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emoving agricultural cellulosic residues from fields for the production of ‘second generation biofuels'has the potential to profoundly alter C and N cycling in soil, increasing the risk of soil organic matter depletion and favoring soil–atmosphere gaseous exchanges. However, these negative impacts could potentially be offset by amending the soil with the solid by-product which is generated during bioethanol production. In a 100 days laboratory study, we investigated the fate of C and N after soil amendment with doubly labeled (13C, 15N) wheat residue (WR) and the corresponding bioethanol by-product (i.e. nonfermentable wheat residue NFWR) with and without extra N addition. Substituting WR with the corresponding amount of recovered bioethanol by-product partially compensated the C losses of full crop residue removal. When the equivalent amount of C was added as WR and NFWR, NFWR-derived C was found in significantly higher proportion in macroaggregates in soil (17.0 vs. 8.9%) after 100 days. Addition of both WR and NFWR reduced soil organic C (SOC) mineralization, i.e. it caused a negative priming effect in soil. However, this pattern was reversed when extra N was added. Both WR and NFWR increased the proportion of soil water-stable macroaggregates from 16% (in control) to 20–24% (in the different treatments). The results suggest that the more recalcitrant compounds derived from bioethanol production may stabilize more strongly and persist within the protected fractions of SOM pools. Our study demonstrates that NFWR, compared with WR application, neither increased N2O emissions nor had a negative impact on aggregate formation in the midterm. This demonstrates that NFWR has potential for replenishing SOC stocks

沖縄島に分布する畑地土壌の耐水性団粒について検討した。得られた主な結果は次のとおりである。1) 畑地土壌はジャーガル>島尻マージ>国頭マージの順に団粒化している。しかし,この傾向は弱く,団粒分布は同種土壌内の方が変化に富んでいる。2) 畑地土壌には小団粒(<0.25mm)や中団粒(0.25&acd;2mm)に比べ,大団粒(>2mm)が少ない。3) 粘土分は微細団粒の形成に寄与しているが,粗大団粒の形成にはあまり寄与していない。4) 国頭マージの土壌団粒が最も安定性と耐久性が低い。5) 風乾率は団粒の安定性のみならず耐久性を表す指標として有効である。, In this paper, the water-stable aggregates were examined for the 3 kinds of upland field soil and a weathered Neogene mudstone which are distributed in the Okinawa island. Out lines of the result obtained are as follows. 1. The upland field soils aggregate in order of Jaagaru > Shimajiri-maaji > Kunigami-maaji. However, the tendency is weak, and the aggregate distribution is rich in the change in the soil of the equal type. 2. There are many small aggregate (< 0.25mm) and middle aggregate (0.25&acd;2mm) but big aggregate (> 2mm) is little. 3. Though the clay fraction contributes to the formation of the minute aggregate, it does not seem to contribute in the formation of the bulky aggregate. 4. The soil aggregate of Kunigami-maaji is the lowest stability and durability in the 3 kinds of soil.