Development of soil organic matter under pine on quarry detritus of open-cast oil-shale mining

Abstract

Formation of soil organic matter in three quarry detritus areas was investigated at Sirgala, north-east Estonia (27°47′E, 59°19′N). The sites were afforested in 1965–1970 with 2-years-old seedlings of Scots pine. During the first decade after planting, forest floor (ground litter) had not formed. In 1988, ground litter occurred as a single layer. After 29–34 years, a brownish black (10YR2/2) A-horizon and a very dark greyish-brown (10YR3/2) AC-horizon had developed to a depth of 20–25 cm. Falling litter (litterfall) and ground litter of a Moder-type had also formed. Organic matter of the ground litter was rich in carbon but poor in nitrogen. A large accumulation of organic carbon and nitrogen in the mineral topsoil, a high C:N ratio, and significant amount of humus accumulation were characteristics of these young soils. As a result of pedogenesis, part of the residual oil-shale (kukersite) in detritus was humified as insoluble fraction. Organic carbon (14.4–19.7 g kg −1) of kukersite, contained in the quarry detritus were subtracted from the measured values to calculate the amount of organic matter of plant origin. Sesquioxides–humic–fulvic humus was rich in substances bound with mineral content of the detritus, but poor in free fulvic acids and Ca–humates. Highly productive forest ecosystems with the formation of Calcaric Regosols have developed on pure skeletal quarry detritus within about three decades.