CHANGES IN MOLECULAR WEIGHT DISTRIBUTION OF SOIL ORGANIC MATTER DURING SOIL DEVELOPMENT

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Abstract
Summary: Ten different topsoils representing members of three soil chronosequences were pre‐treated with 0.1 M HC1 and extracted with neutral 0.1 M Na4P2O7 followed by 0.5 M NaOH. Extracts were purified and fractionated into five different nominal molecular weight fractions using gel filtration. With increasing soil development, the proportion of large molecules (>200 000) in the organic matter decreased with an increase in the proportion of intermediate size molecules (200 000 – 10 000). This effect was more evident in the mild Na4P2O7 extracts than in the subsequent NaOH extracts, and in soils of the Manawatu chronosequence than in those of the other two chronosequences and are attributed to changes in the nature and humification of soil organic matter during soil development.