Blog
We had a really useful meeting at CEH Wallingford in November 2022 where I met our colleagues from CEH and Leeds University for the first time. We got to see the GroDome which really helped me visualise the experiments.
November 2022
ISO-WETLANDS: GETTING STARTED
Sarah Wexler
In my first weeks on the project I've been designing our plant controlled growth experiments, which we'll be running at UC-CEH's GroDome in Wallingford with the help of colleagues Denise Pallett and Dan Reade there. We'll growing rice, barley and Brome grass. Each plant species needs different conditions to grow in, so we have to set up the experiments carefully, to make sure they grow and produce seeds.
I've been working on this growing pot design so that we can switch conditions between pots flooded with standing water, to pots with well drained soil. We need to be able to do this quite quickly as we want the plants to survive our flooding experiments, and this depends on how well the soil drains. We have been sourcing our seed varieties, choosing soil and compost to fill the pots, deciding on how many pots to grow, and exactly which measurements to make.
Denise at CEH was busy ordering parts, soil and compost at the end of 2022, so that the CEH workshop could make this prototype growing pot. Early this year, Denise set up a test using small pots with different amounts of quartz mixed with the soil and compost to see how readily the mixtures drained. Next, we'll test the prototype growing pot to see if we can control the level the soil saturation. We will also carry out a chemical analysis on the soil and compost to see what nutrients and sulphur compounds are in there.
March 2023
Setting up the pots in the GroDome at UK-CEH
After that, we started the pot production line. Denise drilled a single hole in the base of each pot (actually a plastic bin, as pots would have had too many holes in the bottom for our experiment), using a special stepped drill bit.
At the end of March 2023 I stayed in Wallingford for the week to help Denise set up the pots for the barley and brome grass experiments in the GroDome at UK-CEH. The pot set up went very although it was totally exhausting! I arrived with barley seed that I had germinated a few days previously, and the first thing I did was to plant the seed into growing cells in seed compost, along with the Bromus racemosus seeds which was planted directly into the compost. While I was doing this, Denise and her colleague Tim carried in 72 breeze blocks (each weighing over 18 kg) and set them up as stands to put the pots on. I couldn’t even lift one of them, so I’m very grateful that Denise and Tim did this very heavy work.
One evening Denise scooped out some pond sludge from her garden pond, which we expect to contain sulfate reducing bacteria.
At the end of the week, we set up the pots for the first month of the experiment. This involved waterlogging a number of pots so that they have standing water in them. We had to fix a few leaky pots at the start. Each pot received around 1 tablespoon of pond sludge when it was waterlogged, and half the pots received an amendment of sulfate in the form of sulfate of potash. We are hoping that the waterlogged pots will develop conditions suitable for sulfate reducing bacteria to thrive in over this month while our barley and bromus seedlings are growing on in seed compost.
While Denise was doing the drilling, I fitted the end connectors on the pots. Then we stuck some wire mesh over the fitting to stop soil escaping, and attached a length of tubing to the fitting. We filled the very bottom layer of the pot with clean quartz chips, and cut pieces of garden membrane and fitted them on top of the quartz layer. Then we started the really heavy work; mixing the growing substrate. The is a mix of Kettering loam, Carr’s organic soil improver, and more quartz chips to help drainage. Denise has a very useful trolley with high sides which we used to hand mix the substrate, hauled in from outside on another trolley. Over the week we moved and mixed over 1000 kg of material! First we put a thin layer of mixed substrate over the garden membrane in each pot, and watered it so that it was moist. We then carefully poured in two lines of silver sand. We fitted the soil water sampling rhizons into the silver sand and held them in place with plastic pegs. Then we filled up the pots with the growing substrate.
We also visited a local farm which has a crop of winter barley growing to collect a soil sample from the root zone which might contain barley mycorrhizae to help our barley grow, and we collected soil from the root zone of grassland in the floodplain of the Thames at Wallingford which might help the brome grass grow. We’ll add this to the pots when we plant them up in around a month’s time
Each pot has a drainage tube attached to the bottom fitting, which can be set at different heights to control the water level in the pot. There is a bucket for each pot to catch drainage water when we drain the pots, so we can check the volume of water drained and measure it for various parameters.