摘要:

AbstractBulk density data of about 150 soil profiles from America, Europe and Asia were used to obtain the regression curve of void ratio ϵ as a function of vertical stress σz. For virgin soils straight lines were obtained if a linear scale was used for ϵ and a logarithmic scale for σz. The slope of these lines was steepest for forest zone soils, less steep in soils of high‐grass zones and flattest in short‐grass soils. This difference is attributed to varying amounts of loosening by bio‐ and cryoturbation. Thus the compaction state of virgin soils is that of normal compaction caused by pedogenic processes which are superimposed on previous strong overconsolidation due to desiccation. Against this background agricultural land use creates overconsolidation in the upper soil layers, which is particularly pronounced when the previous bioturbate action has been strong. Young soil deposits cannot develop normal compaction, because of the lack of previous drying of the whol

ISSN:0044-3263    

DOI:10.1002/jpln.19861490402

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY

摘要:

AbstractActual evapotranspiration and net groundwater recharge (drainage minus capillary rise) as a function of climate, soil properties, land use and groundwater depth were determined for a 15‐year period in the region north of Hannover, West‐Germany. Calculations were done using a simulation model calibrated for cropland, grassland and coniferous forest. Results of a sensitivity study showed, that the influence of climatic factors on actual evapotranspiration and net groundwater recharge increases with the amount of plant available water during the vegetation period.Under similar climatic conditions, evapotranspiration and groundwater recharge mainly depend on the two basic soil‐physical relations between.– soil water content and suction and – soil hydraulic conductivity and suction.For same groundwater depths, evapotranspiration rises with increasing plant available water in the rootzone, whereas groundwater recharge

ISSN:0044-3263    

DOI:10.1002/jpln.19861490403

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY

摘要:

AbstractThe ecological effects of heavy metals in soils are closely related to the content and speciation of the elements in the solid and liquid phases of soils. Methods for the determination of metal species in both phases are described and critically evaluated. In connection with the possible binding mechanisms of heavy metals in soils the concept of specific and non‐specific adsorption is discussed. Recent results indicate that the adsorption of heavy metals on soil particles is not only restricted to the formation of surface complexes but can also take place in the interior of minerals. Diffusion processes of heavy metals into soil minerals are described for goethite. In order to assess metal mobility and availability in soils, the concentration and speciation of metals in the soil solution or in comparable aeqeous equilibrium solutions of soil samples and the transfer of metals from solid pools to the liquid phase and vice versa have to be assessed. Methods for the determination of the amount of plant available heavy metals are described and the associated problems discusse

ISSN:0044-3263    

DOI:10.1002/jpln.19861490404

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY

摘要:

AbstractAqueous extracts of terrestrial and underwater soils were prepared by Soxhlet extractions at temperatures between 100 and 37°C (under reduced pressure). From the law of mass action, stability constants were derived for the complexation of Cd, Cu, and Pb by these extracts. The activity of the heavy metals was determined polarographically, whereas the concentration of acid functional groups was used for ligand activity.Visible spectra, electrical conductivity, organic matter contents, and complexation constants depended on extraction temperature as well as on soil properties. In most cases, complex stability increased with increasing pH of the polarographic medium, but sometimes maximum stability was found around pH 7

ISSN:0044-3263    

DOI:10.1002/jpln.19861490405

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY

摘要:

AbstractA number of findings are summarized in order to show the significance of individual plant properties and soil factors on the availability of phosphate and potassium to plants growing in soil.The flux of a nutrient into a given plant root depends directly on the concentration of the nutrient in the adjacent solution. In nutrient solution, P and K influx follows Michaelis‐Menten kinetics. Almost maximum rates of influx have been observed in the range of soil solution concentrations usually found in German arable soils. Roots exhaust P and K from solutions to about 0.2 μmol P and 1 μmol K 1−1if not replenished.At the root surface P and K concentrations in soil decrease rapidly within one day; small changes occur after this period. Initially, the extent of the depletion zone is very small but it extends radially with time. After the initial phase therefore, P and K supply to the plant depends on transport from more remote parts of the soil and also on release from undissolved sources.The degree of depletion and the extent of the depletion zone are related to the diffusion coefficient; they decrease with increasing clay content of soil. Root hairs penetrate the soil and extend the volume of soil supplying nutrients to a unit of root. P and K influx therefore increase with the length of root hairs.Proton release of roots mobilize P and K in soil. This is clearly detected by the HCl‐soluble P and K fractions within 2 mm of the root surface.The activity of acid and alkaline phosphatases strongly increase in the soil in the vicinity of the root surface of several plant species. It is supposed that organic P compounds can therefore be utilized by plants.P and K influx per unit of root length and root length per unit of shoot weight differed widely between species. The product of these two parameters however was closely related to the P and K concentration of the shoots.Calculations from a mathematical model were in good agreement with measured K depletion profiles and K uptake by plants. It is therefore concluded that the main factors influencing the P and K availability of plants growing in soil have been accounted for in the mathematical model and that the parameters have been accurately m

ISSN:0044-3263    

DOI:10.1002/jpln.19861490406

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY

摘要:

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 NO3level 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 NO3and 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‐metho

ISSN:0044-3263    

DOI:10.1002/jpln.19861490407

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY

摘要:

AbstractRoot‐induced changes in the rhizosphere may affect mineral nutrition of plants in various ways. Examples for this are changes in rhizosphere pH in response to the source of nitrogen (NH4‐N versus NO3‐N), and iron and phosphorus deficiency. These pH changes can readily be demonstrated by infiltration of the soil with agar containing a pH indicator. The rhizosphere pH may be as much as 2 units higher or lower than the pH of the bulk soil. Also along the roots distinct differences in rhizosphere pH exist. In response to iron deficiency most plant species in their apical root zones increase the rate of H+net excretion (acidification), the reducing capacity, the rate of FeIIIreduction and iron uptake. Also manganese reduction and uptake is increased several‐fold, leading to high manganese concentrations in iron deficient plants.Low‐molecular‐weight root exudates may enhance mobilization of mineral nutrients in the rhizosphere. In response to iron deficiency, roots of grass species release non‐proteinogenic amino acids („phytosiderophores”︁) which dissolve inorganic iron compounds by chelation of FeIIIand also mediate the plasma membrane transport of this chelated iron into the roots.A particular mechanism of mobilization of phosphorus in the rhizosphere exists in white lupin (Lupinus albusL.). In this species, phosphorus deficiency induces the formation of so‐called proteoid roots. In these root zones sparingly soluble iron and aluminium phosphates are mobilized by the exudation of chelating substances (probably citrate), net excretion of H+and increase in the reducing capacity. In mixed culture with white lupin, phosphorus uptake per unit root length of wheat (Triticum aestivumL.) plants from a soil low in available P is increased, indicating that wheat can take up phosphorus mobilized in the proteoid root zones of lupin.At the rhizoplane and in the root (root homogenates) of several plant species grown in different soils, of the total number of bacteria less than 1 % are N2‐fixing (diazotrophe) bacteria, mainlyEnterobacter and Klebsiella. The proportion of the diazotroph bacteria is higher in the rhizosphere soil. This discrimination of diazotroph bacteria in the rhizosphere is increased with foliar application of combined nitrogen. Inoculation with the diazotroph bacteriaAzospirillumincreases root length and enhances formation of lateral roots and root hairs similarly as does application of auxin (IAA). Thus rhizosphere bacteria such asAzospirillummay affect mineral nutrition and plant growth indirectly rather tha

ISSN:0044-3263    

DOI:10.1002/jpln.19861490408

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY

摘要:

AbstractIn order to characterise the term microbial „activity”︁ three different microbial populations belonging to a luvisol (I), a phaeozem (II) and a rendzina (III) were used for studying kinetic parameters such as substrate affinity, growth rate, yield and turnover time and the metabolic quotient of basal respiration. Glucose was used as a carbon source. Specific growth rate values (μ) varied between 0.0037 and 0.015 h−1depending on soil type and glucose concentration and were far below the potential μmax. The calculated turnover time was 3–11 days, respectively. The yield coefficient was in the range between 0.37 and 0.53. The maximal uptake rate of glucose–C of soil population (II) was 0.041 g C g−1biomass‐C h−1. The determined affinity constant (Km) was 57 μg C g−1soil. The affinity to glucose was higher for the glucose‐mediated CO2evolution with Kmvalues of 15.2 and 17.5 than for the glucose uptake system itself. The observed qCO2values of the basal respiration at temperature increments from 0 to 45° C were almost identical for the soils (I) and (II). The calulated Q10lay in the

ISSN:0044-3263    

DOI:10.1002/jpln.19861490409

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY

摘要:

AbstractModern agricultural practices require a new concept of N‐fertilizer management in order to optimize N‐utilization and avoid N‐losses. Nitrification inhibitors or „N‐stabilizers”︁ fit very good into this conception.Dicyandiamide (DCD) is an efficient nitrification inhibitor and blocks the first step of nitrification for 1–3 months (depending on temperature). This effect is bacteriostatic (not bactericidal) and does not affect other (esp. C‐heterotrophic) soil microorganisms („biological activity”︁).DCD is a non‐toxic, water soluble compound and will be degraded to CO2, NH3and H2O without any residues.There are various possibilities to use DCD: addition to liquid manure temporarily prevents oxidation of ammonium nitrogen e.g. of slurry or waste water from potato starch production.In combination with inorganic fertilizers like ammonium sulfate or urea (with 10% of total‐N) it enables the farmer to control NH4‐supply to crop plants in certain stages of growth and to gain certain operational advantages by less frequently split applications of N especially on sand and rendzina soils.Thus, the systematic use of nitrification inhibitors not only represents a progress in agricultural technique but also helps to substantially reduce risks concerning pollution of surface and ground waters that are sometimes inevitable consequenc

ISSN:0044-3263    

DOI:10.1002/jpln.19861490410

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY

摘要:

AbstractThe effect of increasing amounts of nitrogen (nitrate or urea) on the nitrogen fixing capacity (acetylene reduction assay = ARA), growth (fresh and dry weight) and the number of stem‐ and root‐nodules of the tropical legumeAeschynomene afrasperawas studied in hydroponic cultures (in growth cabinet) as well as in pot experiments (field conditions). The experiments were carried out at Dakar in the rainy season of 1985. Plants were grown in the presence of 6 nitrate concentrations (0,3,6,9,12 and 15 mM N/l) in hydroponic solution and with 4 urea concentrations (0,50,100 and 200 kg N/ha) in pots. In both types of experiments, root nodulation and ARA were strongly inhibited by increasing amounts of mineral nitrogen. Stem nodulation and potential nitrogen fixation of stems, however, remained unaffected. Lower amounts of mineral nitrogen even enhanced growth as well as nitrogen fixation. The possible future of this remarkable plant as green manure or fodder in low input countries of the tropics is discus

ISSN:0044-3263    

DOI:10.1002/jpln.19861490411

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY