Sound science helps sort fact from fiction

Sound science helps sort fact from fiction

Cropping
Having well managed perennial pastures are the best way to build soil carbon.

Having well managed perennial pastures are the best way to build soil carbon.

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How does a farmer determine fact from fiction when it comes to soil quality?

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Every so often there is a run of promoting all sorts of products/practises to build soil quality, obtain carbon credits and better manage the environment.

Sometimes these are supported by prominent personnel, but what is often lacking is sound research to support such promotion.

Often long establishes practices, such as traditional fertilisers like urea or superphosphate, are incorrectly claimed as being harmful. Herbicides, insecticides and fungicides are often no-go areas.

Every farmer aims to improve their soil and environment and be profitable. Much research by leading universities, state agencies, CSIRO and private companies have, for years, had a similar focus. But how does a farmer (or any reader) determine fact from fiction?

A key rule is to always check claims on best available scientifically based research, with the transparency of data. Anecdotal only stories are mainly more than questionable unless backed by good science.

An example of sound science is the study of published literature and research that found very limited positive response from a range of biological products promoted for use in cropping (see GRDC website).

Research developing zero or no-till farming, with occasional cultivation, has largely arrested declining soil structure with sometimes gradual improved soil organic matter (OM).

Perennial pasture, in this case Premier digit, has a great capacity to raise soil organic carbon. High soil fertility is a critical aspect of maximising OC build-up.

Perennial pasture, in this case Premier digit, has a great capacity to raise soil organic carbon. High soil fertility is a critical aspect of maximising OC build-up.

Erosion has largely been eliminated when zero-till combines with stubble retention. Correcting soil deficiencies like nitrogen contributes to greater OM as well as production.

Research has repeatedly shown that soil organic carbon (OC) is influenced by pasture productivity. The better the pasture the higher OC is likely to be. This is, for example, a key part of a recent paper 'Parent material and climate affect soil organic carbon fractions under pastures in south-eastern Australia', published in CSIRO's Soil Research journal.

NSW DPI's Dr Susan Orgill, was senior author of a paper reporting on more than 20 years of research focused on management to increase OC permanence stocks.

Globally, improved pasture management that included species selection, nutrient and lime application, was found to increase stocks of soil OC by an average of 0.54t/carbon/ha/year (0-30cm layer).

Research at Broadbalk, UK, assessing wheat production for 175 years on land cropped for centuries prior to 1843, shows continuous wheat without fertiliser averages under 2.0 t/ha. Best yielding wheat is that in rotation and receiving nitrogen, phosphorus and potassium fertiliser (includes maximum of 288 kg/ha nitrogen). It yields just under 12 t/ha.

Zero till cropping is the best way to minimise soil OC loss, and can lead to increased soil OC.

Zero till cropping is the best way to minimise soil OC loss, and can lead to increased soil OC.

Wheat in rotation treated with farmyard manure (35 t/ha per crop) plus added nitrogen (96-144 kg/ha) on average yields just under the best yielding NPK fertiliser treated crops. Mineral nitrogen fertiliser has enhanced OM a little, probably because of increased returns of OM in crop roots and above-ground residues.

In my NSW DPI days, a long-term pasture trial showed sulphur fortified super doubled OM, was higher in biological activity, water infiltration was seven times better and ground cover improved when compared to no fertiliser. Production more than trebled.

Another long-term study (soon to be published) assessed various products for effect on soil quality and productivity is research conducted by South East LLS senior officer Fiona Leech.

Pasture responses have largely been related to a products ability to supply sufficient available phosphorus and sulphur with no product showing any superiority for soil quality. Products tested include super, manure, burnt sewage sludge, crushed rock, various composts, lime, tea extract, liquid fish, reactive phosphate rock with a microbial culture, foliar fertiliser and microbes with a granular fertiliser containing high phosphorus.

Perhaps a final note for how non-science based information can be popularised is illustrated in the book 'Firepower: The Most Spectacular Fraud in Australian History', by Gerard Ryle. It describes how a non-science proven pill could cut fuel consumption and reduce emissions. It all ended ingloriously when science proved it didn't work.

Next week: Rapid feed from drought ravaged pastures once the drought breaks.

  • Bob Freebairn is an agricultural consultant at Coonabarabran. Email robert.freebairn@bigpond.com or call 0428 752 149.
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