it seems that there are three main criteria (at least) that we should assess in relation to the soil in which a tree is growing: soil pH, soil fertility (n:k) , and soil compaction.
there are tools on the market which allow measurement of these factors. i am interested to read of your experiences with the different types of soil test kits, penetrometers, pH measurers you may have come across.
is accuracy with these on site methods good enough or should samples be sent to a lab for analysis? what do you think?
mark

Reply to post by mark lutherborrow, on February 25, 2000 at 06:41:03:

Usually we include "soil texture" (ratio of sand:silt:clay) under the soil parameters to be measured as well.
The extremes of very sandy and very clayey soil drive other factors such as drainage, pH, and cation exchange capacity, so it is pretty important.

Reply to post by Jerry Bond, on February 25, 2000 at 06:41:03:

yes i take your point Jerry. upon re reading my original posting i have left the way open for many interpretations of important soil criteria. my main question though was in relation to the "tools" available to assess soils

Reply to post by mark lutherborrow, on February 25, 2000 at 06:41:03:

There are many ways to assess the characteristics of the soil and the ones you use should be driven by the assignment. How detailed or accurate do you have to be?

The soil pH meters are generally OK, especially those that use a soil solution. The metal probe types are much less accurate. Chemical methods that require a color comparison are not very dependable, unless you have a lot of experience with them, and have 'calibrate' your system against know pH soils.

The penetrometers give you relative measures, and are highly dependent on soil moisture. I suggest you use a moisture meter if you use a penetrometer, and simply record both for reference. We know a clay soil is brick hard when dry, but rather soft when moist. Also, these devices don't give you an absolute reading of bulk density, but rather resistance to a large probe. This is not the same as the resistance to a microscopic root. A direct measure of bulk density is the most accurate, but also a little more difficult to sample.

The basic chemical kits for testing nutrients give moderately accurate results if used carefully. Forget testing nitrogen- it is too volatile to get accurate readings, and N in the soil varies dramatically throughout the seasons. Even the pro labs seldom test for it now.

Soil chemistry is very complex, and measuring just n-p-k does not give you much information. A complete test, including the micronutrients, CEC, base saturation, buffer pH, etc., gives a much better profile. Commercial labs can provide all this for as little as US$20 per sample.

I often take a sample, send it Priority Mail, and get the results faxed back within 4 or 5 days with fertilizer recommendations, for less than $25.

Reply to post by Russ Carlson, on February 25, 2000 at 06:41:03:

Russ,

You did that just to get at me. Testing here is A$120-140.

Mark,

there are many good soil diagnostic tools. Generally they all
have limitations or are verey very expensive (eg EN Probe at
about $15,000 last time I checked). Most will flag that a problem
may exist and that further testing may be required.

Mark H

Reply to post by Mark hartley , on February 26, 2000 at 12:04:04:

At that price, Mark, you could mail them to the States and still come up less!

Reply to post by Russ Carlson, on February 25, 2000 at 06:41:03:

thanx for the info russ. i will see what services are available from soil labs down here
mark

Reply to post by Russ Carlson, on February 26, 2000 at 15:40:24:

Russ,

I have considered it. there are problems with exporting soils
between counties. It would need to be sterilised and this may
impact on results.

Mark