Cause, conseguenze e strategie di mitigazione Proponiamo il primo di una serie di articoli in cui affronteremo l’attuale problema dei mutamenti climatici. Presentiamo il documento redatto, votato e pubblicato dall’Ipcc - Comitato intergovernativo sui cambiamenti climatici - che illustra la sintesi delle ricerche svolte su questo tema rilevante.

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Climate Change 2007: The Physical Science Basis.

The relationship between soil structure and the ability of soil to stabilize soil organic matter (SOM) is a key element in soil C dynamics that has either been overlooked or treated in a cursory fashion when developing SOM models. The purpose of this paper is to review current knowledge of SOM dynamics within the framework of a newly proposed soil C saturation concept. Initially, we distinguish SOM that is protected against decomposition by various mechanisms from that which is not protected from decomposition. Methods of quantification and characteristics of three SOM pools defined as protected are discussed. Soil organic matter can be: (1) physically stabilized, or protected from decomposition, through microaggregation, or (2) intimate association with silt and clay particles, and (3) can be biochemically stabilized through the formation of recalcitrant SOM compounds. In addition to behavior of each SOM pool, we discuss implications of changes in land management on processes by which SOM compounds undergo protection and release. The characteristics and responses to changes in land use or land management are described for the light fraction (LF) and particulate organic matter (POM). We defined the LF and POM not occluded within microaggregates (53–250 μm sized aggregates as unprotected. Our conclusions are illustrated in a new conceptual SOM model that differs from most SOM models in that the model state variables are measurable SOM pools. We suggest that physicochemical characteristics inherent to soils define the maximum protective capacity of these pools, which limits increases in SOM (i.e. C sequestration) with increased organic residue inputs.

Stabilization mechanisms of soil organic matter: Implications for C-saturation of soils

The talk with present the key results of the IPCC Working Group III 5th assessment report. Concluding four years of intense scientific collaboration by hundreds of authors from around the world, the report responds to the request of the world's governments for a comprehensive, objective and policy neutral assessment of the current scientific knowledge on mitigating climate change. The report has been extensively reviewed by experts and governments to ensure quality and comprehensiveness.

Climate change 2014 - Mitigation of climate change

Soil disturbance from tillage is a major cause of organic matter depletion and reduction in the number and stability of soil aggregates when native ecosystems are converted to agriculture. No-till (NT) cropping systems usually exhibit increased aggregation and soil organic matter relative to conventional tillage (CT). However, the extent of soil organic matter changes in response to NT management varies between soils and the mechanisms of organic matter stabilization in NT systems are unclear. We evaluated a conceptual model which links the turnover of aggregates to soil organic matter dynamics in NT and CT systems; we argue that the rate of macroaggregate formation and degradation (i.e. aggregate turnover) is reduced under NT compared to CT and leads to a formation of stable microaggregates in which carbon is stabilized and sequestered in the long term. Therefore, the link between macroaggregate turnover, microaggregate formation, and C stabilization within microaggregates partly determines the observed soil organic matter increases under NT.

Soil macroaggregate turnover and microaggregate formation: a mechanism for C sequestration under no-tillage agriculture

https://www.ipcc-nggip.iges.or.jp/public/gpglulucf/gpglulucf_files/0_Task1_Cover/Cover_TOC.pdf

Good Practice Guidance for Land Use, Land-Use Change and Forestry

Biochar has been heralded as an amendment to revitalize degraded soils, improve soil carbon sequestration, increase agronomic productivity, and enter into future carbon trading markets. However, scientific and economic technicalties may limit the ability of biochar to consistently deliver on these expectations. Past research has demonstrated that biochar is part of the black carbon continuum with variable properties due to the net result of production (e.g., feedstock and pyrolysis conditions) and postproduction factors (storage or activation). Therefore, biochar is not a single entity but rather spans a wide range of black carbon forms. Biochar is black carbon, but not all black carbon is biochar. Agronomic benefits arising from biochar additions to degraded soils have been emphasized, but negligible and negative agronomic effects have also been reported. Fifty percent of the reviewed studies reported yield increases after black carbon or biochar additions, with the remainder of the studies reporting alarming decreases to no significant differences. Hardwood biochar (black carbon) produced by traditional methods (kilns or soil pits) possessed the most consistent yield increases when added to soils. The universality of this conclusion requires further evaluation due to the highly skewed feedstock preferences within existing studies. With global population expanding while the amount of arable land remains limited, restoring soil quality to nonproductive soils could be key to meeting future global food production, food security, and energy supplies; biochar may play a role in this endeavor. Biochar economics are often marginally viable and are tightly tied to the assumed duration of agronomic benefits. Further research is needed to determine the conditions under which biochar can provide economic and agronomic benefits and to elucidate the fundamental mechanisms responsible for these benefits.

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Biochar: a synthesis of its agronomic impact beyond carbon sequestration.

Farmers have long recognized the organic matter content of a soil as a key attribute of soil fertility. The development of agriculture in temperate regions has exhibited patterns of exploitative soil use followed by the introduction of regenerative practices as soil resources fell to unacceptable levels. In the simplest terms, the level of soil organic carbon (C) in a soil will be governed by the difference between inputs of organic matter and outputs through mineralization, erosion, and leaching. The controls on decomposition processes are, in most respects, more complex and less easily manipulated by management than are inputs of organic matter. Climate and soil differences constrain management options and thereby determine which practices are most important in affecting soil C. Plant residues are the major source of C inputs in all terrestrial ecosystems. The history of agriculture is replete with examples of the depletion of organic matter and the subsequent loss of soil fertility through poor management.

Management controls on soil carbon

The low temperature pyrolysis of organic material produces biochar, a charcoal like substance. Biochar is being promoted as a soil amendment to enhance soil quality, it is also seen as a mechanism of long-term sequestration of carbon. Our experiments tested the hypothesis that biochar is inert in soil. However, we measured an increase in CO2 production from soils after biochar amendment which increased with increasing rates of biochar. The ∂13C signature of the CO2 evolved in the first several days of the incubation was the same as the ∂13C signature of the biochar, confirming that biochar contributed to the CO2 flux. This effect diminished by day 6 of the incubation suggesting that most of the biochar C is slowly decomposing. Thus, aside from this short-term mineralization increasing soil C with young biochar may indeed be a long-term C storage mechanism.

The effect of young biochar on soil respiration

Publisher Summary This chapter reviews past progress toward enhancing the level and quality of organic matter in soil. Annual cropping replaced fallow in many areas, which has reduced organic matter loss from soil. Greater fertilizer use and varietal improvement increased cereal grain yield and straw production, which raised the level of C return to the soil. Carbon input has shown to have a significant impact on the organic matter level. Stubble-mulch and no-till systems conserved up to 2% more organic matter per year in surface soil than plowing. Crop rotation, green manuring, and reduced tillage practices have lost some of their glamour with the advent of chemical fertilizers and pesticides, and many of the long-term experiments have been discarded for more pressing research. Fertilizer and tillage research has expanded, and crop improvement has received new impetus. Less reliance on crop rotation and green manure has beenpartially responsible for increasing use of inorganic fertilizer. Soil erosion tends to increase with less crop rotation and greater reliance on mechanical tillage and clean fallow.

Long-Term Impacts Of Tillage, Fertilizer, And Crop Residue On Soil Organic Matter In Temperate Semiarid Regions

Understanding microbial dynamics is important in the development of new management strategies to reverse declining organic-matter content and fertility of agricultural soils. To determine the effects of crop rotation, crop residue management, and N fertilization, we measured changes in microbial biomass C and N and populations of several soil microbial groups in long-term (58-yr) plots under different winter wheat (Triticum aestivum L.) crop rotations. Wheat-fallow treatments included: wheat straw incorporated (5 Mg ha), no N fertilization; wheat straw incorporated, 90 kg N ha , wheat straw fall burned, no N fertilization; and wheat straw incorporated, 11 Mg barnyard manure ha. Annual-crop treatments were: continuous wheat, straw incorporated, 90 kg N ha, wheat-pea (Pisum sativum L.) rotation (25 yr), wheat and pea straw incorporated, 90 kg N ha 1 applied to wheat; and continuous grass pasture. Total soil and microbial biomass C and N contents were significantly greater in annualcrop than wheat-fallow rotations, except when manure was applied. Microbial biomass C in annual-crop and wheat-fallow rotations averaged 50 and 25%, respectively, of that in grass pasture. Residue management significantly influenced the level of microbial biomass C; for example, burning residues reduced microbial biomass to 57% of that in plots receiving barnyard manure. Microbial C represented 4.3, 2.8, and 2.2% and microbial N 5.3, 4.9, and 3.3% of total soil C and N under grass pasture, annual cropping, and wheat-fallow, respectively. Both microbial counts and microbial biomass were higher in early spring than other seasons. Annual cropping significantly reduced declines in soil organic matter and soil microbial biomass. View complete article To view this complete article, insert Disc 5 then click button8

Harold P. Collins

Papers

Biochar: a synthesis of its agronomic impact beyond carbon sequestration.

Management controls on soil carbon

The effect of young biochar on soil respiration

Long-Term Impacts Of Tillage, Fertilizer, And Crop Residue On Soil Organic Matter In Temperate Semiarid Regions

Crop rotation and residue management effects on soil carbon and microbial dynamics