather events, particularly drought and extreme precipitation events, in climate impact assessment on crop yield and adaptation through no-tillage and new genetics reduces yield losses.

Cambios en el contenido de carbono orgánico del suelo tras el rolado de bosques secos en San Luis (Argentina)

Fil: Somovilla Lumbreras, David. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - San Luis. Instituto de Matematica Aplicada de San Luis Prof. Ezio Marchi. Universidad Nacional de San Luis. Facultad de Ciencias Fisico, Matematicas y Naturales. Instituto de Matematica Aplicada de San Luis Prof. Ezio Marchi; Argentina

Long term biochar effects on corn yield, soil quality and profitability in the US Midwest

Corn production in the US Midwest has the potential to generate a large amount of crop residue for bioenergy production. However, unconstrained harvesting of crop residues is associated with a long-term decline in soil quality. Biochar applications can mitigate many of the negative effects of residue removal but data and economic analyses to support decision making are lacking. To explore sustainable and profitable practices for residue harvesting in central Iowa we used 11 years of soil, crop yield, and management data to calibrate the Agricultural Production Systems sIMulator (APSIM) biochar model. We then used the model to evaluate how different biochar types and application rates impact productivity and environmental performance of conventional corn and corn-soybean cropping systems in Iowa under different N fertilizer application rates and residue harvesting scenarios. A cost-benefit analysis was also employed to identify the economically optimal biochar application rate from both producer and societal perspectives. Modeling results showed for both continuous corn and corn-soybean rotations that as biochar application rate increased (0–90 Mg ha−1) nitrate leaching decreased (2.5–20%) and soil carbon levels increased (8–115%), but there was only a small impact on corn yields (–2.6 to 0.6%). The cost-benefit analysis revealed that public benefits, evaluated from decreased nitrate leaching and increased soil carbon levels, significantly outweighed the private revenue accrued from crop yield gains, and that a biochar application rate of 22 Mg ha−1 was more cost-effective (per ton) compared to higher biochar rates. Overall, this study found that applying biochar once at a rate of 22 Mg ha−1 allows for the sustainable annual removal of 50% of corn residue for 32 years, is profitable for farmers even with minimal impact on grain yield, and beneficial to society through reduced nitrate leaching and increased soil organic carbon levels.

Conversion of native rangelands into cultivated pasturelands in subtropical ecosystems: Impacts on aggregate-associated carbon and nitrogen

Soil organic carbon (SOC) plays a critical role in the sustainability of grazingland ecosystems around the world. However, maintaining or increasing SOC levels remains a major challenge, particularly in subtropical regions where coarse-textured soils predominate. This study evaluated the long-term (>20 years) impacts of grazingland intensification (conversion of native rangelands into more intensively managed silvopasture and sown pasture) on SOC and nitrogen (N) responses in particle size/density fractions. Treatments consisted of field replicated (n = 2) experimental sites that represented a gradient of intensification ranging from native rangelands (low intensification), pine (Pinus spp.)-bahiagrass (Paspalum notatum) silvopasture (moderate intensification), and bahiagrass pastures (high intensification). Soil organic C and N increased in response to the conversion of native rangelands into more intensively managed grazinglands, but no difference was observed in total SOC and N between silvopasture and sown pasture. Despite the positive impact of intensification on SOC and N pools, accumulation occurred primarily in more labile fractions. For instance, at the 0 to 10 cm depth, light-free C (LF-C) increased from 12.9 g kg−1 soil in the native rangeland to 24.7 g kg−1 soil in the sown pasture. Largest differences between the ecosystems were observed at the 10 to 20 cm depth where LF-C increased by as much as 170% following the conversion from native rangelands to sown pasture. Similar responses were also observed for N. Grazingland intensification showed no effect on soil aggregation, but SOC and N associated with macroaggregates (2,000 to 250 μm) increased with intensification. Results indicate that grazingland intensification promoted SOC and N accumulation, primarily through an increase in the LF fraction.

Multi-year and multi-location soil quality and crop biomass yield responses to hardwood fast pyrolysis biochar

Biochar can remediate degraded soils and maintain or improve soil health, but specific and predictable effects on soil properties and crop productivity are unknown because of complex interactions associated with climate patterns, inherent soil characteristics, site-specific crop and soil management practices, and the source, production characteristics, and amount of biochar applied. This multi-location field study was designed and conducted to determine if consistent response patterns could be elucidated by controlling the type and amount of biochar applied, depth of incorporation, and soil/crop management practices as much as possible for six U.S. locations. When averaged for five reporting locations, biochar or biochar plus manure (bio+man) treatments significantly (P<0.001) increased surface (0–15cm) soil organic carbon (SOC) levels by 48 or 47%, respectively, relative to control treatments. The SOC levels for the manure only treatment were not significantly different from the control. No other measured soil properties showed significant biochar or biochar×manure interactions, even though applying manure significantly increased extractable K, Mg, Na, and P levels. Analysis of three or four years of pooled biomass yield data from the six locations showed a significant location effect (P<0.001), but treatment effects were not significant. However, dividing annual plot yields by the average for all control plots at each location created a dataset of relative yields that showed a significant location×treatment interaction and higher normalized yields (36%) due to biochar (P=0.017) at one of the six locations. Overall, we conclude that hardwood biochar produced by fast pyrolysis can be an effective soil amendment for increasing SOC levels within a broad range of temperate soils, but crop yield responses should be anticipated only when specific soil quality problems limit productivity.

Effect of organic and mineral fertilizers on soil P and C levels, crop yield and P leaching in a long term trial on a silt loam soil

The main objective of the present study was to compare fertilizer types in their ability to increase the soil organic matter content without increasing potential P leaching losses. Differences in soil organic carbon content, crop yield, P-CaCl2, P-AL, P export by the crop and P leaching from soil supplied with three compost types, cattle slurry, farmyard manure or mineral fertilizers were compared in a 8 years field experiment with arable, vegetable and fodder crops. P leaching losses were assessed separately in a soil column leaching experiment. As expected, farmyard manure and compost are the better options to increase the soil organic carbon level. Cattle slurry and mineral fertilizers tended to produce lower crop yields. P-CaCl2 was increased when farmyard manure was used as organic fertilizer, leading to an increased P leaching but not to an increased crop P export. Therefore it seems that the higher dissolved P concentrations in the soil solution for farmyard manure, measured as P-CaCl2 in the soil, are a source of potential P losses. All three compost types could gradually increase soil organic carbon levels without increasing P leaching losses.

Chinese Grain for Green Program led to highly increased soil organic carbon levels: A meta-analysis

The Grain for Green Program (GGP), initiated in 1999, is the largest ecological restoration project in central and western China. Here, for the first time, we performed a meta-analysis and found that the GGP largely increased the soil organic carbon (SOC). The SOC was increased by 48.1%, 25.4%, and 25.5% at soil depths of 0–20 cm, 20–40 cm, and 40–60 cm, respectively. Moreover, this carbon accumulation has significantly increased over time since GGP implementation. The carbon accumulation showed a significantly more active response to the GGP in the top 20 cm of soil than in the deeper soil layers. Conversion of cropland to forest could lead to significantly greater SOC accumulation than would the conversion of cropland to grassland. Conversion from cropland to woodland could lead to greater SOC accumulation than would the conversion to either shrubland or orchard. Our results suggest that the GGP implementation caused SOC to accumulate and that there remains a large potential for further accumulation of carbon in the soil, which will help to mitigate climate change in the near future.

Uncertainty in soil carbon accounting due to unrecognized soil erosion

The movement of soil organic carbon (SOC) during erosion and deposition events represents a major perturbation to the terrestrial carbon cycle. Despite the recognized impact soil redistribution can have on the carbon cycle, few major carbon accounting models currently allow for soil mass flux. Here, we modified a commonly used SOC model to include a soil redistribution term and then applied it to scenarios which explore the implications of unrecognized erosion and deposition for SOC accounting. We show that models that assume a static landscape may be calibrated incorrectly as erosion of SOC is hidden within the decay constants. This implicit inclusion of erosion then limits the predictive capacity of these models when applied to sites with different soil redistribution histories. Decay constants were found to be 15-50% slower when an erosion rate of 15tsoilha(-1) yr(-1) was explicitly included in the SOC model calibration. Static models cannot account for SOC change resulting from agricultural management practices focused on reducing erosion rates. Without accounting for soil redistribution, a soil sampling scheme which uses a fixed depth to support model development can create large errors in actual and relative changes in SOC stocks. When modest levels of erosion were ignored, the combined uncertainty in carbon sequestration rates was 0.3-1.0t CO2 ha(-1) yr(-1) . This range is similar to expected sequestration rates for many management options aimed at increasing SOC levels. It is evident from these analyses that explicit recognition of soil redistribution is critical to the success of a carbon monitoring or trading scheme which seeks to credit agricultural activities.

The impact of agricultural land use changes on soil organic carbon dynamics in the Danjiangkou Reservoir area of China

Over recent decades, a large uncultivated area has been converted to woodland and shrubland plantations to protect and restore riparian ecosystems in the Danjiangkou Reservoir area, a water source area of China’s Middle Route of the South-to-North Water Transfer Project. Besides water quality, afforestation may alter soil organic carbon (SOC) dynamics and stock in terrestrial ecosystems, but its effects remain poorly quantified and understood. We investigated soil organic C and nitrogen (N) content, and δ 13C and δ 15N values of organic soil in plant root-spheres and open areas in an afforested, shrubland and adjacent cropped soil. Soil C and N recalcitrance indexes (RIC and RIN) were calculated as the ratio of unhydrolyzable C and N to total C and N. Afforestation significantly increased SOC levels in plant root-spheres with the largest accumulation of C in the afforested soil. Afforestation also increased belowground biomass. The C:N ratios in organic soil changed from low to high in the order the cropped, the shrubland and the afforested soil. The RIC in the afforested and shrubland were higher than that in cropped soil, but the RIN increased from the afforested to shrubland to cropped soil. The δ15N values of the organic soil was enriched from the afforested to shrubland to cropped soil, indicating an increased N loss from the cropped soil compared to afforested or shrubland soil. Changes in the δ13C ratio further revealed that the decay rate of C in the three land use types was the highest in the cropped soil. Afforestation increased the SOC stocks resulted from a combination of large C input from belowground and low C losses because of decreasing soil C decomposition. Shifts in vegetation due to land use change could alter both the quantity and quality of the soil C and thus, have potential effects on ecosystem function and recovery.