Growers considering a continuous corn program are asking this question: Will I have enough phosphorus (P) and potassium (K) to switch my soybean acres to corn?

The consequences of running short on these two critical plant nutrients have many wondering if they should apply more this spring or just hope they have enough in the soil.

Not enough potassium can lead to poor standability and weak plants. The fear that comes with not enough phosphorus is poor uptake of other needed plant nutrients, purple plants in the spring, and increased nitrate losses.

The problem has been building over the last two years because growers cut back on their P and K applications due to high fertilizer costs and low grain prices. They have been effectively mining the soil reserves that have been built up over many years. Yields have been exceptionally high, so the nutrient mining has been higher than anticipated.

The other issue is how fertilization was handled in the fall of 2005. Many corn/soybean growers will apply the P and K needs for both crops prior to the corn crop. If P and K were added in the fall of 2005 to cover the 2006 corn crop and the 2007 soybean crop, will there be enough P and K when the 2007 soybean crop is replaced with corn? The only way to settle the debate is to soil sample.

SOURCE: Dr. Dan Froehlich, U.S. agronomy manager for Mosaic.

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