Soil Solution Composition as Affected by Liming and Incubation

Samples of three acid soils were limed with CaCO 3 and incubated at approximately field capacity moisture content. Soil solution samples were obtained by miscible displacement at intervals of 1, 5, 27, and 52 weeks after liming. The rapid influence of added CaCO 3 was shown by the large increases in soil solution pH, Ca, and HCO 3 found 1 week after liming. Other effects of liming included increases in soil solution NO 3 and organic matter, and reductions in K and Si. The activities of the major cations (Ca, Mg, K, and Na) and NO 3 increased substantially, whereas pH decreased during incubation. The decline in pH was accompanied by increases in Al, Mn, and Zn in solutions obtained from unlimed soils. The changes with time were apparently due to liberation of protons along with NO 3 into soil solution as a result of organic matter mineralization. Basic cations were displaced from exchange sites by protons, while Al, Mn, and Zn were released into solution as the acidity of the system increased. Logarithims of activities of Al 3+ , Mn 2+ , and Zn 2+ were linearly related to solution pH. These relationships were such as to suggest that the mechanisms controlling the solubilities of these ions were similar in each soil. The solubilities, however, were not consistent with published solubilities of any common minerals. A tendency for solubilities to be comparatively high at higher pH may be an indication that soluble organic complexes were underestimated.