Prüfung der Nachwirkung organischer Düngungsstufen eines Stickstoffdauerdüngungsversuches (IOSDV/Oldenburg) im Gefäßversuch: (The after effect of long term different organic fertilisation of a permanent nitrogen fertiliser field experiment in a pot experiment)

Abstract

After nine experimental years in a field trial with four fertiliser treatments combined with five mineral N treatments and cultivation of sugar beets, winter wheat and winter barley yearly the after effect has been tested in a pot experiment with raygras. After the end of the field trial soil has been taken from all the four organic treatments, from two mineral N treatments and from each crop in the crop rotation. The after effect of nine years different organic fertilisation has been proved to be apparent, but is heavily covered by the effect of the precrop and partly also by the N-fertilisation in the field. Nevertheless the second organic fertiliser treatment (catch crop, straw, leaves of sugar beets) was concerning the after effect more effective compared with the treatment application of pig slurry yearly to all crops or the application of pig slurry once in three years to sugar beets.The effect of the last cultivated crop in the field trial influenced the after effect of grass in some cases significantly. Sugar beets were superior to winter wheat and winter barley.The N-contents in the grass and the N-uptake were significantly influenced by the additional N-application in the pot experiment. The other factors were only of small influence.Summarizing the results of the pot trial show, that after nine years different organic fertilisation no clear evaluation is possible about its after effect, due to partly significant interactions with the precrop and the mineral N-fertilisation.     

The impact of roads on the densities of four bird species in an open field habitat—evidence of a long-distance effect

Roads may effect animal communities in various ways. One such way is ‘di sturbance’, i.e. emission of stimuli to which animals may respond by avoiding the vicinity of the road. The extent, intensity and mechanism of this effect is almost entirely unknown. Veen (1973), studying the bird species lapwing Vanellus vanellus, black-tailed godwit Limosa limosa, oystercatcher Haematopus ostralegus, redshank Tringa totanus and ruff Philomachus pugnax in open grassland areas, found disturbance over surprisingly long distances, ranging from 500–600 m for a quiet rural road to 1600–1800m for a busy highway. However, his approach has met with serious methodological criticism.The validity of Veen's conclusions was tested by critically reanalysing bird distribution in one of his study plots. It is inferred that his conclusions do hold for the lapwing, the godwit and possibly the redshank, though not for the oystercatcher. An additional field study in four areas yielded similar results, with comparable disturbance distances. The total population loss over this distance may amount to 60%. Rough indications were obtained that the distance-density graph is a logistic one, while the relation between traffic volume and total population loss is possibly logarithmic. In addition confirmation was obtained of the general impression that, apart from roads, disturbance may also be caused by farms, other buildings and plantations, suggesting that disturbance caused by a road is not easily eliminated by planting trees alongside.It is recommended that extra care be taken in planning new roads, while impact statements concerning roads which disregard disturbance and other long-distance effects on the fauna should be rejected.     

Changes in the salinity of solonetzic soil complexes of the Ergeni Upland under long-term anthropogenic impact (soil studies at the Arshan’-Zel’men Experimental Station of the Russian Academy of Sciences)

Unique experiments performed since the 1950s at the Arshan’-Zel’men Experimental Station have formed the basis for afforestation in the dry steppe and semidesert zone without irrigation on the salt-affected soils of solonetzic soil complexes of the Ergeni Upland. Ameliorative measures favored the accumulation of productive moisture in the upper 2-m-thick soil layer, which ensured the growth of trees and the partial leaching of soluble salts to a depth of 1–1.4 m. However, no complete desalinization of the soil profiles took place. The degree of removal of exchangeable sodium from the exchange complex (soil dealkalization) was smaller. The monitoring of changes in the salt status of the soils upon agroforest reclamation was performed until the early 1980s. Our investigations of 2005–2006 showed that the soil amelioration is still in progress: the salt maximum in the profile of the solonetzes descended to a depth of 2.2 m, and the exchangeable sodium was lost from the plow layer (0–40 cm). Plowed soils between forest shelterbelts were also subjected to desalinization and dealkalization of their soil profile, though less intensely than those under the shelterbelts.     

Is the long-term application of sewage sludge turning soil into a sink for organic pollutants?: evidence from field studies in the Czech Republic

Purpose

Long-term microscale field experiments established at four sites in the Czech Republic (since 1996) were used for an assessment of the severity of the wide-scale contamination of treated soils by persistent organic pollutants (POPs) and pharmaceuticals and personal care products (PPCPs) as a result of the long-term regular pollutant load via sewage sludge and farmyard manure applications and for an estimation of the potential environmental risk caused by long-term pollutant inputs to agricultural soils.

Material and methods

The experimental plots were treated as follows: (i) NPK mineral fertilization (NPK); (ii) sewage sludge (SS1); (iii) sewage sludge applied at three times the rate compared to SS1 (SS2); (iv) farmyard manure (FYM); and (v) untreated control. Except for antibiotics, which showed results for all analyses below the detection limit, all groups of the analyzed compounds showed measurable contents in the treated soils.

Results and discussion

Among the POPs, the levels of organochlorine pesticides (OCPs) were detected at two locations at levels exceeding the Czech preventive values for their contents in agricultural soils (7.5 μg/kg for dichlorodiphenyl trichloroethane family, 20 μg/kg for hexachlorbenzene, and 10 μg/kg for α-hexachlorocyclohexane), regardless of the treatment. Similarly, elevated contents of polycyclic aromatic hydrocarbons (PAHs) were occasionally observed without any substantial relationship to the fertilizer application scenario. Thus, these contaminants are connected with atmospheric deposition in the given areas (PAHs) and their long-term stability (OCPs) even several decades after their ban; the role of the fertilizer composition was negligible.

Conclusions

The levels of per- and polyfluoroalkylated substances, brominated flame retardants, and synthetic musk compounds tended to increase in the sewage sludge–treated plots, indicating that sewage sludge can contribute to the abundance of these compounds in soil, although the contaminant levels determined do not represent a direct environmental risk. The levels of these contaminants in sewage sludge and sludge-treated soils should be regularly monitored in further research.

     

Methane oxidation,nitrification, and counts of methanotrophic bacteria in soils from a long-term fertilization experiment (”︁Ewiger Roggenbau” at Halle)

Aerobic soils are important sinks for atmospheric methane. CH₄ oxidation, mediated mainly by methanotrophic bacteria, is the responsible process, which is strongly inhibited by ammonium accessible for nitrification. An inhibitory effect immediately after fertilization as well as a long-term effect exists, which results from repeated ammonium applications and which is independent from the actual concentration of NH₄⁺-N in soil. This long-term effect could be caused by a shift in the microbial population of the soil. Thus, with soil samples from long-term fertilization treatments of the field experiment ”︁Ewiger Roggenbau” at Halle (Germany) incubation studies were conducted to investigate the interference between CH₄ oxidation and nitrification and to determine the cell numbers of methanotrophic bacteria. Including the treatments PK, NPK, and farmyard manure, which were established in 1878, a close negative correlation between CH₄ oxidation and net nitrification was found (r = —0.92). The CH₄ oxidation rates, determined with an initial concentration of 10 μl CH₄ l^—1, varied between 6.7 and 1.1 μg C kg^—1 d^—1 in the PK and NPK treatment, respectively. After application of NH₄Cl a strong inhibition of CH₄ oxidation occurred, which was 91%, 88%, 81%, and 63% in the treatments PK, NPK, FYM, and U (unfertilized), respectively. After a lag-phase of 2 to 3 weeks an incubation with high CH₄ concentrations (20 Vol.% CH₄) could induce CH₄ oxidizing activity in the NPK treatments under continuous rye or maize cropping. An increase of up to 40 times in comparison to the control under atmospheric CH₄ (2 μl CH₄ l^—1) was observed. A negative correlation (r = —0.74) existed between the CH₄ oxidation rates of the soils without recently applied NH₄⁺ and the numbers of methanotrophic bacteria, determined with the ”︁most probable number” method (MPN). Thus, the MPN technique is not suitable to characterize the physiologically active population of methanotrophic bacteria in soils, which oxidize CH₄ in the atmospheric concentration range. The results of this study suggest that in aerobic arable soils methanotrophic bacteria and not nitrifiers are responsible for CH₄ oxidation.     

What are the limits of the drilosphere? An incubation experiment using Metaphire posthuma

The near infrared reflectance spectroscopy (NIRS) method was used in the present study to compare earthworm-made soil aggregates to aggregates found in the surrounding bulk soil. After initially assessing the daily cast production of Metaphire posthuma, boxes with soil incubated with M. posthuma and control soils were subjected to wetting in order to reorganize the soil structure. After two months of incubation, soil aggregates produced by earthworms (casts and burrows), soil aggregates that were appeared to be unaffected by earthworms (bulk soil without visible trace of earthworm bioturbation from the earthworm treatment) and soil aggregates that were entirely unaffected by earthworms (control – no earthworm – treatment) were sampled and their chemical signatures analyzed by NIRS. The production of below-ground and surface casts reached 14.9 g soil g worm^?1 d^?1 and 1.4 g soil g worm^?1 d^?1, respectively. Soil aggregates from the control soils had a significantly different NIRS signature from those sampled from boxes with earthworms. However, within the earthworm incubation boxes the NIRS signature was similar between cast and burrow aggregates and soil aggregates from the surrounding bulk soil. We conclude that the high cast production by M. posthuma and the regular reorganization of the soil structure by water flow in and through the soil lead to a relatively homogenous soil structure. Given these results, we question the relevance of considering the bulk soil that has no visible activity of earthworm activity as a control to determine the effect of earthworms on soil functioning.     

Dynamics of soil properties and organic carbon pool in topsoil of zokor-made mounds at an alpine site of the Qinghai–Tibetan Plateau

The population of burrowing plateau zokors (Myospalax baileyi) was markedly increased in the Qinghai–Tibetan Plateau. The objective of this study was to investigate the effects of zokor foraging and mound-making disturbance on topsoil properties and organic C pools at an alpine site of the Qinghai–Tibetan Plateau. Surface (0–15 cm) soil samples were collected from mounds with different ages (3 months and 3, 6, and 15 years) and from undisturbed grassland. Above- and below-ground plant biomasses were depleted by zokors in newly created mounds (3 months). Plant cover and root biomass gradually recovered thereafter, but were still lower in the 15-year-old mounds than in the undisturbed soils. Organic C contents of coarse (>2 mm), soil (<2 mm), particulate (2–0.05 mm) fractions, and microbial biomass, organic C mineralization, β-glucosidase activity, urease activity, alkaline phosphatase activity, acid phosphatase activity, and soil aggregation were significantly lower in the 3, 6, and 15-year-old mound soils than in the undisturbed soils or newly created mound soils. Fifteen years after mound creation, the soil had only 12% of root biomass, 35% of coarse organic C, 83% of particulate organic C, 58% of microbial biomass C, 57% of 30-day respired C, and 45% of water-stable aggregate mean weight diameter, compared to values of the undisturbed soils. Our results suggested that foraging and mound-making by zokors have negative impacts on properties and organic matter content of the topsoil.     

From a stinking wastewater disposal field toward a recreation area—the story of an unconventional soil remediation in Berlin,Germany

Purpose

Wastewater irrigation is still a common practice in many cities worldwide. After ending the wastewater irrigation, the question arises as to how the highly polluted areas can be reused. Mostly, the remediation costs for liming or adding synthetic soil conditioners are too high for decision makers, often leading to unattractive wastelands in neighboring suburbs. This story shows how part of a former wastewater disposal field in Berlin (Germany) was remediated by adding and mixing loam-rich glacial until excavated from subway construction work. The remediation led to long-term improvements of soil and landscape, which nowadays is an attractive forested recreation area. Part of this landscape is used as an ecological lab for research, art, and education.

Materials and methods

The article summarizes the results of soil analysis of the contamination status and remediation technique over the last 2 decades. We collected and reevaluated historical data, research results, technical reports, and graphic materials concerning the wastewater disposal field in Berlin, Germany.

Results and discussion

The remediation concept without adding any synthetic substances was a successful soft technology leading to (i) a reduction of the long-term groundwater risk, (ii) an immobilization of the trace element concentration in the soil solution, and (iii) a reduction of the metal uptake by plants. Remediation led to much better conditions for plant growth, soil fauna, and microbiological activity, which improved the environment in a sustainable way. The implementation of a new landscape concept combining ecology, culture, and art totally changed the character of the landscape from former stinking wastewater fields to present-day attractive sites that can be used for many purposes.

Conclusions

The remediation of the former wastewater disposal fields, using natural glacial till materials rich in clay and silt, became a “story of success.” However, a remediation project of this type and scope only becomes reality if all responsible actors in society participate continuously. We conclude that stakeholders should not focus only on remediation costs but also on the benefits for society: reclaiming waste sites significantly improves our well-being.

     

Reconstruction of Climate,Soils, and Vegetation in the Turan–Uyuk Basin of South Siberia at the Beginning of the Subatlantic Period of the Holocene

Four Scythian kurgans of the burial site Beloe Lake-3 were studied in the Turan–Uyuk Depression in the Republic of Tyva. They were constructed about 2565–2390 calendar years ago (calibrated with deviation 1 σ). Soil formation after 2500 yrs of the construction of the kurgans was examined in the interkurgan area. The properties of the background surface and ancient buried soils have much in common, and the difference between the soils of the four kurgans is small. This attests to the fact that the paleoclimatic conditions in the period of the necropolis construction remained stable and were similar to the modern climatic conditions. According to palynological data, the climate at the stage of the construction of the first two kurgans was a little more humid in comparison with the modern climate; it became somewhat drier after 95 years, during the construction of the third kurgan (2425 cal. BP) and again tended to humidification at the final stage of the necropolis creation. These changes in the paleoclimatic conditions are indicated by variations in the structure and composition of associations of xerophytes, mesophytes, hydrophytes, and ruderal plants. At the Uyuk stage, the area was mainly occupied by steppe phytocenoses with a predominance of xerophytes over mesophytes, and hydrophilous vegetation was allocated to moistened habitats near water reservoirs. Larch forests grew near water bodies. The variable anthropogenic impact on the landscape was stronger at the initial and final stages of the construction of the Uyuk culture necropolis.     

Vertical stratification and trophic interactions among organisms of a soil decomposer food web – a field experiment using 15N as a tool

In this field study, we explored the spatial segregation between the litter- and humus-inhabiting organisms of the detrital food web using ¹⁵N-isotope technique. The study was established in 11 × 11 m plots fertilized with ¹⁵N-labelled urea. Ten years after urea application, soil samples were taken, both from the litter layer and the combined F+H layer. The samples were analysed for N content and the proportion of ¹⁵N in (i) the residual organic matter in the litter and F+H layer (excluding microbes), (ii) microbial biomass, and (iii) various feeding guilds of soil fauna. The basal resource, soil microbes, and the fauna were more enriched with ¹⁵N in the F+H layer than in the litter layer. In the litter layer, the ¹⁵N enrichment of the expected food source equalled the one of the consumers, whereas in the F+H layer all trophic groups, except microbes and small microbi-detritivores, showed a significantly lower ¹⁵N enrichment than their expected food source. The results indicate that large and mobile humus-inhabiting decomposers exploit the overlying litter layer as a feeding site, whereas the feeding of the more sedentary smaller organisms is restricted to the humus layer.     

Distribution profiles of dry matter and total nitrogen in leaves and stems of oriental field‐grown tobacco plants at different nitrogen levels

Oriental tobacco plants (Nicotiana tabacum L. cv Myrodata Agrinion) were grown without nitrogen (N) fertilization (N₀) and with added ammonium nitrate at a rate of 50 kg‐ha^‐1 (N₁) and 100 kg‐ha^‐1 (N₂). Non‐uniform patterns for leaf FW and DW changes per node showed a decreasing trend from lower to upper nodes during the vegetative stage. From approaching flowering to fruit set, these patterns became more uniform. Plants which were fertilized with N had increased leaf FW and DW accumulation levels and non‐uniform distribution patterns, primarily during the reproductive stage, and leaves of the lower nodes were found in the older plants. By contrast, the median values of leaf FW for the unfertilized plants were reduced during the reproductive period. The DW/FW×100 ratio values revealed a stable relationship between leaf FW and DW from the vegetative to the reproductive stage, while modified patterns of DW/FW×100 appeared later in the plant cycle. Nitrogen fertilization resulted in an early appearance of modified patterns of DW/FW×100 in the plant life cycle and higher accumulation of dry matter per unit leaf area. Patterns of total leaf N concentration showed an increasing trend from the lower to the upper nodes for all plant ages and treatments. Total N concentration values varied from 1.6%, 1.9%, and 1.8% on a dry matter basis, for the lower node up to 5.5%, 6.3%, and 6.1% for the upper node in young tobacco plants in the N _o , N₁, and N ₂ treatments, respectively. After fruit set, a more uniform distribution of total leaf N was observed among the leaves in all treatments. Concentration values for total leaf N in older plants varied from 1.9%, 2.1%, and 2.2% for the lower node up to 3.4%, 3.3% and 3.2% for the upper node in the N ₀ , N₁, and N₂ treatments, respectively. These results suggest a progressive decrease with plant age for total leaf N concentration in the plant as a whole. The increased N fertilizer level affected the total N level in young plants but not in the older ones. Inflorescence and fruit set periods are critical for plant N balance except for the plants which received the increased N fertilization. The determined total stem N concentration was less than that for the leaves. This change in the stem, similar to leaves, showed an increasing trend from the basal to the upper part and a decreasing trend from the vegetative to the reproductive stage. The total stem N level declined from 1.0–1.2%, 1.6–1.7%, and 2.2–2.9% on a dry matter basis to 0.5–0.6%, 1.0–1.2%, and 1.2–1.6% for the basal, middle, and upper part of the stem, respectively.     

Spatial variation of nitrate–N and related soil properties at the plot-scale

Neglecting the spatial variation in soil nutrient status may result in unused yield potential and in environmental damage. Site-specific management has been suggested to reduce inappropriate fertilization that can adversely affect soil, ground and surface water. Decision criteria for determining variable-rate nitrogen fertilization are, however, lacking. This paper analyses the spatial variation of nitrate nitrogen (NO₃–N) and soil properties related to the N cycle at the plot-scale. Three 50×50 m plots were sampled in nested sampling designs of varying complexities. Classical statistics revealed a characteristic ranking in the variability of soil properties. Geostatistical analysis of the NO₃–N data from two plots showed that the small-scale variation found in one small subgrid was not typical for the small-scale variation in the entire plot, indicating bias in the sampling design. A trend component was found in the NO₃–N data and, consequently, the minimal requirement for the regionalized variable theory was not fulfilled. Problems due to design were overcome with a more complex nested sampling at the third plot. However, the spherical model fitted to the NO₃–N data of the first year explained only 21% of the total variance, whereas a pure nugget effect was observed in the second year. The water content data also showed a low structural variance, which was different in the two years. In contrast, two thirds of the variance of total carbon (C_t) and total nitrogen (N_t) could be explained by the fitted models. Seasonal variations, such as varying duration of snow cover, and extrinsic management effects, such as growing of a cover crop, may have contributed to the observed differences in variability between the years. Due to the low proportion of structural variance and the observation that spatial distribution was not stable with time, geostatistical analysis of NO₃–N and water contents data added only little information to classical statistical analysis. However, geostatistical analysis of total C and N contents provided a useful means to calculate spatial distribution patterns of these properties.     

Covered catchment experiment at Gårdsjön: changes in runoff chemistry after four years of experimentally reduced acid deposition

Atmospheric deposition was almost entirely excluded from the forested headwater catchment G1 ROOF, by means of a 7000 m² plastic roof that prevents rain and throughfall from reaching the ground. Under the roof an irrigation system was installed to simulate a natural precipitation regime. The intercepted throughfall was substituted by the same amount of clean pre-industrial throughfall. The experiment started in April 1991. During the four years of the treatment, 2960 mm (18 600 m³) of sprinkled solution was applied under the roof, which is about 15 times the mean water storage of the catchment. After four years of treatment major changes in runoff chemistry were observed. The exclusion of all non-marine sulphate (SO₄ ^2–) input to the catchment (i.e. ca 75 % of total SO₄ ^2– input excluded) resulted in significant decline of sulphate in runoff through all four years of treatment. During the fourth year, annual volume weighted SO₄ ^2– concentration was 46 % lower than the two years prior to the treatment. Concentrations of inorganic aluminium Al³⁺ declined 52 % and Mg²⁺ declined 54 %. No change of H⁺ concentration was detected. As the treatment proceeds there seems to be a trend towards less negative acid neutralising capacity in runoff.     

To what extent can multifractal measures provide an accurate model of the porosity of soils?

Over the last decades, several authors have suggested that multifractal measures, that is, self-similar measures defined on fractal or non-fractal objects, could be useful to describe soil properties, to model soil processes, and to deal with their extreme microscale heterogeneity. In this context, a key question relates to the extent to which multifractal measures can indeed fulfill all the expectations they have generated. To address this question, we discuss the possibility of generating a synthetic soil image exhibiting multifractal porosity. To this end, a simple geometrical multifractal model in 2D is developed, which helps us to better understand the concept of multifractality and to generate images. We show that it is possible to generate synthetic binary images over a limited range of scales, but that a pure multifractal model for the distribution of the solid or pore mass cannot be developed due to physical constraints. Moreover, in the generated images mimicking multifractal solid space, a higher degree of multifractality corresponds to a larger porosity, rendering it difficult to tune model parameters to match actual soil properties. In addition, simple statistics relying on power-law fits appear insufficient to characterize soil architecture even if they may capture some key multiscale indicators of observed spatial heterogeneity. We argue that the same conclusions would be reached in a three-dimensional space, as well as for grey-scales images.     

Can a simple measure of vigorous physical activity predict future mortality? Results from the OXCHECK study

BACKGROUND: As epidemiological studies have become more complex, demands for short, easily administered measures of risk factors have increased. This study investigates whether such a measure of physical activity is associated with the risk of death from all causes and death from specific causes. METHODS: A prospective follow-up study of 11,090 men and women, aged 35-64 years, recruited from five UK general practices who responded to a postal questionnaire in 1989. Self-reported frequency of vigorous-intensity physical activity and data on confounding factors were collected at baseline survey. Death notifications up to 31 December 2001 were provided by the Office for National Statistics. The relative risk (and 95% confidence interval) of dying associated with each level of exposure to physical activity was estimated by the hazard ratio in a series of Cox regression models. RESULTS: After >10 years' follow-up there were 825 deaths among the 10 522 subjects with no previous history of angina or myocardial infarction. Participation in vigorous exercise was associated with a significantly lower risk of all-cause mortality. Similar associations were found for ischaemic heart disease and cancer mortality, although the relationships were not significant at the 5% level. CONCLUSIONS: Simple measures of self-reported vigorous physical activity are associated with the risk of future mortality, at least all-cause mortality in a somewhat selected group. Interpretation of the finding should be treated with caution due to the reliance on self-report and the possibility that residual confounding may underlie the associations. Because moderate-intensity physical activity is also beneficial to health, short physical activity questionnaires should include measures of such physical activity in the future.     

Use of geophysical methods for the study of sandy soils under Campinarana at the National Park of Viruá, Roraima state,Brazilian Amazonia

Purpose

The vegetation of the Campinaranas occurs in humid areas with hydromorphic sandy soils at the Amazon region. Thus, the determination and in situ monitoring of moisture content in Campinarana soils, besides the detection of subsurface layers are key measures for studying these soil–vegetation systems. Also, the application of ground penetrating radar (GPR) in deep sandy sedimentary sequence of Amazonia is a promising tool to enhance the knowledge on depositional and soil formation features.

Materials and methods

We studied representative soils of the Campinaranas at the National Park of Viruá, state of Roraima (Brazilian Amazonia), through the use of geophysical methods (soil moisture sensors and GPR). The study was applied in four sandy soils. Besides chemical and physical analysis of soils, soil moisture sensors were installed for monitoring during an entire hydrological year (2010/2011), and performed the calibration of sensors , coupled with imaging of the soil along transects with GPR.

Results and discussion

As a result of calibration of the soil moisture sensors we obtained a general equation with an R ² greater than 0.9. There is an influence of soil moisture content and soil temperature in the distribution of vegetation types in Campinaranas. The use of GPR identified some determinants characteristics in these soils for the differentiating the Campinaranas, represented by spodic and C horizons.

Conclusions

The spodic horizons in soils under Forest Campinarana provided potential errors in the determination of soil moisture, requiring calibration data for the precise use of this device. The investigation of the soil through the GPR showed interesting results, which allowed continuous visualization of the main soil horizons along transects in the phytophysiognomies of Campinaranas.     

Nitrification and denitrification in an acidic soil of tea (Camellia sinensis L.) field estimated by δ15N values of leached nitrogen from the soil columns treated with ammonium nitrate in the presence or absence of a nitrification inhibitor and with slow-release fertilizers

Forty-two-day-old wheat (Triticum aestivum L. var. Asakazekomugi) plants were treated with complete, K-free (—K), Ca-limited (—Ca), and Mg-free (—Mg) nutrient solutions for 10 days using 2 mM NH₄NO₃ as the nitrogen source, which was replaced with 4 mM ¹⁵ NH₄C1 or Na¹⁵NO₃ for the subsequent 2 days to investigate the absorption, translocation, and assimilation of inorganic nitrogen in relation to the mineral supply. In another experiment plants were grown on NO₃ ^?, NH₄ ⁺, NH₄N0₃, and K-free and Ca-limited NH₄N0₃ nutrient solutions for 10 days, and then in the latter three treatments the nitrogen source was replaced with NO₃ ^? and half of the —K plants received K for 6 days to examine the changes in the nitrate reductase activity (NRA).

Wheat plants absorbed NH₄ ^?N and NO₃-N at a similar rate. Influence of K on the absorption of N0₃-N was stronger than that on the absorption of NH₄-N in wheat plants. The supply of K to the —K plants increased the absorption of NO₃-N, while the absorption of NH₄-N still remained at a lower rate in spite of the addition of K. A limited supply of Ca and lack of Mg in nutrient media slightly affected the absorption of NH₄-N. The influence of K was stronger on the translocation of nitrogen from roots to shoots, while Ca and Mg had little effect. When K was supplied again to the —K plants the translocation of NO₃,-N was more accelerated than that of NH₄-N. Incorporation of NH₄-N into protein was higher than that of NO₃-N in all the tissues; root, stem, and leaf. Assimilation of NH₄-N and NO₃-N decreased by the —K and —Mg treatments.

Leaf NRA of wheat plants decreased in the —K and —Ca plants. Higher leaf NRA was found when K was given again to the —K plants than when the plants were continuously grown in K-free media. Replacement of NO₃ ^? with NH₄ ⁺ as the nitrogen source caused a decline of leaf NRA, while the supply of both NH₄ ^?N and NO₃-N slightly affected the leaf NRA.