Abstract
1.Introduction A total of 98 out of 2666 soil cores taken for Countryside Survey in 2007 (3.7 %) were reported to have pH values > 8.4 indicating that soil pH is not longer controlled by CaCO3 equilibrium but by other processes. Furthermore, the proportion of soils with pH values over 8.4 was greater than that in CS2000. 2.Background Alkaline soils, when combined with a dominance of monovalent cations in the exchangeable complex become dominated by sodium carbonates rather than calcium carbonates due to either natural processes in coastal areas, irrigation, contamination due to road salt or other management practices such as application of biosolids. Alkalinity in soils, or soils with pH values higher than 8.4, is generally considered as part of soil salinity but in reality the negative impact that high pH values confers to soil properties is independent of the salinity itself and they are recognized as a separate type in the soil classification. They exhibit specific threat to soil function characterized by: dispersion of the clay particles and the organic matter, loss of soil structure, migration of colloids with clogging of the soil pores down in the soil profile, compaction, reduction in hydraulic conductivity, increase in runoff, increase erosion, and ultimately the loss of soil productivity. 3.Objectives To test the proposed hypotheses for high soil pH values reported for Countryside Survey 2007 in Emmett et al. (2010): It was proposed in Emmett et al. (2010) that: ‘The soil pH data show an increase over time in the frequency of pH values in excess of pH 8.5. In 2007 approximately two thirds of the 54 plots with pH > 8.5 were in the Arable Broad Habitat, with values approaching pH 9 in some plots. Soil pH values in excess of 8.3 indicate that calcium carbonate solubility is no longer controlling soil pH and there is an influence from sodium salts accumulating in the soil. Two of the sample points with the highest pH values are very close to the coast and are mapped as Littoral Sediment or Supra-littoral Sediment Broad Habitats where sodium will be abundant. Several sample sites are located in the fens of East Anglia and again, there may be abundant sodium in these soils. The remaining sites are further west in Oxfordshire and may be influenced by irrigation which can lead to sodium accumulation in the soil’
United Kingdom