Soil Degradation of Raised-beds on Orchards in the Mekong Delta Field and Laboratory Methods

Abstract: Soil degradation is a complex process which may occur anywhere and at any time. It directly affects the physical, chemical and biological processes within the soil profile. Soil degradation can either be as a result of natural hazards or due to manmade actions, such as mismanagement on cropping patterns, soil preparation and cultivation practices. Regardless of how it is caused, soil degradation has strong negative effects on plant and soil productivity. Soil degradation can accelerate a series of processes such as erosion, compaction, loss of organic matter, loss of whole soil biota, surface sealing and contamination. This thesis presents the assessment of soil properties to improve our understanding of soil degradation on raised-bed orchards in the Vietnamese Mekong delta (MD). Measurements were made on 10 citrus plantations which had been established during a range of years from 1970 to 1998 at Hau Giang province. Soil sampling was made in the dry season of 2010 at two soil depths for each raised-bed to determine soil chemical and physical properties. The soil penetration resistance (PR) was periodically measured once a week together with soil sampling for moisture measurements during a period of 5 months. Analysis indicated the pH value of the soil was tending to decrease, nutrient imbalance and deficiency was developing, and the soil structure was deteriorating during the age since the raised-beds were originally constructed. Preventive and restorative measures need to be considered for restoring and retaining the quality of the soil and the ground water. These measures should consist of (1) neutralizing of excess acidity, (2) balancing of nutrients, (3) maintaining of soil organic matter, and (4) application of appropriate irrigation schedules.