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Exchangeable potassium is in equilibrium with the fixed forms
in the soil, This equilibrium is disturbed tien plants remove the
exchangeable forms and, to re-establish equilibrium, some fixed
potassium is released. The maintenance of an adequate supply depends
upon the reserve and the rate of release. As a guide the following
~ levels of exchangeable potassium may be used:
Very low - less than 30 p.p.m. +
LOW 30 - 60 p.p.m.
Moderate 61 - .90 p.4.m.
Moderately High - 91 - 120 p.p.m.
High
- more than 120 p.p.m.
The analyses for the alluvial soils indicate that vexy low
levels of potassium exist in the soils. Potassium levels for the
upland soils are high. Nagnesium levels are moderate throughout.
Sodium is generally low on both alluvial lowland and upland soils.
Percent base saturation indicates how much of the total cation
exchange capacity is satisfied by the sum of the calcium, magnesium,
potassium and sodium cations present. That portion of the total
cati.on exchange capacity net satisfied by basic cations is mostly
occupied by aluminum and hydrogen.
Ease saturation in the solum of the upland soils is low compared
to the lowland alluvial soils in which it is always 100%.
Copper and Zinc
According to the'work of Lunblad, et a1 (ri-:.>, the copper avai1abl.e
CI
to pl.ants in the lowlands 5s sufficient,to meet their requirements.
Analyses for zinc are also given although no correlation between
plant requirements and zinc are available.
Sulphur
&ilnhur, a minor but essential. element' for trop growth is
moderate-to very low for a11 joils'in the Creston area except the
Leach, Simmons, Shaw and Kuskanook seriez-. In these scils .the
Sulphur status ranges from moderate to high in that order.
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5 parts per million - TO obtain parts per million of potassium from
milli-equivalents per 100 grams multiply by 391..