Watch for K Deficiency
As the crops are finally getting going, potassium deficiency is showing up in some fields. Potassium deficiency symptoms occur on the edges of the lower leaves on most plants.
In corn and soybeans, the symptoms start as yellowing on the edges of the lower leaves. Eventually the edges of the leaves will turn brown and the whole leaf may die. In alfalfa, the symptoms start as small spots on the edges of the leaves which eventually grow together and end up as yellow and finally brown leaf edges. As the deficiency becomes more severe, the symptoms will progress higher up the plant.
Plants take up about the same amount of K as they do N. Also note that removal of K depends on how the crop is harvested. In spite of the large uptake of K, relatively small amounts of K are removed in grain. However, when the whole plant is harvested as silage and hay crops, a very large amount of K is removed. For example corn grain at 200 bu/A removes 60 lb K2O/A, but if the same corn crop is harvested for silage, the removal is 240 lb K2O/A. This can make a big difference in the K levels in different field on a farm. Many fields that get a lot of manure in the corn part of the rotation have good reserves of potassium. Fields receiving little manure or that are late in the forage rotation can have fairly low soil test levels and fields coming out of forages often are lowest in K.
As always, begin with a soil test. Even though it maybe the last minute, the Ag Analytical Services Lab at Penn State normally has about 2 day turn-around with soil samples. So if you overnight your samples to the lab and have signed up for free web access to your results you can still have your results in time to make topdressing decisions. Other labs have similar service. For forage crops low in K, fertilize between cuttings. If you have a forage field with K deficiency, it is especially important to correct this before going into the winter. Potassium is very important for winter survival. For corn or soybeans, if the soil test is low and/or the crop is showing deficiency symptoms, topdressing with potash will be beneficial. Because K is not very mobile, this topdressing will not usually give as good a result as if the soil test was optimum or the K was applied preplant, but it will help. Since the soil needs a K application at some point anyway, if it is practical, you may as well apply it now and get what you can out of it for the current crop and get a start on building K for the following crop.
One thing to keep in mind this year is that wet conditions at planting can result in sidewall compaction which can produce severe K deficiency. If the young plants are showing K deficiency, but the soil tests are optimum or better, this could be the problem. If this is the case adding K, may not provide any benefit. Hopefully, the roots will eventually get past the sidewall compaction and get the K that is already available in the soil.
Low Potassium Levels Linked to Increased Risk of Chronic Kidney Disease
New research determined a link between potassium levels, with the risk of developing chronic kidney disease in a mostly white population.
Potassium is a mineral that aids in proper bodily functioning. Levels of potassium are tightly regulated by the kidneys to help control blood pressure. In chronic kidney disease, a condition that results from kidney malfunction, patients may suffer from unregulated potassium levels in the blood. Hypokalemia is a condition when potassium levels are low (<3.5mmol/L) and hyperkalemia (>5.0 mmol/L) results from increased levels of potassium. Chronic kidney disease (CKD) patients with either hypo or hyperkalemia have a higher risk of mortality, heart attack, and hospitalization. Previous kidney studies have also found that hypokalemia may lead to kidney damage. However, the evidence demonstrating the association of hypokalemia with risk of developing CKD is not yet established.
In a recent study published in Plos One, researchers conducted a prospective study to examine the association between potassium blood level and the risk for developing CKD in predominantly white population. The study enrolled 6,000 participants with a urinary albumin concentration of 10 mg/L, a metric for hypertension and risk for CKD. Furthermore, the study also enrolled 2,592 participants with <10mg/L urinary albumin concentration. Participants who were diabetic, who already suffered from CKD and who were pregnant were excluded, leaving 5,130 participants. Circulating potassium levels, glomerular filtration rate (GFR), serum creatinine, and cystatin C were measured. Hypokalemia was defined as <3.5 mmol/L, normokalemia at 4-4.4 mmol/L, and hyperkalemia at a concentration equal to or greater than 5.0 mmol/L. CKD was determined by low GFR (<60ml/min per 1.73m2) and/or low urinary albumin excretion (UAE) (> 30mg/24h).
The researchers found mean plasma potassium levels of 4.4 mmol/L across the 5,130 participants. Hypokalemia had a low prevalence at 0.5% while hyperkalemia was slightly more common with a3.8% prevalence. Interestingly, participants with hypokalemia do not consume alcohol or smoke. They were also likely to be older, less educated and have high blood pressure as well as likely users of beta blockers and diuretics. In contrast, participants with hyperkalemia were likely to be male, to smoke, and to be White. They also have a higher UAE and non-usage of diuretics.
With regards to hypokalemia and risk of CKD, with a median follow-up of 10.3 years, researchers found that 753 participants eventually developed CKD. Participants with hypokalemia were about 5 times likely to develop CKD than those with normal potassium levels, and the risk further increased in participants who used diuretics. Participants with hyperkalemia, however, were not likely to develop CKD. Furthermore, the link between potassium levels with the risk of developing CKD changed when subjects used diuretics. In non-hypokalemic participants who used diuretics, researchers found an increased risk of CKD. Overall, the researchers concluded that hypokalemia was associated with a higher risk of CKD regardless of use of diuretics. The precise mechanism as to how hypokalemia induces kidney damage remains unclear. The current study could not yet be generalized to a broader population due to a lack of diversity in the participants. It remains to be seen whether a similar association between hypokalemia and CKD would be observed for other patients from other racial ethnicities.
Dietary reference values: advice on potassium
EFSA has set dietary reference values for potassium as part of its review of scientific advice on nutrient intakes. Potassium is an essential mineral in the human diet and plays an important role in many physiological processes in the human body including the distribution of body fluids, nerve impulse transmission and muscle contraction.
The Panel on Dietetic Products, Nutrition and Allergies (NDA) defines daily adequate intakes (AIs) for potassium as follows:
750mg for infants aged 7-11 months.
800mg for children aged 1-3 years.
1,100mg for children aged 4-6.
1,800mg for children aged 7-10.
2,700mg for children aged 11-14.
3,500mg for adolescents aged 15-17.
3,500mg for adults including pregnant women.
4,000mg for lactating women.
Low potassium intakes are associated with raised blood pressure and increased risk of stroke. The Panel considered data on these relationships when setting DRVs.
Food sources of potassium include starchy roots or tubers, vegetables and fruit, whole grains, dairy products and coffee.
EFSA received comments and input on the draft scientific opinion during a six-week public consultation in mid-2016.
Try to get your potassium from foods, not supplements
DEAR DOCTOR K: I have high blood pressure. Should I take a potassium supplement?
DEAR READER: This is a great question, but before I answer, let me take a step back to explain the connection between potassium and blood pressure.
Tens of thousands of years ago, our ancestors survived on wild animals and a variety of plant foods. This diet delivered plenty of potassium but scant sodium. Today, the average American diet contains about twice as much sodium as potassium, as a result of the high levels of salt in processed foods. This sodium-potassium imbalance is thought to be a major contributor to high blood pressure.
Now, back to your question. The short answer is no, you should not take potassium supplements unless your doctor prescribes them. People on blood pressure medications, in particular, need to be careful about potassium supplements.
Many blood pressure medications can lower your potassium level. Very low potassium can lead to dangerous heart rhythms. Many commonly prescribed diuretics lower potassium levels. If you are taking potassium-lowering diuretics, your doctor will check the level of potassium in your blood. If it is low, the doctor may prescribe potassium supplements.
But other types of diuretics, and other commonly prescribed blood pressure medicines, can raise potassium levels. Examples of such drugs are the diuretic called spironolactone, the drugs called ACE inhibitors, and drugs called angiotensin receptor blockers (ARBs). Common painkillers such as ibuprofen (Advil, Motrin) or naproxen (Aleve) can raise potassium levels. Abnormally high potassium levels also can cause dangerous heart rhythms.
If you are taking any medicines known to either raise or lower your potassium to dangerous levels, your doctor should periodically check your blood potassium level. Keeping that level in the correct range is important. This mineral also plays a key role in the function of nerves and muscles, including heart muscle.
Your kidneys help regulate potassium levels in your blood. They tend to keep your potassium level from going abnormally high or low. But age and medical conditions may impair kidney function. As a result, the kidneys are not as good at protecting you against abnormal potassium levels.
The FDA limits over-the-counter potassium supplements to less than 100 milligrams (mg). However, grocery stores carry salt substitutes that may contain much higher amounts of potassium. People trying to curb their sodium intake may use salt substitutes. That's a bad idea if you take a blood pressure medicine that tends to raise potassium levels.
Your best bet is to get your potassium from foods instead of pills. Many fruits and vegetables are rich in potassium. Spinach, sweet potatoes, cantaloupe, bananas and avocado are all good sources. Potassium-rich diets help control blood pressure and also lower your risk of stroke.
Another connection between potassium and high blood pressure is a rare condition of the adrenal glands that can cause both high blood pressure and very low blood potassium levels.
So if you have high blood pressure, ask your doctor what your potassium level is. If the doctor hasn't checked your potassium, gently suggest that it might be a good idea.
New Studies Show Shrinking P + K in Farmer Fields
More and more fields are lacking in P and K, according to recent testing by separate DuPont Pioneer and PotashCorp studies.
A new DuPont Pioneer study, comprised of more than 22,000 soil samples, suggests phosphorus (P) and potassium (K) levels are deficient in a “significant” number of fields tested. The research also confirmed that P and K deficiencies hurt both yields and grain quality, according to agronomy research manager Andy Heggenstaller.
“Growers often think first of nitrogen management when they consider soil fertility decisions because of its important influence on corn production,” he says. “However, deficiencies in P and K can inhibit yields over the long term in both corn and soybeans, limiting profit potential over time.
Testing over a 12-state geography, DuPont Pioneer found P and K deficiencies in a “significant amount” of tested fields. Heggenstaller notes that many states have modified their p and K fertility recommendations and encourages farmers to stay current on the higher nutrient requirements demanded by today’s more productive hybrids and varieties.
At PotashCorp, director of agronomy Robert Mullen says his company conducted a separate state-by-state nutrient balance analysis and also found major P and K deficits. In some states, including Iowa, Minnesota, Wisconsin, Michigan and Arkansas, more than half of the samples were “below critical level” for both P and K.
Mullen says farmers can conduct a simple five-step check of their fields to get the upper hand on potential nutrient deficiencies.
1. Visual assessment. “When in the field, nutrient deficient crops can often be identified by discoloration of the crop,” he says.
2. Soil testing. Mullen recommends collecting about 10 to 15 samples from both unaffected and affected soil areas to get an accurate representation of their field.
3. Conduct a plant tissue analysis. Like diagnostic soil testing, farmers should collect samples form unaffected and affected area, Mullen says. Collect twice in the season – once early season and once midseason, he suggests.
4. Analyze historical information. “If farmers know their fields have a proven history of micronutrient issues, they can skip to step four and be prepared to apply fertilizer to deal with that issue,” Mullen says. “During this step farmers should consider that there is a chance some of their crops won’t show any symptoms, but the fields will produce yields that are lower than predicted. This is an indication of hidden hunger, which can be fixed by paying close attention to the soil test results.”
5. Prescribe corrective course of action. Hopefully, steps 1 through 4 reveal the solution needed, Mullen says. Even if it doesn’t, consider taking an educated guess and apply strips within the field to see what takes care of the problem, he says.
“With nutrient balance levels declining nationwide, it’s important for farmers to be vigilant and identify deficiencies in their crops before it’s too late,” Mullen says. “After conducting this process, there is a chance not every problem will be solved, but these five steps will help get your yields back on the right track.”