57 / 92
55
November 2015
Soil microbial activity
The ability of soil microbial populations to mineralise organic car-
bon, phosphorus and nitrogen, is measured by the ß-glucosidase,
phosphatase and urease enzyme activities in the soil. By implication,
the higher the microbial activity, the faster the nutrient release from
organic substrates available for plant uptake. Enzyme analyses done
for these crop treatments have been aggregated (averaged) to evalu-
ate soil microbial activity (see
Graph 3
).
The legume cover crop (lablab) elicited significant differences in the
potential of soil microbial communities to mineralise carbon, phos-
phorous and nitrogen. The lowest overall enzyme or microbial activ-
ity was present in veld, maize monoculture and babala on winter CC
mix treatments, whereas the highest overall activity was present in
Graph 1: Microbial richness between cover crop treatments.
Graph 2: Microbial abundance between cover crop treatments.
lablab on maize, sunflower on summer mixture and lablab on black
oats treatments. Despite the same cover crops being planted, but
in different sequences, microbial activities differed significantly be-
tween lablab on babala and babala on lablab. The latter demonstrat-
ed the highest overall microbial activity.
Solvita 24 hour CO
2
burst test
Solvita
®
soil test provides the ability to measure soil biology and
evaluate your soil management practices. With Solvita soil tests, soil
labs, producers and crop consultants have the capability to easily
measure soil CO
2
respiration and reserve organic nitrogen; impor-
tant indicators of soil fertility. Being able to evaluate the turnover
of organic matter via CO
2
respiration is important for a number
of reasons:
Indicator of soil health
The rates of CO
2
release is generally re-
garded as an indicator of soil health and is
favourably improved with practices such
as cover cropping, where the quality of soil
is improved by building the organic matter
through accumulation and decay of roots
and plant litter as well as the synthesis of
glomalin through Mycorrhizae fungi associ-
ation with the plant roots, facilitated through
photosynthate exudates as the food source.
Indicator of soil nutrients
The rate of carbon exchange can be used
to estimate the potential release of nutri-
ents such as nitrogen and phosphorus that
are components of soil organic matter. This
Potential Mineralisable Nitrogen (PMN) is in-
tended to help Solvita-users interpret their
CO
2
Burst results to assess how this previ-
ously unmeasured organically bound N-
pool can help decrease fertiliser costs. The
positive correlation that exists between the
PMN through microbial action and Solvita
24 hour CO
2
Burst test has been demon-
strated by several researchers as well as
commercial Agro Analytical Laboratories.
The Solvita CO
2
Burst test was therefore
used as an indicator of the biological fac-
tors present in the same fifteen soils under
different soil management strategies or
crop treatments in the Ottosdal district (see
Graph 4
and
Graph 5
). Note the differences
between cover crop and cash crop treat-
ments, but in particular the monoculture
and bare soil exhibited the lowest respira-
tion rates, while the lablab summer legume
treatments showed the highest respiration.
Solvita tests effectively identify positive
changes in soil management and can track
these changes over time. What is signifi-
cant is the positive correlation when soils
are planted with cover crops in maintaining
the soil microbial diversity, which has been
supported by the Solvita CO
2
burst test
results shown in
Graph 4
.
Particulate organic matter
Particulate organic matter (POM) refers to
all soil organic matter in the soil smaller
than 2 mm and larger than 0,045 mm in
size and it is considered biologically and
chemically active.