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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 21 Jun 2019

Submitted as: research article | 21 Jun 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal Hydrology and Earth System Sciences (HESS).

Estimating water flux and evaporation losses using stable isotopes of soil water from irrigated agricultural crops in tropical humid regions

Amani Mahindawansha1,2, Christoph Külls4, Philipp Kraft1, and Lutz Breuer1,3 Amani Mahindawansha et al.
  • 1Institute for Landscape Ecology and Resources Management (ILR), Research Centre for BioSystems, Land Use and Nutrition (iFZ), Justus Liebig University Giessen, Giessen 35392, Germany
  • 2International Rice Research Institute (IRRI), Los Baños 4030, Philippines
  • 3Centre for International Development and Environmental Research (ZEU), Justus Liebig University Giessen, Senckenbergstrasse 3, Giessen 35390, Germany
  • 4Faculty of Civil Engineering, Technische Hochschule Lübeck, Mönkhofer Weg 239, Lübeck 23562

Abstract. Reliable information on water flow dynamics and water losses via irrigation on irrigated agricultural fields is important to advance water management strategies. We investigated the effect of season (wet season, dry season), irrigation management (flooded, non-flooded), and crop diversification (wet rice, dry rice, and maize) on soil water dynamics and water losses via evaporation during plant growth. Soil water was extracted and analyzed for the stable isotopes of water (δ2H and δ18O), and the fraction of evaporation loss was determined using the Craig–Gorden equation. For all crops, shallow soil compartments (0 to 0.2 m) were more isotopically enriched than deep soils (below 0.2 m). The soil in maize fields showed stronger evaporation enrichment than rice, which increased as the crops progressed through the growth; however, it decreased in both rice varieties during both seasons. Greater water loss was encountered during the wet season even though evaporation signals were stronger during the dry season. The enrichment of surface water was reflected in shallow soils of wet rice, and it decreased towards the end of growth during the wet and dry seasons. Isotope data indicated that soil water flow mechanisms varied depending on field conditions. In flooded conditions, surface soil was consistently affected by piston type matrix flow. During non-flooded conditions, matrix flow via diffusion dominated compared to upwards evaporative flux. Occasionally, preferential flows occurred through cracks, especially in maize fields. In wet rice fields, soil water was largely influenced by short-term variability of precipitation events during the wet season and subsequent formation of hydrogen compounds as a result of continued wetness and anaerobic physiochemical conditions that depleted δ2H with respect to δ18O.

Amani Mahindawansha et al.
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Amani Mahindawansha et al.
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Short summary
Stable isotopes of soil water is an effective tool to reveal soil hydrological processes in rice irrigated agricultural fields. Flow mechanisms and isotopic patterns of soil water in the soil matrix differs depending on the crop and irrigation practices. Preferential flows through desiccation cracks play a major role in water transport processes. Unproductive water losses can be reduced by introducing non-flooded crops during the dry season to the crop rotation.
Stable isotopes of soil water is an effective tool to reveal soil hydrological processes in rice...