Acidification rates in the central wheatbelt of Western Australia. 1. On a deep yellow sand

Abstract

The rate and mechanisms of acidification were determined on a deep yellow sand under a cereal-annual pasture rotation in Western Australia. The rate of acidification was determined from a linear regression analysis between soil pH and years since clearing, using 39 sites that had been cleared for 12-74 years. Uncleared sites were sampled. Soil was sampled to a depth of 80 cm in 10-cm increments. The rate of acidification (kmol H+/ha . year) was calculated from the rate of pH decline, the pH buffer capacity, and bulk density. The rate of acidification 12-74 years since clearing was estimated as 0.19-0.23 kmol H+/ha. year, requiring 10-11 kg CaCO3/ha.year to neutralise. The greatest acidification occurred in the 10-20 and 20-30 cm layers, with acidification occurring to a depth of 80 cm. The rate of pH decline for each depth below 10 cm was 0.007 units/year. The surface soil (0-10 cm) did not acidify. The contribution of potential acidifying processes was estimated using soil measurements and paddock histories. The main cause of acidification appears to be the carbon cycle (grain removal and removal of animal products and waste products to sheep camps), with negligible acidification from the nitrogen cycle. Possible errors in the methodology are discussed.