Effect of agronomic management on rice grain quality Part IV: Sowing rate

Background and objectives

There are no published data on the effect of sowing rate on rice grain quality traits of medium- and short-grain cultivars within the Australian environment. Studies that have reported on the impact of sowing rate on grain quality in other rice growing regions have assessed differences between densities below 100 plants/m², which is the minimum target for Australian grown rice. Furthermore, the cultivars evaluated were long-grain cultivars only. The effect of sowing rate (25–150 kg/ha) on the quality traits of a short (YRK5)- and medium (Viand)-grain rice cultivar was investigated over two seasons. Nitrogen (N) application was included in the study as the appropriate combination of sowing and N rate for maximum yield for both cultivars was unknown.

Findings

Sowing and N rate affected the number of grains per panicle and plants established per m² of both cultivars; however, changes in these parameters did not affect crop yield. The number of grains per panicle affected thousand-grain weight (TGW) and head rice yield (HRY; the percentage of grain that remains whole or at least 75% of the original length after milling), and the response differed between cultivars. Decreasing sowing rate increased the number of grains per panicle, reduced grain length and TGW, and slightly increased HRY in Viand. In YRK5, decreased sowing rate increased TGW and in season two reduced HRY. Protein content was negatively correlated with TGW and positively correlated with HRY. There were no consistent differences in the physicochemical and cooking parameters between densities over both seasons in both cultivars.

Conclusion

These results indicate that plant density has an indirect effect on milling quality by influencing TGW, which affected total protein content, and thus, HRY and the response differ between cultivars. Furthermore, this study demonstrated that within a population of 18 to 231 plants/m² at establishment, the physicochemical and cooking parameters are not affected by sowing rate.

Significance and novelty

This study is the first to analyze the grain physicochemical and cooking quality parameters at densities above 100 plants/m² and evaluate the effect of sowing rate on the grain quality of differing grain types within Australia. Comparisons between the low (50–70 kg/ha) and standard sowing rate (130–150 kg/ha) revealed no difference in HRY, and these results are important to farmers and demonstrate a reduction in plant density due to poor establishment, environmental or bird damage does not affect crop yield or grain quality and thus their economic return.