Effect of liming on the magnesium status of some mineral soils and on the fate of fertilizer magnesium

Authors

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

DOI: https://doi.org/10.23986/afsci.72064

Abstract

Nine mineral soils were incubated in laboratory without lime (Ca0) or limed (Ca1) with calcium carbonate (lab.reag.), and without magnesium fertilizer (Mg0) or fertilized with MgSO4*7H20 (Mg1 = 4 mg/100 g soil Mg). The incubation covered a period of seven weeks in aerobic conditions at constant 20 °C temperature. The relative increase in the effective cation exchange capacity (ECEC) caused by liming seemed to be in coarse mineral soils greater than in clay soils. The differences in pH (CaCl2) values between soil types was not so evident. In seven soils of the nine, liming decreased the 0,01 M CaCl2 extractable magnesium content more than in 1 M KCI or in 1 M neutral ammonium acetate extractable magnesium contents. The limed soils contained ammonium acetate extractable magnesium 2—24 % less than the unlimed soils. The decrease in magnesium content was greatest in acid muddy silt (Littorina soil) and in acid silty clay. Without lime the I M KCI extractable (Al+H) contents of these soils were 6,6 and 2,2 me/100 g soil and pH (CaCl2) 3,9 and 4,5, respectively. In finesand soils liming seemed to increase the magnesium content although not significantly. In limed soils 17—73 %of the fertilizer magnesium was extractable in 0,01 M CaCl2, 67—100 % extractable in 1 M KCI and 57—100 % extractable in 1 M neutral ammonium acetate. The equivalent ratio of exchangeable (1 M ammonium acetate, pH 7) calcium to magnesium in the soils may give pointers to the choice of liming agents, especially in the liming of low cation exchange capacity soils.