Enhancement of the anaerobic digestion of nitrogenous substrate by implementing the approach of microbial electrolysis cell to force a microbial change

openAnaerobic digestion is a natural biochemical process that can convert organic materials into combustible biogas. However, high ammonia levels can inhibit the process of methanogenesis and cause the failure of biogas production. For that reason, this study aimed to improve the stability and efficiency of anaerobic digestion in the presence of high ammonia concentrations and the production of biogas, through the implementation of microbial electrolysis cells (MEC) and direct interspecies electron transfer (DIET). The application of MEC to anaerobic digestion can accelerate the degradation of a substrate by enriching exoelectrogens and methanogens thus increasing biogas production. DIET has been recognized as faster and more stable means to transport reducing equivalents between bacteria and archaea, demonstrating the potential to enhance the rate-limiting steps during anaerobic digestion. The study was conducted with two independent experiments, one lasting 92 days and the other 34 days following the VDI 4630 and DIN 38414-8. Four reactors in each experiment were supplied with electrical energy, while two served as controls with no energy supply. The substrate used in the first experiment was aged, while the substrate in the second experiment had higher ammonia concentrations. The results suggest that the implementation of microbial electrolysis cells had a slightly positive effect on both experiments. However, these technologies did not significantly increase methane production compared to the control reactors.Anaerobic digestion is a natural biochemical process that can convert organic materials into combustible biogas. However, high ammonia levels can inhibit the process of methanogenesis and cause the failure of biogas production. For that reason, this study aimed to improve the stability and efficiency of anaerobic digestion in the presence of high ammonia concentrations and the production of biogas, through the implementation of microbial electrolysis cells (MEC) and direct interspecies electron transfer (DIET). The application of MEC to anaerobic digestion can accelerate the degradation of a substrate by enriching exoelectrogens and methanogens thus increasing biogas production. DIET has been recognized as faster and more stable means to transport reducing equivalents between bacteria and archaea, demonstrating the potential to enhance the rate-limiting steps during anaerobic digestion. The study was conducted with two independent experiments, one lasting 92 days and the other 34 days following the VDI 4630 and DIN 38414-8. Four reactors in each experiment were supplied with electrical energy, while two served as controls with no energy supply. The substrate used in the first experiment was aged, while the substrate in the second experiment had higher ammonia concentrations. The results suggest that the implementation of microbial electrolysis cells had a slightly positive effect on both experiments. However, these technologies did not significantly increase methane production compared to the control reactors

Severe drought rather than cropping system determines litter decomposition in arable systems

"Litter decomposition is a fundamental process in soil carbon dynamics and nutrient turnover. However, litter decomposition in arable systems remains poorly explored, and it is unclear whether different management practices, such as organic farming, conservation agriculture can mitigate drought effects on litter decomposition. Thus, we examined the effects of a severe experimental drought on litter decomposition in four cropping systems, i.e., organic vs. conventional farming, each with two levels of tillage (intensive vs. conservation tillage) in Switzerland. We incubated two types of standard litter (tea bags), i.e., high-quality green tea with a low C:N ratio and low-quality rooibos tea with a high C:N ratio. We assessed litter decomposition during the simulated drought and in the post-drought period during three years in three different crops, i.e., pea-barley, maize, and winter wheat. Subsequently, we assessed whether decomposition in the four cropping systems differed in its resistance and resilience to drought. Drought had a major impact on litter decomposition and suppressed decomposition to a similar extent in all cropping systems. Both drought resistance and resilience of decomposition were largely independent of cropping systems. Drought more strongly reduced decomposition of the high-quality litter compared to the low-quality litter during drought conditions regarding the absolute change in mass remaining (12.3% vs. 6.5 %, respectively). However, the decomposition of high-quality litter showed a higher resilience, i.e., high-quality approached undisturbed decomposition levels faster than low-quality litter after drought. Soil nitrate availability was also strongly reduced by drought (by 32–86 %), indicating the strong reduction in nutrient availability and, most likely, microbial activity due to water shortage. In summary, our study suggests that severe drought has a much stronger impact on decomposition than cropping system indicating that it might not be possible to maintain decomposition under drought by the cropping system approaches we studied. Nevertheless, management options that improve litter quality, such as the use of legume crops with high N concentrations, may help to enhance the resilience of litter decomposition in drought-stressed crop fields.

Using PhenoCams to track crop phenology and explain the effects of different cropping systems on yield

CONTEXT Crop phenology integrates information of how environmental drivers and management practices affect plant performance and crop yield. However, little is known about the impact of cropping systems (CS) on crop phenology and how this relates to differences in yield. OBJECTIVES We assessed the applicability of PhenoCams to track crop phenology, how four CS, i.e., organic vs. conventional farming with either intensive or conservation (no/reduced) tillage affect the phenology of a pea-barley mixture and winter wheat, how crop phenology is related to harvest characteristics, e.g., grain yield and total N uptake, and explains CS effects on these characteristics. METHODS We used time-lapse cameras (PhenoCams) to track vegetation changes in the two crops and extracted the green chromatic coordinate (GCC) to estimate different phenological metrics, i.e., dates with major changes in GCC (PhenoTimePoints), the duration between those (PhenoPhases), and the rate of increasing or decreasing GCC (PhenoSlopes). We assessed how phenological metrics were affected by different CS, and related phenological metrics to harvest characteristics. RESULTS AND CONCLUSIONS CS significantly affected phenological metrics of both crops, with less pronounced effects in the unfertilized pea-barley mixture compared to the fertilized winter wheat, and stronger effects for early-season than for late-season PhenoTimePoints. For winter wheat, organic compared to conventional farming caused an initial growth lag (up to 7 days) and a shorter duration (approximately 10 days) of the period of stable GCC. Winter wheat in reduced/no-tillage systems showed a tendency of delayed phenology (up to 5 days) compared to intensive tillage. While phenological metrics explained harvest characteristics of winter wheat well, they were almost unrelated to those of pea-barley, most likely because pea-barley yields were similar among CS. For winter wheat, effects of CS on harvest characteristics could be well explained by phenological metrics (max. R2 = 0.9). Thus, we demonstrated that delayed phenology acted as an important factor causing lower yield in organic compared to conventional farming. SIGNIFICANCE PhenoCams are valuable tool for high-resolution temporal monitoring of crop phenology. As different CS have been proposed as a tool for climate change adaptation, we suggest that the effects of CS on crop phenology need to be considered as they may impact yield via changes in crop phenology, particularly in organic agriculture

Severe drought rather than cropping system determines litter decomposition in arable systems

Litter decomposition is a fundamental process in soil carbon dynamics and nutrient turnover. However, litter decomposition in arable systems remains poorly explored, and it is unclear whether different management practices, such as organic farming, conservation agriculture can mitigate drought effects on litter decomposition. Thus, we examined the effects of a severe experimental drought on litter decomposition in four cropping systems, i.e., organic vs. conventional farming, each with two levels of tillage (intensive vs. conservation tillage) in Switzerland. We incubated two types of standard litter (tea bags), i.e., high-quality green tea with a low C:N ratio and low-quality rooibos tea with a high C:N ratio. We assessed litter decomposition during the simulated drought and in the post-drought period during three years in three different crops, i.e., pea-barley, maize, and winter wheat. Subsequently, we assessed whether decomposition in the four cropping systems differed in its resistance and resilience to drought. Drought had a major impact on litter decomposition and suppressed decomposition to a similar extent in all cropping systems. Both drought resistance and resilience of decomposition were largely independent of cropping systems. Drought more strongly reduced decomposition of the high-quality litter compared to the low-quality litter during drought conditions regarding the absolute change in mass remaining (12.3% vs. 6.5 %, respectively). However, the decomposition of high-quality litter showed a higher resilience, i.e., high-quality approached undisturbed decomposition levels faster than low-quality litter after drought. Soil nitrate availability was also strongly reduced by drought (by 32–86 %), indicating the strong reduction in nutrient availability and, most likely, microbial activity due to water shortage. In summary, our study suggests that severe drought has a much stronger impact on decomposition than cropping system indicating that it might not be possible to maintain decomposition under drought by the cropping system approaches we studied. Nevertheless, management options that improve litter quality, such as the use of legume crops with high N concentrations, may help to enhance the resilience of litter decomposition in drought-stressed crop fields.ISSN:0167-8809ISSN:1873-230