Evaluating nitrogen response and nitrogen-use-efficiency in perennial rice

Problem or Context Transplanting of rice is under pressure due to labour shortage, especially where rice is double cropped. This has renewed interest in ratooning, with perennial rice providing additional opportunities. Objective or Research Question This paper examines the response of perennial rice PR25 to N management over regrowth cycles, especially in relation to total N uptake, its partitioning, N-use efficiency, and the implications for performance. Methods The experiment was conducted over 6 Seasons from 2021 to 2023, with 3 N timings (5, 10, 15 days after heading; DAH), 4 N rates (0, 75, 150, 225 kg N ha −1 ) and 3 replicates, in a split-split design. Results Indigenous soil N supply plus non-treatment N at tillering and booting yielded 5.11 t ha −1 , with high N recovery efficiency. Highest grain yield (7.60 t ha −1 ) was attained when 150 kg N ha −1 was also applied at 15 DAH. Grain yield was reduced by low sunshine in the 2021 wet season and by heat in the 2023 dry season, which reduced effective panicles ha −1 , spikelets panicle −1 and grains ha −1 . Yield decline in later regrowth cycles was attributed to the combination of environmental stresses and the application of post-heading N after the peak period of crop N demand, which reduced sink size and photosynthetic capacity. Conclusions The results were consistent with 150–180 kg N ha −1 required for ratooned rice and perennial rice, but it would be useful to know if any additional N were needed to support perennial structures, relative to annual rice. Implications or Significance The highest grain yield (7.60 t ha −1 ) was attained with late application of 150 kg N ha −1 at 15 DAH, which may have assisted in delaying leaf senescence in later regrowth cycles. Partitioning of N uptake was useful in separating responses to pre-heading and post-heading N, which differed significantly in grain yield and NUE, especially when significant seasonal variation was encountered.