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United States Department of Agriculture

Agricultural Research Service


item Hayes, Thomas
item Watt, Barbara
item Hayes, Michael
item Clapp, Charles
item Scholefield, David
item Swift, Roger
item Skjemstad, Jan

Submitted to: Humic Substances and Organic Matter in Soil and Water Environments; Charact
Publication Type: Proceedings
Publication Acceptance Date: 11/1/1997
Publication Date: N/A

Interpretive Summary: Soils under long-term grassland management tend to accumulate organic matter (OM). Clay-rich grassland soils in regions of high rainfall can accumulate as much as 50 tons per acre of organic carbon and 5 tons per acre of nitrogen. This tendency is less for soils that are better aerated, such as sandy soils, and clay soils with field drains. There is thus a considerable potential for the leaching of soluble organics from "mature" grasslands, and especially from those that also receive manure from grazing livestock. Water samples were collected from two drainage sites on an experimental farm in southern England. Analyses of the humic materials (dark-colored organic acids) for contents of elements, sugars, and amino acids showed higher values for the undrained compared with the drained plots. Other results for naturally-occurring isotopes of carbon and nitrogen, as well as "finger-print" methods (NMR and FTIR) showed that the drained plots contained more mature organic matter. These materials would appear to be more important in transporting undesirable organic chemicals through soil into surface and ground water supplies. This research will provide information for preventing pollution, so that environmental quality of agricultural ecosystems can be preserved.

Technical Abstract: The humic acid (HA), fulvic acid (FA), and XAD-4 acid fractions of humic substances (HS) were isolated from waters flowing from a grassland soil. In one case, Devon 1 (D1), the waters were collected in March in the flow from tile drains at 0.85 m depth, and in the other, Devon 3 (D3), in November from surface run off. The humic fractions were subjected to elemental, delta **13C, delta **15N, neutral sugar, amino acids, NMR, and FT-IR analyses. The analytical data showed distinct differences between the compositions of the HS fractions in waters which had passed through the soil and those in the surface run off. The differences in the sampling dates were also considered to be significant. The run-off water was sampled when the flush' of the transformation products from the previous season had ended. This showed that the samples from D1 had a longer residence time in the soil, and the analytical data indicated that these humic fractions were more extensively transformed than the fractions from D3.

Last Modified: 8/24/2016
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