Building Soils for Better Crops, Third Edition

Testing Soils for Organic Matter

Overview

A word of caution when comparing your soil test organic matter levels with those discussed in this book. If your laboratory reports organic matter as “weight loss” at high temperature, the numbers may be higher than if the lab uses the traditional wet chemistry method. A soil with 3% organic matter by wet chemistry might have a weight-loss value of between 4% and 5%. Most labs use a correction factor to approximate the value you would get by using the wet chemistry procedure. Although either method can be used to follow changes in your soil, when you compare soil organic matter of samples run in different laboratories, it’s best to make sure the same method was used.

There is now a laboratory that will determine various forms of living organisms in your soil. Although it costs quite a bit more than traditional testing for nutrients or organic matter, you can find out the amount (weight) of fungi and bacteria in a soil, as well as obtaining an analysis for other organisms. (See the “Resources” section for laboratories that run tests in addition to basic soil fertility analysis.)

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