Table 3.6 . Target Electrical Conductivity Thresholds for the Lower Burdekin region . Source : DNRME ( 2018 ).
4 Defining best management practice for nutrient , pesticide and irrigation management in the Lower Burdekin
The following points are highlighted as the priority issues for improved water quality and sugarcane management in the Lower Burdekin :
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Fertiliser and pesticide application rates and timing have a significant role in determining losses from the Lower Burdekin sugarcane area .
Low irrigation efficiencies influence the amount of surface runoff and drainage losses of nutrients and pesticides . In addition , typically low irrigation efficiencies in the Lower Burdekin area have led to substantial modification of local hydrological regimes , resulting in significant impacts on freshwater and coastal ecosystems in the region ( GBRMPA , 2012 ; Shaw , 2014 ).
Rising water tables are evident in the Lower Burdekin irrigation areas ( Shaw , 2014 ) with expression of groundwater at the surface in some locations . The difference in the rate of input of water to the irrigation area compared to natural recharge under rainfall and the rate of outflow of groundwater determines the groundwater imbalance and therefore the response of the water table level to changed hydrology . As water tables approach the soil surface , water logging and increased salinisation of the root zone can occur , leading to reduced or complete loss of productivity . Importantly , the direct interface with the water table diminishes the buffering capacity to absorb recharge during wet conditions , which poses a greater risk for fertiliser and pesticide losses via surface runoff .
A holistic approach to managing these is required , and therefore this document , intended to focus on irrigation management , also refers to the management of nutrient and pesticide losses from sugarcane areas . Groundwater management is also acknowledged as an integral component of the Lower Burdekin Groundwater Strategy Project led by DNRME .
This section describes current understanding of management options for these issues in the Lower Burdekin sugarcane area .
4.1 Paddock to Reef Water Quality Risk Framework
The adoption of improved management practices in the GBR catchments is reported using industry and regional specific management practice frameworks ( water quality risk frameworks ) through the Reef 2050 WQIP Paddock to Reef Integrated Monitoring , Modelling and Reporting program ( Paddock to Reef program ). These frameworks identify the management practices with greatest potential influence on off-farm water quality and articulate a reasonable best practice level which can be expected to result in a moderate-low water quality risk .
The ‘ best practice ’ level is typically the level targeted by Reef 2050 WQIP investments . These practices are described in terms of their relative water quality risk , from lowest risk ( innovative practices that have the lowest water quality risk ) to high risk ( superseded practices that have the highest water quality risk ). They are also weighted depending on their influence on water quality improvement . For example , for nutrients in
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