Soil Carbon and Nutrient Accumulations in Pinus kesiya Plantations at Boa Kaew Watershed Management Station, Chiang Mai Province

Abstract

Accumulations of carbon and nutrients in soils under Pinus kesiya Plantations at Boa Kaew Watershed Management Station, Chiang Mai Province were studied in four different ages of pine plantations; 21, 25, 29 and 33 years old, respectively.  Five soil profile pits each of 1.6 x 2 x 2 m³ were made these stands and adjacent lower montane forest. Soil samples are taken from 11 depths; 0-5, 5-10, 10-20, 20-30, 30-40, 40-60, 60-80, 80-100, 100-120, 120-140 and 140-160 centimeters, respectively for analysis of physical and chemical properties. The results showed that soils had more developing profiles with increasing stand ages. Bulk density of the top soil within 10 centimeters depth was lower in older stands whereas change of soil reaction was unclear. Soil organic matter and nutrients particularly carbon, nitrogen, phosphorus, calcium and magnesium tended to increase with stand ages. Other important factors have influenced on variations of soil carbon and nutrient storages especially present tree densities, species composition and density of succession trees, topographic variables and forest fire occurrence.