Farmers who seed peas at a typical rate of three bushels per acre will find their total seed weight is about 180 pounds per acre. The pea is a big seed and carries a bunch of its own phosphorus. As well, the fertilizer placement couldn’t be better no matter what opener you used. The phosphorus is perfectly placed for the emerging plant.
At that seeding rate, the peas deliver between eight and nine lb. of actual phosphorus per acre, according to Adrian Johnston of the Potash and Phosphate Institute.
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Johnston said when he was a researcher at Melfort, he studied phosphorus fertilizer in peas.
“We could not find much of a response to phosphorus fertilizer. There’s enough phosphorus in the seed itself to get the crop started. The plant lives off its own P early in the season while the roots are establishing their mycorrhizal association with the soil.”
“That association is always stronger in a no-till field because your soil isn’t disturbed. You would not see such a strong association in a conventional system because the mycorrhizae are disrupted by tillage. They have to re-establish every time there is a tillage pass.”
Peas are better nutrient scavengers than most crops, said Johnston. In addition to their high quality interaction with the soil, the roots have more surface area than most other crops.
There is one other factor unique to crops that fix nitrogen. That is the symbiotic relationship between the roots and the soil.
“These kinds of plants have more exudates. Exudates are compounds released by the roots into the soil. There are like attractants. They attract the soil microbes to the plant roots.
“Exudates serve as a food source for the microorganisms in the soil.
“They increase the rhizosphere activity and build a healthier microbe community surrounding the roots.”
But this does not mean that pea producers can ignore the phosphorus needs of their fields, said Johnston.
“Ironically, while peas do not respond very well to phosphorus fertilizer inputs, they are actually very high consumers of phosphorus. One bushel of peas removes 0.65 lb. of P2O5 phosphorus from your soil. Compare that to a bu. of wheat, which only removes 0.5 pounds per bu. of P2O5.
“A 40 bu. pea crop will remove 26 pounds of phosphorus per acre. You have to account for that in your nutrient budget.”
