Sd. Heming et Dl. Rowell, THE ESTIMATION OF LOSSES OF POTASSIUM AND MAGNESIUM FROM CHALKY SOILSIN SOUTHERN ENGLAND - LABORATORY STUDIES, Soil use and management, 13(3), 1997, pp. 122-129
Ten chalk topsoils (0-25 cm) were repacked into columns in the laborat
ory. After leaching similar to one year's throughflow in the field, lo
ss of K was equivalent to between 9 and 74 kg K/ha. This represented b
etween 3 and 30% of the initial exchangeable K with which loss was poo
rly correlated, Loss was dependant on the soil solution concentration
and was inversely proportional to potassium buffer power The loss of m
agnesium in the same columns was between 10 and 22 kg Mg/ha (6 - 21% o
f the initial exchangeable Mg). Magnesium loss was poorly correlated w
ith exchangeable Mg. When KCl fertilizer was incorporated into the soi
ls, the increase in leaching of potassium was 1-35% of the K addition.
Application to the top of the column resulted in less leaching than w
hen the K as incorporated. Leaching of magnesium was increased by up t
o 5 kg Mg/ha. Potassium leaching may be delayed by the underlying A/C
horizon but pure chalk, with an extremely low buffer power for K, has
little ability to retain K. Extremely calcareous topsoils were the mos
t leaky although in practice it is the organic chalk soils on which it
is most difficult to attain adequate K levels. On all chalk soils, ma
intenance of a high K level with K fertilizer is likely to cause unnec
essary long-term leaching losses. Annual, rather than biennial, fertil
izer applications are to be preferred.