The agricultural landscape

Tully Johnstone's floodplains, once rich with vegetation and wetlands, have declined significantly since the arrival of Europeans. Over 60% of freshwater wetlands have been lost. This vegetation once slowed water, retaining and filtering water while holding sediments and nutrients on the land. 

With less vegetation, intense rainfall runoff flows more freely over the land. Now runoff is generated in greater volumes and velocities, and carries more sediments and nutrients. 

Given the short distance from paddocks to catchments, this has heightened the risk of runoff reaching freshwater and marine environments. 

Banana and sugarcane growers are working with scientists to understand how their farming practices connect with the landscape. Growers are adjusting practices to reduce sediment, nutrient and pesticide losses, especially in response to intense rainfall events. 

Banana and cane challenges

Water quality data from the banana and cane catchments and paddocks show distinct variations in fertiliser losses in runoff. This likely reflects the different fertiliser application and usage by these two cropping systems. It is important growers understand these losses, nitrogen dynamics, and how their management plays a role.

Sugarcane farm results

Water quality data collected upstream and downstream of sugarcane farming in the Hull River catchment reveal peak periods of fertiliser loss, coinciding with the first 4-5 runoff events of the wet season. This relates to the more limited window of single fertiliser applications following harvest. 

The results indicate that late-fertilised ratooned cane poses a heightened risk of fertiliser loss, especially during early periods of heavy rainfall. Paddock scale monitoring reveal organic additions used in the industry, such as mill mud and legumes, contribute nitrogen to the crop, and lead to elevated nitrogen losses.  

Banana farm results

Sub-catchment monitoring shows water draining from banana farms consistently have prolonged and elevated dissolved inorganic nitrogen levels throughout the wet season. This is linked to regular fertiliser applications practiced in banana cultivation.  The highest paddock scale losses occur when fertigation is applied just before rainfall triggers runoff. 

Wet season rainfall also led to fertiliser losses in drainage below the root zone, with this fertiliser finding its way to surface water streams.

How can growers adjust practices?

Extension staff work closely with growers to address paddock variability such as soil type, timing of harvest, and fertiliser and pesticide applications. They use water quality data to inform or validate improved management options for each farm:

• Reducing synthetic fertiliser rates by integrating organic nutrient inputs from fallow crops and applied mill mud.

• Profiling and mapping paddocks to pinpoint variations in soil types and conditions, allowing precise nutrient application.

• Better planning of fertiliser, including product selection, timing of application, placement and rates.