Loess Loam Research Articles

Weathering intensity and pedostratigraphy of the Middle to Upper Pleistocene loess/palaeosol sequence of Wels-Aschet (Upper Austria)

On top of a fluvioglacial terrace near Wels-Aschet, a complex loess/palaeosol sequence has been investigated. To date, the terrace is classified as a classical Günz unit (Older Deckenschotter). Sedimentological and mineralogical analyses were carried out on the basis of palaeopedological field data. The results show that in terms of mineralogical composition, the palaeosols can clearly be differentiated and are characterised throughout by interglacial weathering intensity. Bulk mineralogical as well as clay mineralogical data allow a five-stage ranking of weathering intensity based on indicator minerals. From the bulk mineralogical perspective, slightly weathered loess still contains carbonate minerals and primary chlorite, whereas the intensely weathered soil horizons are characterised by the total or near absence of carbonate minerals and primary chlorite, micas, and feldspars. In clay mineralogical results, chlorite and the relation of 14Å- and 18Å-vermiculites, as well as mixed layer minerals, play an important role in determining the weathering stage. Primary chlorite can be present in slightly weathered loess loams, and vermiculite 14Å is dominant there (stage 1 and 2). From weathering stage 3 onwards, the amount of vermiculite 18Å increases considerably and dominates the following stage 4. Most intensive weathering causes the absence of illite (stage 5). Generally, the studied interglacial palaeosols belong to at least stage 3. With the applied methodology, four interglacial palaeosols have been demarcated, as well as a highly weathered palaeosol within the terrace gravels of the Günz in Wels-Aschet.Pedostratigrapy points to a classification of the Older Deckenschotter in MIS 14 at minimum. However, since this glacial period was of low intensity and the weathering intensity of the basal palaeosol was significantly enhanced, a correlation of the Günz terrace with MIS 16 also seems possible.

The dependence of soil H2 uptake on temperature and moisture: a reanalysis of laboratory data

In the past two types of laboratory experiments have been employed to determine the dependence of H2 uptake by soils on temperature and moisture: Head space and flow experiments. The former actually measure the rate constant of the H2 removal from the head space, kH, the latter the uptake rate of H2, UH2, both caused by a given volume of soil. From an analytical solution of the diffusion equation in the soil we derive a mathematical relation between kH and ks, the desired uptake rate constant of H2 in soil. Another equation relates UH2 with ks. Both types of experiments actually determine the product of ks with Θa, the air-filled pore volume fraction. ks.Θa for eolian sand and loess loam show zero uptake at very low and high moisture contents and a well defined maximum in between. Unlike soil moisture which also acts on the soil properties, the soil temperature, T, acts essentially on the enzyme activity only. Thus ks(T) is directly proportional to kH(T) or UH2(T) and the data of all experiments can be superimposed by scaling. The resulting average ks(T) shows a broad maximum around 30◦C with zero uptake below −20◦C and above 80◦C.

Modeling ferricyanide adsorption on goethite: Basics and applications

AbstractFerricyanide, [FeIII(CN)6]3–, is an anthropogenic and potentially toxic contaminant in soil. Its adsorption on goethite has been previously studied, but not evaluated with a surface complexation model (SCM) considering the effects of pH and ionic strength. Therefore, we carried out batch experiments with ferricyanide and goethite suspensions with different ferricyanide concentrations (0.075 mM and 0.15 mM), ionic strengths (0.01 and 0.1 M), and pH (ranging from 4 to 7.4). Adsorption data were then interpreted with the 1‐pK Stern and the charge distribution model assuming monodentate inner‐sphere ferricyanide surface complexes on goethite (lg K = 10.6), which are known from infrared spectroscopy. Furthermore, we applied the SCM to ferricyanide adsorption in previous studies on ferricyanide adsorption in the presence of sulfate and on the solubility of Fe‐cyanide complexes in a suspension of a loess loam. The SCM correctly reflected ferricyanide adsorption in the batch experiments as well as the effects of pH and ionic strength. The SCM also described ferricyanide adsorption in the presence of sulfate, because the ferricyanide adsorption measured and that modeled were significantly correlated (R2 = 0.80). Furthermore, we applied the SCM to a study on the solubility of Fe‐cyanide complexes in soil under varying redox conditions so that ferricyanide adsorption on goethite and precipitation of Fe‐cyanide complexes were considered. The actual ferricyanide concentrations were rather reflected when applying the SCM compared to those modeled in an approach in which exclusively precipitation was taken into account. We conclude that ferricyanide adsorption on goethite should be included into geochemical modeling approaches on the mobility of Fe‐cyanide complexes in subsoils.

Ca-Fe3+-rich, Si-undersaturated buchite from Zelenky, North-Bohemian Brown Coal Basin, Czech Republic

Si-undersaturated Ca-Fe-rich buchite produced by fossil burning of a coal seam occurs in porcelanite deposit at Želenky in the North-Bohemian Brown Coal Basin, Czech Republic. Buchite is highly inhomogeneous, dense (ρ = 2.9–3.1 g/cm 3 ), strongly magnetic rock (10 −2 −10 −1 [SI]) composed of melilite, clinopyroxene (esseneite), spinel-group minerals, hematite, Ca 2 SiO 4 , calcite, aragonite, anorthite, anhydrite, perovskite, barite, two calcium ferrites - orthorhombic Ca 2 Fe 2 3+ O 5 (srebrodolskite) and CaFe 4 3+ O 7 , barium hexaferrite - BaFe 12 3+ O 19 , along with other several poorly identified phases. Clinopyroxene is rich in esseneite component (19–63 mol. %) and in a hypothetical end-member CaFe 3+ Fe 3+ SiO 6 (up to 25 mol. %) due to Fe 3+ substitution in tetrahedral sites (up to 0.26 apfu), and also in a hypothetical component Ca(Fe 2+ Mg) 0.5 Ti 0.5 AlSiO 6 (2–36 mol. %) due to incorporation of Ti (0.012–0.18 apfu), in M1 site. Melilite shows a wide compositional variability (mol. %): gehlenite 21–93, ferrigehlenite 0–34, akermanite 1–49, ferroakermanite 0–25, soda-melilite 0–15. Spinel-group minerals show solid solutions of Mf 12–80, Mt 1–62, Sp 2–68, Hc 0–21 (mol. %). Srebrodolskite, orthorhombic Ca 2 (Fe 3+ Al) 2 O 5 is widely substituted by Si and Ti. There are negative correlations among Fe + Al vs. Si + Ti ( R 2 = 0.998), and Ca (or R 2+ ) vs. total vacancy ( R 2 = 0.94), which are consistent with an exchange vector 2R 4+ □2R 3+ -1 Ca -1 , and suggest a hypothetical end-member Ca □ (SiTi) 2 O 5 . Calcium ferrite associated with srebrodolskite, ideally CaFe 4 3+ O 7 , shows extensive compositional variability: Ca 0.6–0.8 Fe 3+ 2.7–3.6 Al 0.1–0.6 Mg 0.2–0.6 Si 0.1–0.5 O 7 . First natural occurrence of barium hexaferrite, (Ba 0.6–1.1 Ca 0.1–0.2 )(Fe 3+ 10.0–11.7 Al 0.3–0.9 Ti 0.1–0.6 Mg 0.1–0.4 Mn 0.0–0.2 ) O 19 , ideally BaFe 3+ 12 O 19 , is reported. Variations of magnetic susceptibility with temperature were also investigated. Buchite originated by fusion of Tertiary clay and residual ash with overlying Quaternary sediments (loess loam with carbonate horizon) during fossil combustion of Miocene coal seam.

Aspects of nitrogen use efficiency of cauliflower I. A simulation modelling based analysis of nitrogen availability under field conditions

Data from several field experiments (eight crops grown under a widely varying nitrogen supply on a loess loam soil) were used for a simulation modelling based analysis of nitrogen availability of cauliflower. The model was built out of components describing root growth, nitrate transport to the roots and the vertical nitrate transport within the soil.Root observations obtained over 2 years indicated an increased fraction of dry matter allocated to the fine roots under N deficiency. An adopted version of a root growth model for cauliflower described the rooting data with an R2=0·75. Based upon an acceptable description of the soil water budget, vertical nitrate movement during the growth period of cauliflower was accurately described. The magnitude of this movement, however, was limited to soil depths of about 60 cm even after periods of high rainfall, because of a high soil water holding capacity. An analysis of the factors determining nitrate availability indicated that apparent mass flow was only of high importance for conditions of extremely high N supply where high amounts of nitrate nitrogen remain in the soil up to the end of the growing season. Otherwise, the dominating fraction of nitrate has to be transported to the roots by diffusion. Single root model based calculations of maximum nitrate transport to roots overestimated N availability as indicated by estimates of critical soil nitrate N that were too low. The introduction of a restricted uptake activity period of the roots was used to bridge the gap between theoretical calculations and empirical results. Scenario calculations were carried out to obtain functional relationships between N supply and residual soil nitrate levels for different soil conditions and management practices.

Effects of shallow water table on capillary contribution, evapotranspiration, and crop coefficient of maize and winter wheat in a semi-arid region

A lysimeter experiment was conducted during 19866—96 to study the impacts of groundwater tables on the capillary contribution, evapotranspiration, and crop coefficient of maize and winter wheat grown in a semi-arid region in loess loam soils. The depth of groundwater table was set to 0.5, 0.8, 1.0, 1.2, 1.5, 2.0, and 2.50 m, respectively. The results showed that the rate of capillary contribution from groundwater to crop root-zone was influenced mainly by the depth of the water tables. The daily variation in capillary contribution was not the same as pan evaporation; the peak was delayed when the water table was >0.8 m, and the time of delay increased with the depth of water table. The crop evapotranspiration was decreased with increasing groundwater table in the early growth period and harvest period. The maximum evapotranspiration occurred at 1.2 m groundwater table in the other periods. Values of crop coefficients (K c ) were estimated based on the measured evapotranspiration (ET) and reference crop ET computed by the modified Penman method. The estimated K c was significantly different from the values computed and used in the region in the absence of groundwater table effects, and it varied markedly with groundwater tables. Relationships between the crop coefficient and the depth of groundwater table were developed using mean crop coefficients derived from multi-year data. It was found that linear model was better for the period Octobermp;mdash;February in the winter wheat growing season and June in the summer maize growing season. The polynomial model was suitable for the period March;mdahs;June in the winter wheat growing season and from July to October in the summer maize growing season.

Description of the test area and reference sampling at Dornach

The selected test area for the comparative evaluation of European methods on sampling and sample preparation of soils (CEEM Soil) at Dornach near Basel (Switzerland) is located at approximately 400 m a.S.l. on the north-west rolling footslope of the Jura mountain chain that has a temperate climate. The area is known to be airborne polluted by emissions of a non-ferrous metal recycling plant. The geology is dominated by Jurassic limestone and (decarbonated) loess loam. The land use is deciduous forest (beech, oak) in the upper part and traditional cherry orchards with permanent grassland which have mostly been converted into arable land. The detailed soil survey distinguishes four different soil mapping units in the test area of 0.61 ha. The reference sampling was performed in a 190-m-long and 20–40 m large transect area following four devices: (1) composite samples (0–10 cm and 0–20 cm), each from 25 stratified single samples of 61 squares of 10×10 m; (2) hypotheses and soil horizon-based composite samples at nine locations; (3) horizon-related samples from the four described soil profiles representing the mapping units; and (4) three soil cores with 5-cm interval samples taken in the major land use units. Altogether 301 reference soil samples were taken.

The central role of microbial activity for iron acquisition in maize and sunflower

Maize (Zea mays L.) and sunflower (Helianthus annuus L.) grown on a calcareous soil showed poor growth and/or were chlorotic in spite of abundant Fe in the roots. It has been hypothesized that microbial siderophores chelate Fe (III) in the soil, and that in this form Fe is transported towards the root apoplast. On the calcareous soil, total and apoplastic root Fe concentrations were high, probably because of a high apoplastic pH depressing Fe (III)-reductase activity and thus the Fe2+ supply to the cytoplasm. On the acidic soil, total and apoplastic root Fe concentrations were low, probably because of a low apoplastic pH favouring Fe (III) reduction, hence plants showed no Fe-deficiency symptoms. The main objective of the present work was to investigate the role of microbial soil activity in plant Fe acquisition. For this purpose, plants were grown under sterile and non-sterile conditions on a loess loam soil. Plants cultivated under non-sterile conditions grew well, showed no Fe-deficiency symptoms and had fairly high Fe concentrations in the roots in contrast to plants grown in the sterile medium. Low root and leaf Fe concentrations in the axenic treatments indicated that the production of microbial siderophores was totally suppressed. Accordingly, sunflowers were severely chlorotic and this was associated with very poor growth, whereas in maize only growth was drastically reduced. In maize under sterile conditions, root apoplastic and total Fe concentrations were not as low as in sunflowers, which may have indicated that phytosiderophores produced in maize partly sustained Fe acquisition, but due to poor growth were not as efficient in supplying Fe as microbial activity under natural conditions. It may be therefore assumed that in natural habitats soil microbial activity is of pivotal importance for plant Fe acquisition.

Root growth of cauliflower ( Brassica oleracea L. botrytis) under unstressed conditions: Measurement and modelling

Root observations were carried out on cauliflower using the minirhizotron and the soil core method in two years on two locations with different soil types, a loess loam and a humic loamy sand. Total root length (RL) (cm cm-2) of cauliflower was correlated to total shoot dry weight (Wsh) (g m-2) RL=0.0124(±0.005)s*Wsh, r2=0.76. There was an acceptable correlation (r2=0.88) between the minirhizotron and the soil core methods for the sub-soil data, whereas the minirhizotron method underestimated rooting intensity for the top soil. Changes in rooting depth over time could be described for both soil types using a segmented function of temperature sum, consisting of an early exponential and a later linear phase. The increase of rooting depth during the linear phase was 0.107(±0.01) cm °C-1 d-1. A simple descriptive root growth model based on the assumptions of a negative exponential decline of root length density (RLD) with soil depth, of a fixed ratio of RLD at the top of the soil profile and at rooting depth (rRLD) and of a fixed fraction of dry matter increase allocated to fine-roots (ffR) was formulated and used to describe the temporal and spatial variation of RLD found in the field. Slightly different estimates of ffR and of rRLD could be found for the different soil types, indicating a higher fraction of fine-root dry matter for the loess loam soil and a somewhat deeper root system for the humic loamy sand soil. A cross validation using the parameter values obtained from adjusting to the rooting data of one soil type for predicting RLD values of the other soil type, however, indicated that still quite satisfactory estimates (r2=0.91 and 0.95) of RLD could be obtained.

Influence of genotype on phosphate uptake and utilization efficiencies in spring barley

To investigate the genetic variation of phosphate (P) uptake and P utilization efficiency, 24 high-yielding spring barley cultivars were grown in two pot experiments on a loess loam–sand mixture. In the first experiment, the plants grew until maturity under P stress (50% of the maximum yield), and in the second experiment, the plants grew until the stage of tillering (DC 25) at a low or at a high P supply. At maturity, the range between cultivars with the highest and the lowest values were 30% for total dm yield (grain and straw), 28% for grain yield, 24% for P uptake efficiency (P in grain and straw), 26% for P concentration in grains and 24% for P utilization efficiency quotient PEQ (g dm grain per mg P in shoots) (mean of all cultivars=100%). Grain yield was correlated with P uptake per plant, r=0.71***, and with PEQ, r=0.60**. Between P uptake and PEQ, there was only a weak relationship ( r=−0.14). Therefore, a combination of high uptake efficiency and high PEQ in a cultivar may be possible. At growth stage DC 25, the cultivars showed a significant variability in shoot biomass, P concentration, P removal, P influx, acitvity of acid phophatases (P ase) and root length. The ranking of the cultivars, however, was very different at the two P levels, but the root-length and the P ase activity were more influenced by genotype than by the P supply. As the relationships between grain yield, P removal, PEQ and the characters of the young plants cultivated under P stress were very weak ( r<0.43), selection for P efficiency at the stage of tillering cannot be recommended.

Diffusion and solid speciation of Cd and Pb in clay liners

For the assessment of the long-term sorption behavior of landfill clay liners towards contaminants the information given by distribution coefficients or retardation factors is not sufficient. Information regarding the solid speciation, which describes the actual bonding sites of sorbed contaminants, is required. The objective of the study presented in this paper was to analyze the retardation and solid speciation of Cd and Pb migrating into an illitic/smectitic loess loam by diffusion. Apparent diffusion coefficients as obtained from diffusion experiments on compacted loess loam with heavy metal solutions containing 0.001 M Cd or Pb chloride were in the range of 4.9–6.7·10 −8 cm 2/s for Cd and 3.6–7.4·10 −9 cm 2/s for Pb. The solid speciation was analyzed using a sequential extraction procedure giving operationally defined fractions (i.e. exchangeable, carbonatic, oxidic, organic, and residual fraction) of the sorbed heavy metals. The amounts of Cd and Pb migrated into the loess loam by diffusion clearly showed weaker bonding than the geogenic fraction. The speciation itself was significantly dependent on the heavy metal load showing weak bonding at high concentrations and strong bonding at low concentrations. Chemical extraction procedures can be used to analyse the sorption capacity of individual phases of the liner material towards heavy metals. Langmuir adsorption isotherms could be constructed for the individual operationally defined fractions, and the adsorption maxima and affinity parameters of these fractions could be determined. The results show that the specific sorption sites only have a limited capacity for heavy metals compared to nonspecific adsorption sites as represented particularly by the exchangeable fraction. Set in relation to the total sorption capacity of the investigated loess loam towards Cd and Pb, nonexchangeable bound species amount to only 7% (Cd) and 28% (Pb) for the carbonatic fraction, 1% (Cd) and 4% (Pb) for the oxidic fraction, and 0.5% (Cd) and 1% (Pb) for each the organic and residual fraction. The results emphasise that chemical extraction procedures can give important indications about the way heavy metals are actually fixed to the components of a landfill clay liner material.

Nitrogen balance and soil nitrogen dynamics in two areas with different soil, climatic and cropping conditions

Investigations were carried out on the effect of reduced N fertilization on yield, N balances and nitrogen leaching in two watersheds representative of North Germany. N fertilization was reduced according to the expected N offtakes by the crops. The aim of this study was to evaluate the influence of the various N fertilization regimes on N balance, N dynamics in soil, N leaching and crop yield. The usual N fertilization intensity in both watersheds was characterized by a N input excess of 50–80 kg N ha −1 year −1. On fields which regularly received organic manure, N input surpluses of 210 kg N ha −1 year −1 were found. Reducing the usual mineral N fertilization by 45–55 kg N ha −1 year −1 in a sugar beet/winter wheat rotation on a loess loam soil had a negligible effect on the yields (2–4% reduction) while NO 3 concentrations in the soil solution and NO 3 leaching were reduced. In contrast, on two sandy soils, yield decreases of sugar beet, winter rape and spring barley were more severe (5–17% reduction) when the mineral N fertilization was reduced, but omitting organic manure application had little effect. On these soils, the NO 3 − content of the soil solution and N leaching was less affected or even increased by a reduction of fertilizer input.

The effect of carbonates and gypsum precipitation in the root zone on the chemical composition of groundwater

Dissolution of a solid phase in the unsaturated zone is usually assumed to be the main factor transforming the composition of atmospheric water to that of groundwater. However, the opposite mechanism, namely a precipitation of insoluble and slightly soluble salts from rain water penetrating the root zone, may predominate, especially in arid regions. Field study of pore fluids in the unsaturated zone was carried out in the southern Ukraine, where the climate is temperate continental. Pore fluid samples were taken from soils and loessial loams at different depths in boreholes of about 1 m diameter with insulated walls. The bore-holes were drilled to groundwater levels situated in loess loams at depths of 10–24 m. The sampling was performed using vacuum lysimeters. In the upper 0.5–2.5 m well-washed layer the infiltrating water composition changed from a HCO 3SO 4Ca type water to a SO 4Na type, the latter corresponding to groundwater composition. The root zone acts as a geochemical barrier which retains the calcium predominating in rain and irrigation water, owing to calcite and gypsum precipitation. This precipitation is accompanied by HCO 3 and SO 4 removal from the pore fluids and by an increase in the total dissolved solids (TDS) as a result of evapotranspiration. The observed profiles of calcium concentration in pore fluids, the manifestations of alkalization and the calcite accumulation are explained by the precipitating action of the root zone. Similar patterns were found in loess-covered arid regions of southern Israel (the Negev) on the basis of reported data on the composition of rain water, saturated soil extracts and the phreatic groundwater in sediments of the Avedat Group. A simple steady-state model of the transformation of rainwater composition to groundwater composition was developed and applied. It is based on the exclusion of CaMg carbonates and gypsum from rain water. Annual precipitation rates (6–13 g m −2 year −1) and the composition of precipitated salts calculated for the Negev are in agreement with data reported in the literature. It is shown that carbonate and gypsum precipitation in the root zone may explain the change of the HCO 3Ca type of rain water to the SO 4Na or ClNa type of groundwater which is fed by it under different climatic conditions.

New Method for Estimation of Contaminant Travel Rate in Unsaturated Zone under Irrigated Soils

In a thick unsaturated zone, when quick deep penetration of rain and irrigation water is absent, at the depths below 3-5 m there exists a zone of downwards quasi-steady water flow. Darcy's water velocity in this zone remains constant with depth and equal to the groundwater recharge rate; unit hydraulic head gradient occurs above the capillary fringe. Therefore, contaminant travel rate is equal to the ratio of hydraulic conductivity (K) and effective volumetric water content (θef). Field tracer experiments and laboratory K and θef determinations were carried out for several representative irrigated lots in the South Ukraine. The dependence of θef on capillary tension was studied for the first time. For loess loam with a capillary tension decreasing from 46 kPa to 0, θef nonlinearly increases from 12% to 27-28%. The effective water content portion (β1) of the total water content increases nonlinearly from 0.38 to 0.65-0.7. The β1 values were estimated for different unsaturated sedimentary rocks. For a capillary tension of about 5 kPa β1 values were: 0.88-0.99 for sands, about 0.65 for loess loam and chestnut soil, about 0.6 for sandy loam, about 0.32 for limestone and about 0.07 for clay. Calculated chloride travel rates in loess loams under irrigated soils fit the values of 0.001-0.003 m/day, determined by the results of field tracer experiments.

Hydraulics of runoff and loess loam deposition: Discussion

Earth Surface Processes and LandformsVolume 11, Issue 4 p. 463-464 Short Communication Hydraulics of runoff and loess loam deposition: Discussion H. J. Geldof, H. J. Geldof Department of Physical Geography; University of Utrecht; P.O. Box 80.115; 3508 TC Utrecht; The NetherlandsSearch for more papers by this author H. J. Geldof, H. J. Geldof Department of Physical Geography; University of Utrecht; P.O. Box 80.115; 3508 TC Utrecht; The NetherlandsSearch for more papers by this author First published: July/August 1986 https://doi.org/10.1002/esp.3290110413AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL No abstract is available for this article. Volume11, Issue4July/August 1986Pages 463-464 RelatedInformation

Hydraulics of runoff and loess loam deposition. A reply to H. J. Geldof

Earth Surface Processes and LandformsVolume 11, Issue 4 p. 465-466 Short Communication Hydraulics of runoff and loess loam deposition. A reply to H. J. Geldof J. De Ploéy, J. De Ploéy Laboratory of Experimental Geomorphology, Catholic University of Leuven, Redingenstraat 16bis, B-3000 Leuven, BelgiumSearch for more papers by this author J. De Ploéy, J. De Ploéy Laboratory of Experimental Geomorphology, Catholic University of Leuven, Redingenstraat 16bis, B-3000 Leuven, BelgiumSearch for more papers by this author First published: July/August 1986 https://doi.org/10.1002/esp.3290110414AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume11, Issue4July/August 1986Pages 465-466 RelatedInformation

Soil condition, nutrition and growth performance of Norway spruce (Picea abies [L.] Karst.) in fast-growing plantations

By ploughing in the humus layer and soil vegetation, simultaneous CaP application and subsequent N fertilization it is possible to ameliorate acid loess loam soils. Under favourable climatic conditions a high growth performance of Picea abies (L.) Karst. can be attained after such ameliorations.

The Nmin‐method – an aid to integrating various objectives of nitrogen fertilization

AbstractThere is increasing interest in the rate and timing of N‐fertilization from both an economical and an ecological point of view. Fertilizer recommendations for a variety of aims can be made using the Nmin‐method, as shown by experiments on deep rootable loess loam soils.Yields of cereal crops and sugar were increased by 2–3 dt/ha by application of the Nmin‐method. The Nmin‐method led to a reduction in the rate of fertilizer application by 30 kg N/ha with sugar beet.Any stipulated NO3 level in leaf vegetables can be met, if N is fertilized according to Nmin‐method. The necessary data for many vegetable crops are given. In particular low nitrate content in spinach and lettuce at high yield was achieved without loss of yield by adjusting both their NO3 and Cl nutrition.Leaching of nitrate out of soils often follows the application of too much fertilizer, but fertilization errors can be avoided and leaching reduced if the Nmin‐method is used.Applications and limitations of the Nmin‐method are discussed.

Hydraulics of runoff and loess loam deposition

AbstractOn many more or less loamy soils, rill erosion is reported to start on slopes that are equal to or steeper than 2–3°; critical Froude numbers for the start of rill wash on these slopes vary between 2·0 and 3·0. This explains why colluvial deposition often occurs on slopes below 2–3°, when water spreads out at the downslope extremities of the rills.The critical hydraulic conditions for loess loam deposition were tested in the laboratory for slopes of 0·5° and 2°, applying unit‐discharges (q) up to 10 cm2/s. It appeared from these experiments that for afterflow, without raindrop impact, deposition starts for critical load concentrations (ccr) varying between several g/1 and about 60 g/l. Under rain ccr amounts to a minimum value of 100–125 g/l and it increases when the runoff film becomes thinner. Nevertheless, deposition in pluvial runoff is also possible, as was the case during the Weichselian, according to data from quarries in Belgium and in The Netherlands.A modified Kalinske equation is proposed for ccr prediction, with the introduction of a typical empirical coefficient Cr and considering such factors as shear stress and mean particle size. Massive sedimentation may occur when it stops raining and afterflow starts, since ccr values are then much lower. It is shown from the Shields' diagram that loamy suspensions are more sensitive to sedimentation than sands in clear water.

Geochemistry and physics of plutonium migration

Similarities in the distribution pattern of the worldwide Pu-239 fallout and in the filtered industrial release of the same nuclide were demonstrated. This analogy led to the assumption that predictions concerning the subsequent fate of the minute quantities of the HEPA-filtered plutonium released by industrial operations may be drawn by studying the environmental transfer of the worldwide fallout plutonium. The history of Pu-239, 240 concentration in the ground-level air and its deposition known from previous investigations for the vicinity of Heidelberg was brought up to date by new values. After subtracting the wet deposition from the total amount of deposition found in the soil a dry deposition velocity for PuO 2-particles of 0.05 cm/s was obtained under the meteorological conditions of the area studied. Differences were found in the residence time of the worldwide fallout in the troposphera and in the filtered airborne PuO 2 discharge in the ground-level air. Nevertheless, the analogous distribution patterns of the PuO 2 particles and the natural aerosols suggest that in the case of dry deposition velocity, the results obtained can be applied for PuO 2 stack discharge too. The decrease of PuO 2 contamination in the biologically active top soil was estimated by computer simulation. The Pu-239, 240 fallout deposition was used as the input function and the measured Pu-239, 240 depth distribution as the result of the combination of irregular input and continous dissipation. The downward migration found out of a 2-cm-thick layer of Rhine valley loess loam was proceeding at a rate of approximately 50% contamination per 3.5 years. By comparing this migration with the movement of an HTO-tracer a water-transport response as small as 10 −3 was estimated. Unlike the stable PuO 2, hydrolytic changes can be expected for Pu(NO 3) 4 upon contact with an aqueous environment after release. The equilibrium concentration of all valence states of plutonium was calculated for the whole range of natural waters. The sum of all potentially dissolved plutonium oxidation states may reach up to 1 mol/l under extreme but naturally occurring outdoor conditions.