The efficiency of dolomitic limestone, basic slag and peat ash as liming agents, and as calcium and magnesium sources for turnip rape

Authors

• Raili Jokinen University of Helsinki, Department of Agricultural Chemistry, 00710 Helsinki 71, Finland

DOI: https://doi.org/10.23986/afsci.72117

Abstract

Incubation and pot experiments were carried out on muddy fine sand and fine sand soils to determine the efficiency of dolomitic limestone and of industrial by-products, basic slag and peat ash, as liming agents. Calcitic limestone was used as reference material. In the incubation experiment 0, 0.6, 1.2 and 2,4 g calcitic limestone were applied to 390 g (muddy fine sand) or 360 g (fine sand) of air-dry soil. The amount of other liming agents added was 2.4 g. In the pot experiment the weights of soil were 3.9kg (muddy fine sand) and 3.6kg (fine sand) and 24 g of liming agent was applied. The turnip rape (Brassica campestris v. oleifera f.annua cv. Candle) was grown in two growing seasons and the crops were cut at the flowering stage. In both experiments the soils were sampled for analysis after four and sixteen months. The acidity of the soils was neutralized with the liming agents to the same extent in the pot and the incubation experiments. The increases in pH(CaCl2) obtained in the incubation experiment with 2.4 g liming agents were on the muddy fine sand and fine sand for calcitic limestone 2.0 and 1.4, for dolomitic limestone 1.5 and 1.1, for peat ash 0.3 and 0.2, for basic slag 0.8 and 0.6, respectively. At the end of the incubation 2.4 g of dolomitic limestone, peat ash and basic slag had increased the pH(CaCl2) of the soils to the same extent as 1.7 g, 0.4 g or 0.8 g of calcitic limestone, respectively. The proportion of non-exchangeable Ca at pH 7 of the amount added in 2.4 g liming agents was for calcitic limestone 14 and 23 %, for dolomitic limestone 42 and 52 %, for peat ash 27 and 51 %, and for basic slag 59 and 64 %, in the muddy fine sand and fine sand soils, respectively. Of the Mg added in dolomitic limestone, about 45 % was non-exchangeable, and in basig slag about 65 %. In the pot experiment about 13 % (average of the two soils) of the Ca applied in calcitic limestone was not found in turnip rape or as neutral 1 M ammonium acetate extractable from the soil. The corresponding value for dolomitic limestone was 41 %, for peat ash 45 % and for basic slag 65 %. The Mg applied in the liming agents but not found in turnip rape or in the soil amounted to 42 % for dolomitic limestone, 74 % for peat ash and 67 % for basic slag. The efficiency of basic slag as a liming agent will be over estimated if it is measured by the amount of acid neutralized or by the content of Ca and Mg (Ca + 1.65xMg) soluble in 1M HCI. The amount of Ca soluble in 1 M HCI, alone, may provide a better, though not good, measure of the neutralizing ability of basic slag.