:The carbon sink capacity of the world’s agricultural and degraded soils is 50 to 66% of the historic carbon loss of 42 to 78 gigatons of carbon. The rate of soil organic carbon sequestration with adoption of recommended technologies depends on soil texture and structure, rainfall, temperature, farming system, and soil management. Strategies to increase the soil carbon pool include soil restoration and woodland regeneration, no-till farming, cover crops, nutrient management, manuring and sludge application, improved grazing, water conservation and harvesting, efficient irrigation, agroforestry practices, and growing energy crops on spare lands. An increase of 1 ton of soil carbon pool of degraded cropland soils may increase crop yield by 20 to 40 kilograms per hectare (kg/ha) for wheat, 10 to 20 kg/ha for maize, and 0.5 to 1 kg/ha for cowpeas. As well as enhancing food security, carbon sequestration has the potential to offset fossilfuel emissions by 0.4 to 1.2 gigatons of carbon per year, or 5 to 15% of the global fossil-fuel emissions.

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Soil carbon sequestration impacts on global climate change and food security.

Climate Change 2007 Synthesis report

Common understanding of the causes of land-use and land-cover change is dominated by simplifications which, in turn, underlie many environment-development policies. This article tracks some of the major myths on driving forces of land-cover change and proposes alternative pathways of change that are better supported by case study evidence. Cases reviewed support the conclusion that neither population nor poverty alone constitute the sole and major underlying causes of land-cover change worldwide. Rather, peoples’ responses to economic opportunities, as mediated by institutional factors, drive land-cover changes. Opportunities and

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The causes of land-use and land-cover change: moving beyond the myths

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 Intergovernmental Panel on Climate Change (IPCC) Technical Paper Climate Change and Water draws together and evaluates the information in IPCC Assessment and Special Reports concerning the impacts of climate change on hydrological processes and regimes, and on freshwater resources – their availability, quality, use and management. It takes into account current and projected regional key vulnerabilities, prospects for adaptation, and the relationships between climate change mitigation and water. Its objectives are:

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Climate change and water.

Wheat (Triticum aestivum L.) is a major food source supplying nutrients required for adequate human nutrition. Changing fertility and cropping practices could alter the concentration of essential e...

https://bioone.org/journals/Canadian-Journal-of-Plant-Science/volume-98/issue-1/cjps-2017-0079/Effect-of-fertilizer-and-cropping-system-on-grain-nutrient-concentrations/10.1139/cjps-2017-0079.pdf

Effect of fertilizer and cropping system on grain nutrient concentrations in spring wheat1

Cultural weed control methods are becoming more important where efficacious herbicides are limited or herbicide resistance has become prevalent. Manipulating crop fertilization may be one method of reducing weed interference in crops. Nitrogen (N) fertilizer can break seed dormancy of certain weed species and thus may directly affect weed infestation densities. Added N can markedly alter crop-weed competitive interactions. Depending on the species and density, N fertilizer can increase the competitive ability of weeds more than that of the crop. Research indicates that fertilizer placement can alter weed competition with crops. Nitrogen fertilizer placement in narrow insoil bands has been found to reduce the competitive ability of downy brome (Bromus tectorum), foxtail barley (Hordeum jubatum), and wild oat (Avena fatua) more than surface broadcast. However results vary, and other

Weeds Dine Out on Nitrogen and Phosphorus

Effect of crop rotations on soil organic matter in two Black Chernozems

The reliability of reflectivity measurements for the remote sensing of crop productivity may be compromised by possible confounding effects of variation in soil color. An experiment was conducted to determine the influence of selected soil characteristics on reflectance in a broad range of soils typical of those found in southern Alberta. The reflectance of ground (< 2 mm) subsamples of 36 soils previously relocated to a common field site at Lethbridge Alberta was measured indoors with an artificial light source and a 60° field of view. Reflectance was measured between 400 and 1100 nm at 5-nm intervals. Reflectance of ground soils was strongly correlated to that of measurements in the field (r2 = 0.99), though values from the former were consistently higher. Soil reflectance declined with increasing organic carbon content in a quadratic relationship. Furthermore, there was a positive linear correlation between reflectance and soil carbonate content. Variation in organic C and carbonate accounted for 60% o...

Reflectance characteristics of southern Alberta soils

Smith, E. G., Janzen, H. H. and Larney, F. J. 2015. Long-term cropping system impact on quality and productivity of a Dark Brown Chernozem in southern Alberta. Can. J. Soil Sci. 95: 177–186. Long-term cropping system studies offer insights into soil management effects on agricultural sustainability. In 1995, a 6-yr bioassay study was superimposed on a long-term crop rotation study established in 1951 at Lethbridge, Alberta, to determine the impact of past cropping systems on soil quality, crop productivity, grain quality, and the relationship of yield productivity to soil quality. All plots from 13 long-term crop rotations were seeded to wheat (Triticum aestivum L.) in a strip plot design [control, nitrogen (N) fertilizer]. Prior to seeding, soils were sampled to determine soil chemical properties. Total wheat production for the last 4 yr of the study was used as the measure of productivity. The 1995 soil analysis indicated crop rotations with less frequent fallow and with N input had higher soil quality, as indicated by soil organic carbon (SOC) and light fraction carbon (LF-C) and N (LF-N). SOC had a positive relationship to total wheat yield, but was largely masked by the application of N in this bioassay study. Frequent fallow in the previous crop rotation lowered productivity. The concentration of LF-C had a negative relationship, whereas LF-N had a positive relationship to total wheat yield, with and without N fertilization in this bioassay study. Grain N concentration was higher with applied N and when the long-term rotation included the addition of N by fertilizer, livestock manure, annual legume green manure or legume hay. This study determined that long-term imposition of management practices have lasting effects on soil quality and crop productivity.

H. Henry Janzen

Papers

Effect of fertilizer and cropping system on grain nutrient concentrations in spring wheat1

Weeds Dine Out on Nitrogen and Phosphorus

Effect of crop rotations on soil organic matter in two Black Chernozems

Reflectance characteristics of southern Alberta soils

Long-term cropping system impact on quality and productivity of a Dark Brown Chernozem in southern Alberta