Long-term changes in soil biological activity and other properties of raised beds in Longan orchards.

Introduction: The Longan fruit tree of the Vietnam Mekong Delta is grown in raised beds to improve water drainage during the rainy season and can live as long as 100 years. Objective: This research explores the extent to which the soil microorganisms as well as soil physical and chemical properties of these raised beds degrade over a period of 60 years under traditional management practices. Materials and Methods: Raised bed topsoil samples at depths of 0-20 cm were obtained from four different Longan orchards raised bed age groups: group 1) 15-25 years (L1-L5); group 2) 26-37 years (L6-L10); group 3) 38-45 years (L11-L15); and group 4) 46-60 years. Soil biological properties were tested for nitrogen-fixing bacteria, phosphorus solubilizing bacteria, potassium solubilizing bacteria, calcium solubilizing bacteria and silicate solubilizing bacteria, Future Directions: This suggests that more sustainable management practices, such as mulch and cover crops that decrease soil compaction and increase soil organic matter, improve soil porosity, total N, and feed soil microorganisms that are critical to nutrient cycling are needed to improve raised bed soil quality.