Reality Cheques - Agri-culture: Reconnecting People, Land and Nature - page 68

Long-term agricultural experiments in both Europe and North
America indicate that soil organic matter and soil carbon are lost during
intensive cultivation. But both can be increased with sustainable manage-
ment practices. The greatest dividend comes from the conversion of arable
to agroforestry: there is a benefit from both increased soil organic matter
and the accumulation of above-ground woody biomass. Grasslands within
rotations, zero-tillage farming, the use of legumes and green manures, and
high amendments of straw and manures, also lead to substantial carbon
sequestration. There is now good evidence to show that sustainable
agricultural systems can lead to the annual accumulation of 300 to 600
kilogrammes of carbon per hectare, rising to several tonnes per hectare
when trees are intercropped in cropping and grazing systems.
Agriculture as an economic sector also contributes to carbon emissions
through the consumption of direct and indirect fossil fuels. With the
increased use of nitrogen fertilizers, pumped irrigation and mechanical
power, accounting for more than 90 per cent of the total energy inputs
to farming, industrialized agriculture has become progressively less energy
efficient. The difference between sustainable and conventional systems of
production is striking. Low-input or organic rice in Bangladesh, China,
and Latin America is some 15 to 25 times more energy efficient than
irrigated rice grown in the US. For each tonne of cereal or vegetable from
industrialized high-input systems in Europe, 3000 to 10,000 megajoules
of energy are consumed in its production. But for each tonne of cereal
or vegetable from sustainable farming, only 500 to 1000 megajoules are
consumed. 44
It is now known that intensive cultivation of cereals leads to reductions
in soil organic matter and carbon content. However, recent years have seen
an extraordinary growth in the adoption of conservation tillage and zero-
tillage systems, particularly in the Americas. These systems of cultivation
maintain a permanent or semi-permanent organic cover on the soil. The
function is to protect the soil physically from the action of sun, rain and
wind, and to feed soil biota. The result is reduced soil erosion and
improved soil organic matter and carbon content. Zero-tillage systems and
those using legumes as green manures and/or cover crops contribute to
organic matter and carbon accumulation in the soil. Zero-till systems also
have an additional benefit of requiring less fossil fuel for machinery passes.
Intensive arable with zero-tillage results in the annual accumulation of 300
to 600 kilogrammes of carbon per hectare. With mixed rotations and
cover crops, this system can accumulate up to 1300 kilogrammes of
carbon per hectare.
The 1997 Kyoto Protocol to the UN Framework Convention on
Climate Change established an international policy context for the