Category Archives: Green Mantle

compost making at The Oak Tree and sensor network design

Compost research moved to

I’ve moved the study into Elaine Ingham’s techniques of soil restoration using microorganisms and compost over to where it’s made more readable and set in it’s horticultural context by Joanne.

a compost heap tracked all the way from start to thermal equilibrium. The sensr for the green trace was reallocated to ambient about 1/4 way through

a compost heap tracked all the way from start to thermal equilibrium. The sensr for the green trace was reallocated to ambient about 1/4 way through

I recently tracked a compost heap from start to reaching thermal equilibrium. Partway through we started another one, and one of the sensors was allocated to tracking ambient. While a single data point isn’t conclusive, it was interesting to see the week 37 (12-18 Sept 2016) second breath of this heap after the second turn coincided with a week of particularly warm weather. This points to a potential ambient sensitivity and it being worth tracking ambient in future and perhaps insulating the heap more in the later stages.

I will keep the technology of remote temperature sensing here, because I’d imagine horticulturalists aren’t that into electronics 😉

NDVI investigations of compost-enhanced crops

I made a couple of NDVI images of the beans which had been greatly improved using compost compared to those grown without. The principles of NDVI as based on that

Generally, healthy vegetation will absorb most of the visible light that falls on it, and
reflects a large portion of the near-infrared light. Unhealthy or sparse vegetation reflects
more visible light and less near-infrared light. 1

Knowing that, it’s possible to see in the NDVI image that the compost-grown beans do seem to be reflecting more IR relative to visble light, I find this easier to qualify from the greyscale image Continue reading


  1. Understanding the NDVI PDF

Remarkable win on beans with compost extract

Last year we made compost and compost extract for use in the polytunnels. The extract was also looked at with the microscope. Most of the compost after making extract was used in polytunnel which has tomatoes in it. These look healthy and were praised by another local gardener, but there’s no control. However, we did have a control on the extract applied to the beans in another polytunnel.

If you look at the picture at the head of this post, on the RHS of the picture is the control. This is what we would have grown normally.

in the middle on the top you can just see a blue ribbon which is where application of the compost extract stopped. On the left are the plants where compost extract was applied to the ground, it ran out at the blue ribbon point. Same plants, same time planted, and the same set of seeds. The difference in vigour, height of growth and yield is remarkable and clearly to be seen. Continue reading

Growlight experiments using LEDs

We are going to do some experiments trying to lengthen the day light-wise on salad leaves, getting them jump started to harvest earlier. Britain is a funny place to grow things, the maritime microclimate means it is relatively warm for the latitude. The growing season can be limited by temperature and/or light. Because we are warmer than typical for the latitude there might be some mileage in tackling light. Britain is basically warm and dark from a plant POV. You tackle temperature using a greenhouse, or in our case a polytunnel.

the mounts let us set the lights higher as the seedlings grow

the mounts let us set the lights higher as the seedlings grow

plant-level view

plant-level view

Trouble is we have no power on site, so this is an LEDs and leisure batteries job. It’s easy enough to turn off the lights once real light is bright enough 1, but a leisure battery gets trashed if I just let it run down too  much, ideally I want to pull the load once it’s down to 11.5 V or so. This gets complicated when you have something charging the battery too, but the whole point I am trying this is because we are around the Winter Solstice so there’s not much light about. So the only way that battery is going to get charged is for it to be recovered, changed out, charged and reinstalled. So once the battery gets lower than 11.5V it’s time to pull the load and keep it pulled until the battery power is reset. Even if the battery level creeps up above 11.5V off load that load should still stay off.

the batetery, timer and low-voltage cutoff

the battery, timer and low-voltage cutoff

What LED colours?

LEDs give the opportunity to favour certain wavelengths – leaves are green because plants don’t use much green, which gets reflected back for us to see.

Red and a little blue seem to be the principal colours used in this Yorkshire facility

Red and a little blue seem to be the principal colours used in this industrial Yorkshire LED4CROPS facility

Red and blue seem to be the light colours wanted, with more blue in the initial stages, red for the flowering stages. This seems to be starting to be big business, though I do somewhat wonder at the approach taken. Many of the woes of industrial agriculture stem from its arrogance in separating variables and hitting one particular aspect for all its worth – chemical farming addressing nutrients but destroying soil micro-organisms that have cycled nutrients for millennia resulting in veg that increasing lacks trace elements (the McChance and Widdowson The Composition of Foods longitudinal research)  and tastes of bugger all being one example. There’s a difference between trying to push things a bit but still working with natural light and growing stuff in windowless warehouses and hubristic statements like

We are beginning to understand that growing crops in this way can improve their quality in many different ways, from their shape and colour to their flavour and nutritional value. We could, for example, increase plants’ vitamin C content.

Hmm. Maybe if we could answer why the mineral content of industrially grown foods has been falling and often tastes bland compared to 30 years ago or more I’d have more confidence in that statement. Can’t argue that yield has gone up due to industrial farming, but quality?

Back to the LEDs – we will always be short of power, though at least we are growing plants that can grow okay in the UK – salad leaves, just trying to advance them. Many people who use grow lights are trying to grow five-pointed leaf plants that aren’t typical UK horticulture. We should be having an easier job 😉 We are dealing with seedlings, which also makes life easier – we can get the LEDs much closer to the plants, a few centimetres. The RHS publication Science and the Garden: The Scientific Basis of Horticultural Practice seems to support this on page 211 which is just as well given our power limitations

1512_rhsOther sources on the web

LEDgrowlights seems to have to good stuff on what to look for in a grow light. Philips have got into this field, their 18W LED grow-lamps seem to be targeted at the flowering stage and it’s clear that red, deep red and blue seem to be where the action is, and NASA also seems to favour red and blue, indeed they seem to have had grief with just red in their early test.

Constructing a battery monitor/power manager

This is easy enough because I am looking for the battery voltage to drop below 11.5V after which I will shut off the lights. By putting this on our RF network I get the status reported back, and by using the Ciseco RFu I get an almost-free arduino chip so I can throw in a temperature monitor, as well as manage down the shocking 7mA quiescent current of the Arduino by sleeping it most of the time 2.

Measuring the battery voltage depends on the reference voltage which is supplied by a KY5033 linear regulator (Texas LP2950 fixed 3.3V) There are actually pretty good, within 2% across -40 to 100C, which is better than the 5% tolerance of my resistor divider, which I want to arrange so the output is 3.3V/2 when I apply 10.24V, which can be done with a 115kΩ top resistor into a 22kΩ lower resistor. The total string draws 12/137 mA which is about 100uA, and the source resistance is about 18k, above the 10k recommended in the datasheet but I am only looking for about 8 bits of resolution. I could put a capacitor across the ADC input to improve that, but I can live with the error.

Jeelabs shows I could take this a lot further, but it’s good enough. I will be powering a string of LEDs drawing about half an amp for half a day or more, so as long as someone gets to the battery in about a week after it shuts down I will only have drawn another 0.02Ah from this cause, plus a bit more from the temperature and RF reporting for a few seconds every 15 minutes.

system overview

system overview

Results – failed

because we couldn’t keep the power up long enough, it just needed too many changes of batteries. We were also fighting the fact that the lighting blocks some of the daylight, so it was probably overall a reduction of light.

I have had success using three 11W CFL lamps about 60cm above some seedlings at home where power is available, so the idea of manipulating light is sound. But it’s not low-power, unfortunately, even with LEDs.


  1. I went off this after reading the Philips material and some other web research in favour of a straight time switch
  2. the ATMega 328 does have a watchdog timer but it’s a slight git to use with the Arduino

Seed saving beans

The Seed Saver’s handbook says beans are easy to save, so it seems a good idea to start out with them, in this case some Sutton Dwarf beans. The idea if you leave them to dry in the pods and then save the good ones. Beans are an easy win as they adapt over the generations to the local conditions; they don’t use insects for pollination and the book says the gene pool is kept wide to allow self-pollination.
Right off the bat the book says that

The first pods to form are the best for seeds. They are to be found at the base and are larger than subsequent pods, Allow these pods to dry on the bush, and choose those from the most vigorous plants. Such refined steps cannot be taken on a large scale where a whole field is combine-harvested and threshed.

Well, we don’t have a problem picking seeds out of the combine harvester we don’t use 😉

the good bean seeds

the good bean seeds

The guys that wrote that book are Australian, and I guess they don’t have a problem with saying you need to store seeds at a relative humidity of 5%.

Closing the conservatory door at about 9 was a good move, though I am a long, long way from 5%!

Closing the conservatory door at about 9pm was a good move, though I am a long, long way from 5%!

So I am writing on the evening of what has been a reasonably warm sunny day and I see the RH starting to skyrocket to 50% by 10pm and realise that I need to close the door to the conservatory because the dew comes in the evening as the sun goes down, not in the morning. 5% is going to be a tough call in the UK, probably involving silica gel. Interestingly the Seed Saver’s Handbook says good airflow is more important that high temperature, and it should not go beyond 35C anyway.

long bean pods give the best results

long bean pods give the best results

They’re right about those lower pods – long beans are definitely the place to go for the size of the seeds. You have to be pretty discriminating about the seeds, however.

Continue reading

Using near IR to look for photosynthesis and plant health with NDVI

The NoIR Raspberry Pi camera comes with a blue filter to do near infrared photography – the blue filter ices the visible red but passes near IR which records as red, apparently.

NDVI image of something in the polytunnels

NDVI image of something in the polytunnels. Should have made a not of what this plant is 😉 Anyway, more red and going to magenta white overload=more photosynthesis

NDVI (Normalized Difference Vegetation Index) is the near IR plus red divided by near IR minus red. Take a look at this image for the meaning of the colours – red, magenta and white is more photosynthesis, cool colours and black are less. Chlorophyll uses red but doesn’t use near IR which it reflects, hence the difference carries useful information.Lots more at Public Lab. Continue reading

Measuring paramagnetism

There are two approaches to measuring paramagnetism that seem to be common. One is to use a balance to measure the slight attraction to a magnet – put sample in a balance, apply magnetic field, look for difference in weight of sample using a Gouy balance or use a torsion balance to observe the attraction in a horizontal plane which takes out the static weight of the sample.

The trouble with these two is the attraction due to paramagnetism is weak compared to the weight of the sample – these are lab bench instruments and the electromagnet consumes a lot of power. Although taking samples of soil is easy enough to bring back to the lab, one really shouldn’t be taking a hammer and chisel to ancient monuments to get a sample for a Gouy balance 😉

It's not really right to go chiselling a lump off this to insert into a Gouy balance...

It’s not really right to go chiselling a lump off megaliths that have survived thousands of years to insert into a Gouy balance…

The other way of measuring volume magnetic susceptibility is to stick the sample into a coil and measure the inductance – with a different configuration  of the coil as a search coil it can be used to measure susceptibility at the rockface.

Continue reading