Two soils representative of the coast and three representing the Willamette Valley have been studied for their general chemical
characteristics. Exchange capacity and exchangeable cations were
determined by the ammonium acetate and the BaCl₂-triethanolamine
buffer methods. Exchange capacity was also obtained from conductimetric
titrations which were run on each soil before and after
destroying the organic matter.Potentiometric titrations were run
before and after leaching each soil with HCl. Lime requirement was
determined by Woodruff's method and also obtained from the pH-lime
curves.
The two coastal soils, Astoria and Clatsop, have lower pH and
base saturation and higher organic matter content and exchange
capacity than the Melbourne, Olympic, and Willamette soils from the
valley. The Melbourne soil had the highest base saturation percentage
and Astoria had the lowest. The amount of exchangeable
aluminum was also higher in the coastal soils.
The amount of exchange capacity contributed to the organic
fraction was 65 per cent in the Olympic and Willamette soils and 50
per cent in the other three. The value for exchange capacity by the different methods was in good agreement in the three valley
soils before and after the organic matter was destroyed. In the
coastal soils there was no agreement between methods in any case. This would indicate that in the latter two soils, type of clay
mineral present may be more of an influence than in the former soils.
The potentiometric titration curves showed that the two coastal soils were well buffered and the valley soils were only slightly
buffered. After the soils were leached with HCl the Melbourne
soil was the only one which indicated a strong acid property.
The exchange properties of the soils as affected by additions of
lime were studied by incubating the soils for four weeks with added
increments of lime. With each added increment of lime the pH increased
and exchangeable acidity decreased in each soil. The amount
of lime to bring the soils to any given degree of base saturation
appeared to be proportional to the magnitude of the exchange capacity
and inversely proportional to the degree of base saturation. At
any given pH value there was a considerable difference in the degree
of base saturation for these soils. This might well be a reflection
of the type of minerals present in the different soils.
More lime was required to bring the two coastal soils up to
pH 6.5 as indicated by the pH-lime relationship curve than that
estimated by the Woodruff method. Consistent results were observed
in the three valley soils. This suggests that the buffer solution
at pH 7 as recommended by Woodruff was not strong enough to neutralize the acidity in the coastal soils.
There was good agreement between the two methods in the
determination of the exchangeable bases. The BaCl₂-buffer method
gave much higher values of exchangeable acidity than did the
ammonium acetate method. These values, when converted to tons of
calcium carbonate, agree fairly closely with the amount of lime required to bring the soils to pH 7 when added directly to the
soil. When lime was added above the saturation point the amount of
exchangeable calcium as determined by the ammonium acetate method increased but remained relatively constant for the BaCl₂-buffer
method.
The various analysis seem to indicate that the Astoria and
Clatsop soils contain predominantly 2:1 type clay minerals while
the Olympic and Willamette soils contain predominantly the 1:1
type. The Melbourne soil exhibits properties more closely
associated with the coastal soils
