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Optimizing Potassium Critical for Top Yields

27 January 2011

Soil test trends coupled with environmental factors indicate applying potassium (K) fertilizer may be more important than ever for optimum crop yields.

According to studies from the International Plant Nutrition Institute (IPNI), soil test K levels continue to decrease, and as a result, the percentage of soils across North America in negative balance for K continues to rise.

"Research at Ohio State shows that yields increased as soil test K increased above critical soil levels," explains Dan Froehlich, agronomist with The Mosaic Company. "A standard benchmark is that potassium uptake for a 180-bushel corn yield is 240 pounds of potassium per acre. The critical level of potassium in the soil for optimum performance is approximately 165 ppm.

"The Ohio State results show yields increased as K increased to 200 ppm and 278 ppm. Nitrogen use also was enhanced as soil K levels increased," Froehlich adds.

Agronomic and environmental conditions also play a role in the availability of nutrients for plant uptake. These factors make supplemental K even more important to optimize yields.

"Cool, wet years set up agronomic challenges for crops that exacerbate the impact of limited soil nutrients," says Steve Phillips, Southeast U.S. region director with IPNI.

"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 K. Continued wet conditions make the situation more complex," Phillips explains.

Insuficient K 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.

Prolonged cool temperatures plus wet, compacted soils can cause irreparable damage to yield potential since more than 50 per cent of the total K is taken up by corn plants in the irst 50 days. Compaction and wet soils also may limit K uptake shortly before pollination when corn plants remove more than 15 pounds of K2O per acre per day.

"Over time, continued removal of K without annual fertilizer application will lower soil test levels, and yield loss will occur because K removal is a direct contributor to crop yield," says Phillips.

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