Improving Water and Energy Efficiency with K Applications

In recent years, concerns with extreme weather conditions and the amount of water used to successfully grow crops are on the rise. Securing a reliable water supply is one of the most important factors growers must consider to support high-yield agriculture. Given the limited supply of water and energy, farmers must look to improve crop efficiency and resources. Crop production can be increased through a number of practices, including nutrient management.

Proper management and adequate potassium levels can play a critical role in utilizing the water and energy needed to grow crops. Dr. Jeff Volenec, Professor of Agronomy at Purdue University, studies the physiological basis for differences in growth, yield, and stress tolerance of crops. In his research, Volenec found that under ideal conditions, alfalfa takes about 1,500 pounds of water to produce one pound of dry matter, and corn takes 500 pounds of water to produce one pound of dry matter. In areas with poor potassium nutrition, it takes more water to produce the same amount of dry matter.

“If water is limited, crop growth will be limited,” he said. “Sufficient potassium nutrition helps farmers maximize water usage, which helps them reach optimal yields.”

The Relationship Between Potassium and Water

Plants depend upon potassium to regulate the opening and closing of stomates — the pores through which leaves exchange carbon dioxide, water and oxygen with the atmosphere. Proper functioning of the stomates is essential for photosynthesis, water and nutrient transport, and plant cooling.

When potassium moves into the guard cells around the stomates, the cells accumulate water and swell, causing the pores to open and allowing gases to move in and out freely. When water supply is short, potassium is pumped out of the guard cells. The pores close tightly to prevent water loss and minimize drought stress to the plant.

If potassium supply is inadequate, the stomates become slow to respond and water vapor is lost. Closure may take hours rather than minutes, or never fully complete. As a result, plants with an insufficient supply of potassium are much more susceptible to water stress.

“A lot of water is expelled relative to the amount of carbon dioxide going in,” said Volenec. “Potassium is important to moderating water loss, especially when plants are under mild or moderate water stress conditions.”

Cooling the Planet

In addition to letting in carbon dioxide, potassium allows water vapor to leave the leaf, which helps cool plant tissue.

If the stomates close tightly, the temperature inside the plant increases. Internal plant temperatures can increase 5 to 10 degrees above the ambient temperature, which can cause metabolic issues in the plant and reduce growth.

In extreme heat or drought conditions, plants curl their leaves to reduce the surface area exposed to the sun. As a result, the plant takes in less energy and light, reducing its growth and energy efficiency.

Reducing Yields

Potassium is also an important building block for starch and protein formation in the plant; it helps the plant convert energy and water into grain. Potassium is essential to the enzymes that help build starch and also provides the energy to produce proteins within the plant. In plants, potassium activates as many as 60 enzymatic and plant hormonal reactions, regulating many physiological and biochemical processes.

“When potassium is limiting, the plant might have problems producing vegetative tissues and seed. This can reduce yield,” said Volenec.

For example, plants growing in soil testing very low in potassium will likely produce 250 viable seeds with full starch content, as opposed to growing more seeds that are nonviable, containing only half the starch content. Since inadequate potassium levels decrease the plant’s ability to produce energy efficiently, the number of seeds produced is lowered to ensure adequate starch content in those produced. Therefore, less yield is achieved. In forages, such as alfalfa, inadequate potassium levels could result in reduced regrowth after the first cutting and therefore, limited yield.

Improving Efficiency and Yields

Overall, Volenec emphasized the role that potassium plays in helping a plant grow. He advised farmers to follow recommended rates for their crop to maximize the plant’s water and energy use efficiencies.

Tools such as the eKonomics ROI Calculator and the Nutrient Removal Calculator can help farmers to estimate their potassium needs to maximize water and energy efficiency and yields. Farmers with fields testing under the critical levels should consider building up their soil fertility levels. During the growing season, farmers can also visit eKonomics for tips on monitoring nutrient deficiency symptoms that may arise.