Soil management
Tony Pitt
Six years of soil testing
• In 2005/06, recycled water use was fairly minor –
just 47 farms with more than 1 ML/ha.
• For 2006/07, recycled water underpinned crop
production for Werribee
• For the following 4 years, recycled water was by far the
dominant source of irrigation water for the district.
• The salinity of the recycled water is 1700 to 2300 EC
– 1,700 uS/cm to 2,300 uS/cm – units used for irrigation water
– 1.7 dS/m to 2.3 dS/m – units used for soil water.
Average Soil Salinity
8
7
ECe dS/m
6
5
4
3
2
1
0
Baseline
2006
2007
Soil Ece
2008
2009
REIP Threshold
2010
Average Soil Chloride
900
Concentration mg/kg
800
700
600
500
400
300
200
100
0
Baseline
2006
Chloride
2007
2008
2009
REIP Threshold
2010
Average Exchangeable Sodium Percentage (ESP)
20
18
16
ESP %
14
12
10
8
6
4
2
0
Baseline
2006
ESP
2007
2008
REIP Threshold
2009
Sodic
2010
In 2010
• Average surface soil salinity is back to baseline values
• District average chloride has fallen by 40 % in 12 months
• Sodium values however are unchanged
• Sodicity is apparent when collecting soil samples
• Winter rainfall better but still below average
Short term
• The Red Brown Earth soils of Werribee South are very
forgiving and very responsive to rain
• The late summer and autumn period are the most
important times for salinity management
• For every irrigated crop some leaching is required
• A negative impact of rainfall on sodic soils is the
dispersion and sealing of the soil surface
Long term
• Natural leaching from rain will remove the surface
salinity provided the soils are kept permeable
• Rain or low salinity water doesn’t improve sodicity
• Sodicity requires continuous on-farm management
• Gypsum dosing of the irrigation water could be better
option than broadcast gypsum
Sodicity management
• Adding calcium
– Gypsum broadcast
– Gypsum added to water
– Other calcium fertilizers
In summary
• Werribee South soils can handle 2,000 to 2,200 EC
water for a season or two with very good farm
management
• Evidence from six years of soil testing indicates
1,300 EC –1,800 EC, with minimal leaching should be
sustainable provided soil sodicity is kept under control
• Above 1,800 EC leaching has to increase and be
planned for each crop
• Lower salinity water may increase the problems of
surface sealing and poor aeration
• On-going sodicity management important