Influences of nitrogen inputs on nematode populations under highbush blueberry

Nitrogen fertilization is a common practice in conventional blueberry production. Research has shown that nitrogen fertilization can have non-target effects on pests and diseases of some crops. Little is known, however, of how nitrogen fertilization affects plant-parasitic nematodes, which are soil-dwelling microscopic roundworms that attack the roots of many crops. This study examined the long-term effects of nitrogen fertilization rates on populations of three different species of nematodes parasitizing blueberry, as well as the diversity of non-parasitic or beneficial nematodes that are indicators of soil health. Four nitrogen fertilization treatments were applied each year over a ten year period, to a planting of the ‘Duke’ variety of blueberry at a site in the Fraser Valley. The treatments corresponded to 0, 100, 150 and 200% of the annual application rates recommended for conventional blueberry production in the region, which vary with age of planting. Nematode populations were quantified each year of the study. The abundances of two of the plant-parasitic species, Rotylenchus robustus and Pratylenchus crenatus, increased with modest fertilization (100% to 150% of the recommended rate), but there was no additional increase in their abundances at the highest fertilization rate. These results suggest that in the long-term, the buildup of plant-parasitic nematodes could negate some of the benefits of nitrogen fertilization on yields. Several measures of the diversity of non-parasitic nematodes declined with fertilization rate, indicating broader changes in the soil food web that could have had indirect, feedback effects on population dynamics of the plant-parasitic nematodes.