Soil Test Note – No. R001
Dr. Stanley L. Chapman, Extension Soils Specialist
FERTILIZING RAPESEED (CANOLA)
Rapeseed
is a cool season oilseed crop being grown in Arkansas on a trial basis. Rapeseed is grown for two major purposes, industrial
lubricants and domestic cooking oil. The
type grown for edible cooking oil is known as Canola. Canola is different from other rape varieties
in that it contains low levels of two important chemicals: erucic acid and glucosinolate. If the levels of either of these two chemicals
exceed the limits established by the U.S. Food and Drug Administration, the
seed may be rejected or severely docked.
The nutrient
and lime needs of rapeseed are reportedly similar to those of wheat.
The levels of N, P, and K in the plant are not known to affect either
the erucic acid or the glucosinolate levels.
Hence, N, P, K fertilizer recommendations for rapeseed are almost identical
to the recommendations for wheat.
On
a small percentage of soils in Arkansas, rapeseed may suffer a sulfur deficiency.
Sulfur is recommended for rapeseed only on sandy and silt loam bottomland
and terrace soils that have less than 1 percent organic matter.
On such soils, apply 20 pounds per acre of sulfur in the fall or with
the first spring nitrogen application using a sulfate source.
Excessive
sulfur nutrition may cause glucosinolate levels to rise in Canola, because glucosinolate is a chemical compound containing
sulfur. How much sulfur is too much?
The answer to this question is not known.
To help diagnose sulfur deficiency and prevent over-fertilization with
sulfur, consider plant analysis of Canola when it begins spring growth.
Revised 1987
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