A new insight into the warming potential of organically amended agro-ecosystems

Abstract

Organic fertilization enhances the global warming potential of the soil, which is primarily attributed to higher CO2 emission from the soil. However, long-term studies under organic fertilization to observe its impact on soil’s warming potential with respect to CO2 efflux are limited in the dry tropical ecosystem. Therefore, we observed the changes in soil organic matter (C, N), soil CO2 efflux (SCE), soil moisture, microbial biomass C, and dehydrogenase activity in the plots under 1, 3, 5, and 10 years of organic fertilization, designated as OM1, OM3, OM5, and OM10, respectively. Also, a nearby native forest was taken as a standard reference system (NF) in the present study for comparative purpose. We observed that organic fertilization significantly (P ≤ 0.05) increased soil organic carbon (SOC), soil organic nitrogen (SON), SCE, moisture, microbial biomass C, and dehydrogenase activity, whereas decreased the SOC/SON ratio after 10 years, which also approached closer to NF. However, only the plots under 10 years of organic fertilization showed SCE significantly (P ≤ 0.05) similar to NF. It indicates that long-term organic fertilization is required for the improvement in soil properties. SCE showed a significantly (P ≤ 0.05) higher value (on average, by 61%) in OM10 site as compared to OM1. However, SCE on unit C basis (SCER) showed no change (P > 0.05). This increase in SCE after 10 years of organic fertilization might be attributed to the significant (P ≤ 0.05) increase in SOC, soil moisture, microbial biomass C, and dehydrogenase activity. However, no change in SCER after 10 years shows that organic fertilization has possibly been misinterpreted with respect to their impact on soil’s global warming potential. It might be attributed to the C protective nature of the organic fertilization. Overall, our results contradict with the often publicized higher warming potential of the organically amended systems. This indicates that organic fertilization does not increase the soil’s global warming potential, which is often misrepresented because SCE is not observed with respect to the existing SOC content.