Farmers manage soil and fertiliser for water quality outcomes

Crops need nitrogen, an essential plant nutrient and an effective fertiliser, to grow and achieve optimum yields. Increased concentrations in water can have negative impacts on the environment. The movement of dissolved inorganic nitrogen (DIN) from fertilised agricultural lands into rivers and catchments has been identified as a global water quality issue. 

Coral reefs thrive in nutrient-poor environments and nutrient enrichment negatively affects coral physiology and ecosystem functioning. Nutrient degradation of coral reefs and its effects have been observed across the Great Barrier Reef. 

Sugarcane growers have joined forces to manage and improve the quality of the water in the Mulgrave and Russell catchments which discharge more than 4,000 gigalitres of fresh water into the Great Barrier Reef each year. 

Extension staff, Traditional Owners and growers are working together to create positive and long-term Reef health outcomes from local progressive practice changes through the three-year, $6 million Mulgrave-Russell Regional Water Quality program. 

The program has monitored local waterways and supported improved fertiliser (nutrient) management practices to reduce losses and improve the quality of the water leaving sugarcane farms in the Mulgrave and Russell regions.  

The James Cook University Centre for Tropical Water and Aquatic Ecosystem Research (TropWATER) team is monitoring water quality and DIN levels across nine monitoring stations and five drain intervention projects. Growers are actively involved and are viewing nitrate and stream level data in the CSIRO online water quality 1622 App. Data from the real-time water quality monitoring activities is demonstrating how improved farming practices such as run-off management are helping to reduce DIN losses.  

TropWATER Principal Research Scientist Aaron Davis said, "This holistic project is re-connecting floodplain lagoons, capturing, and treating first flushes from agricultural areas, revegetating historically cleared riparian zones, and better managing stock access and use of waterways, for a range of water quality, biodiversity, and cultural benefits."   

Growers in Far North Queensland have unique challenges in their rain-fed sugarcane production system. The average annual rainfall in the region is between 2-4 metres and it is not uncommon for 400 mm of rain to fall in some of the summer months. Most of the rainfall in the Wet Tropics occurs during the wet season, which runs from December to April, which increases the risk of fertiliser and pesticide losses through runoff. 

To meet this challenge, growers have implemented a range of types and scales of drainage intervention to reduce paddock run-off water and DIN losses. Paddocks and drains have been modified using laser levelling to keep early wet season DIN-rich first flows on farms. Contour banks with manual water control gate valves to help control sediment and nutrient losses on higher sloping paddocks have been installed. Drainage has been diverted into constructed wetland complexes and drainage retention basins constructed to capture and hold high nitrate first flush rainfall events on their farms.  

Aloomba canegrower Paul Rossi was keen to make sure that any money he invested in things like gypsum and dolomite to improve his soil health stayed on the paddock and did not make its way into local waterways. 

“We could see a problem where we have slight gradients on lighter soil types. During the fallows we typically grow peanuts which provide good cover but in the following plant cane crop we have bare soil and there is a risk of sediment moving off those paddocks with heavy rainfall events, even though these soils have high water holding capacity,” said Paul. 

Paul modified his headland and installed a bund wall to contain potential runoff and better manage his nutrients and sediment. “Giving the water time to settle allows the nutrients and sediment to settle and fall out of suspension. When the water is full, it will trickle over slowly. Most of the storm water is now pretty much contained in the 30-40 acre paddock area,” he said.  

Through the program, local agronomy service provider Farmacist is supporting growers to reduce DIN losses from their farming systems. Growers are planning their application of nutrients to maximise efficiency, save money and minimise potential losses before they reach the end of the paddock.  

They have achieved this through more effective use of inputs and supporting growers to address constraints to yield with a goal of improving production and profitability. Individual nutrient management plans specific to soil requirements and grower capacity and aspiration have been developed with 82 growers who collectively manage 11,480 hectares of cane land. 

Over 800 soil samples have been collected and electromagnetic (EM) mapping has been completed on over 3,500 hectares to identify areas that are susceptible to yield-limiting constraints and allow for targeted management. Satellite yield analysis using Landsat 8 and Sentinel-2 has been undertaken by University of New England to identify variability in crop performance, with Farmacist agronomists working with growers to understand the source of the variance between and within blocks. 

As a result, growers are optimising their fertiliser application rates to suit crop requirements and minimise losses which also saves money. The data sets provided will allow growers to make more informed decisions now and into the future. 

A combination of farm-specific agronomic support, spatial information related to soil variability gathered using EM mapping, and drone imagery and the satellite yield maps have all played a major part in supporting growers to make informed decisions when developing their whole-of-farm Nutrient Management Plans. These plans aim to reduce DIN losses within the catchment. 

Farmacist's Belinda Billing said they are using these technologies to help farmers to be more precise and get a better understanding of what is happening on their farm. “We make recommendations within the nutrient management plan that are practical to apply and address the needs of their crop,” she said. 

Cane grower David Lauridsen is trialing variable rate nutrient application across different soil types on his Far North Queensland farm. He said, “It is good that Farmacist helped us set the nutrient rates and calibrate our nitrogen application. We will be happy to see at what level we get good sugar cane production, where we are not putting on too much or not enough (nitrogen).” 

Farmacist's Will Higham said the purpose of David's trial was to understand if sugarcane responds differently in different soil types and with different nitrogen rates. “Is the sugarcane growing bigger in one soil type compared to others?” 

David reflected that significant progress that has been made in the Russell-Mulgrave catchment over the years, “Farmers today are aware of the place where they are farming (close to the coast), many have some sort of silt trap to catch water before it leaves the farm. There is a lot cleaner water leaving sugar cane farms today," he said. 

The Mulgrave-Russell Water Quality program is led by the Reef and Rainforest Research Centre and CANEGROWERS Cairns and funded by the partnership between the Australian Government's Reef Trust and the Great Barrier Reef Foundation.  

To date, the program has stopped about 9,000 kilograms (about the weight of a school bus) of DIN per year from entering local waterways and the Great Barrier Reef Lagoon.