Greenhouse temperature

Today is graph day!

This week I have been thinking about temperatures.  If you remember back to when I set up the temperature probes there would be thousands of temperature readings.  All that data in a giant, overwhelming spreadsheet taunting me because I am not so sure how to use it all.  While figuring that out I've been looking at just a few days at a time.  Kind of like snapshots.

The greenhouse temperature itself is a good place to start. 

Soil temperature in control treatments.

I realized after I made the above chart that I had used soil temperature data instead of air temperature.  See what having oodles of numbers in a huge spreadsheet does to me?

Below I graphed soil and air temperatures together.  You can see the treads I highlighted in the soil temperature graph can also be seen in the air.  The major difference is air temperatures are much more volatile.  They seem to jump up or down a few degrees each hour.  This could be due to cloud cover, or air movement from the fans.

Soil and air temperatures in control treatment.

*  This data represents five days in the greenhouse I am working in.  

Other greenhouses or high tunnels may have similar temperature trends but they will not be identical.  *

January light

Lots of light is not a requirement to sprout seeds.  But, light is one of key reasons plants grow and are just so cool.  Taking light and turning it into sugar is pretty amazing.  When I see people outside tanning I know they are just trying really hard to photosynthesize.

Since we had light meters available we set them up to give us a reading of the total moles of PAR light each day.

Moles of light measured in tunnels on a cloudy day (Jan. 27) and a sunny day (Jan. 28).

In January the days are starting to get longer, but they aren't really that long yet.  I graphed the two days above because one was cloudy and one was sunny.  The difference in amount of light that reach the sensors (and thus the plants) is pretty apparent.  There are a couple observations between the different tunnel coverings that deem pointing out:

1. Here it shows that the clear plastic and row cover transmitted about the same amount of light.  Sometimes this is true, and sometimes the clear plastic transmits more moles of light.
2. The white plastic transmits more light than I thought it would and isn't that far behind the other coverings.  The seedlings inside the white plastic treatments are much more etiolated and spindly than all the other seedlings though.

Do you see anything interesting?  If you grow greens in high tunnels, low tunnels or under reemay do you ever worry about light?

* This data is pretty cool, and will be useful for writing my thesis.  

I am not recommending anything besides excitement and interest in plants and photosynthesis. *

Germination trials: measuring light

How much light is actually reaching the inside of the greenhouse?
How much light gets through the low tunnel coverings?

To answer these questions we use watch dog weather trackers.  They measure:

    ~ average daily temperature

    ~ daily high and low temperature and the time at which they     

       happened

    ~ amount light in moles/day

Pretty useful little things.  

Germination trials: measuring temperature

The big fancy data logger from onset.com

One of the major components to this first experiment looking at germination rate is measuring the temperature in each of the treatments.  Happily there are data loggers that continually do this for you.  We are using two models from Onset: a big fancy looking one and a plain box one.  The fancy one is more expensive and is water proof so if I spray it with a hose by accident it will be ok.  The smaller one isn't water proof so I installed it way up high where only the hose shouldn't reach.

The small not-so-fancy looking data logger from onset.com

Both data loggers support four temperature sensors.  For the germination trials we need two sensors per treatment for a total of 24 sensors on 6 data loggers.  The data loggers can be programmed to take a temperature reading at any interval you would like.  We are going to set them to measure the temperature every hour on the hour.  In one week there will be over 4,000 temperature readings!  All this data is downloaded into a software program from Hoboware.

The picture above shows how the data is displayed with Hoboware software.  Each line, or dotted line, shows a temperature probe over a five day period.  Hourly temperature readings can be scrolled through or exported to excel.  

Germination trials: low tunnel coverings

Once the PVC pipes were set up on the greenhouse benches it was time to cover them, creating mini-greenhouses.  This led to an introduction into the world of plasticulture.  Tons and tons of plastic is used to grow our food.  So much, that the word plasticulture is used to describe all the greenhouse coverings, drip irrigation, mulches, wind breaks, post harvest handling, marketing, and fertilization tools used to grow food crops.

There are a lot of different kinds, colors and weights of plastic to use when making a greenhouse, high tunnel or low tunnel.  Here are the four kinds of plastic we picked and one non-plastic treatment:

1. Sun Master 70% Opacity overwintering film

From it's name you can tell that not much light gets through this white polyethylene plastic.  It's the kind of plastic that is put over greenhouses or tunnels that house woody plants in the winter to keep temperatures within from fluctuating too much.  So, it should be "warm" inside which will promote seed germination, but it will not be good place for leafy plants to actually grow.

2. Sun Master Greenhouse Film 

This is the clear plastic that you would expect a greenhouse to be made out of.  It is 6mm thick polyethylene and allows a whopping 92% light transmission through.  So, this one should keep it "warm" inside as well as let plants grow because they will have some light.  (I say some light because all the layers of plastic add up.  If there are two layers of plastic on the greenhouse itself and one on the low tunnel only 78% of the available light can be transmitted through.  On a dark winter day that isn't much light.)

3. Agribon+ AG19 Row Cover

This is a agricultural fabric but it made from plastic as well.  Polyester and polypropylene strands are bonded together in a swirly random fashion resulting in the term "spunbonded".  This makes a cloth like covering that allows water through, but doesn't actually absorb water as a true cloth would.  Spunbonded fabric comes in a range of weights.  The one we're using allows an 85% light transmission and weighs 0.55 oz/yd.

4.  Clear plastic with holes in it

I haven't sourced this plastic so I don't know much about it yet.  It is far thinner than the other plastics we chose so presumably more light will be transmitted through.  It is also covered in holes which allows better air flow.

5. KEN-BAR agritape heat mats

These obviously are not a covering, but they are the final treatment in this experiment.  They still alter the plant's environment by keeping the soil and roots warm.  Heat mats come in all sorts of shapes and sizes.  This brand often is used by people who keep terrariums filled with snakes and other cold blooded animals that I wouldn't want to have for a pet.  Right now we have the heat mats set to be 40 degrees Fahrenheit at night.













6. Control

Every experiment needs a control.   I forgot to take a picture, so you'll just have to take my word for it that there is a bench with a bottom layer of plastic and nothing else.

Greenhouse or tunnel?

High tunnel

looks like a typical greenhouse but is not heated.

Greenhouse

has a source of heat like propane.

Low tunnels

temporary structures that look like mini-greenhouses.  

Sides are held down with sand bags or dirt and have to be uncovered for harvesting.

low tunnels in the greenhouse

Temperature values used are from H. C. Wien's paper
"Use of low tunnels to improve plant growth in high tunnels"

Today we started setting up germination chambers on top of the existing greenhouse benches.  Really our germination chambers are just fancy low tunnels.  Low tunnels are simple hoop structures made from wire or PVC and covered with permeable fabric or plastic.  Their benefits are two-fold for organic and small farmers, they keep insects off plants and warm up the air.  We plan on using the increased temperature to our benefit.

If you put these low tunnels inside a greenhouse or high tunnel (unheated greenhouse) plants are even more insulated from the outside cold.  Our first trials using this arrangement will be looking at the temperature ranges using different materials as covers for the low tunnels.  Permeable fabrics, plastic sheeting and permeable plastic all have their benefits and drawbacks.