Nematode extraction efficiency is influenced by soil depth and inoculation level

Authors: Schumacher, Lesley; GRABAU, ZANE - University Of Florida

Submitted to: Nematropica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/27/2025
Publication Date: N/A
Citation: N/A

Interpretive Summary: Reniform nematode (Rotylenchulus reniformis) is known to infest deep in the soil profile but not much is known about free-living nematodes and their relative extraction efficiency (i.e., nematode recovery) from soil at deeper depths. Therefore, soil was collected after harvest in 2018 from cotton plots in a long-term peanut-cotton rotation in Quincy, FL, USA to determine if soil characteristics from depths up to 120 cm affect nematode extraction efficiency. Soil from each depth was first sterilized and then inoculated with a known number of reniform and free-living nematodes. Samples were then extracted using a modified sucrose-centrifugation method to determine the extraction efficiency of the nematodes from each depth. Both soil depth and nematode inoculation level affected nematode extraction efficiency, but this differed between reniform and free-living nematodes. Reniform and free-living nematode extraction efficiency was 47% and 36% at the shallowest soil depth, respectively, and decreased to 36% and 25% at the deepest soil depth, respectively. The lowest inoculation rate for reniform nematodes led to greater extraction efficiency than higher inoculation rates, yet this same trend was not observed for free-living nematodes. The purpose of this work was to determine the relative extraction efficiency and correct for any observed errors associated with deeper soil depths. This research showed that we are vastly underestimating actual soil population densities of nematodes, which in turn affect management decisions and calculation of nematode ecological indices.

Technical Abstract: There is a need for evaluating nematode abundances from different soil types by optimizing extraction efficiency (i.e., nematode recovery) because soil texture, pH, and soil organic matter change as soil depth increases. Therefore, the extraction efficiency of a modified Baermann technique on soil recovered from different depths (0-30 cm, 30-60 cm, 60-90 cm, and 90-120 cm) at a long-term peanut-cotton rotation study in Quincy, FL, USA was examined. This was accomplished by evaluating the relative efficiency of reniform (Rotylenchulus reniformis) and free-living nematode extraction from these different soil depths based on the addition of known quantities of nematodes to microwave-treated soil. Depth and nematode inoculation levels both significantly affected extraction efficiency of reniform and free-living nematodes, but in different ways. For reniform nematode, extraction efficiency ranged from 36% at the deepest depth (90-120 cm) and increased to 47% at the shallowest depth (0-30 cm). Yet for free-living nematodes, extraction efficiency ranged from 25% at the deepest depth and increased to 36% at the shallowest depth. Reniform nematode extraction efficiency was greatest (39%) with the lowest inoculation rate (i.e., 1,000 reniform nematodes per 100 cm3 soil), while trends with free-living nematode extraction efficiency were inconsistent. This work highlights the need to understand that true nematode population densities may be underestimated due to soil type and correction factors may need to be implemented for diagnostic and management purposes.