Agriculture Reference
In-Depth Information
7.3.2.4
Soil Microbiology
Basic soil biological properties were measured for each crop in the CROA field
trial to examine the effect of the compost treatments compared to farmer practice
and these included soil respiration, microbial biomass carbon, and the hydrolysis of
fluoroscein diacetate (FDA). The results for the first seven crops are presented in
Table
7.7
and Fig.
7.12
.
Soil respiration in the compost treatment (see Table
7.7
) was found to be sig-
nificantly higher (
p
< 0.05) than the farmer practice treatment for broccoli, the first
crop following the initial application of 125 dry t ha
−1
compost, but there were no
significant differences found between the treatments for the soils of the subsequent
four crops (Donovan et al.
2014
). The soil respiration of the compost treatments was
again found to be significantly higher than that of farmers practice in the capsicum
crop (crop 6) which followed the repeat application of 125 dry t ha
−1
compost, and
this significant difference was still observed in the soil of crop 7 (broccoli). The
elevated soil respiration most likely reflects the substantial increase in available
carbon substrate for the soil micro-organisms to utilise, which results from such a
large application rate.
Donovan et al. (
2014
) found no significant differences between the soil micro-
bial biomass carbon levels of the compost and farmer practice treatments for any
of the five crops following the first application of compost at the CROA field trial
(Fig.
7.12
). However, the second application of 125 dry t ha
−1
compost did result
in significantly higher (
p
< 0.05) microbial biomass C levels for the compost treat-
ment compared to the farmer practice treatment for crop 6 (capsicum) and crop 7
(broccoli) (Donovan et al.
2014
). In fact the microbial biomass C levels in the soil
of the compost treatment was found to be up to 100 % higher than that of the compa-
rable farmer practice soil (Fig.
7.12
). The FDA results in contrast found few signifi-
cant (
p
< 0.05) differences between the compost and farmer practice treatment soils
(Donovan et al.
2014
). The microbial biomass results from the second application of
compost suggest some benefit in repeat applications of compost. The initial applica-
tion may have had a priming effect on the biological community allowing it to be
more responsive to subsequent later additions of compost applications.. There may
be merit in following up an initial large application of compost to rejuvenate soil
quality, with smaller more frequent applications of compost to provide sustained
potential benefits to soil biology. Other studies (Kremer and Hezel
2013
; Reeve
et al.
2010
) found that organically managed agricultural systems with high organic
inputs significantly increased soil microbial activity. Kremer and Hezel (
2013
) also
found that organic systems with high inputs of composted vegetable residues sig-
nificantly increased (
p
< 0.05) soil enzyme activity and soil function. The impact of
compost amendments on soil function and the transformation of organic matter and
the cycling of nutrients and carbon is certainly an area of research which requires
more attention.
