Don’t Forget the P and K After Harvest

With grain bins filled, farmers should be turning their attention to field fertility. While nitrogen may be the most important nutrient for crop production, phosphorus (P) and potassium (K) are two elements that shouldn’t be forgotten when creating a fall fertility program.

Regular soil testing is the foundation of sound fertility. Soil samples should be collected every two to four years to provide the best diagnostic information.


“One of the most important investments you can make is finding out what your soil pH is,” said Matt Montgomery, Pioneer Field Agronomist. “Once pH is determined, managing it accordingly is paramount.”

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Soil test results can be used in conjunction with P and K removal rates to develop fertilizer recommendations that best fit fertilizer price, management style and risk position. Rate recommendations can be developed to maximize short-term returns following a nutrient sufficiency approach, or to provide consistent, long-term profitability following a build-and-maintain approach.

Biannual P and K applications can be equally as effective as annual applications, as long as biannual application rates account for the nutrient needs of two crops.

Additionally, various banded and starter application methods have been evaluated for increasing P and K efficiency. Specific cases where banded and starter P and K applications may be beneficial include:

  • Heavy or wet soils that are slow to warm in the spring
  • Soils that have a high degree of P and/or K variability
  • No-till, when there is evidence of P and/or K stratification at the soil surface
  • Strip-till and zone-till, for which P and K are typically banded at planting
  • Calcareous and high pH soils

Farmers should consult state extension guidelines or local sales professionals for region-specific rate recommendations. Precision soil sampling and variable rate technology can help match P and K inputs to crop needs and improve return on fertilizer investment.