What’s water doing to soybean fields?


Tony Nye - OSU Extension



We are fortunate to have many of acres planted, unlike our neighbor farmers in the northern portion of Ohio — but we are not without our own issues.

Earlier this week I was out and about in several fields and the wet weather we have had for many weeks is starting to takes its toll on our crops that are trying to grow.

Last week I highlighted the many colors of corn caused by the stresses of the ongoing weather saga we are experience this year. This week I wanted to look at the soybean situation and share with you a couple pieces from this week’s OSU CORN Newsletter.

According to OSU Agronomy specialists Laura Lindsey and Alexander Lindsey, saturated soils after soybean planting can cause uneven emergence and stand reductions of varying extent depending on the stage of the soybean plant and other environmental factors including temperature and duration of saturated conditions. Additionally, increased disease incidence may further reduce plant stand.

Lindsey and Linsey highlight the effect of wet weather on a soybean stand:

Saturated Soil Prior to Germination: While soil moisture is necessary for germination, soybean seeds will not germinate when soils are saturated because oxygen is limiting.

Saturated Soil during Germination: Saturated soils during soybean germination may cause uneven emergence. In a laboratory study, soybean germination was reduced by ~15% after only one hour of flood conditions (Wuebker et al., 2001).

After 48 hours of flood conditions, soybean germination was reduced 33-70% depending on when imbibition (seed taking up water) began relative to the flooding conditions. Practically, for Ohio, this means if soybean seeds were further along in the germination process when flooding occurred, the seeds will be more susceptible to flooding stress.

Saturated Soil during Vegetative Stage: Warmer temperatures will cause soybean plants to die faster. At temperatures, 80 degrees and greater, submerged soybean plants will likely die in 24 to 48 hours.

However, cool, cloudy days (…and we’ve had plenty this year) and clear nights increase the survival potential of a flooded soybean crop. Flooded plants may also exhibit poor nodulation, resulting in yellow, stunted plants.

Their recommendation is to get out and Evaluate Stands: To quickly estimate stand, count the number of plants in 69’8” of the row for 7.5-inch row spacing, 34’10” for 15-inch row spacing, or 17’5” of the row for 30-inch row spacing. These counts represent 1/1000th of an acre (i.e., 120 plants in 7.5-inch row spacing = 120,000 plants/acre).

Keep in mind, the effect of plant population on yield is very small over the normal range of seeding rates. For soybeans planted in May, final populations of 100,000 to 120,000 plants/acre are generally adequate for maximum economic return.

For example, in our seeding rate trials in Clark County, 100% yield (77 bu./acre) was achieved with a final plant stand of 125,000 plants/acre.

However, a 95% yield (73 bu./acre) was achieved with only 77,000 plants/acre. (This trial was planted the second half of May in 15-inch row width.)

Also this week, Ohio State University Soybean Disease specialist Anne Dorrance shares the fact we have had up to a summer’s worth of rain already in many areas of Ohio in June – and we aren’t even finished planting. Many fields that were planted were under water last week.

Fortunately, the sunny weekend, (finally) kept the waters moving so the plants may be set back a bit. The problem the wet weather has created is differentiating from flooding injury from root rots.

Symptoms of seedling blight and root rot typically begin a week after these rains, but flooding injury is going to be very apparent in the next few days as the warm temperatures hit many fields.

According to Dorrance, under these conditions, flood injured plants will wilt, but if the roots were not infected, they will recover in a few days as new roots begin to form.

Once these plants are removed the soil and the roots can breathe again, they will form new secondary roots and the plants will recover. You can collect some of these symptomatic plants, wrap the roots in a damp paper towel for a couple of days and then see if new roots grow or the plants continue to decline.

Another key symptom to differentiate between flood-injured and root rots is the color of the center of the root, the root stele in botanical terms.

On flood injured plants the outside rows of cells die and can be easily pulled off, leaving almost a mouse tail appearance to the roots. A root rot from Pythium, Phytophthora, Fusarium will turn brown and sometimes soft and easily crushed. Flooding injury, even on a young seedling, the root stele is still tough, almost like a toothpick.

Dorrance is expecting the reports of root rots to start soon, but we had good seed treatment packages on most of the seed, and much of these rains fell during the time period that those fungicides should have been active. This is what she have observed in OSU studies to date but more time will tell.

Flooding can be very severe, where substantial ponding occurred there are no plants at all and the field smells. This is where the carbon dioxide built up and basically smothered every living thing including plants.

The best advice for these fields – give some more time before you look at them.

The cool nights predicted for the coming week will give the plants that are just injured to recover, and then you will know if it was a disease or just an injury.

Tony Nye is the state coordinator for the Ohio State University Extension Small Farm Program and has been an OSU Extension Educator for agriculture and natural resources for over 30 years, currently serving Clinton County and the Miami Valley EERA.

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Tony Nye

OSU Extension