Are sulfurous soil amendments (S₀, Fe(II)SO₄, Fe(III)SO₄) an effective tool in the restoration of heathland and acidic grassland after four decades of rock phosphate fertilization?

Published source details Tibbett M. & Diaz A. (2005) Are sulfurous soil amendments (S₀, Fe(II)SO₄, Fe(III)SO₄) an effective tool in the restoration of heathland and acidic grassland after four decades of rock phosphate fertilization?. Restoration Ecology, 13, 83-91.
Share Tweet Email

Summary

Lowland heath and dry acid grasslands are key habitats for UK biodiversity conservation. Here and elsewhere in Europe many sites have been lost to agriculture especially in the 1940s and 50s, and were subject to heavy fertilization and acidity amelioration. An experiment was conducted on a former heathland and acid grassland southwest England that had been heavily fertilized and limed with rock phosphate, chalk and marl.

This experiment had three aims: to determine whether sulphur addition would lower pH to a level suitable for heathland and acidic grassland re-creation; to determine what effect the soil amendments have on available cations that may affect the plant community; and to determine whether the addition of iron would sequester PO4 ions that might be liberated from rock phosphate by the experimental treatments.

Study site: The experiment was conducted on improved grassland (formerly dry heath and acidic grassland) at Hertland Farm on the Isle of Purbeck, Dorset, southwest England. Prior to treatment the soils were weakly podzolized sands. Soil acidity had been modified from around pH 3.6 to 6.6 by addition of calcareous material over 40 years. NPK fertilizers and rock phosphate had been applied over this period elevating total phosphorus from 1,000 mg/kg in the surrounding heathland to 1,550 mg/kg in the experimental field. The improved sward was dominated by couch grass Elymus repens, rye grass Lolium perenne and smooth-stalked meadow grass Poa pratensis.

Experimental design: The site was mown and fenced to prevent cattle- but permit deer-grazing. Treatments were applied to 2 x 2 m plots (three replicates of each) on 22 January 2000 and comprised:

1) pelletized elemental sulphur (Brimestone 90, 90% S) at rates equivalent to 1,000 and 2,000 kg/ha S;

2) liquid ferric sulfate (Mistrale 600, Fe(III)SO₄, 13% Fe, 13% S) at 500 and 1,000 kg/ha S;

3) powdered ferrous sulfate (Dried Copperas, Fe(II)SO₄, 21% Fe, 11% S) at 500 and 1,000 kg/ha S;

4) unamended (control).

Soil analysis: Soils were sampled from each plot after 0, 70, 150 and 500 days with a soil auger to a depth of 4 cm, and analyzed for: pH; extractable Mg, K, Ca; Olsen P at each sample date; and Mn, Al, Fe, and SO4 at the end of the experiment, using standard methods.

Plant cover: Percent cover of each plant species was estimated on one day in June 2001 within the central 1 x 1 m square of each plot. Subsequently, grass was harvested (cut to 5 cm height) and sward mass and nutritional status (N, P and S) determined.

The application of S and Fe(II)SO₄ to the soil reduced pH, however, only the highest S application (2,000 kg/ha S) lowered pH sufficiently for heathland restoration purposes. Where pH was lowered, basic cations were lost from the exchangeable pool and replaced by acidic cations. Where Fe was added, there was no evidence of PO₄ sequestration from soil test data, but sequestration was apparent because of lower foliar P in the grass sward. The ability of a perennial forb, sheep’s sorrel Rumex acetosella, to apparently detoxify Al³+, prevalent in acidified soils, appeared to give it a competitive advantage over other less tolerant plants.

The authors anticipate further changes in the plant community overtime, as Al³+ toxicity leads to competitive exclusion of less tolerant species.

Note: If using or referring to this published study, please read and quote the original paper, this can be viewed at: http://www.blackwell-synergy.com/journal.asp?ref=1061-2971