Browsing by Subject "Licht"

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Development of a generic, model-based approach to optimize light distribution and productivity in strip-intercropping systems
(2014) Munz, Sebastian; Claupein, Wilhelm
Due to a growing world population, an extension of bioenergy production and the larger proportion of meat and dairy products in the human diet, with the latter particularly in India and China, the demand for agricultural products will further increase. Under decreasing resources and negative environmental impacts related to past intensification, more sustainable agricultural production systems need to be developed in order to meet the future demand for agricultural products. China, as the most populous nation with an enormous economic growth since the end of the 1970’s, plays a major role in global agricultural production. On a national level, agricultural production has to be increased by 35% during the next 20 years. However, land and water resources in China are very limited. With this in mind, the Sino-German International Research Training Group (IRTG) entitled ‘Modeling Material Flows and Production Systems for Sustainable Resource Use in Intensified Crop Production in the North China Plain’ was initiated by the Deutsche Forschungs-Gemeinschaft (DFG) and the Chinese Ministry of Education (MOE). The present doctoral thesis was embedded in the IRTG and focused, in particular, on exploring combinations of different crops produced on the same land at the same time, known as intercropping. In general, the higher productivity in intercropping, compared with monocropping, arises from the complementary use of resources (radiation, water, and nutrients) over space and time by crops that differ in physiology, morphology and phenology. The decisive question is how to optimize intercropping systems over space and time. To address this question, the present doctoral thesis combined field experiments with modeling approaches with the following aims: (i) to investigate the light availability on high temporal and spatial resolutions; (ii) to develop and validate a model that simulates the light availability for the smaller crop and accounts for the major aspects of cropping design; (iii) to determine the effect of the modified light availability on growth of maize and the smaller, shaded crop; (iv) to evaluate the plant growth model CROPGRO for its ability to simulate growth of the smaller, shaded crop; (v) to investigate the interactions between maize cultivar, cropping design and local growth conditions; and, (vi) to identify promising cropping designs and detect future research needs to increase the productivity of strip-intercropping systems. For this purpose, field experiments comprising of strip-intercropping with maize (Zea mays L.) and smaller vegetables, including bush bean (Phaseolus vulgaris L. var. nana), were carried out over three growing seasons from 2010-2012 in southwestern Germany and in the North China Plain. Growing the crops in strips facilitates mechanized management, addressing the ongoing decrease of intercropping in China due to labor scarcity in rural areas. The crop combination of maize, a tall C4-crop with erectophile leaves, and bush bean, a small, N-fixating C3-crop with a more horizontal leaf orientation, was chosen due to the large potential for a complementary resource use. Special emphasis was given on the competition for light as it plays a major role in this cropping system due to the large height differences between the crops. In this context, measurements of the photosynthetically active radiation (PAR) were conducted on high spatial (individual rows across the strip) and temporal resolutions (five-minute intervals) at the top of the bush bean canopy over a two-month co-growing period with maize. The collected data formed the basis of the simulation study towards investigating competition for light and its influence on plant growth with modeling approaches. Experimental results showed that maize yields increased in the border rows of the strip due to a higher lateral incoming radiation in years with a sufficient water supply. On average, maize yields calculated for strips consisting of 18 to four rows increased by 3 to 12% and 5 to 24% at the German and Chinese sites, respectively. Analysis of yield components revealed that yield increases in the border rows of the maize strip were mainly determined by a larger number of kernels per plant. On the other hand, shading by the taller adjacent maize induced considerable shade adaptations of bush bean, such as larger canopy dimensions and a substantially increased leaf area index due to thinner, larger leaves. These shade adaptations increased light interception, and indicated that bush bean could tolerate shading up to 30%, resulting in a total and pod dry matter similar to that of monocropped bush bean. These results suggested that there is a good potential for utilizing bush bean in strip-intercropping systems in combination with taller crops. However, higher shade levels (>40%) resulted in considerable decreases of total and pod dry matter. The high temporal and spatial resolution of the PAR measurements clearly revealed a highly heterogeneous diurnal distribution of PAR across the bush bean strip. The developed light model simulated this heterogeneity with a high accuracy under both clear and cloudy conditions. Comparison of simulated and observed hourly values of PAR across several rows within the strip of bush bean showed a root mean square error (RMSE) ranging between 47 and 87 μmol m-2 s-1 and a percent bias (PBIAS) ranging between -3.4 and 10.0%. Furthermore, the model reasonably captured the influence of different widths of the bush bean strip, strip orientations and maize canopy architecture (height, leaf area index, and leaf angle distributions). Simulations run for different latitudes and sky conditions, including different strips widths, maize canopy heights and leaf area indices (LAI), indicate that: (i) increasing the strip width might only reduce shading in the border rows of the smaller crop at lower latitudes under a high fraction of direct radiation; (ii) at higher latitudes, the selection of a maize cultivar with reduced height and LAI are suitable options to increase the light availability for the smaller crop. The present doctoral thesis presents the first approach to use the monocrop plant growth model CROPGRO to simulate growth of a legume crop grown in an intercropping system. The CROPGRO model was chosen because it provides an hourly simulation of leaf-level photosynthesis, and algorithms that account for the effects of radiation intensity on canopy dimensions and specific leaf area. CROPGRO, calibrated on data of monocropped bush bean, captured, quite well, the effects of the strongly reduced radiation on leaf area, and total and pod dry matter in the most shaded bush bean row. This indicated the models’ applicability on other intercropping systems exhibiting high levels of shading. Under a lower level of shading, cultivar and ecotype parameters had to be calibrated individually for a respective row within the bush bean strip to achieve a high accuracy of the simulations. Model simulations aided in explaining the effects arising from different shares of direct and diffuse radiation on canopy photosynthesis. This is a very important point to be further explored as diffuse radiation remains a part of light distribution and photosynthesis hardly studied in general; and, in particular, becomes more important with the increasing impact of shading. The simulation of the light availability, plant growth and yield formation within the strip of maize can be handled in a similar way as described for the smaller crop, bush bean. Modifications of the light model and a suitable plant growth model are presented and discussed. In conclusion, the main outcomes of this thesis indicate that the selection of cultivars adapted to the modified light environment have the largest potential to increase the productivity of strip-intercropped maize and bush bean. The most important characteristics of suitable maize cultivars include: (i) a high potential of kernel set; (ii) a higher water stress tolerance; and, (iii) reduced canopy height and LAI. The importance given to each of the components would subsequently be determined by the local weather and management conditions and the shade tolerance of the neighboring crop. On the other hand, to optimize yields of the smaller shaded crop, we present two options: (i) to modify the co-growing period of the intercrops temporarily to alleviate light competition during shade-sensitive growth stages; and, (ii) to modify the cropping design spatially and/or select different maize cultivars to reduce shading to the tolerated degree during the respective growth stage of the smaller crop. When the shade tolerance during the respective growth stages is determined, the light model developed can be used to optimize the cropping system temporarily and spatially. In this thesis, a promising approach, which combines a specific light partitioning model with process-oriented monocropping plant growth models, was developed. All models included in the approach can be applied at any location, and their generic nature also facilitates the integration of other crops. These attributes present a highly valuable contribution to intercropping research as their future optimization will depend strongly on the efficiency of the research efforts given: (i) the complexity of the underlying processes that determine the productivity; and, (ii) the minor share of time and money invested in intercropping research. Intercropping research has to prevent reinventing the wheel by identifying aspects in common with and already studied in monocropping systems and focus on aspects particularly inherent to intercropping systems.
Operating strategy to reduce the energy consumption of flat-panel airlift photobioreactors with respect to mixing of thermosynechococcus elongatus suspension cultures : light-specific adaptation of the superficial gas velocity
(2018) Bergmann, Peter; Trösch, Walter
Photoautotrophic microalgae mass production is limited by light availability due to effects of absorption and reflection, especially throughout outdoor cultivation prohibiting the adjustment of photon-flux density (PFD). Generating turbulence within the cultures in order to minimize photolimiting and photoinhibitive effects is the method of choice to overcome that obstacle. Then again, energy required for its generation represents one of the major drivers contributing to overall production costs of microalgae biotechnology. The present work describes the development of an advanced operating strategy for the mixing of flat-panel airlift loop photobioreactors (FPA-PBRs) that through its application decreases the specific energy consumption, thus the energy requirement per unit of biomass produced, when cultivating phototrophic microorganisms. Experiments were carried out with the thermophilic cyanobacterium Thermosynechococcus elongatus BP-1 utilizing distinct FPA-PBRs equipped with culture-flow directing installations and illuminated by high pressure sodium (HPS) lamps. In the first paper, the impact of utilizing respective FPA-PBRs is investigated. Preliminary experiments were performed in order to eliminate any limitations beyond the sphere of influence of photobioreactor (PBR) design. Apart from the NO3- concentration which had to be retained at 2000 mg L-1 to sustain non-limited growth, special attention was paid to the administration of dissolved inorganic carbon (DIC), inter alia in the form of hydrogen carbonate as CO2 gas solubility was limited by the applied cultivation temperature of 55°C. It is for this reason, in conjunction with a short residence time of the CO2-enriched air bubbles that an increase in CO2 concentration showed only minor effects compared to increasing carbonate concentration that directly correlated to maximum productivity attaining 2.9 gDW L-1 d-1, the highest to be reported for T. elongatus BP-1, using 0.04 g L-1 Na2CO3. When comparing PBRs with and without culture flow directing installations, e.g. static mixers, it was found that the former outperformed the latter as an increase in maximum volumetric productivity and final biomass concentration by a factor of 3.4 and 2.0 was recorded, respectively, whilst the energy input in the form of superficial gas velocity remained unchanged. The enhanced growth performance was attributed to improved specific light availability due to the formation of eddies within cultures induced by static mixers. Thereby, light dependent downregulation of quantum-yield and respiratory losses were reduced, ultimately allowing for a more efficient photon-utilization towards assimilatory photochemistry when compared to randomly mixed cultures. In the second study, the joined impact of PFD, biomass concentration and superficial gas velocity is investigated and an operating strategy for FPA-PBRs deduced. Preliminary experiments were performed in order to establish a modified photosynthesis irradiance (PI) curve at default mixing settings which defined the light compensation point and the irradiance of saturation with 100 μmol m-2 s-1 and 400 μmol m-2 s-1, respectively. Cultivations were then performed at sub-, quasi-, and supra-saturating PFDs (180 .. 780 μmol m-2 s-1) utilizing multiple gas flow velocities (0.11 .. 0.83 vvm). It was found that at a given velocity, productivity and final biomass concentration increased with increasing PFD. Moreover, it was found that in comparison with default mixing settings, the superficial gas velocity during sub-saturating PFD and/or biomass concentrations < 3 gDW L-1 can be reduced to cut operational expenditures (OPEX) on mixing, whilst an increase during supra-saturating PFD and/or higher biomass concentrations enhances productivity and final biomass yield. An operating strategy based on the PFD-triggered adjustment of the superficial gas velocity is proposed and results were mathematically translated to exemplary outdoor diurnal cycles of PFD. By applying the strategy on sunny days, productivity is increased by 24%, while reducing not only energy input but also CO2-demand by 11%. On cloudy days, productivity is only slightly increased but energy input and CO2-demand reduced by 37%. Consequently, the specific energy requirement of FPA-PBRs when cultivating phototrophic microorganisms is reduced significantly, especially at locations with only stochastic light supply, e.g. in temperate latitudes.
Untersuchungen zur räumlichen Heterogenität von Kronenstruktur und Bestandesniederschlag in einem tropischen Bergregenwald
(2008) Oesker, Mathias; Küppers, Manfred
The objective of this study was to investigate the distribution and heterogeneity of canopy structure and precipitation throughfall and related with this the factors light, water, and nutrient input. Further to appraise the consequences of this heterogeneity as a factor, which forms ecological niches. The study took place in a tropical mountain rain forest in southern Ecuador, specifically in the Reserva San Francisco located north of the Podocarpus National Park. The area of research covered the altitudinal range from 1950 m a.s.l. to 2275 m a.s.l. Nine plots of 400 m2 (20 m by 20 m) were set up in three forest types, which differed in tree species composition (HOMEIER 2004). Two forest types were located on a ridge and one was in a gorge at the same elevation as the lower ridge forest type. In each forest type three representative plots were chosen and a total of 31 study points were defined. At each point throughfall was collected during a one-year period. In all throughfall samples the following parameters were determined: Volume, pH, electrical conductivity, concentration of K, Mg and Ca, nitrate, ammonium, organic nitrogen, phosphate, P, Mn, Cu, Rb, Sr and Pb. The canopy structure was determined at all points with both structural measurements and hemispherical photography over a period of three years. Lab experiments with a representative selection of tree species were performed in order to determine leaf surface water storage capacity and nutrient leaching out of leaves. For determination of canopy structure hemispherical photography turned out to be a particularly efficient method. The software HemiView (DeltaT) was used to calculate important information such as canopy openness, light environment and LAI. A high spatial heterogeneity with a coefficient of variation (CV) of 59 % was found for all parameters. It was higher than the temporal variability over three years (CV 12 %). The throughfall was most heterogeneous within the investigated parameter with a CV of 64 %. In total close to 82 % (between 0.5 % and 492 % and a CV 29 %) of the volume of the incident precipitation could be collected as throughfall in the forest. With this throughfall 49.1 kg ha-1 a-1 K, 3.7 kg ha-1 a-1 Mg and 8.7 kg ha-1 a-1 Ca (mean values) were transported. During low intensity rain events the proportion of throughfall, expressed as percentage of incident throughfall was significantly lower than the annual mean of the incident precipitation. For high rain intensities no differences were found. With a geostatistical approach to investigate the spatial distribution of the throughfall no clear results could be calculated because the three replicates diverged strongly from each other. Canopy structure and its species composition was influenced by the distribution of throughfall. Related to the amount of throughfall it could be shown that with an open canopy up to 100 % of the incident precipitation could be collected. Underneath a closed canopy, in average less throughfall was collected. However, the volume of throughfall showed high spatial distribution and heterogeneity with even more than 100 % of incident precipitation. Nevertheless, throughfall volume can be predicted using the parameters radiation and canopy openness at a zenith angle of 36°. Average water storage capacity of leaf surfaces from eleven most common tree species resulted in 74.74 ml m-2 leaf area. In a dry canopy with a theoretical equal distribution of precipitation and a given LAI this value equals 0.38 mm of rain. The nutrient leaching out of leaves is species dependent and differs statistically. Those lab results can be extrapolated to the entire forest: Including the water storage capacity and the number of rain events, a maximum leaching capacity of 220 kg ha-1 a-1 K, 14 kg ha-1 a-1 Mg and 67 kg ha-1 a-1 Ca can be calculated. The main focus of this study was to investigate heterogeneity of abiotic factors and its ecological consequences. In the forest type with the most heterogeneous canopy structure and the most heterogeneous distribution of throughfall amounts were found. Lowest heterogeneity of spatial distribution of throughfall element contents was found in forest type with the lowest tree species diversity. The higher the tree species diversity the more heterogeneously scattered is the element content in the throughfall.