Understanding the yield attributes of the popular rice (Oryza sativa L.) hybrids can provide useful information for developing new hybrid rice varieties. Field experiments were conducted at two subtropical sites (Hengyang and Xingyi) in two years (2021 and 2022) to compare grain yield and yield attributes of three currently popular hybrid rice varieties (Jingliangyouhuazhan, Jingliangyou 534, and Longliangyouhuazhan) with three representative super hybrid rice varieties (Y-liangyou 1, Y-liangyou 2, and Y-liangyou 900). No significant differences in grain yield were observed between the group of popular hybrids and the group of super hybrids at Hengyang and Xingyi in 2021 or at Xingyi in 2022, but at Hengyang in 2022, the group of popular hybrids produced a 15% higher grain yield. The grain yield at Hengyang in 2022 was lower than that at Hengyang and Xingyi in 2021 and at Xingyi in 2022. At Hengyang in 2022, the group of popular hybrids had 9–15% higher panicles per m², spikelet filling percentage, and harvest index but similar spikelets per panicle and total biomass production and 12% lower grain weight compared to the group of super hybrids. Correlation plot analysis showed that grain yield was significantly related to panicles per m² but not other yield attributes across six varieties at Hengyang in 2022. These results indicated that the currently popular hybrid rice varieties had higher yield performance than the representative super hybrid rice varieties under the condition of relatively lower productivity, and the key factor for this higher yield performance in the popular hybrids was the higher panicles per m². This finding highlights that more attention should focus on the yield performance under medium- and low-productivity conditions in hybrid rice breeding programs, and an effective breeding strategy is to select the varieties with high panicle numbers.

Spent mushroom substrate (SMS), the residual byproduct of mushroom cultivation, represents a nutrient-rich agro-residues with potential for paddy field application. This study evaluated the effect of direct SMS application on rice yield, yield components, biomass production, and nitrogen uptake (NU), aiming to provide useful information for fresh SMS utilization in paddy. Field experiments were conducted using a split-plot design with three replications, three SMS rates (0, 9, and 18 t ha−1 dry matter) as the main plots and three nitrogen (N) (0, 90, 180 kg ha−1) as subplots in 2023 and 2024. Each plot was planted with rice cultivars Jingliangyou-534 (2023–2024) and Yongyou-1540 (2024). Results indicated that SMS application (9 and 18 t ha−1) significantly increased nitrogen content in straw and grain at maturity by 8.54%–41.42% and 1.71%–16.27%, respectively. Correspondingly, NU in straw, grain, and aboveground increased by 11.85%–92.81%, 11.22%–43.59%, and 11.28%–53.18%, respectively. Aboveground biomass, panicles per m2 and spikelets per panicle increased by 6.83%–27.66%, 0.44%–24.54%, and 5.01%–13.26%, respectively; no consistent effects were observed on setting rate for either cultivar across both years. Grain yield improved by 4.70%–23.57%, compared with no SMS application. These findings provide preliminary evidence that fresh SMS (≤18 t ha−1 dry matters) can be applied directly, without composting, as a convenient and effective strategy to enhance rice productivity, though further studies are needed to clarify the mechanisms underlying increased N uptake.