Effects of bamboo biochar application on global warming in paddy fields in Ehime prefecture, Southern Japan

Abstract

Biochar application can reduce global warming via carbon (C) sequestration in soils. However, there are few studies investigating its effects on greenhouse gases in rice (Oryza sativa L.) paddy fields throughout the year. In this study, a year-round field experiment was performed in rice paddy fields to investigate the effects of biochar application on methane (CH 4) and nitrous oxide (N 2 O) emissions and C budget. The study was conducted on three rice paddy fields in Ehime prefecture, Japan, for 2 years. Control (Co) and biochar (B) treatments, in which 2-cm size bamboo biochar (2 Mg ha −1) was applied, were set up in the first year. CH 4 and N 2 O emissions and heterotrophic respiration (Rh) were measured using a closed-chamber method. In the fallow season, the mean N 2 O emission during the experimental period was significantly lower in B (67 g N ha −1) than Co (147 g N ha −1). However, the mean CH 4 emission was slightly higher in B (2.3 kg C ha −1) than Co (1.2 kg C ha −1) in fallow season. The water-filled pore space increased more during the fallow season in B than Co. In B, soil was reduced more than in Co due to increasing soil moisture, which decreased N 2 O and increased CH 4 emissions in the fallow season. In the rice-growing season, the mean N 2 O emission tended to be lower in B (−104 g N ha −1) than Co (−13 g N ha −1), while mean CH 4 emission was similar between B (183 kg C ha −1) and Co (173 kg C ha −1). Due to the C release from applied biochar and soil organic C in the first year, Rh in B was higher than that in Co. The net greenhouse gas emission for 2 years considering biochar C, plant residue C, CH 4 and N 2 O emissions, and Rh was lower in B (5.53 Mg CO 2 eq ha −1) than Co (11.1 Mg CO 2 eq ha −1). Biochar application worked for C accumulation, increasing plant residue C input, and mitigating N 2 O emission by improving soil environmental conditions. This suggests that bamboo biochar application in paddy fields could aid in mitigating global warming.

Effects of Green Manure Application and Prolonging Mid-Season Drainage on Greenhouse Gas Emission from Paddy Fields in Ehime, Southwestern Japan

“…The high CH 4 emission observed during the growing season of rice indicates that suppressing it during this period help to reduce annual CH 4 emissions significantly. Furthermore, CH 4 flux increased in the early growing season and decreased during mid-season drainage in this study and in previous studies involving other nearby sites [6,7]. In Japan, CH 4 flux in paddy fields has been observed to peak mostly either early or late in the growing season or both (as two peaks, Itoh et al [17]).…”

“…To prevent plant growth on soil surfaces intended for CO 2 flux measurement, herbicide was applied around the stainless-steel bases at least 1 week before CO 2 flux measurement. During the growing season, acrylic chambers divided into upper and lower compartments were used for measuring CH 4 and N 2 O fluxes [6,7]. For measuring CO 2 flux, stainless-steel bases were installed between rows.…”

“…In this study, CO 2 emissions from bare soil surfaces in the fallow season and between rows in the rice growing season were defined as soil organic carbon decomposition or heterotrophic respiration (Rh) [6]. Rh, CH 4 , and N 2 O fluxes were calculated by linear regression.…”

“…N 2 O emission from paddy fields is also considered as a source of atmospheric N 2 O [5]. However, year-round monitoring in a recent study indicated that paddy fields could also be a significant N 2 O sink [6,7]. Therefore, long-term studies of N 2 O emission from paddy fields are necessary because short-term experiments do not provide enough data to evaluate net N 2 O emissions [5,8].…”

Efflux of Soil Nitrous Oxide from Applied Fertilizer Containing Organic Materials in Citrus unshiu Field in Southwestern Japan

“…Each gas flux was calculated by non-linear regression, and integrated values were determined by the trapezoidal method, both based on the methods in Toma et al [11] and Oomori et al [12]. Based on the calculation method provided by Toma et al [13], the emission factor for N 2 O (EF) was calculated using annual N 2 O emission (kg N ha −1 ·year −1 ) and applied N (kg N ha −1 ·year −1 ) as following equation:…”