Zum jahreszeitlichen Nitratgehalt und zur Nitratauswaschung von landwirtschaftlich genutzten Böden in Baden-Württemberg

Seasonal nitrate content in, and nitrate leaching from, agricultural soils of Baden-Wuerttemberg The behavior of soil nitrate was investigated at five field locations in the State of Baden-Wuerttemberg between 1984 and 1987. It was found that the amount of nitrate in the upper 90 cm of soil was not a constant, but fluctuated throughout the year with maxima in the spring and in the fall. Additionally, it was found that the amount of nitrate leaching during winter (from November through April) was correlated to, but not identical with the mineral nitrogen content of the previous fall. It further appeared that nitrate leaching in light sandy soils is mainly a mixing process, whereas in heavy soils it seems to be more a miscible displacement phenomenon.     

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.     

Zum Einsatz von TRIME-TDR zur Messung der Bodenfeuchte auf leichten Sandböden

Using TRIME-TDR for the determination of soil water dynamics on sandy soils In this study the suitability of the TRIME-TDR system for the determination of soil water content was analysed. For this purpose a period of three years with continuous data of soil water contents, measured by TRIME-TDR, and soil water suction measured by tensiometer were available. Additionally soil samples at different times were taken for gravimetric moisture analysis. The determinations of soil moisture with the TRIME-TDR is based on a new measuring technique. The soil water contents measured by TRIME-TDR were analysed by comparison with corresponding soil moisture values from gravimetric measurements of soil samples. The soil water contents determined by TRIME-TDR in comparison with gravimetric soil moisture values show an absolute mean error of 7.9 Vol%. In most cases the soil water contents measured by TRIME-TDR were distinctly higher than the corresponding soil moisture values from gravimetric measurements. After correcting the TRIME-TDR the absolute mean error was reduced to 2.5 Vol%. Due to the results of this study soil water contents measured by TRIME-TDR-technique cannot be used in hydrological or ecological studies without a check based on the comparison with gravimetric soil moisture values.     

Tonmineral- und K-Ca-Austauscheigenschaften von Oberböden des Nährstoffpotentialversuches Hallertau

Clay mineralogy and K-Ca-exchange properties of surface soils from the nutrient potential trial Hallertau (Bavaria) In soils of four locations of the Hallertau nutrient potential trial, with a soil texture consisting of sand, silty sand, silty loam and sandy clayey loam, clay mineral properties were measured with the standardized glycerol expansion method and with n-alkylammonium (Rn_c-NH₃⁺-clay). The expandable minerals of the sandy soils consist exclusively of smectites s.s., (s.s. = sensu stricto) with 0.42 to 0.28 charge equivalents per formula unit (p.f.u.). The expandable minerals of the loams are an assemblage of smectites s.s. and vermiculites. The total layer charge of the smectites s.s. extend from 0.54 to 0.28 charge eq. p.f.u. The fine clay fractions (< 0.1 μm) do not contain vermiculites. The layer charge density of vermiculites with homogeneous charge in the coarse fractions varies between 0.60 and 0.95 charge eq. p.f.u. The immediate K-Ca-exchange was extended with the values of the continued K exchange versus Ca at low K intensity. The Q/I isotherms of sandy soils have a more pronounced curvature than the isotherms of the loams; in all cases, however, the exchange curves have a continuous form. This phenomen is discussed in terms of the clay mineralogy of the soils. After 8 years without K fertilizing, samples gave values between 168 and 497 kg smectite-K/ha for the surface soils. The constant rates of K-desorption vary between 12.8 and 28.7 kg K/ha (surface soil). The rates are better differentiated between unfertilized and fertilized soils for the loams than for the sandy soils. The constant rates of K release were found to be controlled at an AR-level between 1.6 · 10^?4 M^1/2 (unfertilized sandy soil) and 5.2 · 10^?4 M^1/2 (fertilized sandy clayey loam soil).     

Ein Mischzellenmodell zur Abschätzung der Nitratauswaschung aus landwirtschaftlich genutzten Böden im Winterhalbjahr

A mixing-cell model for estimating nitrate seepage losses from agricultural soils in winter A mixing-cell model is developed with which the leaching of nitrate from agricultural soils in temperate regions during winter can be estimated. The model assumes steady-state flow conditions and takes nitrogen mineralization in the upper soil as well as nitrate deposition from the atmosphere into consideration. Model results are compared with results from a convective-dispersive solute flow model. They show that for common field soil dispersivities mixing-cell model results compare well with those obtained from convective-dispersive theory. With the mixingcell model nitrate leaching calculations were carried out for a variety of soil and climatic conditions. They show that the combined effect of N-mineralization and N-deposition may influence the amount of leached nitrate in winter considerably, especially in regions with light soils and high seepage rates. It is shown that the model can be used to derive late fall site-specific upper limits for soil mineral nitrogen for groundwater protection purposes. Such upper limits should reflect the crop-specific rate of N-mineralization that can be expected during winter.     

Standorteigenschaften und Wasserhaushalt von versiegelten Flächen

Site characteristics and hydrology of sealed aereas Soil physical and chemical properties of typical sealed urban sites in Berlin were measured. Water components were determined using lysimeters with differently sealed surfaces. Water storage and infiltration is small and depends on sealing materials. Evapotranspiration and drainage are reduced whereas runoff is increased. During summer time high surface temperatures might occur on sealed surfaces. Because of high dust input, infiltration of old sealed sites is reduced by an order of magnitude compared to sites which have been sealed recently. Long-term input of dust resulted in an increase of clay, silt, organic material and heavy metals. Finally specific recommendations for land planners are given.     

Schätzung der Denitrifikation in landwirtschaftlich genutzten Böden. II. Ergebnisse und Bewertung

Estimating denitrification in agriculturally used soils: II. Results and evaluation This is the second of two papers describing a denitrification model. Whereas in the first paper the model approach was described, the second paper deals with results obtained with the model. To evaluate the model's performance, 14 profiles in the catchment area of a water-work were studied in detail. For each site the potential and the actual annual denitrification rates were estimated. It was found that the least favorable conditions for denitrification occurred in the sandy soils of the study area. Consequently, estimated denitrification rates were lowest (< 10 kg N ha^?1 a^?1) in these soils. Estimated denitrification rates were highest (50 kg N ha^?1 a^?1) in peal and river plain soils, with either a high amount of organic matter and/or a high groundwater table. In silty loess soils, denitrification losses were estimated to be 20 to 35 kg N ha^?1 a^?1. With use of the anion concentrations in the surface layer of the groundwater, a plausibility study was conducted to evaluate the estimated denitrification losses. Its results show that the values obtained are realistic. However, a true calibration of the model is still necessary.     

Schätzung der Denitrifikation in landwirtschaftlich genutzten Böden. I. Grundlagen

Estimating denitrification in agricultural soils: I. Basic assumptions Despite a common interest of soil scientists, groundwater hydrologists, agronomists, and climatologists in quantifying soil nitrogen losses through denitrification, these are often neglected when the nitrogen turnover of agricultural soils is modelled. This is the first of two papers describing a semi-quantitative denitrification model that has been derived from data collected from soils of a catchment area near Viersen in the Lower Rhine Valley in West Germany. A field study was conducted to study the soil environment of denitrifying microorganisms. The results of this study were used to evaluate the effect of soil water, soil air and soil temperature, of the amount and quality of the organic matter, and of the pH-value on denitrification. To this end an existing model to quantify denitrification was extended. Provided the seasonal nitrogen excess of a field is known, the model in its new form enables an estimation of the extent of field-specific denitrification rates. This paper describes the effects of the parameters under consideration on denitrification, the model components used to describe these parameters, and the development of the denitrification model.     

Quantitative und qualitative Veränderungen im A-Horizont von Sandböden nach Umwandlung von Dauergrünland in Ackerland

Quantitative and qualitative changes in soil properties of A- horizons of sandy soils caused by conversion of grassland to arable land Changes in physical soil properties and in soil organic matter of the A-horizons due to the conversion of permanent grassland to arable land are quantified and described as a function of time for sandy soils. The study was carried out in an area northeast of Hannover. A decrease of about 100 t/ha C_org (- 57%), 5 – 6 t/ha N_org (- 58%) and 1 t/ha S_t (- 58%) was measured for a period of 2 – 4 years after grassland conversion. Thereby the quality of the soil organic matter remains unchanged (no changes of the C/N ratio and of the distribution of N_org in 5 N-fractions). However, an increase of soil bulk density from 1.0 to 1.3 g/cm³ and a decrease of total pore volume from 0.59 to 0.47 were observed. The fast mineralization of soil organic matter in the A-horizon following the conversion of grassland soils results in a temporary heavily increased nitrate input into the groundwater. Furthermore mineralization and leaching of nitrate and sulfate induces an acidification push in the soil by a proton release in the order of 350 keq/ha during a 2 – 4 years period. However, this proton production is compensated quantitatively by several applications of lime or marl by farmers and by the buffering of bases cations released from mineralized soil organic matter.     

Mikrobielle Aktivitäten in landwirtschaftlich genutzten Böden Niedersachsens. I. Einfluß der ackerbaulichen Nutzung

Microbial activity of arable soils in Lower Saxony, Germany. I. Influence of agricultural practice A range of microbial functions were measured over four years in field trials on three soil types in Lower Saxony. Generally, glucose-induced short-term respiration and dehydrogenase activity were most susceptible to environmental influences. Higher microbial activity occurred under cereals than under sugar beets. Some microbial functions were affected by soil type and vegetation period. Furthermore, pesticide treatments of sugar beets inhibited some microbial functions.     

Prognose der mechanischen Belastbarkeit und der auflastabhängigen Änderung des Lufthaushaltes in Ackerböden anhand von Bodenkarten

Prediction of soil strength of arable soils and stress dependent changes in ecological properties based on soil maps Based on a database of at present 160 mechanical soil profile datasets, the site and horizon dependent mechanical soil strength expressed as precompression stress can be predicted by multiple regression analysis and used for documentation in maps at different scales. Stress dependent changes in air permeability or air capacity can be derived for the virgin compression stress range as well as the effect of stress propagation in soils or stress attenuation capacity and depth dependent changes of ecological properties. Thus, areas with defined mechanical sensitivity as a function of depth can be derived and recommendations for site adjusted farming techniques can be given. In addition it allows the agricultural machine industry to develop site adjusted machines to support the ideas of good farming practice, defined by the soil protection law of Germany.     

Räumliche Variabilität der Phosphorgehalte im Oberboden landwirtschaftlich genutzter Flächen in kleinen Einzugsgebieten

Spatial variability of Phosphorus contents in topsoils of two small catchments under agricultural use The spatial variability of total phosphorus (P_t) contents was investigated in two small agriculturally used catchments in Saxony/Germany. The mean P_t concentration was 982 mg kg^–1, with 80 % of values between 560 and 1530 mg kg^–1. The largest P_t contents were found at the tops and foots of slope, and the smallest at the middle slope positions. At the scale of slopes (microscale) the spatial variability was caused by the relief and soil properties, whereas at the scale of catchments, agricultural management had the largest influence. These differences must be considered for the modeling of diffuse P inputs to surface waters.     

Mikrobielle Aktivitäten in landwirtschaftlich genutzten Böden Niedersachsens. II. Bodencharakterisierung anhand mikrobieller Stoffwechselaktivitäten

Microbial activity of arable soils in Lower Saxony, Germany. II. Soil characterization by microbial activities Field trials were carried out on six soil types in Lower Saxony and were supported by glasshouse and laboratory trials. Soils were sampled frequently to monitor biomass-related and overall microbial activities as well as the activity of soil enzymes. Similar soils showed comparable activity patterns. Crop plants and, especially, the herbicide ‘Flüssig Herbogil’ (dinoterb) affected some microbial functions. Activity patterns can be used in long-term trials to characterize soil types and agricultural practices. In addition, they may be useful in short-time trials to identify ecological and ecotoxicological effects.     

Die Stabilität von Sandböden in Abhängigkeit vom Gehalt an organischer Substanz und deren Humifizierungsgrad

The Stability of Sandy Soils and its Dependence on Humification Degree and Content of Organic Matter The influence of organic matter on the strength parameters cohesion and friction angle was investigated with mixtures of a fine sand and 0-8% peat of different humification degrees - determined by using a thermobalance - and under different soil water suction. The results show that the strength parameters cohesion and friction angle increase with increasing organic matter content, but the increase is greater with lower humification degree. Especially if the organic matter content is lower than 5%, cohesion and friction angle depend on soil water suction and have a maximum in the range of about 50 hPa soil water suction. A simplified model based on the capillary theory for the calculation of cohesion was proposed to explain the influence of content and humification degree of organic matter on cohesion. One possible reason for the lower cohesion with higher humification degree is its lower wettability. The dependence of friction angle on soil water suction and humification degree of organic matter needs further examinations.     

Untersuchungen über den Einfluß des Kinetins und des Eisens auf den Nukleinsäure- und Proteinstoffwechsel von Karottengewebekulturen

The Influence of Kinetin and Iron on Nucleic Acid and Protein Metabolism of Carrot Tissue Cultures Carrot-root tissues cultured in a nutrient solution containing Kinetin had a high rate of cell division, that led to an undifferentiated callus, and a relatively low DNA content per cell. The same tissues growing without Kinetin had a smaller rate of cell division and a higher DNA content, and showed the ability to form roots. By addition of ³²P to the nutrient solution, the cultures growing with Kinetin showed a higher specific activity of DNA than those growing without Kinetin. From previous experiments and results of other workers the possibility of the occurence of a metabolic labile DNA fraction in the cultures which grew without Kinetin is discussed. A comparison between the influence of iron and Kinetin on cell division activity, root formation, DNA, RNA and amino acid content of the tissue cultures was made on a cell basis. Iron deficiency or absence of Kinetin in the nutrient solution reduced the cell division activity of carrot tissue cultures and increased the content of DNA, RNA and soluble amino acids. The protein content was reduced by iron deficiency but was increased by the absence of Kinetin. Cultures, growing without Kinetin were able to form roots, while those, growing in an iron deficient medium were unable to show the latter phenomenon.     

Ermittlung von analytischen Kriterien zur bodentypologischen Einordnung tiefreichend humoser Sandböden im Westmünsterland

Determination of analytical criteria for classification of sandy soils with deepreaching humus contents in the region of Westmünsterland While mapping agricultural areas in the region of Westmünsterland a problem of soil classification became obvious. There are widespread sandy soils of brown to greybrown colour, which have unusually high contents of humus down to several decimeters depth. Several chemical and physical laboratory investigations were carried out to answer the question of natural or anthropogenic origin. Based on the characteristics of diagnostic horizons from certain classifiable soils like Kultosole espec. Plaggenesche (Plaggepts/Anthrosols, 7 profiles) and Spodosols/Podzols (8 profiles) clearly differentiating characteristics should be derived. Comparing with datas from subsoil horizons of the questionable 11 profiles these should be attached to one of the former groups. Univariate and multivariate statistic methods like discriminant and cluster analysis were used to evaluate the analytical laboratory results. It was possible to attach 5 of 11 systematic questionable soil profiles to the group of Kultosole/Plaggenesch. As there is no better fitting systematical classification (like deepreaching humous Brown Earth o.s.) the remainder must be classified as Brown Earth or Podzol-Brown Earth.