In Sri Lanka where the paddy farmers' income is low and tractor hire rates are considerably high, paddy farmers' tendency to use tractors for tillage operation can hardly be explained in rational terms. However, this paper attempts to assess the significance of some selected socio-economic and physical factors which are considered to be effective in generating compelling grounds to use tractors for the tillage operation of paddy fields.
Three socio-economic variables relating to shortage of labour, shortage of buffaloes and limited time available for the tillage operation, which were considered to be crucial in determining the farmers propensity to use tractors, were regressed on the degree of tractor utilization; and then the residuals from the regression were mapped. Then, the map of residuals was compared with the map of agro-climatic regions in order to ascertain the impact of agro-climatic conditions on tractor utilization.
It was found that the three socio-economic variables collectively explain 51% of the spatial variation of the degree of mechanization. The map of residuals was found to mostly coincide with the map of agro-climatic regions. While all positive residuals were found to be in the dry zone and in the arid zone where the soil is very dry and hard, only negative residuals were found in the wet zone where the soil is wet and soft. Therefore, it seems that the spatial variation of the degree of mechanization which cannot be explained by the selected socio-economic variables may be attributable to the spatially varying soil conditions.
It can be concluded that the selected socio-economic factors and the agro-climatic factors pertaining to dryness and hardness of soils collectively encourage or compel Sri Lankan paddy farmers to use tractors for tillage operation.