Crop Rotations, Soil Fertility, and Digging (Part 2)

I was planting out wheat seedlings today, and looked over at two of the unplanted beds. A couple of days ago I had needed to empty a compost bay, so had tipped two wheelbarrow loads onto a series of unplanted beds. Having just written a post on Crop Rotations, Soil Fertility, and Digging, I realised that the two barrow loads of compost on the beds was three times the level needed to maintain soil fertility needed for the Grow Bio-intensive system of Jeavons. (As explained in the earlier pos)t. I started to think about the actual amount of compost that it takes to feed two people. What follows might make you think twice.

The picture below shows four beds with the compost piled. The plants growing in the front two beds are chicory.

Compost Piled

Compost Piled

How Much Work for No Dig Gardening?

In my last post I explained that a no-dig system uses two inches of compost to build soil fertility, whereas a high level of fertility is maintained in the Grow Bio-intensive system with only half an inch. Whilst it is clear that one takes four times as much compost as the other, what does that actually mean in terms of work? One of the benefits claimed by people who favour No-Dig is that it is less work in terms of digging, and of weeding, however what about in making and moving compost?

Jeavons says that you can meet all of the food needs for one person with 40 x 100 sq foot beds, so 80 beds for two people. It takes 2/3 of a wheelbarrow of compost to make a 1/2 inch layer in one bed, which is 53 1/3 barrows for 80 beds. Organic matter reduces in volume by 1/2 or more in the composting process, so that is 106 2/3 barrows of organic matter into the composting system and turned twice. Add the two totals together makes 160 wheelbarrows of material shifted in total. That’s not bad, but more than most people would do.

For the no dig system that is multipled by four, so 213 1/3 barrows out and turned twice, 426 2/3 barrows in, for a total of 640 wheel barrow loads of organic matter shifted. It equates to about 95 cubic yards of material in a composting system. To put that into perspective if your compost heap was 3 feet wide, and three feet tall, it would be 95 yards long. Yes, that’s right, 95 yards long.

Now I am not a clever urban gardener, or somebody who teaches others how to grow food, but In terms of hard work, I would rather use a hoe, and hand weed, than shift an extra 480 wheelbarrows of organic matter. I realise that my urban growing cousins need the extra exercise to compensate for their sedentary lifestyles, and to save on gym fees, but I like an easy life.

Now I do know that most people are not trying to grow all of their own food, and that many have small(ish) gardens. Many are also importing their compost in ready made, either by their local council, or as aged manure, but there is a serious side to this. All of this organic matter comes from somewhere. One of the ethical principles of Permaculture is to reduce consumption, but this seems to contradict this fundamental ethic. In terms of scale what this highlights is the difference between growing food for fun, and growing to meet your needs, or to make a living.

How was Soil Fertility maintained in the past?

What struck me is how unlikely our ancestors were to do this. The old two field rotation switched growing grain with a fallow, and back. Animals were grazed on the stubble after harvest, and on the subsequent fallow, before sowing with grain again. No compost was used to build soil fertility. Nutrients were returned in the form of manure ‘dropped’ in place by the animals, and the ‘weeds’ grown during the fallow year. Manure was also created from the feeding of crop residues, materials gathered from the commons, and hay. The hay in particular was important as many of the hay meadows were on flood plains. The minerals removed from these by the taking of a hay crop were replaced by the silt deposited during flooding. This is similar to the use of silt in Indian and Chinese systems, effectively importing minerals lost. I recently read a short piece about the Hunza people, and noted references to high levels of minerals carried in rivers, created by the grinding of rock by glaciers. A modern equivalent is the use of rock dust as an amendment to build soil fertility.

On a garden scale the use of livestock could be mimicked by the use of chickens, alternating two or more areas for food production, and poultry forage.

Take care

Deano

3 thoughts on “Crop Rotations, Soil Fertility, and Digging (Part 2)

  1. Pingback: Wood Ash and Soil Fertility « The Sustainable Smallholding

  2. Pingback: Crop Rotations, Soil Fertility, and Digging (Part 2) « The Sustainable Smallholding

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