The exchangeable K content decreased in the 0.05–0.60 m layer
in all treatments except for triticale/chisel + fallow and sunflower/
chisel + fallow, in which the levels decreased in the 0.10–0.40 m
and 0.05–0.20 m layers, respectively. The decreased K content in
these layers was due to K absorption by roots, as these are highly
root-colonized layers, and also K losses by leaching to deeper
layers. This conclusion is supported by the results found in the
0.40–0.60 m layer, where available K was increased (Table 5). Ng
Kee Kwong and Deville (1984) observed K losses between 64 and
136 kg ha1 by leaching at depths below 1.00 m in an area cropped
to sugarcane and fertilized annually with high K rates. Johnston
and Goulding (1992) suggested that approximately 1 kg ha1 of K
is lost for every 100 mm of rainwater leached through the soil in a
field, but this value may be larger if K is displaced with a solution
that contains a higher concentration of Ca2+ ions.