The science of dirt

Much of what my research focuses on involves the chemistry and microbiology of soil. When talking to folks about it, I'll often use the word 'dirt', but the correct technical term is 'soil'. The properties of soil are very important to us. For instance the texture and structure of soil are the main factors influencing water infiltration rate. If the soil is too compacted, water won't flow through it.

We recently visit Williams Farms in Northern California to take a look the soil profile that develops in rice paddies. The picture reveals some interesting things about that environment.

For instance...
The field is about as dry as it gets, but not far below the surface, the soil color and moisture content drastically changes. The lower horizon stays saturated even when the upper horizon dries out, and this phenomena controls the colors. Single-cell microrganisms in the lower soil do not have access to oxygen, but they have the ability to breathe other chemical compounds. One such compound, Fe, is found throughout the entire soil profile. When oxygen is limited, the organisms essentially breathe rust, aka iron (3+) - iron 'missing' 3 electrons, and produce as a by product iron (2+) - iron missing 2 electrons. The upper part of this soil profile has plenty of oxygen, so the iron (2+) has reformed rust. The lower part of the profile never sees much oxygen, so the iron remains in the iron(2+) chemical form. Once the field is flooded for rice farming, the upper horizon of the soil will quickly become void of oxygen and return to a grey color.

Iron(3+) compounds are responsible for controlling nutrient and contaminant mobility in the environment. Thus, iron environmental chemistry is very important and worth understanding.


Here another student and I are taking soil samples and characterizing soil from the profile.


This is a great picture of a soil clod from the transition area between the upper and lower horizons. The patches of orange are rust and indicate where old roots used to be. During the rice growing season, roots pushed through the soil. After the field dried out and rice was harvested, the roots died and were eaten up by microorganisms. Oxygen was able to transfer through the area where the dead root used to be, and this oxygen reacted with the iron to form rust. However, the dense clay texture of the soil limited how far the oxygen could penetrate into the bulk soil, so much of the soil remained iron (2+) - the non-rust form.

Amazing, huh?!

Yuri - the excuse

Michael B. had invited Austin, Kindel, and I to attend the Yuri's Night celebration at NASA Ames facility this weekend. I guess there is a long tradition of celebrating everything regarding 'space' and technology, and in particularly noting that one of the big advancements in came about when the first cosmonaut orbited the earth - Yuri G. I don't remember his last name, and it's not important. Austin came down with the flu, but is still planning to come our way from Indiana sometime this week.

Yuri's Night was a crazy mix of Bay area culture. It was composed of the techy/nerd group (I kind of include Michael in this crowd, but he's no a nerd) and the electronic music/dress in black and think Aliens are real folk. Yeah, this is a gross over generalization of a complex mix of people. Nonetheless, Kindel and I were probably the weirdest people there, being that we weren't dressed up in some ridiculous costume and weren't in the tech industry. The only main group of people not represented (from the Bay area culture) were the yuppies - those with the big bucks and drive the bling-mobiles, or those who act like it.

Nonetheless, there was some incredibly cool stuff that I wouldn't have gotten to see or participate in, such as:

Tesla Roadster - an all electric sports car which Kindel I were able to sit in



Airplane acrobatics show - these guys were in acrobatics and made us sick to watch



Skytran presentation on futuristic mass transportation - this is the stuff sci-fi writers dreamed of, but is now showing great potential
NASA's astrobiology group - I was fairly familiar with their word, but it was nice to put some faces to their names (you know, authors of articles I've read).

Dude's singing karaoke on a machine that they powered by pedaling a bicycle.



Finally, this cool presentation on some recently released and continually updated images of earth from outerspace - the coolest part was when the presenter displayed earth with its thousands of satellites in orbit. We're talking about a massive array of satellites all around the globe. Very cool.




We probably won't do Yuri's Night again, but we're glad to have the time with friends and experience yet another adventure in the Bay area.