STRUCTURAL STABILITY OF SOILS. PART 1 OF 2
Currently I am soil sampling. A week ago frozen ground made getting the gouge auger in the ground difficult. This week I seem, at times, to be sampling water not soil.
The time taken to soil sampling is seldom wasted since there are numerous other considerations to the work along with that of counting footsteps for the field grid. One current thought is that of a soils structural stability.
A large number of my samples have over the years been submitted for textural analysis. This information is useful for many reasons one of which is that it aids in the understanding of water movement within the soil and its structural stability. I would add at this point – much more than does testing for Cation Exchange Capacity and associated Magnesium and Calcium ratios (1*.)
Farmers who talk about wet soils introduce the idea of compaction. It is always “the headlands” and often associated with the colour of the seed drill and whether a new one would help.
So what is happening and why all this “wet soil?”
Some things we cannot change but do need to factor these in as a priority when formulating a solution or conclusion as to “what next.”
First: Rainfall. No control over this one.
Two: Soil texture. That is the amount of sand, silt and clay there is in the fields on our farms. This is fixed for our life times.
Then the basic principles. Fill a plant pot with sand and pour water in at the top, within moments it runs out the bottom. Do the same with clay and it will take much longer to see a similar effect.
Since the majority of soils I have a textural analysis for fall in to the “clay” category you have to expect that the rate of percolation through the profile is going to be limited right from the start.
In fact the text book states something like, “Sand soils have very high percolation rates, 25 to 200 mm per hour. Silty soils, including loam, range from 5 to 25 mm per hour. Clay soils have percolation speeds of 5 mm or less per hour. These soils easily become waterlogged, and plant roots can suffocate as a result.”
(1*.) Assessing Soil Fertility: The Importance of Soil Analysis and its interpretation Johnny Johnston. (Ex: Rothamsted Research Station.)