Author(s):

Shankar Ram, AK Ghosh, AK Nema, Vimal Kumar and Yogesh Pal

Abstract: The long term fertilization experiment was conducted at BHU from 2003 with rice-lentil cropping system. To monitor organic carbon storage in soils with inorganic, 50% organic and organic manures under three tillage practices. The experiments included main plot as three tillage i.e. conventional tillage (T₁), reduced tillage (T₂) and minimum tillage (T₃) and sub plot as three fertilization i.e. inorganic (F₁), 50% organic (F₂) and organic (F₃). Soil samples were collected at 0-60 cm depth at 5 cm increment from the wall of the rectangular pit using stainless steel cores measuring 5 cm in length and 5.1 cm in diameter after rice-lentil cropping sequence in 2012-13. Two such cores were collected from each pit, one for the determination of bulk density and the other for determination of TOC. It was observed that there was no significant difference among the tillage treatments except at 10-15 cm depth. The influence of fertilization however had significant effect on bulk density at 0-5, 5-10 and 10-15 cm depths. The effect of addition of organic manure did not bring in significant changes in bulk density at depths lower than 15 cm. The average bulk density in the inorganically fertilized plots was 1.35 Mg m^-3 in the 0-5 cm depth and increased to 1.37 Mg m^-3 in the 5-10 cm depth and to 1.40 Mg m^-3 in the 10-15 cm. The corresponding value for organically fertilized plot was 1.27 Mg m^-3 for 0-5 cm depth which increased to 1.31 Mg m^-3 for 5-10 cm depth and 1.35 Mg m^-3 for 10-15 cm depth.The increase in TOC content was more in minimum tillage rice-lentil cropping system than conventional tillage of rice-lentil cropping system. Sole organic manures resulted in increased TOC compared to mineral fertilizer alone. Lower soil layers showed no significant difference in TOC under different fertilization. The carbon stock for each 5 cm soil depth was found to decrease with increasing soil depth. The effect of tillage and fertilization was mainly found to influence soil carbon stock upto 0-15 cm soil depth; however their interaction was not significant. At depths lower than 15 cm, soil organic carbon stock was not significantly influenced by either tillage or fertilization. The cumulative carbon stock upto 60 cm depth was however significantly influenced both by tillage and fertilization (Table-3& Fig.-1) and varied from as low as 22.7 Mg ha^-1 in conventional tillage with inorganic fertilization and as high as 37 Mg ha^-1 in minimum tillage with organic manuring.

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