Soil P bioavailability in a heathland restoration study on the Isle of Purbeck, UK

Abstract

The Isle of Purbeck is a multifunctional landscape with competing land uses including arable farming, livestock grazing, and recreational activities. Soil resources in the region have been under pressure from persistent physical and chemical manipulation. Historically, heathlands dominated the landscape but the expansion of agricultural lands and urban areas has resulted in a dramatic decline in lowland heaths. Initiatives such as the UK Biodiversity Action Plan [1] attempt to protect remaining areas and initiate heathland restoration projects on some agricultural lands. Heathlands are typically characterised by low P and N availability but agricultural improvements involved large-scale application of amendments to increase soil pH, along with fertilisation to increase the productivity of the land. Subsequent restoration to heathland often involves chemical manipulations to lower the soil pH and re-establish heathland vegetation, thereby affecting the availability of nutrients and biochemical transformations in the soil. To examine the effectiveness of acidification on heathland restoration, an experiment was initiated in 1999 on National Trust land with applications of elemental sulphur or ferrous sulphate [2]. As part of the RECARE project (Preventing and Remediation Degradation of Soils in Europe through Land Care) funded by the European Commission FP7 Program, we are assessing soil degradation and the long-term effects of chemical and physical manipulations to the soil on the Isle of Purbeck. The heathland restoration experiment provides the opportunity to look at long-term effects of artificial acidification on P biochemistry across a range of soil pH and in relation to above- and belowground biodiversity. Preliminary results collected by Gil-Martinez et al. (unpublished data) in autumn 2014 suggest that treatment with elemental sulphur effectively decreased the soil pH to levels comparable to adjacent heathland. Available P (0-5 cm) had increased to 30.7 and 14.0 mg kg-1 in the ferrous sulphate and elemental sulphur treatments compared to 8.9 and 3.3 mg kg-1 for the control plot and target heathland. The microbial biomass of the acidified plots was significantly lower than the heathland targets and although there was no difference in microbial biomass P, there was a shift towards bacterial communities as demonstrated by phospholipid fatty acid analysis. The potential bioavailability of P is being assessed by sequential chemical extractions to determine operationally defined inorganic and organic P pools. The impact of acidification treatments on soil P, along with changes in enzyme activities as an indicator biological functions, will be discussed in reference to the long-term reestablishment of heathland. [1] DOE, “Biodiversity: UK Steering Group Report”, Action Plans, vol. 2. HMSO, London, 1995. [2] Diaz, A., Green, I., Tibbett, M. “Re-creation of heathland on improved pasture using top soil removal and sulphur amendments: Edaphic drivers and impacts on ericoid mycorrhizas”, Biological Conservation, 141, 1628-35, 2008.