Elemental status (Cu, Mo, Co, B, S and Zn) of Scottish agricultural soils compared with a soil-based risk assessment

Concentrations of six elements copper (Cu), molybdenum (Mo), cobalt (Co), boron (B), sulphur (S) and zinc (Zn) are summarized for Scottish advisory soil samples collected during the period 1996–2008. Accompanying cropping information indicated that the majority of samples collected for Co analysis were from grassland compared with B, S and Zn where sampling was predominantly prior to either potatoes or vegetables. The proportion of samples measured as potentially deficient [very low (VL) or low categories] were 80% for Co, compared with 50, 40, 38, 25 and 18% for Mo, S, Zn, Cu and B, respectively. Only S displayed a significant decline (ca. 2 mg S ⁄ kg) over this 13-year period. However, comparison of Cu and Co data with some collected from an earlier time period (1973–1980) suggested little difference for Cu but a smaller number of VL and low Co status samples. A predicted risk assessment using soil parent material, texture and drainage status suggested that 22, 38 and 40% of the agricultural area of Scotland were at a high, medium and low risk of Cu deficiency; comparable numbers for Co were 48, 30 and 22%. The reliability of the risk assessment was tested using a sub-set of advisory samples with specific information on soil series. Of the soils predicted to have a high risk of Cu deficiency, 52% actually fell into the ‘deficient’ status. A similar comparison for Co indicated 90% of the samples predicted as having a high risk of deficiency were measured as VL or low.