THE CURRENT STATUS AND TRENDS IN THE VARIABILITY OF SOIL ORGANIC MATTER AND MAJOR NUTRIENTS IN COASTAL SANDY SOILS AFFECTED BY ARID CONDITIONS IN VIETNAM’S SOUTH - CENTRAL COAST

Abstract

This study was conducted to assess the current status and trends in the variability of soil organic matter (SOM) and the total content of major nutrients (nitrogen, phosphorus, potassium) in coastal sandy soils affected by arid conditions in the provinces of Khanh Hoa, Ninh Thuan, Binh Thuan, located in Vietnam's South - Central Coast. A total of 160 topsoil samples (0 – 20 cm) were collected from various districts and analyzed for SOM, total nitrogen (N), phosphorus (P), potassium (K) contents. These results were compared to the baseline soil standards established in 2005 for the region. The findings indicated that SOM content in the study area predominantly ranged from low to medium levels (0.48 – 3.45%), with over 60% of samples exhibiting mild to moderate depletion. More than 90% of soil samples had total nitrogen content classified as low to medium, with approximately 84% showing a decline in total nitrogen levels. Additionally, 53.15% of samples were identified as having low total phosphorus content, with Khanh Hoa province standing out with 90% of samples in the low category. About 27% of the samples showed a reduction in total phosphorus levels. Potassium content was low in 35% of samples, medium in 50.97% and high in only 13.80%. Compared to the 2005 baseline, an average of 20% of sandy soil samples across the study area experienced a reduction in total potassium content. Sandy soils in Khanh Hoa province exhibited a greater tendency for depletion in SOM and total nutrient content compared to those in Ninh Thuan and Binh Thuan provinces. The degradation of organic matter and total nutrients necessitates the implementation of integrated measures to maintain and restore soil quality for sustainable agricultural production.