Effects of subsoiling and associated incorporation of fertilizer on soil rehabilitation after opencast mining for coal

Abstract

SUMMARYA trial was set up in South Wales in 1980 on land replaced in 1972 after opencast coal mining, to assess the effects on soil rehabilitation of regular subsoiling, through an established sward, with and without incorporation of a ‘semi-organic’ fertilizer into subsoiling slots. Treatments were assessed on the basis of yield, soil structure indices, root and organic contents and earthworm population densities. Apart from yields, data are for the eighth year of the experiment (1987), 18 months after the fourth programme of treatments.Treatments did not markedly affect productivity, although it tended to be higher with subsoiling and fertilizer incorporation. Subsoiling had little effect on root and organic content, but fertilizer incorporation increased the latter, particularly at depth. Earthworm population densities were markedly higher on subsoiled areas, the increase in the deeper burrowing species Aporrectodea caliginosa being largest. Fertilizer incorporation increased abundance of Lumbricus rubellus, but had little effect on other species. Subsoiling reduced surface wetness, but did not result in any significant improvement in structure. Fertilizer incorporation reduced clay dispersion at depth and, with subsoiling, also increased pore space.Treatment responses in term of soil structure were not large, but the incorporation of fertilizer did markedly accelerate structure rehabilitation at depth. Subsoiling alone contributed to land rehabilitation by controlling surface wetness and encouraging an increase in earthworm populations.