Calcium, magnesium and potassium in clay, silt and fine sand fractions of some Finnish soils

Authors

• Armi Kaila University of Helsinki, Department of Agricultural Chemistry
• Ritva Ryti University of Helsinki, Department of Agricultural Chemistry

DOI: https://doi.org/10.23986/afsci.71693

Abstract

Samples of three layers of ten mineral soils were separated into the fractions <2 μ, 2—20 μ, and 20—200 μ, without destroying organic matter. The separates were analysed for total calcium, magnesium and potassium, and for the nonexchangeable parts of these nutrients released by acid at 50° C. Readily exchangeable calcium, magnesium and potassium were also estimated. The average total content of Ca was 1.09 ± 0.13 % in the clay, 1.53 ± 0.10 % in the silt, and 1.61 ± 0.10 % in the fine sand fractions analysed. The Mg content was 2.01 ± 0.14 % in clay, 1.10 ± 0.10 % in silt and 0.54 ± 0.06 % in fine sand, that of K was 3.02 ± 0.11 % in clay, 2.75 ± 0.10 % in silt, and 2.16 ± 0.13 % in fine sand. Treatment with acid at 50° C released from 100 g of the clay fraction, on an average, 160 ± 30 mg nonexchangeable Ca, 680 ± 110 mg Mg, and 400 ± 70 mg K. From 100 g of the silt fraction was released 130 ± 30 mg Ca, 350 ± 70 mg Mg, and 230 ± 50 mg K. From 100 g of fine sand, averagely 120 ± 30 mg Ca, 90 ± 30 mg Mg, and 60 ± 20 mg K was dissolved. These amounts correspond to about one third of the total magnesium content of the silt and clay fractions, and to about one sixth in the fine sand fraction. The average amounts of calcium and potassium released from the clay fraction corresponded to 13—14 per cent of the total content in this fraction, to 9 per cent in silt, and in the fine sand material to 7 per cent of total calcium and to about 3 per cent of total potassium. The relationship between the total calcium contents in the clay and silt fractions is characterized by the total linear correlation coefficient r = 0.84***, that between the magnesium contents with r = 0.79***, and that between the potassium contents with r = 0.66***. Between these fractions the correlation in the contents of nonexchangeable acid-soluble calcium was r = 0.81***, of magnesium r = 0.81*** and of potassium r = 0.87***. Between the silt and fine sand fractions the relationships are characterized by the following coefficients: r 0.86*** for total calcium, r = 0.70*** for total magnesium, and r = 0.40* for total potassium; r = 0.53** for nonexchangeable calcium released by acid, r = 0.78*** for magnesium, and r = 0.86*** for potassium. The clay fraction contained, on the average, about three times as much readily exchangeable calcium, four times as much magnesium, and almost six times as much potassium as the silt fraction. In the clay fraction there was somewhat less than six times as much readily exchangeable calcium, and about fourteen times as much readily exchangeable magnesium and potassium as in the fine sand fraction. On the equivalent basis, the ratio of Ca:Mg was about 2 to 1 in the clay fraction, about 3 to 1 in the silt fraction, and about 5 to 1 in the fine sand material. In all fractions the ratio of readily exchangeable magnesium to potassium was 8—10 to 1. The results were discussed on the basis of the information about the mineralogical composition of Finnish soils.