Soil health is such a multifaceted subject that it's easy to get lost in the rhetoric. My intention here is to summarize what I have sifted out of a lot of material to be important for soil health, along with the reasoning for these statements.
In general, strive to minimize erosion, and maximize soil biota. To achieve these two goals five criteria emerge
1 ---Manage the farm operation to maximize soil surface residue:
If you see dirt you are short residue! Every primer on soil health will include a section on the need to protect the soil's surface 24/7, 365 days a year. This means, keep it covered! A farming operation does this with crop residue. Residue resists erosion, feeds soil biota, moderates soil temperature, maximizes moisture capture, reduces weed emergence.
<---this pic shows cover with >20,000#/ac. Although this volume is preferable, rotations that include low residue crops will not likely retain this much protection. This pic also shows seed placement of spring wheat in the lower center.
2---Strive for less disturbance of the soil profile:
Use a ULD (ultra-low-disturbance) cropping system. It will maximize residue retention, minimize destruction of soil aggregates, maximize retention of channels made by roots and macro soil biota for water infiltration and gas exchange, minimize weed competition by leaving weed seed high and dry.
<---this field is seeded to mustard that is starting to emerge.
3---Develop a diverse crop rotation:
Soil biota need a diversity of plant cultivar exudates. These exudates are derived from warm and cool season broadleaf cultivars, and warm and cool season grass cultivars. Wheat is King in our region. Basically we are a mono culture. Although other crops haven't given the return like winter wheat, we need to develop crop diversity if there is any hope of recovering the natural productivity our soils.
<---pic of spring peas no-tilled into winter wheat stubble.
4---Plant cover crops to replace fallow:
We need to replace traditional fallow with green fallow(GF). Green fallow is the opportunity to increase cultivar diversity beyond the normal crop diversity. Research is pretty clear that, in our region, fallow is counter productive to building soil health. More SOM is lost during the fallow year than is gained during the cropping period.
<---pic shows a GF field seeded with 9 cultivars, including three radish, one cabbage, one triticale, one pea, two mustard, one winter canola.
5---Measuring progress:
Testing is obvious, but what tests? Unless you understand each test's limitations, they can be quite misleading. There are a number of tests available to measure progress, --chemical soil tests, leaf tests, biological tests using soil, Haney, or Solvita, and also microscopy. Rely on leaf tests to discover crop deficiencies. Every five years or so sample for a soil biological test to determine long term changes. These tests are expensive and also limited to information for a very small area. Because our soils vary greatly from one footstep to another, analyzing any soil sample has limited value. Chemical analysis of soil is good at determining the total quantity of a nutrient but not so good about determining the plant availability of that nutrient. Frequently, leaf tests will show a deficiency when the chemical analysis of the soil shows an abundance of that particular nutrient. As the agricultural industry learns more about plant nutrition, more elements are needing to be tested.
In recent years I have become aware of the importance of soil biology. Soil biology sounds like a very old discipline, and it is; however, the first comprehensive publication on the subject was not printed until the mid 1980's (that absolutely astounded me). Since then we have learned that plants communicate, and that symbiotic systems can develop in the soil that interact with plants. Although a novice, I am convinced that we can rebuild the natural productivity our soils once contained. To do this, we will need multiple field checks to determine what organisms are present, or may need to be added, and food (plant cultivars grown, or amendments applied) provided to grow their population. That is the purpose for buying a microscope, and online classes to learn the basics of soil biology. Armed with these tools one can identify and manage for the different soil biota at a relatively low cost. My equipment and education cost the equivalent of six biological tests. These six tests would give me detailed information on six small areas of a field, and takes a week or two for the results. With the microscope, I can get a general idea of conditions, and get that information in a half hour allowing the opportunity to correct a deficiency in a timely manner.
STILL UNANSWERED TO MY SATISFACTION: The following two subjects have a lot of literature expressing diverse opinions.
--
What depth should you draw your sample for biological and chemical tests? In the literature I discover no consistency on depth from which to pull a sample, when it is even mentioned. It comes down to what you have a question about. An example would be, do you want the nutrient analysis in the top 2" or the top 12"??? So, since most of the plant roots are in the top 12-18", and most of my sampling in the past has been done at 12", I'm going to continue using 12" depth for sampling and comparison. At least I will be able to salvage some useful data from the past. Any real gain in SOM will have to reflect more than 3" profile, so, 12" it is.
This pic shows a soil pit from the Aeschliman farm south of Colfax, WA. The top of the pic just catches the soil surface. The bottom of the pic shows the washed out color of residue on the near bank of the pit. Notice the dark streaks going down into the pit which is ≥ 6' deep. These dark streaks are carbon enriched soils that are left behind in the root channels and worm burrows. As can be seen, these channel sources are important in moving carbon deep into the soil profile. The color variation in this pic goes a long ways in explaining the potential for variability of our soil. Think about coring down a dark area and then a foot or two away coring down a light area. Is the chemical or biological analysis going to come out the same, --no way!
--
What species and number of cultivars should be included in a cover crop? The most consistent advise I hear is, plant cultivars that support your "goal", or needs of the cash crop that follows, --such as, will you need N, or do you need more biomass, or do you need to improve soil structure? My thinking follows along the line of: Include as many different cultivars as economically possible in the cc mix, --at least five with one of them being a radish, and another a legume (unless the next crop is a legume). Radish are good bio-drillers, and the taproot (not the tuber) goes deep and scavenges nutrients, bringing them back near the surface. Caution:--make sure all
brassica's in the cc mix is certified
disease free. Canola is going to be an important crop for us and we want to avoid bringing in soil borne diseases on brassica seed stock. Another caution is to not include a cultivar that will be hard to remove from the following crop.
WHAT THE FUTURE HOLDS:
Our farming methods will change to more closely mirror nature, simply because the forces that impact agriculture will move the industry in that direction. Input costs of equipment, chemistry, and plant nutrition along with increasing regulation and legal liability associated with farming will force agriculture to be more holistic in nature. I fully expect, not too long in the future there will be a requirement to be "licensed" to farm. With the world political, and climate change implications, food security issues will draw more political attention. I expect this to be a slow transition that will come through the metamorphosis of the current required "private applicators license". All it would take is a tweak in the current law to include current soil conservation and biology information. If this becomes the trend of the future I heartily support it. Farmers need to be a highly trained professionals, and that requires a continuing education program. Those of us that regularly attend university research seminars, and direct seed conferences are already exceeding any probable requirement that a law would require.
As a Sanskrit text written in about 1500BC noted: “Upon this handful of soil our survival depends. Husband it and it will grow our food, our fuel and our shelter and surround us with beauty. Abuse it and the soil will collapse and die, taking humanity with it.”
The No-Till Farmer features an article: <
Building Resilient Soil System >
