By Bruce Barker
Barley and, to a lesser extent, winter wheat show responses to potassium fertilizer, even on high-testing soils.
By Bruce Barker
Soil tests are commonly used to develop fertilizer recommendations. However,
in the case of potassium (K), instances have been observed where its addition
in the form of potassium chloride fertilizer (KCl; potash) has produced yield
responses, even when the soils test high in K. In fact, many areas of the prairies
routinely test very high in K, but the practice of adding 10 to 25 pounds of
K2O per acre is becoming common.
"This practice has been adopted in response to reported benefits from
the chloride (Cl) portion of the fertilizer," explains Rigas Karamanos,
manager of agronomy with Westco Fertilizers at Calgary, Alberta. "Our research
is showing that the yield response is related to potassium."
Earlier research had been carried out in the three prairie provinces to calibrate
soil tests against yield, and this work was very successful in identifying K
deficient soils and deriving a critical level below which K deficiency occurs.
A level of 125ppm or an equivalent of 250 pounds K2O
per acre in the top six inches of soils is generally considered critical. The
majority of prairie soil tests are in excess of 300ppm or 600 pounds K2O
per acre in the top six inches.
However, there are areas of deficiency. For example, in Alberta, there are
an estimated three million acres of K-deficient soils with about half a million
of those severely deficient. On soils that show a potassium deficiency, fertilizing
with potash fertilizer is recommended as part of the regular fertility program.
Why a response on high K soils?
In delving into crop responses on high K soils, Westco carried out more than
200 experiments with seed-placed potash across the prairies during the 10 years
from 1989 to 1998. Fertilizer was seed-placed at a rate of 13 or 27 pounds K2O
per acre. In other research sponsored by the Potash and Phosphate Institute
and conducted by Brian Fowler of the University of Saskatchewan, 50 pounds K2O
per acre was broadcast on winter wheat.
|Soil test K (zero to 6in depth)||
General potassium recommendations to correct deficiency*|
|Rating||ppm||lb/ac||Wheat, oats, barley||Canola, mustard|
|Very deficient||Zero to 25||Zero to 50||75||60|
|26 to 50||51 to 100||60||45|
|51 to 75||101 to 150||45||30|
|Moderately deficient||76 to 100||151 to 200||30||15|
|101 to 125||201 to 250||15||10|
|Critical level (marginal)||125 to 150||250 to 300||Zero||Zero|
|High potassium levels (adequate)||150+||301+||Zero||Zero|
In the trials, barley had the highest probability of showing a yield response,
with 15 percent of the trials showing a five to 10bu/ac yield response and 40
percent of trials having at least a two to five bushel per acre yield increase.
Bear in mind that these responses were on high K soils where the soil test would
not have called for any potash fertilizer.
The frequency of response for wheat was lower with 20 percent of the trials
producing a two to five bushel per acre yield increase. Canola and peas never
showed a response on high K soils.
Research in Montana, using broadcast application of 25 pounds K2O
per acre on cereals also showed a response on high K soils. There, winter wheat
responded one-half the time with an average yield increase of 3.9bu/ac. Oats
also responded 25 percent of the time with a four bushel per acre average yield
"In the research trials that I have seen, barley is the most responsive
crop to potassium," says Adrian Johnston, Northern Great Plains director
with the Potash and Phosphate Institute (PPI) at Saskatoon, Saskatchewan. "And
that's where we are seeing most of the starter potassium going down."
|Frequency of response (percent)||Average yield increase (bu/ac)|
|N/A1 means not available|
|2 PPI/PPIC/FAR sponsored research|
by Dr. B. Fowler, University of Saskatchewan.
Speculation for the yield increases has often revolved around the Cl portion
of the fertilizer and yield responses due to disease suppression, especially
in barley. Other benefits of small amounts of seed-placed potash may include
readily available potassium in close proximity to the roots of seedlings in
cool springs, resistance to mild lodging and promotion of early maturity.
"If it is a yield response, the nutrient responsible is probably potassium.
If disease is suppressed, chloride is probably producing the response,"
says Johnston. "Research at a number of locations in western Canada and
Montana has shown seedling leaf and root disease suppression with chloride additions."
In the Westco research, Karamanos analyzed the data to determine where the
yield response originated. He focussed on the barley trials and looked at other
factors such as kernel plumpness, days to maturity and protein content, which
are all important factors in malt barley quality. He also tried to relate the
yield increases to disease suppression by the Cl nutrient, soil type, previous
crop and climatic or regional differences.
"I believe the explanation for the yield responses, especially for malt
barley, is due to the potassium and not chloride," says Karamanos. "We
could not establish a consistent trend or, sometimes, any trend at all, when
looking at the other factors. I think that somehow, the potassium helps the
crop fight off disease stress better."
In fact, Westco's research did establish a very strong relationship between
frequency of response and barley variety. This provided Karamanos with an indirect
link between response to potash and disease resistance, since varieties with
lower disease resistance, such as Harrington, responded more often than others,
such as Leduc, Stander or Manley, which have higher disease resistance. Harrington
had at least a two to five bushel per acre response half the time, while Leduc,
Stander and Manley only responded 15 percent of the time.
Johnston says the Harrington yield response is similar to fungicide research
at Melfort, Saskatchewan, where Harrington often showed a response to a fungicide
application where other more disease-resistant varieties did not. "There
is still a lot of Harrington malt barley grown, so those producers could consider
an application of potash," says Johnston.
If seed-placing potash, the total amount of seed-placed fertilizer should not
exceed 175 pounds per acre, and the amount of N plus K2O
should not exceed 40 pounds per acre, according to Alberta Agriculture, Food
and Rural Development information. This is for average soil moisture conditions
and for medium textured soils, and using a very narrow band opener such as a
Does seed-placed K make economic sense?
Karamanos suggests that for the cost, he would recommend 15 pounds of K2O
per acre seed-placed when growing malt barley. The cost pencils in around $2
to $3 per acre. To help determine the economic viability, he isolated nine years
of data, which produced 42 trials from the Irricana, Alberta site. At that site,
the average yield response was 1.5bu/ac, with an expected yield response in
three out of five years. Karamanos developed a chart to illustrate the marginal
return for every dollar of potash fertilizer seed-applied at a rate of 13 pounds
K2O per acre. Adding in barley price and the actual cost
of potash fertilizer, the break-even point was almost always achieved.
For example, if the barley price was $2.20 per bushel and the cost of potash
was $0.15 per pound of K2O, then applying 13 pounds per
acre of K2O would have produced $1.70 return for each
dollar spent on potash fertilizer.
"Application of potash on soils containing high levels of potassium is
strongly recommended with barley varieties that are susceptible to disease,"
says Karamanos. "And judging from research from other areas, application
on winter wheat may also be justified." -30-