“It seems there are three major claims the organic/biological movement will make. They are about food quality, soil quality and environmental quality,” Edmeades said.
But he cited the first soil fertility study ever conducted in NZ back in 1954 where dung, urine and grass clippings were returned to the test grass areas, and compared with test areas where there were no nutrients returned. Predictably the pasture yields in the returned areas were higher.
“Earthworm numbers were also higher, but it’s the increased residue within the pasture that produces the increased earthworm numbers, that residue that goes back into the soil, half of it is carbohydrates, ideal for bug growth in the soil.”
He also cited Winchmore Research Station research, which started in the early 1950s, comparing different superphosphate application rates.
“Here too earthworm numbers also increased, with double the numbers in the higher super trial, compared with no super.”
Edmeades said his point was that feeding the soil would increase plant production, increase residual plant matter being deposited onto the soil, and with it the organic level within that soil.
“That’s the biological science from a conventional scientist’s point of view – you feed soil which feeds the plant and residues increase. Soils do not make nutrients, they simply store them.”
Edmeades also referred to one of his own studies from 2002 when he reviewed 14 long-term trials studying the use of manures and compost on crop yields compared with conventional fertilisers.
“There was no effect on crop yields or soil quality between the two types,” he said. “The work had been done because scientists at the time were worried those ‘new’ chemical fertilisers would affect soil quality, which they did not.”
When it came to claims organic produce was of better quality than conventional, Edmeades pointed to three international “meta” analyses done in 1997, 2003 and 2009.
“The jury in each case said organic food was no better than conventional.”
In terms of the environmental impact of organic compared with conventional, Edmeades said despite claims to the contrary organic dairy systems could not be expected to be less damaging, simply because of how nitrates in particular were delivered into the system.
“If you take nitrogen leaching on soil, it is delivered via dairy cows urinating,” he said.
“That is the mechanism through which most nitrogen gets into waterways. So whether in organic or conventional systems cows will still urinate.”
The only way to reduce that on either an organic or conventional system was to lower the nitrogen load by lowering the stocking rate. The larger concern for Edmeades was the growing pressure to feed the world’s growing population, and the lower production levels resulting from organic systems.
“Organic production is 30-40% less than conventional. If you went organic we would have to increase the area of production, or let 30% of the population starve, for no proven net gain in either soil fertility, environmental quality or food quality.”
He did agree with delegates over the value of soil bacteria, and suggested there was potential for better understanding of this bacteria population, and how their activity could be made more efficient in the nutrient conversion process. He disputed biological farmers’ claims that soils were fragile systems.
“It amazes me how quickly post-drought we saw pastures bounce back last year,” he said.
“I believe the pastoral system is inherently very robust. All surveys done in NZ over the past years show soil quality is very good in terms of its chemical, mineral and physical content.”
