Impact of soil amendments on organic carbon pools under a rice-wheat cropping system

Rice-wheat cropping is the dominant cropping sequence in the Indo-Gangetic plains (IGP) of India. An experiment was conducted to study the impact of continuous application of farmyard manure (FYM) and rice straw (RS), either alone or in conjunction with fertilizer nitrogen (N), under a rice-wheat cropping system on i) total soil organic carbon (SOC) and slow pool C, and ii) stabilization of cumulative input C. Application of FYM, after seven years of rice-wheat cropping cycles, increased total SOC and slow pool C at 0-0.15 m soil depth by 6.7 t/ha and 1.5 t/ha, respectively, with the highest effect when FYM, RS and fertilizer N were applied together. Incorporation of RS increased total SOC by 4.1 t/ha, with an insignificant effect on the slow pool C. There was no significant effect of fertilizer N application on total SOC and slow pool C. The slow pool C was strongly correlated with the total SOC. About 18.5% and 4.2% of the cumulative input C were stabilized as total SOC and slow pool C, respectively, due to application of FYM; values for RS were 17.9% and 3.3%, respectively.