Carbon and nitrogen differences in rhizosphere soil of annual plants in abandoned lands following shifting agriculture in northeast India

Abstract

This study aims to understand rhizosphere effects on soil carbon (C) and nitrogen (N) differences of three annual plants (Crassocephalum crepidioides, Ageratum conyzoides and Bidens pilosa) in different fallow ages: 2 years (FP-2), 5 years (FP-5) and 10 years (FP-10) in Mizoram, northeast India. In 2 and 10 years fallows, dominant annual plants were A. conyzoides and B. pilosa respectively, however, in 5 years fallow; dominance equally shared among three species. The rhizosphere soil nutrients (organic carbon—SOC, total nitrogen—TN, microbial biomass C-MBC and N-MBN, NH₄-N, NO₃-N, N-mineralization rate—N_min) were significantly (P < 0.05) greater in longer fallow compared to shorter fallow period. Rhizosphere soil of three annual plants showed 11–25%, 10–24%, 28–53% and 49–103% greater SOC, TN, MBC and MBN, respectively in FP-10 compared to FP-2. Similarly, 118–200%, 50–93%, 100–125% and 58–100% greater NO₃-N, NH₄-N, nitrification and N_min rates were recorded in these stands. The concentrations of NH₄-N, rates of nitrification and N_min in rhizosphere soil were greater than bulk soil but the reverse was true in case of NO₃-N. Difference between rhizosphere and bulk soil in the studied plants across fallow periods ranged from 17 to 63% in SOC, 27 to 64% in MBC, 21 to 70% in MBN, 52 to 80% in NH₄-N and 25 to 67% in N_min. The magnitude of rhizosphere effect of the three annual plants on soil C and N properties differed with fallow length. These results suggest that the microbial activity in rhizosphere soil is largely affected by the plant species and soil fertility level depending on fallow period. The differences in rhizosphere soil C and N largely depends on the soil fertility levels and the ability of the host plants to exploit resources.