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Failure to sustain phosphorus (P) and potassium (K) levels will result in “overdraft” fees of lower yields and weaker plant health. No one likes surprises that hit the pocketbook. “Even if you aren’t surprised, no one wants to pay an extra fee,” notes Eric Wilson, Northeast Iowa Field Agronomist for Beck’s. “Yet, many corn and soybean farmers are paying such a fee.”
That fee is in the form of lost yields or additional costs from low soil-test levels of P and K. “Of all the factors that influence final yield, base fertility is the most important factor the farmer can control,” says Wilson. “Much like a slow-moving train headed for a cliff, if we don’t maintain base fertility, yields will eventually drop and they’ll drop hard and fast.”
Low Soil K Problems:
Wilson sees that train already rolling in some fields--racking up “overdraft fees” for farmers. One of the first places you’ll see the impact of low soil K levels is in corn standability, he notes. “Potassium is essential for cell wall structure, stress signaling and overall plant health. In corn, adequate levels of K fertility are critical for stalk integrity, nitrogen use efficiency and the plant’s ability to stave off foliar disease,” says Wilson.
“Corn plants short of K for grain fill will cannibalize their stalks and leaves for K,” he continues. “This ability to cannibalize stalks helps produce ears, but will also contribute to down corn and ears that don’t end up in the combine.”
Low K levels also impact the effectiveness of nitrogen applications. Wilson explains that nitrogen and K are closely linked. “If your soils are short on K, you will probably have to apply more nitrogen to get the result you want.”
Low soil K levels can also impact soybean profitability--not only in yield, but also in the form of extra fungicide applications. Wilson cites a recent Iowa State University study finding that the incidence of soybean diseases tends to drop off as soil test levels of K increase to optimum levels. “If a plant is well fed, it’s more likely to be healthy,” says Wilson. “If we’re coming up short on fertility on our soybean crop, you could make the argument that maybe fungicide applications are covering for a lack of fertility.”
Steps To Maintain Fertility:
Wilson sees the problem of declining soil P and K levels the result of increasing yields and more expensive fertilizer. Corn and soybean crops are removing more P, K and other nutrients from the soil as yields increase. However, many farmers aren’t responding by maintaining their base fertility (see chart).
Wilson understands farmers can only apply what they can afford. “Nevertheless, it’s more important than ever to understand the importance of maintaining base fertility to avoid ‘overdraft fees’ and set themselves up for long-term success.”
The most valuable first step toward ideal fertilizer management is regimented soil tests. “If you’re not soil testing, you really have no idea what’s going on in your fields,” he explains. Soil test information can help identify places where fertilizer costs can be reduced and redistributed to areas of greater need.
Wilson adds, “If money is tight, rather than having all your acres soil sampled every four years, consider spreading out the costs by having a fourth of the acreage sampled each year.
“While ideally you will want to over apply P and K to build a buffer in your soils, if your budget doesn’t allow for this, at minimum, you’ve got to put back what your crop took off.
“With lower grain prices and higher input costs, it’s more critical now than ever to avoid as many surprise ‘overdraft fees’ as possible,” says Wilson.
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