contrasting loss processes due to soil properties . The table also includes the delivery ratio applied to paddock modelling results in the Source Catchments model , which was set at 0.75 for both runoff and drainage DIN losses .
Table 2 . DIN losses for the most common nutrient and irrigation management Most common cane management - Nutrient ( Cf ), Irrigation ( Df )
Comparing effectiveness of management practice change adoption There are three potential / likely management changes these farmers could implement :
1 . Improve from nutrient management Cf to nutrient management Bf 2 . Improve from irrigation management D to irrigation management C 3 . Improve recycle pit management D – C ( note D recycle pit management equates to no runoff capture )
The modelled DIN load reductions for runoff and drainage for each of these potential management changes are shown in Tables 3 -5 .
Table 3 . Improve nutrient management ( Cf to Bf )
Table 4 . Improve irrigation management ( D to C )
Table 5 . Recycle pit ( D to C )
Runoff DIN delivered to Reef ( kg / ha / yr ) delivery factor 0.75
Drainage DIN delivered to Reef ( kg / ha / yr ) delivery factor 0.75
Sugarcane DIN total to Reef ( kg / ha / yr )
Drainage DIN |
|
Runoff DIN ( kg / ha / yr ) |
( kg / ha / yr ) |
|
|
|
Vertosols ( BRIA ) |
14.1 |
2.5 |
10.6 |
1.9 |
12.5 |
Dermosols ( delta ) |
6.1 |
18.0 |
4.6 |
13.5 |
18.1 |
Management Option 1 : Move from Nutrient Cf category to Bf
Runoff DIN delivered to Reef ( kg / ha / yr ) delivery factor 0.75
Drainage DIN delivered to Reef ( kg / ha / yr ) delivery factor 0.75
Sugarcane DIN total to Reef ( kg / ha / yr )
|
Runoff DIN ( kg / ha / yr ) |
Drainage DIN ( kg / ha / yr ) |
|
|
|
DIN load reduction (%) |
Vertosols ( BRIA ) |
12.9 |
2.1 |
9.7 |
1.6 |
11.3 |
-9.6 |
Dermosols ( delta ) |
6.1 |
15.5 |
4.6 |
11.6 |
16.2 |
-10.4 |
Management Option 2 : Move from Irrigation D category to Irrigation C
Runoff DIN delivered to Reef ( kg / ha / yr ) delivery factor 0.75
Drainage DIN delivered to Reef ( kg / ha / yr ) delivery factor 0.75
Sugarcane DIN total to Reef ( kg / ha / yr )
|
Runoff DIN ( kg / ha / yr ) |
Drainage DIN ( kg / ha / yr ) |
|
|
|
DIN load reduction (%) |
Vertosols ( BRIA ) |
10.0 |
2.0 |
7.5 |
1.5 |
9.0 |
-27.7 |
Dermosols ( delta ) |
3.7 |
10.5 |
2.8 |
7.9 |
10.7 |
-41.1 |
Management Option3 : Install a C class recycle pit
Runoff DIN delivered to Reef ( kg / ha / yr ) delivery factor 0.75
Drainage DIN delivered to Reef ( kg / ha / yr ) delivery factor 0.75
Sugarcane DIN total to Reef ( kg / ha / yr )
|
Runoff DIN ( kg / ha / yr ) |
Drainage DIN ( kg / ha / yr ) |
|
|
|
DIN load reduction (%) |
Vertosols ( BRIA ) |
11.5 |
2.5 |
8.6 |
1.9 |
10.5 |
-15.7 |
Dermosols ( delta ) |
5.4 |
18.0 |
4.1 |
13.5 |
17.6 |
-2.9 |
These model results indicate that improvements in irrigation management would provide the best outcome in terms of reducing DIN losses to the reef . This result is different from Report Cards 2014 - 2015 where the benefits from improved fertiliser management were similar to improved irrigation management . A major factor driving this result ( particularly for the BRIA area ) is the quantity of DIN lost from irrigation runoff .
For the 2016 Report Card , irrigation runoff was modelled as a static concentration throughout the year with a concentration of 0.6 mg / l . This DIN concentration is approximately 5 times the default minimum DIN runoff concentration 0.11mg / l ( which is close to rainfall concentrations ) for other sugarcane growing regions . The setting of the irrigation runoff concentration has a very large impact on the modelled DIN losses in the Burdekin and hence , is currently being updated for the next Report Card to be released in 2019 .
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