Farming worldwide is undergoing a profound shift towards sustainable soil management. But what exactly is soil health? André Cilliers, AECI Plant Health marketing manager, explores the essential components of soil structure, chemistry and biology, and why addressing all three aspects is crucial for creating optimal growing conditions and long-term soil health.
Farming worldwide is changing. Farmers are realising that their soils have to be managed sustainably if they are to continue producing high yields and quality produce. As a result, there is a distinct move worldwide to change the focus of agriculture in such a way that it includes building more sustainable soils.
But 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, consists of rock and mineral particles mixed with decayed organic matter and has 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 land masses and how critical it is that we protect it.
A closer look at soil
Any soil comprises three main components. These are soil structure, soil chemistry and soil biology. All of these need to be addressed by the farmer to create the best possible growing conditions for annual and perennial crop plants.
The correct soil structure is important for various reasons. The soil structure, for example, determines the degree of soil aeration. The ideal ratio of air: water in soil is 20-30% air and 20-30% water in a 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, which plays a role in water management and irrigation scheduling. Compacted soils cause run-off, erosion, and loss of minerals from the soil.
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 sustainable soil.
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 others, 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 of 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.
The correct soil chemistry 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, affecting yield, quality and nutritional value of produce.
All three components are crucial
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 to keep the soil chemically in balance.
This is sadly the case in many South African soils where for years farmers have only addressed the chemical requirements of their soils.
Soil is a dynamic medium which should be managed and nurtured. All three components of soil MUST be addressed to build sustainable soils.
- Dr André Cilliers is the marketing manager of AECI Plant Health. The views and opinions expressed in this article are those of the author and do not necessarily reflect the views or positions of Food For Mzansi.
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