Environmental Management

, Volume 43, Issue 6, pp 1061–1070 | Cite as

Changes in Soil Aggregate, Carbon, and Nitrogen Storages Following the Conversion of Cropland to Alfalfa Forage Land in the Marginal Oasis of Northwest China

  • Yong Zhong Su
  • Wen Jie Liu
  • Rong Yang
  • Xue Xiang Chang


Maintenance of soil organic carbon (SOC) is important for sustainable use of soil resources due to the multiple effects of SOC on soil nutrient status and soil structural stability. The objective of this study was to identify the changes in soil aggregate distribution and stability, SOC, and nitrogen (N) concentrations after cropland was converted to perennial alfalfa (Medicago sativa L. Algonguin) grassland for 6 years in the marginal oasis of the middle of Hexi Corridor region, northwest China. Significant changes in the size distribution of dry-sieving aggregates and water-stable aggregates, SOC, and N concentrations occurred after the conversion from crop to alfalfa. SOC and N stocks increased by 20.2% and 18.5%, respectively, and the estimated C and N sequestration rates were 0.4 Mg C ha−1 year−1 and 0.04 Mg N ha−1 year−1 following the conversion. The large aggregate (>5 mm) was the most abundant dry aggregate size fraction in both crop and alfalfa soils, and significant difference in the distribution of dry aggregates between the two land use types occurred only in the >5 mm aggregate fraction. The percentage of water-stable macroaggregates (>2, 2–0.25 mm) and aggregate stability (mean weight diameter of water-stable aggregates, WMWD) were significantly higher in alfalfa soils than in crop soils. There was a significant linear relationship between total SOC concentration and aggregate parameters (mean weight diameter) for alfalfa soils, indicating that aggregate stability was closely associated with increased SOC concentration following the conversion of crops to alfalfa. The SOC and N concentrations and the C/N ratio were greatest in the >2 mm water-stable aggregates and the smallest in the 0.25–0.05 mm aggregates in crop and alfalfa soils. For the same aggregate, SOC and N concentrations in aggregate fractions increased with increasing total SOC and N concentrations. The result showed that the conversion of annual crops to alfalfa in the marginal land with coarse-texture soils can significantly increase SOC and N stocks, and improve soil structure.


Soil organic carbon Nitrogen Aggregation Land use change Alfalfa Northwest China 



We express our sincere thanks to the three reviewers and issue editor of the journal for their valuable comments, suggestions, and revisions on this manuscript. Funding for this research was given by one of the China National Key Projects for Basic Scientific Research (G2009CB421302) and the National Natural Science Foundation of China (30670375, 40771079).


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Copyright information

© Springer Science+Business Media, LLC 2009

Authors and Affiliations

  • Yong Zhong Su
    • 1
    • 2
  • Wen Jie Liu
    • 1
    • 2
  • Rong Yang
    • 1
    • 2
  • Xue Xiang Chang
    • 1
    • 2
  1. 1.Laboratory of Watershed Hydrology and Applied Ecology, Cold and Arid Regions Environmental and Engineering Research InstituteChinese Academy of SciencesLanzhouChina
  2. 2.Linze Inland River Basin Comprehensive Research StationChinese Ecosystem Research NetworkLanzhouChina

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