In order to study the effects of combined application of compound fertilizer and branch fertilizer on the growth and yield of machine-transplanted rice, four hybrid rice varieties were used as experimental materials, and four fertilization treatments were set up by completely random design: compound fertilizer (T0), compound fertilizer + conventional branch fertilizer (T1), compound fertilizer + (branch fertilizer − 20%) (T2), compound fertilizer + (branch fertilizer + 20%) (T3). The results showed that the branch fertilizer could effectively promote the early growth and rapid development of tillers, and increase the agronomic traits such as chlorophyll content, LAI and dry matter accumulation. Among the four varieties, the yield of the V4 variety was the highest under T3 treatment, which was 11,471.15 kg·hm−2, which was 37.34% higher than that of the control, and the yield increase effect was the most significant. The correlations showed that dry matter accumulation and LAI were significantly or highly significantly positively correlated with the number of effective spikes and yield, and the number of effective spikes was highly significantly positively correlated with the yield. In general, the application of pitchfork fertiliser increased the effective number of spikes and the number of grains per spike of each variety to different degrees, which effectively promoted the improvement of the rice yield.

As a photophilous plant, rice is susceptible to low-light stress during its growth. The Sichuan Basin is a typical low-light rice-producing area. In this study, eight rice varieties with different shade tolerances were studied from 2021 to 2022. The physiological adaptability and yield formation characteristics of rice were studied with respect to photosynthetic physiological characteristics and dry matter accumulation characteristics, and the response mechanism of rice to low light stress was revealed. The results showed that the shading treatment significantly increased the chlorophyll a, chlorophyll b, and total chlorophyll contents in the leaves of direct-seeded rice after heading, and the total chlorophyll content increased by 1.68–29.70%. Nitrate reductase (NR) activity first increased and then decreased under each treatment, and the shading treatment reduced the NR activity of direct-seeded rice. Compared to the control treatment, the peroxidase (POD) activity of each variety increased from 7 to 24 d after the shading treatment. The transketolase (TK) activity in direct-seeded hybrid rice increased under low light stress. Compared with the control, shading treatment significantly reduced the aboveground dry matter, grain number per panicle, and seed setting rate of direct-seeded rice at the full heading stage and maturity stage, thus reducing the yield of direct-seeded rice by 26.10–34.11%. However, under the shading treatment, Zhenliangyou 2018 and Jingliangyou 534 maintained higher chlorophyll content and related enzyme activities, accumulated more photosynthetic products, and reduced yield. In general, Zhenliangyou 2018 and Jingliangyou 534 still had a yield of 7.06–8.33 t·hm−2 under low light. It indicated that Zhenliangyou 2018 and Jingliangyou 534 had better stability and stronger tolerance to weak light stress and had a higher yield potential in weak light areas such as Sichuan.

Rape-rice rotation uses large amounts of phosphate fertilizers with low utilization rates and large amounts of straw. Therefore, it is necessary to establish a suitable phosphorus fertilizer application mode for straw-returning in a rape-rice rotation system. The treatments were: P application with straw return (T2) and without straw return (T1), no P application in either rapeseed season (P1), application of 120 kg·ha−1 P2O5 on rapeseed and 90 kg·ha−1 P2O5 on rice (P2), application of 120 kg·ha−1 P2O5 only on rapeseed (P3), and application of 90 kg·ha−1 P2O5 only on rice (P4). The results showed that the maximum rapeseed grain yields of T2P3 were increased by 15.57% and 21.05% in 2019 and 18.02% and 32.69% in 2020 compared with those of T2P2 and T2P4, respectively. In the rice season, the maximum yields of T2P3 increased by 17.31% and 6.67% in 2019 and 16.42% and 5.23% in 2020 compared to those of T2P2 and T2P4, respectively. Meanwhile, soil bacterial diversity reached its highest under the T2P3 and T2P2 treatments, but the difference was not statistically significant. Straw return combined with phosphorus application of 120 kg·ha−1 during rape season increased crop productivity and diversity of the soil bacterial community structure during rape-rice rotation.

Direct-seeded rice is often affected by water accumulation caused by uneven soil preparation in the field after sowing and is vulnerable to flooding. Thus, it is important to select submergence-tolerant rice varieties to guarantee seedling development of direct-seeded rice. Twelve hybrid rice varieties were used to study the effects of different flooding days on germination and seedling growth. The evaluation of submergence tolerance and the selection of submergence-tolerant varieties were conducted using principal component analysis. The results showed that the germination potential, germination rate, leaf age, root number, radicle length, seedling height, leaf area, and the dry weight of aboveground and underground parts of direct-seeded rice were decreased, while the root–shoot ratio was increased. The germination potential, germination rate, leaf age, root number, radicle length, seedling height, leaf area, aboveground and underground dry weight of direct-seeded rice decreased with an increase of flooding days, while the root–shoot ratio increased. The comprehensive evaluation function was obtained by principal component analysis. Using the total value of the comprehensive evaluation as an index, three varieties with strong submergence tolerance, Nei5you768, Chuankangyousimiao, and Shen9you28, were selected. The growth of direct-seeded rice was not affected by flooding stress and damage to rice increased with an increase of flooding days. Three rice varieties with strong submergence tolerance at the seedling stage were selected. This study can serve as a reference for rice variety breeding and production.

To investigate changes in the yield and physiological characteristics of indica hybrid rice varieties sown on different dates, we evaluated appropriate hybrid rice varieties and their optimal sowing dates in the hilly areas of Sichuan. Three popular indica rice varieties were used as experimental materials, and five sowing dates were set uniformly locally [16 May (SD1), 23 May (SD2), 30 May (SD3), 6 June (SD4), and 13 June (SD5)] to investigate differences in the yield characteristics, growth period, and dry matter accumulation. The results showed that, over the two years, the sowing-to-heading period and overall growth period of the three varieties shortened as the sowing date was delayed, and the difference in yield between the SD1 and SD2 treatments was not significant, owing to higher material accumulation after flowering and higher assimilative material transport capacity. These varieties are both photosensitive and tolerant to low temperatures. Among the three varieties tested, the Huangyouyuehesimiao (V3) cultivar had the highest yield, with 10.75 t ha−1 under the SD2 treatment. The impact of shifting the sowing date on yield components varied. Delaying the sowing date increased and then decreased the number of effective panicles, and the number of grains per panicle and the seed setting rate decreased by differing degrees. In summary, a high yield of indica hybrid rice can be maintained by sowing between 16 and 23 May each year in the study area. It indicated that indica hybrid rice in the hilly rice-producing region of Sichuan is highly adaptable to different sowing dates.

Straw is an agricultural byproduct that results from the production of many crops, such as cereals, yet it is often considered a waste product. However, straw has both historical precedent and future potential as an agricultural resource. In this study, we aimed to determine the effects of returning straw to the soil on rice cultivation. To this end, we used the hybrid rice variety Luliangyou Jingling as the test material to study the effect of straw return under four different nitrogen application levels (0 kg N (N1), 120 kg N/hm2 (N2), 150 kg N/hm2 (N3), and 180 kg N/hm2 (N4)) on rice tillering dynamics, leaf area index (LAI), dry matter accumulation, and yield. We found that rice under straw return had a higher number of effective panicles, along with a higher number of grains per panicle, compared to those without straw return. Additionally, the tiller number, LAI, total dry matter, and yield of rice in each main growth period under straw return were higher than those without straw return, and these values increased with an increase in nitrogen application rate. The yield was the highest at 9520.63 kg/hm2 without straw return, while the highest yield with straw return was achieved at 10,738.26 kg/hm2. Our results revealed the optimal nitrogen application level for high yield of two-line direct-seeded rice under straw return, which provides a theoretical reference for the precise reduction of fertilizer application in rice cultivation.

水稻青立病对水稻产量具有较大影响,有效预防该病对保障水稻高产栽培具有重要意义.为有效应对水稻青立病提供依据,在四川省绵阳市水稻种植区青立病发病与未发病的田块内取样,对发病与未发病植株的干物质、重金属成分及土壤的微生物进行分析,探明水稻青立病发生对水稻植株与土壤重金属含量及细菌多样性的影响.结果表明:与未发病植株穗部相比,发病植株穗部铬增加158.80％,锌增加111.70％,砷增加2 000.00％,镉增加94.44％.未发病田块与发病田块的土壤细菌优势菌门组成无显著差异,但与未发病田块土壤相比,发病田块土壤中绿弯菌门(Chloroflexi)、放线菌门(Actinobacteriota)、硝化螺旋菌门(Nitrospirotae)的相对丰度分别增加23.09％、29.75％、17.84％,变形菌门、粘球菌门、芽单胞菌门的相对丰度分别减少5.08％、9.12％、15.89％,其他菌门的相对丰度差异不显著.由此推测水稻青立病发病与水稻植株穗部重金属砷、镉和铜的含量偏高具有一定关系.