Effect of land management in winter crop season on CH4 emission during thefollowing flooded and rice-growing period

A greenhouse pot experiment was carried out to study the effect of land man agement during the winter crop season on methane (CH4) emissions during the following flooded and rice-growing period. Three land management patterns, including water management, cropping system, and rice straw application ti me were evaluated. Land management in the winter crop season significantly influenced CH4 fluxes during the following flooded and rice-growing period. Methane flux from plots planted to alfalfa (ALE) in the winter crop season was significantly higher than those obtained with treatments involving win ter wheat (WWE) or dry fallow (DFE). Mean CH4 fluxes of treatments ALE, WWE , and DFE were 28.6, 4.7, and 4.1 mg CH4 m(-2) h(-1) in 1996 and 38.2, 5.6, and 3.2 mg CH4 m(-2) h(-1) in 1997, respectively. The corresponding values noted with continuously flooded fallow (FFE) treatment were 6.1 and 5.2 ti mes higher than that of the dry fallow treatment in 1996 and 1997, respecti vely. Applying rice straw just before flooding the soil (DFL) significantly enhanced CH4 flux by 386% in 1996 and by 1,017% in 1997 compared with rice straw application before alfalfa seed sowing (DFE). Land management in the winter crop season also affected temporal variation patterns of CH4 fluxes and soil Eh after flooding. A great deal of CH4 was emitted to the atmosph ere during the period from flooding to the early stage of the rice-growing season; and CH4 fluxes were still relatively high in the middle and late st ages of the rice-growing period for treatments ALE, DFL, and FFE. However, for treatments DFE and WWE, almost no CH4 emission was observed until the m iddle stage, and CH4 fluxes in the middle and late stages of the rice-growi ng period were also very small. Soil Eh of treatments ALE and DFL decreased quickly to a low value suitable for CH4 production. Once Eh below -150 mV was established, the small changes in Eh did not correlate to changes in CH 4 emissions. The soil Eh of treatments DFE and WWE did not decrease to a ne gative value until the middle stage of the rice-growing period, and it corr elated significantly with the simultaneously measured CH4 fluxes during the flooded and rice-growing period.