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.
- 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.
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.
- 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.
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