Fertility and Nutrients
Do you really need micronutrients?
November 19, 2007 By Bruce Barker
Micronutrient research on the prairies dates back to the 1960s and originally
identified zinc (Zn), copper (Cu) and manganese (Mn) as potential deficiency
problems. That early work also identified organic (peat) soils as primary soils
where deficiencies might occur. The research also showed that the vast majority
of prairie soils adequately supply micronutrients to cereal crops.
Today, though, many micronutrients and micronutrient blends are pushed across
the prairies as either a maintenance blend, or as a balanced fertility program.
Rigas Karamanos, manager of agronomy with Westco at Calgary, Alberta, says that
in many instances, micros are being pushed when there is little research to
back up the sales.
"Micronutrients should be used when there is an economic benefit to the
farmer," says Karamanos. "I repeat, an economic benefit to the farmer
and nobody else."
Karamanos has 25 years experience on micronutrient research and is credited
in more than 50 publications on micronutrients published in scientific journals
and conference proceedings. Much of this research deals with how deficiencies
can be identified, and whether there is a critical threshold level when addition
of fertilizer could correct the deficiency. Soil testing and plant tissue analysis
are two tools commonly used for identifying deficiencies. Unfortunately, they
do not always work.
Looking at boron (B), Karamanos says it is one of the least studied nutrients
on prairie soils. Hot-water extractable boron (HWEB) soil test levels of less
than 0.35ppm are generally considered deficient, but this critical level has
not been proven on the prairies.
For example, Karamanos published a three year research study in 2003 looking
at the response of canola to boron. The Westco research found that canola did
not respond to boron application on 40 sites across the prairies, even on soils
containing less than 0.15mg/kg HWEB.
"The critical level for boron is unknown. And we cannot correlate HWEB
levels to tissue levels either," says Karamanos. "Responses to boron
are rare on prairie soils. This is directly related to the high organic matter
levels in our soils that constantly provide boron to the crops independently
of what the HWEB test shows."
Copper deficiencies verified
In contrast to boron, many research studies have found the existence of copper
response on prairie soils. Three million acres in Alberta and one million acres
in Saskatchewan have been identified as potentially deficient. Copper deficiencies
have also been identified on organic (peat) soils in Alberta, Saskatchewan and
Provincial fertilizer recommendations, developed in the 1980s, show varying
critical levels in the three provinces. Manitoba sets the critical level at
less than 0.2ppm, Saskatchewan at 0.4ppm and Alberta at 0.4ppm to 0.6ppm.
To further refine those critical levels, Karamanos recently compiled research
data on wheat, barley and canola for Saskatchewan and Alberta and verified the
critical level of 0.4ppm for cereals and 0.3ppm for canola.
"For marginal soils, if you apply copper fertilizer when critical levels
are 0.4ppm or higher, you will lose money," says Karamanos.
Response to copper has also been observed by other researchers on oats, alfalfa
and flax. However, Karamanos says the database for those crops is too small
to draw critical levels. He also cautions that the critical levels were established
on all soil types, but that previous research found that clay soils do not respond
as readily as sandy loams or loamy sands.
Iron and molybdenum not researched
No research in western Canada exists for iron and molybdenum (Mo). Karamanos
says there are anecdotal reports of calcium-induced iron chlorosis in trees
and garden vegetables in a few areas, as well as Cu-Mo imbalances in east-central
Saskatchewan and west-central Manitoba, due to excessive levels of Mo in pasture
soils that results in molybdenosis in cattle. "No calibration work has
been carried out on these two micronutrients, so it is impossible to predict
a response," cautions Karamanos.
Manganese response only on peaty soil
Karamanos says that response to manganese (Mn) on mineral soils is extremely
rare. On mineral soils, researchers have not been able to carry out calibration
work to correlate soil test levels to fertilizer response. However, on peat
soils, extensive work in all three prairie provinces has proposed a Mn:Cu ratio
to establish critical levels. Ratios of less than one indicate manganese deficiency
and above 15 show a copper deficiency.
No zinc response in cereals and oilseeds
Extensive work has been carried out on beans in Alberta and Manitoba, flax in
Manitoba and a variety of crops in Saskatchewan. Researchers have been unable
to find a response to zinc from cereals and oilseeds on the prairies. Seventeen
field trials in the late 1980s were unable to establish a response to the commonly
used critical level of 0.5ppm. These trials concluded that the critical level
could be no higher than 0.25ppm for cereals, except for corn, which has shown
response to zinc.
Research has shown dry bean response to zinc. Ross McKenzie with Alberta Agriculture,
Food and Rural Development established a critical level of 3.0ppm in coarse
soils and 1.5ppm in medium to fine soils for irrigated dry bean production in
southern Alberta. However, his earlier research on irrigated wheat, barley and
canola did not find any response to zinc.
Recently, researcher David McAndrew of Agriculture and Agri-Food Canada found
different zinc responses depending on dry bean variety.
Relevant plant analysis criteria lacking
Karamanos says that plant tissue analysis data is severely lacking for most
crops and micros on the prairies. While some criteria have been assembled by
provincial agriculture departments, most have been derived from research in
other areas of North America. Karamanos was successful in establishing diagnostic
criteria for manganese in oats. However, he and other researchers were unable
to establish plant tissue tests for copper in cereals, canola and flax in western
"Much work remains to be done to develop relevant plant tissue criteria
for western Canada," says Karamanos.
|Table 1. Recommended
methods of application of generalized categories of micronutrient products.
|Nutrient||Fertilizer form||Time of soil application||Broadcast and incorporate||Band||Seed-place||Foliar|
|Copper||Sulphate Oxysulphate >60 percent solubility||Spring or fall||3.5 to 5.0lb Cu/ac||Not recommended||Not recommended||Not recommended-a|
|Oxysulphate <50 percent solubility||Fall||5.0lb Cu/ac||Not recommended||Not recommended||Not recommended|
|Chelated||Spring||0.5lb Cu/ac||Not recommended||0.25 to 0.5lb Cu/ac||0.2 to 0.25lb Cu/ac|
|Zinc||Sulphate Oxysulphate >60 percent solubility||Spring or fall||3.5 to 5.0lb Zn/ac||Not recommended||Not recommended||Not recommended|
|Oxysulphate <50 percent solubility||Fall||5.0 to 10lb Zn/ac||Not recommended||Not recommended||Not recommended|
|Chelated||Spring||1.0lb Zn/ac||Not recommended||Needs verification||0.3 to 0.4lb Zn/ac|
|Manganese||Sulphate||Spring||50 to 80lb Mn/ac – b||Not recommended||4.0 to 20lb Mn/ac||Not recommended|
|Chelated||Spring||Not recommended||Not recommended||Not recommended||0.5 to 1.0lb Mn/ac|
|Boron||Sodium Borate||Spring||0.5 to 1.5lb B/ac||Needs verification||Not recommended||0.3 to 0.5lb/ac|
foliar applications of copper sulphate are effective, the product is extremely
b Broadcast and incorporated rates of manganese are generally
Broadcast, foliar or seed-placed application methods are often cited as appropriate
methods for correcting deficiencies. However, due to the relatively high cost
of micros, broadcast incorporated micronutrients are not economical. Karamanos
lays out the best ways to apply micronutrients for general categories of micros
Is a balanced micro fertilizer needed on sufficient
A number of 'balanced' soil or foliar micronutrient fertilizer products are
now being marketed in western Canada. Karamanos says they are sold under the
premise that balanced nutrition is necessary for optimum yields. He cautions,
though, that little research for these products has been done on the prairies.
Karamanos looked at 13 experiments on wheat and 21 on barley from 1989 to 1994
to ascertain whether 'targetted' or 'non-targetted' use of a single five pound
per acre foliar application between tillering and boot stage of 15-20-20 (also
containing two percent S, 0.15 percent Cu, 0.01 percent Fe, 0.01 percent Mn,
0.08 percent B, one percent Zn and 0.0005 percent Mo) provided an effective
means of alleviating micronutrient deficiencies or simply increased yield due
to a 'balanced' nutrition. He found that application of 15-20-20 to wheat and
barley crops resulted in statistically significant yield increases in only two
of 13 wheat trials and five of 21 barley trials.
The experiments showed that yield increases were both small and unpredictable
even when exceptionally high yields were obtained. Karamanos says that the results
represent random events not related to the treatment and are similar to those
obtained in a study with 23 experiments where two cent coins were thrown on
a plot to simulate a $5.50 per acre treatment.
"All you are doing is throwing money out on the field when you use those
balanced micro products. There isn't any research proof that supports their
use," explains Karamanos.
As a final caution, Karamanos cites 19 maximum yield research trials carried
out by Westco between 1989 and 1998. The goal was to try to break the 200 bushel
of barley per acre barrier. In that research, with an average yield of 160 bushels
per acre, nitrogen contributed 72 percent to the yield response, phosphate 20
percent, potassium four percent, sulphur four percent and micros zero percent.
"We did not see a response to micros at all," says Karamanos. "The
way I look at micros is that if you don't have high blood pressure, why take
the medication. You need to be sure you need micros and that they provide an
economic return to the farmer."
Karamanos says that micronutrient deficiencies are not a widespread problem.
Farmers should be aware of the potential for copper deficiency in cereals, and
zinc in beans and possibly corn. And in all cases, economic return should dictate
the use of micros. -30-