Crop Intelligence Agronomy Insights

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Professor Les Henry – Soil Moisture and Groundwater

June 26, 2018 Professor

Les Henry joined South Country Equipment and the Crop Intelligence Team at a customer field day, near Liberty, SK on June 26, 2018. The Crop Intelligence Team has been in conversation with Professor Les Henry over the last eight months; consulting on ground water interactions and soil moisture mapping strategies. It was a privilege to have him come out to support our project and an honour to listen to him speak with so much passion about a topic that he has dedicated much of his career to.

Professor tells me he is 78 years young. And, as much as we would have loved to get him out into more of our customers’ fields, we would have been remiss to plan anything further than a one or two-hour drive from his home in Saskatoon. The field day attendees walked away with several nuggets of wisdom. Although not comprehensive, the following is some of the information that Professor Les Henry shared with the crowd.

  • He began his talk by declaring that, “Water in the ground is money in the bank!”.
  • He described Wilting Point as the point after which water in the soil is no longer plant available. Soils at the surface may go below wilting point when they are air dried.
  • Field Capacity is how much water the soil holds above the wetting front without gravity moving the water deeper in the soil profile.
  • Different soil textures can hold different amounts of water.
    • A sandy soil that is wet to 1 foot – is equivalent of 1 inch of rain (give or take).
    • A loam soil that is wet to 1 foot – is equivalent to 1.5 inches of rain.
    • A clay soil that is wet to 1 foot – is equivalent to 2 inches of rain.
  • He spoke about the water table fluctuating through the years, depending on whether we are in a wet or a dry cycle.
  • He defined the water table – as when all the pore spaces in the soil are filled with water. The point at which water will seep into a well.
  • If the water table reaches the root zone – you are sub-irrigating.
  • “Anywhere you have salinity – the water table is high.”
  • In wet years, when the soil is at field capacity to the depth of the water table, an additional inch of rain will raise the water table:
    • Sandy soil = 6 inches
    • Loam soil = 8-9 inche
    • Clay soil = 12 inches
  • We are currently in a wet cycle – following a 30-year drought that spanned most of Professor Henry’s career.
  • 2005 was a BIG snow melt and a BIG re-charge year.
  • 2010 was the first big rain year. On his farm they recorded 20 inches of rain, 10 of which was excess that the crop couldn’t use, and the soil wouldn’t hold.
  • Saskatchewan Agriculture has good rainfall information. Over 250 farmers record rainfall data and report weekly. Their rainfall map is meaningful and can be found in the weekly crop report.
  • Saskatchewan soil maps are not that useful on the quarter section basis. However, Assessment Maps have greater validity because the are subject to review when requested.
  • We toured two different fields: a canola field and a wheat field.
  • Professor Les Henry observed changes in soil texture using a hand-held EC meter.
  • In the canola field, he advised as a few of the younger men in the crowd dug a ground water well. “Shut up and dig! Dig you bugger, you wouldn’t go to school!”.
  • The well confirmed suspicions that the water table was very near the root zone of the canola crop. “As sure as god made little green apples, you can grow some bushels here.”
  • We dug root pits to confirm rooting depths in each field. Both crops were rooted to at least 50 cm, which corresponded to the field connect data.
  • Tweets from the day:

 

Field notes from June 26 Field Day, Imperial
- Professor Les Henry, July 3, 2018

1. Field 1

Before arriving at the farm shop meeting location I passed through Imperial and to the extreme southwest corner of field. Google Earth street view goes that far and from that it was obvious that that corner is very saline. I did EM38 measurements there. (If needed more info on EM38 readings interpretation is on pages 82-83 of Henry’s Handbook… )

EM38 readings were 140/180   

140= Vertical reading ~ 0-4 feet

180= Horizontal reading ~ 0-2 feet

i.e salinity a big factor

2. Field 1 Group inspections after lunch.

We entered the field from the NE corner near the old red barn. A bare patch we walked over had EM 38 readings of 180/210 – i.e. very salty

Soil pit site southwest of the entry point.

EM38 vertical reading was ~ 100 – meaning saline medium texture or very heavy texture. It was clay- Hv clay soil and hence the high reading but the crop was still doing just fine.

When the pit was down about 2 feet I sent Tom Senko back for Dutch auger with extensions. After I showed how to do it, a young chap grabbed the auger and continued. We put on one extension so would have been down about 7 or 8 feet and we were into the water table. That was confirmed when small sand lenses showed free water.

In clay soils and till it is possible to be well below the water table with no free water in the hole. Stick in a pipe and wait a couple of days and water table depth can be measured. Visible evidence of free water in small sand lenses confirm you are in the water table.

Slightly higher land southwest of soil pit and enroute to your met station , soil moisture probe etc.

At that location EM 38 readings were about 60/40- very normal for the medium textured soil at that location and likely typical of much of the quarter.

3. Field 2

Immediately on entering that field the EM 38 was 15/ ~ 20-24.

My immediate response was “ SAND” – only a very sandy soil would give that low a reading. In fact, I have trouble remembering when I last saw that low a reading. Soil probing showed 30-40 cm of topsoil and B horizon over PURE SAND to depth of probe (43 Inches).

I suspected that to be a small pocket but we kept on walking and it stayed the same until we were near your instrumented site. There the sandy soil at the bottom of the probe did have some silt/clay as well.

A soil pit was dug at that site and the young lady with the knife was presenting us with very thick wheat roots. By that time we were very far from road and did not want to take time to send a runner back for dutch augers so we did not dig for water table.

It is without doubt that SW6 ( at least the part we examined) is farmland only because of a water table within reach of plant roots. That depth of sand would hold very little water that would be quickly used up and crop would fail without timely rains.

CONCLUSION:

From our field inspections and the water well map for the area I am convinced that much of the land farmed between Imperial and Penzance would include areas where water table interactions are probable.

Your soil moisture probes etc data is excellent and a big jump forward in agronomy. The picture can be completed by also measuring the water table.

Also, EM38 field reconnaissance would be an excellent way to assist with the placement of the single probe in a quarter section.

 

J.L. ( Les) Henry July 3, 2018