Available phosphorus levels in Alberta soils are variable, but usually are in the moderately deficient range. Unlike nitrogen, phosphorus levels do not change quickly as a result of cropping, soil management practices or climate. Application rates of phosphorus fertilizer should reflect the available phosphorus status of individual fields, the requirements of the crop to be grown and the general growing conditions. The level of available phosphorus in soils can gradually be increased by the application of moderate to high rates of phosphorus fertilizer and manure. Crop rotations that maintain or improve soil organic matter levels can also increase phosphorus availability.
Topsoils contain much higher levels of available phosphorus than subsoils.
Therefore, management practices that reduce wind and water erosion will help to maintain soil phosphorus. Potassium and sulphur Deficiencies of these two nutrients are not as widespread as nitrogen and phosphorus deficiencies. But deficiencies to potassium and sulphur are common in particular areas and soil types. If crop yields are low and responses to nitrogen and phosphorus fertilizers appear small, attempts should be made to determine what other factors are limiting crop yields. Soil testing and field test strips are good methods of determining if potassium and sulphur are deficient.