Wednesday, July 28, 2010

Vertisols, veritably difficult.

Once upon a time, I took a class on tropical soil management (SOS 5132) by Dr. Hugh Popenoe, at the University of Florida.  Each day, we would get a slide show of pictures from farms all over the world that highlighted low-input agriculture.   It wasn't my typical technical science class; we learned from stories.  This post is on one of the many cool things I learned. 
I got this photo from here
According to the USDA-NRCS, vertisols are high shrink/swell content clays that have deep wide cracks in the dry season. They shrink (to the point of cracking) when drying and swell when absorbing moisture.  Also according to the USDA-NRCS, I live on a classic vertisol, the Houston Black Clay (associated sob story and fun fact).  The state soil of Texas.

According to my class notes, vertisols typically have a wavy, bumpy surface due to all of their shrinking and swelling.  They are usually dark brown, and are located on flat or low slope soils.  Although they have a high exchange capacity (ability to hold nutrients), their massive* structure makes it easy to erode.  

The shrinking and swelling can damage roots, and the soil is hard to plow unless it has just the right soil  moisture (what that magic number is, I can't tell you, it's magic).  If you plow it when it is too wet, you will be creating clods that harden as they dry, almost to the strength of  rocks.  

So how can you manage it? The notes say two things: 1) "Well, annuals, pasture and rice do best on the soil."  This makes sense to me since my soil developed with prairie vegetation from a parent material of calcareous clays and marls  2) "You must manage soil moisture, and cultivate at right moisture content."  

I have a third tip.  If you build a house on it, enjoy the options of either watching grass grow or the cracks on your wall grow**!!  They are about the same :-l

By the way, remember my post on the five soil forming factors?  Well, vertisols and alfisols (a better drained soil order) are both found in same climactic zone, with the same type parent material, but different topography. They both developed from and found on basic parent materials like andecite, limestone, and basalt.

Links for further study:
*massive in this case means structureless
** from your house foundation shifting

1 comment:

  1. I like the way your professor taught- by stories.
    Your posts are sort of like that too, that's why I keep coming back!!!!!