Thomas Nehls

Nutrient availability and leaching in an archaeological Anthrosol and a Ferralsol of the Central Amazon basin: fertilizer, manure and charcoal amendments

Soil fertility and leaching losses of nutrients were compared between a Fimic Anthrosol and a Xanthic Ferralsol from Central Amazônia. The Anthrosol was a relict soil from pre-Columbian settlements with high organic C containing large proportions of black carbon. It was further tested whether charcoal additions among other organic and inorganic applications could produce similarly fertile soils as these archaeological Anthrosols. In the first experiment, cowpea (Vigna unguiculata (L.) Walp.) was planted in pots, while in the second experiment lysimeters were used to quantify water and nutrient leaching from soil cropped to rice (Oryza sativa L.). The Anthrosol showed significantly higher P, Ca, Mn, and Zn availability than the Ferralsol increasing biomass production of both cowpea and rice by 38–45% without fertilization (P<0.05). The soil N contents were also higher in the Anthrosol but the wide C-to-N ratios due to high soil C contents led to immobilization of N. Despite the generally high nutrient availability, nutrient leaching was minimal in the Anthrosol, providing an explanation for their sustainable fertility. However, when inorganic nutrients were applied to the Anthrosol, nutrient leaching exceeded the one found in the fertilized Ferralsol. Charcoal additions significantly increased plant growth and nutrition. While N availability in the Ferralsol decreased similar to the Anthrosol, uptake of P, K, Ca, Zn, and Cu by the plants increased with higher charcoal additions. Leaching of applied fertilizer N was significantly reduced by charcoal, and Ca and Mg leaching was delayed. In both the Ferralsol with added charcoal and the Anthrosol, nutrient availability was elevated with the exception of N while nutrient leaching was comparatively low.

Modelling agronomic properties of Technosols constructed with urban wastes

The greening of urban and suburban areas requires large amounts of arable earth that is a non-renewable resource. However, concentration of population in cities leads to the production of high amounts of wastes and by-products that are nowadays partly recycled as a resource and quite systematically exported out of urban areas. To preserve natural soil resources, a strategy of waste recycling as fertile substitutes is proposed. Eleven wastes are selected for their environmental harmlessness and their contrasted physico-chemical properties for their potential use in pedological engineering. The aim is (i) to demonstrate the feasibility of the formulation of fertile substrates exclusively with wastes and (ii) to model their physico-chemical properties following various types, number and proportions of constitutive wastes. Twenty-five binary and ternary combinations are tested at different ratios for total carbon, Olsen available phosphorus, cation exchange capacity, water pH, water retention capacity and bulk density. Dose-response curves describe the variation of physico-chemical properties of mixtures depending on the type and ratio of selected wastes. If these mixtures mainly mimic natural soils, some of them present more extreme urban soil features, especially for pH and P(Olsen). The fertility of the new substrates is modelled by multilinear regressions for the main soil properties.

Effect of biochar on reclaimed tidal land soil properties and maize (Zea mays L.) response

Reclaimed tidal land soil (RTLS) often contains high levels of soluble salts and exchangeable Na that can adversely affect plant growth. The current study examined the effect of biochar on the physicochemical properties of RTLS and subsequently the influence on plant growth performance. Rice hull derived biochar (BC) was applied to RTLS at three different rates (1%, 2%, and 5% (w/w)) and maize (Zea mays L.) subsequently cultivated for 6weeks. While maize was cultivated, 0.1% NaCl solution was supplied from the bottom of the pots to simulate the natural RTLS conditions. Biochar induced changes in soil properties were evaluated by the water stable aggregate (WSA) percentage, exchangeable sodium percentage (ESP), soil organic carbon contents, cation exchange capacity, and exchangeable cations. Plant response was measured by growth rate, nutrient contents, and antioxidant enzyme activity of ascorbate peroxidase (APX) and glutathione reductase (GR). Application of rice hull derived biochar increased the soil organic carbon content and the percentage of WSA by 36-69%, while decreasing the ESP. The highest dry weight maize yield was observed from soil which received 5% BC (w/w), which was attributed to increased stability of water-stable aggregates and elevated levels of phosphate in BC incorporated soils. Moreover, increased potassium, sourced from the BC, induced mitigation of Na uptake by maize and consequently, reduced the impact of salt stress as evidenced by overall declines in the antioxidant activities of APX and GR.

Urban Soils in the Vadose Zone

Between the soggy ceiling of the ground water aquifer and the uppermost interface of earth and air is the unsaturated space of soil particles and pores invisible to most surface dwellers – the vadose zone. In cities, this space can be frozen in time under buildings and sidewalks, and contaminated with various kinds and concentrations of polluting substances. With more than 50% of the world’s population living in cities as of 2007, research on the composition, function and dynamics of urban soils is of utmost importance for urban ecological questions as well as the for the wellbeing of city dwellers world wide. Even before the 50% demographic benchmark, interest in anthropogenic soils began stirring in Germany in the 1970s in Berlin and Essen (Burghardt 1995; Blume 1975). At that time, research concerns revolved around the proper classification of soils in urban areas and the dilemma of restoring and re-using former industrial sites. From the 1980s until the beginning of the 1990s, pollution of urban soils with organic and inorganic contaminants became the focus of many studies (Thornton 1991; Lux 1993; Radtke et al. 1997). Since then, research on urban soils has substantially broadened. The BMBF (Federal Ministry of Education and Research) project “Evaluation of Urban Soils” from 1993 to 1996, for example, included groundbreaking work on the chemical, physical and biological properties of anthropogenic soils, involving major soil science institutions from the universities of Kiel, Essen, Hohenheim, Halle, Rostock and Berlin. Results are presented in Blume and Schleuss (1997).

Letter to the editors: Phyto-P-mining—secondary urban green recycles phosphorus from soils constructed of urban wastes

PurposeCities are hotspots of consumption of matter, energy, and water and hotspots of production of wastes, which are also secondary resources. Nutrients such as phosphorus are hardly extracted and recycled from these wastes, except from sewage sludge. This paper discusses a concept for the recycling of P from a great variety of urban wastes (phyto-P-mining).Materials and methodsPhyto-P-mining is based on the plant extraction of P from waste materials, which were used to produce planting substrates. They are intended for the greening of urban structures, which were de-vegetated during urbanization or which were not intended to be vegetated before (secondary urban green). After the newly established plants have extracted P, their biomass can be used to produce bioenergy (biogas, wood) or compost. Phosphorus could then be recycled from digestion residues and ashes or directly from compost.Results and discussionPhyto-P-mining is based on otherwise wasted nutrients and on the greening of a high number of not yet vegetated plots, including public or private plazas, sidewalks, roofs, and fallows. Greening is a major goal for urban planning, as functioning soil-vegetation-complexes provide ecosystem services such as climate regulation, dust absorption, wind brake, or aesthetic improvement. Especially in the dense inner city quarters, where vegetation is rare, new green improves public health and well-being. However, due to the lack of available horizontal but the high abundance of vertical structures like walls and facades in city centers, vertical green will be very important for phyto-P-mining. It can efficiently extract P from wastes due to its high ratio of biomass to ground area. Like the vertical areas, the vertical greens are often private properties. Although private greening is primarily conducted for social and cultural reasons, direct market benefits such as bioenergy or fertilizers may reduce costs for the greening. This will foster private urban greening to the benefit of the community and also the recycling of nutrients from urban resources.ConclusionsPhyto-P-mining based on secondary urban green will reestablish soil functions and natural cycling mechanisms in artificial urban systems. The approach has a great potential (i) to improve the urban living environments and to deliver benefits such as (ii) the recycling of phosphorus and other nutrients from urban wastes for the application in urban or rural agri- or horticulture and (iii) the ethically and ecologically sound production of bioenergy.

Depression storage capacities of different ideal pavements as quantified by a terrestrial laser scanning-based method.

Rainfall partition on paved urban surfaces is governed to a great extent by depression storage. This is especially the case for small rainfall events, which are often ignored in urban hydrology. If storage, infiltration and evaporation (important for urban heat island mitigation), rather than storm water run-off, are of interest, high-resolution simulations with exact values for depression storage capacities are required. Terrestrial laser scanners deliver fast, high-resolution surveys of pavement surface morphology. The depression storage capacity can be quantified from 3D points by generating digital elevation models and applying cut-and-fill algorithms in a geographic information system. The method was validated using a test model. It was possible to quantify depressions with a depth of at least 1.4 × 10(-3) m and a surface of at least 15 × 10(-6) m(2) with an uncertainty below 30%. Applying this method, the depression storage capacities for 11 ideal, typical pavement designs were found to vary from 0.07 to 1.4 mm. Realistic urban pavements must also be surveyed, as cracks and puddles from their use history can have a major impact on the depression storage capacities and thus on infiltration, evaporation and, finally, the annual run-off.

Pools of sulfur in urban rubble soils

AbstractPurposeElevated concentrations of sulfate in groundwater are increasingly becoming a problem in several European cities. Building rubble from the World War II is assumed to be a major source of sulfate. This study characterizes pools of sulfur in rubble-composed technosols, and assesses their potential to release sulfate.MethodsSix urban soil profiles have been analyzed. Fractions of the main technogenic components in the skeleton fractions were determined by hand sorting approximately 100 kg of material. Total sulfur and water soluble sulfate were determined. Microplate-scale fluorometric assays were applied to measure the depth-dependent enzyme activity of arylsulfatase. The mineral composition of soil samples was analyzed using powder X-ray diffractometry. Binding forms of sulfur were determined using X-ray absorption near-edge structure spectroscopy.ResultsThe maximum total content of sulfur is 4.6 g·kg−1; that of readily soluble sulfur is 2.3 g·kg−1. Both gypsum and traces of barite and ettringite were detected in some fine soil and component samples. Samples taken from deeper soil depths exhibited higher total sulfur and soluble sulfate contents. The depth profiles of sulfur and the activity of arylsulfatase suggest advanced leaching of inorganic sulfates from the upper horizons. Hence, sulfur is mainly organically bound in the topsoil. In the subsoil, however, sulfates make up about 90 % of total sulfur, approximately 30 % of which is readily soluble.ConclusionsThe sulfur pool of rubble-composed soils differs completely from natural soils. This is particularly the case for subsoils, in which high contents of sulfur are readily soluble. This suggests that sulfate minerals such as gypsum predominate. Urbic technosols can therefore be assumed to be one of the main sources of sulfates in urban groundwater.

Long-term Release of Sulfate From Building Rubble–Composed Soil: Lysimeter Study and Numerical Modeling

Abstract High sulfate concentrations in the groundwater occur in several cities and particularly in Berlin, Germany. Building rubble–composed soils and landfills are a major source of dissolved sulfates. This study assesses the sulfate release dynamics of such rubble-composed substrates. The substrate was taken from a building rubble landfill in Berlin, which was created after World War II. It was poured into two lysimeters, which were irrigated repeatedly for 2 years to simulate several years of groundwater recharge. Sulfate concentration in the leachate was measured monthly. Sulfate release dynamics were effectively described with PHREEQC, assuming either one or two sulfate pools with kinetically limited dissolution. The volume that percolated the lysimeter column was 2,440 L, corresponding to 17 years of local groundwater recharge. At the beginning, sulfate concentrations increased from approximately 10·10−3 mol ·L−1 to 13·10−3 mol · L−1, which is close to gypsum solubility concentration. After 1.8 pore volumes, a decrease was observed, and after 8 pore volumes, concentrations were relatively constant at levels less than 3·10−3 mol · L−1. The data were best described by a model that included a kinetically limited dissolution of gypsum from two sulfate pools different in their effective surface areas. One pool can be ascribed to fine-grained gypsum particles, whereas the other can be ascribed to coarse-grained ones. Overall, rubble-composed substrates can be a severe long-term source of sulfates.

Water retention characteristics of coarse porous materials to construct purpose-designed plant growing media

ABSTRACT Among potential components to construct Technosols for urban greening purposes, the commercially available geogenic coarse porous materials (CPMs) are mainly used in practice because of their high porosity. However, the knowledge of the hydraulic behavior of CPMs as well as of their mixtures with other substrates is limited, provoking their suboptimal usage. Therefore, we determined the water retention characteristics, including the available water capacity (AWC) of six geogenic CPMs: porlith, expanded shale, expanded clay, tuff, pumice, and lava. In order to obtain the water retention characteristics of the CPMs as well as of their mixture with sand (1:4 per volume), the following methods adapted from soil physics were applied over a wide range of pressure heads: Equi-pF apparatus, ceramic tension plates, pressure plate extractors, WP4C apparatus, and water vapor adsorption. The results were used to parametrize the modified Kosugi model (using SHYPFIT 2.0). Porlith and tuff have the highest AWC (0.37 m3 m−3 and 0.17 m3 m−3, respectively) and are the only ones which can be recommended as effective water-retaining materials. Further materials exhibit an AWC less than 0.10 m3 m−3. The CPMs exhibit a bimodal pore size distribution, which can be well described by the applied model, except for pumice and expanded shale. The mixtures present overall low AWCs up to 0.07 m3 m−3, with the pure sand having less than 0.03 m3 m−3. For practical application a quite high ratio of CPM is needed, and the mixing material must be adapted to the hydraulic properties of the CPMs. The water inside the CPMs may be easily available for plant roots able to penetrate in the CPMs’ coarse pores.