In this blog update, we have posted the first of a three part interview with Dr. Elaine Ingham, President and Director of Research of Soil Foodweb
Compostwerks: Why is it important to have both conventional and biological testing completed on soil and compost
Dr. Ingham: Traditional testing tells us about the levels of micro and macro elements, cation exchange, organic matter percentage, base saturation and pH. These are fundamental components of plant nutrition, but it’s only one part of the equation. We know that it’s the microbial component of the soil that has a majority of the control over nutrient cycling and sequestration. Conventional testing doesn’t quantify the reserves of nutrients which are tied up in non-available forms, or in the microbes themselves. Simply put, a plant can’t uptake the necessary nutrients unless in an available form. Without the right biology in place, we’re locked into conventional (petro-chemical) methods.
Compostwerks: Which is why you founded Soil Food Web, your soil testing and research lab.
Dr. Ingham: Yes, the Soil Foodweb offers professional lab testing of different organisms found in healthy soil, compost, compost tea, and other soil amendments. Using direct microscope methods, we measure populations of bacteria, fungi, protozoa, and nematodes. We offer specialized testing for mycorrhizal colonization and leaf surface foodweb evaluations. Once we know what microbes are missing or inactive, we have data in order to make further recommendations.
The leaf surface examinations monitor the success of foliar applications of compost tea. We also offer general testing for pH, electrical conductivity and E. coli. Mycorrhizal colonization analysis quantifies the level of the symbiotic fungal association with plant roots. We know that benefit to plants that need mycorrhizal fungi begins to occur around 12 to 14% colonization, and reaches full benefit around 40% colonization.
Compostwerks: What type of testing do the assays cover?
Dr. Ingham: Our testing assesses Total Bacteria: (total biomass of all bacteria, active and dormant), Total Fungi: (total biomass of all fungi, active and dormant), Active Bacteria: (biomass of just the metabolically active bacteria), Active Fungi: (biomass of just the metabolically active fungi), Protozoa: (numbers of individual Flagellates, Amoebae, and Ciliates), Nematodes: (numbers of individuals and identification to genus and function), Mycorrhizal Colonization: (percentage of roots colonized by mycorrhizal fungi), Leaf Surface covered by organisms. We also offer general testing for Electrical Conductivity: (high conductivity indicates high salt levels) and pH: Acidity or Alkalinity: (pH is influenced both by the mineral content and the biology in the soil), and Escherichia coli bacteria: (number of Colony Forming Units detected).
Compostwerks: Why are each of these tests important?
Dr. Ingham: Measuring bacterial activity and numbers is important because bacteria promote plant health in many ways. Bacteria, along with fungi, decompose dead plant material into more bacteria, foods for other organisms, and carbon dioxide. Aerobic bacteria build the first step in soil structure, which is the production of “bricks”, the basic building blocks to make air passageways, and hallways to allow water and oxygen to infiltrate into soil. Bacteria take up soil nutrients that plants cannot take up, the first step of converting these nutrients into plant available forms. When too many, or all the bacteria are dormant, their ecosystem services will not provide the full potential benefit to the plants. When too many are active, they may compete with plants for soil nutrients. The right range of activity varies by season in soils. In mature compost, 10% or lower activity is desired so nutrient up-take by bacteria is not so great as to compete with plants.
Measuring fungal activity is important because fungi, along with bacteria, decompose dead plant material into new fungi, foods for other organisms, and carbon dioxide. Fungi build the second level of soil structure, by binding the micro-aggregates built by bacteria into macro-aggregates, allowing better infiltration of water and oxygen into the soil. Fungal filaments transport nutrients to where they are most needed. The optimal range of fungal biomass varies according to crop, climate and season. Measuring fungal numbers in a sample is important because fungi recover from disturbance more slowly than bacteria. Excessive tilling of soil, excessive turning of compost, or use of many synthetic chemicals can devastate beneficial fungi. Active fungal biomass in the right range is a good sign of overall soil health. If activity is low and the local environment is free of physical and chemical disturbance, the dormant part of the fungal population may only need feeding.
We measure protozoa because these organisms, along with bacterial-feeding nematodes, eat bacteria and release nutrients, from nitrogen to zinc, in plant available forms, making them essential to healthy plant growth. Flagellates and amoebae nearly always require aerobic conditions to grow, while ciliates prefer anaerobic conditions. A high ciliate population indicates disease-prone conditions which need to be addressed such as soil compaction and excessive irrigation.
Nematodes are a very large group of very small worms, found everywhere on Earth. Some soil-dwelling species cause crop damage, some prey on other nematodes, and most graze on bacteria and fungi, boosting natural soil fertility. Diverse nematode activity is a sign of healthy soil, and beneficial to any plant because they cycle nitrogen and other nutrients into plant available form.
Mycorrhizal fungi form symbiotic relationships with 90% of all plants on Earth. These fungi increase the nutrient uptake capacity of the plant and protect it against pathogens. They are also sensitive to many toxins in chemical pesticides and inorganic fertilizers, making them a valuable indicator of overall soil health. This test determines what percentage of the plant roots are colonized, and can also detect signs of disease and other damage
The Leaf Surface Foodweb test determines the effective coverage of organisms on the leaf surface, very useful for before and after comparisons of foliar applications of Compost Tea. Adequate coverage of leaf surfaces with beneficial bacteria and fungi helps to reduce disease and pests.
Many growers and consumers are rightfully concerned with disease organisms. We evaluate the number of Colony Forming Units (CFU’s) of E. Coli per gram of compost or milliliter of compost tea, to let you know if these indicators of disease-prone conditions are within or above accepted limits for agricultural fertilizers. These common intestinal bacteria have some disease-causing strains, and indicate other harmful bacteria may be present.
Compostwerks: Thank you so much for your time Elaine.