Testing the answer to phosphorus questions

27 Apr, 2012 02:00 AM
Brett Fowler crops 1500 hectares on his Williams property and carries out soil tests religiously.
Brett Fowler crops 1500 hectares on his Williams property and carries out soil tests religiously.

FARMERS looking at reducing input costs this year are being urged to carefully assess fertiliser application strategies coming into seeding.

According to the Department of Agriculture and Food senior researcher David Weaver, recent and historical soil testing programs across WA agricultural regions showed 80 per cent of cropping paddocks and two thirds of grazing paddocks contained enough phosphorus to meet demands for the growing season.

As fertiliser remains one of the largest input costs for most WA growers, getting fertiliser requirements right through regular soil tests was imperative for their bottom line.

"Despite having enough phosphorus, many of these same paddocks either had production constraints from soil acidity, or deficiencies in other nutrients such as potassium or sulphur," Mr Weaver said.

"If your soil has sufficient phosphorus, your fertiliser budget could be better directed into correcting these other constraints."

Mr Weaver said farmers needed to ask themselves a series of questions to assess their fertiliser program requirements: Do I need phosphorus and how do I find out? If I need phosphorus, how much should I apply to achieve my production target? Is achieving my production target the best economic decision? If I applied phosphorus, how do I know if I have applied the right amount?

"Soil testing will help answer many of these questions," Mr Weaver said.

"This means using the correct sampling method and the appropriate test which has been calibrated for WA.

"Soil samples need to be analysed at an accredited laboratory.

"Once results are known, farmers should discuss their farm nutrient or soil amendment needs with preferably an accredited FertCare adviser."

Mr Weaver said regular soil testing took the guesswork out of soil nutrient requirements.

While phosphorus levels were purportedly high enough to meet crop and pasture needs, Planfarm agronomist Richard Quinlan agreed it wasn't that simple.

Mr Quinlan said although residual phosphorus levels were higher than they had been in the past, there were numerous limiting factors which needed to be considered.

"If there was a dry start to the season, for example, the residual phosphorus would not be as available to the crop as if it were a wet start," he said.

"The fact is the residual levels are very high but even if the soil test results show there are comfortable levels of phosphorus, farmers still should include it in their fertiliser budget, just in case."

Mr Quinlan, who is based in the northern agricultural regions, said farmers in the area were worried about soil nutrients after a record production year.

The record production year exported a record amount of nutrients from the soil and as a result Mr Quinlan said more soil tests had been carried out this year than any other year," he said.

"Growers need to make sure there is enough phosphorus included in their recommendation.

"It is important to use the phosphorus buffering index in conjunction with the Cowell P test which will give an indication of how much phosphorus is in the soil and how much is available."

CSBP Limited sales and marketing manager Ben Sudlow said it was important growers analysed their soils to determine what their crops actually needed.

"CSBP field research manager James Easton presented a paper at this year's Crop Updates showing some WA soils may only need maintenance rates of phosphate or none at all," Mr Sudlow said.

"CSBP trials over many seasons have shown the importance of freshly applied phosphate.

"There's no doubt that the key for farmers is to apply the right balance of nutrients to get the most profitable outcome based on their soils' requirements to optimise yield potential.

"It can become an unnecessary game of risk when a farmer stops applying one nutrient without knowing if it will impact on their profit."

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28/04/2012 1:42:26 AM, on Farm Weekly

Sure nutrients are important, but doesn't soil structure, soil organic matter and assoicated soil biology play equally important roles in soil health and production? If they do, then why not mention them? Or is this just used to help promote ongoing fertiliser use?


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