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    ABSTRACT: Food security will be the biggest challenge for Tanzania in the next decades. Besides, Tanzania has a multifarious ecosystem, which is endangered through not adapted agronomic practices. Current innovation strategies focus mostly either on the issue of food security or on environmental damages, but rarely on both issues. However, both issues are very crucial. With crop models, a wide range of agricultural practices can be investigated to show possibilities to optimize the application of these practices. Model assessments allow to separate the effects of agronomic and climatic conditions. The process-based model SWIM (Soil and Water Integrated Model) can compute the impacts of agronomic practices and thus develop strategies to decrease the yield gap between actual (farm) yields (Ya) and potential yields (Yp). The Yp are limited through the nutrient (Yn) and water supply and reduced by pests, diseases, and weeds. Furthermore, socio-economic impacts are also relevant (knowledge, tradition, or culture). These impacts can be captured by statistical crop models. Due to regional-adapted, integrated agronomic practices, Ya can be increased and thus the yield gap between Ya and Yp can be decreased. However, enhanced yields due to sufficient nutrient supply are more sensitive on climate (higher yield volatility). In particular, for innovative farmers increase the production risk of climate change impacts. These endangered adaptation from farmers and therefore both food security and the environment. However, not all influences between Ya and Yn can be explained by agronomic (fertilizer application, harvest time, tillage, and plant protection) and climatic conditions. Additionally, the Ya are affected by a broad range of non- biophysical, socio economic constraints. To decrease the yield gap on regional level, agricultural practices and knowledge are required, which consider regional-specific the issue of food security and environmental protection in a balanced ratio.
    12/2015; 29:231. DOI:10.1016/j.proenv.2015.07.287
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    ABSTRACT: Water tables are dropping by approximately one meter annually throughout the North China Plain mainly due to water withdrawals for irrigating winter wheat year after year. In order to examine whether the drawdown can be reduced we calculate the net water use for an 11 year field experiment from 2003 to 2013 where six irrigated crops (winter wheat, summer maize, cotton, peanuts, sweet potato, ryegrass) were grown in different crop rotations in the North China Plain. As part of this experiment moisture contents were measured each at 20 cm intervals in the top 1.8 m. Recharge and net water use were calculated based on these moisture measurement. Results showed that winter wheat and ryegrass had the least recharge with an average of 27 mm/year and 39 mm/year, respectively; cotton had the most recharge with an average of 211 mm/year) followed by peanuts with 118 mm/year, sweet potato with 76 mm/year, and summer maize with 44 mm/year. Recharge depended on the amount of irrigation water pumped from the aquifer and was therefore a poor indicator of future groundwater decline. Instead net water use (recharge minus irrigation) was found to be a good indicator for the decline of the water table. The smallest amount of net (ground water) used was cotton with an average of 14 mm/year, followed by peanut with 32 mm/year, summer maize with 71 mm/year, sweet potato with 74 mm/year. Winter wheat and ryegrass had the greatest net water use with the average of 198 mm/year and 111 mm/year, respectively. Our calculations showed that any single crop would use less water than the prevalent winter wheat summer maize rotation. This growing one crop instead of two will reduce the decline of groundwater and in some rain rich years increase the ground water level, but will result in less income for the farmers.
    PLoS ONE 01/2015; 10(1):e0115269. DOI:10.1371/journal.pone.0115269
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    ABSTRACT: The Sturtian and Marinoan snowball Earth episodes initiated 720 and 650 million years ago, respectively, are among the most dramatic events in Earth's history. The ultimate causes of these events remain obscure, however, and there is still uncertainty about the critical levels of greenhouse gas concentrations at which the snowball transition occurs. Furthermore, earlier modelling results (with incomplete representations of important boundary conditions) provided conflicting indications for differences between the critical carbon dioxide concentrations for the Marinoan and the Sturtian, reporting either the earlier or the later epoch to be more susceptible to global glaciation. Both the absolute values of and possible differences between these glaciation thresholds have profound implications for scenarios of snowball initiations during the Neoproterozoic. Here, we present coupled climate simulations (using an ocean general circulation model with dynamic/thermodynamic sea ice coupled to a fast atmosphere) focusing on the differences between the Neoproterozoic glaciations. For the first time, our simulations use realistic boundary conditions in terms of changes in solar luminosity between the two epochs and the most recent continental reconstructions. In agreement with previous studies with models including ocean and sea-ice dynamics, we report low values for the critical carbon dioxide concentration during the Neoproterozoic. But in contrast to hints from earlier studies we find very similar values of 100–130 ppm for the snowball bifurcation point during the Sturtian and Marinoan. This highlights the importance of realistic boundary conditions for climate simulations of the Neoproterozoic glaciations.
    Earth and Planetary Science Letters 10/2014; 404:200–205. DOI:10.1016/j.epsl.2014.08.001


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Top publications last week by reads

Reviews of Geophysics 11/2015;
285 Reads
Hydrology and Earth System Sciences Discussions 08/2015; 12(8):8459-8504. DOI:10.5194/hessd-12-8459-2015
96 Reads

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