In the present study, we measured the CO
2 flux from soil surface of humic andosol under sustainable agricultural practices such as crop rotation, reduced tillage and manure application. We then evaluated the level of the CO
2 flux and investigated the factor which controlled the CO
2 flux under those practices. The CO
2 flux was measured by open chamber technique from July in 1999 to October in 2001 in the experimental field of Tokyo University of Agriculture and Technology (Fuchu, Tokyo) where the soil was humic andosol and the same practices have been continued for 8years. The CO
2 flux under maize cultivation in 1999, wheat in 2000, soybean in 2000, wheat in 2001 and maize in 2000 ranged 0.56-1.16, 0.01-0.37, 0.01-0.41, 0.07-0.39 and 0.22-0.67 g CO
2m
-2h
-1, respectively. A strong relationship appeared between CO
2 flux in each crop growing period and soil temperature (
R2=0.75-0.86). The average CO
2 flux from soil surface in the maize growing period in 1999 was five times larger than that in the soybean growing period in 2000, and the average CO
2 flux from soil surface in the wheat growing period in 2001 was twice larger than that in the wheat growing period in 2000. The level of CO
2 flux in each crop growing period was strongly related to the amount of applied nitrogen, including the preceding crop residue in addition to manure (
R=0.988). Q
10 under maize cultivation, soybean and wheat were 2.3-2.4, 16.2 and 2.8, respectively. Carbon emissions of soybean-wheat rotation and maize-wheat rotation were estimated as 296 g Cm
-2 and 578 g Cm
-2, respectively. This result suggests that it is possible to decrease carbon loss from soil by crop rotation incorporating soybean cultivation in humic andosol, since soybean demands less nitrogen application than other crops because of its nitrogen-fixing ability.
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