Quantifying and mapping topsoil inorganic carbon concentrations and stocks: approaches tested in France

Soils act as a sink or a source of atmospheric carbon, and great efforts are made to monitor soil organic carbon stocks, but soil inorganic carbon (SIC) stocks are not measured by many national- and continental-scale soil monitoring networks. Topsoil (0–30 cm) SIC concentrations were determined for > 2000 sites on a regular 16-km grid as part of the French, Réseau de Mesures de la Qualité des Sols (RMQS). We used design-based statistical methods to calculate unbiased estimates of the mean SIC concentration and total stocks across France. Model-based methods were used to determine the uncertainty of these estimates and to map the spatial distribution of these quantities. Observations of inorganic carbon were highly skewed and did not conform to standard statistical models. Data were normalized using a nonparametric transformation. The estimates and predictions of inorganic carbon are baselines against which the results of future phases of the network can be compared. We found that the total topsoil inorganic carbon stocks in France amount to 1070 ± 61 Tg, ca. one-third of the corresponding organic carbon stocks. Spatial distribution of SIC was strongly linked to the underlying geology. We tested the reliability of estimating SIC concentrations and stocks from the French Soil Test Database, which contains the results of 280 000 soil analyses requested by farmers between 1990 and 2004. A biased estimate of soil inorganic carbon concentrations resulted, presumably because soil samples were selected according to concerns of farmers rather than by a statistical design

Sustainability, certification, and regulation of biochar

Biochar has a relatively long half-life in soil and can fundamentally alter soil properties, processes, and ecosystem services. The prospect of global-scale biochar application to soils highlights the importance of a sophisticated and rigorous certification procedure. The objective of this work was to discuss the concept of integrating biochar properties with environmental and socioeconomic factors, in a sustainable biochar certification procedure that optimizes complementarity and compatibility between these factors over relevant time periods. Biochar effects and behavior should also be modelled at temporal scales similar to its expected functional lifetime in soils. Finally, when existing soil data are insufficient, soil sampling and analysis procedures need to be described as part of a biochar certification procedure.O “biochar” tem um tempo de meia-vida no solo relativamente longo e pode alterar substancialmente as propriedades, processos e funções do solo. A perspectiva da aplicação de “biochar” aos solos, em escala global, evidencia a importância de se lhe atribuir um processo de certificação sofisticado e rigoroso. O objetivo deste trabalho foi discutir o conceito da integração das propriedades do “biochar” com os fatores ambientais e socioeconômicos relevantes do local de aplicação selecionado, como parte de um procedimento de certificação sustentável que otimize a complementaridade e a compatibilidade entre esses fatores, em períodos de tempo relevantes. Os efeitos e o comportamento do “biochar” devem, também, ser modelados em escalas temporais similares às de seu tempo de vida funcional nos solos do local selecionado. Finalmente, onde os dados existentes sobre as características do solo forem insuficientes, procedimentos de amostragem e análise do solo devem ser descritos como parte do procedimento de certificação do “biochar”.publishe

Estimating and mapping the carbon saturation deficit of French agricultural topsoils.

The concept of soil organic C (SOC) saturation suggests that the quantity of stable SOC is limited and determined by the amount of fine particles (clay + fine silt, Clay + fSilt). The difference between the theoretical SOC saturation value and the measured SOC one for the fine fraction corresponds to the soil's saturation deficit and may represent the potential for SOC sequestration in a stable form. We calculate the saturation deficit of French arable soils based on the national soil test database and using the saturation equation. For the whole database (n = 1 454 633), the median saturation deficit was 8.1 gC/kg and this generally increased with the Clay + fSilt content to reach a maximum of 500 g/kg. National mapping of the SOC saturation deficit allowed investigation of spatial variation and controlling factors. Saturated soils were found in localities with specific land use (grassland, meadows) or farming systems (livestock production with high manure production). Smaller deficits occurred at higher altitudes, probably due to the combined effect of cooler temperature and the presence of meadows. Some very sandy soils appeared to be almost saturated, largely due to their very small fine fraction. Soils in the highly cultivated plains in the northern half of the country had a significant saturation deficit. Soils in the southern part of the country had the highest saturation deficit because of the combined effects of climatic factors (low production, high temperature) and land use (vineyards, orchards). Analysis of communal data revealed significant correlations at the national level with Clay + fSilt (r = 0.59), pH (r = 0.44) but also with the proportion of grassland in the cultivated area (r = −0.47). Some areas had apparent oversaturation which may be due to uncertainty associated with the theoretical C saturation equation because of overestimation of the stable soil C fraction. Mapping the C saturation deficit at the national scale demonstrates the influence of climate, soil parameters and land use on the SOC stabilization potential and indicates that a significant proportion of agricultural soils have potential for further SOC storage

Occurrence of natural organic chlorine in soils for different land uses

Consideration of natural formation of organochlorine compounds in soils is necessary in radioecology in order to understand chlorine radioisotope (36Cl) cycling in various environments for safety assessment purposes, but also in ecotoxicology because certain chlorinated organics in soils are toxic compounds. On the other hand, occurrence of organic chlorine in soils is poorly documented, especially in non-forest ecosystems. We measured total and organic chlorine concentrations in 51 French surface soils sampled from grassland, arable and forest sites on a national scale (French soil quality monitoring network) in order to characterize the variability of organic chlorine concentrations for these different land uses. While previous studies reported that the chlorination of soil organic matter is responsible for chlorine retention in temperate forest ecosystems, this study shows that the non-extractable organohalogen pool accounts for the majority (>80 % on an average) of the total measurable chlorine in grassland and agricultural soils. This suggests that natural chlorination is a widespread phenomenon in all kinds of soils. A multiple linear regression analysis performed on the dataset indicated that retention of organochlorine in soils is related to the organic carbon content, Cl input and soil pH

Broad-Scale Soil Monitoring Through a Nationwide Soil-Testing Database

Spatial variability of soil properties strongly influenced by human activity is not well documented by most soil surveys.Soil tests performed at farmers' request represent a large capital of soil information.In France, the results of a large part of these soil tests are continuously gathered in a unique database, the national soil testing database (named BDAT).The aims of the project were to analyse the evolution of soil features within discrete entities over successive time period

Large trends in French topsoil characteristics are revealed by spatially constrained multivariate analysis

Spatially constrained multivariate analysis methods (MULTISPATI-PCA) and classical principal component analysis are applied for the entire country of France to study the main soil characteristics of topsoil and to assess if their multivariate spatial pattern can provide insight on their extent and origin. The results of the MULTSPATI-PCA provided evidence of strong spatial structures attributed to different natural processes. The first axis was interpreted as an axis of global soil richness in clay content. Axis 2 reflected the influence of some parent materials on the geochemical content of K and Al. Axis 3 showed a very large gradient of relative content in coarse silt. Axis 4 was driven by gradients of maritime influence. We show that MULTISPATI-PCA allows better than classical PCA to detect and map large regional trends in the distribution of topsoil characteristics. The two first axes were expected and the maps obtained by both methods were consistent. Interestingly, the other gradients were not expected and were better shown by MULTISPATI-PCA than by classical PCA

Multivariate analysis of the spatial patterns of 8 trace elements using the French soil monitoring network data

International audienc

Multi-scale spatialisation of N2O emissions by soils and their mitigation potential in the Bourgogne Franche-Comté Region: advantages, limits and paths of exploitation for aiding decisions in the framework of ecological transition at local-regional scales

International audienc

Soil phosphorus monitoring at the regional level by means of a soil test database

The practice of applying large amounts of P to agricultural land over several previous decades, particularly in regions with intensive livestock production, has resulted in P accumulation in soils with an increased risk of P losses into water bodies and thus of eutrophication. This work is aimed at analyzing the spatiotemporal changes in extractable soil P content at the regional level by means of a soil test database and then comparing results with independent data from agricultural censuses. A total of 228 079 soil P-test values [Dyer method: 1:5 soil-citric acid solution (20 g/L) ratio] generated between 1980 and 2003 by certified commercial laboratories in Brittany (northwestern France) were integrated into a database. Changes in P were analysed by considering four 4-6 year periods between 1980 and 2003 using cumulative frequencies and summary statistics performed on raw soil test values. Then data were aggregated into discrete entities (canton: administrative entities) and summary statistics, linear regression and spatial distribution were carried out. P balances were measured for the same entities taken from the agricultural censuses of 1979, 1988 and 2000. Over the entire study period, a marked spatial variability was observed with higher P content in the western part of Brittany, as well as a systematic increase in median P content with lower amplitude over the past decade. The mean cantonal soil P surplus accumulated over 24 years amounted to 763 kg P/ha of usable agricultural land. Similar P balances sometimes gave rise to widely different increases in P. Cumulative balances were positively correlated with an increase in soil P (r2 = 0.34)

Phosphorus storage in soil: monitoring and analysis at national and regional scales

Soil is the major storage compartment in the global phosphorus (P) cycle is therefore a potential source of P to surface water.The aim of this paper is to analyse existing French soil test databases in order to evaluate at national regional levels the status of soil P its change over the last decades.Two main databases were considered: i.the French national Soil Test Database, which integrates soil extractable P tests from cultivated fields results from nearly 1 300 000 samples are available for the whole of France with a cantonal (roughly 20-km) resolution ii.the Finistere monitoring network, covers186 fields from western France with slurry loads monitored since 1973.Strong regional disparities are highlighted with in particular large frequencies of high soil content of extractable P in several regions, e.g.Brittany, Nord-Pas-de-Calais Alsace.A detailed study in Brittany corroborates at cantonal level a clear relation between the median Dyer P content of soil the P balance of agricultural practices, with a major influence by the cumulated spreading of animal manure.Nevertheless, the existing databases were designed for agronomic purposes give only indirect indications about the risk to the environment by soil P, as only a fraction of total P is measured.Moreover, to estimate the risk of P transfer to surface water by runoff or lixiviation, soil P retention capacity the saturation level have also to be considered.Such indicators were developed in Canada for regulatory purposes have been tested in an exploratory approach on soil samples from Brittany.Lastly, the influence of farming techniques (minimum tillage, grass strips, spread of animal manure) which strongly impact the concentration of P at the soil surface require better assessment