: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.

Leonardite, an oxidized form of lignite obtained from coal mines, is readily available and high in humic acids (HA). It has potential as a soil amendment and may have positive effects on crop growt...

Response of canola, wheat and green beans to leonardite additions

Many agricultural fields on the semiarid Canadian prairies have areas of inherently low productivity associated with loss of soil quality due to erosion. This study compared the efficacy of various amendments in restoring productivity to a desurfaced fine-loamy, mixed Typic Haploboroll (Lethbridge series) in southern Alberta. In spring 1992, 14 amendment treatments (including livestock manures, crop residues, combinations of straw and chemical fertilizer, and fertilizer alone) were applied to a site where the Ap horizon ( 15-cm depth) had been mechanically removed to simulate erosion. The manures and crop materials were incorporated into the degraded surface on an equivalent dry-weight basis at 20 Mg ha -1 . The plots were seeded to spring wheat (Triticum aestivum L.) in 1992, 1993, and 1994. The overall best amendments were hog manure, poultry manure, and alfalfa hay. In all years, yields from desurfaced plots amended with hog or poultry manure were not significantly different from plots with no topsoil removal. Nitrate-N concentration in the 0- to 60-cm soil depth explained 71% of the variation in restorative ability of the amendments, while extractable P concentrations in the 0- to 15-cm depth explained 16% of this variation. Results demonstrate that livestock manures and crop residues can restore productivity to eroded soils by substituting for lost topsoil. Application of high rates of manure to severely eroded soils offers a means of utilizing the large amounts of manure generated by southern Alberta feedlot operations.

Restoration of productivity to a desurfaced soil with livestock manure, crop residue, and fertilizer amendments

The dynamics of soil organic C after a change in cropping practice are important in defining the potential impact of the new practice on soil behavior and net CO2 exchange. Our objective was to determine the duration and magnitude of a shift in soil organic C after a change in summer fallow frequency in spring wheat (Triticum aestivum L.) systems. Total organic and light-fraction C in continuous wheat (W), fallow-wheat-wheat (FWW), and fallow-wheat (FW) treatments were determined in soil samples collected periodically from 1954 to 1992 from a long-term spring wheat study located in the northern Great Plains. Organic C concentrations in the 0- to 15-cm depth were 11% lower in the FW and FWW treatments than in the W treatment from 1967 to 1992. Organic C concentrations in the 15- to 30-cm depth were not affected by treatment, but varied among sampling years due to differences in effective sampling depth. Light-fraction C concentrations were 38% lower in the FW and FWW treatments than in the W treatment from 1967 to 1992. Reduced light-fraction C accounted for about one-third of the decrease in total organic C due to inclusion of fallow in the crop rotation. The negative influence of fallow was primarily due to enhanced decomposition in the fallow year. We conclude that most losses of soil organic C due to introduction of a fallow system occur within two decades, and that further loss of organic C is negligible provided soil erosion is minimal.

Total and Light-Fraction Carbon Dynamics during Four Decades after Cropping Changes

Increased environmental concern regarding the build‐up of soil phosphorus following application of organic amendments based on plant nitrogen (N) requirements will lead to an application strategy that is based on plant phosphorus (P) requirements. This will create demand for a rapid method of analyzing for total P in organic amendments in order to match application rates to plant P requirements. The wet oxidation method was evaluated in comparison with dry ashing technique for measuring total P in six organic amendments (hog, dairy cattle, beef cattle and poultry manures, municipal biosolids, and composted cattle manure) that ranged in P content from 0.25% to 4.5%. The wet oxidation method produced P concentration that was within 7% of that measured by the dry ashed method in 18 of the 24 samples analyzed and within 15% in the remaining samples. The experimental errors associated with both methods were small and the agreement between the two methods leads us to the conclusion that the wet oxidation method...

Evaluation of Analytical Methods for Total Phosphorus in Organic Amendments

Bt ( Bacillus thuringiensis ) corn is reported to produce lignin-rich residues, compared to non-Bt (NBt) corn, suggesting it is more resistant to decomposition As the Bt gene is expressed selectively in stem and leaf tissue, it could affect lignin distribution in corn, which naturally has greater lignin content in roots than in stems and leaves Our objective was to evaluate the effects of corn plant components, the Bt gene and elevated-lignin inputs on decomposition Roots, stems and leaves from Bt corn and NBt corn isolines enriched with 13 C and 15 N were finely ground and mixed separately with soil, then incubated at 20 °C for 36 weeks The effect of elevated lignin on decomposition was tested by adding a commercial lignin source (indulin lignin) to half of the samples In addition to weekly CO 2 analysis and regular measurement of N mineralization, the degree of lignin degradation was evaluated at 1 and 36 weeks from the acid to aldehyde ratio (Ad/Al) of vanillyl and syringyl lignin-derived phenols The CO 2 production and N mineralization was lower in root-amended soils than stem- and leaf-amended soils The Bt genetic modification increased CO 2 production from stem-amended soils ( P 13 C and 15 N results also showed more residue-C and -N retained in soils mixed with NBt stem residues After 36 weeks leaf- and stem-amended soils with indulin lignin had a lower Ad/Al ratio and were less degraded than soils without exogenous lignin In conclusion, plant lignin and nitrogen contents were good predictors of CO 2 production and N mineralization potential Corn roots decomposed more slowly than aboveground components emphasizing the importance of recalcitrant root residues in sustaining the organic matter content of soil

H. Henry Janzen

Papers

Response of canola, wheat and green beans to leonardite additions

Restoration of productivity to a desurfaced soil with livestock manure, crop residue, and fertilizer amendments

Total and Light-Fraction Carbon Dynamics during Four Decades after Cropping Changes

Evaluation of Analytical Methods for Total Phosphorus in Organic Amendments

Plant lignin and nitrogen contents control carbon dioxide production and nitrogen mineralization in soils incubated with Bt and non-Bt corn residues