Michael Facklam

Simulation of the dry matter production and seed yield of common beans under varying soil water and salinity conditions

Abstract We present a model that simulates the effects of water and salinity stress on the growth of beans. The model derives a combined soil water/salinity stress factor from the total water potential (combination of the matric and the osmotic potentials) and uses this stress factor as a growth limiter in a growth model. The model was tested on data obtained from two greenhouse trials of beans ( Phaseolus vulgaris ) grown under a range of soil water and salinity conditions. The simulated dry weight of the bean generally followed those observed. In the first trial, the comparison between simulated and observed total dry weight and seed yield gave R 2 values of 0.97 and 0.92, respectively. Comparison of the simulated to the observed dry weight for the second trial gave R 2 values of 0.85 and 0.89, respectively. These indicate a good performance of the model in general. The principle of deriving a combined water/salinity stress from the matric and osmotic potentials is simple and can be included as a simple routine in many existing crop models without much difficulty.

Ein autoregressives Verfahren zur Bestimmung der gesättigten und ungesättigten hydraulischen Leitfähigkeit

Mit Hilfe der Augenblicksprofilmethode wurde die Wasserleitfahigkeit fur den wasserungesattigten Bereich (k) bestimmt. Dabei wurden Wassergehalte und Wasserspannungen als Funktion der Zeit und Tiefe an Stechzylinderproben gemessen. Die Messungen der Wassergehalte und Wasserspannungen erfolgten mit TDR-Sonden bzw. Druckaufnehmertensiometern. Das Untersuchungsmaterial umfaste 40 Bodenhorizonte mit einem weiten Spektrum in Textur und Lagerungsdichte. Neben den k-Werten wurden auch die gesattigte Wasserleitfahigkeit kf und die pF-Kurve bestimmt. Anhand dieser Daten wurde ein „autoregressives Verfahren“ zur Berechnung der k-Werte fur die Wasserspannungen 30, 60, 100, 300 und 600 hPa fur lehmige Sande, sandige, tonige und schluffige Boden entwickelt. Dabei wurde zunachst der k-Wert berechnet, der sich mit der grosten Genauigkeit anhand von Kennwerten der pF-Kurve ermitteln last. Bei der k-Wertberechnung der benachbarten Wasserspannungsbereiche geht neben den Kennwerten der pF-Kurve der bereits berechnete k-Wert mit ein. Auf diese Weise wird eine hohere Genauigkeit bei der Ermittlung der k-ψ-Beziehung zwischen Wasserleitfahigkeit und Wasserspannung erreicht, wie der Vergleich mit anderen Verfahren zeigt. An autoregressive procedure to predict the hydraulic conductivity — Comparison of measured and predicted results An instantaneous profile method was used to measure the unsaturated hydraulic conductivity. Relatively new techniques involving undisturbed soil samples instrumented with minitensio-meters and Time-Domain-Reflectometry (TDR) mini-probes were used for the experiments. The laboratory method allows a high spatial and temporal resolution. Laboratory measurements were carried out for 40 soil horizons with a wide spectrum of texture and bulk density. In addition, retention curves were measured using the standard pressure plate apparatus. Using this homogeneous set of data, an autoregressive model was developed which allows a stepwise calculation of the hydraulic conductivity for a water potential range of —30 up to —600 hPa. This model was developed for loamy sands, sandy, silty and clayey soils in conjunction with data from the retention curves. The calculation procedure starts with the determination of an initial unsaturated conductivity (k) close to field capacity, i.e., for water potential from —60 hPa up to —100 hPa. This first value is then used to predict other conductivity values using appropriate changes in soil water content corresponding to a defined range of the soil water potential. Subsequently, the hydraulic conductivities for higher and lower potentials were estimated considering the k value of the previous step in combination with the data of the retention curve of the next water potential range. The advantage of this empirical model is the indirect consideration of soil structure, in contrast to the closed-form van Genuchten-Mualem (vGM) model. To demonstrate these effects on different fitting procedures, the vGM model was also used to describe soil hydraulic functions. The accuracy of both, the vGM model and the autoregressive one, were compared for various fitting procedures and soils.

From a stinking wastewater disposal field toward a recreation area—the story of an unconventional soil remediation in Berlin, Germany

PurposeWastewater irrigation is still a common practice in many cities worldwide. After ending the wastewater irrigation, the question arises as to how the highly polluted areas can be reused. Mostly, the remediation costs for liming or adding synthetic soil conditioners are too high for decision makers, often leading to unattractive wastelands in neighboring suburbs. This story shows how part of a former wastewater disposal field in Berlin (Germany) was remediated by adding and mixing loam-rich glacial until excavated from subway construction work. The remediation led to long-term improvements of soil and landscape, which nowadays is an attractive forested recreation area. Part of this landscape is used as an ecological lab for research, art, and education.Materials and methodsThe article summarizes the results of soil analysis of the contamination status and remediation technique over the last 2 decades. We collected and reevaluated historical data, research results, technical reports, and graphic materials concerning the wastewater disposal field in Berlin, Germany.Results and discussionThe remediation concept without adding any synthetic substances was a successful soft technology leading to (i) a reduction of the long-term groundwater risk, (ii) an immobilization of the trace element concentration in the soil solution, and (iii) a reduction of the metal uptake by plants. Remediation led to much better conditions for plant growth, soil fauna, and microbiological activity, which improved the environment in a sustainable way. The implementation of a new landscape concept combining ecology, culture, and art totally changed the character of the landscape from former stinking wastewater fields to present-day attractive sites that can be used for many purposes.ConclusionsThe remediation of the former wastewater disposal fields, using natural glacial till materials rich in clay and silt, became a “story of success.” However, a remediation project of this type and scope only becomes reality if all responsible actors in society participate continuously. We conclude that stakeholders should not focus only on remediation costs but also on the benefits for society: reclaiming waste sites significantly improves our well-being.