- Manage underlying soil variability before trying to manage in-season crop variation
- Biomass sensing provides the data with which to make nitrogen management decisions
- Managing soil acidity and repairing soil compaction is ongoing
- Organic manures offer an alternative approach to managing crop nutrition and productivity
“Now we have reduced the underlying variation in our soils, nine out of 10 of the crop problems on our farm can be solved by correct nitrogen management.”
Some may consider this a bold statement from Kym I’Anson, but his results speak for themselves. Over the past decade water use efficiency has increased from eight kilograms per millimetre per hectare to 15kg/mm/ha on average. In 2011 their average bread wheat yield was six tonnes/ha with all soil types performing consistently.
“Managing variation in our soils and canopy management has been central to achieving this improvement,” he says.
Marrabel, in the mid-north of South Australia, has reliable winter rainfall and long growing seasons, generally with mild finishes. However, the undulating landscape comprises soils that vary in characteristic and productivity.
At the home farm about 70 per cent of the land is red brown clay loam, which is acidic and sodic and prone to waterlogging. A further 20 per cent is acid grey shale, located at the ridge tops, while the remaining 10 per cent is slightly acid cracking black soils. These soils are mixed across the farm – one paddock may have 40 per cent black soil, another none.
Since joining his parents, Murray and Ann, on the family farm, Kym and his wife, Katie, have applied a strategic approach to improving productivity through a range of management changes.
“When I came home we had to resow crops that were lost due to waterlogging. Today the soil can still become sodden, but soil moisture probes show us we are pushing water down the profile to about a metre.”
Selling the sheep and instituting a no-till, continuous cropping system have both helped to reduce surface compaction. A consistent rotation of wheat (250ha soft, 450ha bread), barley (200ha malt/feed), hay oats (400ha) and canola (500ha) is grown. Last year soft wheat and canola became the most profitable crops, whereas previously export hay had dominated.
Owner: Kym I’Anson
Location: Marrabel, South Australia
Farm size: 1700 hectares – two blocks of 900 and
Growing season rainfall: 391mm and 350mm
Soils: acid, sodic red brown clay loam, acid grey
shale,slightly acid cracking black soil. Sandy loam
soils ranging from acid to neutral pH
Enterprises: continuous cropping – wheat, canola,
oat hay, barley
Deep blade system (DBS) seeding with 17.5 centimetre knife points has ripped through the old plough pan that was only about 7.5cm below the surface. This deep ripping helps incorporate stubble more deeply and Kym is noticing a slight darkening of the topsoil as the organic matter slowly builds.
To minimise re-compaction, Kym has adopted controlled traffic with all equipment on two-metre wheel centres, except the harvester, and implements are based on multiples of 11m widths. The seeding bar is 11m while the boomspray is 33m wide. He has also applied gypsum to reduce the sodic properties that inhibit water infiltration.
Lime and gypsum rates have been tailored to each soil type. Paddock maps were loaded into Farm Works software, a grid was drawn across the paddocks and using this and changes in soil colour, samples were taken at about one per hectare across the farm. The test results were used to create lime and gypsum application zones.
In 2003, when this process was started, zones were identified using a handheld GPS unit and drums to mark the boundaries. A belt-driven Marshall spreader was used to distribute the lime at 2.5 tonnes/ha and gypsum at 3t/ha on the red brown clay loam.
Only lime was applied to the grey shale and to the black soils where required. In the past 10 years the red brown clay has received 7.5t/ha of lime, the grey shale 2.5 to 5t/ha and the black soils no lime. Targeting the lime rather than applying a blanket rate has allowed the I’Ansons to afford these high rates and to achieve an average soil pH of 5.8, up from a pH of 4.2.
“We still have areas that require additional applications and have yet to tackle acidity on a new property as we are waiting to develop new technology to allow easier on-the-go testing of pH,” Kym says.
“Our target was to raise the average pH to six but the increase in snail numbers since raising the pH has made us cautious.”
With the underlying causes of yield variation being managed, the I’Ansons were able to turn their attention to varying inputs to match actual crop requirement. Input rates are modified by crop and soil type and take into account the nutrients supplied from 2.5t/ha of chicken manure applied to a third of the farm each year.
Managing the variation in his soils has allowed Kym
I'Anson to introduce a much more cost-effective crop
nutrition regime. PHOTO: Emma Leonard
Phosphorus is applied on a replacement rate, calculated from the previous year’s yield maps. Nitrogen is only applied in-crop, based on biomass sensing.
On the poorer areas – the acid, sodic soils – Kym uses more nitrogen, especially when soils denitrify due to saturation. His aim is to boost crop biomass and to out-compete ryegrass. More biomass also means more organic matter being returned to these soils.
In the higher-yielding grey shale and black soils, nitrogen is limited, fungicides are increased and growth regulants or slashing are used to limit biomass growth.
“We slash parts of crops, headlands of the oat hay and so on, to restrict early growth to prevent lodging and yield loss later. It is the same principle as an early grazing, just more targeted.”
Kym uses a CropSpec biomass scanner to identify areas with high biomass or low nitrogen status. The sensor with its two wavebands is much more sensitive than the human eye, enabling low nitrogen status to be recorded and addressed before visual symptoms appear.
Cereal crops are scanned at the five-leaf stage, hay a little earlier and canola at early green bud. Nitrogen is spread as soon after scanning as possible, with a urea boom on the Horwood aircart with a Farmscan rate controller, this gives a 33m spread.
Unfortunately, the CropSpec and the Farmscan rate controller are not compatible, so Kym cannot scan and spread on-the-go. However, while this takes more time, it allows him to validate the maps with his own measurements and knowledge of the paddock. He uses areas of the paddock known to be non-nitrogen limited to calibrate the sensor.
“There are grey shale patches where we have not used any nitrogen for six years and they are only now starting to show a requirement,” he says.
Where nitrogen is required rates can be high. In wheat, 250kg/ha of nitrogen is applied in poor soils to replace the soil nitrogen lost by denitrification, and in a good year a further 250kg/ha may follow. This compares to zero to 80kg/ha in the better soils. Targeting rates to requirement has enabled Kym to increase the average yield of the paddock.
“We used to lose yield to lodging and waterlogging. Now we have a more consistent yield across the whole paddock, often with the same total inputs, so our margin per hectare has increased,” Kym says.
“Using the biomass sensor to vary our nitrogen means our proteins are also consistent, with the soft wheat producing between 8.8 and 9.0 per cent protein.”
With a much better handle on his nitrogen management Kym is now reconsidering his management of potassium and trace elements. He believes the poultry manure will be the key to the nutritional future of his crops.
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