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Successful Winter Canola Depends on Soil Fertility

Jagadeesh Mosali, Ph.D.

By Jagadeesh Mosali, Ph.D.

Posted Sep. 30, 2012

Proper fertility management is essential for a successful canola crop. Canola seed yields are affected by levels of nitrogen (N), phosphorus (P) and potassium (K), and are sensitive to changes in soil pH. In addition, boron (B) and sulfur (S) may be needed. To identify nutrient deficiencies prior to reduction in yields and/or crop failure, a representative soil sample needs to be collected and tested for the above parameters.

Canola seed yields are affected when soil pH levels are less than 5.8. Soil pH needs to be corrected prior to planting to take full advantage of any fertilizer applied to the crop. Based on the soil pH and soil test buffer index, lime is added as an amendment to increase the soil pH. Follow the lime recommendations from your soil testing laboratory or consultant.

Nitrogen is a mobile nutrient. N requirements for canola are based on yield goal. For each 500 pounds per acre of yield goal, 25 pounds per acre of actual N is needed. For example, for 2,000 pounds per acre of yield goal, 100 pounds per acre of actual N are needed. A split application of nitrogen is recommended for better nitrogen use efficiency, as well as better winterhardiness. Apply one-third of the required N before planting and two-thirds as topdress during the spring.

Phosphorus and potassium are immobile nutrients in the soil. P and K requirements for canola change, depending on soil test index levels. A phosphorus soil test index of 65 and above is considered 100 percent sufficient for crop growth, and anything less should be adjusted based on the recommendation in Table 1. Similarly, a K soil test index level of 250 or more is considered 100 percent sufficient, and anything less should be adjusted based on the recommendation in Table 2. Phosphorus and potassium needs should be corrected before planting by broadcast application and incorporation into the soil.

Table 1.

Table 1.

For better oil quality, oilseed crops like canola require more sulfur and boron than most crops. As a rule of thumb, sulfur requirements are at least one-tenth of nitrogen requirements. Preliminary research conducted at the Noble Research Institute has not seen any beneficial effect from application of either sulfur up to 40 pounds per acre or boron up to 2 pounds per acre. This is an ongoing research project and the prior crop was small grains. The reasons for finding no effect could be due to sufficient levels of S and B in the soil or possibly atmospheric depositions of sulfur. Also, deficiencies could be noted in a continuous canola production or in crops that are planted after canola. Further research is needed to see the long-term effects of a canola production system in regards to sulfur and boron requirements.

References

Zhang, H., B. Raun, and B. Arnall. 2012. Fertilizer and lime recommendations for canola in Oklahoma. Oklahoma State University. PT 2012-3.
Sulfur and boron effects on yield of canola (ongoing research). 2012. The Noble Research Institute.

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