Denitrification activity in the vadose zone beneath a sludge-amended semi-arid soil

Soil cores were collected to a depth of 14 m from a Southwest semi-arid soil amended with either anaerobically digested sludge or inorganic fertilizer. Twenty sections partitioned from each core were characterized for their physical and chemical properties. Denitrification potential was estimated in each core section in the laboratory using the acetylene reduction method. The sludge-amended soil had significantly higher denitrification rates within and below the root zone than the fertilizer-amended soil. Additionally, significant correlation values were obtained in both cores between denitrification rates and particle size distribution, moisture, and total organic carbon (C). Sludge applications in semi-desert soils may add much needed organic C in the soil profile. This additional soluble organic C may help control nitrate (NO₃) ground water pollution by providing substrate C for denitrifying bacteria below the root zone.