We hear a lot about soil soil health these days so thought I should brush up on the literature. To give the punch line first: in my opinion it is mostly spin.
Any introductory course or soils textbook starts by picking a hypothetical pound of ground and revealing the basics.
- Soil is half solids and half pore space.
- In a healthy soil, ready to grow plants, half the pore space is occupied by water and half by air (FC = Field Capacity). The plants suck the water until the soil sucks back so hard the plants croak (PWP = Permanent Wilting Point). It is the water held between FC and PWP that determines how much crop we can grow.
- The solids are 95 per cent mineral and five per cent organic. That five per cent organic is what separates soils from rock. The organic fraction is also living, teaming with billions of microscopic bugs and bigger things that we can see, like earthworms. (Recent work is learning much about the microscopic critters but precious little about what we see).
The next lesson in soils is about how Mother Nature turns geologic materials into soil. The five Soil Forming Factors are:
- Parent Material (PM): the geologic starting point.
- Climate: the rain, snow, wind, heat and cold that wear away at the PM.
- Topography: the lay of the land determines how the water runs around on and in the soil.
- Vegetation: the plants and other biologicals add the Organic Matter (OM) and life.
- Time: all of the above act for various amounts of geologic times. Soils are much like people. When young they are vibrant and resilient, when old they can be “washed up” and in need of help. Our soils are young.
- Mankind: when talking about soil health we are really talking about the sixth soil forming factor — that is what we farmers do to make a soil better or suck out the productive juices.
When talking about soil health we are really talking about how our farming practices are making a soil better or worse for future crop growth. In the 1960 and ’70s we talked about soil productivity. By the 1990s soils types discussed and defined soil quality and now the buzzword is “soil health.”
To my way of thinking “soil health” is simply the ability to grow a profitable crop while maintaining the ability to do the same down the road, while not messing with our neighbours or other parts of the environment we jointly occupy and value.
Cornell (university) soil health test
Whenever I see Cornell my ears perk up. The soil science textbook I used as a student and professor and still use is The Nature and Properties of Soils now in its 14th edition. Cornell University at Ithaca, New York played a major role in that textbook through the years. Nyle C. Brady was senior author for years and just went to his eternal reward November 24, 2015 at age 95.
The Cornell Soil Health Test is designed for crop production in New York State and considers the following:
- Soil Texture: Every soil sample at the former U. of S. lab from Day 1 had texture as the first test.
- Available Water Capacity: depends on soil texture to large degree.
- Compaction: soil penetrometer readings.
- Soil Structure: (aggregate) stability.
- Organic Matter
- Active Carbon: how active are the bugs?
- Root Health: this is a “less is better test.” Yes, it is a measure of root disease not roots themselves.
- Potentially Mineralizable N: this is the “biggie” missing in our current soil testing. I have been bugging about it for years, and think there is now some headway being made.
- Available P, K and Micronutrients.
Chemical tests are about the same every-where and many of the other “tests” are factors that are a function of the soil itself.
A trip to Israel
A recent (October, 2015) scientific paper from the main U.S. soils journal talked about mapping soil health over a large agriculturally important area in Israel. It was 9,500 acres and they took four-inch soil samples from 130 spots in the area and measured a dozen soil properties.
The soils are high lime clay soils with low organic matter (about one per cent C), high pH (8) and no salinity.
The data was subjected to complex mathematics.
The math gave a soil index which they related to NDVI (normalized difference vegetation index: that is to say “ How Green is my Valley”). They found a significant correlation between the soil index and the NDVI. Significant simply means that there is a good probability that the two are related. But the Soil Health index only explained about 25 per cent of the variation in the NDVI.
Anyway, I used my computer to take a quick virtual flight to northern Israel and visit the site they reported (by latitude and longitude). I found it to be a pivot irrigated site with some small fields of surface irrigation. In the centre of the study area there are many reservoirs that capture the winter rains for use in the summer.
It was great sport to visit Israel. I learned a bit about the geography and soils and one test they did was very interesting. We must all learn until the grim reaper arrives!
They took zero to four-inch soil samples and ran nitrate-N and then incubated them at 30 C for two weeks and measured the nitrate-N produced. The average was 31 lbs. nitrate-N per acre for the four inches. But the maximum was 359 lbs. nitrate-N per acre four inches.
It would make sense to this old fossil to have a look at the management systems that gave the large two-week mineralization result. We desperately need to do the same thing here and have a proper research program to look at the length etc. that is required to design new N soil test benchmarks for our current cropping systems.
Dear Readers: For those of you that have struggled this far I suspect you have reached the same conclusion as I: Soil Health is SPIN3.
Soil health on the Prairies
Our first run at soil health in Saskatchewan was soil productivity studies in the 1960s and 70s. To get at the basic production capacity of the natural soil we used the co-op cereal variety trials. They were managed uniformly as summerfallow planted with good weed control and no fertilizer.
For the first 50 years our agriculture simply “lived off the fat of the land.” We harvested the nutrients that Mother Nature had accumulated in 10,000 years of mostly native grass growth.
Our early agriculture made the Brits angry. When we started exporting wheat to the U.K. their farmers saw us as unfair competition. “All those farmers in Western Canada do is put the seed in the ground and come back with the threshing machine to harvest a bumper crop,” they said. And it was true.
At that time the Brits were already long into soil fertility programs to maintain productivity. Early days (1800s) it was mainly animal manure. In the late 1800s superphosphate was discovered and the fertilizer industry was off.
So, now here we sit with the sixth Soil Forming Factor (mankind) as an important part of our agriculture. In the dry 1980s we discovered that new methods were required. Out of that grew continuous cropping, zero till, crop rotation, adequate fertilization and weed, insect and disease control. As I have said many times, the zero till part came entirely from farm workshops and farmers tired of dust in the air in May.
Soil biological health is often described as “good” when a healthy earthworm population is in place. We have that in spades, and it all happened as a spin-off from our zero till practices. Too bad no one is studying those little critters that do so much for us. Since Jill Clapperton left Lethbridge for Montana, this old fossil is the resident expert on earthworms on the Canadian Prairies. And I know squat about them.
The livestock folks in particular have done good work with many plant species in pastures. They use intensive grazing to use the feed efficiently and spread the manure at the same time at zero cost.
To make a long story short, on the Canadian Prairies we have one of the healthiest soil management systems in the world.
However, we do have some challenges for the future:
- pH: In west central, north west Saskatchewan and central and northwest Alberta and the B.C. Peace there are low pH soils and the constant addition of ammonium based fertilizers does add to that problem. The academic solution is liming but work is needed to make it practical.
- Soil P: Many farms are exporting more than they are adding. In the long run the balance must be restored. My common sense suggestion is to wait for the price of fertilizer P to dip, then pork it on to last for many years.
- Micronutrients: In Henry’s Handbook I said we were a long way from knowing all the micronutrients we may need now and in the future. Copper for wheat is worked out with a soil test that works. Many others are a crap shoot now. Much more detailed research is needed. For every breakthrough there are many false starts. But the Manganese deficiency for a certain wheat variety on a certain soil in Tanzania in 1973 was enough to convince me that we should have an ongoing strong micronutrient program. We do not.
- Crop Rotations: I’m convinced that a two-crop, one herbicide rotation will lead us down the garden path at some time. Disease is a big issue. Fungicides help but crop rotation must be considered.
There you have it. When the soil health topic comes up you can tell folks we have it well in hand.