NEEPAWA, Man. — John Heard bent down to inspect a still developing alfalfa plant and deftly snapped off the top few centimetres.
After peering briefly at the leaves, the Manitoba Agriculture soil fertility expert held up the alfalfa for about 10 forage growers and reporters who had gathered around him.
Whitish spots were clearly visible on the edges of the alfalfa leaves, which are a telltale sign of potassium deficiency.
“We see it in soybeans, corn, cereals and alfalfa,” Heard said during a field tour near Neepawa that was part of the Manitoba Hay and Silage Day held June 11.
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“It (potassium) is mobile in the plant so when the plant runs short the plant tries to move it from older leaves to newer leaves.”
Manitoba Agriculture says regions with sandy and sandy loam soil may be deficient in potassium for alfalfa production. That includes a strip of agricultural land along the Manitoba escarpment from Morden to Swan River.
Research has proven that applying potassium can dramatically increase yield on sandy loam soil. For in-stance, a Manitoba Agriculture document shows that applying 75 pounds of potassium per acre will generate 3.7 tons of alfalfa per acre. Without potassium, the alfalfa crop yielded 1.5 tons per acre.
“Maybe 80 percent of the province (is) heavy clay soils, or clay-loam, that have good supplies (of potassium),” Heard said.
“(But) we do have sandier areas and we need to be cognizant (of potassium deficiency) and the response can be dramatic.”
Alfalfa fields lacking potassium are also more prone to disease and drought, but Heard said winter survival is the most significant risk.
Research done in the 1970s found that the winter survival rate of alfalfa plants with potassium deficiency drops significantly after three years.
For example, less than 50 percent of plants survive the winter if no potassium is added in the fourth year of an alfalfa stand. Almost 100 percent of the plants survive if potassium is applied.
“The big one (with) alfalfa is the dramatic effect on winter survival. That’s why growers might say, ‘gosh, the alfalfa didn’t last very long.’ It may just have been that it petered out quicker than it normally would.”
Saskatchewan Agriculture’s website says that few regions of the province are deficient in potassium.
In Alberta, the black and gray wooded soil in the central and northern regions occasionally test low in soil potassium.
Heard said forage growers might be scrimping on potassium in Manitoba because cost has risen substantially compared to the price of alfalfa.
“Potassium has increased four fold in price, (but) hay has not increased four fold in price,” he said. “(But) hay is the crop that needs it more than many of the others.”
