Fertilizer — best ways to apply macros this spring

May 13, 2020 – Issue 9

May 6, 2020 - Issue 8

Canola seed is very sensitive to fertilizer. To minimize the impact on seedling survival, the recommendation is for no more than about 20 lb./ac. of phosphate (or 40 lb./ac. of MAP, for example) in the seed row.

With narrow row spacing (10″, for example), higher seed-bed utilization (more than 10%), moist soils and safer nitrogen products – ESN specifically – a little more fertilizer could be put in the seed row, but as a general statement, canola growers really should have alternative non-seed-placed methods to apply the bulk of their fertilizer. Nitrogen, potassium and sulphur should be put outside the seed row.

“You don’t seed without starter rates of phosphorus in the seed row, especially in cold soils, but you have options for the rest of the nutrients,” says John Heard, crop nutrition specialist with Manitoba Agriculture.

Alternatives for each macro

Nitrogen (N). Many farmers apply nitrogen in the fall, but didn’t get a chance last fall due to weather conditions. Application options ahead of seeding are broadcast and banding. If broadcasting, incorporate soon afterward and/or use a urease inhibitor to limit losses if rains are delayed. For pre-seed banding, apply at an angle to the anticipated direction of seeding – to minimize plant thinning above concentrated urea or ammonia bands. Time-of-seeding options are side-band or mid-row banding. Another option is post-seeding. Listen to a podcast on nitrogen application options.

“If the priority is seeding and fertilizer pre-plant operations are going to slow down seeding, the door is open for post-plant in-crop applications,” Heard says. Keep in mind that these additional nitrogen applications should be applied no later than the 5- to 6-leaf stage to ensure the plant has access to it at peak uptake.

Also, post-plant nitrogen is not a complete solution. Growers thinking about in-crop applications should get at least 50-60% of their nitrogen on before or during seeding. If broadcasting in-crop, urease inhibitors will reduce losses while waiting for rain to move nutrients into the soil. Canola Encyclopedia section on nitrogen placement options.

Potassium (K). Banding is probably the best choice since seed-placed potassium can damage seedlings. Save seed placement for starter phosphorus. The broadcast-incorporation application method is less efficient, and probably requires rates double that of banding to achieve a similar crop response. However, in situations where banding equipment is not readily available and seed placement is too risky, broadcast incorporation may be useful and not overly expensive due to the relatively low cost of potash fertilizer. The higher fertilizer rates necessary for broadcast K may also benefit subsequent crops with a higher potassium response than canola. Canola Encyclopedia section on potassium placement.

Sulphur (S). Sulphur does not need to go in the seed row, and adding sulphur to phosphorus in the seed-row will increase the risk to seedlings. If placement in a side or mid-row band is not possible, broadcasting before seeding or in-crop applications after crop emergence are good options for sulphur. Canola Encyclopedia section on sulphur placement.

Phosphorus (P). Given that soil supply is reduced under wet, cold conditions, canola benefits from a seed-placed supply of phosphate. Under dry soil conditions with low seedbed utilization, the maximum safe seed-placed rate of phosphate is approximately 20 lb./ac. (40 lb./ac. of monoammonium phosphate, for example). The rate can be safely increased to 25 lb./ac. under good moisture conditions.

With 20” row spacing, the safe rate would be reduced by half. With 30” rows, the safe rate would be one third of the safe rate for 10″ rows, assuming opener width stays the same.

If soil tests recommend higher phosphorus rates, this extra phosphate could go in the band with the other macronutrients, or could be applied to other crops as a way to maintain soil phosphorus levels over time. Canola Encyclopedia section on phosphorus placement.

A quick field test. Growers applying fertilizer rates and blends in the seed row that exceed the recommended 20 lb./ac. of phosphate can do their own quick test to see how this may affect seed survival in their field conditions. Turn off the seed-placed fertilizer run for 50 or 100 feet, mark the spot, and compare emergence in this area versus the rest of the field. Do this every year or in moist and dry conditions, if possible, to see how moisture and soil type can reduce the risk.

Canola Watch