Temporal and spatial aspects of the influence on soil nematodes of depositing artificial pats of sheep faeces containing a range of parasite management agents

Abstract

Populations of soil nematodes may be subject to the influence of sudden localised additions of substrate such as occur with the deposition of faeces on pasture. In modern agricultural practice faeces are likely to contain residues of parasite management agents such as anthelmintic chemicals, or possibly biocontrol agents. To assess the possible duration and spatial scale of the influence of faeces with and without such residues, 50 g fresh weight artificial faecal pats were applied to small plots on drench naïve pastures in early winter (June) and early summer (November) 2001. Treatments were: C− (no faeces), C+ (faeces from untreated sheep), B (from sheep with an intra-ruminal bolus releasing a benzimidazole anthelmintic – ‘albendazole’), ML (from sheep with a bolus releasing a macrocyclic lactone anthelmintic – ‘ivermectin’), F (from sheep receiving a daily feed supplement containing chlamydospores of the nematophagous fungus, Duddingtonia flagrans). Nematodes within the pats and four adjacent soil zones were monitored until the faecal material had dissipated (after 70 and 63 days, respectively). Five replicate pats were sampled on each occasion. A total of 57 nematode taxa were discriminated and their populations, feeding groups and several diversity indices calculated for a total of nine sampling occasions, and assays for D. flagrans undertaken. While D. flagrans was recovered from the ‘F’ treatment faeces and pats for up to 18 days after deposition it was not found in the mineral soil. The most consistent effect found in the various measures of the nematode assemblage was that of position in relation to the faecal pat. Most other effects were idiosyncratic. The only consistent effect was in the total Maturity Index (∑MI) 7 days after the November deposition, with lower values found under faecal pats compared with C−, possibly reflecting the response of r-strategist bacterial-feeding nematodes to pat addition which would be more likely in summer than in winter. The findings provide confirmation of lack of significant effects of parasite control measures on soil nematodes, and add a seasonal component. There seems no soil biological reason why practical aspects of managing gastro-intestinal nematodes using D. flagrans should not be pursued. Significant positional effects recorded after the faecal pats had disappeared indicating they contribute to the known spatial heterogeneity of soil nematodes under pastures.