Thirsty vines Summer girdling Compost teas Organic marketing The ...

24
Active fungal biomass (ug/g)
Figure 2. Active fungal biomass in soil samples from kiwifruit orchards over three seasons, averaged for
all eight sites.
Each season, soil samples were taken and
microbial measurements were carried out
by the Soil Foodweb laboratory using visual
counting methods, while soil, leaf and fruit
nutrient concentrations were determined
by Hill Laboratories Ltd. Packhouse staff
measured fruit weight, soluble sugars (°Brix)
and dry matter on fruit samples (n=90)
collected prior to commercial harvest
each season.
Increases in the density of soil fungi and
bacteria were expected as a direct result of
the compost tea applications, but none was
found. The amount of active fungal biomass,
an important parameter of soil health,
varied widely among the study orchards, as
well as from year to year, but did not show
any consistent change as a result of compost
tea application (Figure 2).
The reason for the dramatic drop in
the fungal biomass values for the
November 2006 sampling, confi rmed by
an additional sample taken in February
2007, is a mystery.
Other soil microbial parameters also
showed no consistent effect in response to
compost tea applications.
Similarly, soil, leaf and fruit nutrients
(nitrogen, phosphorus, potassium, etc.)
showed no differences between the
compost tea-treated plots and the untreated
plots. Fruit parameters, including mean
weight, soluble sugars and dry matter were
also unaffected by compost tea application
(Figure 3). Differences in mean fruit weight
across seasons refl ect sampling time relative
to harvest, rather than growth differences.
CONCLUSIONS
The results obtained demonstrate that use
of compost tea formulations had no effect
on organically grown kiwifruit orchards
during the three seasons over which this
trial was conducted. At the start of the
study all participants, both orchardists
and compost tea manufacturers were
confi dent of positive results, so the lack of
effect following three seasons trialling was
not expected. The outcomes from the
study need to be considered within the
following context:
• The sites chosen for this study had
BioGro certifi cation and, in most cases,
had a reasonably long history of
good organic-based management,
including relatively high inputs of
organic matter and relatively low inputs
of pesticides. These sites may in fact
be near their biological optimum, and
their soils probably already contain
good populations and diversity of