Diversity of fields and farmers : explaining yield variations in northern Cameroon

This research was inspired by the inability of agricultural research to deal adequately with phenomena of variation, diversity and heterogeneity in agriculture. Although these phenomena were observed as long ago as the beginning of this century, they are still causing concern. Until recently, analysis of variance was applied to any form of undesired variation in the experimental results. The statistical elimination of variation from the research coincided with attempts to uniformise agriculture in order to optimise production. For a long time, deviations from the standardised average were regarded as undesirable random effects.Recent research has shown that variations in yield are very common in agroecosystems. They may be large, especially under difficult climatic conditions, and may even be considered as an asset to farmers. There is evidence that variations are not random, but are the result of systematic interaction between environment, crop genotype and management. This agrodiversity has important relations with the higher-level heterogeneity of the environment and diversity of farm households. At present, no comprehensive approach to its analysis is available, largely because agrodiversity is basically multidimensional in nature and may comprise several levels of aggregation.The objective of this study was to contribute to the understanding of diversity in agroecosystems by focusing explicitly on variations of yield and their explanation at field and household level. Between 1991 and 1993, field work was done in one village in northern Cameroon. Yield variations of three crops, field properties, crop and management characteristics and household characteristics were assessed systematically. Various techniques for statistical analysis were employed to determine the magnitude of variation and to define the agrodiversity of Within the agroecosystern of the selected village, variations in yield were observed for rainfed sorghum, cotton and dry season sorghum. The magnitude of variation was more or less constant over the years of observation, but varied between the crops. Two rainfed sorghum cropping systems were distinguished and within one cropping system, three field types were defined according to their distance from the homestead. Thus stratified it was possible to reduce overall yield variation and to explain it within each stratum by a reduced number of variables. It was concluded that the composition of agrodiversity was not uniform over the strata. Yield levels, limitations and constraints of rainfed sorghum production were specific to each cropping system and field type.Of the three crops, yield variation was greatest in cotton, despite many efforts of the cotton agency to standardise its cultivation. This variation was explained by distinguishing between types of variables, each explaining cotton yield variation to a different degree and in a particular way. Dry season sorghum showed least variation in yield, although it is subject to great environmental stress. Crop genotype and management proved to be adapted to one dominant field property, i.e. the water holding capacity of the soil. All farmers, irrespective of ethnic or socio-economic origin, agreed about the need to adjust mouskouari sorghum cultivation to field characteristics that define the water availability. Processes at field level leading to agrodiversity could be summarised by (1) spatial differentiation of the fields, (2) mechanisation of labour and (3) adaptation of cultivation to the environment.Ethnic diversity explained the absolute difference in cotton production, and the distinction between rainfed sorghum cropping systems within the agroecosystem. Socio-economic diversity explained the relative differences in cotton yield, and the distinction between rainfed sorghum field types.Finally, gender differences highlighted variations in rainfed sorghum yields and in non-agricultural income. Gender differences and ethnic and socioeconomic diversity proved to be interrelated, resulting in at least three classes of women farmers.It must be concluded that within one agroecosystem, crop yields may vary considerably. The agrodiversity explaining these variations proves to be cropspecific, One agroecosystern may comprise several cropping systems and field types of the same crop. Agrodiversity is also spatially specific and is largely determined by ethnic and socio-economic diversity and gender differences at household level. The potentials and problems of crops and fields also prove to be specific to the farmer. Within the context of rural development, it is essential to distinguish between well defined target groups in order to prevent interventions from uneffective generalisation. To do so, variation, heterogeneity and diversity must be accepted as realistic phenomena in agroecosystems and considered as an important source of information.