Umsatz von 15N-Harnstoff und 15N-Ammonsulfatsalpeter mit Zusatz von Dicyandiamid unter aeroben Bedingungen im Boden

Turnover of ¹⁵N-urea and ¹⁵N-ammonium sulfa-nitrate with addition of dicyandiamide under aerobic conditions in the soil In aerobic incubation trials, the turnover of ¹⁵N-labelled urea (UR) and ammonium sulfa-nitrate (ASN) was investigated in the soil (silty loam, pH 6.5) under addition of the nitrification inhibitor dicyandiamide (DCD).

• 1 Nitrification of urea at 7°C was markedly inhibited by addition of 10 ppm DCD-N (in relation to soil); at 14°C, a concentration of 20 ppm DCD-N was required for a sufficient inhibition; nitrification of ASN was more inhibited by DCD than nitrification of UR.
• 2 By use of dicyandiamide, up to 14% (as compared with 10% without DCD) of the supplied N was transformed into a non-extractable N-Form from which only a slight release of nitrogen could be observed after 147 days. Also, the proportion of fixed ammoniuum was higher in the treatments with DCD as compared without DCD.
• 3 In all experiments, the recovery was 100% ± max. 2.6%, that means that no essential (gaseous) losses of N occurred under the aerobic conditions of these trials.

     

Stickstoffbilanz von 15N-Harnstoff bzw. 15N-Ammonsulfatsalpeter mit Dicyandiamid in Gefäßversuchen zu Grünhafer und Sommerweizen

Recovery of Nitrogen of ¹⁵N-urea and ¹⁵N-ammonium sulfa-nitrate with addition of dicyandiamide in pot trials with green oats and spring wheat In pot trials with green oats and spring wheat, the effect of ¹⁵N-urea (UR) and ¹⁵N-ammonium sulfa-nitrate (ASN) with addition of the unlabelled nitrification inhibitor dicyandiamide (DCD) was investigated on the basis of equal amounts of N by fully taking into account the DCD-N, with respect to yield, N-removal, distribution of ¹⁵N in plants and soil (sandy loam, pH 6.5) as well as the fate of DCD.

• 1 In Neubauer experiments with green oats, 62–69% of fertilizer-N were found in the shoots, 21–31% in the roots and 4–9% in the soil. In Mitscherlich trials with spring wheat, 85–88% of fertilizer-N were found in grain and straw, 7–10% in the roots and 3–4% in the soil. ¹⁵N-recovery, in all cases was between 98-100%, thus exhibiting pratically no loss in course of the experiment.
• 2 Yields of green oats (shoots), resp. spring wheat (grain and straw) were about 4-11 % lower in pots with DCD; on the contrary, N-contents and removal were somewhat higher compared to control without DCD.
• 3 With conditions given by these pot trials (strong root penetration, favourable temperature, repeated supply during early growth, slow soil-specific decomposition), water-soluble DCD was taken up partly by the plants and appeared mainly in leaves resp. straw. In grains of spring wheat, DCD-contents were, however, very low (maximum 3 ppm DCD-N); in roots it could not be detected. In comparison, analysis of crop-material in field trials showed no DCD in grains and only very few ppm DCD in straw.
• 4 In pots with DCD, the residual-N in the soil was higher, probably because of the prolonged time of reaction between ammonium and the organic matter of the soil.

     

Umsatz von 15N markiertem Nitratstickstoff im Boden in Abhängigkeit von Strohdüngung und Bodenfeuchte

Turnover of ¹⁵N labelled nitrate nitrogen in soil as related to straw application and soil moisture In incubation experiments the effect of straw application on the turnover of ¹⁵N labelled nitrate has been studied at two soil moisture levels (brown podzolic soil). High ¹⁵N losses were found at the high soil moisture level. These losses are supposed to originate from denitrification. At both soil moisture levels straw application reduced significantly the ¹⁵N losses. Straw application resulted in a remarkable decrease of the ¹⁵NO₃ content in the soil and promoted the incorporation of ¹⁵N into the organic soil fraction. The incorporation of ¹⁵N into α-amino N and particularly into the rest hydrolyzable-N fraction was favoured by straw, while the incorporation into the amide-N fraction was hampered. Exhaustive cropping (Lolium multiflorum and Sinapis alba) on the soil incubated before with ¹⁵N, showed that the ¹⁵N incorporated into the organic fraction was poorly available. Thus straw application resulted in significant yield depression. It is assumed that the fraction of the rest hydrolyzable N is hardly available to plants.     

Umsatz im Boden und Ertragswirkung rohphosphathaltiger Düngemittel

Turnover in soil and yield response of phosphate rock containing fertilizers Solubility of phosphate rocks is the better the higher the carbonate substitution in the given phosphate rock type. From the soil factors, pH is of importance. At soil pH < 5 phosphate rocks are fairly soluble and their yield effect equals that of fully processed fertilizers. In a soil pH range from 5 to 7, pH does not play such a decisive role as has been assumed. Other soil factors such as H⁺ buffer power of soil, Ca²⁺ and particularly the phosphate concentration in the soil solution are equally relevant for phosphate rock dissolution. The evaluation of numerous field experiments provided evidence that in the above cited pH range fully processed fertilizer phosphates are superior to phosphate rock containing fertilizers with regard to phosphate uptake, yield formation, and phosphate recovery. Also the residual effect of rock phosphate is poorer than that of fully processed phosphate fertilizers. There is some evidence that phosphate rocks show a relatively good response on deep rooting soils which allow a vigorous root growth and on soils with a sufficiently high level of soil moisture. In a soil pH range > 5 rock phosphate containing fertilizer are not suitable for maintenance fertilization, since under such conditions the phosphate concentration in the soil solution is relatively high thus suppressing the dissolution of phosphate rock.     

N-Wirkung von Rindergülle unter Zusatz von Dicyandiamid bzw. Stroh in Gefäß- und Lysimeterversuchen

Utilization of N in cattle slurry after addition of Dicyandiamide resp. straw in pot and lysimeter trials In a pot and lysimeter trial, leaching of nitrate of cattle slurry applied at different times (August, September, October, March) was tested with and without addition of DCD, and utilization of N by the following crop was determined. In a pot trial (sandy silt loam), the effect of additional straw manuring was also investigated. Pots were exposed to natural weather conditions from start of experiment (August) until sowing of rye grass (April). Application of straw as well as addition of DCD to slurry reduced leaching of N considerably. DCD addition with and without straw resulted in significantly higher N removals by rye grass. Unlike ammonium nitrogen “preserved” by DCD, slurry nitrogen biologically fixed by the rotting straw, however, was not yet available to the following rye grass crop (May to July). Slurry + straw + DCD generally led to higher amounts of residue N in the soil as a result of N balance. Also in the lysimeter trial, DCD reduced leaching of nitrate especially in vegetationless periods and thus improved the effect of cattle slurry applied in August resp. November (higher yields and N removals by silage maize).     

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.     

Biotisch und abiotisch gesteuerter Abbau von organischer Substanz im Boden

Biotic and abiotic decomposition of organic matter in soils The problem area of organic matter decomposition in soils by biotic, abiotic and photochemical mechanisms is tested under administration of uniformly ¹⁴C-labelled wheat straw, humic of fulvic acids; furthermore by the use of conventional methods. In four separate test runs, based on Hapludalf-Ah soil, formed in loess, as well as on Ah soil of a spodic Dystrochrept in pleistocene sand, measurements over years - altogether 57 measurement cycles - revealed similar decomposition rates of ¹⁴C fulvic and 14C humic acid. The approximate magnitudes of turnover were: biotic: abiotic (Hg-sterilization): biotic + UV-irradiation: abiotic + UV-irradiation = 100:20:70:50. The sterilized samples continued to release CO₂. Biotic + UV showed losses, compared with biotic, by partial UV sterilization. Abiotic + UV indicated increasing CO₂ release, compared with abiotic only, due to additional photochemical decomposition. In a larger program with radioactive as well as conventional methods of CO₂ measurement decomposition rates in different soils were tested under biotic, abiotic and photochemical condition in presence of metal ions, such as iron, aluminium, copper, zinc, lead and mercury. The impact by the added metals can be summerized as follows: Calcium and aluminium are favoring the organic matter decomposition under biotic conditions, while mercury, lead, copper, zinc and iron are rather inhibitive. Contrary, under biotic/steril conditions copper and especially mercury, further zinc and lead, at lower extent also calcium, impede CO₂ liberation. Since there are but small differences among the various test soils, soil own parameters seem to exert under abiotic conditions low importance only. Under UV irradiation calcium had in the biotic milieu high, in the steril/abiotic milieu a lower increasing effect upon COz liberation. Also iron indicates a stimulating effect under contemporary UV irradiation, which at lower level applies to lead and mercury too, particularly in connection with the sandloess Hapludalf of Harburg. Based on the observed CO₂ release also under abiotic/steril conditions final tests were conducted with calcinated quartzsand in contrast to soil, otherwise again under biotic, abiotic, as well as biotic or abiotic + UV conditions. Also in these calcinated sands ¹⁴CO₂ release from the ¹⁴C labelled straw continued. Addition of increasing amounts of aluminiumlactate causes decreasing ¹⁴CO₂ rates. An even stronger inhibition was produced by addition of zinclactate.     

Umsetzung 14C-markierter Pflanzeninhaltsstoffe im Boden in Gegenwart von 15N-Ammonium

Turnover of ¹⁴C-labelled plant components and ¹⁵N-ammonium in soil The turnover of ¹⁴C-labelled glucose, cellulose, wheat straw, phenols or of lignin in soil was investigated in the presence of (¹⁵NH₄)₂SO₄. The plant components were more or less rapidly degraded to ¹⁴CO₂ and the amended nitrogen source became organically linked but was also remineralized to a variable extend. Also variable was the incorporation of the ¹⁴C or ¹⁵N into humified residues or microbial metabolites. During the turnover of carbohydrates and straw a rapid increase of ¹⁴C and ¹⁵N in amino-acids or unidentified components of soil hydrolysates occurred which was followed by a decrease. The turnover of phenols was mostly similar to that of carbohydrates but compared to their mineralization rates, a smaller incorporation occurred into the easily hydrolyzable soil fractions. Although lignin was considerably mineralized to CO₂, the incorporation of the carbon remaining in soil into hydrolyzable components especially in amino-acids was, however, very small. A somewhat higher amount became incorporated into unidentified components of hydrolysates, but the bulk of the lignin carbon remained in the non-hydrolizable residue.     

Persistenz von Atrazin und seiner Metaboliten im Boden nach einmaliger Herbizidanwendung

Persistance of atrazine and its metabolites in soil after a single herbicide application The breakdown of atrazine in soil was investigated under field conditions. In spring 1973 the soil was treated with ¹⁴C ringlabeled atrazine. In summer 1981 soil samples were collected and analysed. The investigated soil still contained about 83% from the initial ¹⁴C activity. From this only 40% could be extracted. Besides traces of atrazine were further identified six metabolites which originated from the parent compound through N-dealkylation and hydrolysis.     

Modellversuche zur Phosphatsorption von Unterwasserböden unter oxidierenden und reduzierenden Bedingungen

Model experiments on phosphate Sorption by river sediments under oxidizing and reducing conditions. During intensive reduction by sodium dithionite, phosphate sorbing river sediments often show a pronounced desorption of phosphate. Reoxidation by air causes an increase in phosphate sorption up to five times the original value, the height being linearly related to the ferric oxide content (Fe_d) of the sample. A possible explanation for this phenomenon is the oxidative precipitation of iron(III) oxides with high surface area being very active in phosphate adsorption.     

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.     

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.     

Einfluß variierter Temperatur und Feuchte auf mikrobielle Aktivitäten im Boden unter Laborbedingungen

Influence of varied soil temperature and moisture on microbial activities under laboratory conditions Under laboratory conditions the influence of temperature (10°C, 20°C, fluctuation from 5° to 30°C within 12 h with additional freezing for 3 days) and soil moisture (30%, 60% w.h.c., remoistening to 60% for 1 week) on several microbial activities was investigated. The biomass-related, glucose-induced short-term respiration and the dehydrogenase activity (TTC reduction) were higher at 10°C in most cases as compared to 20°C. Independent of freezing fluctuating temperature caused the lowest activities. The nitrogen mineralization (including nitrification), however, was affected in the opposite way. No marked influences were observed with β-glucosidase, arylsulfatase, and alkaline phosphatase. In the sandy loam nearly no effects of the soil moisture occurred and in the loamy sand especially the dehydrogenase activity was higher at 30% w.h.c., whereas the nitrogen mineralization was lower. From the results it can be concluded, that ecological conditions favouring mineralization without substrate addition may even reduce microbial biomass by decomposition.     

Modellanlage zur Bestimmung von Ammoniakverlusten aus organischen und mineralischen Düngern unter kontrollierten Bedingungen

A model system for the determination of ammonia losses from organic and mineral fertilizers under controlled conditions A closed-dynamic model was developed for the continuous registration of losses of ammonia. NH₃ escaping from the soil surface is introduced to an acid trap. The resulting increase in pH is equivalent to the amount of NH₃ and is recorded by an automatic data recorder. Wind velocity in this system can be adjusted between 100 and 400 L air/h, which corresponds to a 12 to 40-fold total air exchange per minute. Temperature can be regulated between +5°C and +30°C. In addition, air humidity can be controlled. The testing of the model revealed deviations of maximally 0.6% between measured pH value and destillation. The average recovery amounted to 97.2%.     

Kohlehydratfraktionen im reifenden Weizenkorn unter dem Einfluß von Stickstoff und Chlorcholinchlorid

Components of carbohydrates in wheat kernels during the ripening process influenced by nitrogen fertilization and chlorcholinchloride The variability of carbohydrates was analysed in ripening kernels of wheat treated with nitrogen and chlorcholinchloride. 1. Proceeding ripening in wheat kernels (green, yellow, matured kernels) shows an important decrease of monosaccharides and total sugar. A distinct Influence of CCC — just as a possible postponement of ripening — marked with usually higher contents of monosaccharides and total sugar could be ascertained in green kernels only. 2. The synthesis of starch is not influenced by high nitrogen fertilization and essentially finished till the grain is yellow. By CCC-treatment, compared with untreated plants, a much lower content of starch is caused in green and yellow grains, in matured such differences are detectable scarcely. The decrease of starch content with high nitrogen fertilization is more important than that caused by CCC.