I penned a piece with this same title in 1989. Since then, we have learned some new things about how grassland and bush soils function.
In the old days the actual 35 mm slides of the soil profiles had to be sent by snail mail to Winnipeg and the captions were in the paper copy of the article. In the process the pictures and the captions were switched. So, all these years later we will get it right.
For a chemist the periodic table is the symbol that unifies the science. For geologists, that symbol is the geologic time scale. For soil scientists, it’s the soil profile. The layers of the earth from the surface down to the original material — usually a depth of about one metre — lets us know what happened when that soil was being developed. In soils jargon the layers are called “horizons.”
The soil profile is the 10,000-year record of water flowing through a soil and the organic matter that accumulated as a result.
In the brown, dark brown and black soil zones the native vegetation since glaciation was grassland. The grassland was able to manage the vagaries of weather and climate that we experience in this continental area. We all know that there are there are some years and series of years where rainfall is adequate and grass will grow in abundance.
In the wet cycles the grass was up to the buffaloes’ bellies. When dry cycles came along the grass just went into hibernation. The root stocks were still present and still alive and still able to revive the moment some rainfall came along. That system allowed the vegetation to take advantage of any desirable moisture situations while resting comfortably through dry spells.
We own a piece of ground near a pasture adjacent to the South Saskatchewan River south of Kindersley. It is amazing to watch the response of the grass anytime significant rain falls. Within days it turns from brown and crisp to green and juicy for days or weeks, depending on how much rain came along.
Particularly in very heavy soils like Regina and Sceptre clay soils in the brown and dark brown soil zones, there would have been little or no movement of water below the root zone of the grass. That is why water was the main challenge when our grandfathers started to farm that very productive land. There was no near surface water table to allow the development of shallow dug or bored wells.
At the same time there was no or very little nitrate in the system. If a nitrate molecule had nerve enough to appear there was immediately a grassroot ready to suck it up and put it back into organic form.
In the tree-covered area the moisture situation was generally much more favourable, allowing the growth of trees. The leaf litter of a stand of poplar is the nutrient bank that recycles overtime. There is no big accumulation of organic matter below the leaf litter (L – H horizon).
The leaf litter (L-H Horizon) is just that — the accumulation of leaf material over time. Below the leaf litter is a very bleached and washed out grey layer (Ae horizon) where some clay has actually been moved into the subsoil.
The upper subsoil is highly enriched in clay (Bt horizon) that has been translocated form above.
What we know now that we did not know in 1989 was that the grey wooded soils are there not only because of the tree growth but also because of the free drainage to depth.
It was always a mystery to me why areas like Loon Lake in northwest Saskatchewan or Parkerview west of Yorkton, Sask., had grey soils when other soils nearby with the same climate were black or thick black. Many grey soils are at high elevations but at Loon Lake and Parkerview there is only a small difference in elevation between the grey wooded soils and the black soils.
What we now know is that the difference is in the deep underground. In the grey soils the water moves downward to an aquifer and then laterally to a lower elevation where the aquifer pressures up and keeps the water table close enough to the surface to be used as sub-irrigation. If the water is too close to the surface soil salinity is the result.
Cultivated grey wooded soils have the appearance of being washed out and not particularly healthy. It turns out that the appearance is actually equal to the fact. When bush land is cleared and broken the soils are very low productivity for annual crop production without the input of very large quantities of nutrients, particularly nitrogen and sulfur.
In most cases, effective agronomy for grey wooded soils includes a period of alfalfa to assist in raising the nitrogen status of those soils. Even the alfalfa will need considerable help with the addition of phosphorus and sulfur fertilizers and, in areas of sandy soils, potash fertilizers as well. In today’s world, with adequate soil fertility, grey wooded soils are much better than in past times of low input.
There you have it. What happens with grassland and bush are very different and we now know much more about them than we did when the original article was penned in 1989.