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How’s your moly doing out there?

Molybdenum was once known as ‘poor man’s lime’ for a good reason

Under the category “if it ain’t one thing it’s another” when it comes to crop nutrient requirements, the question is now being asked, “have you thought about the molybdenum levels in your canola and pulse crops?” Cereals need it too, but canola, peas, beans, lentils, faba beans, soybeans and others all have higher molybdenum requirements.

Molybdenum, also often referred to in the abbreviated term “moly,” is one of the 16 essential elements for plant growth. It is a micronutrient particularly important in helping plants in their uptake of nitrogen. They don’t need much moly, but if the soil is deficient in molybdenum it can really have an impact on yield.

“The fact of the matter is that we don’t know much about it,” says Mike Dolinski, an agronomy specialist with Agri-Trend Agrology. He’s been speaking about molybdenum at several farm meetings this past winter and early spring.

“A soil analysis for molybdenum really isn’t worth the powder to blow it up, and tissue testing is a bit better, but not many farmers tissue test their crops,” he says. “We really don’t know what’s out there. What we do know is if your soil and ultimately your crop is deficient in molybdenum it affects nitrogen uptake which in turn reduces yields.”

Molybdenum is an essential component in two enzymes that convert nitrate into nitrite and then into ammonia before it is used to synthesize amino acids within the plant. It also needed by nitrogen fixing bacteria in legumes to fix atmospheric nitrogen. Plants also use molybdenum to convert inorganic phosphorus into organic forms in the plant.

While there are many unanswered questions about molybdenum, the good news is farmers don’t need to apply very much, it is relatively inexpensive, and it can be easily applied at just about any stage of crop development.

Dolinski first became aware of concerns when dealing with farmers and in Idaho who were seeing a response to molybdenum.

“The only theory I have about what’s happening in Western Canada is that in the past few years farmers are beginning to push crops for higher yields,” says Dolinski. “We are starting to see much higher yields. And those higher yields are removing more molybdenum.” The only natural source of molybdenum is through mineralization in the soil.

“Crops yields are getting bigger, higher rates of nitrogen are being applied and at the same time soils are becoming more acid — soil pH is dropping. And in most cases when soil pH drops most nutrients become more available. The reverse is true with molybdenum. As soils become more acid, moly becomes less available.“ He says at one time the micronutrient was referred to as “the poor man’s lime.”

Canola, pulses and legume crops have the highest requirements for molybdenum, says Dolinksi. Canola for example, uses about five times more than cereal crops such as wheat.

Crop signs of a molybdenum deficiency aren’t always obvious. In canola a deficiency can show up as cupping of the leaf margins in younger leaves, interveinal chlorosis (yellowing) of leaves, and a condition Dolinski calls “whip tale,” a narrowing of lower leaves.

Have a look at soil PH

So what is the fix? First of all Dolinski says to have a look at soil pH levels. If levels are up in the eight to 8.5 pH range he wouldn’t worry about molybdenum. If they are getting down to six pH range, producers of canola and pulse crops should begin to have concern. And if they’re in the 4.5 to five range, he’d apply molybdenum to all cropped acres.

Idaho farmers are using a product called sodium molydbate to correct molybdenum levels. It is very water soluble and can be applied as part of any field spraying operation. And you don’t need much. Moly levels can be boosted at a recommended rate of 50 grams (less than two ounces) of sodium molydbate per acre.

“Some people apply it as a seed treatment,” he says. “It can also be applied with a fertilizer, herbicide or first fungicide treatment.” Several crop nutrient supplements also carry molybdenum.

“Have a look at your soil pH levels to start with,” says Dolinski. “And if pH levels are getting into that warning zone, at least set up a few acres for an on-farm trial. ”

About the author

Field Editor

Lee Hart is editor of Cattleman’s Corner based in Calgary.

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