Precipitation is predicted to be more extreme in the future. This change will likely alter soil greenhouse gas (GHG) fluxes and have negative impacts on crop growth. Black carbon (biochar) addition in soils has been observed worldwide to mitigate GHG fluxes and improve plant growth, yet there have been no biochar studies to date under simulated extreme precipitation conditions. To explore how biochar affects GHG fluxes and crop growth under more extreme precipitation conditions, we conducted field and laboratory experiments in West Lafayette, IN.
We grew soybeans (Glycine max) in the field using a nested factorial design with precipitation (ambient and extreme precipitation) and biochar (30 t ha-1 application and control) treatments. The extreme precipitation treatment consisted of one-month droughts separated by monthly heavy rain events. We monitored soil CO2, N2O and CH4 fluxes in the field weekly. Soybeans were harvested twice at premature and fully mature stages. In addition, soil samples were collected from the field to measure hourly GHG fluxes after a simulated heavy rain event in the laboratory. We predicted that extreme precipitation would decrease GHG fluxes and soybean growth, and biochar would decrease GHG fluxes and improve soybean growth.
Results/Conclusions
Both field and laboratory measurements of CO2 emissions showed that biochar decreased cumulative emissions under ambient precipitation, but increased them under extreme precipitation. In the field experiment, extreme precipitation reduced cumulative CO2 emission by 3.8±1.4 mol m-2 (29%) compared to ambient precipitation. In addition, biochar lowered cumulative N2O emissions by 1.4±3.2 mmol m-2 (111%). In the laboratory, the extreme precipitation treatment yielded negative CH4 fluxes (CH4 uptake) after wetting, while the ambient precipitation treatment had positive fluxes (CH4 emissions). These results indicate that extreme precipitation decreases CO2 and CH4 fluxes, and that biochar decreases N2O emissions and has opposing effects on CO2 emissions in different precipitation regimes.
Biochar increased soybean shoot length by 3.7±1.7cm and leaf dry weight by 2.7±3.0mg (3%). At the premature stage, the extreme precipitation treatment increased pod dry weight by 0.027±0.011g (11%). However, the final harvest showed that the ambient precipitation treatment had 5.1±12.3mg (3%) heavier seeds. On average, biochar added 20±9 more seeds to every plant, which contributed soybean to a 3.3±1.5g (19%) increase in seed weight per plant. This suggests that extreme precipitation alters the seed formation process, and negatively affects yield, but biochar could mitigate these impacts.