Soil Fertility – Plant Nutrition – Soil Testing


Intelligent landscape and farm design, good growing conditions, compatible plantings, appropriate water management, enhancement of soil fertility are the foundations of plant health.  Not harming the microbial life in the soil, but restoring and maintaining essential biological  processes, is what regulates appropriate plant nutrition, the right amount of growth,  resistance to pests and diseases, flower and fruit production, and healthy appearance, color, fragrance, taste and nutrient density in the food we eat.

Prevention of plant problems and early intervention is more effective and economical than waiting for advanced conditions to develop before taking remedial action.  A plant wellness program relies on establishment and maintenace of good growing conditons, soil and water management, with regular inspections, anticipation of potential plant problems, and utilizing early intervention with bio-rational methods and materials for suppression of pest and disease conditons when needed.


​Fertile soil is essential for plant health, metabolic functions, plant appearance, and productivity.  Healthy soil provides the necessary nutrients, structure, and microbial activity to support plant growth and resistance to pests and diseases. Several key components contribute to fertile soil:

  1. Organic Matter: Organic matter, such as decomposed plant and animal material and stable humus, is a vital component of fertile soil. It improves soil structure, water retention, and nutrient availability. Organic matter also supports microbial activity, which is crucial for nutrient cycling and overall soil health.
  2. Mineral Content: Essential minerals, including nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulfur (S) and micronutrients, are required for plant growth and development. These minerals are obtained by plants from the soil solution through root zone processes and microbial activity, and are crucial for various biochemical processes within the plant.
  3. pH Level: Soil pH (acidity/alkalinity) influences nutrient availability and microbial activity. Most plants prefer a slightly acidic to neutral pH range (around 6.0 to 7.5), although specific preferences vary among plant species. Maintaining soil pH within the optimal range can enhance nutrient uptake and overall plant health.
  4. Soil Texture: Soil texture refers to the relative proportions of sand, silt, and clay particles. Ideal soil texture, often referred to as loam, contains a balanced mixture of these particles, providing good drainage, water retention, and aeration. Soil with a loamy texture facilitates root growth and nutrient exchange.
  5. Soil Structure: Soil structure refers to the arrangement of soil particles into aggregates or clumps. Well-aggregated soil has good porosity, allowing for air and water movement, root penetration, and microbial habitat. Soil structure influences water infiltration, erosion resistance, and nutrient availability.
  6. Microbial Life: Soil microorganisms, including bacteria, fungi, protozoa, nematodes and micro-arthropods, play a vital role in nutrient cycling, organic matter decomposition, and disease suppression. Healthy soil supports a diverse microbial community that contributes to soil fertility and plant health.
  7. Water Holding Capacity: Soil's ability to retain moisture is crucial for plant growth, especially during dry periods. Soil with good water holding capacity ensures adequate moisture availability to plants between rainfall or irrigation events.
  8. Aeration: Adequate soil aeration is necessary for root respiration and the exchange of gases between the soil and the atmosphere. Compacted or waterlogged soil can limit root growth and oxygen availability, negatively impacting plant health and productivity.

By maintaining these components in balance, farmers and gardeners can create and sustain fertile soil that supports robust plant growth, high yields, and overall ecosystem health. Amendments and management practices, such as composting, crop rotation, cover cropping, and mulching, can help enhance soil fertility over time.

Most conventional soil tests are based on chemical agronomy. Depending on the individual lab and the system that they use, the crop context and request, they measure some or all of the following components:

  • Levels of essential mineral elements available for plants (e.g., nitrogen, phosphorus, sulfur, calcium, magnesium, potassium, sodium, boron, copper, iron, manganese, zinc),
  • pH (acidity/alkalinity),
  • SOM (soil organic matter content),
  • CEC (cation exchange capacity)
  • Soil texture (physical characteristics, sand, silt, clay content and percentages)

Conventional horticultural soil analysis does not normally include testing for toxic substances, chemicals, pesticides, heavy metals (arsenic, barium, cadmium, chromium, lead, and nickel). Toxicity testing is separately provided by special laboratories and by specific request.


Soil analysis systems play a crucial role in understanding soil health and fertility, aiding in agricultural productivity and landscape management. Here's a comparison of some commonly used systems (there are others and variations not covered here) :

SLAN (Sufficiency Level of Available Nutrients):

    • SLAN focuses on determining the available nutrients in the soil that are crucial for plant growth. It typically measures the levels of key nutrients like nitrogen (N), phosphorus (P), potassium (K), and sometimes other essential elements such as calcium, magnesium, sulfur, etc.
    • The analysis helps in determining if the soil has sufficient levels of soluble nutrients to support optimal plant growth without excesses or deficiencies.

SLAN is the primary method available from most university and commercial soil labs, as well as home NPK soil testing kits. It is chemical ag based and not consistent with ‘organic’ or ‘regenerative ag’ methods and materials.

BCSR (Base Cation Saturation Ratio):

    • BCSR is a soil fertility concept that focuses on the balance between certain positively charged ions, known as base cations, in the soil. These base cations typically include calcium (Ca), magnesium (Mg), potassium (K), and sodium (Na).
    • BCSR aims to maintain an ideal ratio between these base cations, which is believed to support optimal soil structure, pH, nutrient availability, and microbial activity.

This soil analysis method, which is inspired by the work of Dr William Albrecht covers a wider range of plant nutrients than the SLAN method. It seeks to provide a favorable environment for soil microbial activity and processes, but it does not test for biological content.


    • The Haney Test is a comprehensive soil health assessment that goes beyond traditional nutrient analysis. It includes measures such as microbial activity, organic matter content, soil respiration, and the potential for nutrient cycling.
    • This test provides insights into the overall biological activity and health of the soil, which can help in making informed decisions regarding soil management practices, including fertilization and crop selection.

SOIL-FOOD-WEB microscope microbial analysis:

Soil Food Web advocates and regenerative agriculture growers often use a soil testing system called the Soil Food Web Analysis. This method, pioneered by Dr. Elaine Ingham, focuses on assessing the health and biological activity of soil by examining the diversity and abundance of microorganisms such as bacteria, fungi, protozoa, nematodes, and microarthropods.

The Soil Food Web Analysis typically involves collecting soil samples from various depths and locations within a field or garden. These samples are then analyzed using microscopy and other techniques to identify and quantify the different microbial populations present. The goal is to understand the balance and diversity of organisms in the soil, as well as their interactions with each other and with plant roots.

By understanding the soil food web and its dynamics, growers can make informed decisions about soil management practices, such as composting, cover cropping, crop rotation, and reduced tillage, to promote soil health and fertility in a sustainable manner.


  • Focus: SLAN primarily focuses on the levels of available nutrients, whereas BCSR looks at the balance of specific base cations, and the Haney Test assesses overall soil health, including biological activity. The Soil Food Web analysis is specific for microbiome assessment.
  • Depth of Analysis: SLAN typically provides a basic analysis of nutrient levels, while BCSR delves into the balance of base cations, and the Haney Test offers a more holistic view by considering microbial activity, organic matter, etc.
  • Application: SLAN and BCSR are often used in conventional agriculture for nutrient management and soil fertility improvement. The Haney Test is gaining popularity, especially in sustainable agriculture and regenerative farming practices, where soil health and biodiversity are prioritized.
  • Complexity and Cost: SLAN is relatively straightforward and cost-effective, while BCSR requires more nuanced interpretation and analysis. The Haney Test is the most comprehensive but also the most complex and expensive of the three options.

Regenerative Agriculture, as promoted by Kiss the Ground advocates, The Soil Food Web School and Advancing Eco Agriculture, as well as others, represents a modern movement away from pure chemical soil analysis toward a primary consideration of the soil biology and related processes, and how the microbiome is affected positively or negatively by management of the growing conditions, methods and materials.

Don’t miss this key perspective on soil food web and regenerative agriculture:

Changing Agronomy with Biology - John Kempf, AEA


I use:    MicroBiometer - Professional Lab-Grade Soil Test Kit for Microbial Biomass

Improving the health of your soil is essential to increasing your output, but how can you tell if you are making progress?  Research shows that microbial biomass (fungi and bacteria) is the leading indicator of soil health. Living soil fixes nutrients, improves plant immunity, stores water more efficiently and builds soil structure, therefore, a healthy level of microbes increases productivity while reducing inputs.