Monday, October 28, 2013

Enough with the Potassium, Already!

Since the chemical age of agriculture that began in the 1960s, potassium chloride (KCl) - a common salt known as potash - has been widely used as a major fertilizer in the Corn Belt.

Now, University of Illinois soil scientists are raising serious concerns with agriculture's 50-year potassium habit with research showing that testing soils for potassium is of no value for predicting its availability and that KCl fertilization seldom pays.

The findings came from a field study that involved four years of biweekly sampling for K testing with or without air-drying. Test values fluctuated drastically, did not differentiate soil K buildup from depletion, and increased even in the complete absence of K fertilization.

Explaining the increase, researcher Saeed Khan pointed out that for a 200-bushel corn crop, "about 46 pounds of potassium is removed in the grain, whereas the residues return 180 pounds of potassium to the soil—three times more than the next corn crop needs and all readily available."

Khan emphasized the overwhelming abundance of soil potassium, noting that soil test levels have increased over time where corn has been grown continuously. "In 1955 the K test was 216 pounds per acre for the check plot where no potassium has ever been added. In 2005, it was 360."

A similar trend has been seen throughout the world in numerous studies with soils under grain production.

KCl fertilization has long been promoted as a prerequisite for high nutritional value for food and feed. Yet, researchers have found that the qualitative effects were predominantly detrimental, based on a survey of more than 1,400 field trials reported in the scientific literature.

"Potassium depresses calcium and magnesium, which are beneficial minerals for any living system. This can lead to grass tetany or milk fever in livestock, but the problems don't stop there," Khan pointed out.

"Low-calcium diets can also trigger human diseases such as osteoporosis, rickets, and colon cancer. Another major health concern arises from the chloride in KCl, which mobilizes cadmium in the soil and promotes accumulation of this heavy metal in potato and cereal grain. This contaminates many common foods we eat—bread, potatoes, potato chips, French fries—and some we drink, such as beer. I'm reminded of a recent clinical study that links cadmium intake to an increased risk of breast cancer."

The Illinois researchers see no value in soil testing for exchangeable potassium and instead recommend that producers periodically carry out their own strip trials to evaluate whether potassium fertilization is needed. Based on published research cited in their paper, they prefer the use of potassium sulfate, not KCl.

Sources: University of Illinois College of Agricultural, Consumer and Environmental Sciences;
"The potassium paradox: Implications for soil fertility, crop production and human health" by Saeed Khan, Richard Mulvaney, and Timothy Ellsworth posted October 10, 2013 by Renewable Agriculture and Food Systems.

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Artwork: 1909 Potash Print Ad

Monday, October 21, 2013

Waterhemp Becoming a Superweed

Studying the first known case of waterhemp with resistance to HPPD-inhibiting herbicides such as Callisto, weed science researchers at the University of Illinois have identified two unique mechanisms in the plant that have allowed the weed to “get around” these herbicides.

“Waterhemp is very diverse, which you can see in the field. There are red plants, green plants, tall, short, bushy—basically a germplasm pool. If you  keep spraying the same herbicide over and over, eventually you’re going to find that rare plant that can resist it,” said Dean Riechers, a U of I Professor of weed physiology,

What the U of I researchers find alarming is that waterhemp resisted the herbicide in much the same way that corn naturally resists HPPD-inhibiting herbicides.

“It mimics corn but also mimics the super bacteria that are resistant to all the antibiotics out there. Weeds are kind of like bacteria in that respect; at least this population is. Whatever active herbicide we throw on it, with the exception of glyphosate, it doesn’t work anymore,” Riechers said.

The study was prompted in 2009 when a continuous seed corn grower from central Illinois realized the HPPD-inhibiting herbicides he was using were no longer killing waterhemp plants, which by then had grown into a mat of weeds across the field.

“It became obvious to the grower that something was wrong, but it probably started years before that,” Riechers said, adding that the grower had been planting continuous seed corn every year, using HPPD-inhibiting herbicides for at least eight years in a row.

“Mesotrione and atrazine are normally two very good herbicides that are safe on corn but still kill waterhemp,” Riechers said.

Although the 2009 incident was the first to document this type of resistance, Riechers said four or five other locations in the Midwest have since reported similar occurrences.

“It doesn’t appear to be isolated because it looks like there are other resistant populations coming up,” Riechers said. “The concerning thing is that some of these fields actually did have corn and soybean rotations. They weren’t just growing corn, they were rotating, which is what you’re supposed to do. But it still became HPPD resistant, and we’re not sure how that happened.”

Rong Ma, one of the researchers on the study, said growers should consider not using the same herbicide mode of action repeatedly. “For example, don’t use HPPD-inhibiting herbicides alone for several years in a row because it is then easier for weeds to develop resistance," she said

“Growers could also use tillage because there’s no resistance to tillage,” Riechers pointed out. “Farmers use no-till systems, often plant in narrow rows, and for the most part have gotten away from tillage for weed management. We have aided waterhemp in becoming a problem by not using tillage, using the same chemical over and over, and by not rotating crops.”

Source: Dean Riechers University of Illlinois, tel:+1 217-333-9655

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Artwork: Waterhemp