Microbial assessments on Soil, Compost and Soil Inoculums

Soil Foodweb New Zealand has a unique ‘direct count’ system of assessing soils biological components. Our recommendation is that you test your soils microbial balances on an annual basis as you would do for your soils’ mineral content. If there are concerns regarding production or soil condition during the year it may be necessary to conduct several tests over the growing period. This will permit you to take remedial action if required. There are many options, so contact the lab to find out what is suitable for your situation.

The results from the tests will enable the farmer to:

  1. Assess his soils’ starting point prior to embarking on the method of biological farming
  2. Determine what foods or inoculums are required to maintain or correct his microbial balances.
  3. Ascertain just how effective his biological inputs have been over the past year.
  4. Help him calculate what impact his grazing rotation is having on the soils condition.
  5. Ascertain what damage has been caused by pest and disease treatment – especially important in grape and pip and stone fruit production.

As soon as the tests enter our system you will receive a confirmation by email supplying you with the Soil Foodweb sample number for your samples and letting you know that you should have the results back within 8 working days.

The report is a 1-2 page document with comprehensive description of what is happening with each assay.   You are also invited to phone the lab for a complimentary consultation/interpretation.

These results can indicate your total levels of bacteria and fungi; the percentage of these organisms that are working and doing the job, and if this is sufficient for the season; the diversity of fungi and if it is generally beneficial; nutrient cycling capabilities, whether or not the soil is anaerobic due to compaction etc; supply information on mycorrhizal colonisation in the roots; fungal-bacterial ratios; trends for the coming months, ie more bacterial or more fungal.

How to take samples and send to the lab

This exercise is as easy as taking samples for mineral assessment.


Choose your sampling area as you would for taking samples for minerals. Different soil types or topography may necessitate more than one test ie river flats will be different to hill sides or tops probably both soil types and/or plant growth.

Take around 20 plugs (70mm – 120mm deep) from your designated area ensuring you have a good representation of that area. Keep away from cow pats etc. This should amount to about two handfuls. Place in a strong plastic bag and label clearly. Repeat the process for each area you require a test from.

Mycorrhizal Assessments:

For specific tree or vine crops such as avocado, pip and stone, kiwifruit and grape, care needs to be taken to extract the roots for mycorrhizal assessment. Dig down until you find the very fine roots, the paler the better, and gently tease out enough roots to fit across the palm of your hand. These can be carefully placed on top of the soil in the bag prior to sealing. NOTE: Brassica crops are not hosts of Mycorrhiza.

Download the soil submission form here. Complete and send with the sample(s) by overnight courier to Soil Foodweb NZ. The address and select one of the 2 assay package options. Prices are supplied on the form. Phone the lab for further options.

Total Foodweb Package – 6 Assays includes: Active and Total Bacteria and Fungi, plus Protozoa and Mycorrhiza.

Bacterial and Fungal Package – 4 Assays includes: Active and Total Bacteria and Fungi only.

Compost – Thermal and Vermicast:

Take handfuls from assorted areas all over compost pile ie top, bottom, middle, inside and outside and place in a bucket. Mix well then take to large handfuls and place in a strong plastic bag as described for soil and mark clearly with sample number.

Download compost submission form here. Complete and send the sample(s) by overnight courier to Soil Foodweb NZ. The address and select one of the 2 assay package options. Prices are supplied on the form.

The Soil Foodweb Reference Guide/Glossary

Fungi are comprised of microscopic cells that grow in long threads called hyphae. Fungal hyphae bind soil particles into macro-aggregates which increase the soil’s ability to absorb and retain water. Fungi also play an important part in nutrient retention and disease suppression

Bacteria also play a vital role in breaking down organic matter and maintaining the soils ability to retain nutrients, assisting in disease retention and helping to improve soil structure by forming micro-aggregates. Certain types of bacteria also undertake a range of other functions including the breaking down of toxic compounds and assisting with nitrogen fixation.

At SFI NZ we measure Active Fungi & Active Bacteria in addition to the total fungal and bacteria biomass. Active biomass is a measure of the organisms that are metabolising or “doing the work”. Fungi and bacteria are active when food resources are available and conditions are favourable e.g. moisture and temperature. If activity is low then the organisms may need feeding.

Protozoa are single celled organism that primarily consume bacteria and release nutrient in forms that can be readily absorbed by plants. There are three groups of protozoa in soil – flagellates, amoebae and ciliates. If a soil contains large numbers of ciliates it could indicate low oxygen zones exist (anaerobic conditions.) This has a detrimental effect on plant root, fungal biomass and aerobic bacteria.

Nematodes (assay not yet completed in NZ) are classified in a number of functional groups based on their food source i.e. fungal, bacterial or root feeders. There are also predatory nematodes that eat other nematodes. The majority of nematodes are beneficial as they form an integral part of the soil food web. They convert nutrients into plant available forms by consuming either bacteria or fungi. Beneficial nematodes also consume disease causing organisms, and are an important food source for the larger organisms. The presence of root feeding nematodes in high numbers is an indication that the soil foodweb is in a degraded state.


Mycorrhiza Fungi colonises the roots of most terrestrial plant species, forming a mutually beneficial relationship that has a significant role in nutrient & water uptake, and protects against root feeding nematodes and pathogens. Mycorrhiza are especially important in supplying plant available phosphorus. Many studies have documented a decrease in mycorrhizal colonisation when soluble phosphorus levels are high, usually as a result of excess use of inorganic fertilisers.