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Soil Health and Soil Carbon

In many ways the term "Soil Health" is a rather vague notion. To most farmers or growers it generally equates to crop production or yield capability. It is also commonly commonly linked to the notion of soil fertility, as distinguished from applied synthetic or organic nutrition. In summary, soil health depends on the interaction between a soil biological, chemical and physical properties, and the degree to which these aspects are optimal.

Many agricultural and intensive production systems focus strongly on nutrient applications in isolation as the primary link to net crop yield or productivity. The reality however is that all three aspects of soil health need to be managed in order to optimise soil health and productivity. As with the case for essential plant nutrients such as N:P:K which are drawn down from the soil in the process of crop or pasture growth and production, the same applies for other critical soil parameters such as soil organic matter (SOM). Uniquely, it is SOM which is the critical linkage between soil biology, chemistry and physical properties.

Soil Organic Matter and Total Organic Carbon- What's the difference??

SOM represents the organic constituents in the soil, including un-decayed plant and animal tissues, their partial decomposition products, and the soil microbial biomass which in essence is the living portion of SOM. SOM therefore includes non-humic components such as sugars and fats etc. 

Soil Organic Matter and Humus - What's the difference??

SOM and humus are distinctly different. SOM includes all fractions of organic material in its multitude of stages of degradation, whereas humus is only the humic substances present at the end of the biological degradation of organic matter.

Compost use is strongly associated with benefits to soil health and plant growth. These benefits are derived not only from the chemical and physical impacts resulting in increased nutrient and water storing capacity and yield improvements, but also from the disease suppression and plant health benefits gained from maintenance of soil microbial diversity and adequate soil organic matter and humus levels.

The Practical Value of Humic Substances

As organic matter breaks down in soil, humic acids (Humic acid & Fulvic acid) are formed. To some extent they are the biological heart of natural organic matter. They are the main fraction, the biological centre, of natural humic matter.

Humic acids assist in the physical modification of soil, build capacity to hold plant available nutrients and assist in biological stimulation and microbial activity.

Humic acids are natural chelators of soil trace elements and nutrients. They assist or promote their uptake by plants as they convert nutrients to plant available forms. Without this, elements such as iron, copper, zinc, manganese and other trace elements may form insoluble hydroxides. The presence of Humic acids maintains their plant availability.

Humic acids stimulate and promote plant development, resulting in higher yields. Humic acids improve the structure of soil and increase water retention, seed germination, root growth and quality of yields. For soils to remain fertile, humus must either be replaced or added.

When Humic acids enter plants at early stages of development, they result in increased cell division, root development and eventually dry matter, they act as respiratory catalysts, act as natural chelators of metal ions under alkaline conditions, convert nutrients into forms available to plants, protect plants from chlorosis and increase the permeability of plant membranes.

Basic Properties of Humic Substances

Humic Acids – These are the major humic component of soil and although water insoluble under very acidic conditions (pH<2), are readily soluble at higher pH’s. They are dark brown to black in colour.

Fulvic Acids – Fulvic acids are water soluble in all pH conditions, and are yellow to yellow-brown in colour.

Humin - The fraction of humic substances that is not soluble in water at any pH value and are black in colour.


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