A common question posed by Alabama cotton producers is, “Are Auburn soil tests recommending enough potassium (K) to meet the demands of new, higher-yielding cotton varieties?”
This is a valid challenge, considering that Auburn’s current soil test recommendations are based on cotton varieties which are no longer in production.
To address this question, we set up K rate field trials at five locations in Alabama during 2018 and 2019 growing seasons.
The locations for the study were represented a variety of soil types and climates within Alabama.
At three of our locations, initial soil test K was rated “medium,” and 60 lbs of K2O (that’s 100 lbs of 0-0-60) per acre would have been recommended to maximize yield according to Auburn recommendations.
At our other two locations, soil test K was rated “high” and no additional K2O was recommended according to Auburn recommendations.
In 2018, we saw a yield response to K2O rates above Auburn soil test recommendations at one of our locations, which tested “medium” in soil test K. This yield response was observed at the E.V. Smith Research Center in Shorter where yield was increased by approximately 200 lb/A lint when K2O rate was increased from 60 lbs per acre to 90 lbs per acre.
However, at every other location and year, we observed no yield benefit from adding additional K2O.
An example graph showing lint yield according to K2O rate at the Tennessee Valley Research and Extension Center in Belle Mina is shown here. Even though this soil tested “medium” in soil test K, we did not see a yield response to added K2O.
Yields averaged approximately 2,000 lb/A lint acre, regardless of K2O rate, and that indicate our current soil test recommendations can meet the demand of new, high-yielding varieties.
Overall, our first two years of data indicate that Auburn’s current K recommendations are adequate to maintain maximum cotton yield.
Many commercial laboratories recommend K2O rates above Auburn recommendation. However, the high rates recommended are likely not economical. Other factors, such as drought and soil compaction, can result in K deficiency in the field. These trials will continue in the 2020 growing season.