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Rescuing Canola After Sulfur Deficiency Symptoms Are Present
We know it is easiest if sulfur fertilizer is applied before seeding, though a shortage of time or other inconvenience can prevent the sulfur from being applied pre-plant. When time gets short, the canola comes up, then starts getting big and the sulfur still has not been applied. What are your options?
Research conducted by John Lukach of the NDSU Langdon Research Extension Center has shown good responses to sulfate fertilizer applied to canola with foliar deficiency symptoms. Seed yields of canola when the sulfur applications were made before bud stage have been close to the yield from nearby non-deficient areas of the field. The response of canola to sulfur applications made after bud stage diminishes with plant maturity.
A trial on an eroded knoll near Lankin, ND in 1996 was conducted with sulfur applied to five leaf canola. Sulfur deficiency symptoms were severe on the hill top but no symptoms were seen on the surrounding lower ground. Ammonium thiosulfate (ATS) at 20 lb/a sulfur was sprayed in strips up the slope. Eight paired plots, with and without sulfur applied, were harvested from three hill slope positions. The average seed yield near the top of the eroded knoll was 233 lb/a without sulfur and 802 lb/a with sulfur. The average seed yield on the side slope was 783 lb/a without sulfur and 1413 lb/a with sulfur. The yield responses to sulfur fertilizer applied to 5 leaf canola were, 569, 320 and zero lb/a from hill top, slope and foot positions, respectively. The difference in response reflects the differences in organic matter between the hill slope positions while the actual yield indicates lower yield potential of the hill top.
An application of 20 lb/a sulfur to six leaf Canola on a sulfur deficient hill top near Rock Lake in 1995 resulted in a 580 lb/a yield response. No differences between sulfur applied as dry ammonium sulfate, 2l+0+0+24S or the liquid ATS, 12+0+0+26S, occurred. The rain needed for incorporation of both sulfur forms occurred the day after application.
Canola responses to sulfur applied at flowering stage look impressive based on plant growth, however, the seed yield response was disappointing. Two trials were established in 1995 on canola fields with the non-deficient areas in full bloom and the sulfur deficient areas was in early bloom. The sites, near Langdon and Walhalla, had 100 to 150 lb/a increases in seed yield. Actual yield on those deficient areas was only about 300 lb/a. Nearby non-deficient areas of those fields yielded about 2000 lb/a and had no yield increase to sulfur fertilizer applied during flowering. The maturity of the sulfur deficient areas which received sulfur fertilizer at flowering was about two weeks later at harvest than the non-deficient areas are large enough to conveniently swath separately any yield gain from applying sulfur to flowering canola is lost by cutting the canola to green.
Growing season sulfur fertility applications will be most profitable when deficiency symptoms as shown in Extension Bulletin SF-1122 are identified before bud stage. Scouting can be done at the same time as post-emergence herbicides are applied. Look for leaf cupping, stunting and interveinal yellowing. Scouting time can be reduced by first checking eroded hill tops or areas where top soil was removed, like along some roads, or areas in the field which are drought susceptible due to underlain sand or gravel. These are the areas most likely to be sulfur deficient. Severe sulfur deficiencies after bloom starts can be indicated by delayed maturity and at the end of flowering by a purple coloration, both of which are often apparent while scouting at 55 miles per hour on the road.
Dry ammonium sulfate, 21+0+0+24S, is slightly less expensive than the liquid ammonium thiosulfate (ATS), 12+0+0+26S, and is safest for spreading on small canola. Both need to be incorporated by rain for uptake by the plant. Elemental sulfur is not a choice for growing season surface application because it needs to be converted to the sulfate form before the plant can use it. Foliar application with ATS requires care due to the potential of leaf burn. Large canola is one of the few crops which can tolerate foliar spraying with pure ATS. ATS sprayed on small or lush rapidly growing canola, which has not developed a grayish coloration indicating a waxy coating is present on the leaves, will be severely burned. ATS is much safer on larger plants and the sulfur deficient plants. Rates if 14 gal/a of pure ATS, which is equivalent to sprayer over lap when applying a 20 lb/a sulfur rate, will cause only a small amount of leaf burn on large canola. A spray solution of 5 gal/a ATS plus 3 gal/a of water can severely burn 2 leaf canola. Blending the ATS with water does reduce burn on volunteer small grains. There is no apparent weed control effect from ATS applications as both grasses and wild mustard quickly grow back even after severe leaf burn. The use of ATS is viable option with the main advantage being the convenience of applying a liquid and for aerial application. The accuracy of applying a uniform application is especially good for research plots.
Source: Report written for ND Canola Growers News Letter, by John Lukach, Langdon Research Center, June 27, 1999.
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