Spatial variation of soil characteristics affected by biochar materials from traditional slash and burn agriculture in Sabah, Malaysia

Traditional slash-and-burn agriculture has been practiced for centuries in Southeast Asia. Our past study has identified distinctly different soil profile characteristics over a very short distance within a sloping field. In order to accurately estimate the potential of the traditional slash and burn cropping system for soil C sequestration as well as the maintenance of soil fertility, the spatial variation of soil C stock, soil nutrient status, and soil reactions were studied in Sabah, Malaysia. A triangular grid was used to conduct intensive soil sampling with an interval of about 5.8 m and a total of 71 locations. Total C (TC) stock was high with a mean of 34.9 Mg ha(-1) and the spatial variation was extreme with a CV of 57.3% within a field. The spatial range was also short at 14.3 m. All soil nutrients had high CVs especially for available phosphate at 90.2% and the lowest for exchangeable potassium at 44.0%. Available phosphate was the most limited major nutrient when referencing the Japanese fertilizer guidelines, and its spatial distribution was affected by soil acidity status, especially exchangeable Al. Potential improvements of the production systems can be made by the application of lime materials in locations where TC content was low. However, the introduction of any external inputs requires careful assessment of not just crop productivity but also its consequences for long-term sustainability of the system. Future studies are anticipated in order to understand the response of crop productivity by pH improvement as well as the use of fertilizers.