Published Apr 4, 2014

The Season of Learning: Tidbits from Recent Webinars

By Margaret Chamas

I’m trying to finally set aside some time to catch up on webinars.  Thank goodness for the technology to archive these things!  Some of the ones I’ve got on my “to listen to” list are from last October!  The two I started out with were “The Biology of Soil Compaction” by (the) Ohio State University associate professor and Extension agent Jim Hoorman; and “Soil Health and Production Benefits of Mob Grazing” by Missouri State Extension agent Doug Peterson.  Here I won’t tell what they told, but recount some interesting bits of info.

For instance, did you know?

  • “Ideal” soil is 50% pore space (half of that air, half water) and 50% solids (45% minerals like sand, silt, and clay; and 5% organic matter)
  • When soil is compacted, that pore space decreases, which increases bulk density (the amount of solid material in a given volume of soil).  The maximum theoretical soil bulk density is 2.65 g/cm3 (basically, a ‘solid’ soil with no space for air or water…for instance, concrete has a bulk density of 2.4 g/cm3).
    • This means that if you know the bulk density of a soil – say 1.2 g/cm3 – you can divide that by the theoretical maximum to get the percent of solid material in your soil.  (In this case, the soil is just under 50% solid…so right near ideal!)
    • At too high of bulk densities, root growth of plants into the soil is inhibited (think – plow pan).  In sandy soils, this occurs at a bulk density of about 1.8 g/cm3, in silty soils at about 1.65 g/cm3, and in clay soils at about 1.47 g/cm3.
    • Organic matter particles are full of holes – like a sponge under the microscope.  Thus, having greater organic matter means the soil is more resilient against compaction (it can ‘bounce back’ to an extent) and it can hold much more water.
    • Many crops get about 70% of the water they need from the top half of their root system.  If water runs off your soil or can’t infiltrate, your crops may not be getting what they need for optimal growth and yield!
    • Tillage, while sometimes a useful tool, breaks apart large soil particles and allows the smaller ones to pack together tightly (think about the spaces between a bunch of marbles – the large particles, or macroaggregates – compared to the spaces between a bunch of sand particles – the smaller particles, or microaggregates).  This is a compacted soil, with reduced pore space, through which water and air cannot penetrate.
    • Compaction can reduce yields by up to 60% and can linger for up to nine years.  Combine no-till systems with cover crops to reduce existing compaction and improve the soil organic matter.
    • Control traffic on your fields!  80% of soil compaction from wheel traffic occurs on the first pass of a tire.
    • Why do some farmers first trying no-till find that the soil is cold?  It’s probably a compaction issue.  That compacted soil has moisture trapped in it – and it takes more energy to warm water than air.  After a few years, as soil organic matter increases and compaction decreases, the combination of better aeration and biological activity (heat-generating) within the mulch will help warm soils up.


Regarding high-density grazing:

  • What IS high-density grazing?  Well, there’s no set definition, but a good ballpark figure is a stocking density of 50,000-1,000,000 lb/ac.  Cattle usually utilize 20-50% of the available forage – the rest is trampled into the soil.  Ideally, paddocks are rested for extended periods of time – months to a year
  • Mr. Peterson gave four keystones for soil health: less disturbance, living roots to feed soil livestock, keep the soil covered, and diversity of plants.
  • While grazing is a ‘disturbance,’ it can be managed to be less detrimental than chemical use or physical tillage.  (Plus, you can make money off of grazing animals…don’t get much extra money from a chemical after you use it.)
  • While forage on top of the ground feeds cattle and sheep, the roots and their exudates below the ground feed your microbes.  There are nearly four tons of bacterial biomass per acre of soil.
  • Keep the soil covered with perennial living cover, and the trampled thatch remaining after animals graze through an area.  The animals may only consume 20-30% or so of the forage – they’ll eat the parts that fit their dietary needs – and the rest goes back to the soil.  This thatch cools the soil during the summer, so the microbes stay functional and plants efficiently use water.  (At 70F soil temp, all water in the soil is used by plants…at 100F, this drops to just 15%!  And at 140F, the microbes die.)  Covered soil is also less subject to erosion, and the living roots help with infiltration and nutrient uptake.
  • Diverse plants meet the needs of the above- and below-ground livestock.  It also means that you can produce forage through a greater proportion of the growing season.  One farmer in northern MO gets about twice as many tons of forage per acre than the state average – because he manages his land properly and has a variety of forage types.  The variety of forage, both the species and the maturity, balances the diet of the cattle.  Mature cool-season grasses combined with high-protein, lush legumes makes a balanced diet.
  • High stock density grazing does NOT mean you need to be moving cows two or three times a day.  It can fit into multiple system and management types.  Be sure to consider not just your ecological goals, but your goals for animal performance, finances, and lifestyle.

Any of these ideas speak true to you?  Or have you experienced something different?  What would be YOUR “take-away” points if you held a webinar like this?