The Nutrient Cycle - Soil: Reflections on the Basis of our Existence - page 79

My Compost Bin
Organic matter can decompose rapidly in a compost bin, especially when fresh, and
can lose up to two thirds of its weight in the first few weeks when fungal and bacte-
rial processes are at their most active. But getting the right balance in your compost
bin is not always easy. If the mix is too damp it can smell sour, and you will find the
compost sticky and poorly decomposed when you rake it out from the bottom. After
tipping food scraps into my compost bin I line the bottom of the bucket with a thick
layer of sawdust to absorb excess moisture before putting it back in the kitchen.
The modern compost bins sold for household waste are actually not ideal for
the job. Near-hermetically sealed, they create an ambient environment with too
much moisture and too little oxygen. One way to overcome this is to place your
bin on a pallet and allow excess water to run out, provided there is a drainage hole
in the bottom. I collect this runoff, mix it with tap water and use it to water my
tomatoes. Ideally, you should stir or turn the compost every now and then to oxy-
genate it. Some compost bins are designed to rotate, which makes this easier.
When composting nitrogen-poor materials like straw and twigs, it can be difficult
to get the decomposition process going. Microorganisms need nitrogen to reproduce,
and poor aeration may halt the degradation process. Conversely, kitchen waste con-
taining a lot of food scraps can contain too much nitrogen. Here, sawdust—which
contains much more carbon than nitrogen—plays a balancing role. Any excess nitro-
gen may run off as nitrate or seep out as ammonia or nitrous oxide, though this is
detrimental because nitrous oxide is a greenhouse gas and ammonia and nitrates
cause eutrophication. Leaching of these substances also deprives the compost of
important fertiliser and defeats the object of the exercise. Better, then, to bury the
waste in the vegetable patch so that growing plants can absorb the excess nitrogen.
A pumpkin grower called Börje Gustavsson has developed a special drill for
precisely this purpose. Pumpkins are a demanding vegetable that requires aerated
soil, heat and plenty of nutrients and water to grow to a good size. Food scraps
buried near the plants provide nutrients, aerate the soil and create heat when
decomposing. Börje, who won the Swedish Pumpkin Championship in 2003 with
a monster weighing four hundred and fifty-three kilograms, reveals on his website
a key ingredient in his success: a urine-diverting toilet. I have tried using the drill
in my garden but as yet not managed to grow a pumpkin as large as Börje's. It
looks like the next step will have to be using urine as fertiliser if I am to reach the
upper echelons of the pumpkin-growing world.
My best composting efforts came as a student at Capellag￥rden School on the
Baltic island of Öland, where I took a gardening course and learned to take the
right amount of chicken fertiliser (for adequate nitrogen) and mix it with twigs
from old raspberry bushes (to provide aeration), weeds that had not gone to seed
and food scraps from the school kitchen. I covered the compost heap with a
thick layer of straw and stuck a plastic tube into the middle to provide aeration.
Heat and a good oxygen supply are vital for effective decomposition. I used to
enjoy watching the steam rising from the plastic tube on my morning visits to the
chicken coop to collect the eggs for breakfast.