When phosphorus and potash prices went through the roof a couple years back, did you avoid application, or put on a reduced amount? When the late harvest last year kept you out of the normal fall fertilizer and tillage routine did you forget the application, or did you apply it this past spring? Either way, your P and K application has likely been a bit off schedule and optimum fertility rates may not have been maintained as they would normally. So how do we get back on track with the right amounts?
Cooperative weather this year has allowed crops to be harvested in a timely schedule, allowing an expected opportunity to focus on fertility, and IL fertility specialist Fabian Fernandez offers some of his thoughts about questions you might have.
Assuming your latest soil test says you are short on P & K, you have ordered it from your local supplier and he asks where you want it applied. “On the field,” you hesitatingly say, and you both smile, until he asks how deep. Fabian Fernandez would say it can be left on the surface just fine, lightly incorporated, or banded 4 to 8 inches deep, if soil test levels are low and you need the nutrient to be more available to the crop. But he says for the most part, where it is applied does not matter.
If you have it deep banded, lining up your planter with the applicator may be a challenge, but you might come out with a crop that gets a good cosmetic boost, such as with the use of a starter fertilizer. However, if you are a strip tiller, P & K can be applied during that operation. Fernandez says the deeper the placement of the phosphorous, the more likely it is to remain at a lower level and you are able to reduce its test levels at higher points on the soil profile. That is a benefit if you are trying to keep the phosphorous in the soil and reduce or eliminate its flow into waterways and streams. He does suggest that if you are strip tilling this fall, wait until mid-October to better maintain the integrity of the berm.
The past several years may have interrupted your annual application, and you have begun to wonder if a biennial application is sufficient. Fernandez says it makes no difference, as long as your soil tests are adequate to supply the needs of the crop. However, there are benefits to an application before the corn crop, but not necessarily before the soybean crop. He says no till corn just does not yield well, if it has been two years since P & K were applied.
You have the chance to apply P & K now, but is it better if applied in the spring? Researchers say both are effective in providing the needed nutrient to the crop and one does not do any better than the other. Since you may have more time in the fall, that has become the preferred application time. If the spring soils are damp, heavy equipment can cause compaction, which may be mitigated somewhat if the compaction occurred in the fall, and the subsequent freezing and thawing action were able to loosen it somewhat. The one downside is that if you are obtaining phosphorous from MAP or DAP, the small amount of nitrogen in the formulation could dissipate more with a fall application.
If you are converting to a rotation with more corn than soybeans, Fernandez says there is no need for changing your P & K application, other than to ensure that sufficient amounts of the nutrients are always available. However, he says to keep in mind that corn removes more P than K, and that soybeans remove more K than P from the soil. That will suggest a fertility package with a higher P concentration, if you are switching to more corn in your rotation.
Summary:
To restore your fertility after budgets trimmed application rates and weather denied any application, checking your P & K levels would be a good idea to ensure an optimum yield. Once you needs have been determined, it makes little agronomic difference whether they are applied in the fall or spring, or where they are applied in the soil profile. One issue that is important is to apply P & K prior to corn, if you are in a corn-soybean rotation.
Stu Ellis