Decadal Change of Soil Fertility in Bangladesh: A Spatial Data Analysis of Survey of Three Regions

Intensive agriculture has been practiced in Bangladesh for the last few decades with the use of fertilizer, pesticides, hybrid crops and monoculture having significant impacts on agro-ecosystem. It is necessary to evaluate the present fertility status in comparison with the previous one. This study was carried out on the soil survey data of Soil Resource Development Institute (SRDI) in Bangladesh. The organization has detailed soil surveys along for the last few decades. However, till today no spatial comparison has been made by the institute. The authors compared the surveyed (semi-detailed) data of few agro-ecological zones of the country of three Upazilas (subunit of a district): Monohardi (139.87 km2), Faridpur Sadar (407 km2) and Manikganj Sadar (214.8 km2) comprising of 120 sampling points each 300-m interval across the study area. The study area is under tropical climate with soil texture ranges from clay loam to loam. Response of soil parameters was studied in different layers of soil by performing an ordinal logistic regression to model soil parameters (pH, organic matter, N, P, K, S, Zn, B, Ca, Mg, Cu, Fe, Mn) to categorize soil heights (highland, mid-highland, lowland and very lowland) in relation to flood line. A good fitting of the model showed that soil survey data could be modeled properly by using this regression model. At Faridpur and Monohardi Upazilas, the model fitted well with survey data (chi-square, X2 = 176.923, p = 0.845 and chi-square, X2 = 246.343, p = 0.813) where p > 0.05. However, at Manikganj Upazila, some discrepancy was found. A weak response was found between soil parameters with soil heights from 1990s to 2010s. This weak association was profound in macronutrients than micronutrients. Nutrient interaction of soil also studied in a correlation matrix. The correlation matrix also revealed the decreased association of soil macronutrients across the decades. It was concluded that the weak association among macronutrients in recent decades is due to addition of fertilizers by intensive agricultural practices.