Effect of compost and manure soil amendments on nematodes and on yields of potato and barley: a 7-year study.

A 7-year study located in Prince Edward Island, Canada, examined the influence of compost and manure on crop yield and nematode populations. The compost used in this study consisted of cull waste potatoes, sawdust, and beef manure in a 3:3:1 ratio, respectively. No plant-parasitic nematodes were detected in samples collected from windrow compost piles at 5- and 30-cm depths prior to application on field plots. Low population densities of bacterial-feeding nematodes were recovered from compost windrows at the 5-cm depth. Field plots of potato (Solanum tuberosum cv. Kennebec) received compost applied at 16 metric tonnes per hectare, or beef manure applied at 12 metric tonnes per hectare. An adjacent trial with barley (Hordeum vulgare cv. Mic Mac) received only the compost treatment. In both trials the experimental design was a complete randomized block with four replicates. Data averaged over seven growing seasons indicated that population levels of root-lesion nematodes (primarily Pratylenchus penetrans) were higher in root-zone soil in potato plots treated with either compost or manure compared to the untreated control plots. The soil amendments did not affect root-knot nematode (Meloidogyne hapla) population densities in the potato plots, but clover-cyst nematodes (Heterodera trifolii) were more numerous in the root-zone soils of barley treated with compost compared to the untreated plots. Numbers of bacterial-feeding nematodes (primarily Diplogaster lheritieri) were greater in soil in potato plots treated with manure and in soil around barley roots than in untreated plots. Total yields of potato tubers averaged over seven growing seasons increased by 27% in the plots treated with either compost or manure. Grain yields of barley also were increased by 12% when compost was applied. These results indicated that organic amendments increased crop yields, but the impacts on different nematode species varied and usually increased soil population levels.