Fall Residual

set your crops up for success

Set your crop up for success by planning ahead and spreading the workload between post-harvest and spring by applying fall chemical and fertilizer. Below are some questions you may have regarding Phosphorus and Potassium. As always, contact your Agtegra Agronomist for more information.

1. What are the benefits of managing Phosphorus and Potassium in the fall?

The key benefit to applying phosphorus and potassium in the fall is it allows some of the operational work to be done so next spring’s workload will be less.  Fall application will also allow these nutrients to work through the soil profile somewhat. That said, fertilizer application timing (specific to phosphorus and potassium) has less agronomic differences between Fall and Spring applications, and both timings generally have good effectiveness. Both phosphorus and potassium are non-mobile in the soil so there is very little risk of them moving out of the root zone over the winter, whereas mobile nutrients such as nitrogen and sulfur are at greater risk of movement in the soil profile when applied in the Fall.

2. What effect can Phosphorus and Potassium levels have on your yield?

Phosphorus and potassium are both macronutrients that directly impact a crop’s yield through plant health and rate of plant growth. When stressful conditions such as dry or wet weather, and/or disease pressure is high, phosphorus and potassium help the plant stay healthy longer, holding on to more yield potential. In South Dakota we often experience stress during the growing season, a crop that hasn’t had adequate phosphorus and potassium fertilizer rates applied will often get more disease and can have lodging issues at the end of the season compared to a crop where adequate fertilizer was applied for the yield goal desired.

3. Can you build optimal Phosphorus and Potassium levels in one year?

You can apply a high rate of phosphorus and potassium in one year to hopefully raise the soil test levels to an optimal level, but then constant soil sampling (at least every other year) should be done to examine if the soil test levels are staying at that optimal level. It may be better to use a build program over 4-6 years to slowly build the soil test levels up.

4. My soil tests are showing high Potassium levels…why would I even apply Potassium?

The soil phosphorus pool is generally very large.  However, plant available phosphorus is needed at certain critical growth stages, and an added supply of phosphorus, even on high testing soils, can provide a boost to plant growth, especially early in the season and to bridge soil availability.  A continuous, adequate supply of key nutrients is needed for maximum plant growth and efficiency.

5. Do you have any examples of how managing Phosphorus and Potassium levels have helped growers?

Phosphorus seems to be a key “gateway” nutrient.  Until phosphorus levels are adequate in the soil, other added nutritional amendments do not perform to their maximum potential.  Adequate phosphorus levels allow the plants to establish rapid and larger root systems early in the season and get a jump on early growth.  These robust plants are able to better access crop nutrition throughout the season, and are able to survive through environmental changes and stresses better than plants that start of without adequate available levels of this key nutrient.