Moisture Sensors not Responding to Irrigation

The importance of soil moisture sensors is becoming more evident as we continue forward this growing season.  This week we received a call regarding sensor readings that were assessed early this morning. The following are the data discussed in this scenario:

6 inch depth =  32 cb

12 inch depth =  64 cb

24 inch depth = 112 cb

This information was collected following an irrigation last week. One might wonder where all of the water went and why the sensor readings aren’t closer to 0 after irrigation.  We have had a number of similar calls concerning what appear to be high sensor readings irrigation event or even a rainfall event.

Silt loam and similar soil types have a tendency to seal over and compact.  We are seeing a shallow compaction layer around the 2-3 inch range.  This shallow compaction layer may be present even though the particular field was sub-soiled in the fall.  

The structure or “tilth” of the soil is a relationship between soil, organic matter, and pore space.  Air and water fill these pore spaces.  When these pore spaces become clogged, water movement is restricted and ponding occurs. If you notice areas of fields that tend to pond water after a rain or irrigation event, shallow compaction is most likely the cause.

We have a number of 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. Preliminary results show better infiltration rates than the untilled check.  Where we have tilled at lay-by, sensor readings remain much lower, especially in the deeper regions, signifying much better infiltration rates.

Additionally, surge valves assist in these situations.  Surge valves, with their alternating wetting and soaking cycles are allowing better infiltration of the soil profile.  During the advance cycle water is forced down the furrow at an increased flow rate.  The soak cycle, approximately 75% of the advance cycle time, allows water to infiltrate the soil profile before the next advance cycle.