Land Degradation and Pedology
Influence of Burning Practice in Shifting Cultivation under Different Climates on Nutrient Dynamics
2012 年 55 巻 3 号 p. 403-414
詳細
2012 年 55 巻 3 号 p. 403-414
This paper presents a comparison between the traditional shifting cultivation systems that have been reported in previous studies. The aim is to examine the influence of different burning practices on soil nutrient dynamics under temperate (Japan), tropical monsoon (northern Thailand) and tropical rain forest (the Malaysian state of Sarawak, Borneo) climates. The system in Japan includes cereal cropping continuously for three to four years. The amount of fuel (plant material to be burned) is estimated to be 50 t ha-1 at most. Ignition is started from an upper slope, and the land is burned slowly and carefully downward. The system used by the Karen people of Thailand consists of a single year cropping of rice followed by 10–15 years of fallow. Burning is carried out at the end of the dry season and a fire is ignited at a lower slope. The system in Sarawak is similar to that employed in Thailand. In each of these two regions, the amount of fuel is around 100 t ha-1 after 15 years of fallow. The increases in soil temperature from burning are in the order Thailand > Japan > Sarawak, where the differences can be attributed to soil moisture content and the direction of fire ignition. The effect of soil burning is thus more obvious in Thailand and Japan than in Sarawak. After three to four months of burning, the soil mineral N content in many regions decreases to the initial pre-burning level. A comparison between the level of nutrients in ashes and soils suggests that the addition of ash plays an important role in elevating nutrient levels in Japan and Sarawak. However, this may not be the case in Thailand. The increased nutrients return to their initial levels within one year in Sarawak and Thailand and after three or four years in Japan, which could be due to differences in the nutrient-holding abilities of the soils as well as to climatic influences. These differences in soil nutrient dynamics are considered to be reflected by the different cropping systems used in the regions.
