Regular advice is commonly offered as to how we should run our properties to be carbon neutral.
For example, "switching to organic fertilisers" and expanding "regenerative farming practices to improve soil health". Note also that soil carbon levels rise and fall (as well as hopefully achieve long-term gains) in response to seasons.
Australian farmers feed and clothe 8 billion people as part of world agriculture, on declining agricultural land with areas constantly transformed into cities, national parks and the like. Here are a few home truths: Organic fertilisers, like animal manure, are great, but there is not enough for the nation's crops and pastures at sufficient rates to meet production goals. Many alternative products are not supported by science.
According to a paper published in the world-renowned Agronomy Journal, the average percentage of yield attributable to fertiliser generally ranges from 40 to 60 per cent, which states, "Fertiliser makes up the majority of nutrient inputs necessary to sustain current crop yields".
"Regenerative agriculture" means different things to different advocates. It often advocates not using herbicides like glyphosate, no fertilisers like urea, no drenches, and big areas of trees. Evidence supports crop production relates to aspects like weed control in-crop and in-fallow (weeds use soil water, nutrients and sunlight).
An alternative to herbicides is a return to cultivation for fallow weed control or no fallow weed control. Reverting to constant ploughing is a return to rapid loss of soil structure and organic matter, more erosion, less soil moisture conservation and lower yields.
Various agriculture practices promoted, such as not using so-called synthetic fungicides to control diseases like stripe rust in wheat and Ascochyta in chickpeas, will also cost a lot due to lost production in wetter years like 2020, 2021 and 2022. There are sometimes acceptable alternatives but commonly nowhere as effective.
Genetically modified (GM) crops are demonised by many in the non-conventional agricultural lobby. Yet much of the world's cotton, maize and canola crop is GM based. GM crops generally yield higher and have often resulted in dramatically reduced pesticide use for the control of pests and diseases. The quality is at least as good as non-GM varieties. Many other crops and now some pasture species are also turning to GM.
Using specific practices such as intensive grazing with multiple paddocks per mob is often advocated as part of the best way to build soil carbon. Science suggests good grazing management can be variable with much depending on pasture species and mixes. Retaining good levels of groundcover is almost universally important.
A current fad is multi-species crops and pastures. A major international review of multi-species crops did not indicate superior soil aspects like improved carbon. Research indicates multi-species crops may help improve winter forage production in some cases, but not always. Multi-species pastures have been a common practice for decades and are feasible as long as they boost productivity.
Timber is a sound way to build farm carbon. But in many lower and medium rainfall areas, beyond a sensible level, it is likely to be at the expense of crop and pasture productivity. Note that once mature, no further carbon build-up will occur.
Research over many years has noted that upgraded pastures can build soil carbon. Zero-till farming combined with high soil fertility can achieve close to carbon neutral rates. Farmers and agricultural researchers are seeking new ways to reduce their carbon footprint.
Many avenues are being explored by scientists to further reduce methane emissions. These include various animal supplements. Scientists are assessing gene editing on microbes in the gut of cattle. Gene-edited microbes as oral treatment can carry into adulthood, reducing methane emissions for the animal's life. Avenues to manufacture fertiliser with less energy, or "green" energy, have good long-term prospects.
Next week: North West NSW zero-till historic report.
- Bob Freebairn is an agricultural consultant based at Coonabarabran. Email robert.freebairn@bigpond.com or contact 0428 752 149.
