Composting

By Jenny Hall

Introduction

Composting is a natural biochemical process of decomposition. It is possible for every stockfree grower to produce the darkest, nutrient-rich, earth-smelling compost. Adding well-made compost to the soil will ensure a healthy soil and healthier crops. The compost feeds the soil life, helps the soil retain nutrients, increases earthworm populations, suppresses disease and inoculates the soil, produces beneficial hormones for plant growth, improves drainage and provides air pockets for the crop roots to grow in.

Composting as a technique has advantages over turning in green manures, converting the soluble nutrients in the fresh materials into a more stable form (so preventing nutrient leaching). Composting also mixes materials giving a more balanced end product, can kill weed seeds, pests and diseases (if carried out properly), reduces the bulk of the materials and allows plant nutrients to be stored until they are required. The unfortunate thing is that there is never enough compost to go around and that is why some stockfree growers recommend composting and green manuring as complementary techniques whilst others recommend zero tillage mulching systems as an alternative to composting.

Windrow composting – above 20 tonnes

Different composting methods from around the world are discussed by R.V. Misra and R. N. Roy in their paper “On Farm Composting Methods” (www.fao.org/organicag/doc/on_farm_comp_methods.pdf). Windrow composting consists of placing the mixture of raw materials in long narrow piles or windrows which are turned regularly. The turning operation mixes the plant-based materials and aerates the windrow. The equipment used for turning determines the size, shape, and spacing of the windrows.

Straw bale compost heaps – up to 20 tonnes

Compost heap with straw bale side, with tarp to stop nutrient loss. Photo: Stéphane Groleau

Iain Tolhurst of Tolhurst Organic (www.tolhurstorganic.co.uk) manages the following composting system by hand:

– Line up two parallel rows of rectangular straw bales, three bales high, no more than 3 metres/3 yards apart.

– Stagger the joins of the bales to make a stronger structure with one end closed in with bales, thus forming a bin.

– The structure can be any length desired, with more bales being added as space is required.

– The composting materials are piled half a metre above the bales and this soon sinks down to about half.

Drainage pipes placed under the bales and along the floor every metre will allow air in. Alternatively woody prunings can be laid at the base.

Compost heaps – market garden scale 1 to 5 tonnes per annum

Organic Growers of Durham recommend that heaps are built (either in bays or in a straw bale structure) so that their final size is about 1-1.5 metre³ after the initial piling up. The main advantage is good aeration and heat with no turning.

Allotment scale

Wooden compost bin

New Zealand box: despite several variations on a theme, the simplest New Zealand box is a wooden structure 120 cm/48″ square, 120 cm-150 cm/48″-60″ high. The wooden sides consist of 6-inch wide by ¾-inch thick boards attached on three sides to four corner posts. The box can be movable, or the posts can be sunk 30 cm/12″ into the ground. At the open end a divider in front slides down between two posts so that when you want to empty the box, you can pull the dividers upward and take them out one by one. You can double, triple or quadruple the size of the box. The thick boards forming the back of the bins stretch the entire length of the box. The bin will require end boards 120 cm/48″ long and partitions between each 4 foot bay. The bays should be covered with some form of lid. Simpler bins can be made out of pallets.

Mixing your ‘greens’ and ‘browns’

The golden rule of composting is ingredients of 2 parts ‘greens’ to 1 part ‘browns’ in the presence of air and moisture.

Compost ingredients

Greens, nitrogen-rich, lush and fresh

Vegetables (peelings, cores, grade-outs), crop residues/foliage, grass cuttings, fresh green manure plants, annual weeds not in seed.

Browns, carbon-rich, dry and stemmy

Straw, bean haulm, tomato vines, hay, bracken or any other older plant foliage.

Not recommended

Autumn leaves (better for leaf mould), perennial weeds, unless the heap reaches 50°C for a week, annual weeds in seed, twigs and sawdust (carbon ratio too high). Plant-based cooked food will compost but may attract rodents

Prohibited under the stockfree organic standards

Meats, dairy products, fish products, animal manures or by-products, synthetic materials.

Compost is ideally prepared from plant-based materials with an initial Carbon:Nitrogen ratio of 30:1. During the composting process the nitrogen percentage increases, whilst the carbon bulk is lost to the atmosphere as carbon dioxide. It will reduce its carbon content to have a ratio about 10:1.

When starting composting

– if the C:N ratio is too narrow, then there will be insufficient carbon to provide the energy for the micro-organisms to degrade the organic wastes and losses of nitrogen will increase.

– if the C:N ratio is too high, then breakdown will take a long time and will lock up the nitrogen. Therefore, trunk wood and sawdust are not suitable composting ingredients.

Sieving compost (Langerhorst). Photo: Stéphane Groleau

The difficulty the stockfree grower will often encounter is finding enough ‘browns’. Do not rely on twigs or pernicious weeds to make up this element, as they take a longer time to break down and can ruin the quality of the compost. I’m all in favour of eliminating the hard work of sieving. If you are trying to make fine-grade compost suitable for vegetable growing, it is better to leave woody elements in log piles for beneficial insect life as it is better for them to break down through a fungal process. Using straw will prove the easiest way to find sufficient ‘browns’ in the bacterial process of the compost heap.

Straw has hollow stems and can improve aeration of the heap. Apart from aeration, the advantage of straw (dried cereal stems) over hay (dried grass) is the lower weed seed content.

Layering and chopping materials

Plant-based materials will compost best if they are between 2 cm – 5 cm (1″ – 2″) in size because of the larger surface area for compost microbes to work on. However, growers will not have the time to go around cutting all materials to this size. Of more importance is correct layering. Ensure that the different types of ‘greens’ and ‘browns’ are well mixed by adding layers no thicker than 10 cm/4″. Waste vegetables such as root crops and onions should be kept in individual layers. Brassica stems and prunings can easily be chopped with a sharp shovel or pulverised by a hammer.

Heating the heap

To get a good heat you need to create a 2 cubic metre compost heap. Materials should be stockpiled until there are enough ‘greens’ and ‘browns’. If done correctly, a pile will heat to high temperatures within three days. If it doesn’t, the heap is either:

– too wet and you will need to spread the materials out to dry;

– too dry and you will need irrigate the heap with a hose or watering can; or

– deficient in nitrogen – add grass cuttings from the holding or brewers hops (ensure that they are free from animal inputs).

During composting a maintained temperature of 60°C is strongly advised. A heap that does not heat to at least 50°C for a week is likely to contain weed seed and disease organisms.

Turning the heap

The easiest way to turn the strawbale heap is to extend the side bales by about two bales long and turn the heap into the new area with a fork, adding more greens or browns as required. For the New Zealand or pallet box the heap is moved from one bay to the next.

Covering to prevent waterlogging

Excess moisture drowns beneficial microorganisms. The moisture level should be the equivalent of a wrung-out sponge. Therefore, rain should not be allowed to enter and wash through the heap. There is no point in going to all the other effort with the composting process, only to allow the goodness in the heap to be washed away. Also compost leachate can be a pollutant akin to animal slurry running into watercourses.

It is therefore prudent to cover heaps and ensure that any rainwater shed ends up outside the heap. Covering a windrow may prove difficult, although Eliot Coleman suggests covering them with woven plastic matting (Phormisol brand name) which helps shed the rain but still allows for aeration.

For the straw bale heap a simple way is the one designed by Iain Tolhurst. Drape a tarpaulin over a ridgepole erected on scaffolding posts. The tarpaulin should be tied down by bales on the sides, but be careful not to cover the sides of the bales, as this will prevent air entry. New Zealand boxes and pallet boxes can be covered with slanting rigid boards covered with roofing felt or tarpaulin.

I personally find creating high-quality compost an extremely rewarding process. And if you observe the management techniques I have described you too may find the compost heap a source of excitement and joy. Applying compost to the soil presents the very building block of stockfree systems.

This article was originally VON information sheet Num 10. It was originally from an article in Growing Green International magazine which also covered household composting, but this part has been removed so that it is fully aimed at farmers.