It’s been a wild spring, there is no doubt.  Cloudy, wet, cold conditions have kept many out of the fields. Growers should resist the notion that because they are planting late, they should cut back on starter fertilizer.  That small amount of fertilizer is just what the corn crop needs to thrive until roots can explore more soil volume to collect water and nutrients.  Phosphorus is largely immobile – it doesn’t move with water like nitrogen or sulfur can. The best way to get P into the plant is through root interception and there is no better way to promote that than planter applied phosphorus.

Often later planted corn will be put into warmer soils. Maybe not this year.  Cloudy, rainy, and cold conditions are keeping some soil temperatures low. Iowa State University professor Antonio Mallorino offers three points (click on the link below for the entire article).

1.Do not underestimate the value of starter for corn planted late, mainly in northern Iowa cold soils and with a shorter season.
2.Starter P will provide the most benefit with low or optimum soil test P levels and low pre-plant broadcast application rates. But do not expect much yield response if the two-year P rate for the corn-soybean rotation was applied last fall or this spring.
3.Starter N may also be beneficial, mainly without high N rates applied pre-plant or near planting in the spring and with corn on corn.

Bob Nielsen of Purdue University offers some insights about late planted corn. He says that early planting favors higher yields, but it’s no guarantee. Planting date and and yield are not strongly correlated because planting date is only one of a variety of factors contributing to final yield. It is widely accepted that relative yield potential decreases after some date like May 1. Maybe as much as 0.3% per day.

His advice is to get the crop planted in as timely a manner as possible by reducing tillage operations or other field operations.  Sidedressing N may be beneficial if you don’t have to wait for pre-plant application. Sidedressing is a lower risk if 20 lbs of N can be applied at planting.  Click on the link below to read the entire article.

 

References/links

https://crops.extension.iastate.edu/cropnews/2013/05/dont-underestimate-value-starter-fertilizer-corn-planted-late

https://www.agry.purdue.edu/ext/corn/news/timeless/PltDateCornYld.html

Floods of 1993 and 2011 caused what is known as “flooded soil syndrome” which is also known as fallow syndrome. It happens when soil conditions contribute to the destruction of vasicular arbuscular mycorrhizae (VAM or AM).  Arbuscular mycorrhizae are beneficial fungi that thrive when there are active roots for them to form a symbiotic relationship with.  Mycorrhizae look like long straws in the soil. (Figure 1.) Without active roots, AM don’t survive well.

 

Figure 1.  Stained image of arbuscular mycorrhizae.  Image credit – Jim Ellis, USDA 1994.

Reduced AM populations may appear to resemble phosphate deficiency.  It may be that AM increases the ability of roots to absorb soil P.  The year following flooding corn may appear shorter and may have some purpling.  Soybeans may be less affected to reduced AM populations.  Sugar beets may have some sensitivity to flooded soil syndrome as well.  Crop conditions may appear to have large areas where the crop is doing poorly, may be purple, or may be bare altogether.  The area in Figure 2 was fumigated to simulate loss of AM. The corn is shorter than the surrounding crop and sometimes not present at all.

Figure 2.  Fumigated area simulating loss of arbuscular mycorrhizae. Image credit – Jim Ellis, USDA 1994.

Avoiding Flooded Syndrome

John Sawyer and associates put together a summary on flooded soil syndrome after the 2011 flood (https://flood.unl.edu/311d6f55-3508-4cca-a88c-5f55d6ca077d.pdf). If a crop can be planted, the crop may benefit from high rates of banded phosphorus – 2x the normal rate. Spring applied phosphorus is effective.  Planter applied phosphorus will work if sufficient distance from the seed can be achieved. There is little work on in-furrow products but necessary P rates have potential to reduce germination rates.

If you can’t plant a crop, consider planting a cover crop.  Active roots aid AM colonization.

Tillage also seems to reduce AM populations with or without flooding conditions.

Mahdi Al-Kaisi at Iowa State University has put together some ideas for post flood soil management.  It would be worthwhile checking our his recommendations (https://crops.extension.iastate.edu/cropnews/2019/03/management-considerations-post-flooding-soils)

Raun Lohry, Ph.D.
President, Fluid Fertilizer Foundation