1
Dr James HillsTasmanian Institute of Agriculture (TIA) - University of Tasmania
Water use efficiency and irrigation management of Tasmanian forage options
Summary
• Forages and WUE• Irrigation scheduling• Pasture productivity• Grazing management
Water use efficiency (WUE)
• Ratio of dry matter (DM) production to water used
• Perennial ryegrass 1.1–1.2t DM/ML• Turnips 4t DM/ML• Maize 5t DM/ML
• Achieving high forage yields (t DM/ha) is a key determinant to maximising WUE
Irrigation scheduling
• Need to know– Readily available water– Evapotranspiration– System capacity
– Soil moisture probes are useful to visualise what is in the bucket!!
Readily Available Water (RAW)
• Ranges between 9 and 27mm for pasture with root depth of 30cm
Water in and out
System capacity
• The system capacity is the maximum possible rate at which the machine can apply water to the irrigated field area.
• Expressed in mm/day —NOT the depth applied per pass (mm).
Evapotranspiration
0
1
2
3
4
5
6
7
8
1/06
/201
5
1/07
/201
5
1/08
/201
5
1/09
/201
5
1/10
/201
5
1/11
/201
5
1/12
/201
5
1/01
/201
6
1/02
/201
6
1/03
/201
6
1/04
/201
6
1/05
/201
6
1/06
/201
6
1/07
/201
6
1/08
/201
6
6 to 6.5 mm/day maximum in January
ET0 (m
m)
Deloraine
• RAW 24mm• ETo max 6.5mm/day• Designed system capacity 6.5mm/day• Irrigating one day in three• Depth applied 6.5mm every third day• Managed system capacity 2.17mm/day
‐45
‐40
‐35
‐30
‐25
‐20
‐15
‐10
‐5
0
5
Soil water deficit (m
m)
field capacity refill point water every 3rd day
Irrigation scheduling and pasture productivity
Pasture growth rates 2016Cressy vs Montana
kg DM/ha/da
y
0
10
20
30
40
50
60
70
26/01/20
16
31/01/20
16
5/02
/201
6
10/02/20
16
15/02/20
16
20/02/20
16
25/02/20
16
1/03
/201
6
6/03
/201
6
11/03/20
16
16/03/20
16
Cressy Montana
Cressy
Montana
The green drought
Average ETo = 4.9mm/day Designed system capacity = 6.3mm/dayManaged system capacity= 1.8mm/dayNeed to water 5.5 days out of seven.
The farmer’s calculation
• Cressy averaged 30–40kg DM/ha/day
• Opportunity loss of 20kg DM/ha/day
• Opportunity loss of 210t pasture on 117ha pivot replaced with purchased grain
• $200/t extra cost
• $42,000 extra cost over three months
2016/17 pasture growth rates
0
10
20
30
40
50
60
70
80
90
6/11/2016
26/11/2016
16/12/2016
5/01/2017
25/01/2017
14/02/2017
6/03/2017
26/03/2017
15/04/2017
5/05/2017kg DM/ha/da
y
Cressy
average
Cutting silage Grazing management
2016/17 soil moisture
Under irrigating
675083484283 54 32 kg DM/ha/day
Water budget
kg DM/ha/day
‐40
‐30
‐20
‐10
0
10
20
3025
‐Oct
27‐Oct
29‐Oct
31‐Oct
2‐Nov
4‐Nov
6‐Nov
8‐Nov
10‐Nov
12‐Nov
14‐Nov
16‐Nov
18‐Nov
20‐Nov
22‐Nov
24‐Nov
26‐Nov
28‐Nov
30‐Nov
2‐De
c
4‐De
c
6‐De
c
8‐De
c
10‐Dec
12‐Dec
14‐Dec
16‐Dec
18‐Dec
20‐Dec
22‐Dec
24‐Dec
26‐Dec
28‐Dec
30‐Dec
Soil Moisture De
ficit (m
m) Ra
in and
Irrig
Water budget 25 October ‐ 31 December 2016
irr Rain Def
83 43 54
WUE calculations
• 36.3kg DM/ha/day• 90.5mm rainfall + irrigation• 1.1t DM/ML
• 83.3kg DM/ha/day• 159mm water requirement• 1.5t DM/ML
‐60
‐50
‐40
‐30
‐20
‐10
0
10
20
30
1‐Jan
2‐Jan
3‐Jan
4‐Jan
5‐Jan
6‐Jan
7‐Jan
8‐Jan
9‐Jan
10‐Jan
11‐Jan
12‐Jan
13‐Jan
14‐Jan
15‐Jan
16‐Jan
17‐Jan
18‐Jan
19‐Jan
20‐Jan
21‐Jan
22‐Jan
23‐Jan
24‐Jan
25‐Jan
26‐Jan
27‐Jan
28‐Jan
29‐Jan
30‐Jan
31‐Jan
1‐Feb
2‐Feb
3‐Feb
4‐Feb
5‐Feb
6‐Feb
7‐Feb
8‐Feb
9‐Feb
10‐Feb
Soil M
oisture De
ficit (mm) Rain an
d Irrig
Water budget 01 Jan ‐ 10 Feb 2017
Irrigation Rain Deficit
5054 7144
Grazing management
83 56
kg DM/ha/day
Top three take‐home messages
• Beware of the green drought• Poor watering costs production and money• Grazing management important (utilisation is key to profitability)
Faculty of Science, Engineering & Technology
Tools, resources and training
The Yield IrrisatScheduling Irrigation
Diary (SID)
https://sid.usq.edu.au/http://www.theyield.com/products/free‐growers‐app
https://irrisat‐cloud.appspot.com/
Acknowledgements
David McLaren, TIABill Cotching, TIAReuben Wells, AgLogic
Farmers