By Jenny Hall.
Composting is a natural biochemical process of decomposition. It is possible for every vegan-organic 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 VON members 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. 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
Iain Tolhurst 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 metre cubed after the initial piling up. The main advantage is good aeration and heat with no turning.
New Zealand box – despite several variations on a theme the simplest New Zealand box is a wooden structure 120cm / 48″ square, 120cm–150cm / 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 30cm / 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 120cm / 48″ long and partitions between each 4ft bay. The bays should be covered with some form of lid. Simpler bins can be made out of pallets.
Can buy various plastic bins.
Mixing your “greens” and “browns”
The golden rule of composting is: ingredients of –
o 2 parts “greens”
o 1 part “browns”
in the presence of air and moisture.
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
Autumn leaves (better for leaf mould); perennial weeds, unless the heap reaches 50 degrees C for a week; annual weeds in seed; cooked food, unless it is entirely vegan, but may still attract rodents; twigs and sawdust (carbon ratio too high)
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.
The difficulty the vegan-organic 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 2cm – 5cm (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 10cm / 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-metre-cubed compost heap. Materials should be stockpiled.