Managing soil acidity: old solutions can cause new problems

Abstract

Acid and moderately acid soils (pH 5-6) are widespread in the farmed areas of New Zealand. Application of limestone to raise soil pH has been a common practice and re-acidification of soils requires that this be done regularly. The impact of liming and re-acidification cycles on soil chemistry is discussed and examples presented using a Southland soil: Waimumu silt loam. Wide ratios of Ca:Mg develop in the soil and further lime application is shown to damage growth of white clover but not Grasslands Tama ryegrass. Differences in surface chemistry of roots of legumes and grasses are discussed and the implications of the interactions between changes in soil chemistry and plant roots considered. Keywords acidification, calcium, magnesium, cation ratio, root CEC