Due to global warming in recent years, summer drought and heavy rain is frequently reported. It is known that the wetting of dried soils during several hours or days is accompanied by a sudden increase in the microbial populations and a burst of CO₂ production. On the other hand, biochar is focused to increase soil carbon storage. In this study, we investigated the influence of short cycle of dry-wet repetition of soil on greenhouse gas emission, together with biochar which is expected to suppress greenhouse gas emission.
Incubation experiment was carried out with Andosols and Chernozems soil collected in Japan and Hungary, respectively. Biochar (derived from rice husk, commercially available in Japan, pyrolysis at 600 to 800 ℃ for 5 minutes) was applied at the rate of 0% or 1%(w/w) of oven dried soil. Nitrogen fertilizer was applied to all treatments (100 kg N ha⁻¹). Moist soil equivalent to 10g oven-dried soil was filled in closed bottles, and aerobically incubated for 12 weeks at 20oC in dark place. The moisture was kept constant during the incubation period (CM; Water Holding Capacity (WHC) at 60%) or subjected to 6 cycles of drying and wetting (DW: WHC was decreased from 60% to 30% in one week by silica gel). Headspace gas samples were collected weekly to measure CO₂ and N₂O by gas chromatography. Soil pH, NH₄⁺-N, NO₃⁻-N, microbial biomass c and N, Total C, and Total N were also analyzed before, during and after incubation.
The results shown that soil pH increased by biochar after incubation. NO₃⁻-N increased more in CM than in DW, while at the end of incubation, it leached almost the same level. The N₂O production was observed in Chernozems at 1st and 7th day, higher with biochar in DW. On the other hand, there were two peaks in N₂O production in Andosols, especially higher without biochar and DW than with biochar and CM. Therefore, impact of biochar on N₂O production was significant only in Andosols soil. Relation to other trace gas is also discussed.