Making variable rate application a success on your farm

Rick Rundell-Gordon,

Dodgshun Medlin Ag Management

Keywords: agronomy farming systems, precision agriculture, Vic/SA Mallee, dune / swale

Take home message:

• Variable rate application (VRA) in the SA/Vic Mallee is giving farmers greater control and confidence over seed and fertiliser distribution, resulting in significant cost savings and potential yield gains.

How do I know if Variable Rate Application is a worthy investment for me?

Greatest gains from VRA is when the majority of the paddock is in at least two consistent yield zones of at least 1—1.5t/ha. Ideally the worst performing zone will be higher in fertility and the best performing zone lower in fertility.  Typically this will be the Mallee dune swales.

What are the cost benefits to using VRA?

The cost benefits will be determined by how much variability in soil and fertility your farm has and also the price of fertilizer, particularly phosphorous fertilisers like MAP, DAP, Granulock, 27:12.  For instance on a highly variable soil near Manangatang in 2008,  where fertiliser prices were over $800/t and the previous season was very dry (less nutrient removal) total VRA savings for a three bin box were around $25/ha. In 2012 on a less variable paddock at Ultima, where fertiliser prices were around $650/t and also following a high nutrient removal season, VRA savings for a two bin box were around $7/ha. On average, savings in the SA & Vic Mallee are around $15/ha.

Are there any other benefits from using VRA apart from cost savings?

VRA is not just about cost savings. In the better seasons and on more reliable soil types, growers can use their soil type zone maps to create Urea and SOA topdressing maps for their VRA seeder box or VRA spreaders. This gives confidence around matching nitrogen and sulphur to yield potential. The analogy used is that the plant acts like a pump, if you put fuel in the pump more water is pumped into the plant. So the more fuel added the harder the pump works, particularly on sandy soils where moisture can be held a lot deeper and more available then the sandy clay loam flats (Therese McBeath et al. 2011, N and P VRA response trials, Karoonda).

Summary of benefits in using VRA

1. Confidence in applying fertiliser and seed to the more reliable soil types.

2. Confidence after wet summer profiles and in more reliable growing seasons, in applying more fertiliser or seed.

3. Confidence around reducing fertiliser and seed cost on least reliable soil types and in poorer seasons.

4. Accuracy to farm forecasting and delivery of fertiliser and seed.

5. Improved weed competition from applying higher seed rates to selected soil zones where weeds proliferate (Brome on midslopes and sand).

What equipment do I need to have and what are the costs?

To get into VRA you will need a GPS, variable rate seeder box, and variable rate console and auto steer system. Most of the cost in VRA setup comes from the expenditure in the GPS accuracy. 2cm GPS systems can be justified on larger farms as the cost of investment can be averaged over a larger area and also the extra overlap cost of around 10% that is returned to the business is greater. However an accurate GPS is not necessary to get into VRA. The other significant cost can be if the seeder needs to be converted to VRA capability or not. This can be somewhere between $10,000—$30,000. For instance a Flexi coil box converted in 2008 was around $15,000 including wiring. Finally you will need a compatible console or VRA screen costing around $8000—$10,000. Not all consoles are compatible with all air seeder boxes and auto steer systems. Best to talk with other growers or reputable dealers for support in this area of compatibility.

Which is the easiest console to operate?

 VRA systems are becoming more and more user friendly - The Topcon X 20 or 30 is quite a simple system to use and is compatible with most seeders like Flexi coil, Bagshaw, Bourgault, DBS, Simplicity.  If you are running with John Deere then the GS3 screen is now pretty simple to use. TheTrimble CFX 750 is also compatible with most seeders and easy to use. These are just a few of the more popular systems that our client base uses however it’s always best to talk to your peers.

What do I look for when selecting a simple console system?

Apart from mechanical compatibility, which has improved dramatically in the last 2 –3 years, most of the complexity in VRA systems comes from the software requirements to either, create or convert fertiliser and seed application maps, to a format that the console will read. The Topcon X30 and the updated GS3 screen allows growers to receive an application map (shape file) from a third party like Dodgshun Medlin. This shape file can then be dropped into a created folder on a USB thumb drive, called a ‘Rx’ folder. When the USB is placed in the screen on the tractor, maps are easily converted without the need for additional software requirements. This has made the application map process in consoles much simpler.

A simple, step by step adoption of Variable Rate Application in the Victorian Central Mallee.

The O’Briens first ventured into PA by investing in a sub meter John Deer Autotrac unit. They still operate this today for most operations. In 2009 after seeing and discussing the benefits of variable rate application with their peers at crop walks and discussion groups, they decided to invest in a VRA system. There two bin flexi coil box had to be retrofitted to work as a variable rate seeder for a total cost including wiring and screen (Viper) of $25,000. Dodgshun Medlin zoned there farm using 5 (gamma, thermal, landsat multispectral, elevation, NDVI) remotely sensed data layers for a total cost of $6400 ($1.60ex /ha), which included their fertiliser and seed application maps. Their fertiliser and seed cost savings in the first year were around $15/ha = $60,000 over 4000ha, which paid for all outlay and leaving $30,000 spare for other expenses.

In 2010, the O'Briens used Dodgshun Medlins Phosphorous Audit service, which involves obtaining harvest yield data, previous fertiliser applied and potential yield to create fertiliser application maps.  This worked well and saved on phosphorous expenditure after the previous dry year, particularly when the flats yielded around 0.8t/ha (20kg/ha of 27:12).  The yields of  those last couple of years have been a reversal (flip flop) to the dry years and from risk management purposes, we didn’t want to replace the Phosphorous from wheat yielding 3.5 – 4t/ha (87kg/ha of 27:12) in the heavy flats using the P audit system, particularly when in average years they only yield half that. Also as a result of soil testing, they established that the farms phosphorous levels are still above critical Colwell P levels, which they will continue to monitor in the future.

The approach the O’Briens have taken this year, has been to apply fertiliser and seed using their soil type zone maps instead. Their current nutrient strategy has been focused around low N, due to consecutive good years. Deep N tests in the past, monitoring of paddocks throughout the year and a 2011 farm spring NDVI, have allowed the O’Briens to target paddocks for more N upfront using a 27:12 blend. They also like to do their topdressing plan well ahead of the season. Anything that is low with good potential will be given priority for topdressing. Like most operations on their farm, it’s about having a good operational plan and implementing it.

The O’Briens find that to manage the farm well they need to be able to measure and review successes and failures. Farm NDVI’s (biomass or green stuff) are helpful, particularly in years where yield mapping is difficult due to contractors and time constraints. NDVI’s ask the questions as to why some paddocks are higher in biomass then others. It’s sort of like a pseudo yield map. O’Briens receive the NDVI as a lamented map and also as a KML file, which will auto extract into Google Earth.   This allows us to easily zoom in to paddocks. We had a paddock last year that missed the first summer spray during the 2010 harvest. It still ended up with 3 sprays but the first one in this strip wasn’t done until Jan 2011. It highlighted to us the importance of summer weed control – we must be fussy. This strip yielded 1t/ha while the rest of the paddock yielded around 3.5t/ha.

The O’Brien’s potential PA opportunities are to invest in either a VRA spreader or a triple bin or both. The VRA spreader will allow them to better target N during the season and the triple bin will enable the phosphorous to be managed separate to their N management.  A triple bin could save them, over our current VRA phosphorous savings, approximately another $5-8/ha in starter nitrogen in a dry season start. Compared with our two bin box, where the N goes out with the P as a blend on all soil types in all years.

In summary the O’Briens see that the VRA system has given them confidence around application of fertilizer and seed inputs.

VRA is an ideal tool to manage production risk on higher potential soils and financial or cost risk on less reliable soils.

Contact details

Rick Rundell-Gordon

Dodgshun Medlin Ag Management

rrundell-gordon@dodgshunmedlin.com.au