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Measure subsoil moisture at freeze up

By Ken Panchuk, PAg, Provincial Specialist, Soils

What kind of winter are we heading into? There are many reports suggesting an El Nino climate cycle and a 95 per cent chance that it will persist to the end of this year and possibly until spring. An El Nino means warmer and drier conditions during our winter months. How much warmer and drier it is going to be is largely unknown. After a growing season like this one we know the value of having subsoil moisture reserves. So measuring subsoil moisture recharge at freeze up is very important for crop and input planning.

A soil moisture probe is easy to make in your shop. All you need is a 5/8 inch steel ball bearing for one end, four feet of 1/2 inch rod and a heavy wall pipe for the handle for the other end. The rod can be scored on one-foot intervals for ease of measuring the depth of moist soil. Having a solid bar or heavy pipe handle comes in handy when the soil surface freezes a bit, allowing you to hammer the probe through about one or two inches of frozen soil. To avoid injury, pull the moisture probe out using bent legs and a straight back. The purpose of the steel ball is to make a wider channel to make pulling the probe out easier.

See Table 1 for the amount of plant available moisture held in each foot of moist soil by textural class. Knowing the stored subsoil moisture is an important piece of information for reporting on your soil sample form for each field. The stored soil moisture is used in calculating the realistic target yield used in making the nutrient recommendations. If your soil moisture is not full at freeze-up, then probe those fields again in the spring once the frost is out of the ground. This will allow you to update your realistic yield and nutrient amounts just before seeding.

Table 1. Plant available water stored in moist soil for various soil textures.

Soil Texture Amount of soil water per foot of moist soil
Sand 0.75 inches of soil water
Loamy sand 1.00 inch
Sandy loam 1.25 inches
Loam 1.50 inches
Clay loam 1.75 inches

2.00 inches




October 13, 2015
By Saskatchewan Agriculture