Mid North Coast Microherders

Caring for the little things in our soils

Kempsey Landcare David Hardwick Soils Workshop - part 3: Making sense of Soil Tests. 3 July 2015



Using a soil test to assess my soil: Q. What are the top 2 things to look at? A.  [David asked the group, and it was remarkable how much they came up with different answers!] CEC; organic matter (carbon); ph; exchangeable (soluable) calcium and magnesium; salinity; texture...

Carbon levels are like having a gearbox in the car. (ie. Essential!)

Different people have different priorities.

"Grampa said: 'Take a shovel and dig the perimeter'".

Exercise 1: Look at the soil test results and find the ph measure.

Hitting soil with acid (to test ph) changes it. It is invasive, like the Japanese killing whales to count them. Results in inaccurate estimates.

If testing ph, use distilled water. Need to know which method was used to calculate ph (water, or calcium chloride...)

ph units are on a log scale.

A good lab should tell you the method and the units used and the benchmark and the measurement.

Q. Can we measure soil structure on this test? A. No.

Q. How do we measure soil structure? A. Out in the paddock with a spade.

Q. Would knowing the Total Phosphorus P help us? A. Long term.

Q. Would we want to know Available P? A. Yes - short term.

Morgan was an early (pre-World War I) test. Nutritech does tests. They use a Melick test.

Whatever test method is used, there must be a reliable benchmark for the method.

Stick with the method you choose.

These things run 60-70% accuracy.

Q. How much variation in a test? A. Variable, depending on how long it is shaken in the lab, or how long it is left in the bag in the car on the way to the test. Varies around the paddock.

These are WWII technologies.

DGT - diffuse gradient technologies - diffuse gradients on thin film - a new test method with 90% accuracy. Yield correlations in grains industry is really impressive using this test.

Other ways to work out nutrient levels in your soil: Look at the plants growing in it yields live weight gain in stock egg laying rates deficiency indicators in stock

Some phosphorus is in the organic matter.

Tests don't capture the vam process at all.

Q. Do I have a DPI or LLS agronomist?

Q. What is another way I can validate/crosscheck the measurement/benchmark?

Laboratories that do soil testing: Incitech, SGS (Toowoomba), Divot, Nutritech, CRT Ag Solutions, Plant Therapy, T&N, Lismore Lab (VAL). The different ones use the Lismore Lab, and then put their own interpretations on the raw results. Depends if you want to buy reports with pretty pictures.

Tell the laboratory which tests you want.

"If I get your soil test and I can't sell you fertiliser I shouldn't be in the game"!!!

Q. What score do you give the soil out of 100 after you've gone through the soil test?

Say organic matter benchmark is 4% and the soil test is 1%, then that is a major soil problem and you have to consider the economic cost to improve it.

Q. How often do you soil test? A. If you're putting a lot of money into it, soil test.

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