Ertragssimulation mit “Ceres Wheat” an Grundwasserböden gemäßigter Klimazonen. Teil 2: Verifizierung des geänderten Modelles “Ceres Wheat”

Calibration of the simulation model “Ceres Wheat” under conditions of soils with shallow watertable and temperate climate. Part 2: Verification of the modified model “Ceres Wheat” The Ceres Wheat yield model has been adopted to soils under wet conditions and to humide climate. The basic assumptions of the modified model have been checked. The simulated results of the soil water balance, the plant development and the nitrate losses by drain discharge give fairly well agreements to field data from a Calcaric Fluvisol (Speicherkoog, Schleswig-Holstein). The modification improves the model and leads to the opportunity to simulate special aspects in agronomical and ecological advices.     

Soil hydrology and CO2 release of peat soils

A simple model to predict soil water components and the CO₂ release for peat soils is presented. It can be used to determine plant water uptake and the CO₂ release as a result of peat mineralization for different types of peat soils, various climate conditions, and groundwater levels. The model considers the thickness of the root zone, its hydraulic characteristics (pF, Ku), the groundwater depth and a soil‐specific function to predict the CO₂ release as a result of peat mineralization. The latter is a mathematical function considering soil temperature and soil matric potential. It is based on measurements from soil cores at varying temperatures and soil water contents using a respiricond equipment. Data was analyzed using nonlinear multiple regression analysis. As a result, CO₂ release equations were gained and incorporated into a soil water simulation model. Groundwater lysimeter measurements were used for model calibration of soil water components, CO₂ release was adapted according long‐term lysimeter data of Mundel (1976). Peat soils have a negative water balance for groundwater depth conditions up to 80—100 cm below surface. Results demonstrate the necessity of a high soil water content i.e. shallow groundwater to avoid peat mineralization and soil degradation. CO₂ losses increase with the thickness of the rooted soil zone and decreases with the degree of soil degradation. Especially the combination of deep groundwater level and high water balance deficits during the vegetation period leads to tremendous CO₂ losses.     

Zu Eigenschaften,Horizontaufbau und Gliederung der „Haftnässepseudogleye”︁

Properties, horizons and classification of the “Haftnässepseudogleye” (Stagnosols periodically waterlogged with capillary water) The term “Haftnässe” (soil wetness due to capillary moisture) can be used in describing soils with Sg-horizons in which long-term waterlogging and anaerobic conditions occur in the absence of gravitational water. “Haftnässe” is caused by water held in pores with an equivalent diameter of 0.2–50 μm by soil-water tension (pF) between 1.8 and 4.2, when the air capacity of the horizons is very low. “Haftnässe” moves primarily by capillary forces and is available to plants (available water). In some soils, the horizon below the Sg-horizon contains large pores, is well aerated and tends to impede the movement of capillary water. This type of horizon is often wetter than the overlying and underlying horizons, due to the presence of capillary water in the immediately overlying Sg-horizon. The symbol “So” is proposed for such horizons. In these soils, in the Sg-horizon reduced iron compounds are oxidized and precipitated, forming rusty mottles. The sequence of horizons developed in the “Haft(nässepseudo)-gleye” (Stagnosols periodically waterlogged with capillary water) typically affects the continuity of the pathways along which capillary water normally moves. The “Haft(nässepseudo)gleye” are divided into two subtypes on the basis of the sequence of horizons in the soil profile:

• Typical “Haft(nässepseudo)gley” (Shn) exhibits a sequence Ah/Sg/(II)So and shows transitions to Luvisol and Glossisol,
• Thick “Haft(nässepseudo)gley” (Shm) exhibits a sequence Ah/Sg and shows transitions to “Stau(wasserpseudo)gley” (Gleysol periodically waterlogged due to perched water), Gleysol, Fluvisol and tidal marsh soil.

     

Bodengesellschaften von geomorphen Einheiten unter Berücksichtigung des Gefügestils im Stormarner Jungmoränengebiet (Brandenburger Stadium) in Nordwestdeutschland

Soil associations of different geomorpholocical units of a younger‐moraine area in Schleswig‐Holstein (NW Germany) considering matter fluxes As result of a detailed mapping work, the soil association of different geomorpholocical units of a younger‐moraine area (“Stormarner Jungmoränengebiet”) in Schleswig‐Holstein (NW Germany) is analyzed taking into account soil development in vertical and horizontal direction. The consequences for classification of soil types and soil associations are discussed. We distinguished between different patterns of matter fluxes (unilateral coupling, mutual coupling, no coupling of soils). By morphometric analysis of the relief, five geomorpholocical units were distinguished: till‐plains with dead‐ice kettles (I), tongue‐like basin with moraine slopes (II), terminal‐push moraine (III), moraine slopes with gutter valley (IV), und terminal‐push moraine valley with steep slopes (V). In the examination area with its intense agricultural land use, the regular sequence of erosion and accumulation of soils is a typical consequence of unilateral water‐flow direction. Thus, the truncated Stagnic Luvisols/Anthrosols association is dominating. We suggest to classify the truncated Luvisol with a Bt horizon exposed directly to the surface at the level of soil subtypes in the German soil‐classification system. Additionally soils in depressions such as Calcic Gleysols, Histosols and “subhydric soils”, which are influenced by solute and solid‐matter input, are frequently encountered. Within the till‐plains, a compensation of the relief by (historical) soil erosion took place, recognizable by the high percentage of Anthrosols (20 %). Therefore, no recent lateral transport of solid material can be found. The steep moraine slopes partly already show Regosols, thus indicating a high erosion potential (erosion rate for geomorphical unit IV: 13 t ha^–1 y^–1). In the depressions intersected with small streams, the afflux caused by mills led to an additional peat development.     

Bemerkungen zur Ermittlung der ungesättigten Wasserleitfähigkeit unter nichtstationären Bedingungen

On the Determination of Capillary Conductivity at Unsteady-State Conditions . Therefore it is stated that for obtaining the effective k_u-values. Considering the importance of capillary conductivity for the soil water regime the large differences up to 2 orders of magnitude between determinations on core samples from the same soil using the double-membrane-method (Henseler and Renger 1969) and the evaporation-method (Becher 1971a) initiated a study concerning the error caused by a possible nonlinearity of suction changes between two measuring levels using the latter method. The study was carried out on disturbed and undisturbed core samples from the three textural classes sand, silt and clay and with modified evaporation method. Comparing the geometric means of the obtained k_u-values calculated at unsteady-state and quasisteady-state conditions for different suctions resulted in that with usual application of the method the measured k_u-values must be diminished for obtaining the effective k_u-values. This correction factor increased with suction and is considered to be more important in laboratory than in field use.

• 1 For sandy soils a correction factor of 2 at 150 cmH₂O increasing to 6 at 1000 cm H₂O must be applied. The coarser the sand would be, at the lower suction nonlinearity will start and the more rapidly the correction factor will increase;.
• 2 For silty soils a correction factor of 2–4 must be applied for suctions > 300 cm H₂O;.
• 3 For clayey soils a correction factor of 2 rapidly increasing to 10 must be applied for suctions > 150 cm H₂O, but depending on soil cracks.

. The overestimation of water through-put resulting from the uncorrected k_u-values amounts to 1.5–4.0 [l/m² · d] at 100 cm H₂O, but these values are within the variation of the effective k_u-values. For 800cm H₂O the overestimation amounts to 0.002–0.065 [l/m² · d], but this makes up 300–1000 % of the effective water through-put.     

Evaluation of the rates of soil organic matter mineralization in forest ecosystems of temperate continental,mediterranean, and tropical monsoon climates

The processes of the organic matter (OM) mineralization in forest soils developed under temperate continental (Moscow oblast, Russia), Mediterranean (the central and western parts of Spain), and tropical monsoon (southern Vietnam) climates were studied under laboratory conditions. The potential and specific rates of the OM mineralization (PR _min and PR _min/C_org, respectively), the ecophysiological parameters of the microbial communities status (C_mic, qCO₂, and C_mic/C_org), and the sensitivity of the rate of the OM mineralization to the rise in temperature were evaluated by the temperature coefficients (Q ₁₀) determined in the humus horizons (0–10 cm, without forest litter). The average values of PR _min for the climatic zones decreased in the following order: Mediterranean (57.1 ± 10.6 mg C/kg per day) > temperate continental (23.8 ± 7.1 mg C/kg per day) > tropical monsoon (10.4 ± 1.6 mg C/kg per day). The lowest resistance of the soil OM to mineralization as evaluated by the PR _min/C_org values was found in the Albeluvisol and Phaeozem of the temperate continental climate and in the Acrisol of the Mediterranean climate. The highest Q ₁₀ coefficients were attributed to the OM mineralization in the forest soils of the temperate continental climate. This allowed us to conclude that the observed and expected climate changes with an increase in the mean annual air temperature should lead to the maximum intensification of the OM mineralization processes in the forest soils of northern regions.     

Erodibilität repräsentativer Böden der Hallertau

Erodibility of representative soils of the Hallertau (South Bavaria) Differences between the USA and the Federal Republic of Germany in geology, soil types, and climate necessitate to verify the erodibility of the soils estimated according to Wischmeier and Smith (1978), when using the Universal Soil Loss Equation under local conditions. The erodibility of 5 representative soils of the region Hallertau within the so-called “Unterbayerisches Hügelland” was checked by measuring soil losses using a laboratory rainfall simulator. The estimated and measured erodibilities for two Aquic Hapludalfs from loess and one Ruptic-Alfic Eutrochrept from Tertiary sand compared very well as shown by coefficients of regression of 1. The estimated erodibilities for a Typic Eutrochrept and an Aquic Chromudert, both from Tertiary materials, however, underestimated the soil losses by a factor of 1.5. For all regressions the coefficients of correlation were 0.90. Due to the small number of soils checked, it is only possible to suggest causes for the observed deviations, particularly since the aggregate stability could not be the only property, as demonstrated by measurements.     

Advances in the prognosis of soil sodicity under dryland irrigated conditions

Salt-affected soils, both saline and sodic, may develop under both dryland and irrigated conditions, affecting the physical and chemical soil properties, with negative consequences in the environment, in crop production and in animal and human health. Among the development processes of salt-affected soils, the processes of sodification have generally received less attention and are less understood than the development of saline soils. Although in both, hydrological processes are involved in their development, in the case of sodic soils we have to consider some additional chemical and physicochemical reactions, making more difficult their modeling and prediction. This is especially true where we have to consider the effects of the groundwater level and composition. In this contribution there are presented three case studies: one related to the development of sodic soils in the lowlands of the Argentina Pampas, under dry-land conditions with sub-humid temperate climate and pastures for cattle production; the second deals with the development of sodic soils in the Colombia Cauca Valley, under irrigated conditions and tropical sub-humid climate, in lands used for sugarcane cropping dedicated to sugar and ethanol production; and the last one related to the sodification of soils in the Western Plains of Venezuela, under irrigated conditions, sub-humid tropical climate and continuous cropping of rice under flooding. The development of sodicity in the surface soil is partially related to the composition and level of the ground-water, mainly affected in the Argentina case by drainage conditions, in the case of Colombia to the inefficient irrigation and inadequate drainage, and in the case of Venezuela to the soil management and irrigation system. There is shown how the model SALSODIMAR, developed by the author, based on the balance of water and soluble components of both irrigation water and ground-water, under different water and land management conditions, may be successfully adapted for the diagnosis and prediction of the different processes and problems, and for selection of alternatives for their prevention and amelioration.     

Mineral transformations by fungi in culture and in soils

• 1 Although micro-organisms are regarded as the principal agents of mineral cycling in soils, the role of bacteria has generally been emphasized, while that of fungi has been neglected.
• 2 Fungi are able to transform the majority of elements in vitro but whether they play an important role in soil is as yet unknown.
• 3 There is sufficient circumstantial evidence from soil studies to suggest that fungi may under certain conditions nitrify and oxidize reduced forms of sulphur. Their role in denitrification and sulphate reduction process is more speculative. While they appear incapable of nitrogen fixation, fungi undoubtedly play a major role in the mineralization of organic N,P, and S in soils, in the solubilization of insoluble phosphates, and participate in oxidation of manganese. Perhaps one of their most important roles is in the dissolution of silica and rocks thus releasing ions into the soil solution during weathering.
• 4 The ability of fungi to oxidize elements in vitro does not compare with that of the chemoautotrophic bacteria. On the other hand in vitro activity tells us little about the activity of an organism in the soil.
• 5 At present our appreciation of the part played by fungi in mineral cycling in soils is limited by the techniques available, but there is little doubt that they have a major role to play in the cycling of elements other than carbon.

     

Nitrogen mineralization in a coarse soil of the semi-arid Pampas of Argentina

Use of the nitrogen balance sheet method as a fertilization strategy in the semi-arid Pampas of Argentina is restricted because of a lack of available information regarding nitrogen mineralization in its coarse soils. Our objective was to determine nitrogen mineralization during corn (Zea mays L.) and following wheat (Triticum aestivum L.) growing cycles under contrasting tillage systems in a representative soil of the region. Mineralized nitrogen from decomposing residues was estimated using the litter bag method and mineralization from soil organic matter using a mass balance approach. Soil water content was higher under no-till during the corn growing season and no differences were detected for wheat during this period. Soil temperature was practically not affected by tillage system. Biomass and nitrogen absorption were higher under no-till than under disk till in corn (p ≤ 0.05), as were nitrogen mineralization from residues and organic matter (p ≤ 0.05). In wheat, no differences in biomass, nitrogen absorption and mineralization were detected between treatments. Mineralization during crop growing cycles accounted for 44.8–67.5% of the absorbed nitrogen. Differences in nitrogen mineralization between tillage systems resulted from the greater water availability under no-till than under disk till during the summer.     

Calculation of nitrogen mineralization and leaching in fallow soil using a simple dynamic model

Simple models describing nitrogen processes are required both to estimate nitrogen mineralization in field conditions and to predict nitrate leaching at large scales. We have evaluated such a model called LIXIM, which allows calculation of nitrogen mineralization and leaching from bare soils, assuming that these are the dominant processes affecting N in bare soil. LIXIM is a layered, functional model, with a 1-day time step. Input data consist of frequent measurements of water and mineral N contents in soil cores, standard meteorological data and simple soil characteristics. The nitrate transport is simulated using the ‘mixing-cells’ approach. The variations in N mineralization with temperature and moisture are accounted for, providing calculation of the ‘normalized time’. An optimization routine is used to estimate the actual evaporation and the N mineralization rates that provide the best fit between observed and simulated values of water and nitrate contents in all measured soil layers. The model was evaluated in two field experiments (on loamy and chalky soils) including treatments, lasting 9–20 months. The water and nitrate contents in soil were satisfactorily simulated in both sites, and all treatments, including a ¹⁵N tracer experiment performed in the loamy soil. In the chalky soil, the calculated water balance agreed well with drainage results obtained in lysimeters and independent estimates of evaporation. At both sites, N mineralization was reduced by the incorporation of crop residues (wheat or oilseed rape straw); the amounts of nitrogen immobilized varied between 20 and 35 kg N ha^?1. In the treatments without crop residues, the mineralization rate followed first-order kinetics (against normalized time) in the loamy soil, and zero-order kinetics in the chalky soil. In the latter soil, the mineralization kinetics calculated in situ were close to the kinetics measured in laboratory conditions when both were expressed against normalized time.     

Die Nitrifikation in Böden (Sammelreferat)

Nitrification in soils A literature review is given on the biology of nitrifying organisms, the nitrification process in soil and factors influencing nitrification in soil with special reference to the following aspects:

• 1 Importance of nitrification in the nitrogen cycle.
• 2 Biology of nitrifying micro-organisms.
• 2.1 Chemolithotrophic bacteria and heterotrophic micro-organisms.
• 2.2 Physiology and biochemistry of nitrifying micro-organisms: gain of energy, specifity and concentration of substrate, influence of soil reaction.
• 3. Methods for the measuring nitrification in soil.
• 3.1 Experiments for the determination of nitrification.
• 3.2 Calculation of the nitrification process.
• 4. The course of nitrification in different soils.
• 4.1 Rate of nitrification.
• 4.2 Influence of various environments: soil reaction, temperature, oxygen and water content.
• 4.3 Effect of soil organic matter and vegetation.

     

Modelluntersuchungen zur K-Freisetzung aus Böden mit höherer elektrischer Leitfähigkeit durch die Elektro-Ultrafiltration (EUF)

Model experiments on the potassium release of soils with higher electric conductivities by electro-ultrafiltration (EUF) For investigations on the effects of higher ion concentrations in soils on results of EUF (electro-ultrafiltration), performed at constant current, a light soil (12% clay) was analyzed by adding increasing amounts of a NaCl solution to the soil slurry in the EUF middle cell. Recording the course of voltage and current through the EUF cell, it was found, that,

• 1) a continuous decrease of electrode voltage occurs over extended time periods, when the electric conductivity of the soil was increased.
• 2) As a function of this voltage decline, the potassium concentration in the EUF-20°C fraction was reduced, whereas in the EUF-80°C fraction higher amounts of potassium could be found.
• 3) Unlike at very high levels of electric conductivity, the total K extraction by EUF was nearly unaffected, because losses in K content in the fraction EUF-20°C could be compensated by the fraction EUF-80°C.
• 4) According to Németh and Ziegler (1988) the ratio of EUF-K-80°C to EUF-K-20°C should be between 0.1 and 0.2 for light, but about 0.6 for heavy soils. Under the influence of higher electric conductivities this figure for light soils, however, approached values for heavy soils.
• 5) Also, the contents of magnesium and calcium showed marked decreases at higher electric conductivities in the EUF-fractions a and b (= EUF-20°C). Contrary to the total amount of extractable potassium, the total contents of magnesium and calcium, extract-able by EUF, were markedly decreased by higher electric conductivities in the light soil.

It is recommended, that the parameters voltage and current should be considered in interpretations of EUF-fractions from soils with higher levels of electric conductivity.     

Anwendbarkeit geophysikalischer Prospektionsmethoden zur Bestimmung von Bodenverdichtungen und Substratheterogenitäten landwirtschaftlich genutzter Flächen

Applicability of geophysical prospecting methods for mapping of soil compaction and variability of soil texture on farm land The increasing degree of mechanization in agriculture has resulted in the use of more powerful and heavier tractors and machines. Consequently, mechanical burden to soils has increased, too, which can lead to persistent subsoil compaction at depths below 30 cm. In soils damaged by compaction soil functions like transportation of water and air decrease. Because of that, conditions for plant growth are getting worse and the soils' natural regulation functions could be impaired. In order to take counteractive measures, it is necessary to get information about the status of soil compaction. Up to now, the status of soil compaction can only be determined at single points in laboratory measurements or with less accuracy in field measurements. Therefore, the demand for an efficient planar‐mapping system arises. The applicability of different geophysical prospecting methods with regard to this problem has been examined. For this purpose, geophysical and soil measurements were performed in a field with conventional agricultural land use in Schleswig‐Holstein (Germany) on a young moraine site. We applied GPR (Ground Penetrating Radar) with main frequencies 500 MHz and 900 MHz, supplemented by inductive electromagnetic technique (EM) using the Ground Conductivity Meter EM38 and high‐resolution refraction seismic using compressional and shear waves. Differences in soil type were found by all these geophysical methods and confirmed by soil measurements, therefore, locations with higher risk for compaction (loamy soils) could be distinguished from locations with lower risk (sandy soils). Under humid conditions, radar data showed strong reflections at a depth of approx. 30 cm. During summer, under dry conditions, these reflections did not occur. This temporal variation of radar reflections can be explained by variable water layers inside the soil, which can be regarded as an indicator for compacted soil. The seismic investigation was performed along short (12 m) profiles with dense (20 cm) sensor spacing. Excellent data quality showed that this sort of measurement, known from engineering geophysics, is also feasible for soil investigations. We performed both compressional‐ (P‐) and shear‐(SH‐) wave refraction studies. Differences in soil type of subsoil affected especially seismic velocities of P‐waves. Whether or not areas of compacted soil can be detected is still unknown, because deeper soil horizons of our test area showed only uniformly strong compaction with little contrasts.     

Repeated annual drought has minor long‐term influence on δ13C and alkane composition of plant and soil in model grassland and heathland ecosystems

As a result of global climate change the incidence of drought conditions in Europe is predicted to increase in the future, which also influences plant resistance. Lipids are important plant constituents that protect plants against drought stress and contribute to the intermediate stable carbon (C) pool in soil. However, the extent to which drought influences lipid cycling in the plant–soil system is unknown and, therefore, it remains questionable how the ecosystem recovers after drought. We focused on plant and soil samples from two different plant communities (temperate grassland and heathland) that had been exposed to 5 years of 4.5–6.0 weeks repeated annual drought. They were sampled one year after the last drought to check the recovery of the plant–soil system. Samples were analyzed for their bulk C, stable C and nitrogen (N) isotope (δ¹³C, δ¹⁵N) and lipid composition. Contrary to our expectation, no strong influence of five years of repeated annual drought was observed for above‐ground biomass, roots and soils in the model ecosystems with respect to elemental (C and N concentrations, C : N ratio) bulk isotope (δ¹³C, δ¹⁵N) composition and the total extractable lipid concentration. Thus, plants did not sustain a significant change in their C and lipid concentration as well as their composition after five years of repeated annual drought. This might be related to the comparatively short drought period related to the overall growth season and provides evidence for recovery of the C and lipid dynamics in temperate grassland and heathland model ecosystems exposed to annual drought.     

Influence of municipal waste compost amendment on soil water and evaporation

Abstract

Municipal Waste Compost was added to soils in the glasshouse and field to assess its impact upon soil physical properties. Application was by mulch and incorporation, and the amelioration of temperature, soil water content, unsaturated hydraulic conductivity, and evaporation were investigated. Incorporation in the glasshouse pot experiments increased early season evaporation, while compost applied by either means raised soil temperature. In later stages of drying, the presence of compost reduced the evaporation rate. In the field, compost addition to trials of maize (Zea mays van Melody) improved retention of soil water during a normally wet summer, but not during a very dry summer. Furthermore, soil temperature tended to be reduced by mulching. It is concluded that compost application is beneficial to soil water retention and its subsequent utilization by a crop in conditions of normal rainfall under a temperate climate. Furthermore, it is concluded that the common practice of extrapolating glasshouse‐derived information to field conditions creates serious problems, at least in soil physical experimentation.     

Characteristics of the soils developed under broad-leaved evergreen forests in okinawa prefecture and the kinki district with special reference to their pedogenetic processes

Abstract

Properties of sesquioxides, clay mineralogical composition, and charge characteristics of the soils developed under broad-leaved evergreen forests in Okinawa Prefecture (subtropical climate) and the Kinki District (warm temperate climate) were studied with special reference to their pedogenetic processes in order to reexamine the corresponding parameters of Brown Forest soils and related soils in Japan.

The soils in Okinawa Prefecture were characterized by a higher degree of weathering as compared to the soils in the Kinki District. Major differences involved the values of the Fed/Fet ratio for the soil samples throughout the profile, and those of the ratios of (Fed-Feo)/Fet, CEC/clay, and (Feo + Alo)/ clay and the content of CaO plus Na₂O for the B horizon. The soils in the Kinki District did not show andic soil properties, nor Al translocation in the profile and, both of which were characteristic of Brown Forest soils developed under cool temperate climatic conditions at high altitudes in the same District.

The difference in the degree of weathering were reflected on the charge characteristics at the very surface of the soils, i.e., the surface of the particles of the soils in Okinawa Prefecture exhibited a lower reactivity as compared with those of the soils in the Kinki District.     

Schutzwürdige Böden in Nordrhein-Westfalen — Bodenkundliche Kriterien für eine flächendeckende Karte zum Bodenschutz

Valuable soils in Northrhine-Westphalia — soil scientific criteria for generating a complete map for soil protection At the Geological Survey of Northrhine-Westphalia a map was developed: Soils to be protected in Northrhine-Westphalia at a scale of 1:50.000. It is based on the Soil map of Northrhine-Westphalia at a scale of 1:50.000. This map indicates areas where such land uses should get high priority which need, save and develop the identified main soil functions. There are three groups of land use with main soil functions:

• natural habitat with high potential of biotope evolution
• agricultural production on soils with (regionally) high fertility
• regional specifica, including soils as archives of natural and cultural history.

Land uses disregarding or lowering these soil functions have to be placed otherwhere or have to be compensated by areas with comparable functions. The criteria generating this map are given and discussed. The evaluation of information coming from the digital soil map runs soil protection under the aim of securing the kind and state of soil substrate and characteristics, giving the functionality of soils in favor of other media of the environment.     

Vorstellung der SrCl2-Methode nach Bach zur Bestimmung der effektiven Kationenaustauschkapazität und Vergleich mit der NH4Cl-Methode

Presentation of the SrCl₂-method after Bach for the determination of the effective cation exchange capacity and comparison with the NH₄Cl-method The SrCl₂-method for the determination of the effective cation exchange capacity CEC_eff has been developed by Dr. H. Bach, a former geochemist of the “Geologisches Landesamt Schleswig-Holstein”. Exchangeable metallic cations in soils are displaced by a 0, 1 M SrCl₂-solution and analyzed from the percolate. Reexchange of strontium by a 0, 1 M MgCl₂-solution allows to determine the CEC_eff by analyzing for strontium in the second percolate. In comparison with the customary application of NH₄Cl, SrCl₂ shows the following advantages:

• 1 The nearly unbuffered SrCl₂-solution adopts instantly the pH of the soil.
• 2 In contrast to the weakly acid NH₄Cl-solution, no H₃O⁺-cations compete with the exchange cation. Furthermore, partial dissolution of clay minerals is prevented because of the near-neutral character of the SrCl₂-solution.
• 3 The SrCl₂-method can be applied on all types of soils including carbonate- and salt-bearing soils.
• 4 The amount of free (dissolved) cations can be approximated.

     

Assessment of AquaCrop model in the simulation of seed yield and biomass of Italian ryegrass

Given that the optimal sowing rate and inter-row spacing of Italian ryegrass raised for seed have not been determined, the objective of this research was to assess the effect of crop density on biomass and seed yields under different climate conditions, applying the AquaCrop model. The data came from experiments conducted under moderate continental climate conditions at Stitar (Serbia) and Mediterranean climate conditions at Cukurova (Turkey). At Stitar, there were three different inter-row spacings (high (S_d), medium (S_m) and low (S_w) crop densities), while at Cukurova there was only high crop density (S_n). In the calibration process, the initial canopy cover, canopy expansion and maximal canopy cover were adapted to each crop density, while the other conservative parameters were adjusted to correspond to all climate conditions. Calibration results showed a very good match between measured and simulated seed yields; the values of the coefficient of determination (0.922). The biomass simulation was very good for Cukurova (R² = 0.97), but somewhat poorer for Stitar (R² = 0.72). Other statistical indicators were high such as Willmott index of agreement of both the calibrated and validated data sets, for both study areas >0.916 and normalized root mean square error in the range from 9–18%. The AquaCrop model was found to be more reliable for Italian ryegrass biomass and seed yield predictions under mild winter climate conditions, with adequate water supply, compared with moderate climate and water shortage conditions.