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United States Department of Agriculture

Agricultural Research Service

Research Project: PRINCIPLES AND PRACTICES FOR IMPROVING ORGANIC FARMING IN THE MID-ATLANTIC REGION

Location: Sustainable Agricultural Systems Laboratory

Title: Changes in soil organic carbon and nitrogen fractions with duration of no-tillage management

Authors
item Spargo, John
item Cavigelli, Michel
item Alley, Mark -
item Maul, Jude
item Buyer, Jeffrey
item Sequeira, Cleiton -
item Follett, Ronald

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 20, 2012
Publication Date: July 17, 2012
Citation: Spargo, J.T., Cavigelli, M.A., Alley, M.M., Maul, J.E., Buyer, J.S., Sequeira, C.H., Follett, R.F. 2012. Changes in soil organic carbon and nitrogen fractions with duration of no-tillage management. Soil Science Society of America Journal. 76(5):1624-1633.

Interpretive Summary: The influence of no-tillage management (NT) on soil nitrogen availability is poorly defined. We found that there was a linear increase in concentrations of many forms of soil carbon and nitrogen at the 0- to 2.5-cm soil depth during the first 11 years following adoption of NT. At the 2.5- to 7.5-cm soil depth, there was a smaller linear increase with time in NT for a small subset of these forms of soil carbon and nitrogen. No measured forms of soil carbon and nitrogen increased at the 7.5- to 15-cm soil depth but some readily available forms decreased, suggesting that the recalcitrance of soil carbon and nitrogen at 7.5- to 15-cm increased in 11 years. These patterns indicate that the concentrations of many forms of soil carbon and nitrogen are still changing to a depth of 7.5-cm and that stratification with soil depth increased after 11 years in NT. At the 0- to 2.5-cm depth, two readily available forms of soil nitrogen that are derived from soil microbial and plant biomass approached or reached new elevated equilibrium levels after 11 years. The initial rapid increase in these forms of soil nitrogen likely reflects a decrease in plant available nitrogen as nitrogen is taken up by soil microorganisms. After this initial transition period, nitrogen availability increases compared to levels under the previous tilled system. These results indicate that an absolute value for labile N pools may not be readily interpretable with respect to soil fertility recommendations without considering whether these values are changing over time or are at an equilibrium level. Different patterns of change over time for various labile forms of N indicate that these forms are distinct and may provide different types of information with respect to quantifying changes in soil fertility with time under NT. This information will be of interest to other scientists working to develop soil tests that accurately predict plant available soil nitrogen.

Technical Abstract: The influence of no-till management (NT) on labile N is poorly defined. To quantify changes in soil C and N pools with duration of NT, we sampled Kempsville sandy loam soils in the Coastal Plain of Virginia from farm fields that had similar cropping histories and nutrient management but varied in amount of time in continuous NT from 0 to 11 years. At the 0- to 2.5-cm soil depth, there was a linear increase with time in NT for total organic C, total organic N, particulate organic matter (POM)-C, POM-N, POM-C/total organic C, POM-N/total organic N, hydrolysable unidentified-N (hUN-N) and NH4-N (hNH4-N), and various biochemical classes of pyrolysate compounds determined by pyrolysis-GC/MS. At the 2.5- to 7.5-cm soil depth, there was a linear increase with time in NT for total organic C and N, hUN-N, hNH4-N, and hydrolysable amino acid-N (AA-N) and amino sugar-N (AS-N) only; these rates of increase were lower than at the 0- to 2.5-cm depth. No measured C and N pools increased at the 7.5- to 15-cm soil depth but POM-C/total organic C and POM-N/total organic N declined (p<0.10) at this depth, suggesting that the recalcitrance of C and N pools at 7.5- to 15-cm increased in 11 years. These patterns indicate that a new equilibrium level for these C and N pools had not been reached but that stratification of C and N pools with soil depth increased during 11 years in NT. At the 0- to 2.5-cm depth, the labile N pools, AA-N and AS-N approached or reached new equilibrium levels within 11 years. Since these pools are derived from soil microbial and plant biomass, the initial rapid increase in these pools likely reflects an increase in N immobilization in the short term (three to six years) following adoption of NT. After this initial transition period, levels of AA-N and AS-N approach new elevated equilibrium levels, which would be reflected in a higher net N mineralization rate than under the previous tilled system. These results indicate that an absolute value for labile N pools such as AA-N and AS-N may not be readily interpretable with respect to soil fertility recommendations without considering whether these values are changing over time or are at an equilibrium level. Different patterns of change in POM-N versus AA-N and AS-N indicate that these pools of labile N are distinct and may provide different types of information with respect to quantifying changes in soil fertility with time under NT. [GRACEnet publication].

Last Modified: 9/1/2014
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