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Title: REDUCED CO2 RELEASE FROM WHEAT STRAW UNDER N-LIMITING CONDITIONS: SIMULATION OF CARBON TURNOVER

Author
item HADAS, AVIVA - THE VOLCANI CENTER,ISRAEL
item Parkin, Timothy
item STAHL, PETER - UNIVERSITY OF WYOMING

Submitted to: European Journal of Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/15/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: Organic matter is an essential component of soils, and as a general rule, the higher the organic matter content, the better the soil. Agricultural management can have a large impact on the organic matter content of soils. For example, it is widely recognized that plowing has resulted in long term decreases in soil organic matter levels. However, controversy exists concerning the influence of other agricultural practices (such as nitrogen fertilization) on soil organic matter. Some studies report that nitrogen fertilization increases soil organic matter, while other studies report that nitrogen fertilization leads to a rapid decomposition of plant residue, and can result in decreased soil organic matter levels. In this study we found that in the short term nitrogen fertilization stimulated the breakdown of plant residues to CO2, but in the long term (450 days) the total amount of carbon lost as CO2 was nearly the same for both fertilized and unfertilized treatments. The data were fit to a computer model which accurately described the decomposition of plant material in response to different levels of nitrogen. This information will help scientists understand the complex factors controlling carbon and nitrogen cycling in soils, and ultimately lead to the development of management practices to conserve soil carbon.

Technical Abstract: The turnover of residue carbon in soil under low available N condition is an important issue in high C:N residue management. The effect of extreme N deficiency on CO2 release from decomposing wheat straw was measured in an incubation experiment and interpreted by computer simulation. Straw with a C:N ratio of 91, incubated for 460 days in sand that was inoculated with a soil suspension, released CO2 at a considerably lower rate than when inorganic N was added to obtain a C:N ratio of 5. The evolution of CO2 continued longer without added N, approaching the amount released in the high N treatment with time. The simulation model NCSOIL was modified to simulate reduced CO2 release from decomposing residue when N is limiting microbial growth by: 1) including decomposers' biomass in the rate equation of residue decomposition in the form of a Monod type equation, where the biomass reduced the rate when its concentration was small compared to a saturation constant; and 2) formation of polysaccharide-like pool that received the decomposed C that could not be assimilated by the biomass due to insufficient N. The modified model simulated the reduced CO2 production in the absence of sufficient N, as a result of a smaller microbial biomass that reduced the rate of decomposition, and the formation of polysaccharides as long as the microbial efficiency was reduced by N-limiting conditions.