Olivier Heller


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Heller

First Name

Olivier

ORCID

0000-0002-5918-4161

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2013 - 201912020 - 20242
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Publications 1 - 3 of 3
  • Perspectives on the misconception of levitating soil aggregates
    Item type: Journal Article
    Garland, Gina; Koestel, John; Johannes, Alice; et al. (2024)
    Soil
    Soil aggregation is an important process in nearly all soils across the globe. Aggregates develop over time through a series of abiotic and biotic processes and interactions, including plant growth and decay, microbial activity, plant and microbial exudation, bioturbation, and physicochemical stabilization processes, and are greatly influenced by soil management practices. Together, and through feedback with organic matter and primary soil particles, these processes form dynamic soil aggregates and pore spaces, which jointly constitute a soil's structure and contribute to overall soil functioning. Nevertheless, the concept of soil aggregates is hotly debated, leading to confusion about their function or relevancy to soil processes. We argue here that the opposition to the concept of soil aggregation likely stems from the fact that the methods for the characterization of soil aggregates have largely been developed in the context of arable soils, where tillage promotes the formation of distinct soil aggregates that are easily visible in the topsoil. We propose that the widespread use of conceptual figures showing detached and isolated aggregates can be misleading and has contributed to the skepticism towards soil aggregates. However, the fact that we do not always see discrete aggregates within soils in situ does not mean that aggregates do not exist or are not relevant to the study of soil processes. Given that, by definition, soil aggregates consist of any group of soil particles that cohere more strongly to each other than neighboring particles, aggregates may, but do not necessarily need to be, bordered by pore space. Here, we illustrate how aggregates can form and dissipate within the context of undisturbed, intact soils, highlighting the point that aggregates do not necessarily need to have a discrete physical boundary and can exist seamlessly embedded in the soil. We hope that our contribution helps the debate on soil aggregates and supports the foundation of a shared understanding on the characterization and function of soil structure.
  • Interdisciplinary Assessment of Market Oriented Yam Cultivation in Semi-arid Burkina Faso
    Item type: Journal Article
    Heller, Olivier; Kiba, Delwendé I.; Zida, Kalifa Wend-Doléa; et al. (2022)
    Frontiers in Agronomy
    Yam (Discorea spp.) is a staple food crop in Africa that requires fertile soils and an annual rainfall of about 1,500 mm. However, in the semi-arid North-West of Burkina Faso, farmers produce yam in continuous rotation on degraded soils with annual rainfall of 610–960 mm. Understanding this local know-how can help improve yam cultivation in other regions and cropping systems in Africa. This study evaluated the productivity of this yam farming system in an interdisciplinary manner involving agronomic and economic analyses. We studied the cropping practices and socio-economic conditions of 67 households in 12 villages. We questioned farmers about their yam management schedule and inputs and we measured the yam fresh tuber yields in their fields. We sampled soils, manure and yam tubers for chemical analyses. Then, we calculated soil surface nutrient balances for N, P, and K. We found that the cropping system was characterized by densely planted ridges and relatively small size of harvested tubers. The farmers coped with degrading soils and increasing market demand by applying in average 16.2 t ha−1 of manure. About 31% of the farmers applied an average of 435 kg ha−1 of NPK fertilizer and another 24% applied an average of 300 kg ha−1 of urea. The average yam yield was 16.2 t ha−1, well above the West African average yield of 10.7 t ha−1.The yam had high value (0.59 USD kg−1) at relatively low production expenditure (0.04 USD kg−1), providing farmers the opportunity to increase and diversify incomes. Our results suggest that the development of this intensified yam production may be limited by farmer's low purchasing power of yam seed tubers, fertilizers and labor.
  • Wood anatomical responses of oak saplings exposed to air warming and soil drought
    Item type: Journal Article
    Fonti, P.; Heller, Olivier; Cherubini, P.; et al. (2013)
    Plant Biology
Publications 1 - 3 of 3