I am not very familiar with what is Ying and what is yang and their effect on the body.
The sole of the foot is connected through the nervous system with the rest of the body, and in the practice of reflexology there are maps and charts describing these connections. So, the effects on the sole of the feet are also felt by the rest of the body. The wetness of the grass has the effect of eliminate the electrical potentials that have the tendency to build up in the body. Wet grass is electrically conductive, dry dirt is not. I think at some point it was mentioned wet sand on the beach, again an electrically conductive medium.
Dan G

I was out at a friend's house recently, and have trouble with circulation that is helped by sungazing.   I had sat for some time and felt a need for a boost.   He had sand in his yard cuz we are in the desert.   We were sitting in the patio in the shade.  I took my shoes off and went to stand in the hot sand.   I stood in the hot sand and walked around in it a little bit.   I don't have a practice of barefoot walking mainly cuz I don't want to walk alone, though there are plenty of sand trails on the mesa around here.   I felt so energized by standing in the hot sand even for a few minutes.  It just felt really good and I felt like I was glowing afterward ( a feeling I do not get from standing in the sun with shoes on).  It was about 1:30 in the afternoon.  Hot sand.   

 

I wonder why I have heard people talking about the issue" of electrical conductivity:  If sand does not conduct electricity, fine, but it feels good and there must be a reason for it.  Some psychologist was writing in a book I have about Sand Play and how some therapists have patients play in a sand box cuz it is good therapy.   There is something about sand that feels soothing, at least to me, and obviously to others.
 
I also enjoy walking barefoot in the grass, but since we are in the desert I'm not around grass as much as sand.   It's a different feeling I guess.  All I know is I felt very energized after just a few minutes of walking around and standing in hot sand.
 
Anyway, I did a google search and found a few links: the first one is one I was not expecting to find at all and is about the benefits of walking barefoot on broken glass!  link number six talks about solar radiation absorbed by earth, as heat,which raises an interesting question cuz grass does not get hot like sand.  could the heat of the sand have something to do with the buildup of solar radiation in the sand, since it is a mineral rather than organic substance?   grass transforms solar radiation into it's own element and is cool.   sand is inorganic? link number seven tells the amount of uv radiation reflected rather than absorbed by grass sand and snow.   grass absorbs more radiation but remains cool, and i suspect because grass is organic and transforms the radiation while in sand maybe what is not reflected builds up in the sand.  link number 8 explains that solar radiation is transferred back to the environment and lost from grass through the process of evapotranspiration, which explains why grass is cool and sand is hot.  i have included brief excerpts below the url address for a few of the sites, inlcuding link number 8:
 
1) http://www.lifeevents.org/walking-barefoot-on-broken-glass.htm
2) http://www.swissmasaius.com/about.php?page=benefits
 
3) http://www.shapefit.com/fitness-advice-1.html
It is important to have good foot function and for this reason it is useful for athletes to spend as much time as possible barefoot. Walking on sand is very good.
 
4) http://www.earthisland.org/EIJOURNAL/fall97/ov_fall97doffit.html
 
5) http://www.geocities.com/jetwalkers/naturalwalking.htm
this site says barefoot walking on grass is best but doesn't say why.
 
6) http://www.anamp.org/nescp_curriculum/grade2_heated.html

 

As solar energy moves through Earth’s atmosphere toward Earth’s surface, some of it is absorbed and some is reflected by clouds, air molecules and Earth’s surfaces. The amount absorbed and reflected varies depending on the type of molecule the energy strikes. For example, light colored surfaces, like snow, reflect most of the Sun’s energy. Darker surfaces, like asphalt, absorb much more of the energy. Water also absorbs most of the Sun’s energy that strikes it, although much more slowly than most land surfaces do.

 

Most of the energy given off by the Sun is short wavelength, too small to be directly absorbed by the tiny air molecules in Earth’s atmosphere. As Earth’s surfaces are warmed by the Sun’s energy, however, it warms the air above it through two different means. Air that comes in direct contact with the surface is warmed by conduction of heat from Earth’s surfaces to the air molecules. Earth also reradiates heat from its surface in a longer wavelength that is absorbed by the air molecules that it contacts. Many of these processes also work in reverse, creating a give and take system of several processes that generate a delicate balance of energy sometimes called Earth’s Radiative Budget.
Scientists are studying these complex interactions, in part to determine how human processes are affecting Earth’s climate. For a more thorough explanation of the Radiative Budget, visit the NASA Goddard’s Institute on Climate and Planets web page at icp.giss.nasa.gov/education/radforce/page2.html.

 

Similar to the ideas of the Radiative Budget, many Native American cultures, including the Colville bands, embrace a philosophy of the Circle of Life and the harmony and balance of Nature. Invite an elder to talk with students about these important ideas.

 

7) http://www.who.int/mediacentre/factsheets/fs271/en/
Ground reflection: grass, soil and water reflect less than 10% of UV radiation; fresh snow reflects as much as 80%; dry beach sand about 15% and sea foam about 25%.
 
8) http://www.atmos.washington.edu/1998Q4/211/topics3.htm
From the numbers in the above figure, it is clear that the hydrologic cycle is a major player in the global energy balance.  To appreciate its importance, one need only think about which is cooler on a hot, sunny day: a lush green lawn or bare ground (or pavement).   The lawn is refreshingly cool, even though it may even have a lower albedo than the ground or pavement.  It is cool because of the evaporation (or, strictly speaking, "evapotranspiration") from the grass, which transfers most of the absorbed solar radiation  back to the atmosphere without requiring that the surface heating up the surface excessively, as is the case for conduction and heat transfer by the emission of infrared radiation.
 
-----
end of citation.  my comment:
 
It seems to me if grass conducts electricity, ok fine,but i thought the question was about being charged up with solar radiation.  it is ultra violet radiation from the sun that causes the unclumping of red blood cells, and electrical conductivity has nothing to do with it.   another thing to consider, is that because sand does NOT conduct electricity that means it cannot drain the electrical charge built up in the body.
 
Peace,
Cathie