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United States Department of Agriculture

Agricultural Research Service

Research Project: Value-Added Products from Cottonseed

Location: Commodity Utilization Research

Title: Characteristics of soil water soluble organic C and N under different land uses in Alaska

Authors
item Zhai, Aiqin -
item Zhang, Mingchu -
item He, Zhongqi

Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 14, 2012
Publication Date: February 1, 2012
Citation: Zhai, A., Zhang, M., He, Z. 2012. Characteristics of soil water soluble organic C and N under different land uses in Alaska. Soil Science. 177(12):683-694.

Interpretive Summary: Water soluble soil organic matter (WSOM) is a mixture of compounds of various molecular sizes. Even though the importance of soil WSOM has been recognized, the information on sizes of WSOM and its properties is still lack and inconsistence. In this study, field moist and air dried soils sampled from subarctic Alaska under three land use managements (i. e. forest, agriculture; and grassland converted from agricultural use and under a Conservation Reserve Program) were extracted with deionized water, and separated by filtration into different size fractions (2.5 µm, 0.45 µm, and 1 kDa). Our data indicated that air-drying process increased soluble organic C for all three land uses so that field moist soil samples are more suitable for characterizing the impact of soil management practices on soil water soluble organic matter. Fluorescence spectroscopic analysis revealed no differences in the relative abundance of three fluorophore components between different land uses and size fractions, indicating that the impact of land uses was mainly on the quantity, rather than on the composition, of WSOM. With field moist soil samples, soluble organic C contents decreased in the order: forest land> converted and conserved grassland> agricultural land. This order implied that the long-term agricultural land use could lower the WSOM levels in soils, but the decreasing trend could be reversed by conversion of agricultural land to grassland under conservation.

Technical Abstract: Land use conversion induces the quantitative change of soil water soluble organic matter (WSOM). But, knowledge of such change is still limited. In this study, field moist and air dried soils sampled from subarctic Alaska under three land use managements (i. e. forest, agriculture; and grassland converted from agricultural use and under a Conservation Reserve Program-CRP) were extracted with deionized (DI) water, and separated by filtration into different size fractions (2.5 µm, 0.45 µm, and 1 kDa). Soluble organic C (WSOC), N (WSON), and fluorescence spectroscopy in each fraction were determined. There were little differences in quantitative data between different land uses with air dried samples, implying air dried samples were not suitable for characterizing the impact of soil management practices on soil water soluble organic matter. For field moist soil samples, the WSOC contents decreased in the order: forest > CRP> agricultural land, with similar WSON concentration. Furthermore, WSOC was dominated by large (>0.45 µm) and small (<1 kDa) size molecules in CRP and forest soils, whiles mall molecules predominated in agricultural soils. The WSOM of different size fractions and land uses displayed three similar fluorophore components (two humic-like and a tyrosine-like), indicating that the impact of land uses was mainly on the quantity, rather than on the composition, of WSOM. In conclusion, our data suggested that the long-term agricultural land use could lower the WSOM levels in soils; however, the decreasing trend could be reversed by conversion of agricultural land to grassland under conservation.

Last Modified: 12/20/2014
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