Response of a soil nematode community to liquid hog manure and its acidification

A study was conducted to determine why the number of opportunistic bacterial-feeding nematodes increase following addition of liquid hog manure and acidified mixtures of the manure to soil. A sandy loam soil harboring a wide range of nematode taxa, representing various trophic and colonizer-persister groups (c-p 1 through 5) and augmented with the plant-parasitic nematode, Pratylenchus spp., was used in microcosm experiments. Treatments were additions of liquid hog manure (0.15 v v−1 soil water), mixtures of manure (0.05, 0.10, and 0.15 v v−1 soil water) and sulfuric acid, as well as a sulfuric acid alone and a non-treated control. Three days post-treatment and during the presence of non-ionized volatile fatty acids from manure in soil, numbers of plant-parasitic nematodes, including Pratylenchus spp., decreased by at least 50% for all manure treatments compared to non-manure treatments. Thereafter, c-p 1 and c-p 2 nematode numbers increased in all manure but not in non-manure treatments. At week 4, c-p 1 and c-p 2 nematode numbers were greater by at least 6000 and 5000 individuals kg−1 soil, respectively, compared to non-manure treatments. In contrast, numbers of c-p 3-5 nematodes were not affected by the treatments. At week 4, the enrichment index, an assessment of the abundance of opportunistic c-p 1 and some c-p 2 nematodes compared to all c-p 2 nematodes, was around 70% for all manure treatments and lower, 32 and 29, respectively, for acid alone and non-treated control treatments. The increase in opportunistic nematodes following manure treatment was likely due to the increase in their food resources associated with the enrichment of the soil environment with readily degradable compounds. Volatile fatty acids present in the manure persisted in the soil for only four days before biological degradation. We conclude liquid hog manure is effective in killing plant-parasitic nematodes while increasing bottom-up food web interactions but not, as with soil fumigants, decimating top-down trophic interactions.