Phosphorus and Potassium Fertility for Corn and Soybean Production

In order to help maximum yield potential, it’s important to understand how phosphorus (P) and potassium (K) are utilized in corn and soybean production. Skipping or limiting P and K applications can decrease stress tolerance and consequently reduce yield potential.

Phosphorus is a nutrient required in relatively large amounts by plants. It has a relatively short range of movement in the soil and is considered an immobile nutrient. Plants need P for growth throughout their life cycle, especially during early stages of growth. The primary role of P is to store and transfer energy that is produced through the photosynthesis process to be used during growth and reproduction. The effects of P can increase water efficiency, promote early maturity and improve stress mitigation which all can lead to increased yields. Corn plants increase P uptake rapidly after V6 growth stage and can continue until near maturity. While soybeans demand for P is greatest during pod and seed development where more than 60% of P ends up in the seeds and pods.

Potassium is generally found in the soil in large amounts, but is not readily available for plant uptake to aid in growth and development. Potassium is associated with movement of water nutrients and carbohydrates within the plant. These functions stimulate early growth, increase protein production, improve the efficiency of water use and enhance resistance to diseases and insects. Adequate K levels are important to maximize soybean yield potential. Peak usage of K occurs from flowering through early pod development. A shortage of K at this time can result in yield loss without obvious foliar symptoms.

Also the severity of stalk rot in corn can be minimized with an optimum balance between K and N levels in plant tissue. Potassium has been associated with improvement of stalk strength. When corn plants take up sufficient K stalk dry is moderated after maturity and the risk of lodging can significantly be reduced. In corn K uptake increases rapidly after about the V6 growth stage. When deficiency symptoms become visible K demand is large and supplies are low. Understanding both crop nutrient uptake and removal can help match plant nutrient needs for a targeted yield goal. For corn each bushel harvested per acre removes .45 lbs P and .3 lbs K, in a silage situation K removal is much higher at an additional 8 lbs for every ton silage harvested. For soybeans crop removal varies around .85 lbs of P and 1.45 lbs of K are needed for every bushel harvested.

Although margins are tight in farming right now a sound fertility program is needed to ensure high yield environments in the future.

Thank you, Tom Arndt

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