Joost Brouwer

To make science and technology work for small farmers in sub-Saharan Africa I think it is imperative that account be taken of within-field soil variability.  This is especially true in semi-arid areas, but also in other parts of Africa.

The farmers themselves take variability into account: they often manage different parts of a field in a different manner.  They do this because it is more efficient, and because it reduces production risks. Technology developments and technology transfers that do not connect with this site-specific management by farmers, and with the underlying reasons, risk being ignored or turned down.  Farmer, extension and scientific knowledge about short-distance soil and crop growth variability must be combined for

– improved knowledge, understanding and communication by and for all parties concerned

– better design and analysis of agronomic experiments

– more relevant extension approaches

– better management options for the farmers.It is not difficult to achieve this.

It just needs a change in attitude from seeing variability as a problem to seeing it as an asset and an opportunity for subsistence farmers.  

One simple step is to use an easily assessed environmental parameter as a co-variable in the analysis of agronomic experiments.  A well-chosen parameter will explain a signifcant part of the spatial (and temporal) variability in experimental results.  That same parameter can then be used to extend the experimental results to farmers.  Simple parameters that a farmer can also use include microtopography (high spots and low spots in a field); degree of crusting of the soil; distance from certain termite mounds or from certain trees; wet parts an dry parts of a field; and the presence and absence of certain weeds.

A 12-page brochure on a variability project at ICRISAT Sahelian Center in Niger, that aimed to do just this, was financed by IUCN’s Commission on Ecosystem Management and is available from (2.6 Mb).  Its pictures tell the story and a number of references are included.  Its main conclusions are given below.  I will be happy to discuss this further with whomever may be interested.

The following practical results from the variability research in Niger can already be extended to farmers and/or researchers:·

  • with-in field variability can play a yield stabilising role; this is especially important in times of uncertainty caused by climate change·
  • over-manuring by many farmers in the Sahel can be reduced by spreading the available manure over a three times larger area;
  • different aeolian sand deposits, often found side by side in a single field, should be managed differently;·
  • nutrient use efficiency by farmers can be increased through microtopography-related site-specific management, such as not applying cattle manure and urine in wet and/or crusted areas;         this is important for the management of local fertility resources (manure, urine, compost, crop residues, domestic refuse), as well as for the management of mineral fertilisers: what can happen to cattle manure can happen to N, K and sometimes also P fertilisers;·
  • with-in field rainfall infiltration may be increased by applying lime or gypsum, especially on older aeolian deposits that crust more easily;
  • Macrotermes termites play an important role in local increases in soil fertility on sandy soils;
  • Faidherbia albida seedlings in agro-forestry projects are much more likely to grow well, and survive to adulthood and full utility, if they are planted near an old Macrotermes mound.
  • short-distance soil- and crop growth variability can be better incorporated into agricultural research through the use of covariables and other statistical techniques.