Long-term effects of incorporated lime and topdressed lime on the pH in the surface and subsurface of pasture soils

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Abstract
Soil profiles from limed and unlimed commercial pastures and from lime trials on pastures in the Crookwell district of the Southern Tablelands of New South Wales were sampled and pH measured at 2- or 5-cm intervals to depths ranging from 10 to 60 cm. A single application of lime (3.6-5.6 t/ha depending on the soil) incorporated into the surface 10 cm had a long-term effect and maintained pH above 5.5 in the top 30 cm for at least 12 years. Lime applied as a topdressing to soils on granite raised the pH by at least 0.2 pH units to a depth of 15 cm after 6 years. The depth affected was less on the heavier-textured basaltic soils and on the initially more acid sedimentary soils. There appears to be a role for top-dressing with lime to prevent subsurface acidity from developing under pastures and to correct it in the upper layers of light textured soils. The pH profiles from a given treatment were variable and highlighted the problem of obtaining a field measurement for soil pH that is representative of the plant's environment.