MULL AND DUFF AS BIOTIC EQUILIBRIA

Abstract

A critical analysis of data from the literature, some of them checked by new determinations from American soil, did not support the current view that the duff type of humus layer ("raw humus," etc.) represents a pronounced accumulation of organic matter and a consistently slower decomposition, as compared with the biologically richest type, crumb mull. Comparative determinations of soil respiration and amount of soil organic matter in northern hardwood stands with crumb mull and with root duff in central New York indicated that decomposition is actually slower in crumb mull than in root duff. The nitrate level, however, averaged twice as high in the former as in the latter. It is concluded that variations in type of decomposition, rather than in rate, account for the characteristics of the different types of humus layer in the forest.