SAFEGUARD SULPHUR SOIL SUPPLIES

Bill had high hopes for a bumper canola crop on a newly acquired quarter for his operation near Melfort, Sask. In the past, the quarter had produced canola crop yields in excess of 40 bushels per acre. With a little co-operation from Mother Nature, Bill thought, the crop’s harvest would provide a good return on his investment.

The first signs of trouble appeared around the beginning of June. Bill noticed the plants’ leaves in that field were cupping and turning purple at the edges. Bill kept a close eye on his crop, and by mid-June he noticed that the plants, now at the four-leaf stage, looked worse.

“My crop looks sick,” Bill told me over the phone. “It could be a drift problem.” That morning, I headed out to Bill’s 3,000-acre farm, where he grows canola, wheat, barley and oats. The canola plants in the new quarter looked unhealthy — the cupping and purpling symptoms were present throughout the field and appeared to be more severe on knolls and hilltops. This evidence alone put an end to Bill’s theory that chemical drift was to blame for the damage to his crop, and records indicated herbicide carryover was also not the cause.

The soil was sandy loam, and Bill had applied a 90-25-0-10 blend fertilizer on the field, which is standard for the area. However, several factors led me to believe his fertilizer rates needed to be adjusted!

A consistently high-yielding field with sandy loam soil and a canola-cereal rotation, as well as the symptoms of cupping and purpling leaves — there could only be one diagnosis. The soil in Bill’s new quarter was sulphur deficient. Laboratory results from tissue tests performed on canola plant samples taken from Bill’s field confirmed the deficiency.

The number of acres deficient in sulphur is increasing across Saskatchewan and Alberta. Although all plants need sulphur for proper growth, canola has a higher requirement for sulphur than other crops, and tends to deplete soil stores at a greater rate. Producers must replace depleted sulphur stores to the soil because it is not mobile in plants and is important for plant development and growth.

However, sulphate (the form available to plants) is highly mobile in the soil, especially in sandy soils, and leaching of this mineral can occur. This explains why the symptoms were more severe on the knolls and hilltops in Bill’s field. In this case, supplying 10 pounds of sulphur back to the soil was not enough to support a canola-cereal crop rotation. Sulphur taken out of a field by straw and 40-bushel per acre canola crops can take 20 to 25 pounds of the nutrient out of the ground.

Bill had to act to save his crop’s yield. We decided to float 100 pounds of sulphur fines on the crop at the five-leaf stage. Two centimetres of precipitation were forecast, so incorporation into the soil was likely. Luckily, just over one centimetre of rain fell, and the crop recovered rapidly after that. Bill’s new quarter ended up yielding 47 bushels of canola per acre! Despite the shaky start, his hopes that year for a bumper crop were not disappointed.

I advised Bill to increase the level of sulphur applied with the seed to about 20 pounds per acre in that field. He also began taking soil samples from each of his fields to determine which ones were starting to show deficiencies. Optimum plant growth — and ultimately yield — depends upon adequate supplies of sulphur in the soil. †

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