Kurzmitteilung Bestimmung von Dicyandiamid,Nitrit und Nitrat in Bodenextrakten mit Hochdruckflüssigkeitschromatographie

Determination of dicyandiamide, nitrite and nitrate in soil extracts by high pressure liquid chromatography A method for simultaneous determination of dicyandiamide, nitrite and nitrate in soil extracts and percolation water by means of HPLC has been developed. Extraction is done with water or CaCl₂, followed by separation on a RP–C18 column with tetrabutylammonium hydrogen sulfate and sodium dihydrogen phosphate as mobile phase UV-absorbance is measured at 220 nm. Detection limit is 0.1 mg N/I.     

Bestimmung von nichtaustauschbarem Ammonium in Böden mit einer Halbmikromethode

Determination of non exchangeable Ammonia in Soils by a semicro method A semi-micro version (sample weight 0,1 g) for the determination of nonexchangeable NH₄⁺ of soils, based on the method of Silva and Bremner (1966) is described. The results of the semi-micro version are compared with the original method. The regression-coefficient is r = 0,9906. Analysis time is reduced by a factor of 2, reagent needs approximately by a factor of 20. Exactness and reproducibility are satisfactory for routine measurements. Pampean soils from Argentina, analyzed with the semi-micro method contain between 50 and 90 ppm nonexchangeable NH₄⁺.     

Die Abschätzung von Nitratausträgen aus landwirtschaftlichen Nutzflächen mit Hilfe von Nmin-Daten

Development and application of a method for the estimation of nitrate leaching from agricultural land For two locations in the Rhine Valley in the State of Baden- Württemberg research on the nitrate leaching from agricultural fields was carried out. The investigated sites are located on aquifers that are pumped for drinking water. A new procedure was developed in order to estimate the nitrate losses by leaching from the rooting zone of agricultural fields. The procedure uses seepage estimates from a soil water simulation model and measured nitrate contents in the soil. It is found that for both sites large amounts of nitrate are washed out and that high nitrate concentrations occur in the seepage water. The simultaneous use of the investigated areas for intensive agriculture and for drinking water supply is questioned.     

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.     

Die Validierung von Bodenwasserhaushaltsmodellen mit Hilfe von TRIME-TDR,Tensiometermessungen sowie thermogravimetrischen Bodenfeuchtebestimmungen

The validation of soil water balance models based on measurements of soil water contents by gravimetry and by TRIME-TDR and of soil water suctions determined by tensiometer In this study different measuring techniques for determining soil water contents and soil water suctions were analysed for their suitability for the validation of soil water balance models. For this purpose a period of three years with continuous data of soil water contents measured by TRIME-TDR and soil water suction measured by tensiometer were available. Additionally soil samples at different times were taken for gravimetric moisture analyses. These measurements were compared with the corresponding simulation results of a soil water balance model. This soil water balance model consists of the determination of evapotranspiration according to Penman-Monteith and the calculation of soil water fluxes based on the Darcy-equation. The results indicate the higher suitability of TDR-measurements for evaluating the goodness of fit between the simulated and the calculated results in comparison with the other measuring techniques used in this study, especially in the context of general soil water dynamics. The tensiometer data show the limited measuring range as a well known disadvantage of this technique.     

Bestimmung von Mikronährstoffen und Schwermetallen in Böden mit dem Verfahren der Elektro‐Ultrafiltration (EUF) durch Zugabe von DTPA

With the electro–ultrafiltration (EUF) technique, the plant availability of several plant nutrients in soils can be characterized. The basic principle of EUF is that an electric field is induced using platinum electrodes. Ions in the soil suspension move either to the cathode or to the anode and are filtrated through ultra‐membrane filters. In the standard EUF procedure, two extractions steps are used: 30 min at 20°C and 5 min at 80°C. However, the determination of micronutrients and heavy metals with the standard EUF procedure is not possible, because the solubility of these elements in water is low and most of the watersoluble elements are precipitated when passing the platinum electrodes. The addition of DTPA, a well known complexing agent, during a third EUF fraction (5 min at 80°C) enables extraction of micronutrients and heavy metals. Highest concentrations in the 33 soils of the study were found for iron, followed by zinc, manganese, lead, copper, and nickel. Lower concentrations were obtained for cobalt, chromium, cadmium, and molybdenum. For two soils, the EUF/DTPA procedure was compared to CaCl₂/DTPA and EDTA soil extraction methods, showing that higher or comparable amounts were found with CaCl₂/DTPA and much higher amounts with the EDTA method. These results reveal that the EUF/DTPA technique in principle can be used for the determination of plant‐available micronutrients and heavy metals. However, in a next step the relationship between EUF/DTPA‐extractable elements and their availability for plants needs to be quantified.     

Abschätzung von N2O-Emissionen mit Hilfe eines Windtunnels - ein Methodenvergleich

Estimation of N₂O-losses with a windtunnel - a comparison of methods No systematical investigations into the interactions between NH₃-emissions and N₂O-losses with different kinds of sludge applications have published so far. The use of a windtunnel, which is used for NH₃-measurements, as a possible alternative method to measure N₂O-emissions should be tested. Simultaneous measurements with open chambers and a windtunnel on a Catena in the country of Kraichgau (Baden-Württemberg) were done. Changing the construction of the windtunnel, it was possible to optimize the N₂O-measurements and to eliminate constructional mistakes. But still the dilution factor is too big to take representative amounts of N₂O.     

Reaktionen von Ca-Montmorillonit und Ca-Vermiculit mit Kohlensäure

Reaction of Ca-Montmorillonite and Ca-Vermiculite with CO₂ The treatment of Ca-montmorillonite and Ca-vermiculite with carbonic acid (Pco₂ = 2 atm) has shown the following results: In the pH range of ± 3.9–6.0 Ca is exchanged by H directly only on pH dependent (variable) charge sites (Cav), whereas, Ca on permanent charge sites (Ca_p) is exchanged only by lattice cations mainly Al released by proton attack. Therefore, with regard to proton uptake from carbonic acid the two Ca-clays behave as extremely weak acids. The exchange of Ca_v proceeds rapidly that of Ca_p much more slowly, the first one is essentially reversible the latter at least not within a short period of time. The proportion of Ca_v is found from a graphical extrapolation of the Ca saturation-pH-function (fig. 3). Al released during the initial stage of the reaction is non exchangeable, prevents the expandable minerals partly from collapsing on K tratement (verm. much more than mont.) and has an OH/Al ratio of about 2. On treating the same clay sample several times or at low suspension concentrations exchangeable Al with OH/Al = O occurs. Exchangeable hydrogen was never detected. Vermiculite is less resistent against carbonic acid than montmorillonite. The results were discussed in respect to the mechanism of release of lattice constituents and in respect to Al release under the influence of CO₂-concentrations of soils.     

Ein Beitrag zu Fragen der Methodik von Bodenfeuchtebestimmungen mit Hilfe der Neutronensonde

A Methodical Study on Soil Moisture Determination by the Neutron Scattering Method The use of the neutron scattering probe for the determination of soil moisture content in 60 plots in Dikopshof fertilisation experimental station for two years had required the study of some methodical aspects. One of the points is to get the standard curve. It was found that the standard curves taken from the model and from the field were nearly identical. Although regression analysis of the standard curve yield linear shapes, significance for non linear curves, was also obtained. The centre of sensitivity was more easily obtained by lowering the probe between two water filled containers than by the usual method.     

Die potentiometrische Bestimmung von Nitrat im Boden mit einer Membranelektrode

Soil-Nitrate Determination with the NO₃-sensitive Electrode A NO₃-sensitive ion electrode (Orion, No. 92–07) was tested to determine the nitrate concentration in soil extracts. Some analytical problems are to be respected: 2. During a 2–8 week period of measurement the electrode gradually lost its potential (Figure 2). Therefore it is necessary to replace the sensitive elements (ion-exchanger, nitrate concentration and membran of electrode) at a certain level (in this 165 mV with 0.22 ppm NO,-N-solution). 3. Additional problems are from the heterogenity of thes oil(s = 0.10mg NO₃-N/100g soil in this experiment). With 4 replications in sampling at given site or date, significant differences in the range of 20 kg NO,-N/ha have been obtained. Observing the before mentioned precautions the correlation between nitrate content 1. The optimal range for measurements can be calculated by application of the Peters-Nernst equation between 1 to 10 ppm NO₃-N (Figure 1). This equation is influenced by the used electrode. Because this influence changed, it is necessary, to measure the standard solution before and after the series. determined by the nitrate electrode and conventional method (r = 0.92, Figure 3) was highly significant. The deviation of 0.28 ppm has no influence on the agronomy conclusions based on the nitrate determinations.     

Beschreibung des Verlaufs der Stickstoffaufnahme von Kohlrabi (Brassica oleracea convar. acephala var. gongylodes L.) mit Hilfe von Wachstumsstadien und eines empirischen Wachstumsmodells

Nitrogen uptake of kohlrabi, estimated by growth stages and an empirical growth model Some fertilizer recommendation systems for field vegetables are based on estimated nitrogen uptake curves. The estimation of nitrogen uptake should be as accurate as possible. Therefore 3 estimation methods and their accuracy (standard error of difference between measured and estimated values, sd) are compared. Comparisons were carried out with measured nitrogen uptake curves of kohlrabi (Brassica oleracea var. gongylodes L.) from 16 field experiments. The use of observed growth stages resulted in the smallest estimation error (sd = 14 kg N · ha^?1). This method is recommendable because it is accurate and easy to use. Estimations by applying an empirical nitrogen uptake model (sd = 16 kg N · ha^?1) are more complicated. The estimation based on time after planting is easy to use but showed the largest estimation error (sd = 28 kg N · ha^?1).     

Erfassung der Bodenentwicklung in Hochflutlehmen des Niederrheins mit Hilfe multipler Korrelations-, Regressions- und Clusteranalysen

Demonstration of the soil development in high flood loam of the Lower Rhine using multiple correlations, regressions and cluster analysis Several characteristics have been examined for 26 soils on high flood loam aged from 500 to 12000 years. Main results of discovered relations between duration of development and degree of characteristics are: Using multiple regression analysis continuous soil development could be stated and quantified. Square regression is better than a linear one. Employing regression being determined among some characteristics and age by means of absolutely dated soils, age of other soils in the same region can be estimated. With cluster analysis it is possible to demonstrate soil development from late pleistocene to youngest holocene too, but the relationship in ages is relative.     

Vergleich von Elektro-Ultrafiltration (EUF) und Extraktion mit 0,01 molarer CaCl2-Lösung zur Bestimmung des pflanzenverfügbaren Stickstoffs im Boden

Comparison of electro-ultrafiltration (EUF) and extraction by 0.01 M CaCl₂ for the determination of “available” soil nitrogen The NO₃-N, NH₄-N and N_org content of 25 different farm soils were analysed using the EUF-technique and CaCl₂ extraction in order to compare the reproducibility and reliability of the two methods. Nitrogen available to plants was measured in a micro pot experiment with Lolium multiflorum. - CaCl₂ values were better reproducibel (cv = 2.6%) than those of the EUF method (cv = 6.2%). - Close correlations were found between the soil content of CaCl₂-and EUF-extractable nitrogen (r² = 0.917). - The EUF-extractable N_org-fraction was positivly correlated with the total N-uptake by the test plants (r = 0.921). Most importently these data did not significantly deviate from the correlation of the CaCl₂ extractable N_org-fraction with total N-uptake (r = 0.932).     

Die Reaktion von aromatischen Hydroxycarbonsäuren mit N-Methyl-N-Nitroso-N′-Nitroguanidin und N-Methyl-N-Nitrosoharnstoff

Reaction of Aromatic Hydroxycarboxylic Acids with N-Methyl-N-nitroso-N′-nitroguanidine and with N-methyl-N-nitrosourea The phenols affect the mutagenity of nitroso compounds. Using polarography and voltammetry the redox properties of phenols and N-nitroso compounds were investigated. Changes in half-wave potentials of N-methyl-N-nitrosourea and N-methyl-N-nitroso-N′-nitroguanidine in the presence of gallic acid and in the anodic waves of gallic acid were detected in presence of MNNG. The interaction of the above nitroso compounds with phenols basing on the formation of molecular complexes is discussed.     

Die Bestimmung von selektiv freisetzbarem Kalium in Parabraunerde aus Löß und Pelosol aus Gipskeuper-Tonmergeln

The determination of preferentially releasable potassium in hapludalf from loess and chromudert from gipskeuper clay marl Octadecylammonium-chloride (ODA)-extractable potassium and interlayer potassium (K_ZW), exchanged after thermal dissociation of adsorbed NH₄, were determined on particle size fractions of soils from gipskeuper clay marl (typic chromudert) and loess sediments (shallow hapludalf). The extraction by ODA is a diffusion controlled K-exchange process. This is shown by the increase of K-release at small sample quantity and K-concentration in the extraction solution. The ODA-potassium supplies (= Biotit-K) of the two typic chromudert were significantly higher than that of the shallow hapludalf (34000 and 30000 kg/ha vs. 22000 kg/ha, to a depth of 55 cm). Biotit-K was highest in the 2-6μm-fraction for both soils. The smaller the particle size, the larger were the amounts of K_ZW In the clay fractions of all samples they reached between 70 and 80% of total K (K_t). XRD-data give evidence of different mineral genesis processes between the two types of sediments. This is supported by the K_ZW-values of the particle-size fractions. The selectively releaseable interlayer potassium is associated with wedge shaped layers of illite. It can be differentiated from the bulk interlayer potassium by its preferential extractability in the first 3 to 5 heating treatments. This potassium quantity is, on an average, 22% of total clay interlayer potassium.     

Die Bestimmung repräsentativer Mittelwerte von Schwermetall-Konzentrationen in den Niederschlägen und im Sickerwasser von Wald-Standorten des Soiling

Heavy metals in precipitation and seepage water from forest sites in the Soiling: Determination of representative averages of heavy metal concentrations Concentrations of Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd and Pb were determined in open land precipitation, in precipitation below canopy and in seepage water in two different soil depths, over the period of 3 years, in monthly and half-yearly intervals, in a beech and a spruce forest of the Soiling mountains. The results of the concentration measurements and the element fluxes calculated from these data were treated statistically. The coefficients of variation of the concentrations and the fluxes within a given time period often exceeded 100%. It is proposed that, in order to determine meaningful average values, weighted samples are taken in half-year or year intervals, over the time span of several years, in a number of local replicates sufficient to reduce the error of the mean to less than 30%. For the investigation of time variations in the concentrations and fluxes the sampling of single rain events or of seepage water within short time periods (a few days) is suggested.