Digging Deep Into Soil Education
OPINION: "The worst thing that agriculture does is take land from nature."
The big question should be, do the examples stack up in New Zealand?
If yes, no problem. If no, what might happen? Would there be any unintended consequences?
Answering these and similar questions is the goal of scientific research. The foundation for advancing knowledge is laid by identifying the problem and then analysing what has gone before:
• What is the starting point?
• Relativities – what comparisons are being made?
• Context – what are the concerns?
• Science -- what ‘facts, evidence and data’ support those concerns?
• Alternatives – are there any with more ‘acceptable’ outcomes?
Professor Richard Teague, grazing systems ecologist and professor at Texas A&M AgriLife Research, is an advocate of regenerative agriculture, and puts the state of the research simply.
“In science, we have to try to understand what’s going on. No single experiment solves all the problems. But all the data we’ve collected suggests that the more people who manage their soil better, either in grazing or cropping systems, the more carbon will be sequestered in the ground.”
Regenerative agriculture as explained by Professor Teague uses cover crops, no-till, crop diversity, little or no chemical fertilisers and pesticides, and livestock integration to promote healthier ecosystems by rebuilding soil organic matter. (Soil carbon, which is over half of soil organic matter, has undisputed positive effects on soil chemistry, physics and biology.)
His description includes subdividing existing paddocks with electric fences, grazing for one to three days maximum and giving adequate recovery. In the Dallas area, he estimates 60-90 days in the growing and non-growing seasons, but in dry areas double this recovery time will be required.
Using the regenerative agriculture approach, Professor Teague states that soil carbon increase has been measured at eight tonnes per hectare per year.
The journal article from which this figure came was authored by researchers from Universities of Georgia and Florida. It reported changes in soil carbon over a 10-year period when degraded cropping soil was returned to grazing.
The pastures in the research were ‘managed for maximum forage production, employing N fertilisation, irrigation and selective rotational grazing with a 15 to 45-day rotation’.
The increase brought the soils from about 10 tonnes carbon/ha to 30-40 t/ha in the top 30cm. This was ‘equivalent to under native forests’.
The authors commented that such a high rate of carbon accumulation wouldn’t be maintained indefinitely following conversion to intensively grazed pasture but that further slow accumulation might be possible.
The authors then discussed New Zealand pastures with soil C stocks estimated as high as 109 to 138 tonnes carbon/ha. Citing the work led by Professor Louis Schipper at the University of Waikato, they pointed out that once these soils reach a higher soil carbon, they can become susceptible to carbon loss if management changes.
Clearly the starting point, relativities, context and science are important. New Zealand soils are not degraded and the Ministry for Environment has stated that ‘soil total carbon was within target range for 95% of tested sites’.
Instigating principles out of context could have significant and potentially detrimental unintended consequences. In particular, where current management is optimal for grass harvesting by ruminants, Professor Tony Parsons (now retired from Massey University) has shown that a change in stocking rate and inputs would result in a decrease in soil carbon and more nitrogen being released to the environment.
Professor Teague has stated that he is ‘careful not to extrapolate is the data from bite-sized, snippets to something headline-worthy’.
The same does not appear to be true of some advocates who are promoting regenerative agriculture as the answer to climate change. It certainly might help with carbon sequestration in some degraded soils, where there is access to irrigation and nitrogen, but most of New Zealand has already done what is being promoted.
Doing better than we are already doing takes scientific research done in context, with appropriate examination of unintended consequences. Anything else could distract good farmers from managing their operations optimally with negative implications for environment and economy.
• Dr Jacqueline Rowarth is a soil scientist with a PhD in nutrient cycling. Her research has focused on phosphorus, nitrogen and carbon.
