L'effet supergranule d'urée (SGU) en sols de rizières : un problème de diffusion avec échange d'ions. Essai de modélisation

Abstract : Deep-placed between 4 hills of wetland-rice, urea supergranules (USG, sometimes called LGU, large urea granules) present in numerous situations a high efficiency due to the occurrence of negligeable losses (runoff, NH3 volatilization, nitrification-denitrification) and another mechanism associated with minimal dispersion of nitrogen in the soil. For non-percolating paddy soils with uniform porosity and density, nitrogen dispersion from supergranule is only a diffusion-ion exchange phenomenon. Built upon three main assumptions (point souce, local equilibrium of ammonia, no ammonium retrogradation in clay minerals), the model uses a few parameters (soil density and porosity, mean apparent diffusion coefficient for nitrogen, time for full urea hydrolysis, modified adsorption isotherm) and a calculus algorithm which enable to simulate the evolution of ammonia distribution in the soil or its solution. It agrees with experimental data collected on different soils. At last, two sets of observations : - contour plos showing distribution patterns of ammonia, from Savant and De Datta (1980), - simultaneous pH and ammonia mesurements on solution extracted with a sampler near the USG show that USG-effect is mainly due to NH3 toxicity upon 0,45 mM. Therefore, geometrical factors (placement in the reduced layer of the soil, supergranule form), soil (exchange) and fertilizer (alcalinity from urea hydrolysis) properties associated with NH3 toxicity for rice enable its feeding at request.
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Submitted on : Friday, September 23, 2016 - 3:56:50 PM
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Rémi Gaudin. L'effet supergranule d'urée (SGU) en sols de rizières : un problème de diffusion avec échange d'ions. Essai de modélisation. Agronomie. INPL - INP de LORRAINE; ENSAIA, 1987. Français. ⟨tel-01370986⟩

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