RED DEER – Phosphorus buildup in prairie soil is a growing problem.
“Wherever there is intensive livestock operations, you will see the buildup of phosphorous is intense,” Shabtai Bittman, an environmental agronomist at Agriculture Canada’s research centre in Agassiz, B.C., told the Western Dairy Seminar in Red Deer March 13.
Bittman said the runoff ends up in surface water and results in poor water quality and excessive plant and algae growth known as eutrophication.
“Phosphorus accumulation in farm soil is really an environmental burden we are leaving to the next generation,” he said.
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“We should avoid building up a problem that may not be an immediate problem but will inevitably be a problem.”
Manure also contains nitrogen, but its movement in the soil is slow and is used quickly by plants because it is water soluble. Phosphorus does not leech well into the soil and needs to be near roots for plants to use it effectively.
Plants provide carbohydrates to mycorrhizae fungi that live near their roots, which then provide phosphorus to the plants. Plants typically need a 10 to one ratio of nitrogen to phosphorus, but dairy manure, for example, has a six to one ratio.
Producers who apply manure as a replacement to fertilizer may not obtain a uniform or reliable plant response. It is a universal problem when attempting to apply manure properly without creating phosphorus buildup.
“Nutrient composition is not written on the side of the tank,” Bittman said.
The research centre has experimented with liquid dairy manure on crops in B.C.’s Fraser Valley.
Dairy manure that is stored in a tank before it is spread separates into a supernatant liquid on top and a thick sludge that settles to the bottom.
Researchers applied whole manure at different rates to grass and yields improved. However, the supernatant manure provided a better overall response because it infiltrated the soil better. As well, less nitrogen was lost to the atmosphere.
Dairy sludge is high in phosphorus, and researchers found that the heavier material could be applied to soil at a rate of 12 kilograms per acre about two inches from corn plant rows. The results were as good if not better than those achieved with commercial fertilizer.
Bittman said this means manure sludge has the potential to replace phosphorus fertilizer for corn. It could also reduce the risk of runoff when placed strategically.
However, researchers found that runoff risk differed between the West Coast and the Prairies. Most runoff in B.C.’s Lower Mainland is associated with rainfall, but on the Prairies runoff is from snow melt.
Aerating soil reduced runoff in the Fraser Valley but had the opposite effect on the Prairies.
