Did you know?
Soybeans remove 0.84 lbs P per bushel, which means a 40 bu/ac soybean crop removes 34 lbs P/ac. Attention must be paid to ensure a proper fertilization strategy is adopted to ensure application rates are meeting removal rates through the entire crop rotation – learn more below.
Manitoba fertilizer phosphorus (P) guidelines have not been updated since 1992 and some troubling trends have been identified:
- In several of the past years the crop removal of P has surpassed the application rate of fertilizer P
- More soil test values are declining into the LOW range in some areas of Manitoba
This decline in soil test P levels (STP) may arise for a number of reasons:
- Changing crop acreages– from relatively low P removal crops of cereals and flax to canola, soybeans and corn
- Move to low disturbance seeders and planters with narrow openers and wide row spacings (low seedbed utilization) which limit the safe rate of seed row applied fertilizer, especially with sensitive crops such as canola and soybeans
- Promotion and adoption of low P rate starter fertilizers that do not replace P that is removed by crops
- Increase in grain yields since development of original MAFRD recommendations in the early 1990s due to breeding (ie introduction of hybrid canola, general purpose spring wheats etc.) and technology (ie fungicide use)
- Provincial recommendation tables do not include yield adjustment factors, so rates have been inadequate to meet current yield levels, let alone match rates of P removal
Thinking about your, or your client’s, cropping system does P applied equal P removed? Or are crop removal rates exceeding P applied, leading to a negative soil P balance?
Use the Interactive Phosphorus Balance Calculator to determine your annual P balance:
Manitoba Soil Fertility experts have collaborated to develop “Phosphorus Fertilization Strategies for Long Term Agronomic and Environmental Sustainability” which outlines:
- Why declining P fertility is a concern
- Reasons for adopting a new, long-term strategy to address declining P fertility
- Four options for implementing a long-term strategy to maintain soil test P levels in a “maintenance range”