Soil Organic Carbon Density Research Articles

Effects of Straw Mulching Thickness on the Soil Health in a Temperate Organic Vineyard

Soil mulching is one of the common measures applied in organic agricultural production which could replace plastic films and protect the environment. In order to fully evaluate the effects of different straw mulching thicknesses on soil health, maize straw was mulched with the thicknesses of 0 cm (CK), 2 cm, 4 cm and 6 cm on soil surface to assess the effects on soil temperature (ST) and moisture (SM), soil pH, soil organic carbon (SOC), total nitrogen (TN), C/N, soil aggregates and soil bulk density (SBD) in a temperate organic vineyard. We found that straw mulching had a significant regulating effect, with soil moisture being elevated with increasing mulching thickness by 5.8%, 9.0% and 11.1% compared with CK. The soil SOC content increased by 3.0%, 2.4% and 2.3%. Although soil pH and C/N significantly (p < 0.05) increased, they fluctuated with increasing mulch thickness. Straw mulching also increased the content of >2 mm soil particle size and elevated the mean weight diameter (MWD) and geometric mean diameter (GMD). The increasing mulching thickness prolonged the effect on the stability of soil aggregates. The 4 cm maize straw mulching thickness has the best effect for ecologically and environmentally managing warm-temperate organic vineyards so it may have a great application prospect on a global scale.

Bedrock outcrops weakly promote rather than inhibit soil carbon sequestration after vegetation restoration

Vegetation restoration can increase soil carbon (C) content in karst regions characterized by highly exposed carbonate rocks; however, it remains unclear whether and how bedrock outcrops contribute to soil C-accumulation after vegetation restoration. We aimed to investigate the magnitude and mechanisms of bedrock outcrops on soil C-accumulation after vegetation restoration. Here, we selected 362 fixed locations to investigate changes in soil organic carbon (SOC) content and density before and after cropland restoration in a karst catchment with varying bedrock exposure ratios and initial soil C pools prior to restoration. Active vegetation restoration (i.e., cropland converted to forage grass, plantation forest, and a combination of grass and forest) and natural regeneration (cropland abandoned) were compared, with croplands maintained with no change as the control. Compared to croplands maintained with no change, SOC density significantly increased in the four vegetation restoration types. The SOC accumulation rate was higher for natural regeneration (39 g C m−2 yr−1) than for the three active restoration strategies (18–27 g C m−2 yr−1). SOC accumulation decreased with a higher initial pool size of soil C but increased with nitrogen accumulation and soil exchangeable calcium (Ca2+) concentration. Higher bedrock outcrops reduced soil volume but increased SOC content through their indirect effects on the initial pool size of soil C, external nitrogen inputs, and soil Ca2+ concentration. This weakly promoted rather than inhibited SOC sequestration. Our findings highlight the effectiveness of various restoration strategies in promoting SOC accumulation in karst areas, as well as the need to take bedrock outcrops and initial soil C pools into consideration when modeling SOC dynamics and maximizing C sinks for vegetation restoration.

Effects of Forest Conversion on Soil Ecosystem Services in Liuxihe National Forest Park, China

The transition from natural forest to plantations has increased dramatically in the past decades. Forest conversion will affect soil properties and thus soil ecosystem services. Based on soil indicators, we studied the differences of soil ecosystem services among three forest types in Liuxihe National Forest Park and analyzed the effects of conversion from natural forest to artificial forest on soil ecosystem services. The results showed that the soil carbon sequestration of evergreen broadleaf forest (EBF) was stronger, and the soil organic carbon density (36.43 ± 0.97 kg m−3) was significantly higher than that of moso bamboo forest (MBF) (25.46 ± 1.72 kg m−3) and sugar orange forest (SOF) (19.31 ± 2.68 kg m−3) in the 0–10 cm soil layer. The soil water conservation of MBF was higher, and its soil water content was significantly higher than that of EBF in the three soil layers, which was more than 20% higher than that of EBF. There was no significant difference in soil total nitrogen content among the three forest types, while the soil total phosphorus content of MBF and SOF was more than twice that of EBF. It is important to consider soil ecosystem services in forest protection and restoration in forest parks.

Carbon Stocks Assessment in a Disturbed and Undisturbed Mangrove Forest in Ghana

Mangroves and other blue carbon ecosystems have long been recognised for their carbon sink function, yet the organic carbon stocks of mangroves in many countries in Africa remain to be assessed. This study evaluates the impact of traditional forest conservation on long-term carbon sequestration in a non-degraded (Amanzule) and a degraded (Kakum) mangrove forest system in Ghana (West Africa). The amount of carbon stored in mangrove trees was estimated from diameter-based allometric equations. Tree (above- and below-ground) carbon was ~34-fold higher in the Amanzule forest (mean = 0.89 ± 0.10 t/ha) than in the Kakum forest (mean = 0.026 ± 0.019 t/ha). Soil carbon density was estimated as organic carbon and bulk density at specific depths in both forests. Soil organic carbon density was ~5-fold higher in the Amanzule forest (mean = 2935.79 ± 266 t/ha) than the Kakum forest (mean = 554.01 ± 83 t/ha). The variation in the vertical distribution of soil carbon was not significant in either forest (F = 0.57; p > 0.05). These findings underscore the role of traditional conservation on mangrove carbon stocks and the need to consider the governance of coastal ecosystems when estimating blue carbon.

Effect of Revegetation in Extremely Degraded Grassland on Carbon Density in Alpine Permafrost Regions

Revegetation has been proposed as an effective approach to restoring the extremely degraded grassland in the Qinghai–Tibetan Plateau (QTP). However, little is known about the effect of revegetation on ecosystem carbon density (ECD), especially in alpine permafrost regions. We compared aboveground biomass carbon density (ABCD), belowground biomass carbon density (BBCD), soil organic carbon density (SOCD), and ECD in intact alpine meadow, extremely degraded, and revegetated grasslands, as well as their influencing factors. Our results indicated that (1) ABCD, BBCD, SOCD, and ECD were significantly lower in extremely degraded grassland than in intact alpine meadow; (2) ABCD, SOCD, and ECD in revegetated grassland significantly increased by 93.46%, 16.88%, and 19.22%, respectively; (3) stepwise regression indicated that BBCD was mainly influenced by soil special gravity, and SOCD and ECD were controlled by freeze–thaw strength and soil temperature, respectively. This study provides a comprehensive survey of ECD and basic data for assessing ecosystem service functions in revegetated grassland of the alpine permafrost regions in the QTP.

Soil organic carbon density and its influencing factors in croplands with different cultivation years in the Northeastern Ulan Buh Desert, China

Understanding the changes and influencing factors of soil organic carbon density (SOCD) during the conversion of uncultivated natural soil to croplands is of great significance for the assessment of carbon sequestration in arid areas. In this study, we compared SOCD in the uncultivated soil and that in croplands with different cultivation years (2-5, 12-15, 25-30, 40-50 years) in the Northeastern Ulan Buh Desert. The change of SOCD and its influencing factors at 0-2 m soil depth during the conversion of uncultivated natural soil to croplands were explored by the method of replacing time with space. The results showed that SOCD at the shallow soil depth (0-0.4 m) in croplands increased continuously with cultivation years, but basically at low levels (0.990-1.983 kg·m-2). The SOCD at deep soil (1.2-2 m) increased in the croplands with longer cultivation years (25-30 and 40-50 years), whereas no obvious change trends in both the croplands with shorter cultivation years (2-5 and 12-15 years) and the uncultivated natural soil. The SOCD at deep soil (1.2-2 m) were relatively large (28.9%-38.6%) of the 0-2 m soil depth of uncultivated natural soil and croplands with different cultivation years. The vertical distribution of SOCD in croplands with different cultivation years were well fitted by quadratic functions (with R2 ranging from 0.757 to 0.972). It was noteworthy that soil clay and silt contents had dominant influences on SOCD at all the soil profile (0-2 m), and that cultivation years mainly contributed to the accumulation of SOC at the shallow soil (0-0.4 m).

Soil Carbon within the Mangrove Landscape in Rufiji River Delta, Tanzania

Mangroves are among the most carbon-rich terrestrial ecosystems, primarily attributable to the soil pool. There are substantial differences in soil carbon (C) and nitrogen (N) due to the disparities in geomorphic settings and ecological drivers, but this insight is drawn primarily from observational studies. An objective inventory of carbon stocks in mangroves of the Rufiji River Delta, Tanzania was conducted. Seventy-five soil cores were collected within a 12,164 ha inventory area, comprising the northern portion of the delta. Cores were collected from intact and dwarf mangroves, agricultural fields, and mudflats. The spatial mean soil organic carbon (SOC) density in mangroves was 16.35 ± 6.25 mg C cm−3. Mean SOC density in non-vegetated mudflats was 12.16 ± 4.57 mg C cm−3, demonstrating that mangroves develop on soils with a substantial soil C stock. However, long-established mangroves had had a higher C density (17.27 ± 5.87 mg C cm−3). Using a δ13C mixing model, the source of soil organic matter in mudflats was primarily marine, while long-established mangroves was predominantly mangrove. There were small differences in SOC among long-established mangrove sites in different geomorphic settings. The proportion of marine-sourced SOC increased with soil depth in mangroves. The SOC and nitrogen of agricultural sites resemble those of mudflats, suggesting those sites are developed from relatively young forests. The SOC and nitrogen density in dwarf mangrove sites were lower than others, perhaps reflecting past disturbances.

Urban Land Conversion Reduces Soil Organic Carbon Density Under Impervious Surfaces

AbstractAccurate assessments of soil organic carbon (SOC) storage beneath impervious surface areas (ISAs, SOCISA) are key for understanding the urbanization impact on carbon pools, but previous studies either ignored the SOCISA pool or overlooked the urbanization impacts on the SOC pool. Based on observations from 152 sampling sites in 43 cities, we show that mainland China has a SOCISA stock of 1,016 Tg to 100‐cm depth, with a mean density of 6.21 ± 3.90 kg m−2. Comparison between SOCISA and the SOC of background soil (SOCbackground) indicates ∼19% SOC loss due to ISA conversion, similar to the effect of cropland conversion. Unlike the vertical pattern of SOCbackground, which declined faster in the upper soil layers, SOCISA decreased linearly with depth. Moreover, the SOCISA is uncorrelated with SOCbackground and decreases with precipitation. These unique patterns indicate the SOC loss mainly caused by topsoil removal during land conversion. The fact that the SOCISA of older ISA was not lower than that of newly converted ISA further confirmed that soil sealing preserved SOC. Finally, both the high correlation between SOCISA and SOCPSA (SOC of the adjacent pervious surfaces) and the converging SOC densities in urban soils showed strong influences from urban greenspace on SOCISA. Based on the findings, we recommend improving greenspace management to increase the presealing SOC stock, preventing ISA construction in wet/warm seasons to mitigate SOC loss, and developing technology to seal carbon stock under ISA. We conclude that SOCISA is a major component of the urban carbon pool. It has a unique spatial pattern and cannot be estimated using surrogate data such as SOCbackground or SOCPSA.

Effects of 10 Years of the Return of Corn Straw on Soil Aggregates and the Distribution of Organic Carbon in a Mollisol

The return of straw is a widely used agricultural practice for increasing the soil organic carbon (SOC) content and improving soil structure in Mollisols, owing to the decline caused by continuous high-intensity tillage. We conducted a field experiment where corn straw was continuously returned for 10 years to investigate effects of the straw on the size distribution and stability of soil aggregates and on SOC density fractions. The treatments were no straw return (CK) and four rates of straw return: 6000 kg hm−2 (S1), 9000 kg hm−2 (S2), 12,000 kg hm−2 (S3), and 15,000 kg hm−2 (S4). SOC contents after straw return for bulk soil, a free light fraction (F-LF), an occluded light fraction (O-LF), and a heavy fraction (HF) were significantly higher by 27.0, 644.3, 720.0, and 69.2%, respectively, in S4 than CK. The contents of F-LF, O-LF, and HF in aggregates >2.00 mm were significantly higher by 194.2, 162.1, and 35.8%, respectively, in S4 than CK. Structural equation modeling indicated that SOC contents and aggregates >0.25 mm were directly correlated with the amount of straw returned. We conclude that returning 15,000 kg m−2 of straw would be an effective agronomic practice to restore Mollisol fertility.

The effects of co-utilizing green manure and rice straw on soil aggregates and soil carbon stability in a paddy soil in southern China

The co-utilization of green manure (GM) and rice straw (RS) in paddy fields has been widely applied as an effective practice in southern China. However, its effects on soil aggregate and soil organic carbon (SOC) stability remain unclear. In the present study, the effect of GM, RS, and co-utilization of GM and RS on particle size distribution of soil aggregates and SOC density fractions were measured in a field experiment. The experiment included six treatments, i.e., winter fallow (WF) without RS return (Ctrl), WF with 50% RS return (1/2RS), WF with 100% RS return (RS), GM without RS return (GM), GM with 50% RS return (GM1/2RS) and GM with 100% RS return (GMRS). The results showed that the proportion of small macro-aggregates (0.25–2 mm) and the mean weight diameter (MWD) of aggregates in the GMRS treatment was greater (by 18.9 and 3.41%, respectively) than in the RS treatment, while the proportion of silt+clay particles (<0.053 mm) was lower (by 14.4%). The concentration of SOC in microaggregates (0.053–0.25 mm) and silt+clay particles was higher in the GMRS treatment than in GM and RS treatments individually. The concentration and proportion of free light organic carbon (fLOC) in aggregates of various particle sizes and bulk soil was greater in the GMRS treatment than the RS treatment, whereas the concentration and proportion of mineral-associated organic carbon in small macroaggregates, microaggregates, and bulk was lower in the GMRS treatment than in the RS treatment. The proportion of intra-aggregate particulate organic carbon (iPOC) was greater in the GMRS treatment than in GM treatment. The GMRS treatment had strong positive effects on iPOC in small macroaggregates, suggesting that SOC was transferred from fLOC to iPOC. In conclusion, co-utilizing green manure and rice straw cultivated the SOC pool by increasing the concentration of fLOC and improved soil carbon stability by promoting the sequestration of organic carbon in iPOC as a form of physical protection.

Digital mapping of soil organic carbon density using newly developed bare soil spectral indices and deep neural network

Soil organic carbon density (SOCD) is an important parameter of agricultural soils and is useful for the improvement of environment and agricultural production. Proximal and remote sensing techniques are effective methods for digital soil mapping of SOCD. The current study used three types of spectral data, including laboratory proximal spectra, airborne hyperspectral and Sentinel 2 multispectral images, to predict SOCD in an agricultural land. Bare soil spectral indices (BSSIs) were developed to predict SOCD and compared with the published vegetation indices (VIs). With 45 soil samples, the partial least square regression (PLSR), back propagation neural network (BPNN) and deep neural network (DNN) prediction models were established to map SOCD. The results showed that the laboratory spectra (R2 = 0.70–0.80) had the best performance of SOCD prediction, followed by the airborne (R2 = 0.43–0.81) and Sentinel 2 (R2 = 0.14–0.57) spectra. The SOCD maps derived from airborne and Sentinel 2 images had similar spatial distribution trends. The BSSIs (R2 = 0.24–0.81) obtained higher accuracy than the VIs (R2 = 0.14–0.74) in SOCD prediction. Moreover, DNN model was the best for digital soil mapping of SOCD among three prediction models. This study offered an effective approach for mapping SOCD in bare soil areas.

Evaluation of Soil Organic Carbon Stock in Coastal Sabkhas under Different Vegetation Covers

There has been increasing focus on conserving coastal ecosystems as they have been recognized as high ecosystem carbon stocks and are in the process of land conversion. The present study aims to examine how different vegetation covers impact the soil organic carbon (SOC) stock in coastal sabkhas. To this end, the study was carried out at ten sampling sites represent ten sabkhas in Saudi Arabia’s southern Red Sea coast for two main goals: (1) to examine the vertical distribution of SOC content, SOC density, and the soil bulk density (SBD) based on different vegetation covers, and (2) to assess these locations’ SOC stocks. This study posits that sabkhas with different vegetation covers had distinct parameters specified above. Significant SBD differences were observed in sabkhas with different vegetation covers, with the lowest mean values of sabkhas having &gt;75–100% vegetation cover and the highest mean values of sabkhas having 0–25% vegetation cover. The studied sabkhas also showed significant difference in the total means of SOC density, SOC content, and SOC stock in terms of different vegetation covers, with the highest mean values of sabkhas having &gt;75–100% vegetation cover and the lowest mean of sabkhas having 0–25% vegetation cover. The present study is the first to focus on Saudi Arabia’s sabkha blue carbon stocks and its results can help add to the literature on sabkhas carbon stock, thus aiding relevant government agencies working towards sabkhas management, encouraging public awareness regarding sabkhas conservation stocks, and their part in climate change mitigation.

Proportional allocation with soil depth improved mapping soil organic carbon stocks

Soil organic carbon (SOC) is vital to the assessment of land quality, management of farmland and ecological environment, and carbon cycle. A more accurate spatial prediction of multilayer soil organic carbon density (SOCD) can contribute to a better interpretation of the changes in multilayer SOC stocks and carbon dynamics. However, previous mapping techniques still have limitations, such as ignoring the relationship of profile depths, not further taking advantage of vertical distribution and surface categorical information. In addition, it is unclear whether it is better to model each depth interval of SOC separately or to model the total layer and then allocate it. Here, we propose two new methods based on the proportional allocation of soil depth for multilayer mapping: vertical log-ratio method (VLR) of SOCD by applying the percentage of SOCD data and isometric log-ratio (ILR) transformation, and vertical distribution method (VD) of SOCD by considering different land-use types. We compared five methods, including the two new methods, the exponential and equal-area spline functions, and independent modeling without depth information. We combined these five methods with the generalized linear model (GLM) and random forest (RF) to produce predictions of the Sanjiang Plain, northeastern China. The results demonstrated that SOCD did not always decrease with increasing soil depth, and classification of SOCD vertical distribution features needs to be considered by combining with soil depths. For accuracy assessment, the exponential mode with both GLM and RF over-calculated the predicted values and performed poorly, indicating that the blind use of depth information increased the prediction error. The spline function prediction was scarcely better than that of independent modeling. The proportional allocation methods performed better than other separate modeling methods for accuracy and interpretability with GLM or RF, especially for the middle and surface layers. The GLM generated more aggregated predictions than the RF, losing the distribution pattern of the original data. Therefore, we recommend RF combined with proportional allocation methods for spatial SOCD prediction in large-scale study areas. We calculated the SOC stocks in the Sanjiang Plain using our new methods, which were more reasonable compared with those of previous studies and had the advantages of in-depth information, environmental variable selection, and model optimization. Our findings provide not only other perspectives for SOCD mapping, with more fully integrated depth information and more accurate assessment of multilayer SOC stocks, but also provide guidance for the evaluation of land quality, farmland, and ecological environmental management.

Distribution of SOCD along different offshore distances in China's fresh-water lake-Chaohu under different habitats

Carbon storage in wetland ecosystems is an important part of the carbon cycle of terrestrial ecosystems and provides important ecosystem services. Chaohu Wetland is a typical freshwater lake wetland in China. In this study, soil and plant samples were collected every 500 m through three sample lines of different vegetation habitats (estuarine banks, woodlands and shrub beaches) and different offshore distances, revealing the spatial distribution characteristics of soil organic carbon density (SOCD) in Chaohu wetland. The overall SOCD of Chaohu wetland was low, with different habitats ranking as Woodland > Estuary and riverside > Shrub and beach. SOCD of different offshore distances had no obvious law, and the SOCD decreased significantly with soil depth. The plant biomass was significantly higher at the woodland habitat than at other habitats. Most of soil nutrient indicators were the highest at the woodland habitat, while the estuary-riverside habitat had the highest N and P contents. Soil and plant nutrients at different offshore distances had no obvious change patterns. The contents of soil K, Ca, Mg, and N were significantly positively correlated with SOCD, but soil bulk density and pH were significantly negatively correlated with SOCD, and vegetation P content was significantly negatively correlated with SOCD. The spatial pattern of SOCD changes in this lake coastal wetland was determined by the combined effects of plant nutrients, biomass, and soil physical and chemical properties. Our results indicate Chaohu wetlands may have been experiencing serious degradation. The SOCD of Chaohu wetland is lower than that of other wetlands in China, which is mainly affected by human activities. Different offshore distances and habitat heterogeneity are the main factors affecting the soil carbon cycle of the wetland.

Integrated agroforestry systems improve soil carbon storage, water productivity, and economic returns in the marginal land of the semi-arid region

Environmental crises, land degradation, and frequent crop failure threaten the livelihoods of millions of the populace in the semi-arid agroecosystems. Therefore, different combinations of annual crops with perennial fruit trees were assessed to restore the soil carbon, and enhance farm productivity and profitability in a semi-arid climate. The study hypothesized that the integration of perennial fruit trees with seasonal crops may enhance farm productivity, economic returns, and environmental sustainability. Integration of phalsa (Grewia asiatica) with mung bean (Vigna radiata) - potato (Solanum tuberosum) system recorded the highest system productivity (25.9 Mg/ha) followed by phalsa with cowpea (Vigna unguiculata) -mustard (Brassica juncea) systems (21.2 Mg/ha). However, Karonda (Carissa sp.) with mung bean - potato system recorded maximum net return (3529.1 US$/ha), and water use efficiency (33.0 kg/ha-mm). Concerning the benefit-cost (B:C) ratio, among the agroforestry systems, the karonda + cowpea - mustard system registered a maximum BC ratio (3.85). However, SOC density remained higher (9.10 Mg/ha) under the phalsa + cowpea - mustard and Moringa + mung bean - potato system (9.16 Mg/ha) over other systems. Similarly, phalsa + mung bean - potato system had the highest C sustainability index (27.6), carbon sequestration potential (0.6–0.67 Mg/ha/year), and water use efficiency (33.0 kg/ha-mm). Hence, the study suggested that the integration of short-duration leguminous and oilseeds with fruit trees offer a myriad of benefits and an efficient system for restoring the soil C without compromising the food and livelihood security of the rural populace in semiarid regions.

Growing season grazing promotes the shallow stratification of soil nutrients while non-growing season grazing sequesters the deep soil nutrients in a typical alpine meadow

Grazing management and climate are known to be important drivers influencing soil nutrient accumulation. The change of soil nutrients in pasture depends on the excreta return and the vegetation regeneration. Livestock activities significantly affect plant growth and soil nutrients through feeding, trampling, and excretion. At the same time, grazing time and climate change are stimulating plant growth and altering plant composition. How long-term specific grazing management will affect soil nutrient storage and movement under a warming-humid climate trend needs further study. In 20-year grazing management trial, conducted in a typical alpine meadow in the Qilian Mountains on the Qinghai-Tibet Plateau, sampled and analyzed the soil from under a non-growing season graze pasture (WP) and a growing season graze pasture (SAP) in August 1999 and August 2019 along grazing gradients (GG) at different distances from the pasture entrance (0, 300, 600, 900, 1200, and 1500 m). The experimental results of 2019 compared to 1999 show that SAP and WP increased soil available nitrogen density (SAND) and availability (SAND:soil total nitrogen density [STND] ratio) in the first 300 m along the grazing gradient soil, while SAP showed a decrease in soil available phosphorus density (SAPD) and availability (SAPD:soil total phosphorus density [STPD] ratio), and WP had no significant difference between gradients. Grazing in spring and autumn increased soil organic carbon density (SOCD), and STND in the first 300 m along the gradient soil, whereas it had the reverse effect in WP. At the same time, STPD has no obvious changing trend along the gradient. Growing and non-growing season grazing increased the SOCD:STND ratio in the first 300 m along the grazing gradient but resulted to a lower STND:STPD ratio. The comparison found that long-term grazing from 1999 to 2019 increased the SAND and SAPD. SAP improved soil total C, N, and P density in the topsoil (0–10 cm), but WP improved it throughout the profile (0–40 cm). These findings indicate that time of grazing and the grazing gradient affect the accumulation and migration of different elements under long-term grazing. Furthermore, SAP and WP had a positive effect on the accumulation of topsoil and deep soil nutrients, respectively. We suggest that periodic pasture exchange in SAP and WP should be carried out to maintain the sustainability of the ecosystem. At the same time, for different gradients, especially the first 300 m, regular soil nutrient monitoring and human intervention (such as fertilization) should be carried out to eliminate potential element restrictions and focus on the development of possible problems caused by the livestock locked in the pens at night, such as nutrient enrichment (the excreta as the organic fertilizer and soil improvement material for farmland) and loss (element footprint) in pens, which are of important guiding significance for the grazing system’s stable development of alpine meadow.

Factors controlling the spatial distribution of soil organic carbon in the Chinese medicine producing area of NW China1

Soil organic carbon is an important factor for the cultivation and production of traditional Chinese medicine. This study aimed to reveal the spatial distribution of the soil organic carbon density (SOCD) and the effects of the climatic and topographic factors in Longxi County (Gansu Province, China). The soil organic carbon (SOC) from 200 sampling points were collected and analyzed in 2018. Results showed that the total SOCD was 26.7 ± 10.2 Mg ha-1, while the SOCDs at a soil depth of 0–10, 10–30, and 30–50 cm were 6.3 ± 1.7, 11.0 ± 3.8, and 9.3 ± 4.8 Mg ha-1, respectively. The temperature, precipitation, elevation, and stream power index showed significant correlations with the SOCD at each soil layer. With an increasing soil depth, the correlation between the slope, relief amplitude, surface roughness, and SOCD gradually decreased. From the central plains to the mountainous areas, the SOCD increased with rising elevation, while the valley plain that formed by the river basin showed low levels of SOCD. Therefore, the scientific management of soil fertility and the development of precision agriculture, combined in a soil testing fertilization formula, will guarantee the healthy development of the Chinese herbal medicine planting.

Effects of Soil Map Scales on Estimating Soil Organic Carbon Stocks in Southeastern China

Digital soil maps of different scales have been widely used in the estimates of soil organic carbon (SOC). However, exactly how the scale of the soil map impacts SOC dynamics and the key factors influencing SOC estimations during the map generalization process have rarely been assessed. In this research, a newly available soil database of Zhejiang Province in southeastern China, which contains 2154 geo-referenced soil profiles and six digital soil maps at scales of 1:50,000, 1:250,000, 1:500,000, 1:1,000,000, 1:4,000,000, and 1:10,000,000, and three different linkage methods (i.e., the mean, median, and pedological professional knowledge-based (PKB) methods) were used to evaluate their influence on the estimates of SOC. The findings of our study were as follows: (1) The scale of the soil map was identified as being of crucial importance for regional SOC estimations. (2) The linkage method played an important role in the accurate estimates of SOC, and the PKB method could provide the most detailed information on the spatial variability of SOC estimations. (3) The key factors affecting the estimates of SOC during the map generalization process as the soil map scale decreased from 1:50,000 to 1:10,000,000 were determined, including the changes in the number of soil profiles, the conversions between different soil types, the conversions from non-soils to soils, and the linkage methods of aggregating the SOC density values of soil profiles to represent map units. The results suggest that the most detailed 1:50,000-scale soil map coupled with the PKB method would be the optimal choice for regional SOC estimations in China.

A comprehensive assessment of diversified cropping systems on agro-environmental sustainability in three Mediterranean long-term field experiments

The intensification of agricultural systems has caused a noticeable impact on agro-ecosystem services. Thus, the adoption of more sustainable agricultural practices such as crop diversification and reduction of external inputs represent an alternative strategy to minimize the impacts of intensive agricultural systems to the environment. This study aimed at evaluating the effects of crop rotation, conservation tillage, and low-input strategies on soil quality and farming performance using a set of 7 indicators based on a fuzzy logic approach. Data were collected from three Mediterranean long-term field experiments (LTEs) mostly oriented on cereal-based and vegetables cropping systems, located in Spain and Italy. The selected agro-environmental indicators clearly discriminated both from a geographical point of view and between monoculture and diversification, showing their suitability for the evaluation of diversified cropping systems. Such indicators highlighted that implementing crop diversification and reducing soil disturbance and chemical inputs enhanced soil quality. In this context, the most significant effects of diversified cropping strategies were the increase of crucial variables such as soil organic carbon (SOC), total nitrogen (TN), available phosphorus (Pav), and bulk density (BD) maintaining a stability of yields in all the three LTEs. These results provide strong evidence for the benefits of crop diversification in Mediterranean areas, highlighting that diversification represents a very promising strategy for more sustainable land management. Simple and composite indicators calculated using fuzzy method can be proposed as tool to assess the effects of diversification strategies on cropping systems performance. This approach can be used to define local solutions to help the re-design of cropping system through crop diversification transition across Europe.

Precipitation drives the accumulation of soil organic carbon in the sandy desert of the Junggar Basin, Northwest China

Accurate quantitative estimation of soil organic carbon (SOC) and its storage is crucial for ecosystem response over desert areas, and is an important component of understanding dryland climate change, which can effectively reflect the processes and regulatory mechanisms in the carbon cycle. Nevertheless, the relationship between carbon sources and carbon sinks in sandy soils is a hotly debated subject. In particular, how plants and environmental conditions interact to affect SOC remains unclear in sandy deserts. Here, we investigated 77 sites at depths of 0–100 cm (soil depth was divided by 0–5 cm, 5–10 cm, 10–20 cm,20–30 cm, 30–50 cm, 50–70 cm and 70–100 cm intervals), collected 1617 soil samples, and obtained the climatic conditions, vegetation types, and edaphic factors associated with the sampling sites. This study aims to determine whether there are divisions in the allocation strategies of SOC by various vegetation types, and to analyze the mechanisms of environmental factors on the soil carbon pool in sandy deserts. Our results found that (1) the mean value of SOC in the sandy desert was 2.19 g·kg−1, which differed significantly among different vegetation types (P < 0.05), yet there were no significant changes in aboveground biomass and litter biomass. (2) SOC did not significantly differ among soil layers except for the Ceratoides latent (P = 0.04), and Seriphidium terrae-albae (P = 0.02) communities. (3) The mean value of soil organic carbon density (SOCD) was 3.38 kg·m−2 and increased exponentially with soil depth (R2 = 0.23, P < 0.05). (4) Mean annual precipitation controlled the spatial distribution of SOC variation in sandy desert. Vegetation types, soil variables, topographic factors did not control SOC, but had a strong interactive effect with climatic factors. The explanatory power of interaction effects often showed an improvement over single variables, manifested as nonlinear enhancement and bivariate enhancement. Our results highlighted the nature of the desert’s position in the global carbon cycle and provide key information on missing carbon sinks in the driest zone.