Yield Penalty from Second Year Soybean

John Grove, Agronomic Soil Scientist and Director, Research and Education Center, University of Kentucky

Growers are considering planting soybean after soybean, especially full season soybean after full season soybean, over some acreage in 2017. Many growers have little experience with second year full season soybean, having kept with their existing crop rotations. Other growers, experiencing problems like soybean cyst nematode in some fields, have avoided soybean after soybean on all acres they manage. I observed two extension agricultural economics presentations modeling profit/loss to different crop rotation options, and where second year soybean yield loss relative to first year soybean was set at either 5 or 10 %, in the absence of field data.

Concerns about atrazine carryover this year

Jim Martin and J.D. Green, Extension Weed Scientists, University of Kentucky

Dry soil conditions can enhance persistence of herbicides such as atrazine. Kentucky has had dry seasons in the past, yet atrazine injury to rotational crops was seldom an issue. Having said that, the risk of crop injury due to atrazine carryover is still an issue that we need to consider on a case by case basis. The risk will be reduced if atrazine was applied early spring and had some rain to move into the soil profile. Prolonged periods of dry soil will enhance persistence and increase the chance of injuring rotational crops. If weather conditions improve and we have a mild and wet fall and winter, then the risk of carryover to spring planted crops will be reduced. Using high rates of atrazine will increase the risks. Atrazine may dissipate more rapidly in no-till compared with tilled conditions. High soil pH (pH >7.0) will increase atrazine persistence.