I read an interesting account of closed cycle habitat recently, it related
to Australian forests. Aussie soil is very old and long had most of its
nutrients leached. Forests survived via a process of recycling nutrients
many times over as decaying leaves/trees returned nutrients to the soil to
be reused by new growth. The forest nutrients were located in the trees, not
the soil. Early european settlers through the forest land was lush, a sorry
misconception, and 'mined' the available nutrients through the export of
timber and burning of forests and farming the soils. The exported timber
took irreplacable nutrients away. The farmed soils yielded an immediate
benefit but quickly became exhausted as nutrients were removed as food
through cropping and livestock. The closed cycle was irreversibly damaged,
beyond capacity to recover.
Every food item we consume has some form of cycle. Some are very small, some
very large. Tomatos grown in a backyard plot, consumed by the grower, plants
composted on site, regrown from seed from the previous years harvest and
enriched with green manure and waste tomatos (read poop) from the grower is
a simple closed cycle. The production and inputs are isolated to a backyard.
Tomatos grown in a hot house miles from the consumer might rely on petroleum
derived nitrogen using imported oil & other imported chemical fertilisers.
The seeds are sourced from growers many miles from the hothouse. The produce
is transported via road or rail and sold in markets many miles away from the
origin. The consumer eats the tomatos, whose poop gets taken away for
sewerage treatment and who may compost part of the tomato. Any residual
nutrient from the tomato that benefits the end consumers garden transplants
the residual nutrients (from a mass of inputs) many miles from the source.
The cycle of nutrients may see some returned to the earth but a long way
from where they started.
There are definite issues of sustainability in these, admittedly imperfect,
examples. Made me wonder about various cycles, closed and partially open, in
my gardening. One closed cycle I can identify is with my lawn. The grass
draws nutrients from the soil and puts them to work. I mulch my lawn and
leave the clippings to degrade. The nutrients are recycled back in to the
soil. Any extra nitrogen the lawn may need is supplied through clover. The
deep root structure of grasses will draw up potassium and phosphorous lost
through water leaching. In theory I need not bother fertilising my lawn.
Using a grass catcher and transferring the grass to a compost heap actually
relocated the nutrients from my lawn. In a sense I am mining my lawn for
nutrients. A closed cycle would see me leave everything where it is to cycle
nutrients around. In practise I do use waste coffee grounds and wood ash on
my lawn but that is as much to put 'waste' to good use as any concern with a
pressing need to fertilise.
I feed my dogs and cats various types of tucker. The cats shit around the
garden, often on the lawn or in flower pots as they are lazy, and the dogs
when they go for a walk. The inputs of food are off site however the
disposal of their poop I can use on site. The cat crap is good to amend
flower gardens. The dog poop goes under a hedge as a fertiliser. I can close
the cycle on my own property.
Likewise with growing vegetables. I have been experimenting with seed
collection from various crops. Provided I handle them correctly I can regrow
from last seasons crop. Using green manures can enrich my soil to limit the
amount of nutrients I need to apply, thereby minimising the amounts of
nutrients that are translocated. A guy down the road has chickens. I give
him some veges from time to time, he gives me the chicken poop. Aside from
the food inputs for his chickens, I can complete a cycle of food on a very
local level. The leaves that fall from my tree can be turned in to leaf
mould and used as mulch for the vege gardens. Theoretically quite simple,
even if the working out of the theory takes some learning through trial and
Gardening becomes quite interesting when you consider them as open and
closed cycles. One way of measuring sustainability is the notion of nutrient
mining. When I use prepackaged fertilisers I am mining nutrients from
another part of the planet. When I use chicken poop I am mining nutrients
from other soils. When my neighbour carts his lawn clippings off to the dump
he is mining the nutrients of his soil.