Effect of agronomic management on rice grain quality Part III: Australian water-saving irrigation practices

Background and objectives

Water availability is a significant issue in rice-producing regions that are entirely dependent on irrigation and has led to the development of water-saving (WS) techniques. Delayed permanent water (DPW) and delayed permanent water with a post-flower flush (DPW + PFF) are WS methods suitable for temperate areas such as southeastern Australia. Currently, the impact of DPW and DPW + PFF on rice grain quality in southeastern Australia is poorly understood. We compared the effect of DPW and DPW + PFF with conventional irrigation methods on grain development and quality over three years.

Findings

Above 60 kg N/ha, head rice yield (HRY; the percentage of grain that remains whole or at least 75% of the original length after milling) was higher in the WS methods compared to plants grown with conventional irrigation methods. The WS methods reduced grain-filling duration while prolonging the grain-ripening phase due to a slower infield grain drying, which had a positive effect on HRY. When analyzing cooking parameters, RVA peak viscosity was lower in DPW + PFF compared to permanent flood, which increased RVA setback despite no differences in amylose and total protein content. DPW and DPW + PFF altered the grain protein composition improving HRY and affected the rice flour pasting properties.

Conclusion

These results indicate that DPW and DPW + PFF do not negatively impact milling quality at N rates above 60 kg/ha. However, changes in protein composition by DPW and DPW + PFF affected the cooking parameters.

Significance and novelty

These results are important for Australian and global rice producers who need to reduce their water inputs due to drought and receive financial penalties for poor quality grain. Our study is the first to provide a multiyear analysis of the effect of DPW and DPW + PFF on grain quality.