Einfluß der Bodenentwicklung auf den Zusammenhang zwischen Lagerungszustand und vertikaler Spannung im Boden

Effect of soil formation on packing and on vertical stresses in soils The relationship between void ratio and vertical stress was investigated for 34 profiles (loess, glacial till, sands) mostly under forest and some under meadows. Development in terrestric forest soils obviously results in ?non overconsolidated”? structure. The stress distributions as a function of depth partly point to constant shear parameters, partly to differences in the profile, especially clear in the case of Podsol and Sandbraunerde. Whereas the absolute value of the void ratio can be explained by the soil-own shear parameters, the decrease of void ratio as a result of equal load increments will be explained by the extent of translation, which is necessary to increase the mean number of grain contacts.     

Operator assessment of tractor roll angle with and without a tractor stability visual feedback device

According to a 2004 National Institute for Occupational Safety and Health (NIOSH) report, approximately 250 to 350 fatalities occur each year due to incidents involving production agriculture workers and tractors. Tractor overturns account for about 150 to 200 of these deaths. The goals of this project were to study operators' understanding of tractor roll angles and test a device to effectively deliver stability information to the tractor operator. This project required the design and construction of a full-scale tractor cab roll simulator that was used to identify lateral roll angles at which volunteer participants felt uncomfortable, as well as lateral roll angles at which they would no longer operate a tractor. In addition, the participants performed a series of tasks to test the functionality of a visual slope indicator that was designed to help them estimate slope angles. The project tested 231 tractor operators' perceptions of safe operation on side slopes and 128 participants' interactions with the visual slope indicator. Testing showed that the visual slope indicator was able to influence the angle estimations of the novice tractor operator population and helped the entire population of participants more accurately rank the simulator scenarios.     

Root development of winter wheat in erosion‐affected soils depending on the position in a hummocky ground moraine soil landscape

Agricultural soil landscapes of hummocky ground moraines are characterized by 3D spatial patterns of soil types that result from profile modifications due to the combined effect of water and tillage erosion. We hypothesize that crops reflect such soil landscape patterns by increased or reduced plant and root growth. Root development may depend on the thickness and vertical sequence of soil horizons as well as on the structural development state of these horizons at different landscape positions. The hypotheses were tested using field data of the root density (RD) and the root lengths (RL) of winter wheat using the minirhizotron technique. We compared data from plots at the CarboZALF‐D site (NE Germany) that are representing a non‐eroded reference soil profile (Albic Luvisol) at a plateau position, a strongly eroded profile at steep slope (Calcaric Regosol), and a depositional profile at the footslope (Anocolluvic Regosol). At each of these plots, three Plexiglas access tubes were installed down to approx. 1.5 m soil depth. Root measurements were carried out during the growing season of winter wheat (September 2014–August 2015) on six dates. The root length density (RLD) and the root biomass density were derived from RD values assuming a mean specific root length of 100 m g^?1. Values of RD and RLD were highest for the Anocolluvic Regosol and lowest for the Calcaric Regosol. The maximum root penetration depth was lower in the Anocolluvic Regosol because of a relatively high and fluctuating water table at this landscape position. Results revealed positive relations between below‐ground (root) and above‐ground crop parameters (i.e., leaf area index, plant height, biomass, and yield) for the three soil types. Observed root densities and root lengths in soils at the three landscape positions corroborated the hypothesis that the root system was reflecting erosion‐induced soil profile modifications. Soil landscape position dependent root growth should be considered when attempting to quantify landscape scale water and element balances as well as agricultural productivity.     

Metal accumulation and hydraulic performance of bioretention systems after long-term operation

Purpose

Stormwater bioretention systems are widely used to treat diffuse infiltration of runoff from paved surfaces and roofs. Substantial questions remain about the hydraulic performance and the accumulation of pollutants in systems over the long term. Data of metal accumulation of systems with operational times >10 years currently is limited. This study deals with the accumulation of metals in a variety of long-term operational bioretention systems (11–22 years) to derive further operation recommendations for the water authorities.

Materials and methods

The hydraulic conductivity of the bioretention systems in field was measured using a double ring infiltrometer. Media soil samples from 22 diverse designed systems were collected across the surface and at intervals up to a depth of 65 cm to determine the spatial accumulation of Zn, Cu, Pb and Cd. Leaching experiments of selected bioretention media soils were derived to assess the metal leachability by water.

Results and discussion

The hydraulic performance of most bioretention systems still met the technical guidelines of Germany even after long-term operation. Considerable metal accumulation occurred in the topsoil (0–20 cm). Median concentrations of all metals are highest at the soil surface (0–10 cm), decreasing with increasing depth. High concentrations were determined at the inflow points of the runoff waters, whereas concentrations at more than 1.5 m distance from the inflow were only slightly increased compared to the initial soil concentrations. Leachability tests have shown that most of the metals deposited in bioretention soils are only slightly water soluble. No concentrations exceeding the threshold values of the German Soil Contamination Ordinance for the pathway soil to groundwater could be determined.

Conclusions

The hydraulic conductivity of the bioretention systems is given even well after long-term operation. Most of the metal accumulation is concentrated in the top 20 cm; concentrations decrease rapidly and mostly reach background/initial concentrations after depths of 30 cm. The water-soluble metals are all below the trigger values of the German Soil Act. This underlines the strong retention capacity of long-term bioretention systems after long-term operational times.

     

Biological P cycling is influenced by the form of P fertilizer in an Oxisol

Phosphate rock (PR) is an alternative fertilizer to increase the P content of P-deficient weathered soils. We evaluated the effects of fertilizer form on indicators of biological cycling of P using an on-farm trial on a Rhodic Kandiudox in western Kenya. Treatment plots were sampled after 13 cropping seasons of P applications as Minjingu phosphate rock (PR) or as triple super phosphate (?TSP) (50 kg P ha^?1 season^?1), as well as a P-unfertilized control (0 kg P ha^?1 season^?1). Soils (0–15 and 15–30 cm) were analyzed for microbial biomass P (P_mic), activities of acid phosphomonoesterase, alkaline phosphomonoesterase, and phosphodiesterase, and sequentially extractable P fractions. P additions as Minjingu PR yielded 299% greater P_mic than TSP at 0–15-cm depth despite similar labile P concentrations in the two P fertilization treatments and stimulated activities of acid phosphomonoesterase (+39%). When added in the soluble form of TSP, a greater percentage of total soil P was present in mineral-bound forms (+33% Fe- and Al-associated P). Higher soil pH under Minjingu PR (pH 5.35) versus TSP (pH 5.02) and the P-unfertilized treatment (pH 4.69) at 0–15-cm depth reflected a liming effect of Minjingu PR. The form of P fertilizer can influence biological P cycling in weathered soils, potentially improving P availability under Minjingu PR relative to TSP via enhanced microbial biomass P and enzymatic drivers of P cycling.     

Comparison and sensitivity of measurement techniques for spatial distribution of soil salinity

In Khorezm, a district of Uzbekistan situated in the Aral Sea Basin, soil salinization is an important driver of soil degradation in irrigated agriculture. The main objective of this study was to identify techniques that enable rapid estimation of soil salinity. Therefore, bulk electrical conductivity of the soil (EC_a-meas) was measured with three different devices (2P, 4P, and CM-138) and electrical conductivity of the soil paste (EC_p-meas) was measured with the so-called 2XP device. These measurements were compared with independent estimates of EC_a-calc and EC_p-calc based on laboratory measurements of the saturated extract, EC_e, of soil samples from the same sites. Soil salinity could be assessed satisfactorily with all four devices. EC_p-meas could be well reproduced by the 2XP device (R ² = 0.76), whereas EC_a-meas estimates using 2P, 4P, and CM-138 in the field were less accurate (R ² < 0.50). The sensitivity of all devices to the main ions Cl⁻ and Ca^{2 +} suggests that the measuring principles are similar for all instruments. The devices can therefore be used interchangeably. Field assessment of soil salinity was considerably enhanced by the use of CM-138, because large areas can be quickly assessed, which may be desirable in spite of the lower accuracy.     

Space,Time, and Local Employment Growth: An Application of Spatial Regression Analysis

ABSTRACT Local and regional employment growth is generally studied either by searching for local qualitative explanatory factors such as governance, synergy between firms, and milieu effects, or by searching for general growth factors using statistical techniques. The body of work that relies on this approach has tended, in keeping with economics’ nomothetic tradition, to assume that local and regional growth factors are constant over space. The focus of this paper is on exploring the spatial stationarity of employment growth factors in Canada, but it also seeks to clarify some of the broad principles behind spatial regression techniques in order to provide a point of entry and a conceptual framework for empirical researchers. To do so, we apply a recently developed technique, Geographically Weighted Regression (GWR), and we explore the method's advantages and limits for answering our research question. We find evidence that growth factors differ across Canada, but we also conclude that the GWR technique, given the number and shape of regions available for our analysis and given certain limitations that are currently inherent to the method, can only provide tentative and exploratory results.