Organic C and N storage, and organic C fractions, in adjacent cultivated and forested soils of eastern Canada

Abstract

As a major attribute of soil quality, organic matter is responsive to agricultural land use practices including tillage. A study was initiated in eastern Canada to characterize changes in the masses of organic C and total N, and organic matter fractions in forested and adjacent cultivated 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 paired forest and cultivated sites showed that cultivation decreased the mass of organic C (35%) and total N (10%) in the soil profile of the Podzolic soils, but increased organic C (25%) and total N (37%) in the Brunisolic (Cambisol) and Gleysolic soils. For the Podzolic soils, use of forages increased soil stored organic C and N by 55% and 35%, respectively. Organic C fractions were mainly of significance in the A horizon. 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 greater (2.1%) for the forage soil, compared to the corresponding cultivated (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 decreased (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 large potential to store organic matter. The study illustrates the importance of soil type and cultivation interactions for maintenance of soil organic matter storage, and the positive influence of forages in this regard in agroecosystems.