By Ralph E. Hart, Crop Doctor
Most regions have periodic flooding, and many farmers deal with it at least annually. River bottom fields flood but the flood waters tends to crest and go down usually within a week. This year’s long-term flooding in Nebraska and the Midwest will result in many of the same problems as typical short-term flooding including debris removal and sand distribution. Mobile nutrients will be stripped away and will need to be replaced while some nutrients such as phosphorus actually may be higher than before the flooding.
The critical difference between short-term flooding and long-term flooding is what is called “Fallow Syndrome” or “Post Flooded Corn Syndrome,” primarily characterized by phosphorus deficiency and slow early growth. This slow early growth is not necessarily due to the soil being deficient in phosphorus, but to the plant’s inability to take in the nutrient.
In a normal, healthy field, there are beneficial fungi called vesicular-arbuscular mycorrhizae (VAM) that form a symbiotic relationship with corn plants to assist in the absorption of water and nutrients. The hyphae, or external branching structures, of the VAM can be up to 100 times longer than the roots and extend the nutrient absorption zone of the roots. When the field has been empty or underwater with no host plants for these VAM to live with, their populations decrease significantly.
Most agricultural plants and weeds can be hosts for VAM, with the exception of the brassica species (e.g. canola, cabbage, broccoli, etc.) and sugar beets. When corn or any other host crop is planted, VAM populations increase, however, the amount of time it takes VAM populations to rebound is lengthy and could take up to two years to recover.
As soon as the water recedes, time is of the essence to get a VAM hosted plant back into the field. Research has shown it is best to plant soybeans the first year if water goes off the field by at least May or June. Since many mobile nutrients have been depleted, it is important to replace nutrients such as sulfate sulfur and boron. SUL4R-PLUS® B+Z fertilizer is an excellent product that has sulfate, boron, and zinc readily available and stabilized by a calcium nutrient. Research has also shown that VAM relies on sulfate, and the sulfate is a key catalyst for an enzyme called glutathione, which is the plant’s defense mechanism to combat stress.
If soybeans do not get planted because the water fails to recede in time, it is important that VAM hosted plants get into the field as soon as possible, even if it is weeds. It would be tempting to spray herbicides to control emerging weeds even in the absence of a crop, but most weeds are host plants to VAM, and its population needs to rebound as quickly as possible. Cereal crops, planted in early fall, would be an excellent way to increase the VAM population.
Farming has never been easy, and sometimes the weather can really throw us a curve. This year’s long-term flooding is a terrible disaster, and many thousands of productive acres will lay idle. Our hearts go out to those in the Midwest that are enduring this phenomenon, and we know that they will come out of this stronger and more determined.