CH4 emissions from rice paddies managed according to farmer's practice in Hunan, China

We measured CH4 emissions from ricepaddies managed by farmer's practices inChangsha, Hunan Province, China, from 1995 to1997. During the winter season, rice fieldswere left fallow under either drained(C-Fallow) or flooded conditions (C-Flood), andplanted with either Chinese milk vetch (C-GM)or oil-seed rape (C-Rape). The organic manureproduced in the winter (weeds, Chinese milkvetch, or oil-seed rape straw) was incorporatedin situ before the early-ricetransplanting. Both early-rice and late-ricestraws were removed and the soil was notamended with any exogenous organic manure. For1996 to 1997, the average seasonal CH4emission for the double rice cropping periodwas the highest from the plot that was floodedin the winter (103.5 g CH4 m−2) andlowest from the plot planted and incorporatedwith Chinese milk vetch (32.6 gCH4 m−2). Precipitation in the winternot only affected growth of green manure, whichwas incorporated in situ, but might alsoaffect CH4 emissions during the subsequentrice growing period. Therefore, a simplerelationship could not be found between theincorporated amount of green manure andCH4 emission. In the plots incorporatedwith vetch and oil-seed rape straw CH4emissions were significantly less during thesubsequent late-rice period than during theearly-rice period. This phenomenon might beattributed to a ``priming effect'' of greenmanure, which exhausted soil labile organicmatter. Based on the CH4 fluxmeasurements, the total CH4 emissions fromrice fields in Hunan Province during the ricegrowing season were estimated as 1.56 TgCH4 in 1996 and 1.06 Tg CH4 in 1997.Large variation of precipitation in the winterwould be an important factor controlling theannual variation of CH4 emissions from thetreatments.