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

Liquid hog manure (LHM) addition to soils in corn silage (Zea mays L.) prod uction may benefit microbial activity by providing C and other nutrients. T he 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 Br as silt loam soil (Humic Gleysol) under continuous com production and LHM f ertilization. Amounts of 0 to 120 m(3) LHM ha(-1) and 150 N-150 P2O5-150 K2 O kg ha(-1) were applied to silage corn. The 0- to 15-cm and 15- to 30-cm s oil layers were sampled 28 d after the 18th yearly LHM application. The LHM inputs, particularly at 90 m(3) ha(-1), resulted in higher enzyme activiti es and microbial biomass C (MBC) than IF or the unamended control in the 0- to 15-cm soil layer. The 90 m(3) LHM ha(-1) also gave higher microbial bio mass N (MBN) than IF in this soil layer. Application of LHM had no effect o n the activities of the enzymes studied or on the MBC and MBN contents in t he 15- to 30-cm layer. Ammonifier population was highest with 60 m(3) LHM h a(-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 3 0-cm layer. This study showed that LHM addition may enhance enzyme activiti es, microbial biomass and the N mineralizer population in the plow layer of a soil in a corn silage monoculture.