Illinois Fertilizer Conference Proceedings
January 23-24, 1990

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Canola Fertility

D. Bullock1


Canola is a type of rapeseed (Brassica). Close relatives are mustards, cabbage and broccoli. Canola is grown mainly for its oil, but its meal is used as an animal feed.

Many of the old rapeseed varieties produce oil that contains large amounts of erucic acid that has been shown to cause heart problems in animals. The meal contains a group of compounds called glucosinolates that can prevent its use as an animal feed.

Canadian plant breeders overcame both of these problems, and by the early 1970s, farmers could purchase rapeseed varieties that contained very low levels of erucic acid (less than 2 percent) and glucosinolates (less than 20 micromoles per gram).

These new rapeseed varieties are called canola, double-low rapeseed, or 00 rapeseed to distinguish them from the old rapeseed lines. Canola is the most common term.

The vegetable oil from canola is considered "healthful" and desirable, since it contains less than half the saturated fat of soybean or corn oil. Canola is already one of the world's leading edible oil crops, and demand is expected to increase.

Rapeseed (both canola and non-canola types) is a major field crop in Canada, Europe and Asia, and a great deal is known about its fertility and cultural requirements. Canola, however, is a new crop for Illinois, so we have had to base our fertility recommendations on what they have seen in other parts of the world.

That's not an unreasonable starting point, but the vast majority of those areas are very different from Illinois, and the appropriate recommendations will be different. As an example, wheat is grown in both Britain and Illinois, but we have very different recommendations. Canola recommendations will probably differ as well.

The current recommendations for canola vary from source to source, but the following is close to what most people suggest:

  1. P and K requirements similar to winter wheat.

  2. 20 to 40 pounds more N than wheat

  3. 10 to 20 pounds S

  4. 1 to 2 pounds B

The remainder of this paper will look at the results of a study conducted to examine the validity of these recommendations. Beware that these results are from one year at one location only and should be regarded as tentative.


This soil fertility experiment was conducted during the 1988-89 growing season at the University of Illinois research station at Brownstown, Ill. The soil test indicated a pH of 6.8, a "P1" test of 104 and a "K" test of 272. The P test is much higher than the majority of the soils in that area, and it is very doubtful that any response to P fertilizer would be seen on such a soil. The P fertilizer rate was not a treatment in this study. The K level and pH are typical of soils in that area.

The canola variety, Lirabon, was planted Sept. 14, 1989, at a rate of 6 pounds of seed per acre in 7-inch rows. Individual plots were 24-feet long by 8-feet wide. Non-treated border plots were left between all treated plots. The experimental design was a split-plot design with four replications.

K rate was the major plot and N, S and B rates were applied as a complete factorial within each K block for a total of 144 plots. The treatment rates were: K (0,150 pound K/acre); N (60,120,180 pound N/acre); S (0,10,20 pound S/acre), and B (0,1 pound B/acre).

The K (as muriate of potash) was applied preplant and incorporated. The N (as urea and ammonium sulfate), S (as ammonium sulfate), and B (as soluble boron) were applied to frozen ground on March 21, 1989. Four whole plants were removed from each plot at the start of flowering. The plants were dried, weighed, ground and then analyzed for mineral concentration. The plots were harvested with a plot combine.



The analyses of variance of this experiment are presented in Table 1 and the mean values are in Table 2. Canola was very responsive to N fertilizer. In this experiment, the N concentration and vegetative dry weight of canola at the onset of flowering and grain yield all increased with increasing N rate. Unfortunately, however, this yield increase was accompanied by a delay in maturity and a tremendous increase in grain moisture.

I also noted that increasing N rate delayed flowering onset and lengthened the duration of flowering and increased plant height. The highest N rates flowered about five days to one week later and ended flowering about 10 days later than the lowest N rate. I speculate that N rates in the 150 to 180+ pound N/acre range will result in many of the existing commercial canola varieties being harvested about the same time as wheat or possibly several days to a week later.
This first year, results suggest that our current recommendation of using only an extra 20 to 40 pounds N/acre more than what would be used on wheat may be underestimating the demand of a high-yielding crop (55+ bushels/acre). The current N recommendations seem appropriate for lower yields. We know that 60 and 80 bushel/acre crops would contain approximately 180 and 240 pound N/acre in their tissue, respectively. This N would have to come from a combination of soil reserves and fertilizer N.

We also know that the British use in excess of 200 pounds N/acre on their high-yielding canola. The down side of using these high rates of N, however, will be that maturity will be delayed substantially. This is not an attractive attribute, since double-cropping of soybeans will be delayed. A great deal of effort needs to be put into examining our N fertility program and in finding large-yielding, earlier-maturing canola lines.


Canola needs a substantial amount of K for numerous processes. It is required for photosynthesis and proper N use. Canola yields of 40, 60 and 80 bushel/acre require 95, 144 and 190 pound K uptake, respectively. But much of the European and Canadian work indicates that canola does not respond well to fertilizer K even when soil levels are low to medium. Canola is apparently very efficient in utilizing soil-borne K.

In this study, increasing the K fertilizer rate from 0 to 150 pounds K/acre substantially increased the K content of the plants, but it did not affect grain yield, grain moisture or vegetative dry weight. K rate did slightly decrease the P, Mg and Zn concentrations of the plants at the onset of flowering, but the differences are small and of no practical importance.

This first year, results suggest that the current recommendations of a K fertility program for canola, similar to that of wheat, are reasonable. Since many of our soils have K levels in the 250 to 300 pound K/acre range, I doubt that K deficiency will be common problem for canola in Illinois.


Current recommendations for S fertility of canola suggest 10 to 20 pounds S/acre, either as elemental S in the fall or sulfate S in the spring. In this study, increasing the S rate did increase the concentration of S in the plants at the onset of flowering, but it did not affect grain yield or vegetative dry weight. Grain moisture was reduced slightly at the 10 pound S/acre rate as compared to the 0 or 20 pound S/acre rate, but the difference was small (7.6 vs.7.8 percent) and of limited practical importance.

Canola is quite sensitive to S deficiencies. Outside of Illinois yield responses have been shown with applications in excess of 20 pounds S/acre. However, I did not see a yield response to S in this experiment.

I did not analyze the soil for sulfate content, but this research indicates that ample soil-borne S was available. The soils at the Brownstown location are underlain with a clay layer, and clays have numerous sulfate-binding sites. The clay-binding sites prevent a fair portion of the sulfate from leaching.

This S response is going to be location-specific, and there is no doubt that there will be areas in Illinois that will show a yield response to S consistently. This will be true especially if the soil is sandy, without a significant clay horizon and low in organic matter. But such locations are the exception rather than the rule. Past experience, and this first year's data, do not give strong support to a blanket recommendation of 10 to 20 pounds S/acre for canola. More work needs to be done.


The brassica family of plants are heavy B feeders and B deficiency symptoms and yield-limiting conditions are common on soils that have been heavily limed or soils with a naturally high pH. Few of our soils fall into this category. Yet, most of the current recommendations suggest that 1 to 2 pounds B/acre be applied to each canola crop.

In this study, increasing the B rate from 0 to 1 pound B/acre did increase the B concentration of the plants at the onset of flowering, but it did not affect grain yield, grain moisture or vegetative dry weight. The soil B level at this site is unknown, but these results suggest that ample soil-borne B was available and question a blanket recommendation of 1 to 2 pounds B/acre. As with S, more work needs to be done on B fertility of canola.


Based on this work, I suggest that our attention be focused on N fertility programs. This seems to offer the largest and quickest returns for our investment of time and money. I have not shown a response to K, B or S, but it should be remembered that this is only one year's data from one location. Data from several years and several locations is needed.


Table 1. Abbreviated ANOVA for 89 Canola Fertility Work at Brownstown.

Table 2. Means of 89 Canola Fertility Work at Brownstown


1Don Bullock is Assistant Professor of Agronomy, Department of Agronomy, University of Illinois at Urbana-Champaign

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