Premium
Effect of Lime on Exchangeable Magnesium in Variable Surface Charge Soils
Author(s) -
Grove J. H.,
Sumner M. E.,
Syers J. K.
Publication year - 1981
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1981.03615995004500030011x
Subject(s) - lime , soil water , chemistry , magnesium , cation exchange capacity , soil ph , clay minerals , mineralogy , soil science , geology , metallurgy , materials science , organic chemistry
Early work with commercial‐grade limestones containing small quantities of MgCO 3 (2–10%) demonstrated that exchangeable Mg was reduced as the soil pH was increased in several soils. An incubation experiment was conducted to more precisely determine the extent of the Mg “fixation” and to evaluate several hypotheses regarding the mechanism behind this pH‐dependent phenomenon. Five acid topsoils were used in this study. The clay fractions of four of these were dominated by constant‐surface potential colloids. Five levels of lime (CaO) and three levels of Mg from two sources (MgCO 3 and MgSO 4 ) were applied in complete factorial combination. Exhaustive extraction with 0.2 N NH 4 Cl was used to determine exchangeable Mg and K. Cation exchange capacities were obtained by extracting the NH 4 + saturated samples with 0.2 N KNO 3 . The Mg‐fixation reaction was essentially complete in 24 hours. Lime application reduced NH 4 Cl‐extractable Mg in all soils, although not until the soil pH was raised to 5.1 (1 N KCl). Effective CEC increased with lime addition but was unaffected by Mg treatment. It appears that the Mg was lost to a surface‐solid phase involving Al. For the soils with clay fractions dominated by constant‐surface potential colloids, Mg recovery by NH 4 Cl was inversely related to the quantity of exchangeable Al per unit mass of clay found in the acid‐end member of each soil. The lack of change in effective CEC and exchangeable K with Mg addition at higher soil‐pH values indicated that a charge blocking brucite‐like interlayer was not formed.