Changes in Soil Fertility and Tilth under Shifting Cultivation

Abstract

In response to the world-wide concern on the conservation of forest and soil resources in the tropics, an experiment was conducted in northeast Thailand to study various ecological aspects of shifting cultivation in monsoon tropical Asia. The present study deals with the soil changes during the cropping phase of the experimental shifting cultivation. The experimental site was located on a hilly land at the elevation of 800 m under the tropical savanna climate. The vegetation was a semi-deciduous seasonal forest with about 330 ton/ha of aboveground biomass. The soil is derived from Mesozoic sandstones and shales with a pronounced reddish coloration. Field as well as laboratory characterization revealed that the major soil group in the experimental plots was a Lithic Ustropept, with a few scattered spots of Ultic Haplustalfs and Typic Troporthents. Effect of burning of felled trees on the soil profile was very conspicuous in reburn piles, but generally negligible in other areas. A comparison between the soil conditions before and after burning revealed a remarkable enrichment of soil with nutrients, particularly with P, K, Ca, and a rise of pH by 1 unit in the surface soil. There was also an increase in the content of NH4-N as a result of heating (soil-burning effect).