The anticipated cost of fertilizer has increased more than 30% of 2021 prices.
This shock to production budgets has farmers alarmed and considering less corn acres this year. For corn that will be grown, some are considering changes to their selected source of nitrogen, the total rate applied, and the timing of application in an effort to enhance effectiveness and reduce the total amount used.
For phosphorus and potassium, questions have pertained to how much their rate can be reduced before yield is affected. The University of Kentucky has what some consider conservative nutrient recommendations for the high yields modern corn and soybean brands are capable of.
Actually, UK recommended nutrient additions, based on a soil test, are only made when a yield response has been measured for that crop under Kentucky soil-climate research conditions.
Many field studies have been conducted by the Kentucky Agricultural Experiment Station under Kentucky farm conditions to determine the extent of any primary, secondary, or micronutrient needs.
Yield and soil test data from these studies serve as guidelines for establishing recommendations provided with soil test results and in the Lime and Fertilizer Recommendations AGR-1 publication which can be used to develop recommendations from any laboratory test that uses Mehlich III solution to extract phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and zinc (Zn). AGR-1 is available online at https://soilscience.ca.uky.edu/soilspubs.
UK recommendations supply a sufficient level of available plant nutrients, regardless of seasonal weather, assuming good management practices are in place.
The rates recommended are for the production of a crop to be grown each year and will increase soil test values slowly for P and K.
Using these recommended rates will take four years or longer of annual nutrient application at the recommended rates to result in appreciably higher soil test levels of P and K.
The result of sufficiency recommendation methods are nutrients supplied in an amount adequate for optimum growth in a given year but do not suggest additional material be applied for “maintenance” to increase soil fertility levels.
When making decisions for this year regarding fertilizer, fields testing low in P and K obviously require fertilizer applied at the recommended rates. For planters equipped with fertilizer application, one-third to one-half of the recommended amounts of P and/or K for corn can be used if it is banded 2 to 4 inches from the row in low testing fields. For fields testing in the medium range for P and K, there is a 50% chance fertilizer applied for the crop to be grown will provide any benefit to yield.
If soil test levels for P and K are so high that no nutrient recommendation is made for the current year, any P or K fertilizer applied will have no effect on the yield of the crop grown this year.
Likewise, if no fertilizer is applied there is no assurance that the high levels will be maintained for optimal production in the following years, requiring annual soil testing to closely track levels. If you don’t have recent soil test information about a field, this is the year to get it.
If recommendations without soil test results must be made, you can only assume low levels of residual P and K.
The points to take away from this article regarding P and K fertilizer applied this year are that you can not remove them from production in fields that are already low without reducing yield.
You can’t remove them from production in fields testing medium without encountering a 50% chance you will reduce yield.
You can refrain from applying additional P and K on fields testing high and redirect that to low and medium testing fields. We all know that 2022 makes 10 years since we’ve had a poor crop overall and statistically, we are due for one but we cannot manage with an expectation of lower production due to the environment or we will guarantee lower production based on our own decision.
If the risk is too great on land you farm to swing for a homerun yield in corn this year, then let soybeans be planted where they match your level of risk tolerance.
Clint Hardy is the agricultural extension agent for the Daviess County Extension Office. He can be reached at 270-685-8480.