Vertical Distribution of Nematodes in the Soil

Variation

• Factors such as the season, land use, plant species, fertilization and more affect the distribution of nematodes in soil. What's more, there are countless species of nematodes influenced in different ways by changes in the soil climate. For example, population densities are by far at their highest, regardless of species, in late summer. There is no consensus between researchers on what a healthy density is, only that large numbers of beneficial nematodes are good and large numbers of plant parasitic nematodes are bad.

Distribution

• In most cases, the vast majority of nematodes in any vertical distribution will be found near the top, up to 70 percent between the surface and the first two inches of soil. This does not apply to all species however, and conditions will change this. Some species thrive at 12 to 20 inches deep, and though peak populations are not usually found as low, nematodes are often found at 40 inches.

Causes

• Higher populations of nematodes are usually found in untouched, but not overly compacted soil. In a healthy undisturbed soil, nematode populations will be highest at the surface, but in tilled soils, the highest populations will likely be found below the tilled level. Plant depth also has a huge impact on nematodes. If the soil in which the nematodes are found has shallow rooted plants in it, nematodes will be found at shallow densities. If the plant is deep rooted, the opposite will occur.

Obtaining a Sample

• The best way to obtain an accurate vertical nematode sample is with a soil tube. This is a simple tool that pulls up a core sample of the soil that can maintain it's shape and be analyzed from top to bottom. Your local extension service should be able to diagnose the sample for a small fee as well as answer any further questions you have about nematodes in your soil.