University of Helsinki, Department of Agricultural Chemistry
The effect of drying of soil samples at about 20° C on the phosphorus test values estimated by the acetic acid method, the method for adsorbed P of BRAY and KURTZ (1), and the method of TERÄSVUORI (6) was studied. The material consisted of 32 samples of various kinds of soils. Air-drying did not cause any change in the acetic acid P of about one half of the samples and in the adsorbed P of about one third of the samples. A slight increase in the test values was found for a couple of samples. The tendency to a decrease was markedly higher in the values of adsorbed P than in the values of acetic acid P: an average decrease of 28 per cent in 19 samples was found in the former test while the corresponding value in the latter test was 13 per cent in 13 samples. No changes in the test values of Teräsvuori occurred in about one half of the samples, and the fairly low changes in the other half of the material were almost evenly distributed between increases and decreases. No connection between the changes in the test values upon air-drying and the moisture content of the fresh sample, the pH-value, the content of organic carbon, or the contents of iron and aluminium soluble in Tamm’s acid oxalate solution could be demonstrated. The changes in the various test values did not usually go in same direction. The importance of the possible error caused by air-drying is diminished by the sampling errors and by the variation in the soil P conditions.
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