Agriculture Reference
In-Depth Information
and it has already been demonstrated that the production of EPS by the bacteria is dependent
on their environment (White, 1995). The results of this study indicated that a combination of
no till and irrigation management for barley cropping appears to provide a balance between
the microorganisms and the physicochemical components, favoring growth of specific
bacterial species with ability to aggregate soil, development and potentially the excretion of
polymers, and aggregation.
Soil sedimentation by bacteria in liquid suspension measured by image-based reflectance
is an improvement over the method using pressure to break artificial aggregates amended
with bacteria. Soil aggregation assay based on the formation of artificial aggregates by adding
bacteria to natural soil involves air-drying that induces intermolecular associations between
organic molecules and mineral surfaces (Kemper and Rosenau, 1984) besides the “adhesive”
properties of soil binding agents excreted by bacteria. These physical artefacts can be avoided
with the soil sedimentation method.
C
ONCLUSION
The ultimate aim of research on soil aggregation, most if not all of it publicly funded,
should be improved practices in soil health management. There are different pathways to
reach this goal and we have sought to indicate some approaches in this important field of
research that are justified but perhaps underemphasized or overlooked. Based both on
precedent (discussed above) and on rationale drawn from a significant body of literature, we
have concluded that use of cultural methods will enhance progress in the study of the
microbial ecology of soil aggregation, thus allowing knowledge derived from such work to be
integrated with molecular methods. This means studies with cultures detected at the highest
levels of abundance in soil aggregates through isolation onto low nutrient or selective media,
identification of these cultures and assessing them for traits possibly related to soil
aggregation such as EPS production and further, the development and application of assays to
test their ability to cause water stable soil aggregates. Also, if the goal of managing
agroecosystems, in turn to manage microbial populations in soil and positively affect
microbial functional groups which contribute to soil structure (Elliot and Coleman, 1988)
then cause-and-effect studies can uniquely contribute to that end.
R
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