Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Titre : Immobilization of Nitrogen Fertilizer in Residue-Retained Mediterranean Semi-Arid Cropping Systems

Auteur : Nasrollahi Niloufar

Université de soutenance : La Trobe University

Grade : Doctor of Philosophy (PhD) 2022

Résumé
Nitrogen (N) is the most limiting nutrient for crop production. Synthetic N fertilizeris required to produce enough food to feed the current global population, and human reliance on N fertilizerwill increase with future population growth. Production of N fertilizerrequires fossil fuels, and once applied to croplands can be lost from the soil-plant system with environmentally harmful offsite effects. Therefore, more efficient use of fertilizerN which seeks to minimiselosses will be critical for sustainable achievement of global food production goals. This thesis focused on efficiency of fertilizerN applied to dryland crops in the semi-arid Mediterranean cropping systems of south-eastern Australia. Most grain growers in this region retain crop residues to protect soils from wind and water erosion. Residues with low carbon(C)to N (C:N) ratio such as those of wheat (Triticum aestivum) cause N-immobilizationby soil microorganisms which can negatively affect crop growth, particularly if it occurs at times of high crop N demand. A simulation experimentquantified sources of N inefficiency across a rainfall gradient within these cropping systems and predicted N immobilizationto be the largest source of inefficiency at N application rates currently used by growers. A pot experiment and two field experiments were used to investigate management factors toreduce immobilizationand increase crop access to N in the presence of retained crop residues. A comparison of crop species (wheat vs. canola, Brassica napus) found that canola could accumulate more N, but that was due to longer life cycle rather than suppression of immobilizingsoil organisms. Timing of N application (sowing vs. mid-seasonduring early stem-elongation) interacted with species ; applications at sowing increased N uptake in canola and mid-seasonincreased N uptake in wheat. In-crop mid-row banding improved crop recovery of 15N-labelledfertilizerin both species compared to broadcast application.

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