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United States Department of Agriculture

Agricultural Research Service

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National Program 204: Global Change
Component I: Carbon Cycle and Carbon Storage
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1 - Introduction
2 - Cropping System and Tilage
3 - Grazinglands, CRP and Buffers
4 - Irrigation and Water Managment
5 - Plantation Tree Farming
6 - Organic Carbon Transformations
7 - Inorganic Carbon
8 - Interactions of Carbon and Nitrogen Cycles
9 - Measurement, Validation and Modeling
Interactions of Carbon and Nitrogen Cycles

Problem Statement

Rationale. Most agricultural soils in temperate climates have lost significant amounts of original organic carbon because of excessive tillage. Conservation tillage practices that include reduced and no-tillage farming and increased cropping intensity, along with reseeding of marginal croplands to permanent cover, can increase soil organic matter and store a significant portion of the carbon released during the burning of fossil fuels. However, carbon and nitrogen cycles are linked such that storing carbon in soil requires inputs of nitrogen.

What is known. Several sources of nitrogen contribute to the soil nitrogen pool and can be available for incorporation into soil organic matter. Commercial fertilizer is a major source of nitrogen for conventional farming. Production of commercial fertilizer requires large amounts of energy and consumes fossil fuel. The effect of microbial activity on atmospheric nitrogen, associated with legumes for example, is a low input source of significant amounts of nitrogen. Animal wastes are an important source of nitrogen to the soil, but concentrating animals some distance from the production sites has created distribution problems. Rain and snow annually contribute a small amount of nitrogen to all terrestrial systems. Nitrogen in unharvested plant material is the largest single source of nitrogen returned to the soil in most cropping systems. The availability of this nitrogen for plant use depends on the carbon-to-nitrogen ratio and the quality of carbon in the plant residue. The wider the ratio and the more lignin tissue in the plant material, the slower the release of nitrogen during decomposition. The soil is a major repository for atmospheric methane, but ammonia-based fertilizer has been shown to interfere with methane oxidation.

Gaps. Increasing soil organic matter as stored carbon makes nitrogen less available for plant growth. There are economic and/or environmental problems associated with all available sources of nitrogen, and nitrogen transformations in the soil affect both the storage and release of soil carbon. Both the production and application of commercial nitrogen fertilizer require the use of fossil fuels, thus adding to atmospheric carbon dioxide. Legumes will not economically fit into all crop rotations; methods of increasing nitrogen fixation by free-living (neither parasitic nor symbiotic) microbes are poorly understood; animal wastes are concentrated in locations away from production areas; and deposition of nitrogen in precipitation is a small portion of crop needs. It is known that microbial oxidation of ammonia-containing compounds increases soil acidity, but the amount of acidification and the resulting carbon dioxide emissions have not been quantified.

Goals

  • Define cropping systems, by location, that can economically incorporate legumes into the rotation;
  • Determine how to promote free-living nitrogen-fixing organism in areas or cropping systems not adapted to use of legumes;
  • Quantify the acidification that occurs during the oxidation of organic sources of nitrogen in the presence of growing crops;
  • Quantify the impacts of plants grown with elevated carbon dioxide on plant protein (nitrogen) content and on nitrogen requirements for decomposition;
  • Determine the effects of elevated carbon dioxide on the processes and mechanisms of soil carbon and nitrogen interactions; and
  • Determine the duration and magnitude of interference by ammonia-based fertilizer on methane oxidation.

Approach

Existing experimental data on use of legumes in crop rotations in different geographic and climatic areas will be analyzed to determine where it is feasible to incorporate legumes into crop rotations. Economic models will be used to determine where and when legumes can be used economically. Laboratory and field experiments will be conducted to determine how to encourage nitrogen fixation by free-living microorganisms, and laboratory and field experiments will be used to quantify the acidification that occurs from oxidation of organic nitrogen sources. Long-term research plots and natural systems in various climates will be examined to determine the extent and duration of interference by ammonia-based fertilizers with methane oxidation.

Outcomes

  • New and improved management practices will promote the use of legumes or free-living nitrogen fixing microorganisms, reducing the need for fossil fuel based commercial fertilizer.
  • The amount of soil carbon in cultivated lands will increase in response to increased cropping intensity and the availability of nitrogen.
  • Soil acidification by nitrogen fertilizers will be reduced, decreasing the loss of inorganic carbon from applications of lime or from calcium-containing soils.
  • Conservation practices will remain economically viable, meet the needs of a growing population, and will contribute to the reduction of fossil fuel use for food production.

Impact

Increased nitrogen availability to store carbon in the soil, improve soil productivity, and reduce fossil fuel use in food production

Linkages to Other ARS National Programs

  • Integrated Agricultural Systems
  • Rangeland, Pasture and Forages
  • Soil Resource Management

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Last Modified: 10/28/2008
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