Key soil parameters, organic matter, soil pH and plant nutrients determine the capacity of a soil to sustain plant and animal productivity. Conservation agriculture (CA) and crop diversification or intensification may change these soil parameters positively or negatively, which eventually affect long-term sustainability. We monitored these key soil properties (at depths of 0–15 and 15–30 cm) under CA-based sustainable intensification practices: zero-till (ZT), and crop residue retention, and crop rotations on Inceptisols and Entisols in the Eastern Ganga Alluvial Plains from 2014 to 2017. The rainfall of this sub-tropical region is 1273–3201 mm. Soil organic carbon (C) ranged within 0.46–1.13% and generally followed (positive) rainfall gradients. At all sites, the soil under ZT tended to have higher organic C than conventional tillage (CT). Soil pHH2O ranged within 5.7–7.8 across the region. At all sites, soil pH generally decreased under ZT compared to CT. This was most marked at some acidic soil sites where pH decreased by up to 0.4 units; the lower the initial soil pH, the higher was the decrease in pH under ZT practice. In contrast, the reverse trend was observed for soil organic C. Partial nutrient balances for N, P and K in rice–wheat and rice–maize systems were positive for N and P (<50 kg ha–1) but negative for K (up to 90 kg ha–1) under both tillage practices; more so under ZT practice even though crop residues were retained. Changes under ZT provide an opportunity to maintain soil organic C. However, remediation measures such as liming and efficient use of fertilisers are required for long-term sustainability of the farming systems in this agriculturally important region of South Asia.

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 IJECC, 10(1): 62-73, 2020; Article no.IJECC.54438 63 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. Original Research Article

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Comparison of the carbon (C) stocks among different soil orders allows us to explore the role of various soil characteristics in long-term C storage and their vulnerabilities.This study quantified and compared the accumulation rates of soil organic carbon (SOC) fractions (in 0-60 cm soil profile) in an Alfisol of Malda (25 27 0 33.9 00 N, 88 19 0 10.2 00 E) and an Entisol of Cooch Behar (26 09 0 62.7 00 N, 89 53 0 51.7 00 E) districts of West Bengal, India. We noticed a greater level of SOC (0-60 cm depth) in the Alfisol than the Entisol as the former soils were clayey in nature (fine textured) which provided the maximum stabilization of SOC compared to the Entisol (sandy textured).However, the storage of C fractions showed some peculiar results. The concentration of mineral-associated carbon (Min-C) was more or less similar in both the soil orders, but its stock was maximum in the Alfisol. While in the Entisol, permanganate oxidizable carbon (POX-C) and particulate organic matter carbon (POM-C) stocks recorded maximum among all the studied depths. A positive relation of SOC fractions and stocks with clay (r 2 = >0.500 in the Alfisol; r 2 = >0.700 in the Entisol) indicated the importance of finer fractions in profile storage of C. Min-C contributed to SOC of about 75%-85% followed by POM-C (3.27%-17.87%) and POX-C (2.57%-4.22%).Higher stratification of SOC and POX-C and POM-C fractions was observed in Entisol; while in Alfisol, stratification of Min-C was greater. Overall, this research demonstrated that the Alfisol has a greater potential in stabilizing Min-C than the Entisol with POM-C and POX-C and the distribution of these fractions varied as per its stabilization.