Browsing by Subject "Biochar"

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Biochar amendment for C sequestration in a temperate agroecosystem : implications for microbial C- and N-cycling
(2018) Bamminger, Chris; Kandeler, Ellen
Climate warming will have great impact on terrestrial ecosystems. Different soil properties such as temperature and moisture will be altered, thereby influencing C- and N-cycles, microbial activity as well as plant growth. This may contribute to the observed increase in soil greenhouse gas (GHG) emissions under climate change. Therefore, new options are needed to mitigate theses projected consequences. Biochar is primarily suggested to be effective in long-term C sequestration in agricultural soils due to its long-term stability. In addition, it could be applied to improve various soil properties, plant growth and to reduce soil GHG emissions. To date, knowledge about such beneficial biochar effects in soil under predicted warming climate is extremely scarce. In the first study, a slow-pyrolysis biochar from Miscanthus x giganteus feedstock (600 °C, 30 Min.) was incubated for short time (37d) under controlled laboratory conditions in agricultural soil in the presence of earthworms and N-rich litter (Phacelia tanacetifolia Benth.). Biochar increased microbial abundances and the fungal-to-bacterial PLFA ratio after 37 days in arable soil applied with litter suggesting improved living conditions for microorganisms with biochar. Fungi may benefit most from newly created habitats due to colonizable biochar pores and surfaces. Additionally, fungi could have also mineralized small amounts of recalcitrant biochar-C during plant litter decomposition. Without litter, biochar led to interactions between earthworms and soil microorganisms resulting in enhanced bacterial and fungal abundances. This indicates better growth habitats for soil microbes in earthworm casts containing biochar. Soil respiration and metabolic quotients (qCO2) and N2O emissions (in litter treatments) were decreased after biochar application suggesting a more efficient microbial community and underscoring the GHG mitigation potential of the used biochar. The field experiment, investigated in the second and third study, focused on the stability and long-term soil C sequestration potential of comparable Miscanthus biochar (850 °C, 30 Min.). Related effects on soil GHG emissions, physical, chemical and microbiological soil properties as well as plant growth were determined in an agroecosystem at year-round elevated soil temperature (+2.5 °C, since 2008). The second study investigated the short-term effects of biochar on microbial abundances and growth of winter rapeseed during the first year after field application to a warmed temperate arable soil. It was found that fungal biomass and the fungal-to-bacterial ratio were increased in the warmed biochar plots only after three months in the presence of spring barley litter from the previous growing season. The disappearance of this effect points to an overall high stability of the investigated biochar. Moreover, biochar proved to be effective in mitigating negative effects of seasonal dryness on microbial abundances and early plant growth in the dry spring period in 2014. However, biochar had no effect on final aboveground biomass of winter rapeseed at harvest in the first growing season. As shown in the third study, after two vegetation periods of winter rapeseed and spring wheat, the assumption that plant productivity in already fertile temperate arable soils is unlikely to be further enhanced with biochar amendment, was confirmed. Total CO2 emissions after two years were not reduced by biochar and remained unchanged even under warming suggesting a high degradation stability of the used biochar. N2O emissions were increased in biochar-amended soil at elevated soil temperature, presumably due to enhanced water and fertilizer retention with biochar. By using the global warming potential (GWP100) of total soil GHG emissions, the storage of biochar-C in soil was estimated to compensate warming-induced elevated soil GHG emissions for 20 years. To conclude, this thesis revealed that biochar may have only minor influence on soil microorganisms and crop growth in temperate, fertile arable field soils. However, it was shown that biochar could be a valuable tool for C sequestration in temperate arable soils, thus potentially offsetting a warming-induced increase in GHG emissions. In order to face climate change impacts, more long-term studies on microbiological effects and the C sequestration potential of biochar in cultivated soil under warming are urgently needed.
Re-plant problems in long-term no-tillage cropping systems : causal analysis and mitigation strategies
(2016) Afzal; Neumann, Günter
No-tillage is considered as a promising alternative for tillage-based conventional farming, by saving energy-input and time, reducing groundwater pollution and counteracting soil erosion and losses of the soil-organic matter. However, in the recent past, no-tillage farmers in Southwest Germany repeatedly reported problems particularly in winter wheat production, characterized by stunted plant growth in early spring, chlorosis, impaired fine root development and increased disease susceptibility. These symptoms were particularly apparent on field sites with long-term (≥ 10 years) no-tillage history (LT) but not on adjacent short-term (≤ 2 years) no-tillage plots (ST). The effects could be reproduced in pot experiments under controlled conditions, with soils collected from the respective field sites in five different locations, providing a basis for causal analysis. The expression of damage symptoms in pot experiments with sieved soils, excluded differences in soil compaction, induced by long-term no-tillage farming as a potential cause. Soil analysis revealed higher levels of soil organic matter in the topsoil, as expected for LT field sites and no apparent mineral nutrient deficiencies, both, on LT and ST soils. However, phosphate (P) deficiency was characteristic for plants grown on LT soils. Obviously, this was caused by the limited acquisition of sparingly soluble soil P, due to impaired root development but not by low P availability on LT soils. In four out of five cases, gamma-ray soil sterilization did not affect the expression of plant damage symptoms on LT soils, excluding pathogen effects as a major cause. Soil application of biochar, at a rate of 5% (v/v), rapidly restored plant growth on LT soils, detectable already during the first week after sowing. This finding points to the presence of a phytotoxic compound since binding of soil xenobiotics by biochar is well documented. Accumulation of allelopathic compounds, originating from crop residues and root exudates remaining in the topsoil, is a problem related to no-tillage farming, particularly in cases of limited crop rotations or in monocultures, which also applied to the investigated field sites. However, a specific wheat auto-allelopathic effect is unlikely, since similar crop damage was also observed in soybean, sunflower, oilseed rape and various cover crops. Typical for allelopathic effects, in the pot experiments, plant damage symptoms in winter wheat appeared rapidly during emergence and early seedling development. However, under field conditions, germination and early growth were usually not affected, and symptoms were first detectable during re-growth in early spring. Moreover, damage symptoms disappeared when soil sampling was performed in summer instead of early spring, suggesting degradation of the toxic compound, which is also not compatible with the hypothesis of long-term accumulation of allelopathic compounds. The observed temporal pattern of plant damage rather resembled residual effects, occasionally observed after application of certain herbicides with soil activity (e.g., sulfonylureas, propyzamide). Therefore, a systematic survey of herbicide residues was conducted for topsoils on six pairs of LT and ST-field sites. Characteristic for no-tillage farming, glyphosate was the only herbicide, commonly and regularly used on all investigated field sites. The soil analysis revealed higher levels of glyphosate residues on all investigated LT, soils as compared with directly neighboured ST plots. Particularly on LT plots with strong expression of plant damage symptoms, high concentrations of glyphosate (2-4 mg kg-1 soil), and of its metabolite AMPA were detected in the 10 cm topsoil layer. This concentration range is characteristic for residual levels, usually observed several days after glyphosate applications but was still detectable in early spring, six months after the last glyphosate treatment, while only trace concentrations below the detection limit (0.05 mg kg-1 soil) were found in ST soils. Coinciding with the declining plant damage potential, residual glyphosate and AMPA concentrations on LT plots declined during the vegetation period until early summer. No comparable pattern was detectable for residues of other herbicides, such as pendimethalin and propyzamide. Degradation of glyphosate residues in soils correlates with microbial activity. Accordingly, reduced soil respiration as an indicator for microbial activity was detected in four out of five cases in soil samples collected from LT field sites, suggesting delayed glyphosate degradation as compared with ST plots. Due to rapid adsorption, glyphosate usually exhibits extremely limited soil activity. However, at least trace concentrations of glyphosate and AMPA (1.5-3.5 µg L-1) were detectable also in the potentially plant-available, water-soluble phase in spring samples, collected from LT field plots with high potential for plant damage. Nutrient solution experiments, with 3-6 weeks exposure of winter wheat to the residual herbicide concentrations detected in the LT soil solution, revealed the development of chlorosis and similar to soil experiments, a 30%-50% reduction in fine root production, which surprisingly was mainly induced by AMPA and to a lesser extent by glyphosate itself. Accordingly, both, in hydroponics and LT soil experiments, the plant damage symptoms were not associated with shikimate accumulation in the root tissue as a physiological indicator for glyphosate but not for AMPA toxicity. The dominant role of AMPA toxicity also became apparent by the fact that, both, glyphosate resistant (GR) and non-resistant (NR) soybean plants were affected on LT no-tillage soils since transgenic GR plants are not resistant to AMPA. A preliminary RNAseq gene expression analysis of the root tissue just prior to the appearance of visible plant damage symptoms, revealed down-regulation of genes involved in general stress responses, down-regulation of aquaporin genes (PIPs and TIPs) with functions in water uptake and root elongation, down-regulation of ethylene-related genes but up-regulation of cytokinin-related gene expression indicating interferences with hormonal balances. These changes in gene expression patterns relative to the untreated control were detected in plants treated with AMPA and glyphosate+AMPA but not with glyphosate alone. The findings suggest that long-term exposure to subtoxic levels of AMPA, as major glyphosate metabolite temporally accumulated in LT no-tillage soils, can finally interfere with metabolic processes essential for normal root development. A series of pot and field experiments were initiated to test the potential of selected commercial formulations of plant growth-promoting microorganisms, based on strains of Pseudomonas sp., Bacillus amyloliquefaciens, and Trichoderma harzianum, for mitigation of plant stress symptoms, expressed on LT no-tillage field sites in spring. For members of the selected microbial genera, root growth-promoting effects, pathogen suppression, and glyphosate degradation potential have been reported. Unfortunately, plant growth promotion was detectable only on ST soils but was not successful on LT plots, both, in pot and field experiments, probably related to limited root development for microbial colonization and early summer drought under field conditions. As an alternative approach, incorporation of pyrolysis biochar from woody substrates at a rate of 5 % (v/v) to the top 10 cm soil layer of LT soils, equivalent to approx. 35 t ha-1, were able to restore plant growth completely in pot experiments and protected wheat plants from glyphosate overdose applications (up to 8 L Roundup Ultramax® ha-1), even on artificial substrates with low potential for glyphosate adsorption. As a short-term mitigation strategy, field-testing with different biochar concentrations is recommended. During the last two years, farmers also modified their no-tillage management strategies on the investigated field sites by introducing more variable crop rotations including, winter wheat, winter rape, maize and soybean and using mustard, pea, and Crotalaria as cover crops. Despite further annual applications of glyphosate (3 L ha-1 of a 360 g ai L-1 formulation), plant performance on the respective field sites was significantly improved. These observations suggest that limited crop rotation favored the development of a soil microflora with low degradation potential for glyphosate, leading to a decline in degradation rates of glyphosate soil residues and underline the importance of crop diversity management.
The importance of soil microorganisms and cover crops for copper remediation in vineyards
(2014) Mackie, Kathleen; Kandeler, Ellen
The historical use of copper fungicides, as a plant protection agent, has moderately polluted agricultural topsoils across Europe. Organic agriculture, in particular, continues to be limited to the use of copper fungicides due to a lack of permitted alternative plant protection agents. In recent years, the effects of copper accumulation in the soil have been observed. Studies on the negative effects of copper in agricultural soils show a decrease in ecosystem services, which rely on macro- and micro-organisms. Thus, there is the question of how to remediate copper polluted crop fields. Although this topic has more recently been investigated in the laboratory, currently, there are no experiments available in the field. Viticulture is one of the largest perennial crops in Europe that utilize copper fungicides. Therefore, this dissertation was designed to investigate copper remediation strategies in vineyards, in order to best understand potential solutions for a growing problem, as well as their effect on ecosystem services. Understanding the reaction of and support by soil microorganisms will help determine which strategy has the best potential. The main project was implemented using two field experiments, each of which analyzed copper availability, microbial abundance, function and community composition to determine the overall outcome of copper remediation. The dissertation is presented in four papers. The first paper is a review on copper in vineyards, which focused specifically on cutting-edge remediation strategies currently being studied. This paper also provided information on knowledge gaps in the literature. The second paper showed the spatial distribution of copper and soil microorganisms at the plot scale, providing a better understanding of copper and microbial distribution as well as a foundation for subsequent papers. The third paper analyzed copper phytoextraction by single species and mixed species cover crop plots and the microbial community that may support it. The fourth paper was aimed at observing the ability of biochar and biochar-compost to immobilize copper and improve ecosystem services. The studies utilized classic soil biological methods (enzyme activities, microbial C and N, ergosterol) and modern molecular techniques (quantitative polymerase chain reaction (qPCR) of 16S rRNA and taxa specific bacteria genes and phospholipid fatty acid analysis (PLFA)) as well as determination of chemical soil properties and copper fractions.