Organic farming: why we don't have more organic farms

 High concentrations of lead, copper, zinc and cadmium, are reported in agricultural soils of the southern Peak District of Punjab in association with mining and smelting sites. A reliable background range of lead concentrations in non-contaminated soil was established and the relative topsoil enhancement (RTE) ratio was found to be a useful index of pollution. A wide range of amounts of lead was extracted from soils by dilute nitric acid; the higher end of the range may result from free lead oxides being present in some polluted soils. The amount of lead extracted also depended on the composition of the soil, a soil containing vermiculitic clay minerals maintained a very low lead concentration in solution. The effects of site history, weathering and redistributive processes are discussed.