This is the fourth column in a series on phosphorus (P) management proficiency. Last week I wrote the about (Part 1) phosphorus management evaluation in a continuous corn study done in Nebraska. Today, I will dive into some other research findings besides yield and the fertilizer rates applied between the different management approaches. This research was published in the 2018 Soil Science Society of America Journal by UNL faculty Wortmann, Shapiro, Shaver, and Mainz. One of the objectives of their research was to determine if another fertilizer P management approach was superior to the currently recommended UNL sufficiency approach for continuous corn production.
As a review from last week, there were five P treatments or approaches: no applied P, P applied according to UNL sufficiency or deficiency correction recommendation, P applied to replace P removal in the previous grain harvest, build/maintain soil test P at 25 ppm, and build/maintain soil test P at 35 ppm (Bray P-1 soil test in top 8-inches). In this 6-year Nebraska study, the best management approach for continuous corn yield and fertilizer input cost was P applied to replace P removal in the previous grain harvest. It performed as good or better in terms of yield compared to the other approaches and fertilizer cost was substantially less than maintaining soil test levels at 35 ppm.
Part 2, what about plant P uptake and grain P concentration effects? Total plant P uptake at black layer was frequently higher with the approach to maintain soil P at 35 ppm compared to the other approaches. Likewise, grain P concentration was also frequently higher with the approach to maintain soil test levels at 35 ppm. What does this mean? The corn crop takes up extra phosphorus without an increase in grain yield at soil test levels near 35 ppm. This is called luxury consumption. Therefore, more pounds of phosphorus are being removed off the field in the grain, but without extra bushels, which does not generate more revenue at the elevator. The study found that we cannot store phosphorus in the soil bank the same way we do at a financial bank, it is actually the reverse, and we are getting charged interest for storing phosphorus in the soil bank through luxury P consumption by the corn crop.
Building soil test levels to 35 ppm in the top 8-inches resulted in the following: No increase in yield, corn charging “phosphorus interest” on extra P in the soil bank, and higher P fertilizer cost. This multi-site and multi-year research in Nebraska suggests that neither the current UNL sufficiency approach nor the maintain soil test P at 35 ppm approach were the best phosphorus management plans for continuous corn production. Rather middle of the road approaches including P applied to replace P removal in the previous grain harvest or maintain soil test at 25 ppm would be preferred. Researchers suggested the removal (P applied to replace P removal in the previous grain harvest) approach be used instead of the current UNL sufficiency recommendation when soil test P is less than 20 ppm, but that maintaining soil test P above 25 ppm was not justified either.
Contact me with questions or suggest topics for me to write about in regards to phosphorus management at or 402-821-1722. Know your crop, know your tech, know your bottom line at croptechcafe.org.
