FURTHER STUDIES ON VARIABILITY OF SOIL CHEMICAL PROPERTIES: EFFICIENCY OF SAMPLING PROGRAMMES ON AN UNCULTIVATED BROWN EARTH

Assessments of mean and range of variation for pH, loss on ignition, total nitrogen, and exchangeable K, Na, Ca, Mg, and Mn in the surface horizon of a uniform uncultivated soil have been made by nine sampling programmes. The selected soil was known to have spatial chemical variability of magnitudes widely found in other soils and situations. The effort involved in these programmes was, for sampling and analysis time, from 1.2 to 66 man-days. The most complete sampling programme (275 samples each a composite of 10 cores), was used as a standard against which to compare the efficiency of the other programmes. Mean values for chemical quantities other than loss on ignition differed statistically significantly between programmes but there was no consistent trend with any particular programme. Knowledge of the range of variation is believed to be very important in interpretation of analyses and it is found that a programme using only 6 composite samples measures > 50 per cent of the range for most quantities and that a programme using about 25 composite samples measures at least two-thirds to three-quarters of the total range.