Dry direct seeding rice (DSR) is an emerging production system because of increasing labor and water scarcity in rice cultivation. The limited availability of rice cultivars suitable for dry direct seeding hampers the widespread adoption of this cultivation method in Northeast China. This study aimed to investigate grain production and plant characteristics associated with dry direct seeding rice. We conducted a field experiment on 79 japonica rice cultivars in Shenyang City, Liaoning Province, Northeast China, in 2020 and 2021. This study found that the grain yield of the tested rice cultivars ranged from 5.75–11.00 t ha⁻¹, with a growth duration lasting between 144–161 days across the cultivars. These cultivars were then categorized into high yielding (HY), medium yielding (MY), and low yielding (LY) based on daily yield by using Ward’s hierarchical clustering method. The higher grain yield for HY compared to MY and LY was attributed to more spikelets per unit area. The HY alleviated the conflict between higher panicle density and larger panicle size by improving the seedling emergence rate and productive stem rate. It also significantly increased shoot biomass at maturity. The HY reduced the period between seeding and beginning of heading (BBCH 51) and the proportion of dry matter partitioned to the leaf at the heading stage. However, it also increased the accumulation of dry matter in the grain and the proportion of dry matter partitioned to the grain at maturity. Furthermore, the HY markedly increased the harvest index and grain-leaf ratio, which are beneficial to coordinate the source–sink relationship. A quadratic function predicted that 98 days is the optimum growth duration before heading (BBCH 51) for achieving maximum yield. In conclusion, for dry direct seeding rice, it is appropriate to select high-yielding japonica inbred rice cultivars with shorter growth duration before heading (about 93–102 day), higher panicle number (about 450–500 × 10⁴ ha^–1), more spikelet number per panicle (about 110–130), higher seedling emergence rate (about 70–75%), higher productive stem rate (about 60–70%), and greater harvest index (about 50–55%).

The quality and starch properties of rice are significantly affected by nitrogen. The effect of the nitrogen application rate (0, 180, and 230 kg ha⁻¹) on the texture of cooked rice and the hierarchical structure and physicochemical properties of starch was investigated over two years using two japonica cultivars, Bengal and Shendao505. Nitrogen application contributed to the hardness and stickiness of cooked rice, reducing the texture quality. The amylose content and pasting properties decreased significantly, while the relative crystallinity increased with the increasing nitrogen rates, and the starch granules became smaller with an increase in uneven and pitted surfaces. The proportion of short-chain amylopectin rose, and long-chain amylopectin declined, which increased the external short-range order by 1045/1022 cm⁻¹. These changes in hierarchical structure and grain size, regulated by nitrogen rates, synergistically increased the setback viscosity, gelatinization enthalpy and temperature and reduced the overall viscosity and breakdown viscosity, indicating that gelatinization and pasting properties were the result of the joint action of several factors. All results showed that increasing nitrogen altered the structure and properties of starch, eventually resulting in a deterioration in eating quality and starch functional properties. A moderate reduction in nitrogen application could improve the texture and starch quality of rice while not impacting on the grain yield.

In China, agriculture is currently highly dependent on chemical nitrogen. This leads to low nitrogen use efficiency and high nitrogen losses. Considering the issues caused by excessive chemical fertilizer, integrated nutrient management using organic and chemical fertilizer sources is important. To clarify how partial substitution of chemical fertilizer by organic fertilizer affects rice yield, physiological traits, and nitrogen use efficiency, we conducted a two-year field trial in 2021 and 2022, and used two rice cultivars, Shendao47 (SD47) and Shendao505 (SD505), which were grown in the field with five fertilization treatments: (1) CK (zero N application); (2) CF (100% chemical fertilizer); (3) OR10 (10% organic fertilizer + 90% chemical fertilizer); (4) OR20 (20% organic fertilizer + 80% chemical fertilizer); and (5) OR30 (30% organic fertilizer + 70% chemical fertilizer). The results show that the partial organic substitution (OR) treatments improved the yield by 1–10% for two cultivars by increasing effective panicles and grain filling. The increase in grain filling was related to the photosynthetic parameters, including LAI, chlorophyll content, and net photosynthetic rate during the grain-filling stage. The photosynthetic parameters of OR treatments were higher than those of CF treatment. Additionally, with the increase in organic fertilizer application rates, the grain yield, agronomic N use efficiency, partial factor productivity of applied N, and physiological N use efficiency increased at first and then decreased, peaking in OR20 treatment. Conclusively, the 20% organic fertilizer with 80% chemical fertilizer is a promising option for higher yield and improved N utilization for both cultivars. This study provides a sustainable nutrient management strategy to improve crop yield with high nutrient use efficiency.

The combination of controlled-release urea (CRU) and conventional urea (CU) has become an important practical strategy to simultaneously increase rice yield, economic benefits, and nitrogen (N) use efficiency (NUE) with one-time fertilization management. However, the method by which the combination of CRU and CU intervenes with rice yield, economic benefits, and NUE in saline–alkali paddy fields has not yet been established. Accordingly, a two-year field experiment was set up with a total of seven treatments (CK, no N application; CUF, conventional urea split applications; RCUF, CUF treatment with 20% N reduction; CRBF1, 50%CRU + 50%CU one-time base application; CRBF2, 70%CRU + 30%CU one-time base application; RCRBF1, CRBF1 treatment with 20% N reduction; RCRBF2, CRBF2 treatment with 20% N reduction). The results showed that the controlled-release blended fertilizer (CRBF) treatments significantly increased the yield, economic benefits, and NUE over the two years. The CRBF1 and CRBF2 treatments significantly increased the rice yield by 5.10–6.77% and 10.41–11.04%, N recovery efficiency by 13.30–17.40% and 21.69–26.75%, and N agronomic efficiency by 10.40–13.91% and 21.26–22.10% compared to the CUF treatment, respectively. The RCRBF1 and RCRBF2 treatments maintained rice yields and significantly increased NUE compared to the CUF treatment. The analysis of yield components indicated that the greater rice yields of the CRBF were mainly attributed to increased panicle numbers and spikelet numbers per m². Furthermore, the post-anthesis dry matter, N accumulation, flag SPAD values, flag photosynthetic rates, and soil ammonium nitrogen content were higher during the grain-filling stage of the CRBF treatments compared to the CUF treatments. Compared with the CUF treatment, the CRBF1 and CRBF2 treatments increased economic benefits by 8.74–11.16% and 17.14–17.41%. Therefore, the combination of CRU and CU can increase rice yield, economic benefits, and NUE in saline–alkali paddy fields. Moreover, it is recommended to apply CRU and CU at a ratio of 7:3 in a single basal application as a green and efficient alternative N management strategy for saline–alkali paddy fields. The results provide a scientific basis for N management strategies in saline–alkali paddy fields.

In this research, the effects of organic amendments and planting methods on the grain yields, enzyme activity, soil quality, and the structures of fungal populations in the rhizosphere of rice were evaluated. In comparison to the control group with direct seeding, the transplanting method resulted in a 23.5% higher grain yield. Furthermore, rice straw addition significantly improved fungal diversity indices (i.e., Chao1, ACE, Shannon, and Simpson). Dissimilarity distances and principal coordinate analysis revealed substantial variations in the compositions of root-associated fungal communities across the experimental groups with different planting methods. When the transplanting method was used, the Ascomycota, Basidiomycota, Chytridiomycota, Olpidiomycota, Aphelidiomycota, Monoblepharomycota, and Calcarisporiellomycota phyla became dominant. Biochar and rice straw applications caused substantial increases in the abundance of the Ascomycota, Basidiomycota, Chytridiomycota, Rozellomycota, Mucoromycota, Olpidiomycota, Aphelidiomycota, and Gammaproteobacteria phyla. Changes in enzyme activity and the physicochemical properties of the soil were also observed across the treatment groups with different planting methods and organic amendments. Direct seeding enhanced cellulase activity, microbial biomass carbon and nitrogen, available nitrogen, available potassium, nitrate nitrogen, and ammonium nitrogen, whereas transplanting boosted the activity of sucrase and urease enzymes. Rice straw application enhanced cellulase activity and the concentrations of available nitrogen, available phosphorus, nitrate nitrogen, and ammonium nitrogen in the soil. Biochar addition resulted in increased urease activity, microbial biomass carbon and nitrogen, soil pH, and available potassium. The Ascomycota abundance and grain yield exhibited a positive connection, while unclassified_Fungi exhibited negative correlations with the soil pH, organic carbon, available phosphorus, grain yield, and activity of sucrase and urease. Mortierellomycota was positively correlated with microbial biomass nitrogen and nitrate nitrogen. Overall, both the organic additives and planting methods influenced the soil properties, enzyme activity, rhizosphere fungal populations, and grain yield. These results provide new insights and a theoretical basis for studying the changes in soil fungal diversity and richness with different planting methods and organic amendments in Northeastern China.

Lodging is a major constraint limiting grain yield in dry direct seeding rice (DDSR), yet the key traits and phenotypic relationships governing lodging resistance in japonica varieties adapted to this system remain poorly understood. This study evaluated 79 japonica accessions over two years in Shenyang, Northeast China, to dissect phenotypic variation in lodging index and identify ideotypes for breeding. Based on hierarchical clustering, varieties were classified into strong lodging resistance (SLR), medium lodging resistance (MLR), and weak lodging resistance (WLR) types, with SLR varieties achieving lodging indices 27.4–31.8% lower than those of MLR and 63.2–83.8% lower than those of WLR varieties. SLR varieties reduced lodging risk by coordinately balancing whole-plant bending moment and stem breaking resistance: plant height and center-of-gravity height were 5.2–10.7% lower, while basal internode bending stress was 27.9–81.9% higher than in other types. Structural equation modeling identified culm dry weight, inner diameter, and culm phenotype index as primary determinants of lodging variation. Notably, despite 11.0–13.7% fewer spikelets per panicle, SLR varieties maintained grain yields comparable to those of WLR varieties through compensatory increases in grain-filling rate (6.7–7.3%) and 1000-grain weight (8.1–8.7%). These findings demonstrate that optimizing basal internode structure and enhancing culm tissue density can simultaneously improve lodging resistance and preserve yield potential, providing a practical framework for breeding lodging-resistant, high-yielding japonica varieties for DDSR systems in Northeast China.