Lloyd Murdock and Greg Schwab, Extension Soils Specialists and John Grove, Soils Research
Plant and Soil Sciences, University of Kentucky
At this late stage in the season, priorities should be on planting the corn crop, first, then applying needed fertilizers after planting. Fertilization after the crop is planted is not yield-reducing and, in some cases, can actually cause nitrogen (N) fertilizer use to be more efficient.
Phosphorus (P) and Potassium (K)
There may be a few situations where P and K were not applied prior to corn planting. If the soil test P and K levels for a field were in the medium to high range, any fertility added this year would generally maintain these soil test levels and would have little, if any, effect on yield. This would probably be the situation in a majority of Kentucky corn fields. Therefore, adding P and K fertilizers after planting would not be a problem and, if the field's P and K soil test levels are in the upper part of the medium range or higher, the P and K could be delayed until this fall. If a field tests in the low soil test range, the P and K should be added this season, but can be delayed until after planting.
P and K fertilizers are soluble in water, so they dissolve with rain and move into the soil fairly quickly. They will only move into the top 2 to 3 inches, but this will be enough to make them available to the plant, in most situations. If the field was no-tilled or has a lot of residue on the surface, many corn roots will be close to the surface and will take up added P and K. A clean tilled field might result in reduced uptake. This would more than likely only be a problem if P and/or K were in the low soil test range and there was an extended period of dry weather that resulted in the top few inches of soil becoming very dry.
Nitrogen (N) Management Strategies for Late Planted Corn
Once the optimum planting date has passed, the yield loss from further delayed planting far exceeds the yield loss associated with post-planting N applications. Your goal should be to get corn planted as soon as soil conditions permit. Your corn-N management situation, field by field, falls into one of two categories: a) some or all N has already been applied; b) no N has been applied. Your N loss situation has also shifted. Early N applications should be managed to avoid denitrification loss, while later applications need to be made so as to avoid volatilization loss. Because of the wet spring, the soil will contain less residual N, or N mineralized from organic matter, than normal.
For the full article, go to the Corn and Soybean Science Newsletter.