Hydrochar did not reduce rice paddy NH3 volatilization compared to pyrochar in a soil column experiment

Abstract

Pyrochar (PC) is always with high pH value, and improper application might increase rice paddy ammonia volatilization (PAV), which is the main nitrogen loss through air during rice production. Differently, hydrochar (HC) takes the advantages of high productive rate and always with lower pH value compared with PC. However, effect pattern and mechanism of HC on PAV are still unclear. In the present study, soil column experiments were conducted to investigate the effect of PC and HC application on PAV. In total, treatments with four types of biochar (WPC, SPC, WHC and SHC, i.e., PC and HC prepared with wheat straw and sawdust, respectively) and two application rates (0.5% and 1.5%, w/w) were set up and non-biochar application was used as control. Results showed that, application of HC with low pH value could not reduce PAV compared with PC. Total PAV increased significantly as the increase of HC application rate (especially for WHC). The increment of PAV under high rate HC application might be due to the strong buffer capacity of soil, the aging of biochar, the high nitrogen from HC. The results indicated that HC should be pretreatment before utilization in agricultural environment considering PAV reduction.

Carbon Sequestration Strategies in Soil Using Biochar: Advances, Challenges, and Opportunities

“…Even according to the International Biochar Initiative (IBI) and the European Biochar Certificate, hydrochar is considered to be distinctly different from biochar in its properties and thus excluded from biochar. In fact, according to the definition of biochar presented by IBI, biochar is a solid material obtained from the thermochemical conversion of biomass under oxygen-limited environments. , Clearly, hydrochar belongs to a type of biochar synthesized from biomass through hydrothermal conditions (or wet pyrolysis) at relatively low temperatures (<350 °C), , whereas biochar produced at relatively high temperatures (usually ≥300 °C, Figure ) through (dry) pyrolysis should be termed as pyrochar. , Encouragingly, pyrochar and hydrochar are increasingly used by researchers to indicate specifically these two types of biochars with significantly different physiochemical properties (e.g., refs − ). There are other thermochemical technologies, such as gasification and torrefaction, which can also convert biomass into biochar. , Biochars derived from gasification and torrefaction are minor types and share similar properties with pyrochar , and thus are not specially discussed in this review.…”