Climate is the most important environmental factor influencing yield during rice growth and development. To investigate the relationships between climate and yield under different crop rotation patterns and planting methods, three typical rotation patterns (vegetable–rice (V), rape–rice (R), and wheat–rice (W)) and two mechanical planting methods (mechanical transplanting (T1) and mechanical direct seeding (T2)) were established. The results showed that compared to the V rotation pattern, the average daily temperature (ADT) during the sowing to heading stage increased under both R and W rotation patterns, which significantly shortened the growth period. Thus, the effective accumulated temperature (EAT), photosynthetic capacity, effective panicle (EP), and spikelet per panicle (SP) under R and W rotation patterns significantly decreased, leading to reductions in grain yield (GY). VT2 had a higher ratio of productive tillers (RPT), relative chlorophyll content (SPAD), leaf area index (LAI), and net photosynthetic rate (Pn) than those of VT1, which significantly increased panicle dry matter accumulation (DMA), resulting in an increase in GY. Although RT2 and WT2 had a higher RPT than those of RT1 and WT1, the GY of RT1 and WT1 decreased due to the significant reductions in EAT and photosynthetic capacity. Principal component analysis (PCA) showed that the comprehensive score for different rotation patterns followed the order of V > R > T with VT2 ranking first. The structural equation model (SEM) showed that EAT and ADT were the most important climate factors affecting yield, with total effects of 0.520 and −0.446, respectively. In conclusion, mechanical direct seeding under vegetable–rice rotation pattern and mechanical transplanting under rape–rice or wheat–rice rotation pattern were the rice-planting methods that optimized the climate resources in southwest China.

To determine the optimal drying period for direct seeding rice, we conducted experiments using two rice cultivars: hybrid indica (Shuyou 217) and conventional indica (Huang Huazhan). The experiments explored the influence of varying initial leaf development stages on tillering dynamics, leaf area, dry matter production, yield, and yield components in direct seeding rice. The results indicated a significant correlation between the initial leaf development stage and the yield of direct seeding rice. As the initial leaf development stage progressed, the number of effective panicles increased, while key traits affecting panicle yield, such as grain/spikelet? Number per panicle, seed setting rate, and 1000-grain weight, decreased. Additionally, varietal differences in tillering reduction were observed across different leaf development stages. Shuyou 217 exhibited a decrease in heading rate with increasing leaf development stage, whereas Huang Huazhan showed no significant difference. With delayed seeding planting age, both cultivars demonstrated an increasing trend in the leaf area index, initially leading to a rise in effective leaf area proportion, followed by a decline. At the full heading and maturity stages, the dry weight of the stem sheath and panicles per plant decreased as the leaf development stage was delayed. However, the output and transport rates of stem sheath assimilated first increased and then decreased. From a practical perspective, field drying management should be aligned with varietal characteristics to reduce ineffective tillering, ensure sufficient dry matter accumulation during the full heading stage, and optimize post-heading dry matter export and transport. This strategy promotes the coordination between the “source” and “sink” dynamics in rice, ultimately maximizing yield in direct-seeded rice systems.

To explore the optimal row-ratio in mechanized hybrid rice seed production, a field experiment was conducted in 2024 at Qionglai and Mianzhu using ‘Tiantai A’ × ‘Taihui 808’. Three row-ratio treatments (H1: 18:6, H2: 24:6, and H3: 30:6) were tested using agricultural unmanned aerial vehicles (AUAVs) for pollination assistance. The results showed that row-ratio had little effect on sterile line flowering dynamics. The index of flowers meeting (IFM) was 0.71-0.72 at Qionglai and 0.81–0.86 at Mianzhu, with 11 to 12 days of flowering duration. As the row-ratio increased, total pollen quantity in the panicle layer and grain filling rate (GFR) decreased, while grain infection rate (GIR) increased. The responses of grain blighted rate (GBR), grain empty rate (GER), and fertilization success rate (FSR) to row-ratio varied between sites. Pollen density and GFR followed the pattern of near region (NR) > central region (CR) > far region (FR). Within the panicle, pollen density was generally highest in the upper panicle layer (UPL), followed by the middle (MPL) and lower (LPL) layers, with partial exceptions observed in the H2 and H3 treatments at Mianzhu. The vertical distribution of GFR varied by site: at Qionglai, it was apical parts of panicle (APP) > median parts (MPP) > basal parts (BPP), whereas at Mianzhu the order was MPP > APP > BPP. With wider row-ratios, yield per unit area (YUA) and GFR declined (H1 > H2 > H3), while 1,000-grain weight increased or decreased and then increased. Under H1, yields reached 2,107.50 kg ha ⁻¹ at Qionglai and 2,201.62 kg ha ⁻¹ at Mianzhu, 4.18% and 3.18% higher than H2 and 6.74% and 5.77% higher than H3. However, the equivalent monoculture yield per hectare (EMYH) increased with wider row-ratios (H3 > H2 > H1). Under H3, equivalent yields were 1,645.43 kg ha ⁻¹ at Qionglai and 1,734.59 kg ha ⁻¹ at Mianzhu, increasing by 4.10% and 1.68% over H1 and 5.05% and 1.62% over H2. In summary, although wider row-ratios reduced pollen supply and GFR per sterile row, the increased number of sterile rows compensated, enhancing total seed production. Thus, the 30:6 row-ratio (H3) is recommended for optimal yield.

Ratoon rice is the production of a second rice crop from the stubble left behind after the main crop has been harvested. To identify suitable ratoon rice cultivars for a dual-purpose grain and forage production system, 25 widely cultivated rice cultivars in southwestern China were systematically evaluated based on ratooning ability, forage productivity, ratoon rice yield, and Cd accumulation characteristics. Significant variations were observed among the tested cultivars, indicating substantial differences in their suitability for this production system. Principal component analysis identified three cultivars, CKY637, CKYSM, and FY498, as promising candidates because of their favorable combination of ratooning ability (1.33–1.61), silage rice yield (8.85–11.27 t ha⁻¹), ratoon rice yield (7.83–9.65 t ha⁻¹), and low grain Cd accumulation (0.0430–0.0457 mg kg⁻¹). Among them, CKY637 achieved the highest comprehensive evaluation score, whereas CKYSM exhibited particularly stable performance in maintaining low Cd accumulation, and FY498 was well balanced between yield and quality. These results suggest that cultivar suitability for the dual-purpose system depends on the coordinated performance of multiple traits, particularly strong ratooning ability, high forage and ratoon rice productivity, short total growth duration, and low Cd accumulation in ratoon rice grains. Overall, CKY637, CKYSM, and FY498 represent candidate cultivar resources for the first-season forage + second-season ratoon rice system and provide practical materials for its application in subtropical rice-growing regions.