Two-year responses of earthworm abundance, soil aggregates, and soil carbon to no-tillage and fertilization

Agricultural practices often lead to a decrease in soil carbon (C), which often begins shortly after a natural system is converted to arable land. Conservation agriculture practices, such as no-till farming and weed mulching (NWM), may help maintain soil C. Increases in plant biomass through fertilization can also increase soil C. However, there is limited knowledge of the initial C dynamics following land conversion followed by conservation agriculture and fertilizer application, and of the soil biological and physical processes associated with these dynamics. Here, we studied the effects of two tillage practices (conventional tillage and NWM), fertilizer, and their interaction on earthworm abundance, soil aggregates, and soil C at two years after land conversion from grassland to agricultural land. We conducted a 2 × 2 factorial experiment (tillage/NWM and fertilized/not fertilized) in an experimental field in central Japan. We found that soil bulk densities and C concentrations at 0-5 cm depth were lower and higher, respectively, in the NWM plots than in the tillage plots at two years after the start of land conversion. After two years, earthworms were found only in the NWM plots. The percentage of macroaggregates (> 2 mm) was higher, and larger amounts of C were stored, in macroaggregates in NWM plots than in tillage plots. Amounts of crop biomass, roots, and plant residues were larger in the fertilized NWM plots. In the long term, such organic matter could accumulate in the form of macroaggregates, thereby further increasing soil C stock. Overall, we found that the soil biological and physical parameters that potentially control soil C responded to agricultural practices within a short period. The maintenance of biological activities by NWM and increased organic matter input by crop residues through fertilization can enhance soil C accumulation, which could have significant consequences for sustainable crop yields.