Tuesday, April 2, 2013

Soil for Gen Z: Can you grow things in sand?


Many times I have been asked to write some activities for kids (Gen Z). I think it is a great idea to get kids outside, getting dirty and discovering things! I thought I would write a few simple experiments (following scientific protocol) for Gen Z (up to 13 years). Love to see photos of experiments, or hear if they work, if they need tweaking etc. And will most definitely post results here if you send them in. These can also be modified for Younger, High School and Uni Students as well. 

I have a few experiments in mind, but this one was requested by @lclaessen. Recent floods in Australia has left lots of sand and silt over prime agricultural land. She was wondering, as an agriculturalist, if her and her kids could run an experiment to look at how to fix the land, and get plants growing again. 

Question/Aim: 
Can you grow things in sand? 

Outcomes: 
* To understand the properties of sand for growing vegetables (nutrients and water)
* If growing properties can be improved using other materials

Background:
The floods in Australia have left sand all over land where it shouldn't be. Some of this sand is on farms that are used for growing vegetables. This sand makes it hard for vegetables to grow. 

Plants are just like humans and need lots of food, known as nutrients, and water to grow. Sand does not have good nutrients and it doesn't have much water. So, it can be hard to grow plants in the sand that was left by the floods. 

There are ways that we can improve nutrients and water in sand to grow vegetables. One way is to add compost to sand to increase food and water for plants to grow. 

What is compost? Compost is plant and food scraps that have been allowed to rot and be eaten by worms, bugs, and very very small (so small you can't see) creatures. The animals that eat the food scraps turn it into good food for plants. It can then be put in gardens to help vegetables and plants grow.

By adding compost to sand, we can see if it helps our vegetables to grow. 

A similar experiment I did with my students in a fume hood

What do you need? 
  • 12 x 10cm pots (too many pots? you could reduce this down to 6, but you need to at least double the plants in case they die)
  • 1 large bag of sand to fill the 12 pots
  • 1 small bag of compost (commercial mushroom or other compost is best)
  • 12 healthy vegetable seedlings (I would use tomato, lettuce, broccoli or something that  suits the season)
  • Trowels
  • Labels and pens for marking the pots
  • Scales
  • Ruler and book for record keeping
  • Beaker (200mL), glass or coffee mug
  • Camera
  • Space for growing plants for 6 weeks. This may be an undercover outside space, glasshouse or a fumehood with lighting where water can be allowed to drop out from the pots. Alternatively, you can use drip trays under pots and water less frequently. If the area isn't covered, make sure all the plants will get wet if it rains. 


How do we do it?
  1. Divide the pots into three sets of 4 pots
  2. Label one set of pots as Control (no compost), one set as Low Compost and one as High Compost. Each of the pots should then be labelled as 1, 2, 3 or 4 in that set e.g. Control 1, Control 2, Control 3, Control 4.  
  3. Fill each pot with sand to 3 cm below the rim. 
  4. In the Low Compost pots, add 100g of compost to each pot. 
  5. In the High Compost pots, add 400g of compost. 
  6. Mix the compost and sand in the top of each of the pots down to about 5cm. Do this slowly as to not loose any compost or sand. 
  7. Carefully pull out the seedlings from their container. Using a tap on low or a bucket of water, wash the roots so that most of the soil is removed. 
  8. A hole can be made in the pot and the seedling planted in each pot. 
  9.  The height of each plant (from stem to highest leaf) can be measured using a ruler. This should be recorded with the date, and the pot label in a book or board somewhere. Also make a reference as to whether the plant is healthy, unhealthy or dead. e.g. April 1st, High Compost 4, 5.2cm, Healthy. 
  10. The plants should then be placed in the area that they will grow. Take a photo of each set of pots or of each individual pot. 
  11. Water the plants using the beaker or the same glass/coffee mug every 1 - 3 days (three in winter, 1 in summer)
  12. On the same day each week for 6 weeks, record the plant height, plant health and take a photo. 


Pots in glasshouse from my PhD. All labelled with codes so I know what they are.

Results (a few ideas, depending on age group):
I would do these each week, and then a wrap up at 6 weeks with all the data...
  • Whilst looking at the pots, ask the students: Have the plants grown in the sand? Are they different from last week? Do they look different to each other? What looks different? Are they bigger? Healthier? Why do you think they are different? Ask them if they can see a difference between the pots with compost and no compost.
  • Order the photos chronologically and ask the students questions. 
  • On a whiteboard or computer, get the kids to help you plot a graph using the average for the plants at each point in time. Ask questions. 
  • Writing task for older students: Ask a series of questions related to plant growth and health with the different treatments. Ask the students to make their own graphs.
  • Make a poster showing the changes over time. Explain the changes at each point in time using arrows or word bubbles. 


Some additional notes and modifications:
* If you want to make it more challenging, you could also think about adding clay. You would need pots with 100% clay, 100% sand, and a clay sand mix. For each of these there will need to be +/- compost. This also raises more questions about water holding ability of sand and clay, where clay is better at holding moisture. 
* You could take a sample of soil at the beginning and end of the 6 weeks, weight it, oven dry the sample (105*C for 24 hours) and reweigh. The difference, as a percentage, is the moisture the sand and clay is holding. You could then relate this back to how well the plants have grown.  
* You could also use a range of organic materials. This may include hay, wood chip, manure, paper mulch etc. Just make sure you always have a control (no waste) and the same number of pots for each treatment. 
Simplify? You could compare different soils instead of adding something to the sand. For example, does sand or potting mix work better to grow plants? 6 pots of sand with 6 pots of potting mix and/or 6 pots of soil from the school/home. 
* I am not really sure how this experiment will work! It might work better for some plants than others, or not at all! Either way, you will get a result (difference or no difference) and half the fun is in the doing the experiment. 

Please send in photos, questions, or comments on this. Feedback on whether or not this works, is too complicated etc, would be greatly appreciated. I have tried to use simplified Scientific Method, but it is essentially similar to how I would run my own experiments (minus some statistics, more replicates, and more control in my glasshouse). Love to hear and see it all! 

1 comment:

  1. What a cool way to teach kids about ecology and soil conservation!
    I just wanted to pipe in to extol the virtues of compost: my garden in Montreal started out as a patch of sandy soil once used as a parking spot. After adding heaps of compost over 4 years, the soil in the garden turned into the most beautiful black topsoil. Not only that, the soil has great water retention, and seems to impart some disease resistance to the veggies.

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