Crops [photo] 


Omnia’s Soil Health Prism- Measuring and Managing the Basis of Life

Soil is arguably the most valuable and non-renewable resource, considering that it is the absolute basis of plant life which is therefore central to sustaining human life. Soil has been long denoted as such as stated in a Sanskrit text in 1500BC “Upon this handful of soil our survival depends. Husband it and it will grow our food, our fuel and our shelter and surround us with beauty. Abuse it and the soil will collapse and die, taking humanity with it.”

Soil management is fundamental to all agricultural systems, but the rude awakening is that there is still evidence for widespread degradation of agricultural soils in the form of erosion, loss of organic matter, contamination, compaction, increased salinity and other harms (European Commission, 2002).Sustainable soil management has to be within the context of soil health which is a term widely used within discussions on sustainable agriculture to describe the general condition or quality of soil. It is said that a healthy and productive soil is a resilient soil. A healthy soil produces plants with optimum vigour, using soil moisture and nutrients optimally and is therefore less prone to diseases. Conversely, poor management of soil results in greater inputs of water, nutrients, pesticides and energy to maintain yields, which becomes economically unviable to maintain.

Given the complex and multicomponent nature of soil, individual functions are closely interconnected and cannot be studied independently of each other. Therefore, soil health is a concept that deals with the integration and optimisation of the chemical, physical, and biological processes of soil that are important for sustained productivity and environmental quality.

Subsequently, Omnia’s Soil Health Prism was developed; a tool which provides a holistic analysis of the complex nutrient, physical and biological aspects of soil health and translates this into a simple visual representation that makes data interpretation and solution recommendation simple and accurate. It allows for the accurate recommendation of a tailor made solution to ensure sustainable optimum soil health.

The soil health prism

The Soil Health Prism is based on evaluating and characterising specific quantitative and qualitative soil indicators which may very well be the major constraints for crop yield and quality. These indicators fall within the guidelines of Doran and Parkin, 1994, which ensure that the indicators integrate soil physical, chemical and biological properties and processes, correlate well with the ecosystem, are sensitive to management and climate, can be interpreted and lastly, are components of existing databases and relevant to South African soils.

Focussing on the latter, to date, chemical and physical properties of soil have been well studied, documented and accepted. The chemical characteristics of top and sub soils are analysed by Omnia’s SANAS accredited laboratories which determine the nutrient levels in soil. The data is further deliberated to determine nutrient interactions based on soil texture with the intention of improving nutrient use efficiency. Selected physical characteristics of soil are evaluated using a combination of laboratory analyses and on-field analyses, conducted by Omnia’s agronomists. Amongst these physical indicators which represent soil functions such as physical stability and support as well as water relations, are water infiltration rate, penetration resistance and water holding capacity.

Contrary to the chemical and physical properties of soil, the biological properties of soil are not as well understood and studied. In this light, Omnia’s OmniBio™ laboratory has done extensive research over the past 12 years studying various soil biological indicators. Omnia’s field research included analysing in the order of 9500 geo-referenced samples for soil biology from across South Africa, providing a diverse and reliable knowledge base.

Omnia’s biological indicators include; enzymes activities such as β-glucosidase, Acid and Alkaline phosphatase along with Urease activity to determine functional diversity of soil micro-organisms as well as the impact on nutrient use efficiency. These enzymes are indicators of Carbon, Phosphorus and Nitrogen cycling, respectively, which are integral nutrient cycles for crop production. Another important analysis conducted is the identification and quantification of both free-living and plant parasitic nematodes, which also play vital roles in functional biodiversity of soil and is an essential component in determining soil microbial health.

The key edge of these biological analyses however lies in their interpretation, which comes with a balance of theoretical knowledge coupled with extensive field research. The ability to interpret the nematode analyses and enzyme activities in an integrated configuration, together with other soil aspects, have resulted in the development of four biological indices, viz, the Nematode Risk Index, Rhizo-health Index, Urease Mineralisation Index and the Phosphate Mineralisation Index. 

  • The Nematode Risk Index generates a score based on free-living and plant parasitic nematodes, which is crop specific. Plant parasitic nematodes are a huge constraint on sustainable crop production; however, they can be managed once the role of each type is specified. This allows clients to reduce the risk of quality and yield losses of crops, by taking proactive measures
  • The Rhizo-health index focusses on the rhizosphere. The rhizosphere is the zone of soil around plant roots where the biology and chemistry are highly influenced, making it the most dynamic environment in the soil. This index calculates specific root biological indicators which either indicate root stress or optimum root health. Biologically based products may be used in improving the Rhizo-health, which is critical for holistic crop health
  • The Urease Index represents the nitrogen cycle and gives an indication of the risk associated with the use of urea as a nitrogen source under your soil conditions. Urease is the enzyme that is responsible for the hydrolysis of urea into plant available forms and therefore this index provides a tool to make informed decisions on nitrogen use efficiency. Urease is also dependent on organic matter in the soil and therefore also used as a measurement for soil microbial activity
  • The P-Mineralisation Index focusses on the phosphomonoesterase enzymes. Roots and microbes have the ability to secrete phosphatase enzymes under various conditions, which mineralise phosphate in the soil making it plant available. This score gives an indication whether or not the soil and roots have the capacity to convert unavailable phosphate into a form that can be taken up by your plant roots, ensuring nutrient use efficiency.

Measuring these soil biology indicators is a critical part of soil health and can provide key information about the rhizosphere. Plant growth promoting microorganisms which interact with plant roots enhance plant growth by a wide variety of mechanisms. Therefore, measuring and understanding plant-microbe interactions in the rhizosphere within soil health can improve crop productivity by better managing risk.

However, again, it is re-iterated that a critical point to consider when studying soil biology is not to approach it as an independent research subject. Studying soil health characteristics independently has been criticised by interdisciplinary soil researchers John Crawford and Iian Young, 2004, who have stated that “No-one discipline will be able to understand the most complex biomaterial on the planet.” Therefore, it is important to have cross disciplinary approaches to understanding soil health and particularly soil biology. Interpretation of soil biological indicators without in depth understanding of soil chemical and physical characteristics, on farm practices and fertilization strategies can be misleading. For this reason Omnia understands the integrated significance of concurrently studying all three aspects of soil health, i.e chemical, physical and biological.

The Soil Health Prism is an essential tool in reducing risk and sustainably optimising quality and yield. The Soil Health Prism is also the first step towards a healthy soil based on measuring and managing soil health for sustainable farming.

Sustainability is the cornerstone of our approach, as it is an essential part of achieving longevity and success for our farmers and our business.


  • Doran, J.W., and T.B. Parkin. 1994. Defining and assessing soil quality. p. 3-21. In: J.W. Doran et al., (ed.) Defining Soil Quality for a Sustainable Environment. SSSA Spec. Publ. No. 35, Soil Sci. Soc. Am., Inc. and Am. Soc. Agron., Inc., Madison, WI.
  • Crawford J and Young, L, 2004, Soil Security: Solving the global soil crisis. Global Policy (2013) doi: 10.1111/1758-5899.12096

By Venessa Moodley – Manager: OmniBio™