Home' Grower : March 2011 Contents The South Australian Grower -- March 2011
Figure 5: Handheld salinity meter.
Table 2: Conversion factors to deci-Siemens per metre (dS/m).
Adapted from: Rengasamy and Bourne (1997)
Total dissolved solids (TDS) or concentration is the amount of salt per
unit volume of water. Mass is normally given in milligrams (mg), volume
in litres (L), and concentration in milligrams per litre (mg/L).
Important conversions factors between different units of electrical con-
ductivity and from concentration to electrical conductivity are provided
in Table 2.
Many fertilisers show the relative contents of major components such
as nitrogen (N), phosphorus (P), and potassium (K) as per cent (%),
which is how many kilograms of N, P, or K supplied when the fertiliser
is applied at 100 kg/ha. When diluting liquid fertilisers a 5% solution
would contain 50 mL of the fertiliser, made up to one litre by adding
950 mL of water.
Applied nutrient salts (fertilisers) will contribute to the measured salin-
ity levels in soil. Generally this component of the overall soil salinity level
will rapidly decrease as plants use the nutrients.
Know the salinity of YOUR irrigation
Increasing number of irrigators use recycled water sources which can
vary in salinity during the growing season. The quality of many natural
water sources is also declining hence it is important that growers con-
tinuously monitor these trends.
General crop response to root zone salinity
Crops usually have a threshold root zone soil salinity above which pro-
ductivity is reduced by a combination of water stress, nutrient imbalance
and toxicity effects. Nutrient imbalance and toxicity are important when
overall salinity is moderately low. At high salinity water stress becomes
the dominating issue.
Establishing plants and seedlings are particularly susceptible to the
dehydration effect of salinity and do not exhibit a threshold salinity tol-
erance. Crops already stressed by other factors have reduced tolerance to
root zone salinity.
If root zone salinity can be maintained below the threshold level
throughout the cropping season, yield potential is unlikely to be affect-
ed. For many irrigators, this management goal is unlikely as the salinity
of the water source already exceeds the threshold value of crops being
Management options for crops of varying sensitivity to root zone salinity are illustrated below.
Type of measure units
Convert to dS/m by:
m S/cm or EC Units
per litre (mg/L)
parts per million
Figure 6: Salt accumulation around
the wetted edges. (Image: Anthony
Above the threshold level a steady
loss in yield potential with increasing
root zone salinity is observed (Figure
3). The rate of decline is usually
lower for more salt tolerant crops.
Figure 7: General crop response to soil
salinity. (Data from: Ayres and Westcot 1989)
Advances in irrigation system design and best
practice management, use of salt excluding
root stocks, and maintaining healthy crops will
influence both the threshold level and crop
response to root zone salinity observed in the
Plants can also directly absorb salt through
their leaves. Leaves do not have the ability to
exclude salt in the same way as roots do.
Thus crops can suffer severe damage when
spray irrigated using salty water, especially in
hot dry windy weather.
Figure 8: Management options for varying soil salinity and crop tolerance. (Data from: Ayres and Westcot 1989)
(adapted by Jeanette Chapman from Arris pers. comm). Salt sensitive crops not only have low critical threshold
levels (green bars, Figure 8), they also have a narrower range of soil salinity beyond the threshold level in which
removal of salt by leaching is likely to be effective (yellow bars). This places higher demands on managers to
rapidly respond to changing root zone salinity. In comparison, more salt tolerant crops have higher threshold levels
and a wider range of root zone salinity in which leaching is likely to be effective. To successfully manage root
zone salinity, growers should develop an understanding of how their irrigation systems distribute salt within the
root zone, and how salt accumulates within the root zone without targeted management. These topics will be
covered in subsequent articles in this series.
Soil Salinity (ECe, dS/m)
Yield Potential (%)
MYPOLONGA S.A. 5254
Ph. 8535 4188
Fax. 8535 4271
for all your
to discuss further how
we can assist you
with the 2011 season
Chemicals, Seed, Hardware
Granular & Liquid Fertilisers
Personal Safety Equipment
HARDI Spray Equipment
Links Archive February 2011 April 2011 Navigation Previous Page Next Page