Attention to soil pH restores productivity
GroundCover™ Issue: 104 | Author: Catherine Norwood
Detailed attention to soil chemistry across 20 different soil types is the answer to achieving a productive, resilient cropping enterprise for the Glass family in Western Australia’s central wheatbelt
With farm profit margins continuing to be squeezed, Western Australian grower Rex Glass says his annual soil tests have become crucial to making the most of money spent on soil and crop inputs.
In 2012, the $3600 he invested in soil tests across the three properties he farms in WA’s central wheatbelt saved him $30,000 on his fertiliser of choice, the post-emergent liquid nitrogen fertiliser Flexi-N®.
With a clear understanding of his soil capacity and nutrient levels, he is able to vary application rates across the wide range of soil types on his properties from zero up to 100 litres per hectare, rather than the standard flat-rate application of 60L/ha.
“Clearly there’s no point putting a heap of fertiliser on if the soil is never going to yield a crop of more than 1.5 tonnes/ha,” says Rex, who has been working to identify and address soil constraints for more than 15 years.
Also, maintaining a good soil pH balance has been crucial in maximising the soil’s cropping potential, he says.
Rex and his wife Tracey, with their son Corey and his girlfriend Krystal Benjafield, farm in Calingiri, north-east of Perth. They have another property in Wongan Hills and lease a third farm, also in Wongan Hills.
They first started soil testing in Calingiri in 1997, trying to identify what was causing poor grain-fill in their wheat. The soil tests of the top 100 millimetres identified topsoil acidity. Further soil tests at the 100 to 200mm and 200 to 300mm shallow subsoil levels indicated that acidity was also a deeper issue.
The ongoing soil sampling has been undertaken by Precision SoilTech and has been used to map the different soil types on the properties, and has allowed different management zones to be created. Rex says there are more than 20 different soil types across the three properties, from blue clays to white sands.
A long-term liming regime has now successfully restored the soil pH balance. On the most acidic areas two surface applications at a rate of 2t/ha were followed by a third, at 1 to 1.5t/ha, which was deep-ripped then spaded to a depth of 300 to 350mm.
When the Glasses added the Wongan Hills property to their holdings in 2004, improving the soil was again a priority. In some areas the pH was as low as 3.7, particularly on the yellow sand plain soils. Two surface applications of lime at rates of 2t/ha were followed by a further 2t/ha deep-ripped.
Rex says while the surface applications took four to five years to work their way through the soil profile, they started to pay for themselves in the couple of years after application, particularly where pH-sensitive crops such as canola and barley were grown.
Addressing the subsoil acidity has allowed crops to access the moisture held deeper in the soil profile. In 2012, with only 230mm of growing-season rainfall, Rex produced his highest-yielding canola crop ever, and also equalled or bettered his benchmark for other grains.
In 2007 the Glass family leased a third property in Wongan Hills and have also undertaken soil testing there to identify potential constraints. Across the three properties they have 160 testing sites – up to eight in each paddock – although only two sites in each paddock may be tested each year, with the two selected changing from year to year.
With such a good picture of the properties’ soil types plus management plans in place to address long-term issues, the focus of testing now is to finetune soil nitrogen levels for crops. In the past two years the wet spring and summer periods have generated large amounts of mineralised nitrogen, which was identified by the testing and allowed Rex to trim his nitrogen applications.
With soil pH now holding steady at about 5.7 or 5.8 on the Wongan Hills farms, and 6.2 at Calingiri in even the most problematic paddocks, Rex is now considering scaling back the tests to every second year.
Owners: Rex and Tracey Glass, Corey Glass and Krystal Benjafield
Location: Calingiri and Wongan Hills, Western Australia
Farm size: Calingiri 2450 hectares (2060ha arable), Wongan Hills 2300ha (1925ha arable), 460ha (arable, leased)
Average rainfall: Calingiri 380 to 400 millimetres, Wongan Hills 320 to 340mm
Soil types: blue clay, red clay, white sands, yellow sands, sandy gravels, whitegum gravels and york gum loams
Soil pH: 5.2 to 6.5 in the top 10 centimetres Grain crops: wheat, barley, canola, lupins, clover
Livestock: Suffolk and White Suffolk studs, with 1650 Merino ewes joined to stud sires
The pH and nutrient results of the tests are passed to the Glasses’ private agronomist, Erin Cahill of agVivo, to determine a variable-rate fertiliser program. They use 60L/ha of Flexi-N® at seeding, placed under the seed, which Rex values as the equivalent of 100 kilograms of surface-applied urea.
This is supplemented with rates ranging from 60 to 130kg/ha of compound fertiliser for phosphorus and other trace elements, usually a choice of either AgStar® (14.3 per cent nitrogen, 14 per cent phosphorus, 9.6 per cent sulfur, 0.04 per cent zinc) or K-Till®
Extra (10.2 per cent nitrogen, 12 per cent phosphorus, 11.2 per cent potassium, 6 per cent sulfur, 0.1 per cent copper, 0.2 per cent zinc), and a follow-up application of Flexi-N® or Flexi-NS® if the soils and season provide the potential for a greater crop response.
Rex says the pH is crucial. “If you don’t have the right pH, you won’t get access to the phosphorus, and if you don’t get that right you won’t get access to the potassium. And then it won’t matter how much nitrogen you apply, you won’t get the best response for your money.
“We have found that if you are working from a low base, 1t/ha of lime does almost nothing. It takes 2t/ha to achieve any improvement and it takes time for the lime to work down from the surface.”
Rex says the improved pH has allowed the family to choose from a wider range of crop varieties. In other words, they are no longer limited to those that are more tolerant of acidity. This provides a broader range of sowing times to take advantage of seasonal conditions and manage frost risk.
Crops stay in the flowering window they were sown into and are not forced on due to periods of moisture stress. They are also healthier and better able to access nutrients such as subsoil potassium.
Rex says he has also found that once the soil pH balance was improved in the most troublesome paddocks, herbicides also began working more effectively, in conjunction with a change in chemical regime.
He has taken a long-term view in his choice of crops and herbicides. Although he has grown GM canola for a couple of seasons, he has swapped back to triazine-tolerant varieties CrusherTT and ATR-Stingray for the time being. It is part of a wider strategy to manage the potential risk of herbicide resistance and maintain access to as many different chemical options as possible.
Rex has also changed his herbicide application strategies, with new boomspray equipment that offers an improved range of spray velocities. “I used to think that if I was applying a lethal dose using only 30L/ha of water, that was a good thing. But now we try to keep the water up and use 70 to 80L/ha. It gives us better coverage and a more effective application.”
Control of summer weeds and the use of pre-emergent herbicides allows Rex to get in early with sowing, even if it has not rained. Wild radish and annual ryegrass are the most troublesome weeds.
Canola planting starts on Anzac Day and is followed immediately by barley and wheat. For radish control Rex uses a post-emergent broadleaf herbicide (Jaguar®) after seeding, up to the two-leaf stage of the crop, and follows that with another post-emergent herbicide (Velocity®) if needed three weeks later, up to the five or six-leaf stage.
“Everything comes together to help improve production – the soil, fertilisers, equipment, weed control,” Rex says. “Each ‘tool’ might only contribute five per cent, but it is five per cent, and it all adds up.”
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