Applying potassium fertilizer may be more important than ever this year. According to a study released last fall by the International Plant Nutrition Institute (IPNI), 39% of the soils across North America were in negative balance for potassium, and this study didn't take into consideration the cutbacks of the 2009 growing season.

The decreasing soil levels for potassium, combined with agronomic factors held over from the 2009 growing season, may place 2010 yields in greater jeopardy for nutrient deficiency than what is normally expected.

"Cool, wet years like 2009 set up agronomic challenges for crops which exacerbate the impact of limited soil nutrients," says Steve Phillips, Southeast region director with IPNI, a not-for-profit, science-based organization with a focus on agronomic education and research support. "Season-long excess soil moisture and resulting compaction from planting, spraying and harvest cause poor soil aeration.

"Oxygen is required for root nutrient uptake; damp, compacted soils are lower in soil oxygen, thus limiting plants' ability to uptake potassium. If we see continued wet conditions in 2010, the situation only becomes more complex."

Potassium is very important for plant function as it activates more than 60 different enzymes and plays an important role in photosynthesis and plant metabolism. It's particularly essential in protein crops, such as soybeans, for converting nitrogen to protein and also plays a role in reducing plant disease.

Insufficient potassium may lead to reduced nitrogen uptake, less developed roots, lower protein content, greater susceptibility to water loss and wilting, as well as weaker stalks that are more prone to lodging.

Another season of prolonged cool temperatures plus wet, compacted soils could cause irreparable damage to yield potential since more than 50% of the total potassium is taken up by corn plants in the first 50 days. Compaction and wet soils also may limit potassium uptake shortly before pollination when corn plants remove more than 15 pounds of potassium oxide (K2O) per acre per day.

“Over time, continued removal of potassium without annual fertilizer application will lower soil test levels. Yield loss will occur because potassium removal is directly related to crop yield,” Phillips says.

Low potassium levels are detrimental to yield levels

"Yield losses are inevitable when nutrient levels drop below certain levels," explains Dan Froehlich, director of agronomy for The Mosaic Co. "A 180-bushel corn crop requires 240 pounds of potassium oxide. The critical level of potassium in the soil for optimum performance is approximately 165 ppm, and yield losses can be severe when the soil potassium levels drop below 165 ppm."

Froehlich says studies show that when soil potassium levels are at 100 ppm and the field does not receive potassium fertilizer, yields will only be about 85%, compared to soils that are not below the critical level.

"We can only wonder where 2009 yields may have been if essential nutrients had been at recommended, balanced levels on 100% of corn acreage," Froehlich says.

Consider 15% additional yield on the 39% of the acres that have a negative balance for potassium, he adds.

"We encourage growers to visit with their local fertilizer retailer soon to get a handle on the nutrient balance situation in their area and to begin planning for spring application, and choosing the products, rates, application method and timing to best meet the nutrient needs of the 2010 crop," Froehlich says. "With a clear picture of the situation on their own farm, they can develop a fertility plan for 2010 that will meet the crop nutrient needs and optimize their production and profitability."