Going further under the microscope of Macro-to-Microaggregates

I wrote on the 4th of February on this site some details of how Strip-Till is complimentary to developing more stable macroaggregates, those that are between 1.0mm up to 4.0mm in size and maybe larger.  Within that structural unit I displayed a closeup of an oat root with a cottony mass around the bright white root growing through a small soil ped.  Let us delve a bit closer to see some more.

Macro-Micro-Primary sized units of soil structure with key features highlighted.

All of this is to say, what we soil scientists are getting to know more about and I want to offer you what some of  those important facts are:

The image on the far-left depicts how roots and microscopically fine mycorrhizal hyphae along with roots interconnect the soil and help hold smaller particles of silt, sand and clay together to form granular, crumb or fine subangular blocky structural units. The image in the middle gives a close-up of the microaggregate, spores in close enough proximity to the root that they can spear the root with an appressori and inject its rNA into the root and begin the formation of its symbiotic relational organism (called an “arbuscle” – tree-like form) within the root interior cells to feed itself and feed the host root.  As this all occurs the hyphae can extend outward from the root up to 10cm in length.  This hyphae stores a thick glyco-protein within the hyphal tubular walls, when the fungal hyphae die or dessicate it is this extremely sticky glue-like substance glomalin that aids in tightly holding organic particles along with microbial debris to soil clay and silt particles.  This complex substance can last up to 21 years. Scientists have found from soil sampling at various depths, glomalin is in and along old root channels to the depth of 140cm (55 inches) [1].

In the diagram above, on the far right side, microbial sized debris is pointed out.  These materials are the sites where soil organic carbon (SOC) exists and stored to provide easily available nutrients and also hold up to 400 times its weight with water.  This SOC is very important to bacteria for their food source of carbon.  Earthworms that consume small mouthfuls of soil bacteria, nematodes, amoeba, all who hide in these crevasses and nourish the earthworm.  As the worm passes the material through its gut it too excretes stable microaggregates with mucous-like substances that can release to other bacteria foodstuffs.  These materials can stabilize soil structural units with specific chemical and electronic bonds.  With Strip-Tillage as a once-a-year minimal disturbance will aid mixing this some in the upper 6 to 11.5 inches and cause minimal disruption in the storing of soil carbon.  The glomalin substances can mix and stick more particles together along with a redistribution of the fungal spores to find more roots and restart the infection of more roots and continue the cycle.  Strip-Till does not turn or tumble soils such as a disc or moldboard plow will.  That kind of tumbling effect dries the soil out, exposes spores, soil carbon, mycorrhizae fragments to the atmosphere, dries them out and will cause rapid oxidation – losing the important substances that help the health and stability of soils.  Many times worms are exposed, their tunnels and home burrows are broke open and the cut or torn-in-two worm may die or try to burrow down and again and then die.  Yes strip-till disturbs the earthworms in the till-zone.

My studying of the till-zone after the strip-till implement pass (over the past 10 years) has shown me the strip-till pass is much less destructive and earthworms can recover in 7 to 14 days, still sense where their tunnels are and continue existing.  Due to our tilling of less than 33% of the total soil matrix across a 20 foot zone by 10 inches deep and not turning it over I believe we are aiding the building up of soil health.  Even “direct seeding” efforts can cause some set back of the fungal/bacterial interaction.

I will keep digging into what Strip-Tillage can do to aid soil health to remain strong, viable and accumulating soil carbon.  Stay tuned to us here at precisiontillage.com and we will provide a ‘below the boot on the ground look”.



References used:

  1. Glomalin: an arbuscular mycorrhizal fungal soil protein.   Pradeep Kumar Singh, Meenakshi Singh, and Bhumi Nath Tripathi;   Found in: Protoplasma (2013) 250:663–669
  2. Mycorrhizal Symbiosis, S.E Smith and D.J. Read, Second Edition, Academic Press, 1997.
  3. Plant-Environment Interactions., R.E. Wilkinson, Second Edition, Marcel-Dekker AG, 2000.