The ecological consequences of biochar application to grasslands.

Abstract:

Biochar application to soil is widely proposed as a means of sequestering carbon (C) in soils to aid climate change mitigation while concurrently improving crop yields. Other benefits include issues such as waste disposal. While there are numerous studies investigating the effects of biochar application to agricultural systems, the impact of application to grasslands is still an understudied area. We studied the impact of biochar application on aboveground (plant) and belowground community composition and effects on the functional repertoire of soil microbial communities under a semi-natural grassland in the Netherlands. We investigated the impacts and the underlying mechanisms behind observed effects. We found that biochar application to soil caused a transient competitive effect, enhancing legumes biomass when compared to grasses and forbs. Biological nitrogen fixation was shown to increase following biochar application, with potassium (K) introduced with the biochar the most likely reason. Furthermore, we found lasting effects on the functional repertoire of the soil microbial communities after three seasons. Different responses to C substrate additions of field soil under laboratory conditions indicated lasting effects on C utilisation of soil microbial communities following biochar application. Stable isotope techniques showed pyrolysis to increase the predicted C residence time in soil from ~30 years to >520 years as well as reducing N availability by ~70% compared to the unpyrolysed feedstock. Combined, these results suggest biochar production and application can be used to control the nutrient status of grasslands while concurrently storing C for extended periods. These results have implications for grassland management, including grazed pastures which may benefit from increased BNF. Further they demonstrate the potential of grasslands for climate change mitigation through increased C storage following biochar application.