Considering Residual Soil Mineral Nitrogen in Corn Fertilizer Recommendations in an Irrigated Mediterranean Area

Management of nitrogen (N) fertilization for economic crop production in water-stressed areas relies heavily on irrigation. The objectives were to determine the depth distribution of mineral N (N_min) at pre-plant and post-harvest seasons and assess the residual mineral N pool as a potential source of plant-available N for irrigated corn (Zea mays L.) in southern Turkey. Pre-plant and post-harvest composite soil samples were collected randomly from farmer’s fields at 0–30, 30–60 and 60–90 cm depths, respectively, analyzed for nitrate (NO₃) and ammonium (NH₄) concentrations, and the N_min values were correlated with corn yields and N uptake. Results showed that substantial amounts of pre-plant (76 to 94 kg N_min/ha) and post-harvest (70–78 kg N_min/ha) N_min accumulation at different soil depths. However, the N_min did not correlate with crop yields and N uptake. Results suggested that residual N_min could be the ?basis for recommending N fertilization to support crop production.     

Chemische und mikrobiologische Veränderungen in einem Rigosol nach mineralischer Düngung im langjährigen Feldversuch und kurzzeitigen aeroben Inkubationsversuch

Chemical and microbiological changes in a Rigosole after mineral fertilization in long-term field experiments and short-term aerobic incubation trials A sandy clay loam which often showed priming effects in a differently fertilized (control, 120 kg N/ha, 240 kg N/ha) long-term field experiment, was aerobicly incubated (25°C) and analysed for chemical and microbial parameters. The total nitrogen and C_org contents in the 240 kg N/ha treatment were markedly lower than in the unfertilized as well as in the 120 kg N/ha treatment. Long-term fertilization with 240 kg N/ha increased the dehydrogenase activity by about 34% in comparison to the control and about 54% to the 120 kg N/ha variant and enhanced the population of amino acid ammonifying and proteolytic bacteria. After analogous fertilization in model trials, positive as well as negative priming effects were shown. Thereby no linear dependence occurred in relation to the amount of nitrogen added. The effects on biological criteria were similar both under laboratory conditions as well as in long-term field experiments. The total nitrogen and C_org contents of humus fractions partly showed differences in dependence on fertilization.     

Einfluß von Düngemaßnahmen auf die Stickstoffauswaschung bei mehrjährigem Silomaisanbau

Influence of fertilization on nitrogen leaching after cultivation of maize for silage over four successive seasons In a field trial, nitrogen leaching from soil was determined between February 1983 and May 1986 by analyzing soil water from 50, 80 and 110 cm below the soil surface every 14 days. On a Stagno-gleyic Luvisol, maize after maize was cultivated over four successive seasons. Nitrogen was applied either minerally in spring according to N_min or as a semiliquid cattle manure. The time of application (autumn and/or spring), application rate and use of nitrification inhibitor dicyandiamide (DCD) were varied. Under very low N-fertilization (underground fertilization only), nitrate nitrogen losses by leaching dropped from 100 kg N/ha in the first year to 33 kg N/ha in the 3^rd. Nitrogen leaching from the various treatment plots depended on the maize growth and rainfall conditions. Because of an intensive and long lasting seepage of gravitational water, nitrogen leaching from the root zone ranged from 113 to 208 kg N/ha during the fall and winter seasons of 1983/84 and 1984/85. Under the more balanced infiltration conditions of the leaching period 1985/86, and after a high yield of maize in 1985, losses due to leaching were reduced to values between 69 to 108 kg N/ha. Under these experimental conditions (deliberately high quantities of semiliquid cattle manure; DCD-application in autumn) no reduction in nitrogen losses could be proved due to the addition of dicyandiamide.     

Leaching of mineral nitrogen in the soil influenced by addition of compost and N-mineral fertilizer

This paper deals with the problem of mineral N leaching from arable lands due to the fertilization method. The influence of different doses of compost (50 and 100?Mg ha^?1) and N-mineral fertilizer (35-70-140 kg N ha^?1) on leaching of N_min in a lysimetric experiment with winter wheat. The area of our interest represents the main source of drinking water for the city of Brno and its neighborhoods. To demonstrate the effect of compost and mineral nitrogen addition, the lysimetric experiment was established there. Seven variants of the experiment with different fertilization schemes were studied during two vegetation seasons (2013 and 2014), each with three repetitions. The experiment was carried out in plastic experimental containers of 0.3 m diameter and 0.5 m height. Therefore, each lysimeter was the same size and was filled with 25 kg of subsoil and 25 kg of topsoil. The highest leaching of N_min was detected in the variant C2 where 140 kg N ha^?1 was applied, in both vegetation periods (5.97 kg N_min ha^?1 after the first vegetation period and 17.02 kg N_min ha^?1 after the second vegetation period). The positive effect of compost application (individually or in combination with the mineral N) on decrease in mineral N leaching was found during both vegetation period in comparison with variant C2. The highest doses of compost (100?Mg per ha) significantly decreased the concentration of mineral nitrogen in the soil eluate in both periods (3.03 kg N_min ha^?1 and 5.79 kg N_min ha^?1, respectively), by 197% and 293% in comparison with variant C2. There is evidence that the application of compost has a positive effect on the reduction of N_min leaching.     

Vorräte und Nachlieferung an Mineralstickstoff im Boden eines Meliorationsexperiments zu Kiefer

The influence of soil amelioration procedures on the content and production of mineral nitrogen in the soil of a formerly litter raked pine stand in Upper Palatia In 1964 a soil amelioration experiment was started in a 87-year-old, Scots Pine stand of site class III.8., situated in the growth district ?Oberpfälzer Jurarand”?, East Bavaria. The soil, degraded in former times by litter removal, is a podsolic pseudogley, derived from cretaceous sediments with diluvial loess depositions. The trial comprised of the following treatments: NPKCaMg-fertilization, the N-input was repeated three times (I- ?Volldüngungsvariante”?); PKCaMg-fertilization and tillage to a depth of 20 cm (II–?Fräsvariante”?); PKCaMg-fertilization, tillage and underplanting of the perennial legume Lupinus polyphyllus (III-?Lupinenvariante”?); control (O). In the 15^th vegetation period after the beginning of the experiment and 6 years after the last N-fertilization respectively, the effects of these amelioration procedures on the content and production of mineral nitrogen (incubation in the field) were investigated. The mean N-net mineralization rate in the upper soil increased in the following sequence: control 100% – Fräsvariante 114% – Volldüngungsvariante 400% – Lupinenvariante 628%. A significant linear correlation could be detected between N_min-production and the nitrogen content in pine needles; methodical problems of incubation however caused an underestimation of the absolute mineralization level on all treatments. The nitrification was promoted by N-fertilization and lupine treatment. On the ?Volldüngungsvariante”? the N_min-production rose in the organic layer, on the ?Lupinenvanante”? in the mineral soil. Characteristic of lupine treatment were a low actual content of mineral nitrogen at the beginning of vegetation period and a rapid mineralization during springtime. The highest actual N_min-contents in the upper soils were generally observed in the summer. On the ameliorated treatments a significant decrease occurred in the late summer, followed by a small increase in the autumn.     

N-Umsatz von verschiedenem Pflanzenmaterial im Boden in Gefäß- und Feldversuchen

Turnover of nitrogen of different plant material in the soil in pot and field trials In pot and field trials, effects of various plant materials like green rape, sugar beet leaves, potato foliage, straw of wheat, maize, or field beans, on the turnover of N in the soil (mineralization, N_min-concentrations, NO₃-leaching) and on yield and N uptake by some crops was tested in relation to mineral N fertilizer application. In both experiments, widely corresponding results were obtained: Irrespective of the N contents of the plant material, biological immobilization of N always was combined with beginning mineralization (pot trial: decrease of NO₃ leaching in late fall). Green rape (C/N = 12/1) showed already after 4 weeks in the field trial a marked net mineralization (N_min) of 20–30% of the added nitrogen which was quantitatively reflected in higher removals of N. Beet leaves (C/N = 20/1) were decomposed at a much slower rate in combination with an increase in N removals of subsequent crops by 6-20 % depending on the rate of mineral fertilizer application. All types of straw (CM = 57-8611) and potato foliage (CM = 73/1) caused a marked biological immobilization of N which resulted in reduced N removals depending on turnover rate (potato foliage: fast, wheat straw: slow) and N contents of the organic material. Different plant residues (straw, leaves) were applicated on a harvested field with cereal to test comparatively one part of the total value of different preceding crops; at onset of vegetation the N_min-contents in soil, depending on the climatic conditions during the non-growing season for mineralization, were analyzed.     

Die n-versorgung der getreidepflanzen im iosdv?-?tartu?-?pflanzenanalysen und n-bestimmung im boden

Der Internationale Organische Stickstoffdauerdüngungversuch (IOSDV) Tartu wurde 1989 mit den N-Stufen: 0-40-80-120-160 kg N/ha und den verschiedenen organischen Düngungsstufen: 400 dt/ha Rübenblatt, 40 dt/ha Stroh und 600 dt/ha Stallmist auf einer Fahlerde angelegt. Es wurden NH₄- und NO₃- N im Humushorizont des Bodens untersucht und der N-Gehalt im Aufwuchs von Sommerweizen und Sommergerste. Die mineralische und die mineralische-organische Düngung beeinflussten die Bestockung und Blüte der Getreidepflanzen. Die Getreidepflanzen waren während dieser Zeit ausreichend mit Stickstoff versorgt. Die gemessenen Werte stimmten mit den Angaben zur optimalen N-Versorgung in der Literatur überein (<citeref rid="b1">Bergmann, 1986</citeref>). Die N-Gehalte im Korn korrelierten positiv mit den Erträgen. Die N_min-Werte im Boden zeigten erwartungsgemäß im Herbst eine bessere Korrelation zum Ertrag von Sommergerste als die im Frühjahr gemessenen N_min-Werte. Sie wurden stärker durch den mineralisch gedüngten Stickstoff als durch die Nachwirkung der organischen Düngung beeinflusst. Die Ertrag von Sommerweizen war mehr durch die Witterungsbedingungen während der Vegetationszeit beeiflusst. The aim of the international organic-nitrogen long-term experiment (Internationaler organischer Stickstoffdauerdüngungsversuch (IOSDV), initiated in 1989) is to compare the effects of different forms of mineral nitrogen fertilizer (0-40-80-120-160 kg N/ha) with different organic amendments (beet leaves, 400 dt/ha; straw, 40 dt/ha; and FYM, 600 dt/ha) on loamy Podzoluvisol (FAO). The ion-exchangeable NH₄-nitrogen and NO₃-nitrogen content in humus layer and N-content in shoots of different stages of spring barley and spring wheat were studied. Mineral and organic fertilization influenced N-uptake at anthesis and tillering stage. Cereal plants had a sufficient supply of nitrogen at this time. Measured data are well in accordance with published results (Bergmann, 1986). Results of optimal N-content of shoots at different stages correlated positively and significantly with grain yields. N_min content in the humus layer in autumn was correlated better as in spring with grain yields of spring barley. In the vegetation period, N_min content correlates better with treatment with mineral nitrogen fertilizer than with use of organic amendments. In addition, yield of spring wheat is significantly correlated with weather conditions.     

Soil mineral nitrogen dynamics in fallow periods in a rainfed semiarid Mediterranean agricultural systems

Rainfed agricultural systems in semiarid Mediterranean environments are subject to erratic but often heavy rainfall events.As an agronomic practice,fallow periods can be included even within the existing European Union common policy for crop diversification.This study aimed to quantify the effects of previous mineral fertilization on soil mineral nitrogen (Nmin) content and potential nitrate leaching during no-till fallow periods of crop rotation.The Leaching Estimation and Chemistry Model (LEAC...     

Wirkung einer langjährig differenzierten mineralisch-organischen Düngung auf Ertrag,Humusgehalt, N-Bilanz und Nährstoffgehalte des Bodens

Abstract

Since 1966, the effects of increasing mineral N fertilization in combination with different organic fertilizers (without, farmyard manure, straw) were examined at two sites in Saxonia (Methau: loam, Spröda: loamy sand) in two-factorial static experiments with regard to yield, humus content, N-balance, N_min content and DL-soluble contents of phosphor and potassium. During the period 1966–2010, rising N application caused a significant yield increase. Farmyard manure treatments always showed the highest yields. Particularly, the yields of potatoes and sugar beets were considerably increased by applying manure, while this had substantially smaller effects on winter wheat and summer barley. The humus contents decreased clearly on both sites. They were almost halved with omitted organic fertilization. With manure supply, the starting contents could not be kept upright, but they were, in relation to omitted organic fertilization, on a clearly higher level. The effect on humus content, resulting from the straw fertilization, was comparatively weak. Under these experimental conditions, high yields with slightly negative to slightly positive N-balance results, were realised. Before winter, the N_min content increased with rising N supply and showed a significant dependence to the N-balances. In case of manure fertilization, they always were on a higher level. The long-term differentiated fertilization strongly affected the DL-soluble contents of phosphor and potassium of the soil.     

Untersuchungen zur Anpassung des Stickstoff-Angebots aus unterschiedlichen N-Quellen an den Verlauf der N-Aufnahme von Maisbeständen

Investigations on the adjustment of nitrogen supply from different N sources to the N uptake of maize A two years field experiment was conducted to study the effects of the nitrogen fertilizers: wheat swill, BASAMMON (NH₄ + nitrification inhibitor DCD) and calcium ammonium nitrate (CAN) applied at N rates of 0.60.120 or 180 kg N/ha on yield, N uptake and soil mineral N residues of maize for silage or grain production. CAN was either broadcast or placed in the maize rows, with or without the addition of an Azospirillum-biopreparation (AZOGREEN). Due to initially high soil mineral N contents (50–70 kg N/ha) and a high mineralization from the soil (unfertilized: 100–170 kg N/ha), neither effects of fertilizer type, nor interactions between fertilizer type and N rate on biomass production and N uptake of maize were observed. The economically optimum total dry matter production and grain yield were obtained with a fertilization of 60–120 kg N/ha. In contrast to the biomass production the soil mineral N was considerably influenced by fertilizer type and N rate. The nitrate content of the soil increased during the early developmental stages of maize after an early application of swill or BASAMMON, and also during the ripening period after a late high dose of CAN. Though the placement of CAN was reflected in the soil, the soil nitrogen content per unit area could not be much reduced by row fertilization. The effects of AZOGREEN were only small. The results were greatly influenced by the high mineralization potential at the experimental site.     

Kalkulatorische Ermittlung des Nmin-Sollwertes im Gemüsebau unter besonderer Berücksichtigung der Stickstoffimmobilisierung bzw. - fixierung

Calculation of the N_min target value (N_min-Sollwert) in vegetable cultivation with special regard to N-immobilization respectively N-fixation When establishing target values for N fertilization (N_min-Sollwert = optimal sum of soil mineral N at the beginning of cultivation and fertilizer N) experimentally the components of the N balance are restricted to N_min target value, N_min supply of the soil and N fertilizer amount. In fertilization experiments any other processes in N dynamics are included in the target value without being noticed. If N_min target values are to be calculated such simplified reflection is not longer possible. In this case the most important components of the N balance have to be determined and quantified. Up to now the formulas to calculate the N_min target value have included the N uptake of the crop (also called “N demand”), frequently the necessary minimum mineral N content at harvest time in the rooted soil layer, sometimes the N release during the cultivation period. Immission, denitrification, leaching and others during the summer half-year have been considered in only a few cases. Calculated N_min target values from N uptake of the crop plus necessary minimum mineral N content in the soil at harvest time minus N release yields in all cases studied distinctly lower values than determining them by fertilizer experiments. Only if a calculated quantity “deficit” is included a satisfactory agreement between the two values is attained. There are indications that this quantity consists mainly of temporarily bound or immobilized nitrogen.     

Düngung mit gebranntem Magnesit und Magnesiumhydroxid zur Standortmelioration in einem stark geschädigten Fichtenökosystem

Fertilization with calcined magnesite and Mg-hydroxide for site amelioration in a heavily damaged Norway spruce ecosystem Fertilization experiments with calcined magnesite and Mg-hydroxide were carried out in a heavily damaged, 60-year old Norway spruce ecosystem at Hohe Matzen in the Fichtelgebirge/NE-Bavaria. The site is characterized by high atmospheric inputs with deposition rates of 1.25 kg H, 42 kg S, and 32 kg N per ha and year, and low pH-values of the soil (typic Dystrochrept derived from granite). The trees show severe symptoms of needle yellowing due to Mg-deficiency. Fertilization resulted in manyfold increased Mg-concentrations in soil solution down to 70 cm soil depth and a significant increase of pH down to 25 cm mineral soil depth. Nitrate concentrations were higher after fertilization, but decreased within 15–24 months below the control level. The higher solubility of the Mg-hydroxide resulted in an earlier and clearer pH-increase paralleled by a decrease of the NO₃-concentrations. As a mean over the whole experimentation period no increased N-output from the soil was found after hydroxide application. Fertilization also increased the amount of exchangeable Mg down to 40 cm mineral soil depth. Application of Mg-hydroxide leads to higher Mg-contents in recent-year needles three vegetation periods after fertilization. The lower solubility of magnesite results in a half- to one-year delay in its effects on soil chemical parameters with no reaction of the needle contents within this period.     

施氮量、土壤和植株氮浓度与小麦赤霉病的关系

【目的】赤霉病已成为影响小麦产量和品质的重要病害之一,为了解施用氮肥对小麦赤霉病的影响,本文通过研究不同施氮水平下小麦赤霉病的发病情况,探索施氮、土壤供氮、植株氮浓度与小麦赤霉病的关系。【方法】采用田间小区试验,以多穗型豫麦49-198(YM49-198)和大穗型周麦16(ZM16)为供试品种,设N 0、120、180、240、360 kg/hm25个施氮水平(N0、N120、N180、N240、N360),根据"小麦赤霉病测报技术规范"调查小麦赤霉病的发病情况。【结果】土壤硝态氮含量及0—90 cm土层土壤硝态氮累积量均随施氮量的增加而增加,小麦收获期N0、N120、N180处理0—30 cm土层硝态氮含量及0—90 cm累积量差异不显著,但显著低于N240和N360处理。两个品种小麦赤霉病病穗率和病情指数(DI)随施氮量的增加而增加,各处理间差异显著;豫麦49-198施氮处理的病穗率和DI比不施氮处理分别增加29.5%~132.0%和35.9%~225.2%,周麦16施氮处理的病穗率和DI比不施氮处理分别增加42.4%~161.8%和41.7%~206.9%;两个品种小麦N180处理赤霉病的病穗率和病情指数与N0、N120差异较小,显著低于N240和N360;周麦16较豫麦49-198发病严重,各处理的病穗率和病情指数比豫麦49-198分别高出7%~25%和28.0%~63.6%。小麦赤霉病病穗率和DI与硝态氮含量显著正相关,与0—90 cm硝态氮累积量呈线性正相关。孕穗期、开花期和灌浆期茎基部硝酸盐含量和拔节期~开花期植株的全氮含量各处理间差异较大,且与小麦赤霉病病穗率和DI显著线性正相关。【结论】土壤硝态氮含量及累积量随施氮量增加而增加,小麦收获后施氮量低于N 180 kg/hm2时土壤中硝态氮残留较低,赤霉病发病较轻。小麦赤霉病病穗率和病情指数随施氮量的增加而增加,说明施氮量过高会加重小麦赤霉病病害;小麦拔节期~开花期的氮浓度过高会加重赤霉病病害,因此在这一时期,适宜的施氮量、土壤硝态氮和植株氮浓度在赤霉病发生年份可以减轻病害,综合考虑土壤硝态氮残留、产量和赤霉病害等因素的适宜施氮量为N 180 kg/hm2。     

施氮对春玉米氮素利用及农田氮素平衡的影响

田间试验研究了玉米对不同土壤氮素供应水平下作物氮素吸收利用、土壤氮素供应以及农田氮素平衡的影响。结果表明,玉米产量随施氮量的增加而显著提高,当施氮量高于N 240 kg/hm2时,产量有减少趋势;氮素当季利用率随施氮量的增加逐渐降低。土壤中硝态氮含量在玉米整个生育时期呈现先迅速下降后缓慢升高的趋势;玉米成熟期,施氮处理的各层土壤中硝态氮含量显著高于不施氮处理,各层硝态氮含量基本随施氮量的增加而升高。适量施氮促进玉米对氮素的吸收和利用,进而提高玉米生物量和产量;过量施氮导致硝态氮在土壤中大量累积,提高了硝态氮淋溶风险。施氮处理显著提高了收获后土壤中残留无机氮(Nmin),土壤残留Nmin随施氮量的增加而增加;当施氮量高于N 240 kg/hm2时,残留Nmin有下降趋势。氮素表观损失随施氮量的增加而增加。在本试验条件下,综合产量、氮肥利用率和土壤硝态氮累积情况考虑,合理施氮量应控制在N 1802~40 kg/hm2左右。     

Effect of crop residues on the organic matter composition of a leached chernozem in the Western Siberian forest-steppe

In leached chernozems used in crop rotations with different amounts of plant residues for nine years, the following parameters have been determined: the changes in the contents of the total carbon and carbon and nitrogen from the readily hydrolyzable components of the soil organic matter: the labile humus, detritus, and mortmass. No significant differences in the content of C_org in the soil among the crop rotations have been found. The different inputs of plant residues have significantly affected the contents of carbon and nitrogen in the readily mineralizable soil organic matter. The decrease in the mean annual input of the aboveground plant residues to the soil from 1.5 to 0.2 t C/ha resulted in the reduction of the carbon and nitrogen contents in the soil by 19–25% for the labile humus, 24–28% for the detritus, and 33–36% for the mortmass. The labile humus formed the largest fraction (3890 mg of C/kg soil or 10.3% of C_org on the average for the crop rotations); the fractions of the detritus (1546 mg C/kg soil or 10.3%) and mortmass (627 mg C/kg soil or 1.7% of C_org) were the next.     

Nitrat‐Austräge auf intensiv und extensiv beweidetem Grünland,erfasst mittels Saugkerzen‐ und Nmin‐Beprobung II Variabilität der NO3‐ und NH4‐Werte und Aussagegenauigkeit der Messmethoden

Nitrate leaching from intensively and extensively grazed grassland measured with suction cup samplers and sampling of soil mineral‐N II Variability of NO₃ and NH₄ values and degree of accuracy of the measurement methods Data from a grazing experiment — comparison of mean values, see Anger et al. (2002) — were used to estimate within‐field variability to asses the accuracy of two frequently used methods of estimating NO₃ leaching on pastures: (1) the ceramic suction cup sampling (with 34 cups ha^—1 minimum, calculated climatic water balance, 4 leaching periods) and (2) using the soil mineral‐N method (vertical soil NO₃ and NH₄ content in 0—0.9 m (N_min) measured at the beginning and end of two winters on a minimum of 10 different areas of 50 m² each with a minimum of 7 different sample cores). These methods were used on two permanent pastures with high mean stocking density of cattle of 4.9 LU ha^—1 on 1.3 ha with N‐fertilization of 250 kg N ha^—1 (= intensive [I]) and 2.9 LU without N fertilization on a 2.2 ha pasture (= extensive [E]). The results show that NO₃ leaching on pastures was largely due to few selectively extremely high NO₃ amounts under a few excrement spots — mainly urine spots — which would not be sampled representatively with an acceptable effort in a conventional grazing experiment. In both grazing treatments, very large spatial variation occurred. This was greater between the different suction cups than between the compound mineral N samples of each area. Therefore, a marked skewness and kurtosis demonstrated a non‐normal distribution of samples from suction cups, while mineral N values did not show this effect consistently. Sampling selected mostly spots without noticeable influence of excrement, but a few samples with very high values identified evidently urine spots from summer or autumn grazing. The differences in mean coefficient of variation (CV) between the grazing treatments and estimation methods were mainly based on the stocking rate and the density of excrement spots. CV values were 131 % [I] / 242 % [E] for NO₃ leaching measured with suction cup samplers and of 71 % [I] / 116 % [E] for soil NO₃ values and 24 % [I] / 34 % [E] for soil NH₄ values in 0—0.9 m according N_min‐method. Results of the N_min method are obviously inaccurate even with a sampling intensity much greater than 70 cores ha^—1; and so making an estimation of NO₃ leaching by this method is unsatisfactory for pastures. Compared to this, the results of suction cup sampling are more convincing; but even with a tolerated deviation of ± 20 % from the empirically estimated average and with a 95 %‐confidence interval, the calculated mean minimum number of samples in our experiment should be increased to 146 and 265 suction cups ha^—1 for the intensively and extensively grazed treatments, respectively. This requirement would be prohibitive for many field experiments.     

Nmin−Gehalt im Boden,mineralische N-Düngung und N-Entzug von Winterweizen im Internationalen Organischen Stickstoffdauerdüngungsversuch (IOSDV) Berlin-Dahlem

N_mim content in the soil, N-fertilization and N uptake of winter wheat in the international organic nitrogen long-term fertilization experiment (IOSDV) Berlin-Dahlem During the 9th and 10th year of the long-term IOSDV field experiment micro plots were put in three treatments. Labelled¹⁵ N (160 resp. 110 kg/ha N as ammonium sulfate) was fertilized to winter wheat subdivided into three portions. N_min in soil was determined five times during the season, plant biomass was harvested at different growth stages and N uptake was calculated. Using the¹⁵ N-technique permitted a discrimination between fertilizer-N and soil-N. Preferential uptake of fertilizer-N by the wheat crop but also immobilisation in soil were observed until June. Subsequently the immobilized N was remineralized and assimilated by wheat. But the native N_min of soil was minimaly utilized during the initial growth of wheat. Therefore the absolute amount of soluble N temporarily increased caused by a mineralisation of the organic matter.     

Einfluß langjähriger Gülledüngung auf den Nährstoffhaushalt des Bodens. 1. Mitteilung: N-Akkumulation und N-Nachlieferungsvermögen

Influence of long-term slurry application on soil nutrients. 1. N accumulation and N mineralization potential The influence of longterm slurry applications on the total N content, N fractions and N mobilization potential of the soil was investigated. The following results were obtained:

• – Application of high amounts of slurry over a long period of time resulted in higher total N contents not only in the upper soil layers but also in the layer 60–90 cm.
• – In two sites the higher total N contents are mainly resulting from higher contents of hydrolyzable organic N compounds and in one site of higher contents of non hydrolyzable organic N compounds.
• – The influence of the slurry application on the content of non exchangeable NH₄⁺ is depending on the K saturation of the clay minerals.
• – In incubation experiments N mobilization of the soils supplied with slurry was higher as compared to soils supplied with mineral fertilizer.
• – A highly significant correlation is existing between N mobilization and the content of hydrolyzable organic N compounds and the N_org fraction, determined by means of EUF, respectively.
• – The N_min content of the soils supplied with slurry was higher during the whole growing season.

     

Nitrat‐Austräge auf intensiv und extensiv beweidetem Grünland,erfasst mittels Saugkerzen‐ und Nmin‐Beprobung I Einfluss der Beweidungsintensität

Nitrate leaching from intensively and extensively grazed grassland measured with suction cup samplers and sampling of soil mineral‐N I Influence of pasture management Leaching of nitrate (NO₃^—) from two differently managed cattle pastures was determined over four winters between 1993 and 1997 using ceramic suction cup samplers (with min. 34 cups ha^—1); additionally, vertical soil mineral‐N content in 0—0.9 m (N_min) was measured at the beginning and end of two winters (with min. 70 different sample cores ha^—1). The experimental site in the highlands north‐east of Cologne, Germany, is characterized by high annual precipitation (av. 1,362 mm between 1993 and 1996). An intensive continuous grazing management (1.3 ha, fertilized with 250 kg N ha^—1 yr^—1, average stocking density 4.9 LU ha^—1, = [I]) was tested against an extensive continuous grazing system (2.2 ha, av. 2.9 LU ha^—1; no N‐fertilizer but an estimated proportion of Trifolium repens up to 15 % of total dry matter in the final year, = [E]). The results can be summarized as follows: (1) Mean leaching losses of NO₃‐N, estimated from suction cup sampling and balance of drainage volume, were 85 kg NO₃‐N ha^—1 [I] and 15 kg NO₃‐N ha^—1 [E] during three wet winters with drainage volumes between 399 and 890 mm; in a dry winter with 105 mm calculated percolation, nitrate leaching decreased by a factor of 5 for both grazing treatments. (2) Although the amount of mineral N in soil (N_min) sampled in late autumn showed differences between intensive and extensive grazing, the N_min method permits no certain indication of the risk of NO₃ leaching. For example, during the winter period 1994/95 a reduction of mineral N in the soil (0—0.9 m) in both grazing treatments was found (—33 [I] / —8 [E] kg NO₃‐N ha^—1 and —26 [I] / —21 [E] kg NH₄‐N ha^—1) whereas during the winter 1996/97 an increase in almost all mean mineral N values occurred (+10 [I] / +2 [E] kg NO₃‐N ha^—1 and +10 [I] / —10 [E] kg NH₄‐N ha^—1). (3) In spite of the differences between both methods, the experiment shows that NO₃‐N leaching under extensive grazing could be reduced almost to levels close to those under mown grassland.     

Einfluß der Kaliumdüngung auf die Verfügbarkeit des Kaliums in K-fixierenden Böden im Verlaufe der Vegetationszeit

Effect of potassium fertilization on K-availability in potassium fixing soils over the vegetative period The effect of potassium fertilization on the K-availability over the course of the vegetative period was tested on nine potassium fixing soils over two years. The availability of potassium fertilized at the beginning of vegetative period falls (on a soil with 50% clay) to half of the original amount within one month. The availability decreases especially during the time without vegetation. Only after fertilization with 1200 kg K₂O/ha are substantial amounts of potassium available for the plants until the end of the vegetative period (determined by electroultrafiltration). An annual application of 300 kg K₂O/ha only slightly increased the CAL-K and exchangeable K in comparison with the unfertilized plots, although the plants showed marked yield responses. A significant improvement in potassium supply was not obtained with less than 600 kg K₂O/ha. The potassium wet fixation values are relatively constant on the plots without or with low K-fertilization: after high potassium application they show considerable fluctuation. The fixation potential is considerably reduced with an annual application of 1800 kg K₂O/ha, but is not completely removed. Potassium can be removed by repeated extraction with a dilute CaCl₂-solution but the rate at which it is released into the soil solution is too slow compared to the needs of rapidly growing crop plants. The rise in the level of available potassium by fertilization is reverse to the clay content. There was considerable variation between the different available potassium forms over the vegetative period on the highly fertilized plots; consequently a soil test made annually can only give a rough idea of the K-level in potassium fixing soils.