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Puzzling Low Yield? Think Micros

It has always been my opinion that we are a long way from knowing all the micronutrient deficiencies that exist on the Canadian Prairies. Micronutrient research is not “glitzy” from a research person’s perspective because almost all experiments show a positive response.

A recent discussion with a colleague at the U. of S. brought micronutrients to the top of my mind. Neighbours of his at Mossbank, Sask., had applied zinc sulphate to a field of mustard and fortunately the product ran out before the field was done. The field could provide a good trial opportunity.

Western Ag Labs tested the soil and discovered that zinc levels were low by their technique and suggested a zinc trial. (Their technique uses ion exchange probes instead of the usual chemical extractants.) A dramatic visual response and a good mustard yield was the result.

My first thought was that sulphur (S) could also be involved as mustard needs S just like canola does. However, the S rate with a low rate of zinc sulphate would be very small.

In general, because the amounts of micronutrients are small, soil testing is much more difficult and less reliable and any given nutrient can have a much different reaction in different soils and for different crops. In my book, Henry’s Handbook of Soil and Water, I organized these differences using the terms Pet Crops and Pet Soils.

PET CROPS

Wheat is a pet crop for copper deficiency. Wheat often benefits from a copper application. In fact, within a crop we should probably also be talking about “pet” varieties. Rigas Karamanos with Viterra often talks about Park wheat in Alberta, which was very susceptible to copper deficiency but was popular for other reasons. When Park wheat was used as the test crop, responses were obtained in part because of the variety. Other regions of the world have also shown benefits from copper fertilization in wheat. In East Africa, I read literature on copper deficiency for wheat in Kenya as long ago as the 1950s.

Oats are a pet crop for manganese deficiency, and a search of literature usually finds oats being the test crop when manganese is being studied.

Beans are a pet crop for zinc deficiency and especially on soils leveled for irrigation or soils with high fertilizer P additions.

For boron the main pet crop is alfalfa, but we often see canola also mentioned when dealing with boron problems.

For iron, fruit trees and shrubs are pet crops. Rose bushes often show iron deficiency.

Keep in mind when you read or hear anything about micronutrient studies, that the crop and the soil type are critical factors in the success. You can’t necessarily apply good results for wheat in the Black Soil Zone and assume you’ll get the same results for oats in the same zone, or even for wheat in another zone, for that matter.

PET SOILS

Pet soils include peat soils, which are notorious for copper and manganese problems. High

Every year around this time I get excited.

I know my grower planted InVigor hybrids

and I can hardly wait to experience the

organic matter sandy soils are also prone to copper deficiency.

Grey Wooded soils, particularly when sandy, are pet soils for boron problems and high pH, high lime soils are pet soils for iron deficiency.

When we combine a pet soil with a pet crop and perhaps even a pet variety, then a specific micronutrient problem can give us a serious problem. The pet variety thing has received little research attention and is almost totally ignored in plant breeding programs. And, very little variety evaluation work is done on soils that may be most susceptible to micronutrient problems. Most experimental farms that are used for plant breeding programs are on some of the best soils with few micronutrient problems.

In the 1970s, in Tanzania we ran head on into just such a problem. A new variety was released that had done well on average over many sites even though it was a dog at one site. That site turned out to be a seed multiplication site and an attempt to bulk up the seed resulted in a failure due to manganese deficiency. At that site, other wheat varieties and corn and other crops did OK, but our new and supposedly improved variety failed completely.

So if you find that a certain variety of a certain crop just does not perform in your area, just maybe a micronutrient is involved. And just maybe mustard is a crop that needs zinc.

J. L. (Les) Henry is a former professor and extension specialist at the University of Saskatchewan. He farms near Dundurn, Sask.

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