Vertical Distribution of TOC, TN and Other Important Soil Attributes and Their Relationship in Alfisol and Entisol of West Bengal

A study to assess the profile distribution of important soil attributes in Alfisols and Entisols of West Bengal was conducted during 2016-17. Purposefully selected random sampling was carried out to collect the soils from different locations of two study sites, viz., Kalinagar (25º27'33.9"N, 88º19'10.2"E) from Malda district and Durganagar (26º09'62.7"N, 89º53'51.7"E) from Cooch Behar district of West Bengal at 0-15, 15-30, 30-45 and 45-60 cm depths. Understanding of vertical distribution of soil fertility indicators like soil organic carbon (SOC), total nitrogen (TN) and other important properties in two different soil and climatic conditions will provide an insight regarding the behaviour of soil with the change in environmental conditions. Soil bulk density (BD), porosity, pH, SOC, TN, C:N ratio and texture were determined using standard laboratory procedures and computations. Obtained results were subjected to statistical analyses. Soils of Kalinagar sites were slightly acidic in nature while soils of Durganagar were neutral in nature. Kalinagar soils were silt clay loam in texture where Durganagar soils classified as loam to sandy loam. Soil BD values increased with depth in both Kalinagar (Alfisol) and Durganagar (Entisol). The porosity percentage progressively decreased with an increase in depth. Soils of Durganagar reported higher soil porosity at all the depths studied. An increase in soil pH with increasing depth was observed in both the sites. The mean total organic carbon (TOC) content recorded maximum in surface soil and its concentration decreased with the depth. Kalinagar soils observed 7.63% higher TOC (17.94 g kg-1) content than Durganagar (16.57 g kg-1) at surface depth (0-15 cm) and its accumulation at the lower depths was also maximum in former soil. Mean TN values were also found to decrease by increasing the depth. The accumulation of total nitrogen at the subsequent depths was relatively higher in Kalinagar than Durganagar. Increase in C:N ratio with increasing depth was noticed in Kalinagar site but the opposite trend was accorded in case of Durganagar. Accumulation of SOC and TN throughout the soil depth was found to be greater in Alfisol (Kalingar) due to higher clay and silt fractions as compared to Entisol (Durganagar). There was a significant positive relation of TOC with clay and silt (r = 0.285, p<0.05, r = 0.314, p<0.01, respectively) and of TN with clay and silt (r = 0.328, p<0.01, r = 0.262, p<0.05, respectively) irrespective of soil orders. Alfisols with high bulk density have a greater capacity to accumulate SOC and TN throughout the soil profile due to higher clay and silt fractions in comparison to Entisols with loose textural properties.