EFFECTS OF LINZ-DONAWITZ (LD) SLAG ON SOIL PROPERTIES AND PASTURE PRODUCTION IN THE BASQUE COUNTRY (NORTHERN SPAIN)

Linz-Donawitz (LD) slag, containing 29% calcium (Ca), 21% iron (Fe), a nd 5% magnesium (Mg), is a by-product of the iron and steel-making ind ustry. It is produced in large quantities in Europe and poses a substa ntial disposal problem. A field trial was conducted to study whether L D slag could be used as a dolomitic liming agent for pastures. The eff ects of six LD slag rates (0, 1000, 1500, 3000, 5000, and 7500 kg LD s lag/ha), with or without NPK fertiliser, on soil properties, pasture y ield, and botanical composition were investigated at two locations, De rio and Abadiano (Bizkaia, northern Spain). Soil at Derio was a fine s ilty, mixed (acid), mesic Typic Udorthent and at Abadiano a fine loamy , mixed (nonacid), mesic Aquic Udifluvent. At Derio, the 3-year trial was laid out on a newly established pasture of perennial ryegrass (Lol ium perenne L.), cocksfoot (Dactylis glomerata L.), and white clover ( Trifolium repens L.), whereas at Abadiano the trial was on a resident pasture dominated by yorkshire fog (Holcus lanatus L.) and browntop (A grostis tenuis Sibth.). Application of LD slag increased the soil pH l inearly at both sites. At Derio, the 7500 kg slag/ha rate increased th e soil pH from 5.3 to 6.4, whereas at Abadiano the pH was raised from 5.7 to 6.5 and from 5.8 to 6.7 with and without NPK fertilisation resp ectively. The increase in pH was accompanied by a decrease to less tha n 5% in the percentage of Al saturation in the cation exchange complex . At Derio, soil exchangeable Ca increased in comparison with the cont rol, by a factor of 1.8 and 2.3, with and without NPK fertilisation, r espectively. At Derio, pasture yield increased with slag application, the second year responses being the largest (41% increase with 3000 kg slag/ha). At Abadiano, pasture yield did not respond to slag, but the botanical composition changed, with the contribution of browntop and yorkshire fog decreasing, and the contribution of red fescue (Festuca rubra L.) and ribwort (Planrago lanceolata L.) increasing. According t o the results, LD slag appears to be a useful liming material for corr ecting soil acidity on pasture soils. As a consequence, the agronomic use of LD slags will contribute towards solving the environmental prob lem of their disposal.