Effect of different soil cultivation systems, including no-tillage, on electro-ultrafiltration extractable organic nitrogen
The effect of different long-term soil-cultivation systems (ploughing, two types of cultivator, notillage) on organic N, extracted with the electroultrafiltration (EUF) technique, was studied in two arable soils, a Luvic Phaeozem derived from loess and a Eutric Cambisol. A modified EUF extraction procedure (the 80°C fraction extended from 5 to 90 min) was used to investigate the release of organic N from the ploughing and no-tillage treatment, and the content of hydrolysable N was measured in the combined filtrates. No-tillage and the two non-turning cultivation systems led to an accumulation of EUF organic N in the 0- to 10-cm depth compared to the ploughing treatment. In the lower horizon (15–25 cm) the reverse pattern was found in the loamy soil, with higher concentrations after ploughing than after reduced tillage. However, in the sandy soil all four cultivation treatments showed similar values in the 15- to 25-cm depth. During the time of investigation (May 1987 to February 1989) an EUF organic N accumulation occurred, which was about twice as high in the loamy as in the sandy soil. Therefore we conclude that in the sandy soil the mineralization of organic N was faster, and that reduced tillage retarded its degradation. In the total 0- to 25-cm depth, this delay was not observed in the loamy soil. The N release rates were much lower in the sandy than in the loamy soil and they were higher for the notillage than for the ploughing treatment. Only 30–40% of the total organic N desorbed was hydrolysable and the amino acid composition indicates that part of it originated from microbial Cells. The overall evaluation showed clearly that EUF-extractable organic N is a sitespecific factor.
CaCl2 extractable N fractions and K2SO4 extractable N released on fumigation as affected by green manure mineralization and soil texture
A soil incubation experiment was carried out over 70 days (aerobic, 15°C) using a clay and a sandy soil produced by amendment with bentonite and quartz sand respectively. Fresh endive leaves were added as green manure (109 ng N kg−1 soil). Controls without green manure were also included. Samples were taken periodically in order to determine CaCl2 extractable N fractions and N in microbial biomass by a fumigation-extraction method.With the green manured soils CaCl2 extractable organic N was maximal at day 2 of incubation followed by an exponential decrease until constant levels were reached. At day 2 of incubation the apparent recovery rate of applied green manure as CaCl2 extractable organic N was 44% (clay) and 46% (sandy soil). Without green manure the organic N extracted was only 0.3% (clay) and 0.5% (sandy soil) related to the total soil organic N. NH4+ showed an intermediate increase (maximum at day 14) with green manured soils and was always negligible with controls. From day 14 onwards the NOinf3−accumulation was more pronounced with green manured soils compared with controls. The apparent extent of green manure mineralization at the end of incubation was 47.2 and 43.3% of the applied N in the clay and the sandy soil respectively.To summarize, bentonite amendment had no substantial effect on the rate and extent of N mineralization nor on the amount of CaCl2 extractable organic N.The extractability of N released on fumigation appears to be restricted by bentonite. Green manure increased the amount of extractable N released on fumigation with both soils.It is concluded that CaCl2 extractable organic N largely consists of organic substances which, in contrast to some constituents released on fumigation are only weakly adsorbed to clay surfaces and therefore are highly accessible to mineralization.
Organic constituents in process water from the in-situ retorting of oil from oil-shale kerogen
Capillary-column gas-chromatography/mass-spectrometry (GC/MS) was performed on the acid, base, and neutral fractions o'f liquid- and particulate-phase methylene chloride extracts of a composite sample of raw process water collected from separator Tank 6 by the Laramie Energy Technology Center. Of. the 160 extractable and chromatographable organic comP.ounds tentatively :identified, the following compou~d classes were found· (listed in decreasing order of. abundance):