Facing rising phosphate prices, Prairie farmers who have routinely applied 30 to 40 pounds of phosphorus an acre each year may be able to cut back to 20 pounds this spring, or even altogether, one Manitoba soil scientist suggests.
With prices not expected to get much cheaper until new mines come on line, farmers are looking for ways to stretch their supplies.
“In cases where seeding equipment puts the seed and fertilizer into a narrow row you can actually get excellent reactions to phosphate at rates as low as 10 pounds per acre because of the starter or pop-up effect,” said soil scientist Don Flaten of the University of Manitoba, in an interview May 2.
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“If I had some inexpensive phosphate I might try to stretch it out over a couple of years.”
Prairie soils aren’t typically “desperately low” in phosphorus, Flaten said. And most farmers see the biggest bang for their buck in the first 20 pounds of phosphorus an acre they apply, he added.
But there are exceptions. Farmers who haven’t been applying any phosphorus or not enough to offset what is removed by the crops they harvest, will have soils low in phosphorus and under those conditions crop yield and quality could be hurt by not applying phosphorus this spring.
“Overall (in Manitoba) we’ve been applying 15 per cent more phosphate (annually) than we’ve removing in our crops,” Flaten said. “We’ve got room to cut back without hurting our capacity to maintain soil P level.”
That means some farmers have applied enough phosphorus to meet a high target yield, but didn’t achieve it, so more phosphorus than expected remained in the soil, he said.
“We could, on average, cut back our phosphate fertilizer by 15 per cent just to balance application with removal,” Flaten said.
Averages, however, are misleading. Some farmers apply more P than required by crops, while others haven’t applied enough. The latter farmers are mining the soil of P and will have to replace it eventually or suffer consequences of soil infertility.
When considering their phosphorus strategy as it relates to P prices, there are four main considerations, Flaten said.
- How much phosphorus is already in the soil? The only way to know is through a soil test. “High rates of P aren’t going to be as important in a phosphorus rich soil as in a very phosphorus deficient soil,” Flaten said.
- Environmental conditions. Cold, dry weather is the worst for making soil P available to crops. That’s where a “starter” application of 10 to 15 pounds of phosphorus per acre can really pay off.
- Consider the crop. Potatoes and corn respond more than some other crops to starter applications of phosphorus.
- Application equipment. The crop will respond better if the phosphorus is closer to the seed, especially under cold, dry conditions. Farmers who can’t place phosphorus close to their seed might see little or no benefit to a starter application.
— Allan Dawson is a reporter with the Manitoba Co-operator.
