Assessment of soil nutrient status and spatial variability in the Sundarbans Mangrove Forest, Bangladesh

Sundarbans is the largest contiguous mangrove forest in the world and is located in the southwest of Bangladesh. This study assessed the nutrient status and spatial variability of soils within the Sundarbans mangrove forest, Bangladesh, across four administrative ranges: Chandpai, Khulna, Sharonkhola, and Satkhira. We collected and analyzed 96 composite soil samples for electrical conductivity (EC), pH, total nitrogen (N), phosphorus (P), potassium (K), sulfur (S), sodium (Na), iron (Fe), and chlorine (Cl), as well as their available nitrogen (N), phosphorus (P), potassium (K), sulfur (S), sodium (Na), calcium (Ca), and magnesium (Mg), and their sodium absorption ratio (SAR). Results showed substantial regional heterogeneity in pH, electrical conductivity, and nutrient concentrations. The soils in Satkhira range had higher levels of salinity-related factors like higher EC (3.52 dS/m), pH (5.94) available sodium (0.43%), chloride (0.80%), total iron (5.10%) and sodium adsorption ratio (SAR) (2.16w). On the other hand, the soils in Chandpai and Sharonkhola had more total phosphorus (0.097% and 0.099%), available potassium (0.066% and 0.67%), and total sodium (0.51% and 49%) respectively. And, Khulna soils have more available magnesium (0.16%).While Sharokhola soils have the highest amount of total sodium(0.68%) and available sulfur (0.053%).Correlation and principal component analysis showed that phosphorus, potassium, and sulfur were very closely linked. In Satkhira, however, salinity-driven factors were the main cause of variability. Most of the ranges were classed as medium to high fertility based on soil nutrient index values, with phosphorus levels staying consistently medium. Overall, the soils in the Sundarbans showed different nutrient dynamics along natural environmental gradients. These findings provide a comprehensive baseline for understanding the spatial distribution of soil physiochemical properties and nutrient cycling, thereby supporting future assessments and sustainable management of this globally significant mangrove ecosystem.