Why is Soil Health Important?

11 February 2021

Farming worldwide is changing. Farmers are realising that their soils have to be managed in a sustainable fashion if they are to continue producing high yields and quality produce. Soil health management is a worldwide tendency that includes building more sustainable soils.

What is soil?

Below are three definitions from different sources.

• Soil can be defined as the organic and inorganic materials on the surface of the earth that provide the medium for plant growth.

• Soil is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life.

• The top layer of the earth's surface in which plants can grow, consisting of rock and mineral particles mixed with decayed organic matter and having the capability of retaining water.

The second definition is probably the most accurate one, but perhaps the third definition frighteningly shows us how dependent we are on this thin layer covering the landmasses and how critical it is that we protect it. Let us look more closely at soil.

Any soil comprises of three main components. These are:

Soil Structure, soil chemistry and soil biology. Soil health management must be implemented by the farmer in order to create the best possible growing conditions for annual and perennial crop plants.

Soil health indicators are listed as the following:

  • Organic carbon.
  • pH.
  • Water-stable aggregation.
  • Crop yield.
  • Texture.
  • Penetration resistance.
  • Cation exchange capacity.
  • Electrical conductivity.

These are the markers of good soil health.  Many of these can be addressed by using the correct soil health products.  These include products such as Biocult and DeKompakt from AECI Plant Health.

So why do farmers care about soil quality and health?

The correct soil texture is important for various reasons. The soil structure, for example, determines the degree of soil aeration. The ideal ratio of air: water in the soil is 20-30 % air and 20-30 % water in the soil. The other components of soil apart from air and water are minerals (45%) and organic materials (5%).

Aeration allows beneficial aerobic microbes in the soil to thrive and perform their metabolic functions optimally. In contrast to this, compacted soils become anaerobic and beneficial microbes become inactive.

These include mycorrhizae which are plant symbionts and enhance nutrient and water uptake. Correct soil structure also allows irrigation or rainwater to penetrate the soil without waste in the form of run-off, this plays a role in water management and irrigation scheduling. Compacted soils cause run-off, erosion and loss of minerals from the soil.

The correct chemistry of healthy soil

The correct soil chemistry, including pH and CEC is just as important as the two other factors since soil chemistry is closely linked to both. Incorrect soil chemistry leads to, among other things incorrect soil pH which directly influences nutrient uptake, microbial life and soil structure.

Soils in certain areas of South Africa are severely compacted. Aeration decreases, the microbial population in the soil shifts from aerobic to anaerobic organisms, water run-off increases and crop plants are forced to grow in sub-optimal conditions, effecting yield, quality and nutritional value of produce.

The chemical composition of soil also includes the inorganic nutrients in the soil, which have to be in balance with each other. Each year inorganic nutrients are withdrawn from the soil by the crop plant or orchard tree.

Different crops extract elements in different quantities depending on the nutritional requirement of the crop. These have to be replenished in the same ratios in which they were removed in order to keep the soil chemically in balance.

The soil structure plays an important role in the soil water balance and the amount of plant-available water. Correcting poor soil structure is therefore the first step towards a sustainable soil.

The value of soil microbes for soil health

The natural microbial life in soil can be practically destroyed by incorrect soil structure and soil chemistry. This is sadly the case in many South African soils where for years farmers have only addressed the chemical requirements of their soils.

The value of soil microbes in agriculture is apparent with the entry of numerous microbial products into the agricultural marketplace in recent years. Planting soya without a rhizobium inoculant is unheard-of in agriculture today.

Microbes play a critical role in soil. Among other microbes break down organic matter, recycle nutrients, fix nitrogen and promote plant growth.

If the microbiology in the soil is balanced, microbes can also contribute towards the control pests and diseases. By far the majority of beneficial soil microbes are aerobic, once again highlighting the importance of correct soil structure and aeration.

Anaerobic soils promote the growth of algae and pathogenic bacteria.

It is clear that soil is a dynamic medium which should be managed and nurtured. All three components of soil MUST be addressed in order build sustainable soils.

Illustration References

1. https://www.slideshare.net/tcooper66/weathering-erosion-and-soil-present...

2. https://ascelibrary.org/doi/10.1061/%28ASCE%29GM.1943-5622.0000792

Written by Dr. André Cilliers