By Mike Toohill, AgVenture WSC

Bloomington, IL

The following are main soybean yield influencing factors that I monitor heading into August:

Current soil moisture: In looking at the late July observed rainfall map, I first look for the green colors (less than 2”) where rainfall has been well below normal over the last month. The green colors are most widespread in the Dakotas, northern Nebraska, far northwest Iowa, southern Kansas and eastern Ohio. While corn has the ability to root down into sub soil reserves, the soybean tap root is limited on how much deeper water it can access in the soil profile. That’s why good moisture heading into August and August rains are so important to soybean yield.

For April planted soybeans, I move $ time up a couple weeks (mid-July to Labor Day). Another factor to consider is that recent research indicates that the soybean nodules only supply about HALF as much N as high yield soybeans require. Thus, the areas with better July rains (but not flooding) are most likely to have active “alive” soils that increase nitrogen recycling and mineralization.

Early into mid-August temperatures: This week’s hot weather is expected to continue through at least the first 10 days of August. Humidity is expected to be high though, limiting crop stress. Showers should also limit heat. Thus, I don’t think that soybean yield will be impacted nearly as much as the maps suggest.

Planting date influence: According to USDA/NASS only 18% of the U.S. soybean crop was planted on the April 28th survey (Illinois 26%, Iowa 25% and Missouri 24%). Probably not enough early planted acres for a record national yield unless the mainly very favorable July weather pattern continues throughout August.

Other main factors that influence soybean yields in August:

Disease. The main two that limit yields in the Midwest are White Mold and SDS. So far reports of these diseases are limited. Hopefully it stays that way.
Insects. Growers are watching aphid numbers in the northern belt but not much insect wise happening in Illinois (generally low numbers of Japanese beetles, bean leaf beetles and stink bugs in the fields I have been in).
Standability. Standing beans are always desirable to final yields and so far, the beans out my windows and under my feet are vertical.
Sunlight. We’ll take all we can get.