Nitrogen forms of humic substances from a subalpine meadow soil, a latentic red soil and a weathered coal and the effect of acid hydrolysis on N structures of soil humic substances were studied by using 15N cross-polarization magic angle spinning nuclear magnetic resonance (CPMAS NMR) spectroscopy. Of the detectable 15N-signal intensity in the spectra of soil humic substances 71%-79% may be attributed to amide groups, 10%-18% to aromatic/aliphatic amines and 6%~11% to indole- and pyrrole-like N. Whereas in the spectrum of the fulvic acid from weathered coal 46%, at least, of the total 15N-signal intensity might be assigned to pyrrole-like N, 14% to aromatic/aliphatic ammes, and the remaining intensities could not be assigned with certainty. Data on nonhydrolyzable residue of protein-sugar mixture and a 15N-labelled soil fulvic acid confirm the formation of nonhydrolyzable heterocyclic N during acid hydrolysis. Project (No. 39790100) supported by the National Natural Science Foundation of China.
WEN QIXIAO, ZHUO SUNENG and CHENG LILI (Institute of Soil Science, the Chinese Academy of Sciences, P.O. Box 821, Nanjing 210008 (China))
Resources and ecological distribution of Arbuscular mycorrhizal fungi(AMF) on wild plants in Shandong vegetation region were investigated during 1995-1997. A total of 182 rhizospheric soil samples were collected from 50 wild plants. Spores of AMF occurred in all samples. More than fourty species of AMF were isolated and 35 species in five genera were identified. Among the five genera,the frenquency of occurence was Glomus (51.7%)> Scutellospora (23.1)> Gigaspora(14.1%)>Acaulospora(9.5%)>Entrophospora (0.8%). Glomus mosseae, Gigaspora margarita are prominent species, G.versiforme, G.constrictum, S.gilmorei are common species to be isolated. The spore density of AMF was different: Gigaspora>Glomus>Scutellospora>Acaulospora>Entrophospora . The occurence and distribution of AMF are related to regional difference, soil factors(contents of N, P; organic matter and pH) and host plant.The prominent species in eastern part were Gi.margarita, G.mosseae and G.versiforme , while in middle and western part of Shandong province was G.mosseae . The occurence frequency of Glomus, Gigaspora and Scutellospora was much higher than that of other genera in eastern and middle part of Shandong province. While Glomus and Acaulospora were higher in the western part. The spore number of Gigaspora and Scutellospora were much more than that of other genera in the samples collected in the eastern and middle area, while Glomus and Acaulospora are more frequently encountered in the western part of Shandong provence.
A greenhouse experiment was conducted to investigate the effect of surface film-forming material (SFFM), a mixture of 16-18-octadecanols by emulsification, on water evaporation. Air-dried soil with distilled water was incubated firstly for 7 days to reestablish soil biological activity and then for another 7 days after treated with SFFM at rates of 0, 1, 2, 4, 6 and 8 g m-2, respectively. Everyday during the 7-day incubation after addition of SFFM, water losses due to evaporation were ~measured by an electronic balance. The rate of water evaporation with the addition of SFFM was reduced significantly compared with the control treatment and the effectiveness of SFFM on water evaporation reduced with time. According to the equation expressions of the effect of SFFM on water evaporation, the half-life of electiveness of SFFM on water evaporation was introduced and calculated to analyze quantitative relationship between the effectiveness of SFFM on water evaporation and the addition rate of SFFM. The calculated half-life increased with the addition rate of SFFM and the confidence of the calculated values of the half-life was high, suggesting that the half-life of effectiveness of SFFM on water evaporation could be described quantitatively and may be helpful for ameliorating application method of SFFM and screening surface-film forming materials in order to improve nitrogen fertilizer use efficiency in flooded rice fields.
ZHUANG SHUNYAO, YIN BIN and ZHU ZHAOLIANG (Institute of Soil Science, the Chinese Academy of Sciences, Nanjing 210008 (China))
