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.