Institut für Bodenkunde und Standortslehre

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Ecosystemic Effect Indicators to assess Effects of agricultural Landuse on Ecosystems
(2000) Merkle, Andrea Hildegard; Kaupenjohann, Martin
Agricultural production and its material and non-material emissions may cause side-effects in ecosystems. These effects have to be assessed and evaluated. The aim of the present study is to provide a tool that relates emissions of agricultural production and affected ecosystems. This tool represents an indicator approach. The needed indicators are defined as ecosystemic effect indicators (EEI). Within the study a multistage procedure is developed which should be pursued in identifying indicators. To assess which emissions must be regarded in detail an estimation of relevance by means of an emission and input classification preceeds the indicator development. Subsequently, EEI are developed for the relevant emissions and inputs. The derivation of EEI is carried out by the following steps: 1) One starts top-down at the target 'maintaining the ecosystem functioning' in this work depicted by the utility functions. A list with characteristics that are dependent on hierarchical levels is compiled for each relevant function. 2) Starting at one specific input a list of potential receptors is compiled bottom-up. These represent potential effect indicators. 3) By overlapping the lists of the steps 1 and 2 one yields EEI specific for the utility function and the input under consideration. The step 3 is performed by means of expert knowledge. The advantage of the indicator approach is its operativeness which is site-independent. The results of the study show that EEI may be deemed to be promising tools to picture human influences in particular of agricultural production on ecosystems. The results of the case study provide the basis to assess effects on ecosystems for some major stressors. In cases where critical values are available site specific quantitative statements concerning ecological effects within the frame of sustainable agriculture are enabled by the present method for the derivation of indicators. Subsequently, necessary measures can be deduced
Gamma-ray spectrometry as auxiliary information for soil mapping and its application in research for development
(2019) Reinhardt, Nadja; Hermann, Ludger
Sustainable yield increase is desperately needed for enhancing global food security, in particular, in Sub-Saharan Africa. There population growth and resulting land degradation accompany with extreme weather events. As a consequence, famines frequently occur. For planning result-oriented agricultural research for development (R4D) like in the Trans-Sec project (www.trans-sec.org), in which this thesis was embedded, local environmental, as well as social realities must be taken into account prior to any cropping experiment. Only this way, cost-efficient and adapted solutions for local subsistence farmers, but also conclusive outcomes for researchers, can be obtained. For this purpose, methods that work quick and cost-efficient are a prerequisite. In this respect, gamma-ray spectrometry as rapid soil survey method is reviewed in the first part of this thesis. Soil or geological exploration are easily accomplishable, in either airborne (with helicopters, airplanes or drones) or proximal (stationary or on-the-go) surveys. Gamma decays of the naturally occurring isotopes 40-potassium (40K), 238-uranium (238U) and 232-thorium (232Th) that appear in sufficient amounts and decay energies for field measurements are counted per time. The counts are then transferred to the respective element contents. Water and soil organic matter attenuate gamma signals, on one hand hampering signal interpretation, on the other hand indirectly enabling soil water content and peat mappings. Gamma-ray signatures of soils depend on (1) mineral composition of the bedrock, as well as (2) weathering intensity and related soil forming processes, that, in turn, influence the environmental fate of 40K, 238U and 232Th. Hence, due to soil formation heterogeneity at the landscape scale, resulting gamma signatures are locally specific and make soils readily distinguishable. In two villages in central Tanzania, participatory soil mapping in combination with gamma-ray spectrometry served as rapid and reliable approach to map local soils for later cropping experiments. Local farmers indicated major soil types on satellite images of the village area, which were the basis for further mapping steps. Fingerprint gamma-ray signatures of reference soil profiles were collected. Subsequent gamma-ray surveys on transect walks accelerated soil unit delineation for the final soil map. Challenges were misunderstandings related to language issues, variable soil knowledge of individual farmers and erosion leading to staggered soil profiles and non-distinctive signatures in some places. The combination of indigenous knowledge and gamma-ray spectrometry, nevertheless, led to a quick overview of the study area and made laboratory soil analyses largely redundant. The gained gamma-ray signal information were further statistically evaluated. For this purpose, distinction of major local soil types via K/Th ratios were graphically and statistically tested. The results showed that gamma-ray spectrometry is a sound method to distinguish certain local clay illuviation soil types by their K/Th ratios. The last part of the thesis covers the Trans-SEC approach of testing innovations for sustainable agricultural yield increase. Pearl millet (Pennisetum glaucum (L.) R.Br.) as the typical staple food in the study region was used as example crop. The process was scientist-led but local farmers selected the innovations that they considered adequate to their needs. Tied ridging for enhancing the water storage and placed fertilizer for increasing fertilizer efficiency was offered for their choice. Transferability of results from on-station experiments and demonstration plots in the village to farmers plots and trans-disciplinary issues are discussed. The number of factors that influence the result, as well as data insecurity increased with every level of spatial aggregation (on-station, demonstration plot and on-farm plots in the village). Soil type, position of the plot in the landscape (lateral water flow, distance to homesteads and, hence, fertility status) were the major influencing factors. In particular, the data insecurity related to on-farm trials due to low control intensity suggests to only conduct such experiments if large numbers of replicates (large N-trials) are feasible in future approaches. In conlusion, the thesis shows, that local knowledge combined with modern science is beneficial for agricultural R4D projects. Shortcomings within the transdisciplinary experimental approaches are pointed out. In particular, with respect to knowledge gained from the linkage of local experience and scientific approaches, there is still high potential. For this purpose, social and applied natural sciences should both strive for more interdisciplinary collaboration.
Turbulent exchange of energy, water and carbon between crop canopies and the atmosphere : an evaluation of multi-year, multi-site eddy covariance data
(2019) Eshonkulov, Ravshan; Streck, Thilo
The increase of anthropogenic CO2 emissions and other greenhouse gases has raised concern about climate change. Climate change has manifold impacts on yield and yield quality, crop rotations, carbon and nitrogen cycling, water regime and agricultural production systems. To understand its consequences on environmental systems, measuring the matter and energy exchange at the land surface provides data to help validate and inform a wide range of process models. Such flux measurements at the land-surface provide an opportunity to test simulations of processes in the soil-plant-atmosphere continuum. Currently, such measurements are mainly based on the eddy covariance (EC) method, for the quality of which the energy balance closure (EBC) is a problem. The EBC significantly influences the calibration and validity of land-surface models, especially in regard to the energy and water balance at the Earth’s surface. The EBC quantifies the deviation between turbulent fluxes and available energy. It is crucial to obtain high-quality EC measurements to determine the reasons for the EBC. The research aims of this dissertation were: 1) to clarify the role of minor storage and flux terms in the energy balance, 2) to determine the possible reasons for the energy imbalance using a long-term dataset (2010-2017) from agricultural croplands, and 3) to investigate the effects of region, site, year and crop type on carbon fluxes and budgets. In the first study (Chapter 2) the contribution of minor storage terms to the EBC were investigated. I also determined the contribution of ground heat fluxes calculated by different methods. A harmonic analysis method was used to calculate ground heat fluxes from measurements of heat flux plates and soil temperature sensors. Soil heat storage and enthalpy change in the plant canopy were determined at different locations within the EC footprint. Considering minor storage terms improved the energy balance closure on average by 5.0 % in 2015 and by 6.8 % in 2016. The greatest energy balance closure improvement occurred in May of both study years. The dominant fraction of minor energy storage was energy uptake and release through photosynthesis and respiration. Additionally, the energy fluxes related to soil temperature change were also observed. The ground heat flux calculated by harmonic analysis from soil heat flux plates narrowed the EBC by 3 % compared to the calorimetric method. The results indicated that the typical correction approach to achieve energy balance closure, i.e. the Bowen-ratio method, overestimated the turbulent fluxes. The second study (Chapter 3) investigated the effects of crop type, site characteristics, wind directions, atmospheric conditions and footprint on the EBC. The long-term evaluation of EC measurements showed that, with the EC method, 25 % of the available energy could not be detected. Decreasing the flux footprint area increases the chance of a more homogeneous area. Homogeneity plays an important role in achieving a better energy balance closure. The synthesis of long-term EC data indicated that the sonic anemometer is very sensitive to orientation, not allowing accurate measurements from all wind directions. Discarding the measurements from wind directions 0° and 90° at EC4 improved the EBC from 80 to 84 %. In the third study, presented in Chapter 4, a long-term and multi-site experiment was evaluated to clarify the effects of site, year and region on the CO2 fluxes and budgets in agroecosystems. The net ecosystem exchange of CO2 fluxes – measured on six sites during eight years – was comprehensively examined. Winter rapeseed had the lowest CO2 uptake, cropping of silage maize resulted in the highest C losses. The management of harvest residues was the most effective means of controlling the C budgets. Comparing the CO2 fluxes processed with the recently developed ogive optimization method versus the conventional calculation showed that eliminating low-frequency contributions had a considerable effect. On average, the ogive optimization method delivered 6.9 % higher net ecosystem exchange rates than the conventional method. This dissertation provides new insights into how to obtain better measurements of matter and energy fluxes from EC measurements by a) considering storage terms otherwise neglected, b) using harmonic analysis for calculating ground heat fluxes, c) discarding fluxes from behind the anemometer and d) applying the ogive optimization method.

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