Prior to the placement of the greenhouses and planting of vegetable
seeds, soil samples were taken from the 0-3, 3-6, and 6-9 cm segments
of the vertical trench profile.
Similarly, soil samples were col-
lected during the harvest of mature plants from within the greenhouses
at the same depth intervals.
Forty-eight soil samples were collected.
Previous experiments in NTS soils had shown that no major changes in
the microbial population could be expected to occur during the time
period of these experiments
(Au, 1972).
Accordingly, no further soil
samples were collected from outside of the greenhouse structures.
Soil moisture of the collected soil samples was determined in separate
experiments according to standard procedures
(Pramer and Schmidt,
1964).
Dilution plate counts were made of the collected soil samples to
quantify and differentiate the fungal and bacterial populations.
From each soil sample, an amount corresponding to 20 g of oven-dried
soil was added to 100 ml of sterile distilled water and shaken for 10
min.
Coarser particles were allowed to settle, and 1-ml samples of
the soil suspension were used to prepare dilutions for plate counts
according to standard procedures
(Clark,
1965).
The dilutions used
were 5 x 1077 and 5 x 107? for molds, and 5 x 107* and 5 x 107° for
bacteria and Streptomyces counts.
dilution.
Five plates were poured of each
Cooke's Rose Bengal agar with antibiotic added was used
for fungal determinations,
and sodium albuminate agar was used for
bacteria and Streptomyces determinations.
The plates were incubated
at room temperatures; fungal and bacterial counts were made after 2
and 14 days, respectively.
In addition to the microbial plate counts,
the classification and the relative abundance (in percent of the
total fungal and bacterial numbers) were determined for the fungi
Muecors, Aspergttllus, Pentcilltum,
and Demattaceae as well as for the
bacterial genus Streptomyces.
RESULTS AND DISCUSSION
In this discussion, only the overall changes of microbial population
caused by the agricultural use of the soil will be highlighted.
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