Biochar application is currently considered to be an effective soil
organic carbon (SOC) management to prevent land degradation by enhancing
SOC stock. However, quantitative information on the impact of biochar
application on carbon dioxide (CO2) flux and associated microbial
responses is still scarce, especially in degraded tropical
agroecosystems. Here, we evaluated the impact of land management
(control (C), biochar (B; 8.2 Mg C ha−1), farmyard manure (FYM) (M; 1.1
Mg C ha−1 yr−1), and a mixture of both (BM; 8.2 Mg biochar-C ha−1 and
1.1 Mg FYM-C ha−1 yr−1)) on CO2 flux, SOC stock, microbial biomass C
(MBC), and metabolic quotient (qCO2) in degraded tropical alkaline
cropland of southern India, based on a 27-month field experiment.
Cumulative CO2 flux over the experiment was 2.4, 2.7, 4.0, and 3.7 Mg C
ha−1 in the C, B, M, and BM treatments, respectively. Biochar
application increased soil moisture and SOC stock, though did not affect
CO2 flux, MBC, and qCO2, indicating the limited response of microbes to
increased soil moisture because of small amount of SOC. Combined
application of biochar and FYM did not increase CO2 flux compared with
FYM alone, due to little difference of microbial responses between the M
and BM treatments. Additionally, SOC increment (8.9 Mg C ha−1) and the
rate of C-input retention in soil (0.78) was most significant in the BM
treatment. Hence, the combined application of biochar and FYM could be
sustainable land management by efficient increase of SOC stock in the
tropical degraded cropland.