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Accueil du site → Doctorat → Australie → 2020 → Managing crop residues and nitrogen fertiliser to improve wheat yield potential in water-limited environments

University of Adelaide (2020)

Managing crop residues and nitrogen fertiliser to improve wheat yield potential in water-limited environments

Muschietti Piana, Maria del Pilar

Titre : Managing crop residues and nitrogen fertiliser to improve wheat yield potential in water-limited environments

Auteur : Muschietti Piana, Maria del Pilar

Université de soutenance : University of Adelaide

Grade : Doctor of Philosophy (PhD) 2020

Résumé partiel
Nitrogen (N) supply to rain-fed crops is becoming increasingly challenging due to the decline in organic N reserves. In low-rainfall wheat cropping systems, low crop N uptake has been linked to asynchrony in soil N supply through mineralisation. This is especially true on sandy soils of south eastern Australia which have a low N supply capacity and are considered highly ‘risky’ in a management context. When the N released from soil and residues is insufficient, and/or the timing of biological supply is not well matched with crop demand, management of N inputs to the soil (i.e. legume residue addition and/or fertiliser N) is essential to achieve yield potential and to return a neutral soil N balance for environmental sustainability. The general aim of this thesis was to improve our understanding of the seasonal pattern of the soil N supply capacity via mineralisation for increased wheat N uptake and grain yield, by combining N inputs from different crop residues (removed, wheat or lupin) and fertiliser N inputs (nil, or low, or high N) in a low-rainfall sandy soil environment. Field experiments were conducted over 2 years (2015-2016) at low-rainfall Kandosols based on-farm in the Mallee environment of South Australia. The temporal patterns of the soil profile mineral N and plant available water to 100 cm depth, wheat aerial biomass and N uptake were measured in both years (Chapter 2). In 2016 we also measured the disease incidence as a key environmental variable. There was 35 kg ha⁻¹ more soil mineral N to 100 cm depth following lupin compared with wheat residues at the end of the fallow in both years. In a below average rainfall season (Decile 4), wheat biomass produced on lupin residues was responsive to fertiliser N input with soil profile mineral N depleted by increased crop N uptake early in the season. In an above average rainfall season (Decile 9), a higher soil mineral N supply increased actual and potential grain yield, total biomass, N uptake, harvest index and water use efficiency of wheat, regardless of the source of N (legume N/fertiliser N). These experiments showed that the combination of lupin residues with N fertiliser application increased soil profile mineral N at early growth stages, providing a greater soil N supply at the time of high wheat N demand, and the inclusion of a legume in the rotation is critical for improving the N supply to wheat, with added disease break benefits (Chapter 2). The 2016 field experiment involved the quantification of decomposition rates and N release from wheat and lupin residues over the fallow and the subsequent wheat crop growing season with and without fertiliser N application. It also involved measurements of the temporal patterns of the surface soil mineral N, potentially mineralisable N, microbial biomass N, dissolved organic N and with temperature and rainfall as key environmental variables in all treatments (Chapter 3). Residue decomposition and N release over the fallow and the wheat growing season was measured in the field using litterbags with wheat or lupin residues. Fertiliser N input treatments at wheat crop sowing time and surface soil N pools were measured at key growth stages. A higher potential N supply to wheat following lupin residues at early stages was evidenced through greater decomposition rates and N release via mineralisation than wheat residues, which resulted in increased surface soil N pools.

Mots clés : Legumes nitrogen mineralisation wheat nitrogen uptake nitrogen supply sandy soils semi-arid environments

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