Regional simulation of long‐term organic carbon stock changes in cropland soils using the DNDC model: 1. Large‐scale model validation against a spatially explicit data set

Abstract

Because of the large spatial and temporal variability of soil organic carbon (SOC) dynamics, a modelling approach is crucial in detailed regional analyses. Several estimates of regional scale SOC sequestration potential have been made using dynamic soil organic matter (SOM) models which have been linked to spatial databases contained within a Geographic Information System. In all these previous studies, a large‐scale model validation, which provides information on the general model performance for the study area under concern, was impossible because of lack of data. A data set of over 190 000 SOC measurements, grouped as means per community and covering the period 1989–2000 was available for Flanders in northern Belgium. In order to validate the DNDC model at a large spatial scale, we used this data set along with detailed pH, soil texture and crop areas which were all available at the municipality scale to simulate SOC stocks for the entire study area during the period 1990–2000. A minor adjustment of the initial distribution of SOC in the model's SOC pool was necessary to fit the simulated SOC stock changes to the measured decrease of −475 kg OC ha−1 year−1 (0–30 cm). Although DNDC was able to simulate the SOC stock changes well for the whole study area, the simulated decrease in the SOC stocks was overestimated for communities predominantly having sandy textures and underestimated for communities with silt loam to silt textures. This study also urges caution with the application of SOM models at regional scales after limited validation or calibration at the field scale as these do not guarantee good simulation of spatial variation in SOC changes.

Linking an economic model for European agriculture with a mechanistic model to estimate nitrogen and carbon losses from arable soils in Europe

“…The combination -sub-continental coverage on one hand and detailed and consistent assessment of land use and agricultural management on the other hand -distinguishes our approach from other studies (e.g. Kesik et al, 2005;Neufeld et al, 2006;Schröter et al, 2005;Sleutel et al, 2006). The linkage and consistency with national and international statistics regarding land use, crop production and nitrogen application is especially important in view of potential future applications for reporting requirements (such as the reporting under the United Nations Framework Convention on Climate Change -UNFCCC).…”

“…DNDC has been widely used for regional modelling studies in the USA (Tonitto et al, 2007), China Xu-Ri et al, 2003), India (Pathak et al, 2005) and Europe (Brown et al, 2002;Butterbach-Bahl et al, 2004;Neufeldt et al, 2006;Sleutel et al, 2006). The simulations reported here were done with a modified version of DNDC V.89, allowing a more flexible simulation of a large number of pixelclusters.…”

Soil‐organic‐matter stability in sandy cropland soils is related to land‐use history

“…Bulked samples were then mixed and dried to the air. In addition, a group of 5 "permanent" sandy cropland soils under cultivation for hundreds of years, previously collected in the W of Flanders (Sleutel et al, 2006), was also included. Their historical land use as croplands was confirmed from the Ferraris maps at least until 1775 and intermediately from the National Soil Survey dating back to the 1950s (Van Orshoven et al, 1988).…”

“…Based on a very large SOC database (over 100,000 fields sampled between 1989 and 2000), Sleutel et al (2006) found sandy soils in Flanders (the N part of Belgium) to have an average organic-carbon (OC) percentage of 1.9% OC compared to only 1.2% OC for example in silt soils. Previously, both regional-scaled OC modeling exercises (Sleutel et al, 2006) as well as OC balances (Sleutel et al, 2007a) indicated that differences in current management in terms of both crop rotation as well as fertilization are unable to explain these differences in SOC levels. The higher stability of the organic matter (OM) present in these soils may, however, be explained by specific types of earlier land use, e.g., heathland and the use of plaggen manure over centuries, which was practiced in NW Europe.…”

State-Space Estimation of Soil Organic Carbon Stock

“…Forests represent one of the largest carbon pools on earth (van de Walle et al, 2001), and their soils an essential carbon sink. Factors like management and texture (Sleulet et al, 2006), aggregate turnover (Oades, 1988) and oxides (Carter, 1996), in oxide-rich soils, play an active role in SOC stabilization. A considerable positive association of clay and SOC contents has been reported on the Broadbalk wheat field at Rothamsted (Watt et al, 2006).…”