Each year when plants begin their rapid growth stage producers notice leaf striping on the newest leaves that causes concern. Most commonly this is due to a shortage of magnesium in the plants. Unless you have soils that are sandy with a magnesium soil test less than 100 ppm, this will be temporary and will soon grow out of it. Reasons for this temporary shortage can be due to any of the following:
- Soil Temperature: Soil temperatures less than 60 degrees reduce magnesium uptake.
- Transpiration rates: Magnesium is taken up by mass flow. If soils are wet and humidity is high the plants won’t transpire as much. Reduced transpiration affects magnesium more than other cations.
- Nitrogen rates: High nitrogen rates will reduce magnesium uptake especially in soils that have high K levels and/or low pH soils where aluminum levels would be higher.
- Form of nitrogen: Higher amounts of ammonium nitrogen is antagonistic to magnesium uptake. Nitrate nitrogen will enhance the uptake of magnesium.
- High Rates of Moisture Causing Nitrate Leaching: With less nitrate available, more nitrogen may be taken up as ammonium nitrogen which again is antagonistic to magnesium uptake.
- Plants Growing Rapidly: When Corn plants are in the rapid growth stage it is not uncommon to see low levels of plant tissue magnesium. This is short term and usually does not affect final yield.
Research over the years have shown only mixed responses to foliar applications of magnesium at this stage. If you are in soils with low magnesium levels, you may want to consider a broadcast application of 100# of K Mag even at this stage to improve magnesium uptake. If you have any questions about plant nutrition or foliar application please give us a call.