Comparisons of red ratings (RR) with Fe_d, Fe_d/Fet, clay content, andmagnetic susceptibility (x) of two loess-paleosol sequences at Luochuan and Lingtai on China's LoessPlateau were conducted to study the possibl...Comparisons of red ratings (RR) with Fe_d, Fe_d/Fet, clay content, andmagnetic susceptibility (x) of two loess-paleosol sequences at Luochuan and Lingtai on China's LoessPlateau were conducted to study the possible relationship between RR and pedogenic degrees of thetwo loess-paleosol sequences, and to discuss whether the RR could become new paleo-climaticindicators. Results showed that the RR of the two loess-paleosol sequences had positive, highlysignificant (P < 0.01) correlations with: 1) citrate-bicarbonate-dithionite (CBD) extracted iron(Fe_d), 2) ratios of CBD extracted iron to total iron (Fe_d/Fet), 3) clay (< 2 mum), and 4) magneticsusceptibility (x). This suggested that the RR of these loess-paleosol sequences could indicatedegreesof loess weathering and pedogenesis and were potential paleo-climatic proxies. The strongcorrelations of RR to Fe_d and x also implied that during pedogenic processes, pedogenic hematite inloess and paleosols were closely related to the amount of total secondary iron oxides and pedogenicferrimagnetic minerals (predominantly maghemite).展开更多
The effects of tillage methods on percent surface residue cover remaining and decomposition rates of crop residues were evaluated in this study. The line transect method was used to measure residue cover percentage on...The effects of tillage methods on percent surface residue cover remaining and decomposition rates of crop residues were evaluated in this study. The line transect method was used to measure residue cover percentage on continuous corn ( Zea mays L.) plots under no tillage (NT), conventional tillage (CT), chisel plow (CH), and disk tillage (DT). Samples of rye ( Secale cereale L.) and hairy vetch ( Vicia villosa Roth) were used for residue decomposition study. Results showed that the percentage of residue cover remaining was significantly higher for NT than for CH and DT and that for CT was the lowest (<10%). For the same tillage system, the percent residue cover remaining was significantly higher in the higher fertilizer N rate treatments relative to the lower fertilizer N treatments. Weight losses of rye and vetch residues followed a similar pattern under CT and DT, and they were significantly faster in CT and DT than in NT system. Also, the amounts of residue N remaining during the first 16 weeks were always higher under NT than under CT and DT.展开更多
基金Project supported by the National Natural Science Foundation of China (No. 40101013) the Outstanding Overseas Chinese Scholars Fund of the Chinese Academy of Sciences (No. 2003-1-7).
文摘Comparisons of red ratings (RR) with Fe_d, Fe_d/Fet, clay content, andmagnetic susceptibility (x) of two loess-paleosol sequences at Luochuan and Lingtai on China's LoessPlateau were conducted to study the possible relationship between RR and pedogenic degrees of thetwo loess-paleosol sequences, and to discuss whether the RR could become new paleo-climaticindicators. Results showed that the RR of the two loess-paleosol sequences had positive, highlysignificant (P < 0.01) correlations with: 1) citrate-bicarbonate-dithionite (CBD) extracted iron(Fe_d), 2) ratios of CBD extracted iron to total iron (Fe_d/Fet), 3) clay (< 2 mum), and 4) magneticsusceptibility (x). This suggested that the RR of these loess-paleosol sequences could indicatedegreesof loess weathering and pedogenesis and were potential paleo-climatic proxies. The strongcorrelations of RR to Fe_d and x also implied that during pedogenic processes, pedogenic hematite inloess and paleosols were closely related to the amount of total secondary iron oxides and pedogenicferrimagnetic minerals (predominantly maghemite).
文摘The effects of tillage methods on percent surface residue cover remaining and decomposition rates of crop residues were evaluated in this study. The line transect method was used to measure residue cover percentage on continuous corn ( Zea mays L.) plots under no tillage (NT), conventional tillage (CT), chisel plow (CH), and disk tillage (DT). Samples of rye ( Secale cereale L.) and hairy vetch ( Vicia villosa Roth) were used for residue decomposition study. Results showed that the percentage of residue cover remaining was significantly higher for NT than for CH and DT and that for CT was the lowest (<10%). For the same tillage system, the percent residue cover remaining was significantly higher in the higher fertilizer N rate treatments relative to the lower fertilizer N treatments. Weight losses of rye and vetch residues followed a similar pattern under CT and DT, and they were significantly faster in CT and DT than in NT system. Also, the amounts of residue N remaining during the first 16 weeks were always higher under NT than under CT and DT.
