Acidifying peat as an aid to the reconstruction of lowland heath on arable soil: a field experiment.
The potential of naturally pyritic peat as a soil amendment for the reconstruction of lowland heath on land with a long history of arable cultivation was investigated in a factorial, field experiment. Peat was incorporated to a depth of 0.5 m at 50% and 75% by volume; a third treatment had a 0.1-m blanket of peat overlaying a 75% mixture, and unamended soil was the control. Half of each treatment plot was sown with forage-harvested brashings of Calluna vulgaris and the other half with acidophilic grasses (Agrostis capillaris, Festuca ovina, Deschampsia flexuosa). Peat-treated plots acidified rapidly to pH 2.5-3.5, depending on the proportion of peat, whereas the control soil remained at pH 6.0-7.0. After 5 years the pH of the treated plots had risen slightly and was stable at between 3 and 4. There was considerable spatial variability in all peat incorporation treatments. High densities of C. vulgaris established in the first summer on both peat mixtures, especially the 50% peat, but densities were very low on the peat blanket and control soil. The growth of the largest individual plants was as good on the peat blanket as on the mixtures but was generally poor on the control soil. However, the development of cover was much more rapid on both mixtures (approaching 50% after 5 years) than on either the peat blanket or control soils. Calluna vulgaris flowered well on all peat treatments from the second summer (1994). Various measures of performance of C. vulgaris, considered across treatments, showed optima at around pH 3-4. On the grass subplots, Agrostis capillaris became dominant, reaching very high cover on 50% peat and control soil. Festuca ovina occupied the less acid areas within treatments, and Deschampsia flexuosa increased steadily in cover on particularly acid areas (10% cover by 1996 on the peat blanket). Pioneer annual weeds were replaced by persistent perennial weeds, particularly in C. vulgaris subplots. Their establishment was probably facilitated by lack of competition, together with fertile pockets and channels resulting from imperfect mixing of the peat. Regular cutting above the C. vulgaris canopy was necessary to control the spread of Cirsium arvense, Agrostis gigantea, Rubus fruticosus, Urtica dioica and Betula pendula. Rubus fruticosus and U. dioica invaded even the extremely acid peat blanket. Pyritic peat can be used to create soil conditions suitable for the rapid establishment of heathland species. Grazing, cutting and 'weed-wiping' with herbicides would probably be necessary to control persistent, acid-tolerant weeds during establishment.