Carbon Stocks In Agricultural Soils Research Articles

Testing the feasibility of quantifying change in agricultural soil carbon stocks through empirical sampling

There is disagreement about the potential for regenerative management practices to sequester sufficient soil organic carbon (SOC) to help mitigate climate change. Measuring change in SOC stocks following practice adoption at the grain of farm fields, within the extent of regional agriculture, could help resolve this disagreement. Yet sampling demands to quantify change are considered infeasible primarily because within-field variation in stock sizes is thought to obscure accurate quantification of management effects on incremental SOC accrual. We evaluate this ‘infeasibility assumption’ using high-density (e.g., 0.1 ha sample–1), within-field, sampling data from 45 cropland fields inventoried for SOC. We explore how more typical within-field sampling densities, as well as field numbers and magnitude of simulated change in SOC stocks, impacts the ability to accurately quantify management effects on SOC change. We find that (1) stock change estimates for individual fields are inaccurate and variable, where marked losses and gains in SOC stocks are frequently estimated even when no change has occurred. Higher sampling densities (e.g., 1.2 versus 4.0 ha sample–1) narrow the range of estimated stock changes but inaccuracies remain large. (2) The accuracy of stock change estimates at the project level (i.e., multiple fields) were similarly sensitive to sampling density. In contrast to individual fields, however, higher sampling densities, as well as a greater number of fields (e.g., 30), generated robust and accurate, mean project-level estimates of carbon accrual, with ∼ 80 % of the estimates falling within 20 % of the simulated stock change. Yet such monitoring designs do not account for dynamic baselines, which necessitates measurement of stock changes in control, non-regenerative fields. We find (3) that higher sampling densities (e.g., 1.2 versus 4.0 ha sample–1), field numbers (e.g., 30 versus 10 pairs of fields), and magnitudes of simulated SOC stock change (+3 and +5 versus +1 Mg C ha−1 10 y–1) are then collectively required to make accurate estimates of management effects on stock change at the project level. The simulated effect sizes that could be consistently detected under these conditions included rates of SOC accrual considered achievable and meaningful for climate mitigation (e.g., 3 Mg C ha−1 10 y–1), with field numbers and sampling densities that are reasonable given current sampling methods. Our findings reveal the potential to use empirical approaches to accurately quantify, at project scales, SOC stock responses to practice change. We provide recommendations for data that government, farmer and corporate entities should measure and share to build confidence in the effects of regenerative practices, freeing the SOC debate from overreliance on theory and data collected at scales mismatched with agricultural management.

Testing the feasibility of quantifying change in agricultural soil carbon stocks through empirical sampling.

Abstract There is disagreement about the potential for regenerative management practices to sequester sufficient soil organic carbon (SOC) to help mitigate climate change. Measuring change in SOC stocks following practice adoption at the grain of farm fields, within the extent of regional agriculture, could help resolve this disagreement. Yet sampling demands to quantify change are considered infeasible primarily because within-field variation in stock sizes is thought to obscure accurate quantification of management effects on incremental SOC accrual. We evaluate this 'infeasibility assumption' using high-density (e.g., 0.1 ha sample -1 ), within-field, sampling data from 45 cropland fields inventoried for SOC. We explore how more typical within-field sampling densities, as well as field numbers and magnitude of simulated change in SOC stocks, impacts the ability to accurately quantify management effects on SOC change. We find that (1) stock change estimates for individual fields are inaccurate and variable, where marked losses and gains in SOC stocks are frequently estimated even when no change has occurred. Higher sampling densities (e.g., 1.2 versus 4.0 ha sample -1 ) narrow the range of estimated stock changes but inaccuracies remain large. (2) The accuracy of stock change estimates at the project level (i.e., multiple fields) were similarly sensitive to sampling density. In contrast to individual fields, however, higher sampling densities, as well as a greater number of fields (e.g., 30), generated robust and accurate, mean project-level estimates of carbon accrual, with ~80% of the estimates falling within 20% of the simulated stock change. Yet such monitoring designs do not account for dynamic baselines, which necessitates measurement of stock changes in control, non-regenerative fields. We find (3) that higher sampling densities (e.g., 1.2 versus 4.0 ha sample -1 ), field numbers (e.g., 30 vs. 10 pairs of fields), and magnitudes of simulated SOC stock change (+3 and +5 versus +1 Mg C ha -1 10 y -1 ) are then collectively required to make accurate estimates of management effects on stock change at the project level. The simulated effect sizes that could be consistently detected under these conditions included rates of SOC accrual considered achievable and meaningful for climate mitigation (e.g., 3 Mg C ha -1 10 y -1 ), with field numbers and sampling densities that are reasonable given current sampling methods. Our findings reveal the potential to use empirical approaches to accurately quantify, at project scales, SOC stock responses to practice change. We provide recommendations for data that government, farmer and corporate entities should measure and share to build confidence in the effects of regenerative practices, freeing the SOC debate from overreliance on theory and data collected at scales mismatched with agricultural management.

Soil Carbon Stock and Soil Properties under Different Land Use Types of Agriculture

Agriculture soils play a crucial role in carbon storage and food security. However, uncertainty remains about soil carbon stocks due to spatial variability. This study estimated soil carbon stocks in agricultural land and examined the impact of land use and soil properties on soil organic carbon in Ratchaburi Province, Thailand. Soil samples were collected at three depths (0-10, 10-20, and 20-30 cm) within five different land use types: cassava, coconut, paddy fields, pineapple, and sugarcane. The results revealed that soil organic carbon decreased with increasing depth. Significant differences in soil carbon and soil properties were observed among land uses. The carbon stocks at 0-30 cm depth were as follows: coconut (35.87 mg C/ha), paddy fields (31.17 mg C/ha), sugarcane (28.02 mg C/ha), pineapple (21.79 mg C/ha), and cassava (16.12 mg C/ha). The carbon stocks were significantly correlated with sand, density, clay, silt, and pH. This study highlights the impact of land use types on carbon stocks in agricultural soils and emphasizes the role of soil properties, particularly soil texture, in influencing carbon storage variability. Furthermore, the study highlights the carbon storage potential in agricultural areas, which could guide the formulation of policies to utilize agricultural land to offset CO2 emissions from other sectors.

Importance of resilient pastures for New Zealand’s agricultural soil carbon stocks

New Zealand’s agricultural pastures contain significant soil carbon (C) stocks that are susceptible to change when impacted by management and natural processes (e.g., climate). Inputs of C to these pastoral soils is through photosynthetic uptake of atmospheric CO2 either on-site or elsewhere. Changes in soil C stocks are in response to the management of the system that alters the input-output balance. Increasing the resilience of pastures to climatic events such as hot and dry summers or cool and wet winters can increase inputs of C to the soil while sustaining above-ground production and so provide an opportunity for C sequestration. Furthermore, increased pasture for grazing can reduce the need for management practices identified as detrimental for soil C stocks such as irrigation or the production of cropped supplemental feed. A reduction in the need for renewal and its associated soil C losses, and the establishment of a more diverse sward, especially if deeper-rooting species are included, has the potential for increasing soil C stocks provided the diversity can be maintained. From a soil C perspective, a resilient pasture maximises CO2 uptake to ensure adequate above- and below-ground inputs to maintain or increase soil C stocks and minimise the need for management activities detrimental to soil C.

Factors controlling the variation in organic carbon stocks in agricultural soils of Germany

This study gives an overview of soil organic carbon (SOC) stocks in Germany's agricultural soils, and quantifies and explains the influence of explanatory variables such as land use and management, soil type and climate. Over 2500 agricultural sites were sampled and their SOC stocks determined, together with other soil properties. Machine‐learning algorithms were used to identify the most important variables. Land use, land‐use history, clay content and electrical conductivity were the main predictors in the topsoil, whereas bedrock material, relief and electrical conductivity governed the variation in subsoil carbon stocks. We found that 32% of all soil profiles were anthropogenically transformed. The influence of climate variables was surprisingly small, whereas site variables, in particular in the subsoil, explained a large proportion of the variation in soil carbon. The understanding of SOC dynamics at the regional scale requires a thorough description of the spatial variation in soil properties. The effect of agronomic management on SOC stocks was important near the soil surface, but was mainly attributable to land use (grassland or arable and not to other management factors.Highlights Factors affecting spatial variation of soil organic carbon stocks are largely unknown. More than 200 possible predictors for this variation were assessed for over 2500 sites. Land use (history), texture, electrical conductivity, bedrock and relief were main controlling factors of carbon stock variation. Aggregation and carbon storage capacity of soil determine much of the spatial variation in carbon stocks.

Potential impacts of climate change on soil organic carbon and productivity in pastures of south eastern Australia

Increasing soil organic carbon (SOC) stocks is an often-mentioned option to mitigate greenhouse gas emissions. However, increasing carbon stocks in agricultural soils is difficult and the ability of soils to store carbon as the climate changes is uncertain. This is due to many interacting factors, including those that vary spatially, contributing to organic matter inputs and decomposition rates. We used two models, the Sustainable Grazing Systems whole-farm system model (SGS) and the RothC soil carbon model, to investigate the potential impacts of climate change on SOC stocks in pastures in a temperate, winter-dominant rainfall region of south eastern Australia. A wide range of possible future climates were simulated from 2017 to 2090 at two sites, each with two soil types. Results demonstrate that projected rainfall, the factor with the most variability between climate scenarios, was the primary source of uncertainty in SOC response. Dry climate projections resulted in lower SOC content than other scenarios. The two models were similar in their projected trends, but the RothC model generally gave larger percent changes in soil carbon over the simulation period and a larger range of responses due to changes in site characteristics, particularly clay content. Sustainable stocking rates were determined by the whole-farm system model based on climate, pasture production, and maintaining minimum dry matter coverage. Wet future climates lead to increased production that supported increases in stocking and increases in SOC stocks. While soil carbon accumulated at slower rates or remained steady under dry projections, lower production meant this was accompanied by decreased average 2070–2090 stocking rates, which approached zero by 2090 on the low-rainfall site. This highlights an important interaction between SOC and grazing management. The results demonstrate the extent of the uncertainty associated with soil carbon trading for farmers and the need for adaptation options that allow farms to remain sustainable and productive as the climate changes.

Soil carbon stocks along an altitudinal gradient in different land-use categories in Lesser Himalayan foothills of Kashmir

The carbon sequestration potential of soils plays an important role in mitigating the effect of climate change, because soils serve as sinks for atmospheric carbon. The present study was conducted to estimate the carbon stocks and their variation with altitudinal gradient in the Lesser Himalayan foothills of Kashmir. The carbon stocks were estimated in different land use categories, namely: closed canopy forests, open forests, disturbed forests, and agricultural lands within the altitudinal range from 900 to 2500 m. The soil carbon content was determined by the Walkley–Black titration method. The average soil carbon stock was found to be 2.59 kg m–2. The average soil carbon stocks in closed canopy forests, open forests, and disturbed forests were 3.39, 2.06, and 2.86 kg m–2, respectively. The average soil carbon stock in the agricultural soils was 2.03 kg m–2. The carbon stocks showed a significant decreasing trend with the altitudinal gradient with maximum values of 4.13 kg m–2 at 900–1200 m a.s.l. and minimum value of 1.55 kg m–2 at 2100–2400 m a.s.l. The agricultural soil showed the least carbon content values indicating negative impacts of soil plowing, overgrazing, and soil degradation. Lower carbon values at higher altitudes attest to the immature character of forest stands, as well as to degradation due to immense fuel wood extraction, timber extraction, and harsh climatic conditions. The study indicates that immediate attention is required for the conservation of rapidly declining carbon stocks in agricultural soils, as well as in the soils of higher altitudes.

Multi-scale land-use disaggregation modelling: Concept and application to EU countries

Changes of carbon stocks in agricultural soils, emissions of greenhouse gases from agriculture, and the delivery of ecosystem services of agricultural landscapes depend on combinations of land-use, livestock density, farming practices, climate and soil types. Many environmental processes are highly non-linear. If the analysis of the environmental impact is based on data at a relatively coarse-scale (e.g. farm, country, or large administrative regions), conclusions can be misleading. For an accurate assessment of agri-environmental indicators, data of agricultural activities and their dynamics are needed at high spatial resolution. In this paper, we develop and validate a spatial model for predicting the agricultural land-use areas within the homogenous spatial units (HSUs). For the EU-28 countries, we distinguish about 1.5 × 105 HSUs and we consider 30 possible land-uses to match with the classification used in the Common Agricultural Policy Regionalized Impact (CAPRI) model. The comparison of model predictions with independent observations and with a simple rule-based approach at HSU level demonstrates that the predictions are generally accurate in more than 75 % of HSUs. The frequent crops or land-use are better predicted. For non-frequent crops and/or crops requiring specific cultivation conditions, the model needs further fine-tuning.

Organic carbon stocks in agricultural soils in Ireland using combined empirical and GIS approaches

Substitution of the Intergovernmental Panel on Climate Change (IPCC) default methodology by country-specific activity data is recommended for improved estimation of baseline soil organic carbon (SOC) stocks and their changes. In the Republic of Ireland (ROI), previous studies focused either predominantly on grassland or on all land cover types but were depth-limited. To improve the accuracy, Tier 2 approaches are proposed by the IPCC. This requires an analysis of high spatial resolution databases (such as the Irish NSDB – National Soil Database) and maps, collated for major land cover, soil types and land use areas in Ireland. In this study, data were overlaid using ArcGIS to derive information for disaggregated soil types and agricultural land use areas. Empirical models were developed using separate measurement data to estimate the NSDB-derived SOC concentrations for deeper layers, using a depth distribution function and the bulk density (ρd) using pedotransfer functions. The soil type specific models (R2=0.87–0.99) had an improved estimate of SOC densities when mineral and organic soils (peat) were treated separately. The estimated SOC densities for grasslands on mineral plus organo-mineral soils at the 0–10, 0–30, 0–50 and 0–100cm depths were 52.2, 127.1, 170.9 and 213.8t C ha−1, respectively. For arable lands, the corresponding SOC densities were 29.9, 81.3, 117.6 and 167.5t C ha−1. Nationally, for all soil types, the corresponding stocks (the products of SOC density and land cover area) were estimated to be 246.9, 608.1, 829.5 and 1079.3Tg for grassland, and 13.5, 36.7, 50.2 and 67.0Tg for arable lands in the three soil layers. The total national SOC stocks were estimated to be 888 at 0–30cm and 1832Tg at 0–100cm reference depths. For the complete soil profile, including peats >100cm depth, the national estimate was 2824Tg. The combined empirical models and Geographical Information System technique provide robust estimates of SOC stocks for disaggregated land covers and soil types, enabling Ireland to consider moving from Tier 1 to Tier 2 accounting methodology. This improved national inventory of the ROI is important for estimates of the C stock related to the Land Use, Land Use Change and Forestry (LULUCF) categories.

Carbon and water balance of European croplands throughout the 20th century

We assessed the effects of rising atmospheric CO2, changing climate, and farmers' practice on the carbon and water balance of European croplands during the past century (1901–2000). The coupled vegetation‐crop model ORCHIDEE‐STICS is applied over western Europe for C3 crops (winter wheat) and for maize, with prescribed historical agricultural practice changes. Not surprisingly, the enormous crop yield increase observed in all European regions, 300–400% between 1950 and 2000, is found to be dominantly explained by improved practice and varieties selection, rather than by rising CO2 (explaining a ∼11% uniform increase in yield) and changing climate (no further change in yield on average, but causing a decrease of ∼19% in the southern Iberian Peninsula). Agricultural soil carbon stocks in Europe are modeled to have decreased between 1950 and 1970, and since then to have increased again. Thus, the current stocks only differ by 1 ± 6 tC ha−1 from their 1900 value. Compensating effects of increasing yields on the one hand (increasing stocks) and of higher harvest index values and ploughing on the other hand (decreasing stocks) occur. Each of these processes taken individually has the potential to strongly alter the croplands soil carbon balance in the model. Consequently, large uncertainties are associated to the estimated change in carbon stocks between 1901 and 2001, roughly ±6 tC ha−1 a−1. In our most realistic simulation, the current cropland carbon balance is a net sink of 0.16 ± 0.15 tC ha−1 a−1. The annual water balance of cropland soils is influenced by increasing crop water use efficiency, one third of which is caused by rising CO2. However, increasing water use efficiency occurred mainly in spring and winter, when water is not limiting for plant growth, whereas no strong savings of soil water are achieved in summer through elevated CO2. Overall, trends in cultivation practices have caused a 3 times larger increase of water use efficiency than rising CO2.

Limited Increase of Agricultural Soil Carbon and Nitrogen Stocks Due to Increased Atmospheric CO2 Concentrations

SUMMARY Increased atmospheric concentrations of CO2 may lead to increases in agricultural soil carbon and nitrogen storage, but the impact is likely to be small and is uncertain due to limitations in other resources (e.g., nutrients, water) and interactions with climatic changes. Since only a small percentage of carbon added to the soil becomes stabilised, the impact of CO2 fertilisation of crops is considered to be very small compared to deliberate efforts to increase soil carbon by improved agricultural management. Even if agricultural soil carbon stocks are increased, carbon credits cannot be claimed under the Kyoto Protocol since the increases are not directly human-induced, a condition which must be met in order for any carbon sink to be included in emission reduction targets.