Variable Rate Technology (VRT)

EM 38 survey map

EM38 survey map

Precision agriculture has come a long way from the early days of adoption. Mallee farmers have been early adopters with this technology and are in fact leading the way in Australia with Variable Rate Technology (VRT).

AGRIvision Consultants are at the forefront of this technology and have helped many growers to understand the technology and develop VRT maps and plans. AGRIvision follow 5 simple steps to implement a Variable Rate system on your farm.

For our clients VRT is about identifying the various production zones within a paddock or farm and then accurately targeting inputs to the capabilities of the zone. VRT is also a risk management tool and one of the greatest benefits for growers so is the ability to accurately apply nutrients based on a zones requirements rather than a “blanket rate” over the whole paddock. In many cases this has helped to reduce inputs, saving the grower money and maximising profitability.

Step 1 - Developing the VRT plans

A base data layer for any VRT map is extremely important. Our preferred base layer is an EM 38 survey of the paddock to help define accurate paddock zones. Paddock zones can be developed from many sources and they all vary in their accuracy. We have surveyed vast areas of the Mallee with EM 38 and are very confident with the results. The EM 38 maps are accurate and can be replicated over and over again, they do not change from year to year. There are some points to remember with EM 38 maps:

They are a very useful tool but not the be all and end all. Don't get bogged down in the science (paralysis by analysis). The interpretation needs to be accurate and relevant to the Wimmera/Mallee. Make sure someone experienced in EM 38 interpretation and agronomy handles your maps - an EM 38 map is only as good as the person interpreting it. They are addictive - once you map a paddock and study the results you will want to do more.

Other options for obtaining a base layer for a VRT map include elevation maps, yield maps, satellite images, GAMA Radio Metrics, manual zoning etc. Elevation maps are OK in some areas and can be a useful starting point but they do not provide accuracy. Yield maps in a dry season can be accurate as long as the variables such as nutrition, weeds, frost and crop establishment was the same across the whole paddock. Make sure that your historical treatments and methods are not influencing the yield map results. We like yield maps for assessing large on-farm trials and for checking VRT results.

Step 2

Soil testing

Soil testing

As with all base layers for a VRT map you need to undertake ground truthing. We need to inspect the paddock with the grower and then carry out soil testing in the appropriate zones. Segmented deep soil testing often provides the answers to why different zones have different yields. In many cases Ec, boron and soil type provide the answers, not nutrition. Accurate soil testing together with an EM 38 map, grower experience and agronomic expertise will provide you with a VRT map you can use. The number of zones in a paddock will depend on the amount of variability in the paddock.

Step 3

The next step is to determine the rates of inputs. The common inputs that can be varied are phosphorus, nitrogen, sulphur, zinc and seed. These are determined after careful analysis of all the available data and then basing the rates on minimising risk and maximising profitability per zone. The rates are initially based on crop removal figures for the potential yield and water use efficiency.

Step 4

Prescription phosphorus map

Prescription phosphorus map

Step 4 is producing the prescription maps. Each rate of input is prescribed to the pre determined zones to produce a VR map and data files for the final step. We may have a map for phosphorus (MAP, DAP, single), nitrogen (sulphate of ammonia, urea) and seed determined by the requirements of the paddock zones. AGRIvision Consultants has the ability to produce VR prescriptions for any air seeder with any data layers you have available.

Step 5

The final and one of the most important steps is getting the prescriptions to the paddock. Once the maps are produced they need to be saved to a format that is readable to your monitor or task controller. There are many different makes and models of equipment each with their own capabilities and compatibilities so ensure you equipment is Variable Rate capable and compatible before taking out the earlier steps. Many air seeders are VR capable, be it electric metering drives, linear actuated metering etc., but it is the task controller or monitor that does all the hard work and many of these are not capable of automatically varying rates. It is also essential that your GPS is compatible with the other equipment to provide an accurate location signal to the monitor so each input can be applied accurately to. The most important thing to remember with VRT is to get the basics right first. If your confidence in the technology is low, get your equipment right, keep your prescriptions simple and work up from there. VRT is relatively simple and user friendly and once everything is in place it will become an extremely valuable tool for your cropping system.