Ag 101 Week 28

What’s the Most Chemically Active Fraction of Soil?



Soil Fertility is based on balancing/adjusting cation (+) and anions (-)

Usually, the organic matter gets all the attention, but you need clay. I think it's often underrated and misunderstood. 

Soil chemistry is mainly surface chemistry - its taking place at the interface between the particle and soil solution(water)

Clay has up to 8 million times more surface area than other soil particles such as a coarse sand. A lump of clay weighing one pound can have as much total surface area as 50 football fields (How Soil Works, Paul Syltie, pg. 25) Basically making it the life of the party because it's so big

No clay is created equal

It starts from the decomposition of micas, biotite, etc.

Which leads to Tetrahedral (Silica) & Octahedral (Aluminum) layers

          kaolinite 1:1, Montmorillonite 2:1,  Illite 2:1 it's technically in between  a 1:1 and a 2:1

Clay predominately has a negative charge due to isomorphic substitution, the replacement of similar size atoms resulting in a negative charge and exposed crystal edges, basically weathering

2:1 clays can swell causing them to be able to hold 10-12 times the cations that a 1:1 can

1:1 is fixed making it better for use as a protectant on fruits, used in fungicides, etc.

The negative charge of clay, along with organic matter leads to the CEC or Cation Exchange Capacity of a soil - Its potential to hold nutrients

It also leads to physical properties such as structure – compaction and drainage traits, also that sticky feel when it's wet

Heavy clay soil can be remedied with the addition of organic matter. Sand lacks structure and will only lead to a hot mess, otherwise known as cement 

Zeolite, Greensand, Kaolin (hydrated aluminum silicate) are like the red headed step children that turned out to be Rockstar’s