Assessment of Soil Fertility Status in Longan Growing Areas of Northern Thailand

Abstract

Effective management of plant nutrients requires the integration of soil properties, fertilizer effectiveness, and plant nutrient requirements. Improper fertilizer application can lead to nutritional imbalances, soil degradation, elevated production costs, and limited output capacity. Harvesting and pruning continuously decrease soil nutrients. Inadequate replenishment leads to reduced soil fertility, resulting in nutritional deficits in plants. Thus, evaluating soil properties in longan cultivation areas is essential for understanding nutritional requirements for soil improvement and efficient management. This study aimed to evaluate the soil fertility status of longan orchards in Northern Thailand and to develop site-specific recommendations for soil improvement and fertilizer management. A field survey was conducted in farmers' orchards located in Chiang Mai (24 orchards), Lamphun (33 orchards), and Chiang Rai (20 orchards). Soil samples were collected from the surface layer (0-15 cm depth) and analyzed for selected soil chemical properties to determine plant nutrient status and assess soil fertility.The results showed that soils in Chiang Mai exhibited considerable variation in soil pH, whereas available phosphorus, exchangeable potassium, and exchangeable calcium were generally at adequate levels. However, soil organic matter was low, indicating the need to increase organic matter inputs. In Lamphun, soils generally exhibited better fertility and higher organic matter content than those in the other two provinces. Nevertheless, magnesium application is recommended, particularly in areas with alkaline soils. In Chiang Rai, soils were characterized by acidic conditions, low organic matter content, and insufficient levels of exchangeable calcium and magnesium. Therefore, soil improvement through the application of organic amendments and liming materials is recommended to increase calcium and magnesium availability and to adjust soil pH to an appropriate range.The soil fertility assessment indicated that most orchards (50%) had a moderate fertility status, followed by high (32%) and low (18%) fertility status. These findings highlight the importance of site-specific soil management and nutrient management practices to improve fertilizer use efficiency, reduce production costs, and enhance the sustainable productivity of longan orchards.