CORRECTING SOIL ACIDITY OF A HIGHLY WEATHERED ULTISOL WITH CHICKEN MANURE AND SEWAGE-SLUDGE

The seriousness of soil acidity and the unavailability of "conventional" liming materials in many developing countries necessitate a search for alternatives. With this goal in mind, the liming potential of two organic manures was investigated. The investigation was conducted in the greenhouse, using a highly weathered, acid Ultisol. Application rates were 0, 5, 10, 20, and 40 g kg-1 for chicken manure and 20 g kg-1 for sewage sludge. Treatments of Ca(OH)2 at 2, 4, 6, and 8 cmol(c)kg-1, were included for comparison. Based on growth response of Desmodium intortum, a tropical forage legume with a relatively high Ca requirement and low A1 tolerance, it was demonstrated that soil acidity can be corrected by either Ca(OH)2 or organic manure additions. Both lime and manures raised soil pH and inactivated A1. In terms of pH increases, 5 and 10 g chicken manure kg-1 were equivalent to 3.4 and 6.7 cmol(c)kg-1; and 20 g sludge kg-1, equivalent to 6.5 cmol(c)kg-1 as Ca(OH)2. The manures also detoxified soluble A1 by organic complexation and enhanced Ca uptake of the Desmodium. The plant's maximum growth required at least 1.0% Ca in leaves, and this growth was reduced by half when leaf A1 greater-than-or-equal-to 76 mg kg-1 and soil-solution A1(3+) activity greater-than-or-equal-to 4-mu-M.