Statistics for Spatial Data.

Natural organic biomass burning creates black carbon which forms a considerable proportion of the soil’s organic carbon. Due to black carbon’s aromatic structure it is recalcitrant and has the potential for long-term carbon sequestration in soil. Soils within the Amazon-basin contain numerous sites where the ‘dark earth of the Indians’ (Terra preta de Indio, or Amazonian Dark Earths (ADE)) exist and are composed of variable quantities of highly stable organic black carbon waste (‘biochar’). The apparent high agronomic fertility of these sites, relative to tropical soils in general, has attracted interest. Biochars can be produced by ‘baking’ organic matter under low oxygen (‘pyrolysis’). The quantities of key mineral elements within these biochars can be directly related to the levels of these components in the feedstock prior to burning. Their incorporation in soils influences soil structure, texture, porosity, particle size distribution and density. The molecular structure of biochars shows a high degree of chemical and microbial stability. A key physical feature of most biochars is their highly porous structure and large surface area. This structure can provide refugia for beneficial soil micro-organisms such as mycorrhizae and bacteria, and influences the binding of important nutritive cations and anions. This binding can enhance the availability of macro-nutrients such as N and P. Other biochar soil changes include alkalisation of soil pH and increases in electrical conductivity (EC) and cation exchange capacity (CEC). Ammonium leaching has been shown to be reduced, along with N2O soil emissions. There may also be reductions in soil mechanical impedance. Terra preta soils contain a higher number of ‘operational taxonomic units’ and have highly distinctive microbial communities relative to neighbouring soils. The potential importance of biochar soil incorporation on mycorrhizal fungi has also been noted with biochar providing a physical niche devoid of fungal grazers. Improvements in soil field capacity have been recorded upon biochar additions. Evidence shows that bioavailability and plant uptake of key nutrients increases in response to biochar application, particularly when in the presence of added nutrients. Depending on the quantity of biochar added to soil significant improvements in plant productivity have been achieved, but these reports derive predominantly from studies in the tropics. As yet there is limited critical analysis of possible agricultural impacts of biochar application in temperate regions, nor on the likelihood of utilising such soils as long-term sites for carbon sequestration. This review aims to determine the extent to which inferences of experience mostly from tropical regions could be extrapolated to temperate soils and to suggest areas requiring study.

Potential mechanisms for achieving agricultural benefits from biochar application to temperate soils: a review

A key aspect of biochar management is its 
proposed effect on soil fertility and plant production (Lehmann, 2007). Plant productivity 
is directly infl uenced by nutrient availability, 
which is a product of nutrient transformations in the soil environment (Marschner, 
2006). For that reason, there is a great deal of 
interest in how biochar infl uences nutrient 
transformations and availability of those 
nutrients for plant uptake. And although 
increasing evidence suggests that biochar 
addition to soil may enhance plant production in a variety of natural and agricultural 
environments (Lehmann and Rondon, 2006; 
Atkinson et al, 2010; Jeffery et al, 2011), the 
direct infl uence of biochar additions on soil 
nutrient cycling are inconsistent and remain 
somewhat poorly understood. This is partially due to differences in the soils, crops and 
biochar amendments used in experiments 
and the predominance of short-term studies 
in the literature.

Biochar effects on soil nutrient transformations

Biochar is increasingly being recognized by scientists and policy makers for its potential role in carbon sequestration, reducing greenhouse gas emissions, renewable energy, waste mitigation, and as a soil amendment. The published reviews on biochar application to soil have so far focused mainly on the agronomic benefits, and have paid little attention to the potential unintended effects. The purpose of this chapter is to provide a balanced perspective on the agronomic and environmental impacts of biochar amendment to soil. The chapter highlights the physical and chemical characteristics of biochar, which can impact on the sorption, hence efficacy and biodegradation, of pesticides. As a consequence, weed control in biochar-amended soils may prove more difficult as preemergent herbicides may be less effective. Since biochars are often prepared from a variety of feedstocks (including waste materials), the potential introduction of contaminants needs to be considered before land application. Metal contaminants, in particular, have been shown to impact on plant growth, and soil microbial and faunal communities. Biochar has also been shown to influence a range of soil chemical properties, and rapid changes to nutrient availability, pH, and electrical conductivity need to be carefully considered to avoid unintended consequences for productivity. This chapter highlights some key areas of research which need to be completed to ensure a safe and sustainable use of biochar. In particular, understanding characteristics of biochars to avoid ecotoxicological impacts, understanding the effects of biochar on nutrient and contaminant behavior and transport, the effects of aging and the influence of feedstock and pyrolysis conditions on key properties are some of the areas that require attention.

Biochar Application to Soil: Agronomic and Environmental Benefits and Unintended Consequences

The remarkable complexity of soil and its importance to a wide range of ecosystem services presents major challenges to the modeling of soil processes. Although major progress in soil models has occurred in the last decades, models of soil processes remain disjointed between disciplines or ecosystem services, with considerable uncertainty remaining in the quality of predictions and several challenges that remain yet to be addressed. First, there is a need to improve exchange of knowledge and experience among the different disciplines in soil science and to reach out to other Earth science communities. Second, the community needs to develop a new generation of soil models based on a systemic approach comprising relevant physical, chemical, and biological processes to address critical knowledge gaps in our understanding of soil processes and their interactions. Overcoming these challenges will facilitate exchanges between soil modeling and climate, plant, and social science modeling communities. It will allow us to contribute to preserve and improve our assessment of ecosystem services and advance our understanding of climate-change feedback mechanisms, among others, thereby facilitating and strengthening communication among scientific disciplines and society. We review the role of modeling soil processes in quantifying key soil processes that shape ecosystem services, with a focus on provisioning and regulating services. We then identify key challenges in modeling soil processes, including the systematic incorporation of heterogeneity and uncertainty, the integration of data and models, and strategies for effective integration of knowledge on physical, chemical, and biological soil processes. We discuss how the soil modeling community could best interface with modern modeling activities in other disciplines, such as climate, ecology, and plant research, and how to weave novel observation and measurement techniques into soil models. We propose the establishment of an international soil modeling consortium to coherently advance soil modeling activities and foster communication with other Earth science disciplines. Such a consortium should promote soil modeling platforms and data repository for model development, calibration and intercomparison essential for addressing contemporary challenges.

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Modeling Soil Processes: Review, Key Challenges, and New Perspectives

Differential sorption behaviour of aromatic hydrocarbons on charcoals prepared at different temperatures from grass and wood.

Rapid assessment of black carbon in soil organic matter using mid-infrared spectroscopy

Crop protection seldom takes into account soil heterogeneity at the field scale. Yet, variable site characteristics affect the incidence of pests as well as the efficacy and fate of pesticides in soil. This article reviews crucial starting points for incorporating soil information into precision crop protection (PCP). At present, the lack of adequate field maps is a major drawback. Conventional soil analyses are too expensive to capture soil heterogeneity at the field scale with the required spatial resolution. Therefore, we discuss alternative procedures exemplified by our own results concerning (i) minimally and non-invasive sensor techniques for the estimation of soil properties, (ii) the evidence of soil heterogeneity with respect to PCP, and (iii) current possibilities for incorporation of high resolution soil information into crop protection decisions. Soil organic carbon (SOC) and soil texture are extremely interesting for PCP. Their determination with minimally invasive techniques requires the sampling of soils, because the sensors must be used in the laboratory. However, this technique delivers precise information at low cost. We accurately determined SOC in the near-infrared. In the mid-infrared, texture and lime content were also exactly quantified. Non-invasive sensors require less effort. The airborne HyMap sensor was suitable for the detection of variability in SOC at high resolution, thus promising further progress regarding SOC data acquisition from bare soil. The apparent electrical conductivity as measured by an EM38 sensor was shown to be a suitable proxy for soil texture and layering. A survey of arable fields near Bonn (Germany) revealed widespread within-field heterogeneity of texture-related ECa, SOC and other characteristics. Maps of herbicide sorption and application rate were derived from sensor data, showing that optimal herbicide dosage is strongly governed by soil variability. A phytoassay with isoproturon confirmed the reliability of spatially varied herbicide application rates. Mapping areas with an enhanced leaching risk within fields allows them to be kept free of pesticides with related regulatory restrictions. We conclude that the use of information on soil heterogeneity within the concept of PCP is beneficial, both economically and ecologically.

Soil heterogeneity at the field scale: a challenge for precision crop protection

Modeling global C cycles requires in-depth knowledge about small-scale C stocks and turnover processes, yet different soil organic C (SOC) pools reveal considerable spatiotemporal heterogeneity at the fleld scale, which is scarcely known due to the considerable workload associated with traditional fractionation procedures. We investigated the potential of mid-infrared spectroscopy combined with partial least squares regression (MIRS-PLSR) for rapid assessment of different particulate organic matter (POM) pools and their spatial heterogeneity at the field scale. Locally calibrated prediction models estimated the contents of SOC, POM of three size classes (POM1: 2000-250 μm; POM2: 250-53 μm; and POM3: 53-20 μm), and lignin contents for 129 locations in a 1.3-ha test field. Relations between the parameters were described using correlation analysis and fuzzy- κ statistics. All parameters were predicted successfully by applying local calibrations for MIRS-PLSR (R 2 = 0.77-0.96). The prediction model for POM1 chiefly relied on specific signals of lignin and cellulose; contents of POM2 were estimated by spectral bands assigned to degradation products as aliphatic C-H groups and aromatic moieties; carboxylic groups essentially contributed to the prediction of POM3. There was a close spatial relation between the coarse POM1 and POM2 fractions and lignin (κ = 0.77), which largely also explained variations in bulk SOC. In contrast, POM3 exhibited a less deterministic pattern in the field, thus contributing little to the spatial variation in SOC content.

Ludger Bornemann

Papers

Differential sorption behaviour of aromatic hydrocarbons on charcoals prepared at different temperatures from grass and wood.

Rapid assessment of black carbon in soil organic matter using mid-infrared spectroscopy

Soil heterogeneity at the field scale: a challenge for precision crop protection

Particulate Organic Matter at the Field Scale: Rapid Acquisition Using Mid-Infrared Spectroscopy

Differentiation of charcoal, soot and diagenetic carbon in soil: Method comparison and perspectives