Agriculture Reference
In-Depth Information
There are numerous techniques for characterising the biological characters of
compost teas, such as microbial biomass, activity, and/or diversity of compost and
compost teas (Bandick and Dick
1999
; Palmer et al.
2010b
; Ryckeboer et al.
2003b
);
however, there is a lack of standard procedures for the purpose of quality control
(Anonymous
2006
). This situation is analogous to on-going attempts to develop
practical indicators of the biological properties of soil (Bezuidenhout et al.
2012
;
Knight et al.
2013
; Ugarte et al.
2013
).
9.4.3
Extraction Time and Compost to Water Ratio
It has been suggested that the efficacy of ACT depends on the duration of extraction
(Scheuerell
2003
). Palmer et al. (
2010b
) steeped compost in in aerated water for 24,
48 or 72 h before application to detached bean leaflets and single-point inoculations
of the fungal pathogen
Botrytis cinerea
. Relative to water, all batches of ACT, re-
gardless of extraction time, reduced lesion development to a similar extent.
It has also been postulated that the quantity of compost in water influences bio-
logical and chemical characters of ACT and potential to control plant pathogens.
According to Weltzien (
1990
), NCT controlled the plant pathogen
Phytophthora
infestans
on detached potato leaflets when the compost to water ratio ranged be-
tween 1:3 and 1:10 but not when the compost to water ratio was 1:50. A more de-
tailed in vitro experiment by Cronin et al. (
1996
) with
Venturia inaequalis
, the cause
of apple scab or black spot, determined the EC
50
(the concentration that inhibited
germination of 50 % of
V. inaequalis
conidia) of non-aerobic slurries of compost.
There was a linear relationship between the log
10
cfu (colony forming units) of the
extract concentration and spore germination inhibition. The extracts were mixed
with sterile deionised water in ratios ranging from 1:3.16 to 1:100. In contrast to
these studies, the quantity of compost in water did not influence grey mould sup-
pression on field grown strawberries (Welke
2004
). Similarly, compost weight to
water volume ratios of 1:3, 1:10 or 1:30 tested by Palmer et al. (
2010b
) reduced the
growth of
Botrytis cinerea
on bean leaflets to a similar degree.
9.4.4
Amendments and Adjuvants
Nutrient availability is critical for microbial metabolism and growth (Egli and
Zinn
2003
). It has been postulated that nutrients added to compost tea during or
after its preparation increase the activity and abundance of microorganisms, and/
or microbial composition, including materials rich in protein and amino acids, like
fish emulsion or fish hydrolysate (El-Tarabily et al.
2003
). Practitioners attempt to
promote microbial growth by amendment of ACT with nutrients such as yeasts,
sugar, molasses, kelp extract, fish hydrolysate, rock dust and/or humic acid (Ing-
ham
2005
). The effect of amendments on pH should be checked and aeration levels
during preparation of ACT need to be monitored regularly to ensure any increase in
microbial activity does not consume oxygen faster than it is introduced by aeration.
