Die Bedeutung der Festigkeitsverteilung in Einzelaggregaten für den Wasser- und Stofftransport im Boden

Relevance of strength distribution within aggregates to the movement of soil water and soil solution Different transport processes exist not only between the total soil and single aggregates, but also within individual aggregates. To clarify the structure of single aggregates without thin-sectioning, resistance to penetration was repeatedly measured on the same aggregate at a predefined soil water tension. The aggregates were sampled from the G_{o 2} horizon of a Typic Fluvaquent (Φ 15-25mm) and from the B_{g 2} horizon of an Aquic Chromudert (Φ 30-50mm) and equilibrated with water tensions ranging from roughly OhPa to 1000hPa. The strength distributions within individual aggregates were calculated using penetration resistance values of all measurements on one aggregate at a single water tension. These distributions, as exemplified by those at 300hPa and 1000hPa. show that the aggregates are surrounded by a thin, but very strong mineral skin which may be discontinuous, especially for aggregates from the Aquic Chromudert soil. In these aggregates, slickenside-like friction planes were found to penetrate through the skin. The deviation in the skin composition from that of the inner-aggregate described in literature, together with the finding of its strength, suggest that the exchange of water and solutes between the inter-aggregate and intra-aggregate pores is strongly impeded. The weaker parts within the skin, however, must be interpreted as preferred pathways, perhaps resulting in some fingering within aggregates at the prevailing matrix potential. The significance of different pathways within aggregates for the general transport of matter in soils is briefly discussed.     

Zur Frage der N-Formen im Grund- und Bachwasser aus hydromorphen Böden

N-sources in groundwater and outlet channels of hydromorphic soils NO₃- and NH₄-concentration was observed in the surface flow (1972–74) and in groundwater (1974–76) of the catchment area “Honigau” with a size of 1375 ha. During summer with low surface discharge and groundwater tables high NH₄-concentration was measured as compared to NO₃-concentration. High ammonium content during summer appears to be typical for many hydromorphic soils, as confirmed by N-content in Sphagnum peat soils and marsh soils. During winter season only a correlation exists between surface discharge and NO₃-content in the Honigau area. This correlation disappears during very high discharge levels.     

Zur Physiologie und Biochemie der Glykosidbildung

Zusammenfassung An Hand der Literatur und von eigenen Versuchen wird die Physiologie und Biochemie der Bildung von Glykosiden erörtert. Im Vordergrund stehen dabei einfache Phenolglykoside. Es hat sich gezeigt, daß die Glykosidbildung in starkem Maße zu Zeiten einer erhöhten Stoffwechselaktivität erfolgt und vornehmlich in grünen Blättern ohne Mitwirkung der Wurzel abläuft. In biochemischer Hinsicht kann die Glykosidbildung als Gruppenübertragungsreaktion charakterisiert werden, bei der der Zucker durch Anknüpfung an Uridindiphosphat aktiviert werden muß.

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Summary With regard to citations in literature and own investigations the physiology and biochemistry of glycoside biogenesis are discussed. Simple phenolic glycosides are considered preferably. It could be shown that glycoside formation is taking place to a considerable extent at the time when the metabolic activity is increased and that this reaction occurs especially in green leaves without interaction of the root. With regard to biochemistry glycoside formation can be characterized as a group transferring reaction, in wich the sugar unit must be activated by uridine diphosphate.

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Bedeutung der Mikroorganismen für die Bildung von Aggregaten im Boden

Significance of microorganisms in aggregate formation In soils microorganisms are the biological link between the physicochemical processes of synthesis and degradation. Because of their metabolic activities and their mechanical binding capacities they are directly involved in the development of soil structure. This review attempts to summarize knowledge of experimental work concerning aggregate formation by microorganisms. Especially distribution, adhesion processes, significance of biopolymers in aggregate formation and destabilization will be covered. The current state of art and open research areas will be indicated.     

Zur relativen Bedeutung von Massenfluß und Diffusion beim Nitrattransport zur Wurzel

Relative contribution of mass flow and diffusion to nitrate transport towards roots Experimental data from a field experiment with oats and faba beans were used to quantify the contribution of mass flow to nitrate transport towards roots. Two different approaches were used. The first was the calculation of apparent mass flow from average nitrate concentration and water uptake rate. The second was the computation of the increase of nitrate transport rate caused by mass flow. This was done using a mathematical model for nutrient transport. A comparison was made for a reference situation of transport by diffusion only. Calculation of apparent mass flow resulted in a nitrate transport to faba bean roots of 88 and 42 kg N-ha^?1 in 1982 and 1983, respectively. This accounted for 27 and 16% of total N accumulation of the faba bean shoots. For oats a transport of 38 and 23 kg N-ha^?1 by mass flow was calculated. These values correspond to 30 and 16% of total N uptake of oats in both years. The model calculations, however, showed that apparent mass flow overestimated the contribution of mass flow drastically when the nitrate concentration at the root surface is much lower than the average nitrate concentration of the soil solution as was found for faba beans in the soil layer 40–60 cm depth. In that case apparent mass flow overestimated the real increase of nitrate transport to roots by mass flow by a factor of 2.7. Under the given conditions diffusion was the more important process involved in the nitrate transport towards roots. The increase in maximum nitrate transport rate towards roots is much lower than apparent mass flow.     

Bilanz und Dynamik der organischen Substanzen eines sandigen Lehmes unter tropischen Kulturen

Balance and Dynamics of Organic Matter under tropical Cultures The Ah-horizon of sandy soil was cultivated with tea, coffee and banana under tropic conditions in a green house. After a cultivation period of six years, the soil under the cultures as well as the original soil was analysed for its contents of humic- and non-humic organic fractions. The soil planted with tea contains greater amounts of the non-humic substances and precursors of humic acids than those of the original soil. These organica undergo a permanent humification and lead to higher amounts of humic substances under tea plants than in the original soil. The humic system under coffee plants, however showed a dominated dehumification. Both processes (humification and dehumification) took place under banana cultures but with displaced timing.     

Infrarotspektren der mikrobiellen Biomasse und der Huminsäure im Podsolboden

IR-Spectra of Microbial Biomass and Humic Acid from Podzol IR-examination of soil samples from podzol with or without different pretreatments was carried out in order to check the possibility of humic acid and microbial biomass detection. Pure humic acid and microbial biomass, both isolated or enriched from the soil under controle, showed distinct absorption bands or shoulders at 1730cm^?1, 1620cm^?1 and 1380cm^?1. Only weak absorption bands at the respective wave numbers were detected in the untreated soil sample.     

Die Bedeutung der Umsetzung von Weizenstroh im Hinblick auf den C- und N-Haushalt von Löß-Ackerböden

The significance of wheat straw decomposition with regard to the C- and N-cycle of a cultivated loess soil In 1984/85, a microplot experiment with ¹⁵N-enriched fertilizer was carried out on a field of the Calenberg loess area near Hannover (surface area of the plots: 1 ± 2 m; experimental soil: stagnigleyic cambisol from loess). On the one hand, the extent of immobilization as well as remobilization of native soil- and fertilizer-N associated with straw incorporation (± 8 t/ha) was quantified. On the other hand, the turnover as well as the alteration of C- and N-masses in the decomposing straw material was studied. About 70% of the initial dry organic matter of straw was mineralized within one year. An enrichment of fertilizer-N as well as native soil-N in the residues of up to 20 kg/ha was observed as compared to the initial N-mass. On a microplot cropped with winter-wheat, microbial N-immobilization of about 30–40 kg/ha (native soil-N and fertilizer-N) occured in the soil after straw incorporation. The immobilization extended to march 1985. Subsequent, associated with a C/N-ratio in the straw of 43, N-remineralization as well as -extramineralization was observed with 40 kg/ha at maximum in december 1985.     

Zur statistischen Abhängigkeit der Adsorption verschiedener Herbizidwirkstoffe vom Anteil der organischen Substanz in Böden

On the relation of herbicide adsorption and soil organic fraction Freundlich adsorption isotherms were measured for four herbicides (atrazine, terbuthylazine, chlorotoluron, isoproturon) and 24 soil horizons, which are typical of Schleswig-Holstein, northern Germany. The relationship between the adsorption constant (K_Fr) of a chemical and the fraction of organic carbon (f_OC) of the soil horizons was evaluated. Chemical specific K'_OC-values, that are independent of soil organic carbon fraction varied considerably for each herbicide (CV about 50%); therefore these values as well as K_OC-values, that are determined by linear regression of K_Fr and f_OC should be evaluated critically before application. K'_OC- and K_OC-values derived from experiments showed decreasing affinity of the herbicides to soil horizons in the order terbuthylazine > chlorotoluron > atrazine ? isoproturon. Calculation of K_OC from K_OW or water solubility of each herbicide, however, led to changes in the above mentioned ranking. Hence, especially K_OW or water solubility based K_OC-values may lead to false conclusions concerning chemical mobility. For atrazine, terbuthylazine and isoproturon Freundlich adsorption constants increased overproportionally with increasing organic carbon content of soils. The relationships between K_Fr and f_OC therefore were described better by a non-linear equation (second order polynom) than by a linear approach. Contrary, for chlorotoluron a linear relation between K_Fr and f_OC holds at least for the range of f_OC investigated in this study.     

Zur Definition von Humusformen ackerbaulich genutzter Böden. II. Quantität und Qualität der organischen Bodensubstanz

The definition of humusforms from soils under cultivation. II. Quantity and quality of soil organic matter In the new edition of the German textbook “Practical Studies in Soil Science” the authors presented a proposal of mapping humusforms in arable soils in order to characterize soil and site ecology (Schlichting et al., 1995). This proposal was developed from the definitions “Ochric”, “Mollic” and “Umbric” of the Soil Taxonomy and the FAO classification. The characterization of humusforms in 45 arable surface soils was carried out according to this proposal while soil organic matter (SOM) composition was investigated by means of wet chemistry and CPMAS ¹³C-NMR spectroscopy. “Mollic” in contrast to “Umbric” humusforms could be characterized by a higher carbonyl/carboxyl carbon content probably deriving from proteins, polysaccharides and humic substances. In addition the mollic epipedon contains 10% more litter compounds, whereas in the umbric epipedon humic acids are of major importance. The humin fraction in the mollic epipedon is thought to be raised by the formation of Ca-humates. Our data suggest, that with regard to microbial decomposition a surplus of available organic matter is present in the mollic horizons. The ochric-like epipedon has a much lower humus content compared to “Mollic” and “Umbric” horizons and exhibits the highest amounts of soluble organic matter as well as aromatic and carboxylic C-compounds in the humic fraction. Our data suggest, that SOM quantity and quality of the mollic, umbric and ochric epipedons differ substantially. These findings suggest that the proposal of Schlichting et al. (1995), which was extended by Blume & Beyer (1996), should be regarded as a useful basis to discuss the development of humusforms in soils under cultivation and facilitate soil survey in order to improve site characterization.     

Bedeutung der Kalium-Verarmung in der Rhizosphäre und der Tonminerale für die Freisetzung von nichtaustauschbarem Kalium und dessen Bestimmung mit HCl

Significance of K-depletion in the rhizosphere and clay minerals for the release of nonexchangeable potassium and its determination with HCl Experiments were carried out with four different soils (basaltic soil, C-horizon of a keuper, sea alluvium, and a podsolic brown earth from loess) to investigate whether the fractions of exchangeable K and HCl-soluble nonexchangeable K are decreased in root vicinity by the K uptake of ryegrass (Lolium perenne). After a growth period of 70 days with five cuts distinct K depletion profiles were obtained showing that in the direct vicinity of the root the decrease in exchangeable K was the most pronounced. The K depletion in this fraction extended to 2 cm distance from the root zone. Also the concentration of HCl-soluble nonexchangeable K of the interlayers was decreased in root vicinity. It is assumed that the decrease in K concentration in soil solution is a prerequisite for the net release of interlayer K. The decrease in exchangeable K plus HCl soluble nonexchangeable K was equal to the amount of K taken up by the grass from the basaltic- and the alluvial soil. In the case of the podsolic brown earth and the keuper soil, however, much more K was taken up by the grass than was found in the decrease of exchangeable K plus HCl soluble nonexchangeable K. It is assumed that in these two soils the fraction of the HCl soluble K was more altered by the expansion of interlayers during the growth of rye-grass. The net release of interlayer K was neither related to the concentration of exchangeable K, HCl-soluble non-exchangeable K, the K fixation power nor the clay concentration. It is supposed that the net release of interlayer K also depends on clay mineral characteristics.