Comparing forking/no dig, different composts, and no rotation
A trial I have run since 2013 looks to understand the effects on plant growth of soil cultivation, compost use, and no rotation. Or I should say minimal rotation, as you see below.
The trial came about after meeting some Japanese growers near Avebury. They followed the Shumei teachings of Mochiki Okada (1882–1955), who advocated cultivating gratitude to soil for health in mind and body:
- No compost or manure is added to soil, as this can prevent it from achieving its ‘natural composition of complexity and balance’.
- No rotation, so continuous cropping of the same plants in the same place every year, to ‘encourage growth of specific soil organisms beneficial to each one’.
- Seed is saved, so that all seeds contain the genetic information they require to grow best in the location and soil they ‘know’.
- Weeds are tolerated and so is cultivation. At Avebury they even use a rotavator – I observed this frequently during the time I was working with them.
I like some of their approach, except for one thing in particular: I feel no dig and surface mulching both express maximum gratitude to soil! The only home-saved seeds I use are climbing and broad/fava beans. All other seeds are from Bingenheimer Saatgut, raised in the broadly similar climate of Germany and organic or biodynamic as well.
The Three Strip Trial
The three strips of this trial each measure 2 × 9 m (7 × 30 ft). Between each strip is a 40 cm (16 in) path, from the concrete path to the trees.
In 2013 we didn’t add any organic matter to Strips 1 or 2, compared to 5 cm (2 in) of old, but rather lumpy cow manure, which was added to Strip 3. Weeds were killed by digging Strip 1, and by mulching the other two strips with polythene. The main growth before this trial was grass, with creeping buttercup and dandelions.
First year summary (2013):
- Strip 1 – dig, no compost, weeds killed by the digging
- Strip 2 – no dig, no compost, weeds killed by polythene mulch
- Strip 3 – no dig, 5 cm (2 in) of compost, weeds killed by compost and polythene mulch
In the first two months after planting, growth was much the slowest in Strip 2. I believe there were two reasons for this:
- No compost meant that new plants were in competition for nutrients, with weed roots that were still decomposing. A milder version of having wood in the soil, which has a similar effect. Hence my recommendation to apply some compost/organic matter on top of decomposing weeds, especially when you want to crop immediately, at the same time as weeds are dying.
- The digging of Strip 1 happened four months before first plantings: time for bacteria to decompose many weed roots and thus have more nutrients available for plant growth. Digging stimulates bacterial activity in the short term – through introducing oxygen at the time of cultivation – but not in a sustainable, long term way.
By autumn the difference between Strips 1 and 2 was much smaller, such that their final harvests were similar (although skewed by the beetroot, which swelled a lot in autumn).
- The standout result was a 50% higher total harvest from Strip 3. This persuaded me to change the trial parameters.
One factor to be considered in my trials is that I am running a market garden, not a research station. I do not have funding for trials, unless I fund them from private income or sale of goods. I did not want the lower yields and lower revenue that resulted from not adding compost to Strips 1 and 2. Also it would have taken more time to keep them weed free, meant more watering, and would have depressed the bountiful look of Homeacres’ garden.
A table showing harvests from the Three Strip Trial in 2013
Changes in 2014
In May 2014, I used my sharp spade to scrape 4–5 cm (1.5–2 in) of soil from the 30 cm (12 in) width of what became sunken paths, between slightly raised 1.2 m (4 ft) beds. Steph was helping, and together we spread compost on Strips 1 and 2. This raised the beds enough to demarcate them in a clear way, with six beds in each strip.
The lowering of paths and raising of beds is an optional extra in any garden. At Homeacres I mostly have beds ‘raised’ with compost only, which are not very high – a more accurate term would be mounds. However if your site is wet, say with water lying in winter, I would lower the paths to raise the beds; this does involve some earth moving.
The other change was to switch from annual digging to forking, from autumn 2014. In February 2014 I had already dug Strip 1, so the effect of forking is from 2015 onwards.
Strip 1 is different to the dig bed of my other trial, because of forking and not digging, and applying compost as a mulch rather than incorporating it.
Summary from 2014 onwards:
- Strip 1 – soil loosened by forking each winter without inversion, then 5 cm (2 in) of green waste/mushroom compost (half of each) on the surface in December. (In 2014 it was all green waste.)
- Strip 2 – no dig, then the same compost as Strip 1: 5 cm (2 in) of green waste/mushroom compost (half of each) on the surface each December. (In 2014 it was all green waste.)
- Strip 3 – no dig, then 5 cm (2 in) of composted cow manure on the surface in winter; the paths had a wood chip mulch in March.
Looking at the photo from May 2014, you can see the six beds of each strip and the narrow paths between. I left these paths as old pasture without any mulch; some of the dead grass and weeds were still visible for almost two years.
I numbered the beds, with Bed 1 nearest the concrete path and Bed 6 nearest the apple trees. Therefore each of the three strips has six beds, shown in the drawing below.
Green manures or vegetables?
After the squash harvest in each of the first three years, I sowed mustard as a green manure because I didn’t need the space for other vegetables. This mustard is suitable for no dig, because of being killed by frosts of -5°C (23°F) or lower. Some gardeners worry because it’s a brassica, but I rotate less than they do, and that is another aspect of this trial.
Since 2016, I have taken to planting brassicas and spinach after the squash harvest and often on the same day, in late August. Kuri squash are brilliant for this because they mature so early, compared to say, butternut.
We noticed more pest damage on Strip 3 in 2014 (mostly slugs), thanks to the cow manure being not fully composted and rather lumpy, with some straw still visible. Since 2016 I have been careful to use finer cow manure, making a more even surface with only small lumps.
2014 was a difficult spring for leatherjacket damage. They are larvae of craneflies (Tipula spp). Mostly the brown larvae live among grass roots and may be a problem in year one, when you are planting into compost on old pasture where the larvae are already present. It was unusual for them to be such a problem in year two.
The only remedy I know is to hunt with one’s fingers in the compost, near to seedling plants which are visibly damaged. You can see holes in base leaves and even plants that have fallen over due to stems being eaten. Steph and I found a fair few leatherjackets, especially among small beetroot and lettuce; most damage is to spring plantings, then the larvae pupate in June.
2015–17
Again in 2015 there was more slug damage on Strip 3, especially to carrot seedlings and even to some parsnips. Strip 2 gave more harvests than Strip 1, for reasons yet to be discovered. I suspect it’s because of damage to mychorrizal fungi.
The forking we do is as gentle as possible; I aim to loosen only, with almost no lifting of soil lumps. The soil always feels pretty loose while forking.
2016 was a year of bountiful harvests, after a warm spring and fine summer, and the totals from each strip continued to rise. This was also due to changes in the vegetables grown, such as lettuce – always high yielding by weight.
Furthermore I had more help. and could be more rapid with second plantings, often on the same day after clearing the first crops. For example, on the same morning we might harvest all remaining potatoes and then plant leeks.
Another factor in the higher totals is cabbage. The Filderkraut had time to make heavy hearts, after we had cleared the broad beans. And Chinese cabbage is mostly water! In this climate its best time of growth is autumn, from sowing between 30 July and 7 August. Slugs love Chinese cabbage, and Strip 3 suffered again, as did the carrot seedlings.
In autumn 2016 we spread older (3 years) and finer cow manure compost, and this helped growth on Strip 3 in 2017. Nonetheless there was damage to carrot seedlings again, and in August I filled gaps in Bed 6 of Strip 3 with plants of kohlrabi.
- Leek yields in 2017 were the highest ever, growing for the third year in Beds 4, after potatoes. The Filderkraut cabbage heads grew enormous, also their third year in Beds 3.
- There was an interruption to ‘no rotation’ in Beds 2, after high winds on 7 June ripped out the plants. I had some spare beetroot from a sowing in early June and we planted them instead.
Adding the harvests of 2014–17 gives interesting totals. The figures suggest that forking soil is not helping growth, and that finer compost gives best results. Also that continuous cropping (no rotation) is less terrible than one often hears!
I was wondering how this would all go in 2018, and whether the totals from each strip would continue to rise.
2018
The 2018 results reflect a dry growing season from early May until November, with only 272.2 mm (11 in) of rain in that half of the year. This compares to the average of 474 mm (19 in) for that period, an unusually large anomaly for such a long length of time. Plus it was warmer and often breezy, with high rates of evapotranspiration.
Considering the weather, growth was good. We watered from rain butts when possible and with a hose as well – maintenance rations, except for salads and plants close to harvest. Moisture levels looked similar on all beds, judging by the amount of wilting leaves on hot afternoons in the summer.
Our watering helped the neighbouring apple trees, and by October I was noticing plenty of new growth on trees adjoining the kale of Beds 6, which struggled for moisture as a result! In contrast, the apple trees – which are bordered by grass and received no water – made almost no new wood after their July pruning; normally they would have added another 10–20 cm (4–8 in).
The table below reveals continuing trends and some new differences, in particular larger second crops from Strip 3. Leeks, cabbage and chicory noticeably grew stronger in this strip in autumn 2018.
Perhaps there is a higher nutrient status in the cow manure, although it was three to four years old by 2018. Furthermore, the cow manure heap had been open to rain washing through for two years, and had grown squash in 2016, then potatoes and kohlrabi in 2017.
For some reason the squash harvest on Bed 2 of Strip 3 continued to disappoint, and I have noticed, when dibbing holes to plant, that the soil is harder there. This bed puzzles me.
Once again, forking has slightly depressed the yields of Strip 1. Sometimes the growth looks similar between Strips 1 and 2, but harvests weigh less, from leaves being less dense. Possibly this is related to damaged soil fungi, resulting in lower availability of nutrients and moisture.
A table showing harvests from the Three Strip Trial in 2018
Photos and tables for 2019 show strip 3 catching up, continuous cropping going well
Two things were especially notable in 2019:
- There were higher harvests from Strip 3 – though we did use a different cow manure (from a depot rather than a farm), and the straw was chopped.
- There was the highest ever harvest of broad beans, cabbages and potatoes, in the fifth consecutive year of growing in the same soil. In case you may wonder, these plants root deep into the soil. I am often asked if the annual application of compost is equivalent to ‘new soil’. The answer is no, it’s just food for soil organisms, and plants are rooting into the same soil which is well fed.
The 2019 harvests total 363 kg on 65 m2, including paths. That equates to 56 tonnes/hectare or 22 tonnes/acre of kitchen ready food (except for the pods of broad beans).
And the trial continues. This chart shows harvests in subsequent years.
No rotation of potatoes and cabbages
This has become one of the most interesting parts of the trial. It’s actually something I find difficult, having been brought up in the farming world where rotation is seen as a fundamental necessity.
2022 was the eighth year of growing potatoes in the same soil. The harvest was higher than ever at 58 kg/128 lb of Charlotte potatoes on 11th July. They were from homesaved seed potatoes.
Cabbages in 2022 were super healthy, again in year eight of growing in the same place. The harvest from 18 cabbage plants was 38.5 kg/85 lb of cabbage hearts, trimmed of outer leaves. Over 2 kg/4.4 lb per cabbage.
Many visitors marvel at this when they are from allotments where clubroot is common. That is from soil being over cultivated and from soil life being underfed.
When you get these basics right, no dig with organic mulches on top, the rules change. Growing becomes easier!
