Verteilung von Stickstoff auf Sproß und Wurzel bei jungen Bohnenpflanzen nach der Aufnahme von NO und NH

Translocation of nitrogen to the shoot of young bean plants after uptake of NO and NH by the root Phaseolus vulgaris plants (var. nana, cv. Saxa) at the primary leaf stage (without nodules) were fed during 6 hours with ¹⁵NO and ¹⁵NH, respectively. 24 hours after the absorption period more ₁₅N from the absorbed NO was translocated from the root to the shoot. The presence of NH in the nutrient solution enhanced the translocation of ¹⁵NON, probably by an inhibition of nitrate reductase. NH_4-⁺¹⁵N is mainly retained in the root by a high incorporation into the root protein. It can be concluded that nitrogen from newly absorbed NO is not retained and used for protein synthesis in the root according to the root's potential to synthesize protein. Nitrate reduction in the root is considered to be the limiting factor. This is supported by the fact that withdrawal of NO in the nutrient solution prior to the ¹⁵N-experiment increased NOtranslocation to the shoot as a consequence of a lowered level of nitrate reductase. In an experiment with ¹⁴NOsupply to the roots and ¹⁵NOapplication to the primary leaves (infiltration method) a considerable amount of ¹⁵N was translocated from the leaves to the roots. This indicates that an insufficient NOreduction in the root can be substituted by a retranslocation of reduced N-compounds from leaves to the roots. The proportion of NO reduced in the root influences also the pattern of primary distribution of nitrogen in the shoot of plants at the 4 leaf stage. At a concentration of 0,2 meq/l NO in the nutrient solution as compared to 20 meq/l NO during 10 hours a relative higher amount of ₁₅N was transported from the root to the younger, growing leaves i.e. via the phloem to metabolic sinks.     

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.     

Ferrous and ferric iron ratio in normal and chlorotic bean plants (Vicia faba L.)

The objective of this study was to determine the ratio and amount of Fe II and Fe III iron in different parts of 20 and 40 day old bean plants grown in pots under normal and HCO-treatment. The Fe II and Fe III iron determination was carried out by a modification of a method described by Vogel (1969). The Fe II and Fe III concentrations in the plant varied according to its age, the plant part, the order of leaves and HCO-treatment. At the second sampling date, the lower total iron content in the lower leaf particularly under the HCO-treatment suggests that the supply of iron from the roots was restricted. The iron content of the different leaves was almost evenly divided into Fe II and Fe III at the first date. At the second date, most of the iron in the bud leaf was present as Fe II. Under HCO-treatment the Fe II content of the bud leaf and the flower was similar as in the corresponding parts of the normal green plants whereas the Fe III content was considerably lowered in these plant parts as result of the HCO-treatment. The results indicate a substantial retranslocation of iron from older to younger leaves and a higher Fe II/Fe III ratio in flowers and bud leaves particularly under HCO-induced chlorosis.     

Einfluß von Stroh und Nitrapyrin auf den verfügbaren Stickstoff im Boden,den Ertrag und den Stickstoffentzug von Lolium multiflorum

Effect of straw and nitrapyrin application on the nitrogen availability in the soil and the yield and nitrogen uptake of Lolium multiflorum. In pot experiments the effect of straw and nitrapyrin application on the turn-over of fertilizer NH and on the nitrogen availability in the soil was investigated. The investigation comprised two sections: an incubation experiment in which straw and nitrapyrin together with NH-N were incorporated into a brown podsolic soil and a subsequent pot experiment with ryegrass. Nitrapyrin inhibited the nitrification and reduced the nitrogen loss of the soil. Compared with the treatments without nitrapyrin application, nitrapyrin resulted in a lower dry matter yield and in a lower nitrogen uptake of the ryegrass. Straw application reduced the nitrate content in the soil significantly. This effect was particulary evident in the treatments which did not receive nitrapyrin. Accordingly, nitrogen uptake and yield of ryegrass were significantly lower in the ‘straw treatments’ as compared with the treatments without straw. It is suggested that the impared nitrogen availability in the ‘straw treatments’ was mainly due to nitrogen losses caused by denitrification.     

Interaction between microbial biomass and activity and the soil chemical conditions and the processes of acid load in coniferous forest soils

The primary aims of the present investigation were to determine the proportion of microbial driven soil processes associated with acidification in coniferous forest soils, and the response of microbial communities with respect to soil acidification and to acidification processes. Lysimeters containing undisturbed soil columns from five forest sites in Europe were installed in a spruce forest in the Soiling (northern Germany) and exposed to the same input and climatic conditions. In the present study root uptake was excluded. Under these conditions, during the 21 months of the experiment, acid load by microbial N-transformations especially mineralization and subsequent nitrification were the most important processes ranging from 50.2% to 79.1%. Except for one soil the balances showed, that increasing levels of soil acidity decreased the potential of mineralization. This agreed with the observation that microbial biomass Cmic decreased. The biomass Cmic (kg ha^?1 a^?1) was significantly correlated to N-output. The caloric quotient qW increased parallel to decreasing pH. During the experiment the PH in all mineral soil horizons decreased significantly. This change in soil chemical conditions did not affect the microbial biomass Cmic but the caloric quotient increased during the experiment, especially in the upper mineral soil.     

Response of acid sulphate soils to different liming treatments I. Solubility of sulphate and phosphate

In a preliminary laboratory experiment, samples from three cultivated and three virgin acid sulphate soils (pH 3.9-4.7) were treated with water or equivalent amounts of Ca(OH)₂ or KOH and incubated at about field capacity for three months. Both base treatments (133 meq/kg) similary reduced soil acidity and, thus, the same influence on the pH-dependent biological and chemical reactions was concluded. The liming-induced mineralization of organic S seemed to account for increased extratability of sulphate, being in most soils of the same magnitude in both treatments. Inversely, the solubility of P hardly was affected by the decomposition of organic matter but rather by the reactions of inorganic P. KOH markedly raised water-soluble P, whereas Ca(OH)₂ did not. The results of a rapid extraction test suggested that the poorer extractability of P in the soils amended with Ca(OH)₂ could partly be ascribed to a higher Ca saturation and its impact on the electrochemical properties of charged surfaces. In addition, a higher base-associated ionic strength created by Ca²⁺ was of great importance in reducing the P desorption in the Ca(OH)₂- treated soils.     

Soil Acidification and Solute Budgets for Forested Lysimeters in Nordrhein-Westfalen

Solute budgets and nitrogen use were quantified in two 400 m² forested lysimeters in St. Arnold, Nordrhein-Westfalen. The lysimeters are covered by a mixture of oak-beech and Weymouth pine, respectively. The average bulk deposition between May 1985 and May 1987 of NH, SO and NO₃ was 1.1, 1.7, and 0.4 kmol_c ha^?1 yr^?1 in the deciduous stand and 2.1, 2.1, and 0.8 kmol_c ha^?1 yr^?1 in the coniferous stand. The input of N is almost completely retained in the deciduous stand. In the coniferous stand about 30% of this N-input is leached as NO₃. Due to N-transformations, total proton turnover is 4.4 kmol_c ha^?1 yr^?1 in the coniferous stand and only 2.5 kmol_c ha^?1 yr^?1 in the deciduous stand. Ca-mobilization is the major acid buffering process in both lysimeters. Only the deciduous stand was limed in 1980 (90 kmol_c/ha). Mobilization of Al is only relevant down to a soil depth of 30 cm. Below a 30 cm depth, Al is immobilized. The amounts of exchangeable and silicate-bound Ca in the soil underlying the coniferous stand are very small, but no evidence was found for explanation of the observed high Ca-mobilization by artificial Ca-sources.     

Response of acid sulphate soils to different liming treatments II. Exchangeability of soil cations

Liming-induced changes in cation exchangeability were studied in six samples from acid sulphate soils (pH 3.9-4.7) incubated with water or with equivalent quantities of Ca(OH)₂ or KOH. The extractability of acid cation species susceptible to hydrolysis was shown to be affected not only by increased pH but also by the kind of the cation and related electrochemical properties of the base used. Both liming treatments practically eliminated the exchangeable Al. In the virgin soils, however, the polynuclear Al-complexes formed by Ca(OH)₂ treatment seemed to have been hydrolyzed further. The superiority of Ca(OH)₂ was assumed to be due to the higher valency of its cation and its act of provoking a higher increase in ionic strength. The liming agents affected to varying extents also the extractability of base cations. Exchangeable soil K seemed to decrease by the KOH treatment and the soil Ca by the Ca(OH)₂ treatment, whereas K and Ca were only slightly, if any, affected by the Ca(OH)₂ and KOH treatments, respectively. Thus, the reductions were assumed to be attributable to other factors than increased pH. A fixation of K and a possible precipitation of Ca as CaSO₄ were discussed. Ca(OH)₂ decreased in all soil samples the exchangeability of Mg more than did KOH. The depression was not related to the Al polymerization and, thus, cannot entirely be ascribed to specific sorption on Al gel. The results imply that liming may affect base cation exchange reactions by neutralizing exchangeable Al of high bonding strength and by replacing it by cations of the liming agent.     

Gradienten von Bodeneigenschaften im Randbereich kleinflächiger Waldstandorte des östlichen Münsterlandes

Gradients of soil characteristics at fringe areas of small forest habitats of the Eastern Münsterland In four habitats of the Eastern Münsterland transects, perpendicular to south-western exposed forest fringes, were investigated. Subject of the investigation was to determine statistically detectable gradients of the following soil properties: C/N-ratio, pH- and pH_KCl-value, ECEC standardized with respect to the C_org content and the EDTA-extractable fraction of Pb and Zn in the humic layers Of and Oh. Towards the inner forest, the C/N-ratio increasingly expands, the pH-values and ECEC decrease and the Pb-contents increase. Zinc does not show a trend concerning a gradient. Differences between the C/N-ratio of the Oh-layer and the Of-layer are obviously a consequence of the N-deposition. Higher pH-values at the forest fringe appear to be due to the deposition of dust from the field clod. The interception deposition caused by the coniferous trees in the inner part of the forest effects lower pH-values than that of the deciduous trees at the forest fringe. The Oh-layers have a higher Pb content than the Of-layers because of the specific kind of sorption concerning this heavy metal and the change of the situation of deposition during the last years. For the same reasons the Of-layers have a higher zinc content than the Oh-layers. The results show that the forest fringes of the investigated habitats, in a range of 5—10 m, work as a buffer zone for laterally deposited substances.     

Effect of Rate of Urea Application and Soil Moisture on the Behaviour of Urea in Soil

A sandy clay loam soil was used to study the effect of (a) urea application at rates equivalent to 250, 500, 1000 and 2000 ppm-N, at moisture content level of 100 % WHC, and (b) soil moisture levels of 30, 60 and 100 % of the WHC in addition to water-logging conditions, when urea was applied at the rate of 500 ppm-N, on urea-N transformations. In both cases, the incubation took place at 30°C and lasted for 6 weeks. The experiments were carried out in a closed system daily aerated. Complete hydrolysis of the added urea was attained after 1, 2 and 3 weeks for 250, 500 and 1000 ppm urea-N, respectively. Six weeks incubation period was not enough for full hydrolysis of the 2000 ppm urea-N. The rate of urea hydrolysis increased linearly for urea concentration up to 1000 ppm N. This concentration must have been sufficient to saturate the urease present in the soil used. The peak of NON was higher the higher the rate of urea applied. Delay of the nitrate formation was always accompanied by the accumulation of nitrites. At the end of the experiment, the nitrate-N formed represented 93,90,77 and only 20 % of the initially applied nitrogen for 250, 500, 1000 and 2000 ppm-urea-N, respectively. The rate as well as the total ammonia loss increased with increasing the rate of urea application. No appreciable differences were observed in urea hydrolysis due to the variations in moisture levels within the range of WHC. Under water-logging conditions, urea hydrolysis was slower and extended to the 6th week, also the rate of urea hydrolysis was no more than 50 % of the rate produced in moisture treatments within WHC. NON accumulation persisted for one week in the moisture levels within the range of WHC, while it continued in the water-logged treatment till the end of the experiment. Nitrate formation was slightly favoured at 100 % WHC and decreased somewhat with lowering the soil moisture levels. However, it was completely inhibited under water-logging conditions. Ammonia volatilization was not markedly affected by moisture levels within WHC, however, the water-logged treatment showed the highest total loss.     

Chemische Bindungen des Lignins mit Ammoniak und Aminen

Chemical bounds of lignin with ammoniak and amines By using absorption spectroscopy in the visible (340–700 nm) and infrared (4000–400 cm^?1) region it was possible to proof reactions between natural lignin and N-compounds like NH₃, Ag(NH₃)₂OH as well as o- and p-anisidin. All reactions can be of practical importance in soil. The nitrogen was bound on lignin ionically as NH3-cation or covalently as primary and secondary amin. The chemical bounds between lignin and ammoniak were influenced by the concentration of hydrogen ions. Increasing pH-values (from 5,15 to 12,5) improved the condition of reaction between carbonyl groups of lignin and ammoniak. Possible reaction mechanisms are discussed.     

The effect of cation–anion interactions on soil pH and solubility of organic carbon

Alkaline soil is widely distributed and cultivated throughout the agricultural regions of the world. Organic carbon (OC) concentrations in alkaline soil are often small, partly because of the limitations of a high pH on the productivity of crops and pastures together with the effects of high pH on the chemistry of soil OC. Soil pH is often hypothesized to be a major factor in regulating OC turnover in agricultural soil, but there are few detailed studies on the effects of high pH on carbon cycling in alkaline soil. Sodium, K⁺, Mg²⁺ and Ca²⁺ are the major cations in alkaline soil, whereas Cl^?, , and are the major anions. The effect of different combinations of these cations and anions on soil pH and OC is not well described in the literature. The objectives of this study were to evaluate the effect of cations and anions on soil pH and to quantify the dissolution of OC in relation to these changes in pH. The results showed that (Na⁺, K⁺ and Mg²⁺) salts and CaCO₃ dominate in the pH range 7.0–8.5, and salts of Na⁺ and K⁺ dominate above pH 8.5. The amount of dissolved OC (DOC) increased significantly as pH increased. Therefore, the presence of large concentrations of and not only increased pH but also promoted the dissolution of soil OC. The concentration of Ca²⁺ modified this effect; large concentrations of Ca²⁺ increased the adsorption and reduced the concentration of DOC.     

Zur Kalkwirkung von Phosphatdüngemitteln

Basic effect of phosphorus fertilizers To test the basic effects of Thomas slag (Basic slag), Rhenaniaphosphate, Superphosphate, Hyperphos (soft rockphosphate) and Novaphos (partly water soluble phosphate), model, pot and longterm field trials were carried out. Changes in soil pH and base saturation served as a measure of the basic effect. The basic effect results from chemical reaction (oxides, hydroxides, carbonates and silicates of alkali- and earth alkali components as well as Ca-phosphates) and physiological reaction (different uptake of P and Ca by plant roots in exchange with HCO and H⁺). In contrast to Thomas slag and Rhenaniaphosphate the basic effect of Hyperphos due to chemical reaction is small; Superphosphate and Novaphos both have a chemically acidic reaction. Plant growth increased the basic effect of all fertilizers, especially of Hyperphos. On acid and weakly acid soils (field and pot trials), Hyperphos achieved about the half effect of Thomas slag expressed on a total phosphate basis whereas the effects of Superphosphate and Novaphos were only poor. The basic effect of P-fertilizers is directly associated with their solubility and P-effectiveness depending on particular soil conditions (pH). In a pot trial using loamy soils with a requirement for lime and small requirement for phosphorus, Thomas slag, Rhenaniaphosphate and Hyperphos showed nearly the same basic effect (50kg CaO per 100kg fertilizer). This value contrasts with the much lower figures for Novaphos (10–20kg) and Superphosphate (0–10kg).     

Einfluß chemischer Bodeneigenschaften auf Ausmaß und Zusammensetzung der Denitrifikationsverluste drei verschiedener Bakterien

Effect of soil properties on the quantity and quality of denitrification with different bacteria The influence of 4 different soils on the intensity and quality of gaseous denitrification losses from 3 bacteria (Aeromonas “denitrificans” S224, Azospirillum lipoferum DSM 1843 and Bacillus licheniformis ATCC 14580) was examined in model experiments at complete anaerobic conditions at the expense of a relatively high nitrate concentration (300 μg NO₃^? N/g dry soil) at standard conditions (30°C, 80% WHC). The soils (Ah-material) were obtained from gleyo-eutric Fluvisol (A), orthic Luvisol (L), calcaric Fluvisol (AR) and eutric Cambisol (KB) and represented different chemical properties. Gas production (CO₂, NO, N₂O, N₂ and CH₄) was analyzed by gaschromatography in regular intervals, whereas changes in N_t, C_t, water extractable organic carbon (C), nitrate, nitrite, ammonium, pH (H₂O) were determined at the end of each experiment. The intensity and composition of denitrification (NO, N₂O, N₂) differed considerably from organism to organism and from soil to soil. With A. “denitrificans” NO was released from the calcaric Fluvisol and orthic Luvisol, whereas B. licheniformis produced this gas only from the Cambisol. A. lipoferum did not produce NO in any of the soils tested. N₂O was liberated by A. “denitrificans” in all soils, but A. lipoferum produced it only in the Fluvisol and B. licheniformis exclusively in the Cambisol. Apparently, the production of NO and N₂O as products of incomplete denitrification at relatively high nitrate concentration is determined primarily by the organism in question and in the second place by the chemical properties of the soil. The main properties that govern the quality of denitrification in soils are discussed.     

Correlating phosphorus extracted by simple soil extraction methods with foliar phosphorus concentrations of Picea abies (L.) H. Karst. and Fagus sylvatica (L.)

Phosphorus (P) concentrations in needles and leaves of forest trees are declining in the last years in Europe. For a sustainable forest management the knowledge of site specific P nutrition/availability in forest soils is vital, but we are lacking verified simple methods for the estimation of plant available P. Within this study, four soil P extraction methods [water ( ), double‐lactate (P_lac), citric acid (P_cit), and sodium bicarbonate ( )], as well as total P content of the soil (P_tot) were tested to investigate which method is best correlated with foliar P concentrations of spruce [Picea abies (L.) H. Karst.] and beech [Fagus sylvatica (L.)]. Mineral soil samples from 5 depth levels of 48 forest sites of the Bavarian sample set of the second National Forest Soil Inventory (BZE II) were stratified according to tree species (spruce and beech) and soil pH (pH < 6.2 and > 6.2), covering the whole range of P nutrition. The extractable amount of P per mass unit of soil increased in the order << P_lac < < P_cit, decreased with soil depth, and was higher in soils with pH < 6.2. Citric acid extracted up to 10% of P_tot in acidic soils. Whereas P_cit delivers adequate regression models for P nutrition in the case of spruce (R² up to 0.53) and beech (R² up to 0.58) for acidic soils, shows good results for spruce growing on acidic soils (R² up to 0.66) and for beech on soils with pH > 6.2 (R² up to 0.57). P_lac produces adequate models only for beech on high pH soils (R² up to 0.64), while did not produce acceptable regression models. P_tot seems suitable to explain the P nutrition status of beech on acidic (R² up to 0.62) and alkaline soils (R² up to 0.61). Highest R²s are obtained mostly in soil depths down to 40 cm. As and P_cit showed good results for both investigated tree species, they should be considered preferentially in future studies.     

Changes in soil nitrogen availability due to stand development and management practices on semi‐arid sandy lands,in northern China

Soil nitrogen (N) availability is one of the limiting factors for plant growth on sandy lands. Little is known about impacts of afforestation on soil N availability and its components in southeastern Keerqin sandy lands, China. In this study, we measured N transformation under sandy Mongolian pine (Pinus sylvestris var. mongolica Litv.) plantations of different ages (grassland, young, middle‐aged, close‐to‐mature) and management practices (non‐grazing and free‐grazing) during the growing seasons using the ion exchange resin bag method. Results showed that, for all plots and growing season, soil NH‐N, NO‐N, mineral N, and relative nitrification index, varied from 0·18 to 1·54, 0·96 to 22·05, 1·23 to 23·58 µg d⁻¹ g⁻¹ dry resin, and 0·76 to 0·97, respectively, and NO‐N dominated the available N amount due to intense nitrification in these ecosystems. In general, the four indices significantly increased in the oldest plantation, with corresponding values in non‐grazing sites lower than those in free‐grazing sites (p < 0·05). Our studies indicated that it is a slow, extended process to achieve improvement in soil quality after afforestation of Mongolian pine in the study area. Copyright © 2009 John Wiley & Sons, Ltd.     

Performance of nitrification inhibitors with different nitrogen fertilizers and soil textures

Nitrification inhibitors (NIs), DCD (dicyandiamide), and DMPP (3,4‐dimethylpyrazole phosphate), in combination with urea (UR) and ammonium sulfate nitrate (ASN) fertilizers were studied under contrasting soil textures (sand, loam, and clay) from cultivated soils collected in Brazil and Germany. Soil samples were incubated over 50 days and the content of ammonium ( ), nitrate ( ), and soil pH were measured periodically. Applied NIs delayed the nitrification process across all soil textures. Correlation analysis indicated that combining ASN with NIs resulted in higher content and efficiency in delaying the nitrification process with high N‐conversion rate (r = –0.82). The combination of ASN+ DMPP increased the efficiency of the N‐conversion rate (r = –0.86) due to H⁺ release in soil, while UR+DCD (r = –0.50) had an efficiency of the N‐conversion rate similar to UR (r = –0.42). All the NIs had a better performance in reducing formation in sandy soils as compared to the loam and clay textured soils. Use of DMPP with an N fertilizer results in a soil pH decrease and can be an option to increase the efficiency of the N‐conversion rate, reducing N losses in soil. Overall, our results suggest that NIs have a better performance in reducing formation in sandy soils as compared to that of the loam and clay textured soils. Use of DMPP with ASN results in a soil pH decrease and can be an option to reduce N losses in soil.     

Einfluß einer hohen Nitratdüngung auf Kinetik und Gaszusammensetzung der Denitrifikation in unterschiedlichen Böden

Effect of high nitrate application on the kinetic and gaseous composition of denitrification in different soils Kinetic and gaseous composition of denitrification were studied with 16 different soil horizons after application of a relatively high amount of nitrate (400 μg NO N/g dry soil) at defined conditions (He atmosphere; 80 % WHC; 30°C; 3 weeks). At the conditions given, denitrification followed zero-order kinetics depending on the amount of decomposable organic matter rather on than the nitrate concentration. Denitrification intensity was most significantly correlated with the amount of extractable or mineralizable organic carbon (C_H2O and C_min, respectively). N₂ and N₂O (but not NO) were liberated by all samples, the amount and ratio depending on the soil and time of sampling. At the end of the three week's incubation period, the N₂/N-N₂O ratio varied between 8.1 and 1.4/1 (with an average of 3.1/1), except for the acid Ah-sample of the Pararendzina (N₂/N-N₂O = 1.0/1.2). The incorporation of an excess of easily decomposable leaf-powder resulted in an increased nitrate turn-over (from 64.7 % to 95,7 % of the nitrate loss) with N₂ as the single denitrification product. N₂O could be detected only with the acid “B”-material of the Pararendzina. The denitrifying capacity Y (in μg N₂+N-N₂O/g soil) of a soil at the conditions given may be predicted by the amount of water-extractable organic carbon X (in μg C_H2O/g soil) according to the equation Y = 0.808 X + 120,1.     

Impact of urease and nitrification inhibitor on NH4+ and NO3− dynamic in soil after urea spring application under field conditions evaluated by soil extraction and soil solution sampling

The application of mineral nitrogen (N) fertilizers is one of the most important management tools to ensure and increase yield in agricultural systems. However, N fertilization can lead to various ecological problems such as nitrate () leaching or ammonia and nitrous oxide emissions. The application of N stabilizers (i.e., inhibitors) combined with urea fertilization offers an effective option to reduce or even prevent N losses due to their regulatory effect on ammonium () and release into the soil. The present field experiment therefore aimed at soil N speciation dynamics after urea spring fertilization (225 kg N ha^?1) in the presence of a urease inhibitor (UI), a nitrification inhibitor (NI), both inhibitors (UI+NI) or when no inhibitor was applied at all. The study focused on the distribution of N species among soil matrix and soil solution. Plant cultivation was completely omitted in order to avoid masking soil N turnover and speciation by plant N uptake and growth dynamics. Application of UI clearly delayed urea hydrolysis in the top soil, but a complete hydrolysis of urea took place within only 10 days after fertilization (DAF). Nitrification was significantly reduced by NI application, leading to higher and lower concentrations in treatments with NI. Due to sorption of to the soil matrix a significantly larger fraction of was always detected in the soil extracts compared to soil solution. However, while in soil extracts the impact of NI application was less apparent and delayed, in soil solution a quick response to NI application was observed as revealed by significantly increased soil solution concentrations of . Because of the “asymmetric” soil phase distribution soil solution was predominant over only initially after fertilization even in inhibitor treatments (≈ 8 to 10 DAF). Nevertheless, inhibitor application tended towards closer ratios of to concentration in soil solution and hence, might additionally affect concentration dependent processes like plant N uptake and root development. Despite cold spring conditions urea application along with UI and/or NI did not indicate a limited supply of plant available and .     

Nitrogen turnover in bare soil planted subsequently with grass as investigated by electro‐ultrafiltration (EUF)

Changes of EUF‐extractable nitrogen (N) (nitrate, ammonium, organic N) in 20 arable bare soils, subsequently planted with ryegrass (Lolium multiflorum L.) and cutting three times were investigated in pot experiments. All 20 soils responded qualitatively in the same way. During the period of bare soil, there was a significant increase of EUF‐extractable nitrate (EUF NO ), while extractable ammonium (EUF NH ) remained on the same level and organic N (EUF N_org) decreased. This decrease, however, was not significant. From sowing until the first cutting of the grass, EUF‐NO concentration decreased to almost zero. This low EUF‐NO level was maintained throughout the subsequent experimental period (three cuttings of grass). During the growth of the first cutting, EUF N_org decreased while EUF NH remained constant, however, on a low level. EUF NH fell during the growth of the second and third cutting. In this period, however, the N supply of the grass was insufficient. EUF N_org decreased during the growth of the second cutting, but increased during the growth of the third cutting. This shows that the EUF‐N_org fraction represents a transient pool, which gains and loses N. EUF NO , EUF NH , and EUF N_org correlated with the N uptake of the grass. Strongest correlation for EUF NO was found for the first cutting (p < 0.001), and for EUF NH and EUF N_org for the second and third cutting (p < 0.001). Total soil N was not correlated with the N uptake of the grass. EUF N_org was only about 2% of the total N. This relatively small EUF‐N_org fraction, however, is relevant for the mineralization of organic soil N, and the N quantity indicated by EUF N_org is in the range of the N amount mineralized in arable soils within a growing season.