Hydraulic conductivity reduction due to ponded hog manure

Results are presented from a study concerning the reduction in soil hydraul ic conductivity due to ponded hog manure. Of specific interest is how much of the reduction is 'at the soil surface' as opposed to within the soil. Se ven different soils with clay contents ranging from 9 to 33% were studied u sing 200 mm long soil columns in a low-temperature (5-6 degreesC) environme nt. Hydraulic conductivities, as measured with water, ranged between 3.0 x 10(-8) and 1.3 x 10(-6) m/s before manure application. Fresh hog manure was ponded on these soil columns for a period of 634 days. Hydraulic conductiv ity, for all soils, decreased rapidly to about 1.0 x 10(-9) m/s and maintai ned this value except during the time of failure of the cooling system. A b lack layer was observed to have developed at the manure-soil interface of a ll columns within 36 hours of manure pending. Visual observations conducted between days 136 and 618 showed that the black layer grew downwards into t he soil at a rate of 0.3 mm/month. The hydraulic conductivities of the soil s at different depth intervals indicated that most, if not all, of the redu ction occurred at the black surface layer. At the end of the 634 day period , the black layer was removed and soil hydraulic conductivities were measur ed once again using a prepared chemical solution of similar ionic concentra tion to that of manure. The hydraulic conductivities of all soils increased to that of 'pre-manure' conditions. The results of this study suggest that the hydraulic conductivity reduction from ponded hog manure under these ex perimental conditions is mainly related to the development of the black lay er at the manure-soil interface.