2015 年 59 巻 3 号 p. 101-111
Swidden agriculture, which is still widespread in the mountainous areas of northern Laos, is evolving rapidly due to the economic, political, and social changes related to the practice. In this study, as part of efforts to clarify important changes and causal factors related to future agricultural development in this region, field surveys were conducted to ascertain the current conditions of the cultivation, labor input, and previous conditions related to swidden agriculture in a village of northern Laos. In the study area, upland rice was the main crop, and its swidden fields were found to average 1.22 ha in size and had fallow periods averaging 8.8 years. It was found that fallow periods varied widely from two to 20 years, and were longer in remote areas than in locations close to the settlement, but no significant differences were noted in the upland rice yields of swidden fields with different fallow periods. Among swidden farm practices, weeding required the largest labor input, and accounted for 67 man-days per ha, or 46% of all labor input. Furthermore, labor shortages were observed in some households because family members engaged in other work to generate cash income. This caused delay of weeding and weed infestation, which resulted in abandonment of the swidden field in some cases. Based on the result of interviews with elder villagers, the swidden agriculture practices in the area from 1980s to 1990s can be summarized as follows: in a normal year, field sizes averaged 3.2 ha, fallow periods tended to be longer than nine years, or averaged between 10 to 15 years, and full-field weeding was practiced two to three times per crop cycle. While this weeding requirement is similar to the present time, less labor was required because there were less herbaceous weeds. In the study area, there have been three primary changes to swidden agriculture: field area reduction, gradual fallow period shortening, and increasing burdens of the swidden works. The main causal factors were the government’s resettlement program, population concentration in roadside areas, increased labor requirements resulting from increased weed, and increased distance of swidden field from residences. These changes and their causes were interrelated and synergistic. Especially, increased weed and weed management programs are closely related to them, and the transformation of swidden agriculture could proceed more conspicuously and rapidly by the future introduction of herbicides or other new technologies that can be expected to alleviate weed problems.
