Saturday, February 27, 2010

Why you wait to walk on wet soil

Our gardens love the rain! But be careful, wet soil is more vulnerable to compaction, especially clayey soils. The physical damage from compaction can
  • increase bulk density, where soil pores are now too small to accommodate the root cap's growth
  • increase soil's ability to resist deformation (soil strength), and prevent root penetration.
  • crushes natural soil aggregates and associated macropores, thereby preventing adequate water and air flow.
All this means reduced root growth and therefore less overall vigor of a plant, from your garden plants to large trees! Clay soils are more vulnerable to having their structure damaged due to their increased plasticity and cohesion. Try not to walk too much on your wet soils; perhaps make a permanent path in your garden to help you remember.

Here are some definitions:

Bulk density: weight per volume of soil
Soil Strength: ability of a soil to resist deformation (change in shape)
Plasticity: ability of a soil to be molded or deformed by pressure
Cohesion: stick/stay together
Soil aggregates: soil particles that are held together in one mass
Macropores: soil pores large enough to allow for air and water flow, and even some small animals (some animals make macropores!)

Sunday, February 21, 2010

Enjoying the Archived PDF County Soil Survey

If you are someone who likes to read paper more than a screen, you may consider using the Archived PDFs of the County Soil Surveys instead of the online web soil survey.

From the archived Travis County survey, I found out that the soil under our house is part of the Blackland Prairie Texas ecosystem. We live on the Houston Black series, which is the state soil of Texas. Its usefulness in crop production is mentioned, and it also warns that its shrink-swell capabilities ... well, let me just quote it.
"The main limitations in use of the soils of this association in urbanization are the shrink-swell characteristics, as they affect foundations and streets; corrosivity, as it affects pipelines and cables; and the poor suitability of the soils for septic systems."
Our whole street is on this soil, and many of us are having foundation issues, and pipeline issues. The corrosivity that the survey mentions is showing up on our own rusted pipes.

Why is it corrosive? Is it more than just the high water holding capacity? Interesting...

Anyways, if there is anything for which you'd like to use your soil, you'll find it here in these soil surveys. Awesome!

Monday, February 15, 2010

When clay soil and cast iron pipes meet

My house is among the many houses built in East Austin in the late 1950s (and maybe other places) that used a unique type of iron pipes for the sewer pipes leading from the house to the city sewer mains in the street. Typically houses are built with cast iron pipes, but this iron was centrifugally spun to create the hole in the center instead of in a cast (info courtesy of our plumber). Somehow this makes them more vulnerable (not sure of the details). Anyways, over time, the chemicals we pour down our drain can damage any iron pipes. Also, in the case of our house, if you don't have enough slope in your pipes, standing water can them rust away. It is possible that over time, corrosion of your pipes will accumulate such that you get a hole in your pipe, and instead of waste water being delivered to your city sewer system, you are also watering the ground underneath your house with chemicals (shampoo, household cleaners etc.) and other gross human goo. Another reason these pipes may be seeing their last days is that they reside in clay soil. Clay soil retains water very well, and we all know what happens when you mix water and iron: rust! Anyways, it is 2010 and this is a picture of the pipes that are now being excavated from our soil not a moment too soon.

Find out more about the soil under your feet; NRCS Web Soil Survey

Have you ever wondered about the soil under your feet, or somewhere else specific within the US? The USDA NRCS Web Soil Survey can answer SO MANY of the questions you may have about the soil of a small (10,000 acres or smaller) area. Learn things like the following:
  • Native vegetation most adapted for the soil
  • Recommended uses and limitations (e.g.:agriculture, building, recreation)
  • Potential hazards (e.g.: prone to flooding, easily eroded, low fertility)
  • Chemical and physical characteristics
  • Name of the soil
It is quite easy to use and there are instructions on the home web page. Basically, this info is pretty much taken from the most recent county soil surveys, which have been written for almost all of the counties in the US and describes the types of info listed above. You can type in your address or graphically select the area you are interested in, instead of going the old-fashioned way and reading a map yourself. Reading the archived county soil surveys is easier for me when I am trying to learn about multiple soils within a larger area. You can also make pretty reports with some of the the same information using the Soil Data Mart.