Using farmers' knowledge
about soil types

In some countries, ministries of agriculture issue blanket recommendations for fertilizer applications and crop types, covering large areas of the country. While these are useful as a general guide, the best amounts and types of fertilizer and organic matter will vary from place to place, even within a very short distance. Extension services do not have the staff or resources to test the soil in every field to develop specific recommendations for that field. But by drawing on the farmers' knowledge about their soil types and matching this with the scientific knowledge on the same soils, extensionists and researchers can suggest new crops or crop varieties, recommend fertilizer rates and ways of improving the soil fertility, or work with farmers to test new technologies.

Farmers have a detailed knowledge of their local soil types: the soil characteristics, problems, and their suitability for various crops. They may use many different criteria to distinguish one soil from another: for example, texture (sandy, clayey), colour, origin (eg, from limestone), fertility, organic matter content, depth, ability to retain water, ease of ploughing, type of vegetation, and presence of a hardpan or stones. The way they classify the soils is likely to reflect features that they have found important in growing crops.

In order to draw on this knowledge, the scientist or development worker must ask farmers to identify the various soil types in their area and to describe their characteristics. These characteristics can then be compared with the scientific classification. On this basis, scientific information on the soil can be translated into terms that the farmers can understand and use. Instead of having to do soil tests in many different places, development workers can suggest fertilizer rates or crops that are likely to perform well in the whole area covered by a particular type of soil.

The local names of the same soil type may differ from place to place, even among people who speak the same language. By matching the local names against a common standard (the scientific classification), development workers can advise farmers in different areas that share the same type of soil.

Location

This approach is most useful in areas where farmers have a detailed knowledge of their soils (for example, in areas that have been settled for a long time). It is less useful where farmers are new to an area (since they know less about their soils), or where extension and soil-analysis services are strong and can provide detailed advice to large numbers of farmers.

Procedure

The procedure below describes one way of involving farmers in identifying local soil types, matching them with the scientific classification, and then using this information to run on-farm trials on promising technologies. A similar technique can be used to collect and map information for land-use planning (see the section on Participatory land-use planning).

If the farmers are involved in this, they can use the skills they have learned to teach others how to map their soils, analyse them and test new farming methods. Throughout the process, make sure that all farmers participate freely. Provide guidance on the next step in the process, but do not interfere in the farmers' decision-making.

In the village (during the dry season)

1. Ask farmers to draw a map of their village, their fields and the surrounding area. They can draw on the ground using sticks or chalk, or on a large sheet of paper. Ask them to include on the map rivers, wooded areas, fields, administrative boundaries, and other important features.

2. Ask the farmers to name the different soil types in the area and to mark them on the map. They can use black beans to show black soils, red beans for sandy soils, etc. Make sure that all farmers agree on the types of soils shown and their locations. Copy the map onto paper to get a permanent copy.

3. Verify the map by walking with groups of farmers along one or more transects (lines or paths from one edge of the area to the other). Make sure you walk across all the different types of soil the farmers have identified.

4. During the walk, ask farmers to describe the type of soil in each place, and the farming practices they use on each type of soil. Write this information on a transect diagram showing the location, topography, crops and vegetation and soil types.

5. Ask the farmers to dig small pits (about 1 m long and 50 cm wide, and up to 1 m deep) in each soil type. At least one side of the pit should be "clean": a smooth, vertical face that shows the layers in the soil.

6. The soil scientist notes the soil profile (eg, the soil colour and texture in each layer), and takes samples of soil from various layers each pit.

In the laboratory

7. Take these samples to a soil laboratory for chemical and physical analysis. Determine the soil type according to the scientific classification (eg, the classification used by FAO, USAID or UNESCO).

8. Match the farmers' descriptions and the local names with the scientific classification. Try to match each individual local name with a scientific soil type. If a soil map of the area already exists, compare it with the samples collected from the farms. However, may soil maps are drawn at too small a scale to be useful for making recommendations for individual farms or fields.

9. On the basis of the scientific classification, identify major problems and ways of overcoming these for each soil type.

In the village (before the planting season)

10. Discuss with the group of farmers the problems and possible improvements in the farming system for each soil type. Ask them to suggest technologies (eg, a new crop type or fertilization method) that might help overcome the problems. Also suggest possible solutions based on the scientific evidence you have obtained.

11. Help the farmers plan on-farm trials to test the most promising technologies. Identify volunteer farmers cultivating each soil type to carry out the trials in their own fields.

12. Help the farmers to implement the on-farm trials and to maintain records of what they have done (eg, inputs, timing of activities, and labour used). See also the section on On-farm technology testing in this book.

13. At an appropriate stage during the season, organize field days for groups of farmers to inspect the results of the trials.

14. When the trial plots are harvested, make sure that the farmers record the yield and other important information.

15. Evaluate the results of the trials together with the group of farmers. Help the farmers decide which technologies have performed well enough for them to want to use on a larger scale in the next season.

16. Discuss plans for further trials in the next crop season. For example, the farmers may want to verify promising technologies on similar soil types, or adapt a technology to suit the amount of labour they have available.