The Importance of P and K: Back to the Basics

By: Tyson Miller | ProVantage Advisor

Farming and crop production have always been a balancing act with Mother Nature, and this year was certainly no exception. The dry conditions experienced at the end of the 2022 growing season carried over into the start of 2023. These conditions were compounded by excessive cool temperatures in the last two weeks of April. As the crop emerged and began to develop into the vegetative stage, some drought-induced deficiencies symptoms appeared — phosphorus and potassium notably. This was not a rare sighting for some of the historically lower performing parts of a field, but it was abnormal for these deficiencies to also show up in higher-yielding and well-fertilized areas, in both corn and soybeans.

So, What Happened?

Dry conditions reduce plant uptake of nutrients, including phosphorus and potassium. Additionally, factors such as soil compaction, side-wall smearing during planting and root pruning further limit the plant’s ability to uptake nutrients during a period of abnormally dry soil conditions like we witnessed (Sawyer, 2000). With whole fields and sections of fields already being low in phosphorus and potassium at the start of the growing season, dry conditions only made the nutrient deficiency symptoms worse. Even some of the fields or sections of fields which started the growing season with adequate P and K levels were impacted by the dry conditions, limiting the plant’s uptake ability of these nutrients.

How Should Growers Respond?

Although we can’t control the rain patterns and in many areas of southeastern Iowa we grow crops without irrigation, we can minimize the factors that reduce nutrient uptake when the weather is favorable so we’re always maximizing our potential. Consider the following:

1. Know the nutrient value of your soil by soil testing every four years. Use grid sampling to get the best representation of your fields high performing and low performing areas. Consider 2.5 acre grids for sampling.
2. Consult with an agronomist to determine the amount of nutrient removal from your fields each year from harvest and at what pace you want to build the “lower than optimum” nutrient levels in your soil.
   • Many factors impact the rate at which you build P and K levels, including your designated budget for dry fertilizer application, application timing, weather, tillage program, etc. An agronomist can help you drill into a potential yield return on your investment in building P and K levels in your soil so you can be profitable while improving your soil.
   • Consider reading the recently updated, February 2023 publication from Iowa State Extension and Outreach about optimum fertility levels for crop production.
3. Phosphorus and potassium are foundational nutrients for crop production and can be maintained at optimum levels with fall applied dry fertilizer applications. Fall applications provide a timeframe for nutrients to be plant-available in the following growing season. Applications can be made using variable rate prescriptions to precisely place nutrients in key locations of the fields for the greatest yield potential and best return on investment (it’s a win-win situation). Finding balance in your soil chemistry through maintaining optimum nutrient levels can also help alleviate compaction in your fields.
4. Consider using dry fertilizer additives, like Trivar, to reduce phosphorus tie-up in your soil. Negatively charged phosphorus ions can form a strong positive bond with positively-charged soil ions and limit nutrient uptake in your crops. Trivar can be blended with dry fertilizer and once active in the soil, can break the soil’s bond to phosphorus and make phosphorus and other micronutrients more plant-available (CHS Agronomy, n.d.).
5. The management of soil pH levels is also a key factor in P and K availability in the soil. Even if you have considered the items above, if your pH balance is off, limited availability of P and K will still exist (Preston, n.d.).

How Can Stutsmans Support Growers with P and K Deficiencies?

If phosphorus and potassium deficiencies are something that you are already seeing, or if you want to get ahead of any potential issues, there are ways we can help.

1. We offer complete soil sampling services, allowing you to stay on top of the nutrient value in your soil.
2. We can make recommendations for crop nutrient removals and nutrient build rates to meet your goals for your fields and budget.
3. We can provide manure sampling lab results. Many fields receive applications of manure as a primary source of nutrients for crop production. There is a lot of variability in the nutrient value of manure, and it’s important to measure the applied nutrients accurately as you consider the next season’s crop production. We have manure sampling bottles available and can process your manure sample in just a few days to help you keep up with your fall workload.
4. We can create custom dry fertilizer blends and custom apply variable rate fertilizer applications. Maximize your trip across the field with a custom blended dry fertilizer tailored to your fields’ nutrient needs and yield goals. We have any and all dry fertilizer products and can blend them together in different proportions based on your crop production goals. We can also deliver products to your farm or field and apply them for you at either a flat rate application or using variable rate technology, taking the work out of getting your fertility management under control.

In recent years, costs for dry P and K fertilizer have trended to all-time highs, pushing some growers to reduce or even eliminate their long-term plans for building P and K nutrient levels. However, markets have begun to swing downward, and costs for dry P and K this fall are less than the highs experienced in recent years. It is the perfect time to re-engage your P and K to more optimum levels in your fields and reduce nutritional deficiencies for the coming year’s crop.

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Sources

CHS Agronomy. (n.d.) Trivar. https://www.chsagronomy.com/trivar.
Preston, C. (n.d.). Soil pH effects potassium and phosphorus fertility availability and Management. eKonomics. https://nutrien-ekonomics.com/news/soil-ph-effects-potassium-and-phosphorus-fertilizer-availability-and-management/#:~:text=Increasing%20the%20soil%20pH%20with,plant%20availability%20(Figure%201).
Sawyer, J. (2000). Potassium deficiency symptoms in corn. Iowa State University Extension and Outreach. https://crops.extension.iastate.edu/encyclopedia/potassium-deficiency-symptoms-corn.