The effect of chemical fertilizer and city compost application was evaluated on the biomass of Stylosanthes guianensis on the barren land after a tin mining at the Mine Area Rehabilitation Station, Takuapa, Phang-nga, Thailand. Clayey materials were added to every plot at the ratio of 300 m3 ha-l to prevent plant from mortality and to enhance the nutrient holding capacity. An optimum biomass yield (5.12 t ha-l), which was lower than the maximum yield (6.15 t ha-l) realized through heavy fertilization, was obtained by the application of city compost (6.25 t ha-l) and chemical fertilizer (1.25 t ha-l). The soil fertility was improved at the end of the experiment, through the cultivation of S.
guianensis.The amount of precipitation, soil moisture (at 15 cm in depth) and soil temperature (at 0 and 15 cm in depth) was monitored throughout the experiment. The severe drought and over-wetting conditions reduced the biomass yield of S. guianensis, significantly. The crude fiber and crude protein content in the stems and leaves showed an appropriate amount as food for cattle.It can be concluded that the cultivation of S. guianensis is one of the promising way of agriculture in Takuapa and very good practice to improve the very low native soil fertility, in combination with the incorporation of clayey materials to diminish the water deficiency problem and to increase the nutrient retention capacity.Key Words: barren land after mining/Stylosanthes guianensis /biomass / clay application / city compost Soils at mine areas in Thailand are mainly characterized by their coarse texture. During mining operation, clayey materials are washed out to the river and eventually to the ocean, and only gravel deposits are often left in situ. The resultant land becomes barren, because there are little clay left and lack of moisture content in soils results in a severe drought problem in the dry season (Tanpibal and Sahunalu, 1989). Morphological description of the soil profile in this station was given previously for both original soil and barren soil after mining (Sakurai et al., 1989).The tropical monsoon climate and a high ground water table in the rainy season are the other causes of infertility. Since it brings various amounts of rain throughout the year, every plant is often exposed to severe water stress, i.e., deficiency in the dry season and over wetting due to the stagnation of surface water and high level of ground water in the wet season. As a result, the absence of surface plant cover after the mining operation yields a very high soil temperature that may damage plant roots at the surface layer (Sakurai et ai., The quantitative evaluation of the growth of S. guianensis in relation to the soil treatrnents has a practical significance in Takuapa. Thus, the present paper aims at discussing the following aspects; l) the effectiveness of soil dressings on this barren and abandoned land, i.e., clayey materials, chemical ferttlizer, city compost, and their combination, which are all easily available and not too much expensive ...