Conventional tillage damages soil

A three-year Massey University study has confirmed findings that a significant amount of carbon dioxide is lost into the atmosphere through conventional tillage.

The study, carried out by graduate student Amandeep Singh Ghatohra, showed that tillage or ploughing loses approximately three tonnes per hectare more CO₂ into the atmosphere than Cross Slot no-tillage, said to be the most effective form of no-tillage. This significant loss contributes to global warming and depletes the nutrients in the soil.

Ghatohra’s co-supervisor, Dr Craig Ross, says the loss from conventional tillage is serious. “Only about 20% of the million hectares of annual agricultural seeding in New Zealand is carried out by no-tillage, so we’re discharging about 2.4 million tonnes of CO₂ into the atmosphere annually as well as reducing the organic content of our soils,” he said.

Dr Ross says the conclusions reached in the study “illustrate the importance of retaining organic matter in the soil and reducing carbon emissions”.

“Carbon is essential in the soil to retain water, soil structure and microbes and to provide nutrients to plants,” he said.

The effects of conventional tillage are particularly serious during cropping, which doesn’t return much organic matter to the soil because the above-ground crop residues (straw) are often removed and, as a result, earthworm numbers decline. Earthworms process residues through their digestive system and keep the soil in good health.

As with the findings of overseas studies, Ghatohra’s thesis points to no-tillage as the means of minimising carbon emissions and retaining soil quality.

“The ultimate outcome of such a study is to see the decline of conventional ploughing and the greater use of Cross Slot no-tillage technology which has been refined in New Zealand,” Dr Ross said.

The study was a combination of field testing to compare no-tillage with cultivation and incubation tests in the laboratory where soil samples from The Manawatu and Waikato were examined and evaluated.

The study has been welcomed by international soil scientist Dr John Baker. He says soil is the biggest storer of CO₂ that people have influence over, with global tillage estimated to account for 15-20% of the total CO₂ in the atmosphere.

“People can see and smell pollution from car emissions and factory chimneys because they contain other pollutants in addition to CO₂, but carbon dioxide escaping from ploughed soil goes unnoticed because it’s a colourless and odourless gas and people only see the dust,” he said.

“If New Zealand wants to be serious it should cease tilling or ploughing the soil and instead use low-disturbance no-tillage.

“Australian farmers and those in the prairies of North America realise that ploughing has been destroying their soils by reducing the organic matter levels. The long-term effects have been reduced crop yields, dust storms and soil erosion.”

Dr Baker says if left unchecked, these factors would ultimately cause famine in some areas.

“Because our soils and crop rotations in New Zealand are kind, many of our arable farmers still have their heads in the clouds in this respect but won’t be able to remain so forever.

“To our credit, the more progressive New Zealand arable farmers now lead the world in applying low-disturbance no-tillage.”

Dr Baker believes ploughing should be as actively discouraged as smoking, as it is in most arable countries in the world.

He says soil is “a living biomass of its own and if you kill the biology that nature provides, it will reduce the yield potential and make the soil unable to sustain itself, let alone feed 50% more human mouths by 2050”.

“We lose 27 billion tonnes of soil per year from the Earth’s surface through tillage and it’s time to take steps to rebuild the biology of the soil so we can keep on feeding ourselves.”

Dr Baker says the trend can be reversed overnight through changing to low-disturbance no-tillage technology which reduces carbon emissions, enriches the soil and increases yields.

Through the development of his Cross Slot no-tillage machines and systems which are used extensively throughout the world, Dr Baker has been nominated for the 2013 World Food Prize.