Identifying Soils that “Seal” and Improving Irrigation Application Efficiency in “Sealing” Soils

This summer we had multiple conversations with producers that either irrigated or had significant rainfall events on their field, but the soil moisture sensors below the 6 inch depth never “detected” the irrigation or rainfall event (see https://www.mississippi-crops.com/2014/06/26/is-my-soil-moisture-sensor-broke/ ). The producer assumed the sensors were “broke”, but we attributed the phenomenon to “surface sealing”. Surface sealing in the Mississippi Delta typically occurs in soils that have a low clay and organic matter content but have a high silt fraction, i.e., most of our silt loam soils. Surface sealing, from an irrigation management standpoint, is problematic because it can drastically reduce rainfall or irrigation infiltration rates. Following is a list of means to determine if you have a soil that is prone to surface sealing:

1) Soil classified as Silt Loam
2) Battle “crusting” problems
3) PHAUCET or Pipe Planner indicates 24 hrs to apply 2 acre-inches but you reach the tail-ditch in half the time, i.e., 1 acre-inch applied
4) Platy soil structure present in the top quarter inch of soil surface (see pictures(s) below, click to enlarge)

To identify sealing soils that may have issues with poor  infiltration rates first take notice of surface characteristics.  The surface of a sealing soil is smooth with no visual cracks apparent.  Second, take a knife and peel away the top one inch or so. Analyze the cross section of the soil for “platy” structure.   Platy soil structure consists of  multiple, thin plates stacked on top of each other (see above pictures).

We have a number of 2014 trials where we have tilled the soil at or near the lay-by timing with a Nichols parabolic anhydrous knife at a depth of 8 to 10 inches.  ( click on the picture to the right you can see the platy structures.)  Preliminary results show better infiltration rates than the non-tilled check. Where we have tilled at lay-by, sensor readings remain much lower, especially in the deeper regions, signifying better infiltration. Yield data from recently harvested soybean test showed a 2 bushel yield advantage where the anhydrous knife was ran as compared to the no tillage control.  Additional yield data is in process.

Placing surge valves on sealing soils has also proven beneficial. In nearly every case where a surge valve was deployed and used properly the advance cycle promoted water penetrated to a depth of at least 12”. We are continuing to evaluate the use of surge valve and in season tillage as a means to address sealing soils.  Some soils may require a combination approach.

We continue to look for research locations for the 2015 season.  If you are interested, please give us a call.