Reducing the risk of herbicide runoff in sugarcane farming through controlled traffic and early-banded application
Highlights
► We measured rainfall-runoff losses of PSII herbicides on sugarcane with trash cover. ► Controlled traffic reduced runoff losses of each herbicide by 47–60%. ► Banded applications reduced herbicide losses by 32–42% compared to broadcast. ► Herbicides on cane trash dissipated with time and were more resistant to runoff. ► Consequently, herbicide losses declined rapidly with time after application.
Introduction
The detection of agricultural chemicals, including pesticides (herbicides, insecticides and fungicides), in freshwater and marine ecosystems is recognised world-wide and continues to be of increasing concern (Warren et al., 2003, van Dam et al., 2010). As such, the Australian sugarcane industry is under immense pressure to implement improved farm management practices that reduce the off-site transport of these chemicals (Rayment, 2003, Anon, 2009). The majority of the sugarcane (Saccharum officinarum) grown in Australia is along the eastern coast of Queensland, where approximately 587,500 ha of farm land (determined from QLUMP, datasets 1999–2006) drains into the World Heritage listed Great Barrier Reef (GBR) lagoon. This area is characterised by a tropical to sub-tropical climate with summer dominant rainfall. The highest risk period for the off-site transport of agrochemicals is in high intensity rainfall-runoff events in the period leading into (October–December) and during the wet season (January–April). During these events the residual herbicides commonly used in the sugarcane industry, diuron, atrazine, ametryn and hexazinone, have been consistently detected in creeks and rivers in catchments with sugarcane (Mitchell et al., 2005, Rohde et al., 2008, Bainbridge et al., 2009, Lewis et al., 2009), as well as in the resulting flood plumes in coastal waters of the GBR lagoon (Rohde et al., 2008, Bainbridge et al., 2009, Lewis et al., 2009, Shaw et al., 2010).
The presence of these herbicides in marine ecosystems is of particular concern as they inhibit photosynthesis (PSII) and long-term chronic exposure may have adverse ecotoxicological effects on coral (Jones, 2005) and seagrass communities (Haynes et al., 2000a, Haynes et al., 2000b). Albeit, these herbicides have an important role in the economic viability and sustainability of the sugarcane industry and have contributed to the historic shift to a new farming system for sugarcane (Johnson and Ebert, 2000), which promotes green cane trash blanketing (GCTB) and minimum tillage practices. This has substantially reduced rates of soil erosion (Prove et al., 1995), which was previously perceived as the primary threat to the GBR (Rayment, 2003).
Financial incentives, as a component of the Reef Rescue Initiative (Reef Rescue, 2008) have been developed by the Australian government to assist sugarcane farmers with the adoption of best management practices (BMPs), which reduce the risk of off-site movement of agrochemicals. In particular, two of the primary management practices promoted are controlled traffic (CT) farming and banded herbicide applications. However, there is little supporting water quality data to validate the perceived improvement that will be gained by adoption of these practices. Most research on herbicide runoff in sugarcane farming provides seasonal or short term quantitative measurements of losses in field, focusing on the persistence and fate of herbicides in soils (Hargreaves et al., 1999, Simpson et al., 2001, Selim, 2003, Stork et al., 2008), and to a lesser extent, cane trash (e.g. Selim et al., 2003), rather than comparing management practices.
Controlled traffic farming has been considered a solution to a significant soil compaction problem in sugarcane. Soil compaction has been shown to contribute to a decline in soil health and yield (Stirling, 2008). Moreover, soil compaction can reduce permeability and infiltration, therefore increasing runoff (Li et al., 2001, Li et al., 2007, Tullberg et al., 2001). One of the major disadvantages of the conventional sugarcane cropping system is that the standard 1.5 m row spacing configuration does not match the 1.83 m track width of harvester and haulout machinery (Braunack and McGarry, 2006). As a result, wheel traffic overlaps the edges of each row, compacting at least 61% of the paddock (Price et al., 2004). To reduce this area of compaction, the row width and wheel track of machinery are matched, restricting traffic to a narrow interspace. In sugarcane farming, CT usually involves an increase in row width from 1.5 to 1.8–2 m (farm and equipment dependant), which also allows for a second row of sugarcane in the bed and the establishment of permanent beds. The 2 m row spacing conversion can reduce compaction to 26% of the paddock (Price et al., 2004).
The most direct method of reducing residual herbicide loss is to reduce the amount applied, as there is a proportional relationship between concentration of herbicide in runoff and concentration in the soil at the time runoff occurs (Silburn and Connolly, 1998, Silburn and Kennedy, 2007). Conventionally, residual herbicides in sugarcane are broadcast to the bed and furrow, resulting in 100% coverage of the paddock. The area of application can be reduced by restricting application to a band across the top of the bed, immediately around the base of the cane stool. Weed control in the furrow can then be managed with knockdown herbicides, such as glyphosate, applied through hooded or shielded sprayers to prevent drift onto the sugarcane foliage. Glyphosate has a short half-life (persistence) and a strong sorption coefficient, and therefore has a reduced potential for loss in runoff (Shipitalo et al., 2008).
The highest risk period for herbicide loss in surface runoff and leaching is within a few weeks following application when concentrations are highest, with variations due to the herbicide type, soil type and weather conditions (Hargreaves et al., 1999, Simpson et al., 2001). Therefore, the time of herbicide application in relation to heavy rainfall is an important consideration in herbicide management and use. Mitchell et al. (2005) reported that 470 kg of diuron (as well as smaller amounts of atrazine, ametryn and hexazinone) was exported from the Pioneer River (Mackay) in a single runoff event in February 2002. Herbicide applications throughout the catchment would have occurred between November and January prior to the event (Mitchell et al., 2005).
The objective of this paper is to evaluate herbicide runoff and infiltration of CT and banded spraying practices, in comparison to their conventional counterparts. This study was part of the Water Quality Improvement Plan for the Mackay Whitsunday region (Drewry et al., 2008)
Section snippets
Methodology
In this study, we used a rainfall simulator to evaluate herbicide runoff and infiltration. Additionally, a natural rainfall study was also undertaken as a validation phase. This paper presents the effects of: (1) 1.5 m conventional rows and 2 m CT rows; (2) broadcast and banded application of herbicides; (3) time of rainfall after application; and (4) herbicide washoff and retention on cane trash.
Runoff and infiltration
The 2mCT rows significantly (P < 0.05) reduced total runoff and peak runoff rate by 38% and 43% respectively, when compared with CONV rows under rainfall simulation (Table 2). Runoff as a percentage of rainfall was 29% on CONV rows and 18% on 2mCT rows. The rainfall simulation plots which experienced flooding from the first natural rainfall event had a greater percentage of runoff, but maintained treatment differences with 66 and 57% of rainfall from CONV and 2mCT rows, respectively. Total
Controlled traffic and herbicide transport
The reduction in both runoff (by 38%) and consequently herbicide loss (Table 3) on the 2mCT rows compared with the CONV rows was a result of reduced compaction in the 2mCT rows (Li et al., 2001, Li et al., 2007, Tullberg et al., 2001). Silburn et al. (2013) also reported lower runoff volumes and reductions by 50–58% in total losses of pyrithiobac sodium, metolachlor, diuron, DDE and trifluralin on non-wheeled traffic furrows compared with wheel traffic furrows in cotton. Furthermore, Silburn et
Conclusions
This study demonstrated that early application, banding and the use of controlled traffic (2mCT rows) reduced rainfall-runoff losses of the residual PSII herbicides ametryn, atrazine, diuron and hexazinone in sugarcane farming. These practices combined were most effective in reducing herbicide losses in runoff. However, individually the timing of application with respect to rainfall had the strongest influence on herbicide losses.
Controlled traffic is an important management practice when
Acknowledgements
This research was funded by Reef Catchments Mackay Whitsunday Inc. (previously Mackay Whitsunday Natural Resource Management Group) through the Coastal Catchments Initiative for the Water Quality Improvement Plan. We would like to thank Gerry Deguara, Noel Kallaghan and David Blackburn for contributing their time, equipment and property access. Further thanks are due to the dedicated Mackay Whitsundays Healthy Waterways team for assisting with field work. We also appreciate the extensive
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