RED DEER Ñ Researchers are almost ready to recommend how to change manure spreading standards in Alberta.
Seven years of research shows some Alberta soil contains too much phosphorus, even though nitrogen levels are adequate under provincially set manure management guidelines.
ÒWe felt that a soil that had roughly 50 milligrams of phosphorus per kilogram in the soil, if you applied any more phosphorus you probably wouldnÕt get the proper plant response,Ó said Barry Olson, one of the researchers working on the phosphorus study.
The province is looking at agronomic ways to limit the amount of phosphorus placed on land during manure applications, but scientists cannot say if the research findings will be incorporated into legislation, Olson told a recent manure management conference in Red Deer.
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Ironically, 80 percent of Alberta soil is deficient in soil phosphorus and would respond well to more. However, Ross McKenzie of Alberta Agriculture said excess manure has led to phosphorus overload in parts of southern AlbertaÕs intensive livestock regions.
ÒWeÕre taking our prime agriculture land right now and we are using it as a dumping ground for manure,Ó he said.
In southern Alberta, soil that has received manure at rates of 12 to 16 tonnes per acre every two or three years for 20 years has high phosphorus levels in the surface soil, he added.
He said three to six times more land would be required for spreading if the rules were changed to a phosphorus-based regime.
Research projects have looked at soil and water quality where heavy loads of manure were applied as compared to land receiving conventional fertilizers.
The research measured the allowable level of phosphates in water bodies, including small streams in eight major Alberta watersheds.
The provinceÕs water quality guideline suggests a limit of 0.05 mg phosphorus per litre, but the new study has found as much as 0.20 to 1.57 mg per litre exists in some water courses, mostly because of spring runoff.
Phosphorus tends to accumulate in the soil and is subject to movement into surface water, resulting in eutrophication. This is a natural process of lake aging but can be accelerated by human activity when excessive fertilizer or manure use puts too much phosphorus in the water. Phosphorus overloads cause excessive plant and algae growth with subsequent decay, which depletes the oxygen supply and kills fish.
There are also limits to how much phosphorus plants can absorb. The research project examined commercial fertilizer, manure and compost application rates based on soil tests measuring the amount of nitrate and phosphate that is available to plants.
Soil test results showed no net accumulation or depletion of nitrate during the treatments, but Olson said phosphorus increased 8.9 fold in the manure treatment and 13 fold in the compost treatment.
Phosphorus is a highly complex mineral found in organic and inorganic forms.
In Alberta soil, inorganic phosphorus in the first 15 centimetres is usually 50 to 75 percent of total phosphorus content while the organic form is generally 25 to 50 percent.
McKenzie said soil test laboratories report results in elemental phosphorus, which does not exist in soil.
Plants take up phosphate PO4 for growth, energy transfer, photosynthesis, root development, water use efficiency and faster maturity.
Phosphorus content varies, depending on soil type and the kind of crop management that is used to remove it from the soil. Many pools of phosphorus exist in the soil that may or may not be available to plant roots.
Crop yield response to phosphorus levels will increase to a certain point and then level off regardless of how much more is added. Higher levels may result in increased risk to the environment even before crop damage occurs because other components in manure can enhance or reduce crop performance, McKenzie said.
