23/3/26 - Broad Bean Experiment: The End

Towards the end of Winter on our allotment site, we were lucky enough to receive a delivery of well rotted manure and organic matter.  This was different to our usual deliveries of digestate, being mostly derived from animal manure and a mix of gypsum and other organic waste.  When it arrived, I derived an experiment to see how good, or bad it was and to gauge the effect it had on a simple broad bean crop.  A full description of the experiment can be found here.  

The start of the experiment was 2 months ago, almost to the day.  So how did we get on?  Regular readers of my allotment diary musings will have come across occasional updates on progress, but it's time to sum up the last two months, and perhaps bring some conclusions.

Observations

After the first two weeks of leaving the 6 pots in the polytunnel, there was no sign of any sort of germination or growth.  But this was a particularly cool part of the year, so if anything was going to happen, it was going to be slow.  Actually, it was nearly a full month before the first signs of action, and that was observed in the two pots that were being used as the control set, so the ones that contained regular shop bought multipurpose compost.  The signs were minimal, with the smallest suggestion that something was pushing against the top surface of the compost, ready to poke through.

Progress was slow, but eventually on the last day of February, we had some action!  Signs of growth in the control pots, and the earliest signs in the pots containing the 50/50 mix of manure and compost.

Once germination had started, and the first leaves were visible, progress stepped up a bit.  The following week, on 6th March, the control pots (the furthest away in the picture below) seemed to be developing nicely, and were becoming nicely established.  The 50/50 mix were growing, but were a little behind compared to the control.

On my following visit on 10th March, things had pushed on a bit more, and it was now that we started seeing some key differences.  The control pots had maintained their growth rate and were developing nicely as we might have expected to be the case at the start of the experiment.  But the pots containing a 50/50 mix of compost and manure had started to exhibit some different behaviour.  One plant had put on only a small amount of growth, and was yet to catch up on the control pots, but the second of the 50/50 pots not only had continued to grow well, but had easily grown larger than either of the control plants.  Importantly, notice that both pots containing 100% manure have no sign of germination!

By the 15th March, growth had continued across all 4 pots with no sign of germination in the last two pots.  It also became very apparent that by this time, the 4 other pots were pushing roots out of the bottom of the pots, however that's not visible in picture below.  Another key observation on this visit was that the second of the 50/50 mix plants had put on another growth spurt, had overtaken the control plants in terms of size, and was on the way to catching up it's partner.

Come the 21st March, it was time to bring the experiment to a close and looking at some conclusions.  The plants had outgrown their small pots and were in desperate need of being planted out.  The last week in particular, where growth was happening, all 4 plants enjoyed some very warm temperatures in the polytunnel.  By now, the 50/50 pots were dwarfing the control pots which are tucked away in the background in the picture below.

When I was planting out the 4 successful plants, I looked at root structure in all 6 pots.  You might assume that in the pots with no growth or germination (filled 100% with manure) that there would be no sign of growth.  But, when I turned on of the pots upside down, there was a little bit of evidence to suggest the seed had germinated and started to produce roots, but they soon died back and were very small and brown when compared to the roots of the other plants.

The root structure of the 50/50 pots was very healthy and creamy coloured.  Plenty of evidence of healthy growth.

When compared to the root growth on the control plants, there was very little difference between them although there does appear to be more root on the control pots as shown below.

These healthy plants were all moved outside and planted in a bed amongst my other broad bean plants.

Conclusions

From the 2 months of that the experiment was run and the observations that were carried out, I can now make the following conclusions based on the findings of this case.

• For prompt and reliable germination, just using normal shop bought, multi purpose compost will give you slightly quicker germination, but only by a matter of days.  However, cooler temperatures will slow the process down, no matter what the growing medium used is made up of.
• If you have a manure mix in with the compost, it inhibits germination slightly, but it will still take place.  After a delayed start, the plants will not only germinate, but will likely catch up and overtake plants grown in purely in compost over the course of a 6 to 8 week period.  This could be because of the additional nutrient content.
• Leaf quality throughout all successful plants was excellent.  There was no sign of leaf curl or deformity which has previously been proved to be a result of contamination, typically cause by aminopyralid based weed killers.  This experiment is good evidence that there was nothing present in this sample that could cause any issues with growth.
• Root growth in 100% compost growing medium was more significant when compared to the 50/50 manure compost mixed.  The additional root growth could be a sign of the plant putting extra effort into searching for added nutrients to aid it's growth.  The 50/50 mixed would have presented more nutrients, easily accessible to the plant in it's early stages, and therefor would not have needed more significant root growth.

Summary

In summary, when applied specifically to broad beans in these conditions, sowing direct into a 100% medium of manure is almost guaranteed to fail.  If you a gardener who likes to start their beans undercover in late Winter or early Spring, it's worth considering introducing a mix of well rotted manure into your potting mix, but not essential.  It depends if you value a strong early root growth, that could help server the plant better when it is transferred out into it's bed, as a priority, or, if you want a larger plant (but I wouldn't say any stronger or healthier) when it comes to transplanting in early Spring.  

The whole concept of this experiment was to find out the effect of introducing manure in different quantities into the growing medium of beans started out under cover.  In reality, I will probably continue to direct sown broad beans rather than start them in pots.  What isn't known is the effect it will have on other seeds of other plants.  

Thanks for reading 😀