Effects of Intensive Forestry Ploughing Practices on an Upland Heath Soil in South East Scotland

Abstract

The effects of deep tillage and soil mixing, using a rotary mouldboard forestry plough, on soil physical properties are reported for a peaty ferric stagnopodzol in S.E. Scotland. Ploughing intimately, mixed the surface organic horizon with mineral subsoil and produced diagonal bands of organic matter in the soil to a depth of 60 cm. The surface of ploughed soil consisted almost entirely of mineral material which delayed the recolonisation by competing weed vegetation for four years. The resulting weed flora consisted of soft grasses and herbs indicative of a fairly fertile site. Three years after ploughing, total and stone-free bulk densities in cultivated sol were significantly lower than for mineral horizons in undisturbed soil. Tilled soils were generally well aerated, while untilled soil showed evidence of anaerobic conditions with waterlogging occurring for at least part of the year. The moisture storage at field capacity was slightly lower in tilled soil compared to undistrubed soil but there was a more even distribution of moisture retention throughout the cultivated rooting volume, probably related to organic matter distribution. Four years after ploughing, infiltration was faster into tilled than into undisturbed soil. The diurnal temperature range in the top 10 cm was 2–3 times greater in tilled compared to undisturbed soil, while the mean temperature at 60 cm was 0.5 C degrees higher in tilled soil. Three and a half years after planting, the roots of an excavated Sitka spruce plant extended to 60 cm depth and over 250 cm horizontally with many finely-branched root tips ending in lumps of buried organic matter.