[Edited_by_A._Ciancio,_C.N.R.,_Bari,_Italy_and_K.(Bookos.org)

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R. CAMPOS-HERRERA ET AL.
(1997) noted the apparent usefulness of composted animal manure for conservation
biocontrol after showing that long-term applications of manure increased EPNs by
3-fold. Animal manure mulches likely increase availability of insect prey and were
also shown to decrease the prevalence of some nematophagous fungi that prey on
EPNs (Jaffee, Ferris, Stapleton, Norton, & Muldoon, 1994; Duncan et al., 2007). If a
number of physical properties can be identified that consistently affect EPN spatial
patterns then this information might be used to incrementally improve biological
control achieved by either augmented or endemic EPNs.
Understanding the basis of relationships between EPNs and other variables in
the field can require a substantial research investment. Whereas EPN associations
with some variables have a causative basis, others arise indirectly through the effects
of unmeasured hidden variables. Therefore, identifying those variables that are most
likely to modulate EPN prevalence or behavior in predictable ways is important. A
comparison of the results of surveys using different sample criteria can be helpful in
selecting variables of interest.
Campos-Herrera et al. (2007) found that soil moisture was positively associated
with EPN recovery frequency in a survey of 100 undisturbed sites (natural areas and
field borders) in La Rioja, Spain. However, in a temporal survey of 18 agricultural
fields with different management regimes and bordering natural areas, EPNs were
unrelated to soil moisture but inversely related to soil disturbance (Campos-Herrera et
al., 2008). Because greater irrigation was employed in tilled annual cropping systems
with few EPNs than in natural areas or organically grown perennial crops with
numerous EPNs, Campos Herrera et al. (2008) speculated that soil disturbance is more
important than moisture in regulating EPN spatial patterns. Similarly, Campos-Herrera
et al. (2008) reported linear correlations between EPNs and certain soil characteristics
that were also studied by Alumai, Grewal, Hoy, and Willoughby, (2006) and Duncan
et al. (unpublished). Differences in the survey protocols among these studies suggest
the possibility that some of the correlations between soil properties and EPNs are due
to the influence of soil texture on both EPNs and certain chemical properties (Fig. 5).
Because greater sand content of soil generally favors EPNs, chemical properties
associated in some manner with sand content would likely be similarly associated with
EPNs. The relationships measured in Ohio and Florida (shown in small font in Fig. 5)
are strikingly similar. Organic matter, K + and Mg ++ tended to be negatively associated
with both EPNs and percentage sand whereas P was positively associated with both
variables. In contrast, these relationships had exactly opposite trends in the Spanish
survey. Nevertheless, soil chemicals in each of the three surveys were associated with
EPNs in the same manner that they were associated with percentage sand. The Ohio
and Florida surveys occurred on several golf courses and within a single citrus
orchard, respectively. Thus, cultural practices were similar among sites within each of
these surveys, and the effects of porosity and soil colloid surfaces on leaching of some
chemicals and the adsorption of others operated on similar levels of nutrient inputs.
However, the Spanish survey compared EPN populations in natural areas and in a
variety of different annual and perennial cropping systems. The very different levels of
inputs between the Spanish sample sites might have caused different relationships
between chemicals and percentage sand and, therefore, with EPNs than seen in Ohio
or Florida.