The 4 Rs, as described by the Canadian Fertilizer Institute and other crop nutrition organizations, are the right fertilizer source at the right rate, at the right time and in the right place. The 4 Rs will help you make the most of your fertilizer investment.
Here are the three basics of canola crop nutrition:
1. Put only phosphate in the seed row. All other fertilizer should go outside the seed row. Safe and effective seed-placed rates of phosphate are generally around 20 lb./ac. of actual phosphate. With lighter soils, dry conditions and very low seed-bed utilization (SBU), the 20 lb./ac. rate could cause some reduction in emergence.
The 4 Rs for phosphate:
Right source: Phosphate is phosphate and all inorganic forms are useful if adhering to the remaining Rs. The one exception is rock phosphate, which is fairly insoluble under our conditions and would not provide plant available P.
Right rate: 20 lb./ac. provides enough prills or droplets for each seed to have relatively good access, and 40 lb./ac. is probably the maximum safe rate as long as soils are moist.
Right time: Place safe amounts in the row. Band the remainder.
Right place: Seed row.
2. Apply some sulphur. Canola has a high need for sulphur, and sulphur deficiencies can lead to costly yield loss. Even if a composite soil test says a field is sufficient in sulphur overall, unless you have sampled enough sites to be convinced your sample can represent the entire field, some sulphur is recommended to meet basic needs for all acres. Sulphur is highly variable across a field.
The 4 Rs for sulphur:
Right source: Sulphate is plant available and most suitable for spring applications.
Right rate: 10 to 20 lb./ac. is suitable if the composite soil test says overall supply is sufficient — 20 lb./ac. or more in every area of the field. If soil tests indicate sulphur deficiency, 20 lb./ac. should be sufficient.
Right time: Have it in place before the crop needs it. Sulphate can be broadcast in spring or fall. Application at seeding can reduce field passes. Rescue applications post-seeding can help if a deficiency is noted, but are not ideal.
Right place: Anywhere outside the seed row. Sulphur can go in the banded nitrogen blend or broadcast.
3. Use a rate of nitrogen that makes economic sense based on the yield potential for the soil and region. A recent study led by Bob Blackshaw with Agriculture and Agri-Food Canada in Lethbridge, Alberta, found that current nitrogen rates may not match the yield potential of today’s hybrids. A summary of the study stated that canola yield responded positively to the 150% fertilizer rate versus the recommended 100% rate in about half the cases.
The 4 Rs for nitrogen: These depend a lot on the individual grower’s system and appetite for risk.
Right source: Urea, UAN or anhydrous ammonia. Each has its benefits and most farms have made a choice based on which fits best with their seeding systems.
Right rate: It might be higher than you think, but the decision to increase rates depends on the rate of return for that next 10 lb./ac. of nitrogen.
Right time: Spring placement has the lowest risk for loss compared to fall, however fall application can present an economic advantage. Time, supply, logistics and weather influence the decision for each grower.
Right place: Limit nitrogen in the seed row, and make sure it’s available when and where the crop needs it.