Soil microbial biomass and enzyme activity following liquid hog manure application in a long-term field trial

Abstract

Liquid hog manure (LHM) addition to soils in corn silage (Zea mays L.) production may benefit microbial activity by providing C and other nutrients. The objective of this study was to compare the effects of a LHM application to that of inorganic fertilizers (IF) on the biological activity of a Le Bras silt loam soil (Humic Gleysol) under continuous corn production and LHM fertilization. Amounts of 0 to 120 m3 LHM ha−1 and 150 N–150 P2O5–150 K2O kg ha−1 were applied to silage corn. The 0- to 15-cm and 15- to 30-cm soil layers were sampled 28 d after the 18th yearly LHM application. The LHM inputs, particularly at 90 m3 ha−1, resulted in higher enzyme activities and microbial biomass C (MBC) than IF or the unamended control in the 0- to 15-cm soil layer. The 90 m3 LHM ha−1 also gave higher microbial biomass N (MBN) than IF in this soil layer. Application of LHM had no effect on the activities of the enzymes studied or on the MBC and MBN contents in the 15- to 30-cm layer. Ammonifier population was highest with 60 m3 LHM ha−1 in both soil layers. Nitrifier population was not affected by LHM in the top soil layer, but was linearly increased by LHM rates in the 15- to 30-cm layer. This study showed that LHM addition may enhance enzyme activities, microbial biomass and the N mineralizer population in the plow layer of a soil in a corn silage monoculture. Key words: Corn, pig slurry, microbial biomass, monoculture, soil enzyme