A thick black soil with more consistent rainfall will often outdo a loam soil in the dark brown zone, but the differences are nowhere near what they were when the biggest input was the seed in the ground.
Soil fertility is the ability of a soil to supply the necessary plant nutrients to a growing crop at the time a plant root goes looking. But some soils can be highly fertile but not at all productive. Case in point — saline soils.
Most saline soils are highly fertile. Take a soil test on a saline part of your field and it will show very high levels of nitrate N. Sulphur levels will be off the scale because the salts are mainly sulphates. Phosphorus and potassium tests will also be high in most cases. If you dig in a saline soil where little or no crop grows, you will find loads of good black topsoil in a beautiful moist condition.
So saline soils have a lot going for them, but have very low productivity. Salts prevent the abundant nutrients from entering the plant root.
Improving the productivity of saline soils is super simple — just install tile drains and apply generous quantities of good irrigation water. Nice in theory, but in practice there must be a source of water and an acceptable place to dump the salt water that is leached out.
Soil productivity is the ability of a soil to produce crops. Period. One of the best measures of natural soil productivity that I know was the Cereal Variety Co-op tests. In fact, many of those tests may still be a good measure of natural soil fertility. They are mostly done in garden patch agriculture with no weeds and no fertilizer. I think most of them are still done on summerfallow.
When studying soil productivity years ago, we used that data to clearly show which soils would fill the bins. In the brown and dark brown soil zones, the Sceptre and Regina heavy clay soils stuck out like blue diamonds and Melfort silty clay was the runaway winner.
Another good test of natural nitrogen soil fertility was the N soil test summaries for fallow fields. A graph with soil zones on X axis and soil test N on Y axis gave a perfect bell shaped curve if plotted as brown, dark brown, black, thick black, grey black and grey.
But much of the above is nothing more than a history lesson in today’s crop production. Management, particularly crop rotation, fertilizer, precision seeding and weed control, has become the great leveler in yields. Sure, a thick black soil with more consistent rainfall will often outdo a loam soil in the dark brown zone, but the differences are nowhere near what they were when the biggest input was the seed in the ground.
MANAGEMENT, AND MOISTURE
In the 1970s, I grew canola yields from 10 to 50 bushels per acre on the same garden patch of Bradwell loam at Outlook. The differences were just due to varying water and nitrogen. Based on that data, I made a statement at national meetings in Guelph, Ontario in August 1977. I questioned the real meaning of soil productivity when management was such a big issue.
Wow, I almost got ran out of town on a rail. But I think I was right and still do.
The founder of Doane’s consulting service in the U. S. had this motto: “Because there is more in the farmer than there is in the land.” In other words, good management can overcome some natural challenges.
The two soil characteristics that are most important in determining natural fertility and productivity are soil organic matter and soil texture. And we must always remember that Mother Nature is always in charge. In the Palliser triangle, moisture in the ground at seeding plus the rainfall in the growing season is still the biggest single factor in crop yield.
The final article of the soil quality series will deal with topsoil. Some recent research work provides new insight on that old topic.
J. L. (Les) Henry is a former professor and extension specialist at the University of Saskatchewan. He farms near Dundurn, Sask.