Rico Hübner

Carbon sequestration potential of soils in southeast Germany derived from stable soil organic carbon saturation

Sequestration of atmospheric carbon (C) in soils through improved management of forest and agricultural land is considered to have high potential for global CO2 mitigation. However, the potential of soils to sequester soil organic carbon (SOC) in a stable form, which is limited by the stabilization of SOC against microbial mineralization, is largely unknown. In this study, we estimated the C sequestration potential of soils in southeast Germany by calculating the potential SOC saturation of silt and clay particles according to Hassink [Plant and Soil 191 (1997) 77] on the basis of 516 soil profiles. The determination of the current SOC content of silt and clay fractions for major soil units and land uses allowed an estimation of the C saturation deficit corresponding to the long-term C sequestration potential. The results showed that cropland soils have a low level of C saturation of around 50% and could store considerable amounts of additional SOC. A relatively high C sequestration potential was also determined for grassland soils. In contrast, forest soils had a low C sequestration potential as they were almost C saturated. A high proportion of sites with a high degree of apparent oversaturation revealed that in acidic, coarse-textured soils the relation to silt and clay is not suitable to estimate the stable C saturation. A strong correlation of the C saturation deficit with temperature and precipitation allowed a spatial estimation of the C sequestration potential for Bavaria. In total, about 395xa0Mt CO2 -equivalents could theoretically be stored in A horizons of cultivated soils - four times the annual emission of greenhouse gases in Bavaria. Although achieving the entire estimated C storage capacity is unrealistic, improved management of cultivated land could contribute significantly to CO2 mitigation. Moreover, increasing SOC stocks have additional benefits with respect to enhanced soil fertility and agricultural productivity.

Stagnating crop yields: An overlooked risk for the carbon balance of agricultural soils?

The carbon (C) balance of agricultural soils may be largely affected by climate change. Increasing temperatures are discussed to cause a loss of soil organic carbon (SOC) due to enhanced decomposition of soil organic matter, which has a high intrinsic temperature sensitivity. On the other hand, several modeling studies assumed that potential SOC losses would be compensated or even outperformed by an increased C input by crop residues into agricultural soils. This assumption was based on a predicted general increase of net primary productivity (NPP) as a result of the CO2 fertilization effect and prolonged growing seasons. However, it is questionable if the crop C input into agricultural soils can be derived from NPP predictions of vegetation models. The C input in European croplands is largely controlled by the agricultural management and was strongly related to the development of crop yields in the last decades. Thus, a glance at past yield development will probably be more instructive for future estimations of the C input than previous modeling approaches based on NPP predictions. An analysis of European yield statistics indicated that yields of wheat, barley and maize are stagnating in Central and Northern Europe since the 1990s. The stagnation of crop yields can probably be related to a fundamental change of the agricultural management and to climate change effects. It is assumed that the soil C input is concurrently stagnating which would necessarily lead to a decrease of agricultural SOC stocks in the long-term given a constant temperature increase. Remarkably, for almost all European countries that are faced with yield stagnation indications for agricultural SOC decreases were already found. Potentially adverse effects of yield stagnation on the C balance of croplands call for an interdisciplinary investigation of its causes and a comprehensive monitoring of SOC stocks in agricultural soils of Europe.

Projected loss of soil organic carbon in temperate agricultural soils in the 21st century: effects of climate change and carbon input trends

Climate change and stagnating crop yields may cause a decline of SOC stocks in agricultural soils leading to considerable CO2 emissions and reduced agricultural productivity. Regional model-based SOC projections are needed to evaluate these potential risks. In this study, we simulated the future SOC development in cropland and grassland soils of Bavaria in the 21st century. Soils from 51 study sites representing the most important soil classes of Central Europe were fractionated and derived SOC pools were used to initialize the RothC soil carbon model. For each site, long-term C inputs were determined using the C allocation method. Model runs were performed for three different C input scenarios as a realistic range of projected yield development. Our modelling approach revealed substantial SOC decreases of 11–16% under an expected mean temperature increase of 3.3u2009°C assuming unchanged C inputs. For the scenario of 20% reduced C inputs, agricultural SOC stocks are projected to decline by 19–24%. Remarkably, even the optimistic scenario of 20% increased C inputs led to SOC decreases of 3–8%. Projected SOC changes largely differed among investigated soil classes. Our results indicated that C inputs have to increase by 29% to maintain present SOC stocks in agricultural soils.

Climate-Smart Soil Management in Semiarid Regions

Abstract Given the expanding pressures on the fragile soils of semiarid regions, there is an urgent need to implement climate-smart soil management in those regions. Climate-smart soil management promotes high vegetation cover, resulting in well-structured soils with greater carbon (C) and nitrogen (N) stocks, thereby minimizing the risks to soils in semiarid regions, in particular degradation by human activities and the vicious “climate change-desertification loop,” while simultaneously helping to mitigate climate change. Climate-smart soil management encompasses all sustainable management options and associated environmental, cultural, social, and economic activities within the framework of a changing climate. In this chapter, we present a holistic and multidisciplinary understanding of management practices for semiarid areas within specific land uses under a diverse cultural and socioeconomic context. In semiarid grasslands, the reduction of grazing intensity, grazing exclusion, rotational grazing, and haymaking are all promising options for mitigating greenhouse gas emissions. In croplands, conservation tillage combined with the organic amendment of soils promotes the stabilization of C and N through the entire soil profile. In agroforestry, tree plantations design is optimized for the goals of the system, whether to minimize erosion risk or climate stresses. In semiarid forests and woodlands, the ultimate goal of management must be to conserve and, where possible, restore these fragile and threatened ecosystems. In general, climate-smart soil management entails recognizing and mirroring naturally occurring cycles and processes in semiarid regions, which are adapted within the context of a changing climate and cultural and socioeconomic conditions.

Risk assessment within agricultural production: soil conservation strategies and its environmental and economic aspects - a case study for Bavaria

The definition of risk within agricultural production systems is summarised and an overview of different sources of risks in agriculture is provided. Focusing on risks associated with the soil, the influencing factors are analysed in detail. From this, a simple methodology for a probabilistic modelling approach to evaluate the effect of the different cropping tillage system and soil conservation practices is developed concerning environmental as well as economic aspects. Selected uncertainty factors, such as rainfall and crop yields are simulated using the program @RISK. With this method, the possible future performance of various combinations of crop and management practice under given environmental conditions can be simulated and compared, considering not only soil erosion control but also increasing farmers income.