Julian Helfenstein

Last Name

Helfenstein

First Name

Julian

ORCID

0000-0002-5012-2589

Show all metadata

Search Results

Publications 1 - 10 of 17

Boron and zinc deficiencies and toxicities and their interactions with other nutrients in soybean roots, leaves, and seeds
Pawlowski, Michelle L.; Helfenstein, Julian; Frossard, Emmanuel; et al. (2019)
Journal of Plant Nutrition
A dual isotopic (32P and 18O) incubation study to disentangle mechanisms controlling phosphorus cycling in soils from a climatic gradient (Kohala, Hawaii)
Siegenthaler, Maja Barbara; Tamburini, Federica; Frossard, Emmanuel; et al. (2020)
Soil Biology and Biochemistry
Understanding soil selenium accumulation and bioavailability through size resolved and elemental characterization of soil extracts
Tolu, Julie; Bouchet, Sylvain; Helfenstein, Julian; et al. (2022)
Nature Communications
Dietary deficiency of selenium is a global health threat related to low selenium concentrations in crops. Despite the chemical similarity of selenium to the two more abundantly studied elements sulfur and arsenic, the understanding of its accumulation in soils and availability for plants is limited. The lack of understanding of soil selenium cycling is largely due to the unavailability of methods to characterize selenium species in soils, especially the organic ones. Here we develop a size-resolved multi-elemental method using liquid chromatography and elemental mass spectrometry, which enables an advanced characterization of selenium, sulfur, and arsenic species in soil extracts. We apply the analytical approach to soils sampled along the Kohala rainfall gradient on Big Island (Hawaii), which cover a large range of organic carbon and (oxy)hydroxides contents. Similarly to sulfur but contrarily to arsenic, a large fraction of selenium is found associated with organic matter in these soils. However, while sulfur and arsenic are predominantly found as oxyanions in water extracts, selenium mainly exists as small hydrophilic organic compounds. Combining Kohala soil speciation data with concentrations in parent rock and plants further suggests that selenium association with organic matter limits its mobility in soils and availability for plants.
Organic wheat farming improves grain zinc concentration
Helfenstein, Julian; Müller, Isabel; Grüter, Roman; et al. (2016)
PLoS ONE
Zinc (Zn) nutrition is of key relevance in India, as a large fraction of the population suffers from Zn malnutrition and many soils contain little plant available Zn. In this study we compared organic and conventional wheat cropping systems with respect to DTPA (diethylene triamine pentaacetic acid)-extractable Zn as a proxy for plant available Zn, yield, and grain Zn concentration. We analyzed soil and wheat grain samples from 30 organic and 30 conventional farms in Madhya Pradesh (central India), and conducted farmer interviews to elucidate sociological and management variables. Total and DTPA-extractable soil Zn concentrations and grain yield (3400 kg ha-1) did not differ between the two farming systems, but with 32 and 28 mg kg-1 respectively, grain Zn concentrations were higher on organic than conventional farms (t = -2.2, p = 0.03). Furthermore, multiple linear regression analyses revealed that (a) total soil zinc and sulfur concentrations were the best predictors of DTPA-extractable soil Zn, (b) Olsen phosphate taken as a proxy for available soil phosphorus, exchangeable soil potassium, harvest date, training of farmers in nutrient management, and soil silt content were the best predictors of yield, and (c) yield, Olsen phosphate, grain nitrogen, farmyard manure availability, and the type of cropping system were the best predictors of grain Zn concentration. Results suggested that organic wheat contained more Zn despite same yield level due to higher nutrient efficiency. Higher nutrient efficiency was also seen in organic wheat for P, N and S. The study thus suggests that appropriate farm management can lead to competitive yield and improved Zn concentration in wheat grains on organic farms.
An approach for comparing agricultural development to societal visions
Helfenstein, Julian; Diogo, Vasco; Bürgi, Matthias; et al. (2022)
Agronomy for Sustainable Development
There is broad agreement that agriculture has to become more sustainable in order to provide enough affordable, healthy food at minimal environmental and social costs. But what is “more sustainable”? More often than not, different stakeholders have opposing opinions on what a more sustainable future should look like. This normative dimension is rarely explicitly addressed in sustainability assessments. In this study, we present an approach to assess the sustainability of agricultural development that explicitly accounts for the normative dimension by comparing observed development with various societal visions. We illustrate the approach by analyzing farm- and landscape-scale development as well as sustainability outcomes in a Swiss case study landscape. Observed changes were juxtaposed with desired changes by Avenir Suisse, a liberal think tank representing free-market interests; the Swiss Farmers Association, representing a conservative force; and Landwirtschaft mit Zukunft, an exponent of the Swiss agroecological movement. Overall, the observed developments aligned most closely with desired developments of the liberal think-tank (72%). Farmer interviews revealed that in the case study area farms increased in size (+ 57%) and became more specialized and more productive (+ 223%) over the past 20 years. In addition, interpretation of aerial photographs indicated that farming became more rationalized at the landscape level, with increasing field sizes (+ 34%) and removal of solitary field trees (− 18%). The case study example highlights the varying degrees to which current developments in agriculture align with societal visions. By using societal visions as benchmarks to track the progress of agricultural development, while explicitly addressing their narratives and respective systems of values and norms, this approach offers opportunities to inform also the wider public on the extent to which current developments are consistent with different visions. This could help identify mismatches between desired and actual development and pave the way for designing new policies.
A method to analyse the isotopic composition of oxygen associated with organic phosphorus in soil and plant material
Tamburini, Federica; Pistocchi, Chiara; Helfenstein, Julian; et al. (2018)
European Journal of Soil Science
Selenium accumulation and speciation in soils along a climate gradient
Tolu, Julie; Bouchet, Sylvain; Chékifi, Sara Dorina; et al. (2020)
Selenium Research for Environment and Human Health: Perspectives, Technologies and Advancements: Proceedings of the 6th International Conference on Selenium in the Environment and Human Health (ICSEHH 2019), October 27-30, 2019, Yangling, Xi'an, China
Landscape ecology meets landscape science
Helfenstein, Julian; Bauer, Lea; Claluena, Aline; et al. (2014)
Landscape Ecology
Landscape ecology is a broad field in a patchwork of related disciplines. Giving landscape ecology a definition and delimiting it from related research areas is both a challenge and a necessity. Past endeavors have focused on expert opinions, analyses of published papers, and conference proceedings. We used a mix of all three, including a unique keyword analysis in two leading landscape-related journals, to highlight latest developments in landscape ecology between 2010 and 2013. Our analysis confirms the key topics of Wu (Landscape Ecol 28(1):1–11, 2013), and suggests that of those connectivity is dominating in terms of research output. However, we also found evidence that the borders of the journal Landscape Ecology are fuzzier than sketched in recent publications. There is a large overlap with the journal Landscape and Urban Planning, and in general a growing weight of conservation, landscape management, and planning related issues in the landscape ecology community. We conclude by encouraging the continued inclusion and strengthening of socio-ecological hot topics such as urban studies and landscape-human interactions in landscape ecological studies and subsequently in the journal landscape ecology.
Soil Phosphorus Exchange as Affected by Drying-Rewetting of Three Soils From a Hawaiian Climatic Gradient
Helfenstein, Julian; Frossard, Emmanuel; Pistocchi, Chiara; et al. (2021)
Frontiers in Soil Science
Current understanding of phosphorus (P) dynamics is mostly based on experiments carried out under steady-state conditions. However, drying-rewetting is an inherent feature of soil behavior, and as such also impacts P cycling. While several studies have looked at net changes in P pool sizes with drying-rewetting, few studies have dynamically tracked P exchange using isotopes, which would give insights on P mean residence times in a given pool, and thus P availability. Here, we subjected three soils from a climatic gradient on the Kohala peninsula from Hawaii to 5-month drying-rewetting treatments. The hypotheses were that physico-chemical and biotic processes would be differently affected by repeated drying-rewetting cycles, and that response would depend on climatic history of the soils. Soils were labeled with 33P and 18O enriched water. At select time intervals, we carried out a sequential extraction and measured P concentration, 33P recovery (only first 3 months), and incorporation of 18O from water into phosphate. This allowed tracing P dynamics in sequentially extracted pools as well as O dynamics in phosphate, which are driven by biological processes. Results showed that P concentration and 33P recovery were predominantly driven by soil type. However, across all soils we observed faster dilution of 33P from resin-P into less mobile inorganic pools under drying-rewetting. On the other hand, O dynamics in phosphate were mostly governed by drying-rewetting treatment. Under drying-rewetting, considerably less O was incorporated from water into phosphate of resin-P, microbial-P and HCl-P, suggesting that drying-rewetting reduced biological P cycling. Hence, our results suggest that repeated drying-rewetting increases inorganic P exchange while reducing biological P cycling due to reduced microbial activity, independent of climatic history of the soils. This needs to be considered in P management in ecosystems as well as model representations of the terrestrial P cycle.
Combining spectroscopic and isotopic techniques gives a dynamic view of phosphorus cycling in soil
Helfenstein, Julian; Tamburini, Federica; von Sperber, Christian; et al. (2018)
Nature Communications
Current understanding of phosphorus (P) cycling in soils can be enhanced by integrating previously discrete findings concerning P speciation, exchange kinetics, and the underlying biological and geochemical processes. Here, we combine sequential extraction with P K-edge X-ray absorption spectroscopy and isotopic methods (33P and 18O in phosphate) to characterize P cycling on a climatic gradient in Hawaii. We link P pools to P species and estimate the turnover times for commonly considered P pools. Dissolved P turned over in seconds, resin-extractable P in minutes, NaOH-extractable inorganic P in weeks to months, and HCl-extractable P in years to millennia. Furthermore, we show that in arid-zone soils, some primary mineral P remains even after 150 ky of soil development, whereas in humid-zone soils of the same age, all P in all pools has been biologically cycled. The integrative information we provide makes possible a more dynamic, process-oriented conceptual model of P cycling in soils.

Publications 1 - 10 of 17

Julian Helfenstein

Last Name

First Name

ORCID

Organisational unit

Filters

Search Results