Zur Bestimmung der ungesättigten Wasserleitfähigkeit im Felde

Remarks on the determination of the unsaturated hydraulic conductivity based on field measurements In a previous paper hydraulic conductivity — moisture tension functions have been evaluated by a field method for various layers of a fallow loess soil (grey brown podzolic soil). The aim of the paper presented here, is to demonstrate the magnitude of error when the hydraulic functions are calculated in the presence of transpiring plants, as it was done elsewhere. The error arises, because the water uptake rates of roots are added to the capillary water flux through the soil matrix. From the present investigation it becomes clear that with advancing growing stages of winter wheat and the increasing water extraction ability the error becomes more and more pronounced. The conductivity values may then be overestimated by a factor of half the power of ten as compared to the results computed from the fallow soil.     

Ein Verfahren zur Messung der ungesättigten Wasserleitfähigkeit

Course of cellulose decomposition in a brown earth under a Trisetum flavescens – meadow after different fertilization The cellulose decomposition in the soil of a Trisetum flavescens-meadow untreated and treated with NPK. and PK fertilizer was determined by means of burial of pieces of cellophane. The rate of decomposition of the cellulose film was chosen as a measure of cellulolytic activity in soil. The cellulolytic activity had its maximum in the summer months and near the surface. The decrease with increasing depth was more obvious in the untreated lot than in the lot treated with NPK fertilizer. Under field conditions the influence of fertilization on the cellulolytic activity was low. In the laboratory there was a slight effect of the addition of soil from the NPK-lot on the decomposition of filter paper only with a slightly alkaline nutritive solution. The determination of soil cellulose content and mineralization of soil cellulose showed no differences between fertilized and untreated soil.     

Ein autoregressives Verfahren zur Bestimmung der gesättigten und ungesättigten hydraulischen Leitfähigkeit

An autoregressive procedure to predict the hydraulic conductivity — Comparison of measured and predicted results An instantaneous profile method was used to measure the unsaturated hydraulic conductivity. Relatively new techniques involving undisturbed soil samples instrumented with minitensio-meters and Time-Domain-Reflectometry (TDR) mini-probes were used for the experiments. The laboratory method allows a high spatial and temporal resolution. Laboratory measurements were carried out for 40 soil horizons with a wide spectrum of texture and bulk density. In addition, retention curves were measured using the standard pressure plate apparatus. Using this homogeneous set of data, an autoregressive model was developed which allows a stepwise calculation of the hydraulic conductivity for a water potential range of —30 up to —600 hPa. This model was developed for loamy sands, sandy, silty and clayey soils in conjunction with data from the retention curves. The calculation procedure starts with the determination of an initial unsaturated conductivity (k) close to field capacity, i.e., for water potential from —60 hPa up to —100 hPa. This first value is then used to predict other conductivity values using appropriate changes in soil water content corresponding to a defined range of the soil water potential. Subsequently, the hydraulic conductivities for higher and lower potentials were estimated considering the k value of the previous step in combination with the data of the retention curve of the next water potential range. The advantage of this empirical model is the indirect consideration of soil structure, in contrast to the closed-form van Genuchten-Mualem (vGM) model. To demonstrate these effects on different fitting procedures, the vGM model was also used to describe soil hydraulic functions. The accuracy of both, the vGM model and the autoregressive one, were compared for various fitting procedures and soils.     

Das hydrologische Verhalten ungesättigter Bodenschichten am Beispiel forstlicher Ökosysteme

The hydrological behaviour of unsaturated soil layers in forest ecosystems. Water transfer and storage processes in the unsaturated zone of soils are subject to permanent variations. They may be described by appropriate differential equations. Although in this way relationships become transparent the degree of abstraction nevertheless hinders their desirable utilisation in such cases as rough estimations in the field. To stimulate efforts in this respect, results and experience as gained from long-term investigations in forest ecosystems are discussed in this paper. First, steady state fluxes in homogeneous soil regions are dealt with in order to discuss basic interrelationships such as the effect of varying input rates on suction and air content. This discussion covers differently textured soils. Next, layered soils are considered in order to examine typical suction profiles and the effect of layers with low conductivity. Subsequently, basic response patterns for instationary fluxes are described, in particular infiltration and desorption. The processes considered so far become mixed and integrated once they are looked at as continuous functions of time. From those functions water budget determinations may be derived. A discussion of the role of the unsaturated zone would be incomplete without including evapotranspiration. Here an example is given showing the distinctly different impact of a beech and a spruce stand on the water budget.     

Bemerkungen zur Ermittlung der ungesättigten Wasserleitfähigkeit unter nichtstationären Bedingungen

On the Determination of Capillary Conductivity at Unsteady-State Conditions . Therefore it is stated that for obtaining the effective k_u-values. Considering the importance of capillary conductivity for the soil water regime the large differences up to 2 orders of magnitude between determinations on core samples from the same soil using the double-membrane-method (Henseler and Renger 1969) and the evaporation-method (Becher 1971a) initiated a study concerning the error caused by a possible nonlinearity of suction changes between two measuring levels using the latter method. The study was carried out on disturbed and undisturbed core samples from the three textural classes sand, silt and clay and with modified evaporation method. Comparing the geometric means of the obtained k_u-values calculated at unsteady-state and quasisteady-state conditions for different suctions resulted in that with usual application of the method the measured k_u-values must be diminished for obtaining the effective k_u-values. This correction factor increased with suction and is considered to be more important in laboratory than in field use.

• 1 For sandy soils a correction factor of 2 at 150 cmH₂O increasing to 6 at 1000 cm H₂O must be applied. The coarser the sand would be, at the lower suction nonlinearity will start and the more rapidly the correction factor will increase;.
• 2 For silty soils a correction factor of 2–4 must be applied for suctions > 300 cm H₂O;.
• 3 For clayey soils a correction factor of 2 rapidly increasing to 10 must be applied for suctions > 150 cm H₂O, but depending on soil cracks.

. The overestimation of water through-put resulting from the uncorrected k_u-values amounts to 1.5–4.0 [l/m² · d] at 100 cm H₂O, but these values are within the variation of the effective k_u-values. For 800cm H₂O the overestimation amounts to 0.002–0.065 [l/m² · d], but this makes up 300–1000 % of the effective water through-put.     

EDV-gestütztes Meß- und Auswerteverfahren zur Bestimmung der ungesättigten Wasserleitfähigkeit nach der Verdunstungsmethode

A Computer-aided Measuring and Evaluation Method for the Determination of the Hydraulic Conductivity in the Unsaturated State according to the Evaporation Method Multiple methods for the determination of the unsaturated flow depend on the water content or the soil-moisture tension have been published by so far. Their major drawback is the large consumption of time for the measuring and/or for the evaluation. The here presented combination of devices for the application of the evaporation method including its software permit a faster determination of parameters and a presentation in an analytic mode.     

Kapillar-GC — MS von Huminsäureabbauprodukten eines Podsols

Capillary GC — MS of degradation products obtained from podzol humic acids Humic acids' degradation products, formed by permanganate oxidation, mostly consist of aliphatic und aromatic dicarboxylic acids as well as fatty acids, whose distribution downwards a podzol profile will be discussed. Because of improved chromatographic techniques it is possible to detect 200–300 compounds. Their identification is based on the interpretation of mass spectra, high resolution mass spectrometry, and the use of N-, P- and S-spezific gaschromatographic detectors.     

Entwicklung eines Computerverfahrens zur Berechnung der hydraulischen Leitfähigkeit von wassergesättigten Böden mit der Bohrlochmethode

A computer program for the calculation of the hydraulic conductivity with the auger hole method An iterative procedure is applied for the calculation of the hydraulic conductivity with the auger hole method. Results are compared with data from Ernst (1950) and from Boast and Kirkham (1971). It is found that the achieved results compare well with the data from Boast and Kirkham, but frequently deviate considerably from those of Ernst. It appears that results from Boast and Kirkham are more reliable than those from Ernst. An advantage of the iterative procedure, as compared to the method of Boast and Kirkham, is its simplicity. Calculations are easily performed for sets of data not tabulated by Boast and Kirkham. Calculations can be carried out on a desk-top computer, but do require some computer time. A computer program (in Quick-BASIC) has been developed and can be obtained on request.     

Einbaubedingte Gefügeänderungen in der Bodenzone um keramische Saugkerzen

Soil fabric changes due to the installation of ceramic suction cups Samples from different sites containing ceramic suction cups with the surrounding soil were taken. After embedding and hardening in polyester resin polished blocks and thin sections were prepared. Soil zones up to 2 cm wide around the cups show up as more or less influenced. Former interaggregate or channel voids disappear. Clay coatings or infillings are smeared over into reoriented streaks. These features appear in dependence upon the predominant grain size distribution. In medium to fine grained soils the said zone is superimposed by a concentric system of fine cracks forming scaly shaped lamellae in perpendicular orientation around the cups. In coarse grained soils the extent of displacement and regrouping of sand grains is hardly visible. Piercing through a banded fabric (B_t-Band), a striking side and downward displacement of grains became obvious. In all cases a flushed silt or fine sand sludge works well to improve the soil/cup contact.     

Die Ermittlung des Bulk-Stomata-Widerstandes und der aktuellen Evapotranspiration aus Saugspannungsmessungen des Bodenwassers - dargestellt am Beispiel von Acker-Unkrautgesellschaften auf Hochflutlehm

The determination of bulk stomata resistance from tensiometric measurements of soil water - represented at the example of field weed societies on high flood loam It was shown that the computation of actual evapotranspiration from water losses above the zero flux layer is reliable enough to determine as well the bulk stomata resistance, used in Monteith's formula, as the shape of the reduction of potential to actual evapotranspiration. For field weed societies the bulk stomata resistance was determined to 37 s/m and, assuming a leaf area index of 3.0, the according plant resistance was calculated to 28 s/m. The reduction function from potential to actual evapotranspiration was linear one, starting at a water content of 70% of the available field capacity and ending at permanent wilking point. Both results are in good agreement with data from literature.     

Entwicklung,Eigenschaften und Klassifikation von Dünenböden der Ostfriesischen Inseln – am Beispiel Spiekeroogs

Pedogenesis, properties, and classification of dune soils of the East Frisian Islands (southern North Sea coast of Germany)—exemplified by the island Spiekeroog The aim of this study was a detailed pedological investigation and exact classification of dune soils of the East Frisian Islands. The following soil‐forming processes were identified on a laboratory‐data basis: humus accumulation and dislocation, carbonate loss, acidification, modification of exchangeable cations, and base‐saturation decrease. A slight iron oxide accumulation was visible in the field, but not confirmed by laboratory data. Applying the qualitatively and quantitatively defined horizons from the German classification, these soils cannot be classified as Regosols, Braunerden, and Podsols but they fit perfectly in the Arenosols as defined in the WRB.     

Vergleichende Betrachtung von Verfahren zur Auswertung von Nährstoffsteigerungsversuchen am Beispiel Phosphor

Comparison of two procedures to evaluate phosphate‐fertilizing field trials Growth response of agricultural crops to different input levels (e.g., fertilizer rates) can be described by the “law of diminishing increments”, which has been formulated mathematically amongst others by Mitscherlich (1928) and von Boguslawski and Schneider (1962, 1963, 1964). In the present paper, the economically optimal phosphate‐fertilizer requirements in 43 long‐term phosphate (P)‐fertilization experiments were calculated using equations on the basis of the yield functions of Mitscherlich or von Boguslawski and Schneider, respectively. For three field trials with linear or disproportionately high yield responses on P fertilization, none of the two procedures could be used. The same held for four trials with maximum yields already appearing at the first fertilization level. Similar P‐fertilization optima were calculated for 36 trials following the “law of diminishing increments”, resulting in a highly significant correlation (R² = 0.946) between both procedures. The correlation coefficients between the phosphate balance at the calculated optimum profitability and CAL‐P content in the soils at trial start were R² = 0.70 (Mitscherlich, 1928) and R² = 0.65 (von Boguslawski and Schneider, 1962, 1963, 1964), respectively. An optimal soil P content of 8–10 mg CAL‐P (100 g soil)^–1 was deduced. Both methods are applicable to calculate the optimum phosphate‐fertilizer requirement if yield effects due to P fertilization follow the “law of diminishing increments” and the increments of fertilization levels in each trial are established in a way that diminishing yield increments can be expected.     

Abbau und biozide Wirkung von Pflanzenschutz-und Schädlingsbekämpfungsmitteln im Boden am Beispiel von Kelevan

Degradation and biocide effect of chemical plant protecting agents and pesticides in soils by the example of the insecticide Kelevan By the example of the insecticide Kelevan it is proved that by means of a combined test plan degradation and biocide effect of chemical plant protecting agents and pesticides in soils can be tested simultaneously. For this test two different test soils as described in leaflet No. 36 of the Biologische Bundesanstalt (BBA), Braunschweig, are each divided in test samples of about 200 g dry matter. To answer the question whether besides the biotic an abiotic degradation of Kelevan and its primary subsequent products takes place in top soil, too, one part of the soil samples was sterilized by overheated steam. Afterwards these and the non-sterilized soil samples were treated with known amounts of Kelevan[cage-U-¹⁴C] and in accordance to leaflet No. 36 of the BBA stored in the dark at 22°U65% r. h. or under field conditions for different periods. To investigate the effect of Kelevan and its metabolites on microorganisms in top soil, further soil samples were treated with increasing amounts of Kelevan and also stored for different periods. At the end of storage periods on an average W,2 % of applicated radioactivities were recovered in the soil samples with Kelevan[cage-U-¹⁴C]. Whereas readioactivities of sterilized soil samples were nearly quantitatively extractable, increasing radioactivity amounts were held back under the same extraction conditions by the native soil samples, which were present as organic residue components of Kelevan(cagc-U-¹⁴C) and not as ¹⁴C-containing carbonate. During degradation, in both test soils as well under laboratory conditions as under field conditions, about one third of Kelevan[cage-U-¹⁴C] was transferred within 30 months via Kelevan acid[cage-U-¹⁴C] to Chlordecon[cage-U-¹⁴C] and about two thirds were transferred into various unknown ¹⁴C-labelled degradation products. The results of microbiological investigation prove that microorganisms were evidently neither selected nor decimated in both test soils by Kelevan and its degradation products.