When Manure Meets The Microbes
Manure application increased microbial biomass nitrogen in two out of three fields.
Manure applications to soil may have substantial effects on soil organisms and their activities. These effects may be beneficial or detrimental to the sustainability of crop production. The objectives of the soil biology studies were to analyze the impact of manure application rate on biological activity, microbial biomass, and earthworms in the SARE plots.
Microbial Biomass
The substrate-induced respiration
method was used to estimate active biomass carbon, the fumigation-incubation
method was used to measure total biomass carbon, and the fumigation-extraction
method was used to measure microbial biomass nitrogen. Both sites
(two replicates) were sampled in the fall of 1997. In 1998, both
sites were sampled twice (in June and September). Each sample consisted
of ten soil composites taken to a depth of 15 cm .
Both active and total biomass carbon tended to be greater in the clayey sites than in the sandy sites. However, manure application increased microbial biomass nitrogen in both the sandy and clayey soils in 1998. Manure also increased total biomass carbon in the sandy soil in 1997. Sidedressed nitrogen fertilizer also influenced microbial activity. Sidedressing significantly increased the biomass nitrogen in all three fields. Therefore, both manure and nitrogen fertilizer stimulated microbes and increased microbial biomass nitrogen. The nitrogen contained in microbial biomass is not available for plant use until the cells die and the organic nitrogen in the biomass is mineralized to form ammonium-nitrogen.
Earthworms
Soil samples were collected for earthworm counts from each site in
fall 1997 and in both June and September of 1998. Earthworms (adults and
cacoons) were counted and identified to the species level. Preliminary
results indicate that earthworm counts are too low to analyze statistically.
Factors such as tillage, rootworm pesticide applications, or salts may
have a strong dampening effect on earthworm populations at these sites.
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