Organic carbon stocks in Mediterranean soil types under different land uses (Southern Spain)

Carbon stock quantification in a floodplain restoration chronosequence along a Mediterranean-montane riparian corridor

Uncertainty in the global carbon (C) budget has been reduced for most stocks, though it remains incomplete by not considering aquatic and transitional zone carbon stocks. A key issue preventing such complete accounting is a lack of available C data within these aquatic and aquatic-terrestrial transitional ecosystems. Concurrently, quantifiable results produced by restoration practices that explicitly target C stock accumulation and sequestration remain inconsistent or undocumented. To support a more complete carbon budget and identify impacts on C stock accumulation from restoration treatment actions, we investigated C stock values in a Mediterranean-montane riparian floodplain system in California, USA. We quantified the C stock in aboveground biomass, large wood, and litter in addition to the C and total nitrogen in the upper soil profile (5 cm) across 23 unique restoration treatments and remnant old-growth forests. Treatments span 40 years of restoration actions along seven river kilometers of the Cosumnes River, and include process-based (limited intervention), assisted (horticultural planting and other intensive restoration activities), hybrid (a combination of process and assisted actions), and remnant (old-growth forests that were not created with restoration actions) sites. Total C values measured up to 1100 Mg ha-1 and averaged 129 Mg ha-1 with biomass contributing the most to individual plot measurements. From 2012 to 2020, biomass C stock measurements showed an average 32 Mg ha-1 increase across all treatments, though treatment specific values varied. While remnant forest plots held the highest average C values across all stocks (336 Mg ha-1), C values of different stocks varied across treatment type. Process-based restoration treatments held more average biomass C (120 Mg ha-1) than hybrid (23 Mg ha-1) or assisted restoration treatments (50 Mg ha-1), while assisted restoration treatments held more average total C in soil and litter (58 Mg ha-1) than hybrid (35 Mg ha-1) and process-based restoration treatments (37 Mg ha-1). Regardless of treatment type, time was a significant factor for all C stock values. These findings support a more inclusive global carbon budget and provide valuable insight into restoration treatment actions that support C stock accumulation.

The possibility of spatial mapping of SOC content in olive groves under integrated production using easy-to-obtain ancillary data in a Mediterranean area

Background

Unlike most of Europe, Andalucía in southern Spain as a Mediterranean area still lacks digital maps of SOC content provided by machine learning algorithms. The wide diversity of climate, geology, hydrology, landscape, topography, vegetation, and micro-relief data as easy-to-obtain covariates facilitated the development of digital soil mapping (DSM). The purpose of this research is to model and map the spatial distribution of SOC at three depths, in an area of approximately 10000 km 2 located in Seville and Cordoba Provinces, and to use R programming to compare two machine learning techniques (cubist and random forest) for developing SOC maps at multiple depths.

Methods

Environmental covariates used in this research include nine derivatives from digital elevation models (DEM), three climatic variables and finally eighteen remotely-sensed spectral data (band ratios calculated by the acquired Landsat-8 OLI and Sentinel-2A MSI in July 2019). In total, 300 soil samples from 100 points were taken (0-25 cm). The purpose of this research is to model and map the spatial distribution of SOC, in an area with approximately 10000 km2 located in Seville and Cordoba Provinces, and to compare two machine learning techniques (cubist and random forest) by R programming.

Results

The findings showed that the novel approach for integrating the indices using Landsat-8 OLI and Sentinel-2A MSI satellite data had a better result.

Conclusions

Finally, we obtained evidence that the resolution of satellite images is more important in modelling and digital mapping.

Soil OC and N Stocks in the Saline Soil of Tunisian Gataaya Oasis Eight Years after Application of Manure and Compost

Soil organic matter plays an important role in improving soil properties, crop productivity and is a key constituent and driver of the global carbon cycle. Nevertheless, relatively limited quantitative information is available on the organic carbon (OC) stocks and the actual potentials for OC and total nitrogen (N) sequestration under arid cropping systems. In this study, we evaluated the immediate and long-term (after eight years) effects of compost or manure additions, at a rate of 100 t ha−1, on the soil OC and N stocks in the Gataaya oasis in Southern Tunisia. The oasis had been abandoned and no additions had taken place in the 10 years prior to experiment. Soil samples were taken systematically every 10 cm up to a depth of 50 cm. After adding compost (CMP) and manure (MAN) in 2013, the bulk density (BD) decreased in the surface layers, especially at the 0–10 cm soil layer where it declined from 1.53 g cm−3 to 1.38 g cm−3 under compost and 1.41 g cm−3 under manure. Soil OC and N stocks, however, increased after adding compost and manure. Manure contributed more to OC stock increase than compost, with +337 and +241%, respectively. Correspondingly, the N stock increased by + 47 and +12%, respectively, due to manure and compost. After four years, compared to 2013 stocks, the decrease in OC stock was almost identical with −43 (CMP) and −41% (MAN). However, N stock seemed more stable under compost compared to manure, with −2 and −19%, respectively. After eight years, the N stock remained higher in the deepest layer 30–50 cm compared to other layers. This suggested that high gypsum application can inhibit N mineralization. The initial enhanced OC stock after the organic amendment, both for compost and for manure, was very quickly lost and after eight years had virtually returned to the initial OC state by the end of the eight years. Therefore, these oasis ecosystems require a near annual supply of exogenous organic material to maintain OC at an enhanced level. After eight years, manure amendment was found to be better than compost for increasing soil OC (3.16 against 1.86 t/ha, respectively) and for increasing N (0.35 against 0.18 t/ha, respectively). However, the cost and availability make the amendment with compost more interesting in oasis (400 Tunisian dinars/t for compost against 1016 Tunisian dinars/t for manure).

Short-term effects of land management change linked to cover crop on soil organic carbon in Mediterranean olive grove hillsides

The spatial distribution of soil organic carbon (SOC) is essential to estimate the SOC reserves. Therefore, the soils ability to store organic carbon is a key factor for climate regulation and for other soil functions. The soil management and the topographic position play an important role in SOC variation, especially when the landscape is not uniform (Mediterranean areas). Many researches have explored the SOC distribution according to topographic position in hillsides for long-term, but very few studies have focused on the short term. Therefore, it is necessary to know, the changes that taking place in the soil due to land management change (LMC) in these irregular surfaces for sustainable agricultural production and its implications on climate change regulation. This study aims to assess the influence of topographic position and LMC on SOC stock (SOC-S) in Mediterranean olive groves (OG) soils in short term (2 years). In this line, three experimental plots were selected in three topographical position (summit - S, backslope - B and toeslope - T). In these plots, the land management was modified from conventional tillage (CT) to no tillage (NT) with application of pruned olive branch chippings branches and vegetation cover (spontaneous vegetation) in the OG streets. The studied soils did not show important changes due to LMC in their physical properties for short term, in addition, these soils were characterized by low organic matter content (<1.2%). LMC caused a SOC reduction in surface, and a SOC increase in the Bw horizon. The N concentrations showed a similar trend to SOC and the C:N ratios were highly variable (4.37: C horizon-NT-S; 13.45 Bw/C horizon -CT-B). Normally, the SOC-S concentrations decreasing in depth. LMC for two years showed soil carbonization (S and T position) and decarbonization (B position) processes. The SOC-S increased 1.88 Mg ha^-1 y^-1 and 0.47 Mg ha^-1 y^-1 for S and T topographic position respectively, however the SOC-S decreased in B position 5.27 Mg ha^-1 y^-1. Therefore, LMC has a positive effect on soil carbon reserves in S and T position, conversely in B position, this effect was negative.

Deep soil inventories reveal that impacts of cover crops and compost on soil carbon sequestration differ in surface and subsurface soils

Increasing soil organic carbon (SOC) via organic inputs is a key strategy for increasing long-term soil C storage and improving the climate change mitigation and adaptation potential of agricultural systems. A long-term trial in California's Mediterranean climate revealed impacts of management on SOC in maize-tomato and wheat-fallow cropping systems. SOC was measured at the initiation of the experiment and at year 19, at five depth increments down to 2 m, taking into account changes in bulk density. Across the entire 2 m profile, SOC in the wheat-fallow systems did not change with the addition of N fertilizer, winter cover crops (WCC), or irrigation alone and decreased by 5.6% with no inputs. There was some evidence of soil C gains at depth with both N fertilizer and irrigation, though high variation precluded detection of significant changes. In maize-tomato rotations, SOC increased by 12.6% (21.8 Mg C/ha) with both WCC and composted poultry manure inputs, across the 2 m profile. The addition of WCC to a conventionally managed system increased SOC stocks by 3.5% (1.44 Mg C/ha) in the 0-30 cm layer, but decreased by 10.8% (14.86 Mg C/ha) in the 30-200 cm layer, resulting in overall losses of 13.4 Mg C/ha. If we only measured soil C in the top 30 cm, we would have assumed an increase in total soil C increased with WCC alone, whereas in reality significant losses in SOC occurred when considering the 2 m soil profile. Ignoring the subsoil carbon dynamics in deeper layers of soil fails to recognize potential opportunities for soil C sequestration, and may lead to false conclusions about the impact of management practices on C sequestration.

Effects of Long-Term Successive Rotations, Clear-Cutting and Stand Age of Prince Rupprecht’s larch (Larix Principis-Rupprechtii Mayr) on Soil Quality

A decline in soil quality is a major factor contributing to the degradation of forest ecological function. Vegetation plays a vital role in maintaining soil quality; however, the influence of plantation length on soil quality remains unclear. In this study, we collected soil samples in Northern China using a space-for-time substitution method. Soil were collected from control grassland; a clear-cutting site; 16-year-old (young, first, and second generation), 28-year-old (immature, first, and second generation), and 44-year-old (mature, first generation) Larix principis-rupprechtii Mayr stands in May, July, and September 2016. We measured soil physical and chemical properties, microbial communities, and enzymatic activities. We selected soil bulk density, non-capillary porosity, volume humidity, soil organic carbon and activity of polyphenol oxidase to calculate a soil quality index (SQI) for each site. Our data indicated that clear-cutting greatly decreased soil quality of Larix principis-rupprechtii forests but returning the harvesting residues to the forest floor could reduce the negative impact of clear-cutting on soil quality. The soil quality improved significantly by prolonging the cultivation cycle and it took about 39 years for the first-generation forest to restore soil quality to the level of the control plot. Our study confirms that SQI provides a comprehensive measurement of soil quality with the identification of a minimum data set. Comparing SQI with other soil quality indicators would help us to optimize the method for assessing soil quality.

Dynamic Changes in Carbon Sequestration from Opencast Mining Activities and Land Reclamation in China’s Loess Plateau

Opencast coal mining causes serious damage to the natural landscape, resulting in the depletion of the carbon sequestration capacity in the mining activity. There are few studies on the variation of carbon sequestration capabilities caused by land use changes in opencast mining areas. This paper uses six images were used to quantify the changes in land use types from 1986 to 2015 in the Pingshuo mining area in northwest China. At the same time, used statistical analysis and mathematical models to study soil and vegetation carbon sequestration. Results indicate that the total carbon sequestration exhibits a significant downward trend from 4.58 × 106 Mg in 1986 to 3.78 × 106 Mg in 2015, with the decrease of soil carbon sequestration accounting for the largest proportion. The carbon sequestration of arable land accounted for 51% of the total carbon sequestration in the mining area, followed by grassland (31%) and forestland (18%). Land reclamation contributed to the greatest increase in carbon sequestration of arable land from 17,890.15 Mg (1986) to 27,837.95 Mg (2015). Additionally, the downward trend in the carbon sequestration capacity of the mining ecosystem was mitigated after 2010 as the positive effects of land reclamation gradually amplified over time and as the mining techniques were greatly optimized in recent years in the Pingshuo mining area. Thus, terrestrial carbon sequestration can be improved through land reclamation projects and optimized mining activities. These results can help guide the utilization of reclaimed land in the future.

Runoff initiation, soil detachment and connectivity are enhanced as a consequence of vineyards plantations

Rainfall-induced soil erosion is a major threat, especially in agricultural soils. In the Mediterranean belt, vineyards are affected by high soil loss rates, leading to land degradation. Plantation of new vines is carried out after deep ploughing, use of heavy machinery, wheel traffic, and trampling. Those works result in soil physical properties changes and contribute to enhanced runoff rates and increased soil erosion rates. The objective of this paper is to assess the impact of the plantation of vineyards on soil hydrological and erosional response under low frequency - high magnitude rainfall events, the ones that under the Mediterranean climatic conditions trigger extreme soil erosion rates. We determined time to ponding, Tp; time to runoff, Tr; time to runoff outlet, Tro; runoff rate, and soil loss under simulated rainfall (55 mm h^-1, 1 h) at plot scale (0.25 m²) to characterize the runoff initiation and sediment detachment. In recent vine plantations (<1 year since plantation; R) compared to old ones (>50 years; O). Slope gradient, rock fragment cover, soil surface roughness, bulk density, soil organic matter content, soil water content and plant cover were determined. Plantation of new vineyards largely impacted runoff rates and soil erosion risk at plot scale in the short term. Tp, Tr and Tro were much shorter in R plots. Tr-Tp and Tro-Tr periods were used as connectivity indexes of water flow, and decreased to 77.5 and 33.2% in R plots compared to O plots. Runoff coefficients increased significantly from O (42.94%) to R plots (71.92%) and soil losses were approximately one order of magnitude lower (1.8 and 12.6 Mg ha^-1 h^-1 for O and R plots respectively). Soil surface roughness and bulk density are two key factors that determine the increase in connectivity of flows and sediments in recently planted vineyards. Our results confirm that plantation of new vineyards strongly contributes to runoff initiation and sediment detachment, and those findings confirms that soil erosion control strategies should be applied immediately after or during the plantation of vines.

Climate and land use changes effects on soil organic carbon stocks in a Mediterranean semi-natural area

A thorough knowledge of the effects of climate and land use changes on the soil carbon pool is critical to planning effective strategies for adaptation and mitigation in future scenarios of global climate and land use change. In this study, we used CarboSOIL model to predict changes in soil organic carbon stocks in a semi-natural area of Southern Spain in three different time horizons (2040, 2070, 2100), considering two general circulation models (BCM2 and ECHAM5) and three IPCC scenarios (A1b, A2, B2). The effects of potential land use changes from natural vegetation (Mediterranean evergreen oak woodland) to agricultural land (olive grove and cereal) on soil organic carbon stocks were also evaluated. Predicted values of SOC contents correlated well those measured (R2 ranging from 0.71 at 0-25cm to 0.97 at 50-75cm) showing the efficiency of the model. Results showed substantial differences among time horizons, climate and land use scenarios and soil depth with larger decreases of soil organic carbon stocks in the long term (2100 time horizon) and particularly in olive groves. The combination of climate and land use scenarios (in particular conversion from current 'dehesa' to olive groves) resulted in yet higher losses of soil organic carbon stocks, e.g. -30, -15 and -33% in the 0-25, 25-50 and 50-75cm sections respectively. This study shows the importance of soil organic carbon stocks assessment under both climate and land use scenarios at different soil sections and point towards possible directions for appropriate land use management in Mediterranean semi natural areas.

Spatial assessment of soil organic carbon and physicochemical properties in a horticultural orchard at arid zone of India using geostatistical approaches

Soil organic carbon (SOC) is a major indicator of long-term sustenance of agricultural production system. Apart from sustaining productivity, SOC plays a crucial role in context of climate change. Keeping in mind these potentials, spatial variation of SOC contents of a fruit orchard comprising several arid fruit plantations located at arid region of India is assessed in this study through geostatistical approaches. For this purpose, surface and subsurface soil samples from 175 locations from a fruit orchard spreading over 14.33 ha area were collected along with geographical coordinates. SOC content and soil physicochemical properties of collected soil samples were determined followed by geostatistical analysis for mapping purposes. Average SOC stock density of the orchard was 14.48 Mg ha(-1) for 0- to 30-cm soil layer ranging from 9.01 Mg ha(-1) in Carissa carandas to 19.52 Mg ha(-1) in Prosopis cineraria block. Range of spatial variation of SOC content was found about 100 m, while two other soil physicochemical properties, e.g., pH and electrical conductivity (EC) also showed similar spatial trend. This indicated that minimum sampling distance for future SOC mapping programme may be kept lower than 100 m for better accuracy. Ordinary kriging technique satisfactorily predicted SOC contents (in percent) at unsampled locations with root-mean-squared residual (RMSR) of 0.35-0.37. Co-kriging approach was found slightly superior (RMSR = 0.26-0.28) than ordinary kriging for spatial prediction of SOC contents because of significant correlations of SOC contents with pH and EC. Uncertainty of SOC estimation was also presented in terms of 90 % confidence interval. Spatial estimates of SOC stock through ordinary kriging or co-kriging approach were also found with low uncertainty of estimation than non-spatial estimates, e.g., arithmetic averaging approach. Among different fruit block plantations of the orchard, the block with Prosopis cineraria ('khejri') has higher SOC stock density than others.

Soil organic carbon stocks assessment in Mediterranean natural areas: a comparison of entire soil profiles and soil control sections

Soil organic carbon (SOC) is an important part of the global carbon (C) cycle. In addition, SOC is a soil property subject to changes and highly variable in space and time. Over time, some researches have analyzed entire soil profile (ESP) by pedogenetic horizons and other researches have analyzed soil control sections (SCS) to different thickness. However, very few studies compare both methods (ESP versus SCS). This research sought to analyze the SOC stock (SOCS) variability using both methods (ESP and SCS) in The Despeñaperros Natural Park, a nature reserve that consists of a 76.8 km(2) forested area in southern Spain. Thirty-four sampling points were selected in the study zone. Each sampling point was analyzed in two different ways, as ESP (by horizons) and as SCS with different depth increments (0-25, 25-50, 50-75 and 75-100 cm). The major goal of this research was to study the SOCS variability at regional scale. The soils investigated in this study included Phaeozems, Cambisols, Regosols and Leptosols. Total SOCS in the Despeñaperros Natural Park was over 28.2% greater when SCS were used compared to ESP, ranging from 0.8144 Tg C (10,604.2 Mg km(-2)) to 0.6353 Tg C (8272.1 Mg km(-2)) respectively (1 Tg = 10(12) g). However, when the topsoil (surface horizon and superficial section control) was analyzed, this difference increased to 59.8% in SCS compared to ESP. The comparison between ESP and SCS showed the effect of mixing pedogenetic horizons when depth increments were analyzed. This indicates an overestimate of T-SOCS when sampling by SCS.

Effects of long-term grazing disturbance on the belowground storage of organic carbon in the Patagonian Monte, Argentina

The objective of this study was to analyze the effect of grazing disturbance on the amount and the spatial distribution (vertical and horizontal) of root biomass and soil organic carbon (SOC) in order to evaluate whether grazing alters the belowground storage of organic carbon (C) in arid rangelands of the Patagonian Monte. We selected three representative sites (3 ha each) with low, moderate and high grazing disturbance located far, mid-distance and near the watering point, respectively, in rangelands submitted to sheep grazing for more than 100 years. We assessed the canopy structure and identified the four most frequent plant patch types at each site. We selected four replications of each patch type and extracted a soil sample (0-30 cm depth) underneath the canopy and in the middle of the nearest inter-patch bare soil area in winter and summer. We assessed the root and soil dry mass and the respective organic C concentration in each sample and then we estimated the total belowground organic C storage at each site. Total plant and perennial grass cover were lower with high than low grazing disturbance while the reverse occurred with dwarf shrub cover. High grazing disturbance led to the increase in total root biomass in the whole soil profile of patch areas and in the upper soil of inter-patch areas. SOC was higher in patch than in inter-patch areas at all sites but at both areas was reduced with high grazing disturbance. This was probably the result of the low total plant cover and the low and recalcitrant contribution of above and below-ground plant litter to soils at sites with high grazing disturbance. Accordingly, these changes did not result in variations in the total belowground organic C storage. We concluded that high grazing disturbance did not affect the total belowground organic C storage but led to changes in the spatial patterning of this organic C storage (i.e shifting from soil to roots).