Fallow Syndrome (Don’t Skimp on Starter P!)

Several million acres went unseeded in the northern plains this year due to excessive rainfall and flooding. One nutrient issue that comes along with flooding is called “fallow syndrome.” “Fallow syndrome” is primarily a phosphorus deficiency caused by a lack of mycorrhiza fungi in the soil. Mycorrhiza (Vesicular arbuscular mycorrhiza or VAM) is a beneficial fungi found in most soils and needs living plant roots to flourish. This fungi has a symbiotic relationship with plants and is especially important for grass crops like corn and wheat. VAM fungi act like an extension of the plant roots, to help them absorb more nutrients like phosphorus and zinc.

The population of these fungi goes down rapidly in a year with little plant growth. In 2011, growers did their best to control weed growth on acres that did not get seeded. If the weed control was good during the summer, these fields are set up for “fallow syndrome.” The population of VAM fungi decreased during the summer and will be low next spring when crops are planted. If the unseeded acres had cover crop seeded on them early in the summer, the VAM fungi population is probably OK and “fallow syndrome” should not be an issue.

For the unseeded acres that were kept free of weeds with chemical control or tillage, “fallow syndrome” must be considered. The cure for fallow syndrome in wheat, is a high rate of P fertilizer placed near or with the seed regardless of the P soil test level. Placing P fertilizer in a band near the seed is a common practice for wheat growers. They just have to make sure the P rate with the seed is high (be sure to apply a safe rate).

Corn growers who already place starter P fertilizer with or near the seed, should not have any issues with “fallow syndrome.” They just need to increase the rate to about 30 lb/a P2O5 in their starter. A rate of 10 gallons of 10-34-0 would be the limit for seed placed fertilizer with corn seed on 30″ spacing. Using 2-3 gallons of a low phosphorus concentration liquid fertilizer will not be enough P to avoid fallow syndrome. If a corn grower does not have the equipment needed to apply a high rate of P fertilizer in a band near the seed at planting, “fallow syndrome” will likely cause yield loss. Research has shown that broadcasting P fertilizer (even a high rate) will not fix the “fallow syndrome” induced P deficiency. A high rate of starter P is required. Hopefully we will have an early dry spring in the northern region next year and we won’t have to worry about issues like this.