Effects of plant population and row spacing on grain yield of aerial-sown and drill-sown rice

Objective guidelines about plant population are essential to ensure that yield potential of rice grain is not compromised. Drill-sowing of rice is increasing in popularity in many rice-growing regions of the world in response to a requirement for increased water productivity, but little information is available on row-spacing widths required to maximise grain yield potential. This research investigated the impacts of plant population on grain yield and yield components for aerial- and drill-sown rice, and the effects of row-spacing width for drill-sown rice grown in a temperate environment. Ten aerial-sown and five drill-sown experiments were conducted in south-eastern Australia over three seasons using four semi-dwarf rice varieties. Plant populations ranged from 7 to 396 plants m–2. Plant populations as low as 30 plants m–2 were able to achieve grain yields >12 t ha–1 but only when the plants were uniformly distributed. At a population of ~100 plants m–2, the impact of plant-stand distribution was negligible. Grain yield was maintained across a large range of plant populations, mainly through compensatory effects of more tillers per plant and more grains per panicle at lower plant populations. For aerial-sown rice, maximum grain yield (up to 14.9 t ha–1) was always achieved with a minimum plant population of 100 plants m–2, and likewise for drill-sown rice provided the row spacing was ≤27 cm. At equivalent plant populations, 36-cm row spacing produced lower grain yield than narrower row spacings. When large gaps existed between plants within the rows, neighbouring plants could not compensate for the gap at the wider 36-cm row spacing, and grain yield was reduced. A practical optimal plant population of 100–200 plants m–2 was found to be suitable for the semi-dwarf varieties used in this study for both aerial- and drill-sowing methods.