Soil Types and Herbicide Rates

As for many growers across the Midwest, weed control and suppression has been a struggle for 2024.  Due to warm temperatures and high winds some may think twice about relying on their post-emergence application for the following year.  One of the best options, weather willing, is investing more in the pre-emergent rather than one or more post applications.  A crucial part of residual herbicide use is soil type.  Some of the herbicide applied is bound by soil.

Soil types can be categorized by sand, silt, loam and clay etc., but how do these affect herbicide applications?  Many of these categories are a combination of several different soil types.  These are generalized into different soil textures.  For pesticide application, they are separated into four different groups: Coarse, Medium, Fine and Organic.

Coarse soils include sands, loamy sands and sandy loams.  These have a general CEC of 1-5 for light colored soils and 5-10 for dark colored.  Medium soil include sandy clay loams, sandy clays, loams, silt loams and silts.  These have a CEC range of 11-15 for light colored and 15-20 for dark colored soils.  Fine soils include silty clay loams, silty clays, clay loams and clays.  Their CEC range is 20-25+.  Organic soils are most often referred to as peat or muck soils.  The CEC range can be 50-100. 

Textures are important to identify because each texture category corresponds to a different CEC range, or Cation Exchange Capacity.  CEC is the total capacity of a soil to hold exchangeable cations, which is usually included in soil test results.  Since soil is negatively charged, primarily due to clay and organic matter content, certain soils can hold onto more cations than others.  This too means that some soils will hold more herbicide than others.  Below is a chart showing herbicide rates in correspondence to organic matter and soil textures. 

Comparing the coarse, low organic matter soil to the fine, greater than 3% organic matter soil; it requires double the amount of herbicide applied to obtain proper weed control.  If over application occurs in a coarse soil type, too much herbicide is processed in the crop and can cause damage and/or death.  This can also cause movement through leaching, or runoff, to off-target locations.  Over application in a high clay or organic matter soil can potentially cause carryover to the following rotation. 

For more information on the different CEC ranges within textures and how this successful weed control, visit: https://www.canr.msu.edu/news/determining_soil_type_important_for_successful_preemergent_weed_control