Conversion of climax Dipterocarp forest for agricultural purposes has resulted in a decline in productivity of light textured soils in Northeast Thailand. To quantify the degree of chemical degradation that these soils have undergone, a survey was undertaken of six paired sites where adjacent Dipterocarp forest soils were compared to continuously cropped systems that had been under production from 37-100 years. Surface charge fingerprints along with soil chemical and physical attributes were determined on selective depth intervals. Significant declines in exchangeable cations and soil organic carbon were observed under the cropped systems resulting in dramatic declines in the surface charge charcteristics. The amount of soil organic carbon lost in the 0-10 cm depth interval under the cropped system ranged from 3.8 to 10.1 t/ha. A saturation index (Su) that encompasses an assessment of the degree of degradation taking into account the previous land use and that due to anthropogenic disturbance was used to quantify charge diminution. Su values ranged from 53-90 percent clearly indicating the degree of degradation these systems have undergone. Mean net acid addition rates (NAAR) were calculated for cassava and rice production systems. Values averaged 1.05-1.50 kmol H+ ha/y for the cassava and rice systems, respectively. A highly significant pedotransfer function was established to estimate pH buffering capacity (pHBC) using soil organic carbon and clay content. Using this pedotransfer function and the NAAR rates of each of the cropping systems, acidity risk maps were produced for Northeast Thailand for each of the crop production systems. These maps can be used to asess the potential for accelerated soil acidification and allow informed decisions to be made in order to address or reduce the risk of soil degradation associated with acid generation.
Authors and Publishers
Noble, A.D.(International Water Management Institute, Penang (Malaysia). c/o WorldFish Center) E-mail:firstname.lastname@example.org
Ruaysoongnern, S.(Khon Kaen University, Khon Kaen (Thailand). Faculty of Agriculture. Department of Land Resources and Environment)
Sukchan, S.(Department of Land Development, Bangkok (Thailand). Soil Survey and Classification Div.)
Berthelsen, S.(CSIRO Land and Water, Davies Laboratory, Townsville (Australia))
Webb, M.J.(CSIRO Land and Water, Davies Laboratory, Townsville (Australia))