Three of the most important nutrients for plants are nitrogen, phosphorus and potassium, affectionately known as N-P-K. If a plant can’t get enough of one or more of these, it won’t grow or won’t be healthy. These three nutrients make up most of what is in fertilzer– with nitrogen being especially important.
We tested the soil samples for the amounts of N-P-K. it was a hard working lab that needed close attention to directions.
This is the last of the soil tests. Next, onto the bioindicator– how well do plants grow on the soils?
This was a lab intensive week. In addition to the physical characteristics of soil, which greatly affect how water interacts with the soil, the amount of nutrients in soil is important for all life on earth.
Plants are able to absorb nutrients directly from soil. These well adapted organisms are also able to make their own sugar, for energy, from water, carbon dioxide, and the sun. That’s another story, by the name of photosynthesis, but it just goes to show how extraordinary plants are. After all, if you sat in the sun all day and snacked on soil and water as your only source of nutrition, you would not survive very long.
For this first lab, students prepared the organic matter test, to be read later, and then prepared a soil extract to use for further testing.
The summative activity for our study of the physical characteristics of soil was a collaborative project. Students had to write a script for a commercial for soil, or some aspect of soil– and the audience had to be plants.
The interval of time for this project looks long because we had Introductions due and peer editing, and we had a snow day and a delayed opening.
Here are some shots of the script writing. Notice that students really spread out through the school to do this work– and I am always pleased that they are responsible members of the PDS community and focused on the work when they are allowed to move about the campus.
They look good enough to drink. Milk chocolaty brown with a foam top.
It’s a half full jar of soil sample, topped with water and a drop of dish detergent. The particles disperse in the liquid and settle. We will measure the total height and then the height of each layer: sand, silt and clay. The percentage of each will determine, quantitatively, what the soil texture is. We can compare this to the texture determined from the texture-by-feel analysis of a few weeks ago. Quantitative and qualitative analysis of the same sample: Will the findings agree?
While we worked on that, David and Steve set up temperature probes in the soil outside. We have probes located at 36″, 24″, 12″, 6″ and in the outside air. The probes are hooked up to a little computer, connected to the ethernet. That means the temperatures will feed out all day and all night, whether we are in school or not. We can look at the temperature readings at this website: https://cosm.com/feeds/97558
Each student is analyzing a soil sample brought from home. The first analysis was to calculate the percent of water, by weight, in the soil. This number, though, tells only how much was in the soil when it was brought to school. It may give a slight idea of how much water it is possible for the soil to hold, but because it represents only a snapshot in time, it doesn’t give a very complete picture.
To get an objective view of the water holding capacity, we set up a test. We filled a cylinder with a standard volume of soil, and then let the soil fill with water through capillary action over a few days. (Translation: we let the soil sit in a tube of water and “soak” up the water.) By calculating the weight change, we will be able to compare our samples for water holding.
What makes soil hold water? Up until now we have understood this to be determined by the spaces between the particles in the soil. After all, if you don’t have spaces between particles, there is nowhere for the water to go. But spaces don’t explain everything. The types of particles also matter. Sand has lots of spaces, but it doesn’t hold water well. Clay, on the other hand, can also have space, but holds water like a magnet holds to metal. The amount of clay that a soil has has a huge influence on how well soil holds water.
Is high water holding capacity good? Not necessarily. Plants grow best in soil that holds some water, but also drains well. So, having a very high water holding capacity is not desirable.
If you were planning to grow plants, the most important aspect of the soil to consider would be the soil’s texture. Texture is a description of the relative amounts of each size particle a soil has. The particles that make up soil are categorize by size and called sand, silt and clay– in order from largest to smallest.
Soils that have too much clay do not let water move through them. Soils with too much sand don’t hold water. With a bit of training, it is possible to feel the amounts of each particle by working the soil through your hand.
Agriculturists train to do this– in fact, students at agricultural schools have contests to see how well they can judge a soil’s texture by feel.
Texture by feel is a qualitative analysis: the results are in words, not numbers. We will also be doing a quantitative analysis of particles by using a settling jar.
We continued to weigh the soil. These classes had a non-lab component to them as well: While writing a research proposal, student have to read the literature and cite sources. That is an on-going skill across many parts of the curriculum and science is no exception.
It was a choppy week, with a snow day right in the middle.
I took the chance of a holiday weekend to try out a new video editing application called WeVideo. It is an on-line application that will allow more than one editor to work on a project. I used to use a great program called JayCut. Then RIM (makers of Blackberry) bought the company and JayCut vanished. (I think Blackberry is vanishing too.) I don’t understand the economics of this, but was happy to see WeVideo as a new choice!
All four classes weighed the soil and calculated the amount of water lost– so far.
Follow up questions were:
Is there still water in the soil? (We need to weigh again next week.)
How does the water get from the center of the pile of soil to evaporate? (As water evaporates, the empty space is connected to the atmosphere– meaning water in the middle of the pile is connected to the atmosphere through pore spaces and can evaporate.)
The land and atmosphere year of the 7-8 science curriculum may be best known for its soil study unit. Students were asking about it in September, and the first day has finally arrived.
Before it snowed, each student brought in a bag of soil from home. As we study soil, each student will be researching their own.
We started by asking the question, what is soil, anyway? Some of the components are possible to see: small stones, grains of sand, roots, detritus. But what is everything else? Eventually in every class, someone named a mineral, and that started a cascade of names: iron, calcium, sodium, potassium, magnesium….they are all in soil! These minerals are also all elements– and living things need them in order to construct their own bodies. The source of every mineral is in the soil– and fortunately, plants are able to take them up and make them available to animal life.
As we study soil, the investigations fall into two categories: the physical characteristics of soil and the chemical characteristics. The physical characteristics relate to how well soil holds water. Today’s second big question was, how can we determine the amount of water in our soil?
Each lab group talked to create a protocol for determining the amount of water. The first times I taught soil science, I told the students how to make the water determination. I don’t teach that way anymore. Instead, the students had to figure it out. In every class, lab groups were successful in designing the protocol for determining soil moisture– by weighing a sample, letting the water evaporate, and then weighing again to calculate the percent water by subtraction. When the PDS mission statement asks that students be “creators of knowledge,” this is an example of what that means. The lab was not a cookbook procedure, but rather an investigation where the students had to figure out what to do on their own. The science outcome will be just as accurate, but the understanding and retention of the information will be stronger.
The last part of class was spent learning how to write a science proposal. Students can start the project work now, and they also must read background literature and begin to write. Science work is pretty plentiful right now, but there is a lot of variety in the homework, and each student has a slightly different to-do list, depending on the project.
The humble ball point pen is actually a triumph of engineering. It’s predecessors have had a longer tenure though. For a thousand years, people wrote with quills. Fountain pens, still used by some, were a great improvement. The metal nibs were more reliable and refilling a pen instead of dipping was much more convenient.
Still, writing could be taxing. The ink comes out of a fountain pen rather wet, which means writing requires gracefulness. And, waiting for the ink to dry takes time. Lazlo Biro thought it took too long. As a journalist, he wondered if the quick drying ink used to print newspaper could be used in fountain pens instead. That ink was too think, so he invented the ball point as a way to use the ink. That’s right– the pen was invented to serve the ink!
Ballpoints were popular with pilots in WWII, but their inferior writing style did not make them catch on with the public after the war. Marcel Bich improved the pen, and the Bic Cristal is still one of the best selling pens today. Bic pen bought out the USA’s favorite fountain pen company, Waterman, and ballpoint pens became popular throughout the country. (Waterman pens are still made under the Waterman name. They are quite fine.)
We examined the engineering of pens y taking them apart. Even capped pens are engineered– someone had to figure out how to make a cap stay on. Retractable pens are a bit more complex. Students disassembled the pens and drew exploded diagrams to show how they work. It doesn’t matter if you draw well or not; putting pencil to paper is good for observation and figuring out the positions of the working parts.
We were lucky to have a some loans of fountain pens and a vial of ink. Everyone was able to try the old-fashioned way of writing. It’s a slower process, but as the photo above showed, also an enjoyable one.
What surprised (and delighted) the teacher about this lab: How happy and involved the students were. Adding engineering into the program from time to time is a goal of mine this year, and this is the third time we have analyzed how something works for that purpose. More to come!