ORGANIC C AND N STORAGE, AND ORGANIC C FRACTIONS, IN ADJACENT CULTIVATED AND FORESTED SOILS OF EASTERN CANADA

As a major attribute of soil quality, organic matter is responsive to agricultural land use practices including tillage. A study was initiat ed in eastern Canada to characterize changes in the masses of organic C and total N, and organic matter fractions in forested and adjacent c ultivated or forage sites. Generally, the cultivated and forage sites had denser soil profiles than the forest sites. Based on an equivalent soil mass, to accommodate differences in soil bulk density, the paire d forest and cultivated sites showed that cultivation decreased the ma ss of organic C (35%) and total N (10%) in the soil profile of the Pod zolic soils, but increased organic C (25%) and total N (37%) in the Br unisolic (Cambisol) and Gleysolic soils. For the Podzolic soils, use o f forages increased soil stored organic C and N by 55% and 35%, respec tively. Organic C fractions were mainly of significance in the A horiz on. Soil microbial biomass C was greater in the forested, compared to the cultivated soil, but the proportion of soil organic C as microbial biomass C (1.3% to 1.6%) was similar. The proportion, however, was gr eater (2,1%) for the forage soil, compared to the corresponding cultiv ated (1.3%) soil, suggesting that organic C was continuing to increase under the former. The relatively large proportion (19%) of organic C found in the light fraction of forest soils in the A horizon was decre ased (up to 70%) by cultivation. In contrast, the proportion of macro- organic C present in the soil sand fraction was not greatly influenced by cultivation. Overall, soils in eastern Canada have a relatively la rge potential to store organic matter. The study illustrates the impor tance of soil type and cultivation interactions for maintenance of soi l organic matter storage, and the positive influence of forages in thi s regard in agroecosystems. (C) 1998 Agriculture and Agri-Food Canada. Published by Elsevier Science B,V.