Organic soil tests analyze the biological activity in soil as well as the organic matter content. Traditional soil tests provide data on mineral content with emphasis on nitrogen, phosphorus and potassium, along with other soil chemical characteristics, such as pH levels. Healthy organic soil has billions of living organisms, according to the Michigan State Department of Agriculture report titled “Earthworms and the Soil Foodweb.” These include earthworms, bacteria, fungi, small mammals, protozoa, anthropods and nematodes. There are several testing procedures for organic soil testing.
Take soil samples from five to 10 randomly selected sites in the agricultural area of interest. Important microbial activity is located with plant root structures, so some of the soil samples should include roots. Take soil samples with an apple corer near the plant root zone. Mix together the samples in a clean bucket or bowl. Place 2 cups of soil in each sandwich size zip-top bag. Do not freeze or store the samples because it will kill certain types of bacteria. Send samples to the testing laboratory immediately.
Soil is tested at an alternative testing laboratory, which are sometimes identified as soil food web laboratories. The soil is analyzed to determine the total biomass of all active and dormant bacteria and fungi; the number of protozoa and nematodes; and the percentage of plant roots that are colonized by beneficial fungi. The tests also determine acidity and alkaline soil levels and the level of escherichia coli bacteria.The National Sustainable Agriculture Information Service publishes a list of labs that do organic microbiological soil testing (see Resources).
The University of Massachusetts Soil and Plant Tissue Testing Lab recommends testing to "provide test results and recommendations that lead to the wise and economical use of soils and soil amendments." Some testing labs give a free oral consultation with the test results, while others give written recommendations. Recommendations may include analysis of soil structure and how to change it; individual soil amendments to correct pH balance problems; recommendations for fungal foods if fungi biomass is too low; or bacterial food to increase biological activity.