From shifting cultivation to permanent cropping in the cotton belt of Mali: Insights from the duration of the use of fields

摘要

Since 1960, farming practices have been deeply modified by the demographic increase and by cotton cultivation. Most farmers have abandoned the traditional shifting cultivation, with 4-5 years of cropping and 15-20 years of fallow and many of the fields have been cropped permanently during the last 20 to 30 years. Area under cultivation is increasing rapidly. Can these modifications induce a drastic decrease in the fertility of the soil? Many authors fear it, but farmers’ production increases regularly and more fertiliser is used. No clear description of the actual farming system has been proposed: Is the cultivation still shifting or has it become permanent? How many years of cultivation before returning to fallow? … and so on. The age of fields, that is to say the number of years elapsed since the last fallow lasting several years, is known in the Mali cotton belt through surveys conducted by the Compagnie malienne pour le développement des textiles (CMDT). This age of fields retains an information about the number of years fields are cropped before returning to fallow. But in recently cleared fields, it is not evident to determine those that will be cropped permanently, and those under shifting cultivation that will be returned to fallow. A very simple model enabled us to conclude, in terms of percentage of total area. The model considers three different systems: shifting cultivation, rather continuing cropping and continuing cropping. A set of parameters describe the model: numbers of years of cultivation before returning to fallow in shifting cultivation, rather continuing cropping, percentage of total cropped area under each system, and the increase percentage from year to year of the total cropped area. The set of parameters which gives the best fitting between model and observed curve is retained. Data from CMDT surveys are available from 1994 to 1999. They have been interpreted, year by year, for 4?different regions: the “old” cotton belt (Koutiala, Fana, San), the Sikasso region, the Bougouni region, and the Kita region. The results for 1997 are shown in a figure and a table summarizes the results from all available data: differences from year to year reflected the different sampling. From these results, clear differences appear between regions. The traditional shifting cultivation system, with 4 to 6 years of crops before a return to fallow, remains only in the Kita region where cotton growing is recent. Two systems coexist in the other regions: a system with 8 to 10 years of cropping and an almost permanent system with at least 30 years of cropping. This is markedly dominant in ’the old cotton belt’ (the Koutiala, Fana and San regions). Eight to ten years is a lengthening of the cultivation period in the shifting system: the farmers better exploit the work done for clearing, but they still benefit from the fallow. In the almost permanent system, farmers suggest that they intend to cultivate permanently and return to fallow only for incidental, often social, reasons (labour shortage, cattle destruction of crops, etc.). So the almost permanent system appears as a gradual transition to permanent cultivation. The almost permanent system started to develop in 1965-1970 when landholding pressure was low and when cotton growing was accompanied by the introduction of several new techniques: draugh