Einfluß von Herbiziden auf die N2-Fixierung und Atmungsaktivität von Mikroorganismen in Ackerböden

Influence of herbicides on nitrogen fixation and respiration activity of microorganisms in arable soils The influence of pesticides on nitrogen fixation (acetylene reduction test) as well on respiration activity was determined in model experiments. The following soils were used: Chernozem from loess (Boroll), Luvisol from loess (Boralfs), Rendsina (Lithic Rendoll), Pelosol (Fine textured Cambisol) and Humic Podzol (Humod). The tested soils differed considerably in both parameters. The rendsina showed remarkably low fixation rates whereas the podsol reduced acetylene only at higher water contents. The soil herbicides chlortoluron, terbutryne, metabenzthiazuron and chloridazon did not affect the course and the magnitude of the tested parameters even not at higher doses. Only the leaf herbicide dinosebacetate revealed a distinct inhibition of nitrogenase activity in the podsol and in the luvisol from loess. The fungicide carbendazime caused a strong stimulation of the nitrogenase activity in all soils. The respiration activity could not been influenced significantly.     

Zum Einfluß organischer Bodenbedeckung auf den lateralen Transport von Isoproturon auf der Bodenoberfläche

On the Effect of Organic Surface Cover on Lateral Transport of Isoproturon on Soil Surface The losses of the herbicide isoproturon with the surface runoff and the sediment loss have been measured by means of rainfall simulations on microplots (0.5 × 1 m²) with different mulch materials and increasing soil cover percentages (wheat straw vs. rape leafs). Soil cover by straw showed no significant effect on the runoff discharge, but the total loss of isoproturon increased between 22 and 37%. Soil cover by rape leafs diminished the runoff by between 13 and 61%, the reduction of isoproturon loss was in the same range. It was shown, that the different influences of different mulch materials on runoff and soil loss can lead to different pesticide losses. Therefore, the only giving of “mulch” without specification does not describe such experiments sufficiently.     

Wirkung der Kaliumdüngung auf die Kaliumverfügbarkeit in der Rhizosphäre von Raps

Influence of potassium supply on the availability of potassium in the rhizosphere of rape (Brassica napus) Potassium depletion of the soil in the proximity of roots was studied in order to obtain quantitative information on the availability of potassium. For this purpose rape seedlings were grown in pots which separate roots from soil by a fine meshed screen; root hairs penetrated the screen. The soil adjacent to the screen was sliced by microtome into layers about 0.1 mm thick which were separately analysed for k. Plant roots strongly depleted the soil in their proximity; further distant ranges remained unchanged. A loess derived loam, brought to different levels of exchangeable K by precropping or K application, was equally depleted to 150 μmoles/100g soil at the root surface. Therefore, the quantity of K released from this source increased with initial K level. In addition, the distance of the depletion zone extended with K level from 4,6 to 6.3 mm from the surface of the root cylinder. Hence, the volume of soil contributing K to the root increased from 0.7 to 1.2 cm³ per cm root length. The combination of these two parameters, i.e. the quantity of exchangeable soil K released per unit of root length increased by a factor of 20 whereas exchangeable soil K was raised by a factor of 4.5 only. K uptake of the plants after 4 days was in agreement with the depletion of exchangeable soil K in the high K treatment only. The other treatments had obviously taken up considerable percentages of nonexchangeable K. This fraction was released from the soil ranging less than 1.5 mm from the root. The distance of the K depletion zone was also extended by application of NaCl and MgCl². Because of cation exchange, K concentration of the soil solution was increased, K buffer power decreased and, therefore, K diffusion was enhanced. It is concluded that plants in the field do not uniformly deplete the total rooted soil volume. Whereas roots in their proximity strongly deplete the soil including parts of nonexchangeable K they do not even use exchangeable K in a slightly greater distance. The quantity of K available per unit of root length is, therefore, determined by both - the degree of soil K depletion at the root surface and -the distance of the depletion zone, i.e. the volume of soil that contributes K to the root. Either factor was markedly affected by the level of soil K and thus by K application.     

Einfluß der Kalkung und Düngung auf den Ionenaustausch und die chemische Zusammensetzung der Bodenlösung am Beispiel von vier Waldstandorten im Hessischen Bergland

Impact of liming and fertilization on ionic exchange and chemical composition of soil solutions from four forest sites in the colline region of Hesse Between February 1985 and July 1987 soil seepage experiments were carried out on fertilizer trial plots in mature beech stands of four forest districts of Hesse. Encompassed by this study are in addition the most important results from soil-chemical analyses of the subsequent years 1988 to 1991. Aim of the investigations was to study the influence of liming and K/Mg-fertilization on the chemical composition of soil and soil solution under different site conditions. In the percolated soil solution liming did not led to a significant pH increase in subsequent years. In contrast, in some cases the pH level dropped by 0.1 to 0.2 units on average and Al-concentration increased correspondingly. In most cases, fertilization led to a significant increase in soil solution concentrations of the metal cations potassium, calcium and magnesium, especially at a depth of 50 cm. On those trial plots where a pH decrease was observed, the concentrations of K, Ca and Mg exhibited either a slight or no increase at all. Furthermore on some trial sites with freely drained soils, liming led to a faster mineralisation of the humus layer and thus to an increase of nitrate contents in the percolated soil solution from about 1–2 mg/l to 10–20 mg/l on average. Increased concentrations of sulfate and in most cases also of heavy metals (Mn, Zn, Cu. Cd) were observed in the soil solution which was attributed to the mobilizing effect of Ca-fertlization. In general, the mobility of most chemical parameters showed a slight increase following liming and soil tillage. Even after 5 to 8 years considerably higher pH-values and base saturation were evident in limed and fertilized soils, especially in the top 15 cm of soil profiles.     

Einfluß der Cl-Ernährung auf Ertrag und Nitratgehalt von Spinat und Kopfsalat

Effect of Cl-supply on yield and nitrate content of spinach and lettuce The N-supply for maximum yield could be reduced for spring spinach from 250 to 200 kg N/ha, for autumn spinach from 200 to 150 kg N/ha without yield depressions by optimized Cl-supply. The optimal Cl-supply consisting of Cl-content in 0–60 cm soil depth and Cl-fertilization was about 350 kg Cl/ha. However, Cl-supply in top soil should not exceed 300 kg Cl/ha in order to avoid emergence decreases. Different amounts of Cl-fertilizer were necessary because soils of experimental sites contained chloride in the range of 66 to 435 kg Cl/ha. The nitrate content was reduced up to 50% by Cl-fertilization. This was caused by reducing the N-supply by 50 kg N/ha and to an increased nitrate reduction. The heighest head weight of lettuce could be achieved with N-supply of 90 kg N/ha and additional Cl-fertilization. Reducing the N-supply from 120 to 90 kg N/ha and improvement of Cl-nutrition decreased nitrate content considerably. Cl-supply should not exceed 150 kg Cl/ha in 0–30 cm, because lettuce reacts sensitive to saline conditions.     

Erfassung der Variabilität von Bodenmerkmalen in einem Blindversuch auf Fahlerde mittels Methoden der räumlichen Statistik

Variability of soil parameters in a uniformity trial on a Luvisol evaluated by means of spatial statistics The relationships between soil parameters and indicators of soil genesis were investigated in a uniformity trial on Luvisol by means of classical and spatial statistics. The following properties were investigated in the topsoil (0–30 cm) and subsoil (31–40 cm): content of total carbon (C_t), content of clay plus fine silt (FAT), concentrations of available potassium (K) and phosphorus (P), and pH values. The depth loamy Bt horizon and microrelief were considered as indicators of soil genesis. Smoothing of the raw data by means of block kriging eliminated the small scale variability of all parameters. In this way, the rank correlation coefficients between soil parameters increased by factor 2 and were to 0.52 for C_t–FAT; 0.69 for C_t–K, and 0.55 for C_t–P in the top soil. The maps for smoothed data allowed a much better visual analysis of spatial distribution of investigated properties compared to the raw data. The significant correlations as well as the similarity of maps and variograms suggested that the spatial variability of FAT, C_t, K, and P in the top soil was determined by the same factors. The depth of the loamy Bt horizon and the relief were the most important factors defining the distribution of the investigated soil parameters. The rank correlation coefficients of the smoothed and detrended relief with the soil parameters amount to –0.63, –0.77, –0.71, and –0.57 for FAT, C_t, K, and P, respectively.     

Korrelationen von Enzymaktivitäten im Boden

Correlations of Enzyme-Activities in Soil Enzyme-activities often have been used as indicators of the biological state of soil. In this connection some questions may be posed: Which enzyme is the best indicator of biological activities in soil, what is the relationship of enzyme-activities to other ecological parameters and what is the interdependency between different enzymes? To answer these questions we measured activities of amylase, catalase, invertase, pectinase, urease, xylanase and cellulase at nine alpine and subalpine sites. Furthermore the CO₂-evolution, contens of nitrogen, carbon, organic matter, the soil density, total bacterial number and water capacity were determined. With these data correlation coefficients were calculated. The best relationships were found between cellulase-xylanase and amylase-invertase activities (Table 1). While catalase and pectinase are in the middle range, urease shows relatively low values. There are highly significant correlations between enzyme-activities and the content of nitrogen, carbon, organic matter, soil density or the CO₂-evolution (number of samples used for calculations was 68). Almost no correlations were found with total bacterial count (Table 2). For these calculations 34 samples of each parameter were used. To prove that the lower number of samples is not the reason for low correlation coefficients we computed data of 17 samples (Table 3). The water capacity is depending on soil density and content of organic matter and the correlations are in the same range (Comparison Table 1 and 3). This means that 17 samples of each parameter are enough for these calculations. Enzyme-activities proof therefore to be good indicators of the biological state of soil. It is inappropriate to characterise biological activities of soil by total bacterial counts only.     

Bereitstellung von van-Genuchten-Parametern zur Charakterisierung der hydraulischen Bodeneigenschaften

Providing the Parameters of Unsaturated Soil Hydraulic Functions on the Basis of Soil Texture, Bulk Density and Type of Horizon The hydraulic conductivity function can be described by the van Genuchten equation, whereby its parameters are estimated from typical water retention data of soil types and textural classes. The value of saturated hydraulic conductivity can be derived from tables (e.g. Kartieranleitung, 1982) in case measured data are lacking. Especially in well structured or sandy soils saturated conductivity may differ by 1…2 orders of magnitude. This will lead to a shift of the conductivity function. But nevertheless for the first approximation of fluxes in soils such parameters can be used. Thus, soil dependent values of groundwater recharge and pollution can be roughly quantified.     

Einfluss von Bodeneigenschaften auf die Segetalflora von Ackerflächen

Impact of soil properties on weed distribution within agricultural fields Occurrence and distribution of weeds on agricultural fields are often heterogenous. The influence of various soil properties on the spatial structure and density of weed populations was investigated on two agricultural fields with special regard to three weed species (Polygonum amphibium, Cirsium arvense, Veronica hederifolia). Based on field specific sampling grids, weed counting and soil sampling were done. For all grid points, soil analysis was carried out (texture, organic C, total N, pH, soil nutrients P, K, Mg). Soil texture, soil organic C, and soil nutrients are the factors with the highest influence on the occurrence of the species studied.     

Einsatz der Taupunktmethode zur Charakterisierung von Matrix- und osmotischem Potential in einer Gefäßkultur mit unterschiedlichen Salzgehalten

Use of the dew point method to determine matrix- and osmotic soil water potentials in pot cultures under different salt stress Water consumption of festuca rubra was investigated under different salt stress as measured by the dew point method. Water content of the soil, total tension and water consumption was measured daily. At the end of the growing season the low salt stress plants had used nearly completely all water available and were under water stress. Plants under medium salt stress reduced transpiration in time and showed highest water content in the soil and in the plants after growing season. For the high salt stress plants the total water potential remained low due to the osmotic component. Dew point measurements were compared with other methods (Cl-concentration; electric conductivity). A close correlation was found in all cases, demonstrating the usefulness of the dew point method.     

Einfluß von Ethrel auf Form und Zuckergehalt der Zuckerrübe

Influence of Ethrel upon morphology and sugar content of sugar beet Repeated spraying of growing sugar beet plants with 100 and 200 ppm solutions of Ethrel changed the shape of the storage roots and reduced their sugar content. When CCC was added to the Ethrel solutions, the negative influence of Ethrel upon the sugar content was nearly abolished.