My Soil is Different

This article first appeared in The Grower in March 2012


“It won’t work here; our soils are different.” A common response to a new idea.

Two excellent events in Australia had me thinking, “Wow, their soils really are different!” But as to “It won’t work here,” that’s like saying you can’t cook carrot cake in a casserole dish. You can, if you are a bit adaptable. It is principles and processes we need to focus on.

The SPAA Precision Agriculture Expo was held in Port Lincoln in South Australia. The conference was in Maroochydore, Queensland. Both were characterised by excellent speakers, strong farmer representation, varied topics, and good industry support.

Speakers discussed nutrient tests we don’t use, plants we seldom grow, pests, diseases and weeds that remain thankfully foreign, and yields most New Zealand farmers would consider disastrous. They talked of soil electromagnetic sensors, pH sensors, biomass sensors, protein sensors, animal trackers and robots.  Of precision farming in Canada, Scotland, England, New Zealand, Queensland, New South Wales, Victoria and South Australia.

At both events, the farm was the focus, the technologies merely tools to help manage better. Much, much better.

Some of their Australian soils must be among the most inhospitable places on earth for a plant: three inches of sand on a deep, highly saline and toxic sub-soil; heavy compacting clay on compacted clay with horrid pH levels. In our young landscape the soils are quite different indeed.

But for all that, the messages were strikingly familiar. In essence; know and look after your soil, monitor your crop, and apply inputs where they give the best returns.

After decades working their land, farmers know their soils very well.  From cultivating and observing patterns in crops they learn about areas that perform differently. Most can draw a pretty good “mud map” if asked. They know where their soil changes physically and use nutrient and pH tests to monitor fertility.

There are new tools to help understand variation, such as the EM38 soil electromagnetic sensor and Thorium sensors. Light sensors can pick up organic matter variation. With GPS the variability can be mapped accurately and we can make more detailed maps. But be cautious.

Sensors almost always measure something other than the thing you are interested in. They have been shown to “correlate well” – under certain conditions. But remember, your soils ARE different! The numbers a sensor provides are not necessarily true for you; the sensor needs to be calibrated to your site. And that goes for practically every sensor I know.

Sensors can be very good at identifying differences, and directing our attention to areas worthy of further investigation. EM maps certainly provide evidence of electrical difference. The numbers the sensor generates vary enormously depending on soil moisture, clay content, density and salinity. So the same number in two different parts of a field may be due to different combinations of any of these.

The maps tell us where to investigate further. The most important tool of all is a spade. Decide on a small number of management zones, sample them separately to understand the causes of variability.

Dan Bloomer, LandWISE

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