Soil pH and assuring the correct amounts of phosphorus and nitrogen are important considerations for Southern Plains farmers intending to plant winter canola before the September 10-October 10 planting dates arrive, according to Brian Arnall, Oklahoma State University Extension crop fertility specialist.
Arnall, who recently co-authored an OSU Extension fact sheet on winter canola fertilization—PT 2012-3, with Hailin Zhang and Bill Raun—said: "We had a lot of learning opportunities in 2012 with winter canola. One of the biggest lessons was to make sure soil pH, nitrogen and phosphorus were working together for the benefit of the canola seed being planted.
"Twenty to 30 pounds of nitrogen needs to be available in the soil at planting or sometime before December. At any location with a low phosphorus soil test canola needs to have that ingredient available at planting. Our studies have not observed any differences between broadcast and banded applications; it just needs to be available.
"Soil pH has a large impact on a canola stand and productivity. Any time you have a soil with a pH lower than 5.5, yields will be lost," he said.
"However it is applied, canola needs phosphorus to make it through the winter."
Arnall and his fellow OSU researchers report canola yield goals should be sufficiently greater than long term average yields to ensure nitrogen will not be the factor limiting crop production during years with better than average growing conditions.
An appropriate canola yield goal is the average of the three highest yields from the last five years or a five year average plus 20 percent, they say.
Excessive preplant nitrogen levels can reduce the winter hardiness of winter canola. Arnall recommends farmers apply one -third, or 35 to 50 pounds per acre, of their total nitrogen pre-plant and the rest as a topdress in the spring.
Arnall reports recent field trials in Oklahoma did not show any response to applied sulfur fertilizers. No lime applications are necessary when soil pH is 5.8 and higher, no matter what the buffer index is, he says.
Both phosphorus and potassium fertilizers should be planted in the fall before or at planting. Arnall cautions growers not to band fertilizers in canola production. Banding fertilizers with canola seeds may cause injury to seeds and seedlings if the distance between fertilizer and seeds is inadequate.