https://pubag.nal.usda.gov/download/25515/PDF

Global soil characterization with VNIR diffuse reflectance spectroscopy

Agricultural greenhouse gas (GHG) emissions contribute approximately 12% to total global anthropogenic GHG emissions. Cereals (rice, wheat, and maize) are the largest source of human calories, and it is estimated that world cereal production must increase by 1.3% annually to 2025 to meet growing demand. Sustainable intensification of cereal production systems will require maintaining high yields while reducing environmental costs. We conducted a meta-analysis (57 published studies consisting of 62 study sites and 328 observations) to test the hypothesis that the global warming potential (GWP) of CH4 and N2O emissions from rice, wheat, and maize, when expressed per ton of grain (yield-scaled GWP), is similar, and that the lowest value for each cereal is achieved at near optimal yields. Results show that the GWP of CH4 and N2O emissions from rice (3757 kg CO2 eq ha � 1 season � 1 ) was higher than wheat (662 kg CO2 eq ha � 1 season � 1 ) and maize (1399 kg CO2 eq ha � 1 season � 1 ). The yield-scaled GWP of rice was about four times higher (657 kg CO2 eq Mg � 1 ) than wheat (166 kg CO2 eq Mg � 1 ) and maize (185 kg CO2 eq Mg � 1 ). Across cereals, the lowest yield-scaled GWP values were achieved at 92% of maximal yield and were about twice as high for rice (279 kg CO2 eq Mg � 1 ) than wheat (102 kg CO2 eq Mg � 1 ) or maize (140 kg CO2 eq Mg � 1 ), suggesting greater mitigation opportunities for rice systems. In rice, wheat and maize, 0.68%, 1.21%, and 1.06% of N applied was emitted as N2O, respectively. In rice systems, there was no correlation between CH4 emissions and N rate. In addition, when evaluating issues related to food security and environmental sustainability, other factors including cultural significance, the provisioning of ecosystem services, and human health and well-being must also be considered.

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An agronomic assessment of greenhouse gas emissions from major cereal crops

Old-growth forests have traditionally been considered negligible as carbon sinks because carbon uptake has been thought to be balanced by respiration. We show that the top 20-centimeter soil layer in preserved old-growth forests in southern China accumulated atmospheric carbon at an unexpectedly high average rate of 0.61 megagrams of carbon hectare-1 year-1 from 1979 to 2003. This study suggests that the carbon cycle processes in the belowground system of these forests are changing in response to the changing environment. The result directly challenges the prevailing belief in ecosystem ecology regarding carbon budget in old-growth forests and supports the establishment of a new, nonequilibrium conceptual framework to study soil carbon dynamics.

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Old-growth forests can accumulate carbon in soils.

Determining soil carbon stock changes: Simple bulk density corrections fail

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Remote sensing of regional crop production in the Yaqui Valley, Mexico: estimates and uncertainties

Changes in soil and vegetation management can impact strongly on the rates of carbon (C) accumulation and loss in soil, even over short periods of time Detecting the effects of such changes in accumulation and loss rates on the amount of C stored in soil presents many challenges Consideration of the temporal and spatial heterogeneity of soil properties, general environmental conditions, and management history is essential when designing methods for monitoring and projecting changes in soil C stocks Several approaches and tools will be required to develop reliable estimates of changes in soil C at scales ranging from the individual experimental plot to whole regional and national inventories In this paper we present an overview of soil properties and processes that must be considered We classify the methods for determining soil C changes as direct or indirect Direct methods include field and laboratory measurements of total C, various physical and chemical fractions, and C isotopes A promising direct method is eddy covariance measurement of CO2 fluxes Indirect methods include simple and stratified accounting, use of environmental and topographic relationships, and modeling approaches We present a conceptual plan for monitoring soil C changes at regional scales that can be readily implemented Finally, we anticipate significant improvements in soil C monitoring with the advent of instruments capable of direct and precise measurements in the field as well as methods for interpreting and extrapolating spatial and temporal information

L. K. Mann

Papers

Monitoring and verifying changes of organic carbon in soil