Agriculture Reference
In-Depth Information
Box 5.3 Field Observations for a Biologically Healthy Soil
The following simple steps can be taken to assess the soil's biological health in a
vineyard:
1. Scrape away any surface litter to reveal the top of the A horizon. A litter
layer that is thin and well fragmented shows that organic residues are being
broken down quickly and incorporated into the soil. The topsoil should
have a friable tilth and be rich in humified organic matter (a dark color).
The deeper is this enriched zone, the better the soil's condition.
2. Observe the litter layer and soil surface for small insects such as wood lice
and springtails. These should be plentiful and moving about actively.
3. Turn over a full spade depth of the topsoil and look for lively earthworms
(see figure 5.4). More than 10 earthworm burrows per 15
×
15
×
15-cm
block of soil indicates good drainage and aeration, facilitating root growth
and microbial activity.
Table 5.7
Soil Tests for Evaluating the Biological Health of Australian Vineyard Soils
Soil test
Method of measurement
Benchmarking values for topsoil
SOC
Acid digestion (W-B) or dry combustion;
W-B does not give complete digestion
so the same method should be chosen
for all measurements; dry combustion
values need to be corrected for any free
calcium carbonate; depth of soil chosen
must be specified
Low <0.5 to <1.2
Medium 0.5 to 1.7
High >1 to >2
(In each class range, values
increase from sandy to clay
soils; values as %C
a
for
0-15 cm depth)
SMB
CFE or SIR; SIR values (in μL CO
2
/g
soil/hour) are multiplied by 40 to give
a value comparable to SMB by CFE
(Anderson and Domsch, 1978); depth
of soil chosen must be specified
Low <150
Medium 150-400
High >400
(All values in mg C/kg soil for
0-15 cm depth)
PMN
Anaerobic incubation of soil for one week
at 40
o
C; depth of soil chosen must be
specified
Low <8
Optimum 8-18
High >18
(Values in mg N/kg soil/week for
0-10 cm depth)
Note
. SOC = soil organic carbon; W-B = Walkley-Black; CFE = chloroform fumigation-extraction;
SIR = substrate-induced respiration; SMB = soil microbial biomass; PMN = potentially mineralizable
nitrogen.
Compiled from Balachandra et al. (2009), and Riches et al. (2013).
a
To express values as soil organic matter, multiply by 1.72.
