Watch Those Soil K Levels for Maximizing Yields

K Levels

As the 2011 growing season closes out, it is time to think carefully about how to maximize yields in 2012. Of course there are numerous factors which will impact grain yields this next year, but I thought I would address one important factor that we can control. It can have a major impact on plant health, standability, and grain yield. Let’s talk about the nutrient potassium.

A standard benchmark for a 180 bu/acre corn yield is that it will uptake 240 lbs. of potassium per acre. To supply this level of K to the plants the soil test must show 165 ppm of the nutrient. As yield expectations increase above this level, typically plant populations and units of nitrogen are also increased. Given these trends and expectations, the standard benchmark levels of K may not be enough. Studies have shown that increasing K levels in the soil test to 200 – 250 ppm enhanced grain yield and standability as nitrogen units and plant populations were increased. One study showed that 40 and 100 additional ppm of K over and above the 165 ppm level increased corn grain yields by 40 and 70 bu/acre, respectively. Nitrogen application was held at 160 lbs. of N/acre; an excellent return on investment.

A corn crop that does not have access to adequate amounts of K may have poor root development, low protein content in the grain, susceptibility to water loss and wilting, susceptibility to diseases, and weak stalk strength. Therefore, any environmental stress that the crop encounters in its growing season will be exaggerated if the plant has not had optimum availability of K. One of the largest stresses that a plant may encounter is high grain yield. In some high yield environments, this yield stress can lead to stalk lodging from the plant cannibalizing itself. If adequate K levels are available to the developing plants, the plant will have a better chance of having healthier, stronger stalks at harvest. And the grower will have a much happier combine season.

Compaction in wet soils can limit the uptake of potassium. So, whether the K is available but is not
in optimum quantities or it is not available due to other factors like compaction, the result is the same. Optimum performance will be compromised and it begins very early in the plant’s growth stages. More than 50% of the total K that is required by the plant is taken up in the first 50 days of plant growth. In the critical weeks just prior to pollination, the corn plant removes over 15 lbs. of potash from the soil per day. It is no wonder why we see such positive responses from keeping optimum levels of K available to our valuable crop.

In closing, I recommend fertilizing for a great crop and avoid compaction. Keep all the nutrients and micronutrients in proper balance with your expectations and cultural practices. Conduct some studies of your own to see if increasing K levels beyond the soil test recommendation gives you a positive return. Don’t let inadequate K levels be a limiting factor to achieving maximum yields and plant health.