Einfluss der Kaliumdynamik im wurzelnahen Boden auf die Magnesiumaufnahme von Pflanzen

Influence of potassium dynamics at the soil-root interface on magnesium uptake of plants At the soil-root interface potassium concentration of the soil solution can be depleted by potassium uptake of the plant. The influence of this effect on the magnesium uptake of ryegrass, barley, maize and rape was studied in pot experiments with luvisols from loess. The results have shown that the rate of magnesium uptake was doubled when the potassium concentration at the root surface decreased below 20 μmol K/1. Magnesium uptake is therefore inhibited by K concentrations above this limit. Application of potassium fertilizer increases the potassium concentration of the soil solution. However, via exchange of adsorbed Mg ions from the soil matrix, K application also increases magnesium concentration of the soil solution. As a result of K application magnesium uptake increases in this case if K concentration of the soil solution at the root surface is kept below 20 μmol K/1 by K buffering or K uptake. Magnesium uptake decreases however, if K concentration exceeds 20 μmol/1 soil solution because the inhibitory effect of potassium on Mg uptake is stronger than the favourable influence of Mg concentration.     

Erfassung der Mineralstoffverteilung in Wurzelnähe durch getrennte Analyse von Rhizo- und Restboden

Estimation of the nutrient distribution around plant roots by separate analysis of rhizo and bulk soil A procedure is described to separate rhizo soil from bulk soil. For this purpose the living plant roots along with the strongly adhering soil are taken out of the surrounding soil. After a short period of drying, roots are separated from rhizo soil by gently sifting. Chemical analysis of the samples has shown that the nutrient content of rhizo soil usually differs markedly from bulk soil. Phosphate and potassium content of the rhizo soil of wheat and maize is lower than in bulk soil. Percentagewise, these differences are higher by using water as an extractant when compared to the slightly acid lactate or formate solutions. The water soluble calcium content of several wheat fields was in most cases higher in the rhizo than in the bulk soil. In sandy soil the depletion zone of phosphate does not exceed the length of the root hairs markedly whereas in the case of potassium it does. This is concluded from data showing that the potassium content, but not the phosphate content, was decreased in the bulk soil if compared to the uncropped soil. In heavier loess soils the nutrient concentrations of rhizo and bulk soil were not always found to be markedly different. It is assumed that the depletion zones are smaller than in sandy soils. In addition, because of aggregation, rhizo soil cannot be separated from bulk soil as neatly as in sandy soils. Therefore, in heavier soils the method does not yield satisfactory results.     

Kaliumdynamik im wurzelnahen Boden in Beziehung zur Kaliumaufnahme von Maispflanzen

Potassium dynamics at the soil-root interface in relation to the uptake of potassium by maize plants Young maize plants were grown in flat containers on a sandy and a silt loam soil after addition of ⁴³K as tracer. Changes of the K concentration in soil in the vicinity of the roots were determined by scanning the film density of autoradiographs. A distinct zone of K depletion in the soil adjacent to the root surface was observed, similar to those found earlier with phosphate and rubidium. The highest degree of depletion occured within a distance of 0.7 mm from the surface of the root cylinder which corresponds to the average length of root hairs of the cultivar used. The quantity of K released within 2.5 days per unit of this part of the soil exceeded the exchangeable K by a factor of two. In a radial direction the zone of maximum depletion was followed by a depletion profile which extended over 5 mm in the sandy and over 3 mm in the silt loam soil. The K concentration of the soil solution decreased to 2–3 μmoles K/l at the root surface. In order to determine the effect of depleting the K concentration by plant roots on the release of soil K, desorption studies were carried out in parallel. For this purpose the soil was successively extracted by solutions with cation concentrations corresponding to the soil solution, except for K. With this procedure a massive release of K from the soil was observed after the equilibrium concentration decreased to 2–3 μmoles K/l. It is concluded that

• – in one growing season only part of the soil volume of the rooted layer contributes potassium to the plant and, on the other hand
• – substantial part of the potassium absorbed by plants is derived from nonexchangeable soil K, even in short periods of time.

     

Rubidium-Verarmung des wurzelnahen Bodens durch Maispflanzen

Rubidium depletion of the soil-root interface by maize plants Maize plants were grown in flat containers with radioactive labelled rubidium. Changes of the Rb concentration in soil in the vicinity of the roots were determined by means of the film density of autoradiographs. Results were as follows: The Rb concentration of the soil at the root surface decreased markedly within one day; only small changes occured after this period. Initially, the width of the depletion zone was very small. It extended in the following days in a radial direction. Therefore, after the initial phase the Rb supply of the plants depended on transport from more remote parts of the soil. Soil texture and Rb level strongly influenced both degree and distance of Rb depletion. Thus, the Rb concentration at the root surface decreased by 80% of the initial value in a sandy soil (4% clay) and by only 30% in a silt loam soil (loess, 21% clay). The depletion zone extended to a distance of 2 mm in the silt loam soil from the surface of the root cylinder and to 5 mm in the sandy soil. Hence, in the silt loam about 20% and in the sandy soil almost 100% of the total soil volume contributed Rb to the plant, assuming a root density of 1 cm per cm³ of soil. Increased levels of Rb enhanced Rb availability by increasing both the degree of soil depletion near the root surface and the size of the depletion zone. The quantity of Rb available per cm of root varied between 0.05 μmol in the silt loam with low Rb application and 2.7 μmol in the sandy soil with high Rb application. The amount of Rb depleted from the soil, expressed as per cent of the Rb exchangeable by ammoniumacetate ranged from 3 to 7% in the silt loam and from 20 to 30% in the sandy soil, calculated on the basis of 1 cm root per cm³ of soil. The Rb concentration of the soil solution near the root surface was reduced to 2 μmolar.     

Methoden zur relativen Quantifizierung der pilzlichen Biomasse im Boden

Methods for relative quantifying fungi biomass in soils To estimate the mycological contribution in soil microflora, the amount of chitin and ergosterol and the decolorisation of Poly-B-411 dye was measured in three different soils. The tests showed a linear proportionality between the amount of soil and the respective quantities of the substances. Due to the methodic procedure, ergosterol was measured more accurately than chitin. The decolorisation of the Poly-B-411 dye was in wet humidic aerobic soil higher than in soil suspension. The stability of the adsorbance ratio (593/483 nm), which is a measure for the degradation, was obtained between the 5th and 7th day.     

Bestimmung des Wasserentzuges aus dem Boden durch die Pflanzenwurzeln im Gelände als Funktion der Tiefe und der Zeit

Field determination of water withdrawal from soil by plant roots as a function of depth and time . The water flow through roots as a function of depth and time can be determined in homogeneously rooted, level soils with closed plant canopies, provided the total vertical water flow and the capillary water flow are known for the soil profile. Theory, measuring methods and some results on water withdrawal of wheat (fig. 2–4) and sugar-beet (fig. 5) roots on a loess grey-brown podsolic soil profile underlain by gravelly sand (fig. 1) are described. The time averaged rates (2–7 day periods) for water extraction by roots are up till about 12 × 10^?3 \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{{{\rm cm}^3 {\rm water}}}{{{\rm cm}^3 {\rm soil} \cdot {\rm day}}} $\end{document} During the growth period variations of the depth of the effective root zone and of the extraction rate in distinct layers were found (fig. 6 + 7). A capillary rise from the subsoil into the effective root zone exists for some time (fig. 3); seepage water within the lower root zone causes a strong increase of extraction rates in these depths (fig. 4). The relative water extraction rate at the depths of 15 and 25 cm decreases with increasing soil water suction in the range between 150 and 10⁴ cm (fig. 8).     

Das Verhalten von Bleitetraalkylen im Boden und deren Aufnahme durch die Pflanze

The behaviour of leadtetraalkyls in the soil and their uptake by plants In pot experiments the behaviour of the leadtetraalkyls leadtetramethyl and leadtetraethyl in soil and their uptake by spring wheat was investigated. In the soil the leadtetraalkyls were converted quickly to water soluble lead compounds, which showed a high plant toxicity and plant availability. Consequently there was a relatively large lead enrichment in the vegetative and generative plant parts. At higher concentration also a yield depression occured. Comparable amounts of lead in the form of an inorganic salt did not result in Pb-accumulation in plants. From the continuous uptake of lead, which was observed over a period of 3 months, it is concluded, that leadtetraalkyls were decomposed to Pb²⁺ slowly and the Pb-fixation was correspondingly slow. The soluble lead compounds resulting from the leadtetraalkyls could be leached out easily from soil by water. There was a close relation between the level of leadtetraalkyl applied and the waterextractable lead. Moreover it is demonstrated, that plants, which have taken up only inorganic lead salts, are capable to synthesize lead compounds soluble in unpolar organic solvents even in cases in which the soils did not contain leadtetraalkyls.     

Dicyandiamidabbau im Boden in Abhängigkeit von der Temperatur

Effect of temperature on the breakdown of dicyandiamide in the soil The breakdown of dicyandiamide in a soil (sandy silty loam, pH 6.2, 0.13 % N) was investigated in relation to temperature. 1. The rate of conversion of dicyandiamide (DCD) (20 mg DCD-N/100 g soil) to guanylurea increased with rising temperature (10°–90°C). After 20 days, 14–100 % of the added DCD was metabolized. Small amounts of DCD (0.67 resp. 1.34 mg DCD-N/100 g soil) were broken down completely within 20–80 days at 8°–20°C. 2. Guanylurea was transformed to guanidine and then to ammonium. Increasing temperature in the region of 10° and 30°C accelerated the transformation. At higher temperatures (up to 70°C) an accumulation of guanidine occurred.     

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.     

Nitratammonifizierung im Boden mit Abwasserverrieselung

Nitrate Reduction to Ammonium in a Soil with Wastewater Irrigation Flooding with wastewaters including 48 mg/l NH-N, 15 mg/l organic N and 63 mg/l K¹⁵NO-N has led to strong nitrogen losses by denitrification from a sandy Cambisol. Beside this ¹⁵NH was formed also. Possible reasons of the nitrate reduction to ammonium are discussed and conclusions for practical wastewater irrigation are drawn.     

Aufbau und Betrieb einer Lysimeterstation zur Erfassung der Verlagerung von Pflanzenschutzmitteln im Bodenprofil

Engineering and operation of a lysimeter station for the estimation of pesticide leaching through soil profiles An above ground, air-conditioned, lysimeter station was constructed for measuring pesticide leaching into soil profiles (Fluvisol; Cambisol). Specially transport in soil macropores was investigated by using sprinkler irrigation simulating high precipitation. Twelve soil monoliths (30 diameter, 100 cm depth) can be investigated simultaneously. Engineering and operation of this station are described. The lysimeters consist cf stainless steel cylinders with a special leaching water collector and low pressure equipment. In the soil monolith tensiometers with electronic pressure transducer and temperature sensors are installed. Measured data are recorded with a PC continously.     

Enzymatisch-colorimetrische Bestimmung von Purin-Stickstoff im Boden

Enzymatic and colorimetric determination of purine nitrogen in soils This paper describes a method for determination of purine nitrogen of nucleic acid components in soils. The method is based on the enzymatic degradation of purine containing nucleotides, nucleosides and nucleobases to uric acid which is determined colorimetrically. The nitrogen content of a rendzina, for example, related to the monomeric nucleic acid compounds is very low and was found to be less than 1 percent compared to the total nitrogen content.     

Beziehung zwischen dem Stickstoff-Entzug der Pflanzen und der Abnahme von spezifisch gebundenem NH4-N im Boden

Relationship between the N uptake of plants and the mobilization of nonexchangeable NH₄-N In a pot experiment with ryegrass (Lolium multiflorum) the relationship between the release of nonexchangeable NH₄⁺ and the N uptake of plants was studied. For this purpose the surface soil of an alluvial soil and of a grey brown podsolic soil was labelled with ¹⁵NH₄-N. The following results were obtained: After treating the soil with 15-N the alluvial soil contained 4,55 mg and the grey brown podsolic soil 1,64 mg nonexchangeable ¹⁵NH₄-N/100 g soil. In the alluvial soil 72% and in the grey brown podsolic soil 66% of the nonexchangeable ¹⁵NH₄⁺ had been released during the growing season when ryegrass was planted. However, without plants there was no change in the content of labelled nonexchangeable NH₄⁺ in the alluvial soil or only a slight decrease in the grey brown podsolic soil. A highly significant correlation was found between the ¹⁵NH₄-N released and the ¹⁵N uptake of ryegrass in the alluvial soil (r = 0,78⁺⁺⁺) as well as in the grey brown podsolic soil (r = 0,98⁺⁺⁺).