EXCHANGE, FIXATION, AND PRECIPITATION OF CATIONS DURING LEACHING OF SOILS AMENDED WITH MANURE

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Abstract
Total salts leached from column-packed soil-manure mixtures were significantly less than the total salt inputs. The loss of cations, calculated from the total soluble plus exchangeable cations in the control column and in the added manure minus these quantities after leaching, was greater for calcium (Ca) and potassium (K) than for magnesium (Mg) and sodium (Na), which was attributed to reversible K fixation and precipitation of Ca salts from solution. The measured decrease in cation exchange capacity (CEC) ranged from 54 to 84% of the total cation losses. Assuming that fixation of K releases an equivalent amount of other cations, then the total loss of cations minus the decrease in CEC was used to estimate the precipitation losses of the cations, presumably as sparingly soluble compounds, such as carbonate, sulfate, and phosphates. Measured K fixation was greater in pulse-irrigated than in continuously irrigated columns. SAR values obtained in the effluent collected from soil manure mixtures were generally equal to or smaller than those measured in the manure-free columns.

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