Effect of manure ponding on soil hydraulic properties
Fonstad, Terrance Alden
The purpose of this study was to extend previous studies investigating the clogging of soil by ponded hog manure and to clarify the meaning and the magnitude of the "manure seal". Specific objectives are related to the effect of clogging upon soil hydraulic conductivity: to measure the effect of clogging with time, to measure the effect of clogging with depth, and to determine the effect of soil texture upon clogging. Seven soils were studied in column tests in a controlled environment. Hog manure was ponded on the soils for a period of 185 days and the soils were monitored for changes in apparent hydraulic conductivity, hydraulic conductivity with depth and visual alterations. The soil-manure interface was found to govern infiltration into the soil and the apparent hydraulic conductivity of the soil column. This layer was 5 mm to 7 mm thick and was a result of particulate matter in the manure clogging the surface soil pores which increased in thickness with time. Soils below this layer retained their ability to conduct flow with the exception of some reduction in hydraulic conductivity caused by small particulate matter passing through the clogged layer and air entrapment caused by fermentation. The clogging of the soil reduced the apparent hydraulic conductivity of the soil columns to less than 10-6 cm/s within 5 to 25 days and to less than 10-7 cm/s within 20 to 30 days. The time required to reduce the apparent hydraulic conductivity of the soil column was dependent on soil texture and was less for soils with less than 25 % clay content and more for soils with more than 25% clay content.