Stubble Burning In Canterbury Damages The Soil

Stubble Burning In Canterbury Damages The Soil

March 11, 2014

An international soil scientist is critical of the practice of burning residue which often occurs on farms after harvest.

Dr John Baker visited Mid Canterbury recently and witnessed a large scale burn off near Chertsey polluting the atmosphere. While it may not have harmed the soil at the time, it certainly will destroy much of the opportunity to improve the soil health in the future he says.

He says burning residues simply removes most of the carbon present in the residues of the previous crop by converting it to CO2 by combustion.

“The main way to maximise arable soil quality and health is to increase its carbon content, not burn it off. Increasing carbon and soil microbial activity in turn builds soil structure and is one of the strongest indicators of soil health or quality,” Dr Baker says.

Dr Baker, who has a MAgrSc in soil science and Ph.D in agricultural engineering from Massey University, has reacted with caution to a recent Foundation for Arable Research (FAR) report that “stubble burning is valued by some farmers as a rapid, economic and relatively benign way of dealing with crop residue.”

“Burning is bad for the soil as it destroys all the available new organic matter which is used to build humus. Residue feeds worms and builds soil organic matter,” he comments.

Dr Baker concedes that occasional burning can help with weed and pest control but is critical that FAR sees burning as creating a basis for a more productive and profitable farming system. Most of the evidence is to the contrary he points out.

“Retaining residue and seeding through it with low-disturbance no-tillage is a far superior method than intensive tillage (ploughing) with or without burning. Any form of tillage is also detrimental to soil quality,” he says.

Dr Baker, who was a finalist for the World Food Prize in 2013, cannot over-emphasise the importance of good quality soil. He says the single greatest challenge facing the world today is feeding the extra 50 percent population by the year 2050.

“Only four percent of the world’s surface has arable soil and that’s not likely to increase so we have to farm it more sustainably which we simply haven’t been doing,” he says.

“To farm it sustainably and increase crop yields requires preserving and maintaining soil quality and organic matter. I don’t see that happening on properties where stubble burning is a regular occurrence.”

Dr Baker has been researching no-tillage for 40 years and invented and manufactured a low-disturbance no-tillage drill that penetrates through crop residue on top of the ground and sows seeds and fertiliser directly into unploughed ground.

“No-tillage is the equivalent of keyhole surgery as opposed to ploughing which is invasive surgery,” he says.

“Good no-tillage causes minimal disturbance to the soil, traps the humidity, preserves micro-organisms and soil life, largely prevents carbon from escaping into the atmosphere and significantly improves crop yields. One kilogram of humus in the soil holds as much water as nine kilograms of clay. So it’s a no-brainer really.”

“It will simply become the key to feeding our world in the years to come.”

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