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.
Soil organic matter (SOM) in any agro-ecosystem is regulated by interaction of factors that determine its formation and promote decomposition, with a relative importance as: management > climate > biota > topography = parent material > time. Different land use practices under diverse climatic conditions in Hassan district (Karnataka) were selected for the study. Land use systems receiving frequent biomass additions through litter viz., Forest systems (both natural and manmade) and coffee plantations were observed with surface organic layer with higher SOC (10.6-13.2) content (g kg -1 soil). Agricultural systems mainly paddy, potato, vegetable, coconut and mulberry systems sparse OM additions were observed with reduced and lower SOC status (4.6-6.6). Humic acid (HA) and fulvic acid (FA) under these land use systems were dependent on land management i.e. source, form, amount, rate of organic materials added to soil. The HA fraction ranged from 0.2 g 100 g-1 soil in soils of coconut and paddy systems to 0.4 g 100 g-1 soil in natural forests. Quantitatively higher HA in forest and coffee systems was observed than agricultural systems. Proportionately to total SOM content (%), the HA was higher in agricultural soils (24.4-28.0) than coffee and forest soils (19.6-20.7). The systems with tree vegetations (forests and coffee) recorded higher proportions of FA (29.4-30.5) than agricultural systems like potato (26.5) and paddy (27.4). Forest systems with litter biomass additions (fresh organic materials) were with higher FA content while, agricultural systems receiving with almost decomposed OM (FYM) indicated higher HA than FA.
The study aimed to assess the effects of combined application of urea nitrogen (N) and tank* silt (TS) on greenhouse gases (GHG) emissions [i.e., carbon dioxide (CO 2 ) and nitrous oxide (N 2 O)] and agronomic productivity of maize-horsegram system. A factorial [urea (0, 60, 120, and 180 kg N ha À1 )] and tank silt (0 and 30 t ha À1 ) replicated thrice randomized block design was employed for this investigation.Results of the study showed that maize grain yield was significantly influenced by the sole application of both N fertilizer and TS. When both the N fertilizer and TS were combined, the grain yield was significantly (p < 0.01) improved by 5% (4870 kg ha À1 ) over the highest yield observed under only N. We have noticed a significant (p < 0.01) residual effect of N and TS on horsegram straw yield during all the years of experimentation. With the increase in N-rate, there was an increasing trend in CO 2 emission noticed in all the years including the pooled year data. Compared to CO 2 emission, N 2 O emission was greatly influenced by nutrient management and amendment application. Among the seasons, the post-rainy season (Rabi) had a slightly lower emission trend of CO 2 , during all the years as compared to the rainy season (Kharif). The observed results marked the marginal increasing trend of cumulative CO 2 (cCO 2 ) emissions with regard to increasing doses of urea. Tank silt addition slightly favoured a CO 2 emissions. The trend of cumulative N 2 O (cN 2 O) emission was greatly influenced by the dose of urea following the order of N 180 > N 120 > N 60 > N 0 . However, N fertilizer application influenced the cCO 2 emissions (r = 0.83), and significantly increased the cN 2 O emission (r = 0.99). Therefore, optimum and timely application of urea combined with TS is recommended as an effective strategy to combat GHG-based emissions (specifically N 2 O based) in semiarid rainfed regions.
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