Microbial respiration as an index of soil aeration in compacted and sewage sludge amended soils

Abstract

The use of liquid sewage sludge on agricultural soils may improve productivity, but cause compaction due to an application procedure requiring multiple passes with heavy machinery. The movement of water through the soil profiles was used as an index indicating a greater degree of compaction in soils amended with high amounts of sewage sludge vs. low amounts or inorganic fertilizer. Laboratory studies developed a method to utilize CO 2 evolution from microbial respiration as an index of soil aeration. Samples of Pima clay loam soil of varying moisture levels were amended with inorganic fertilizer or sewage sludge and compacted to several bulk densities. Aeration restricted microbial respiration at 1.6 Mg m-3 bulk density and 0.24 g g -1 , and 1.4 Mg m -3 bulk density and 0.26 g g -1 moisture, with no variation due to soil amendments. Respiration rates increased in a compacted sewage sludge amended soil, after an incubation period, indicating an improvement in soil structure due to the sludge.