The impact of crop management practices on rice grain quality in south eastern Australia

Rachael Wood

Research output: ThesisDoctoral Thesis

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Abstract

The main objective of this thesis was to determine the impact of crop management practices on the grain quality of rice grown in Australia's southern rice growing region to help reduce the variability found within the industry. Nutritional management, irrigation protocols and planting density are controlled farming practices that impact grain quality with effects specific to variety. Analysis of grain quality under various pre-permanent water (PW) and panicle initiation (PI) nitrogen (N) rates revealed increasing the rate of N applied pre-PW significantly increased whole grain yield (WGY; the proportion of unbroken grain expressed as a percentage of harvested grain) in all tested varieties, however, the effect of splitting the same total N rate into two applications on WGY was variety specific. The results in this thesis revealed N applied at PI altered protein composition affecting WGY and pasting properties. Comparison of the water saving technique delayed permanent water (DPW) with conventional irrigation methods revealed at N rates above 60 kg ha-1, WGY was higher in DPW compared to plants grown with conventional irrigation methods. DPW reduced grain filling duration while prolonging the grain ripening phase due to a slower in-field grain drying, which had a positive effect on WGY (Reiziq, r = 0.32; Sherpa, r = 0.29; Langi, r = 0.67; Topaz, r = 0.52; p < 0.05). When analysing cooking parameters, RVA peak viscosity was lower in the water saving irrigation method compared to permanent flood which increased RVA setback for all varieties despite no differences in amylose and total protein content. DPW altered the grain protein composition improving WGY and affected the pasting properties of rice. Analysis of grain quality under various sowing and N rates revealed changes in plant architecture. The differing densities that resulted from varying the sowing rate significantly affected grain weight and milling quality and the response differed between varieties. Decreasing sowing rate increased the number of grains per panicle, reduced grain dimensions, the thousand grain weight (TGW) and slightly increased WGY in the medium grain variety. In the short grain variety, decreased sowing rate increased TGW and reduced WGY in one season. There was a negative correlation between protein content and TGW (r = -0.58, p < 0.001) but a positive relationship between protein content and WGY in both varieties (r = 0.52, p < 0.001). Analysis of grain quality of Reiziq grown with increasing rates of Zn fertilisation demonstrated the Zn content of paddy and milled grain increases with increasing Zn fertiliser rate. However, Zn fertiliser rate did not affect protein content and WGY. Results in this study also demonstrate that RVA trough viscosity was increased by Zn fertiliser, possibly due to increased water absorption and increased starch granule swelling or a change in the amino acid profile. However, the impact on the overall RVA curve was minor. These results indicate that increasing the Zn content of the grain through fertilisation will not affect grain quality but may improve the Zn level delivered to consumers. This study demonstrated progress in understanding the effect of crop management on rice grain quality. Results in this thesis also demonstrated the importance of protein composition on grain quality parameters. A significant challenge for rice growers in Australia and globally is to reduce water usage without impacting crop yield and grain quality. This thesis demonstrated that grain quality is improved when rice is grown using water saving methods, increasing farmer profit per megalitre of water used in crop production.
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • Charles Sturt University
Supervisors/Advisors
  • Blanchard, Christopher, Principal Supervisor
  • Waters, Dan, Principal Supervisor
  • Mawson, John, Principal Supervisor
  • Dunn, Brian W, Principal Supervisor, External person
  • Oli, Prakash, Principal Supervisor, External person
Award date20 Nov 2019
Place of PublicationAustralia
Publisher
Publication statusPublished - 2019

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