This project demonstrates management of input costs and risk by zoning in different soil types, understanding input requirements in different zones, and fertilising accordingly. This is particularly relevant following dry or drought years, when nutrients may be left behind and less will need to be replaced, and also in years with good soil moisture and rainfall to maximise the opportunity for higher yields.
Project description:
Mallee Soils are highly variable, and this variability provides significant challenges in optimising fertiliser inputs across paddocks but where implementation of Variable Rate Technology could prove beneficial. This project aimed to build on work produced in 2022 across three farmer groups in the SA mallee region. This work set the first stage of the importance of soil type variability and impacts on residual nutrient banks which drive current return on investments of fertiliser input.
The current project set out to guide growers further down the VRT track but helping them create zones and demonstrate variability of crop responses to changing fertiliser management. Growers were asked to select a paddock of interest and create different soil and therefore management zones through publicly available satellite and NDVI data. Growers were then encouraged to implement fertiliser strip trials by adjusting fertiliser rates (50% down, 50% up compared to grower practice) across these zones. Assessments of crop behaviour to different fertiliser programs across zones will assist growers to start the journey of implementing VRT.
Results from two focus farms in addition to multiple other paddocks with zoned information outlined the power of 1) creating zones for informed soil sampling and analysis, 2) soil analysis for outlining residual nutrient levels, constraints and fertiliser recommendations and 3) adjusting fertiliser rates based off the processes 1 and 2 to maximise partial gross margins compared to flat fertiliser rates.
Key achievements and results:
Fertiliser inputs are one of the highest input costs farmers encounter and in a low rainfall environment, it is important to manage input costs to manage risk. The Mallee environment is also characterised by highly variable soil types, which vary in nutrient availability and productivity and, therefore also vary in nutrient inputs required. Farmers in the low rainfall Mallee region can manage their input costs and risk by zoning their soil types, working out what inputs are required in different zones and fertilising accordingly. This is particularly relevant following dry or drought years where nutrients may be left behind and less will need to be replaced and in years with good soil moisture and rainfall to maximise the opportunity for higher yield potential.
Despite this knowledge, uptake of variable rate fertiliser technology was low prior to starting this project and therefore, the continuation of this project is a significant step in building confidence that variable rate fertiliser (VRT) through paddock zoning increases profitability. After several years of this project building on the adoption of VRT it has demonstrated significant variability in crop responses to applied fertiliser across varied paddock zones. Project outcomes have been extensively presented to the participants and grower groups which has increased the knowledge and understanding that each paddock has variable soil zones and that each zone should be fed to its potential.
Three low-rainfall Mallee regions were selected from the first year of this project and participants involved in the first year were keen to keep these areas as they represented different soil types and constraints: Murray Plains, Lowbank and Lameroo farmer groups. (Pinnaroo moved across to Lameroo)
Across three key locations—Murray Plains, Lowbank, and Lameroo—focus farms were established over varying paddocks for the second year of the Variable Rate Technology (VRT) project. The goal was to assist farmers in implementing their own trial strips. Each location had two focus farms, resulting in a total of six sites across the state. Farmers managed their trial strips by varying nitrogen (N) and phosphorus (P) inputs or adjusting in-season N top-up rates. These were established across the six sites, each representing specific management zones determined through Google Earth imagery or previous EM38 mapping. Site characterization was conducted via soil sampling and testing, which helped predict the N and P requirements. Additionally, crop rotation data spanning 2-3 years was used to ascertain the paddock’s suitability for trials. This data was crucial in determining the best approach for VRT implementation, as it provided valuable insights into soil and crop conditions that could have affected outcomes.
The six on-farm paddock demo sites enabled each location to demonstrate the potential of VRT application at the farmer paddock level. This setup allowed local and neighbouring farms to closely observe the implementation, monitor the growing season, and harvest benefits of using variable rates of fertilizer in their own regions. This fostered a sense of trust and credibility within the farming community, as they observed tangible results in their local areas. Consequently, interest and adoption of Variable Rate Technology (VRT) have significantly increased in the project’s target areas.
Farmers stand to benefit significantly from these trials, as they provide a practical foundation for making data-driven decisions on nutrient management. By implementing VRT, farmers can optimize the application of fertilizers, which leads to more efficient use of resources and cost savings. Additionally, the tailored approach to nutrient application ensures that crops receive the right amount of nutrients at the right time, promoting healthier plant growth and potentially increasing yields.
Moreover, these trials can greatly benefit agronomists and researchers by providing valuable on farm practical data. This data can be used to refine Variable Rate Fertiliser inputs and enhance future recommendations, furthering our commitment to sustainable and profitable farming practices in the regions. The insights gained can help in understanding the variability within and between paddocks, leading to more precise and effective farming practices.
In a summary of current project outcomes extensive soil sampling program on the back of generating zones through Google Earth and NDVI can significantly tighten soil characteristics that drive nutrient availability which should maximise the effort and cost associated with soil sampling and costs at the laboratory. The benefit of this zonal approach compared to traditional transect sampling has been outlined by differences in N supply > 100 kg N/ha resulting in an equivalent N application of > 200 kg Urea/ha. Phosphorus recommendations based on zonal approaches can range from > 20 kg P/ha down to replacement of 5-6 kg P/ha depending on the growing area. These recommendations will maximise grain yields across the paddock but not significantly change overall expenditure of P inputs, just refining applications to zones which need it.
Grower demonstration strip trials outlined profitable increases in cereal grain yields were obtained in certain paddock zones through increasing P rates through MAP and addition of small amounts of urea. These were accurately identified by narrowing zones down to soil type by NDVI signatures. Both data layers are free and easily accessible to growers.
In most cases by developing a VRT program we could demonstrate increases in PGM between $20-$50/ha by either increasing yields through increased P or N inputs in deficient areas or by cutting back starter inputs in zones where significant N x P banks are present.
Growers and advisors are encouraged to use zonal paddock approaches to identify different performing areas and investigate poor performing parts of the paddock before starting replacement fertiliser programs. As outlined in this project, reducing starter fertiliser inputs on poor performing zones without identification of the cause of poor production can reduce grain yields and PGM.
This project has expanded on recent work through the Mid-North and YP which has outlined that poor NDVI areas can be often associated with poor P reserves and can return a bounce in yield with increasing P inputs compared to the strategy of decreasing P inputs with overly simplified replacement P programs.
Zone allocation for informed soil sampling programs and analysis can provide significant benefits to refining fertiliser strategies and implementation of VRT programs. Zonal soil sampling and taking representative samples allows for more freedom in the budget that allows extensive analysis to depth and incrementation compared to grid samples which is based on 0-10 cm samples and down to a couple of soil tests at the laboratory. While not a focus of this project sampling to depth has identified potential constraints at depth which would explain poor crop performance, build-up of nutrients in particular Nitrogen and Sulphur which provides additional supporting evidence towards effective nutrient applications.
Both industry experts have been invaluable assets to this project, aiding our farmers in adopting VRT in their farming systems. Farms have significantly benefited from the expertise and technical support of these specialists, while continuous communication and support from MSF have effectively bridged the gap in the industry’s shortage of VRT specialists. As we move into the third year of this project, we aim to have a readily available contact list for farmers and industry professionals seeking assistance with VRT adoption.
Further information:
Further information and resources are available on the Mallee Sustainable Farming website.