Table of Contents

1. Overview

“To be a successful farmer, one must first know the nature of the soil,” wrote the ancient Greek Xenophon (400 B.C.)

Healthy soils produce life. It is no surprise that in the creation epic recorded in the book of Genesis, it is from the soil that Adam is created. It is the soil which determines which crop will be planted, and what livestock is supported. What we do with our soil determines how our ecosystems serve us – and how well we eat.

National identities and characteristics are ascribed in some writings to the soils of their people, and even though the exploration is more metaphorical it grabs something within us which recognises the profound connection between ourselves and the soil.

In addition to this chapter, the reader will find other chapters in this book of relevance e.g. “Precision farming”; “Conservation Agriculture”; “Fertiliser”; “Speciality fertilisers”; “Compost and organic fertilisers” and more.

Soil teems with life, yet because of bad farming and forestry practices, it is being washed away very many times faster than it is being replenished. On soil’s health depends much of the world’s food and water supplies, the growth of most plant and insect life and therefore the food of life itself.

Source: John Vidal, the article “The seven deadly things we’re doing to trash the planet (and human life with it)” on www.theguardian.com.

 

2. International business environment

  • www.fao.org/nr/lada – read about the Land Degradation Assessment in Drylands project (LADA). The project is now over but the website remains available for interested parties.
  • International Union of Soil Sciences (IUSS), www.iuss.org
  • International Erosion Control Association, www.ieca.org and www.austieca.com
  • Read about what the World Overview of Conservation Approaches and Technologies (WOCAT) has to say at www.wocat.net.
  • www.terrafrica.org – regional sustainable land management African network
  • The Soil Science Society of America, www.soils.org

 

3. Soil sampling and analysis

Soil sampling is the weakest link in the soil testing process – a few grams of soil represent millions of kilograms in the field. Soil’s composition varies horizontally and vertically: the sample should incorporate these variations. It is therefore important that controllable factors, such as the time of sampling, sampling depth, relation to rows and the sampling path through the land, are identical to the previous years.

There are various methods to sample soils. How, where and when the sub-samples should be collected depend on the application of the analytical results. You may be wishing to formulate a fertilisation programme, for example. Here, the method of soil sampling is determined by the crop cultivated. Or you may be investigating plant production problems, or doing a nematode count (here too there are different guidelines depending on where you are doing the sampling e.g. orchards and annual crops require different sampling methods). Or perhaps you are wanting to determine the water-holding properties of your soil.

Several role players have compiled guidelines on soil sampling for their clients. Some examples are:

  • soil sampling to formulate a fertilisation programme for annual crops;
  • soil sampling to formulate a fertilisation programme for perennial corps;
  • site-specific sampling;
  • soil sampling to diagnose plant production problems;
  • soil sampling to establish permanent crops;
  • soil sampling to assess the current fertilisation programme of tree crops;
  • soil sampling to determine the water-holding properties of soils;
  • soil sampling for nematode counts.

Agricultural role players like the members of the South African Soil Survey Organisation (SASSO), the ARC, and your nearest agricultural college, Provincial Department of Agriculture or university will be able to help you with soil sampling.

 

4. Soil erosion and Good Agricultural Practice

Soil erosion by wind occurs where a dry, loose soil that is reasonably finely divided on a soil surface that is smooth on which little or no vegetative cover is present.

  • Each year approximately 300 million ton of top soil is washed away.
  • At present 3 million ha topsoil cannot be used for agriculture as a result of erosion and bush encroachment.

A land user can combat wind erosion:

  • by using rotational cropping
  • by not leaving land fallow
  • by creating alternate strips of natural land with undisturbed cover crops
  • by leaving strips of natural vegetation at right angles to the prevailing wind direction
  • by creating suitable wind breaks, either mechanically or biologically