| In order to investigate the effects of nitrogen-density intercropping on morphology,photosynthetic performance,and nitrogen utilization of different types of hybrid rice,high-quality two-line hybrid indica rice Jingliang You 534(C1)and three-series hybrid indica rice Yixiang You 2115(C2),which have similar fertility and were widely grown in the southwest rice region,were selected as test materials from 2019 to 2021,with conventional N1(150 kg/hm~2),N2(225 kg/hm~2)and no N(N0,control),and two planting densities:150,000 holes/hm~2(D1,33.3×20 cm)and 180,000 holes/hm~2(D2,33.3×16.7 cm).The plant leaf morphology,plant root structure,yield composition,and nitrogen utilization characteristics of two typical hybrids under different nitrogen levels and population densities were mainly explored.The nitrogen-density interaction effects between different types of high-yielding hybrid rice planting and nitrogen utilization were further elaborated to lay the theoretical and practical foundation for high-yielding rice planting.The main research results are as follows:1.The average yield of the two-series hybrid rice Jingliang You 534 was 4.54%～14.56%higher than that of the three-series hybrid rice Yixiang You 2115.In the three-year experiment,the highest yield of Jingliang You 534 was 12,364 kg/hm~2,and that of Yixiang You 2115 was 10,155 kg/hm~2.The results of the interaction between N application and density on the yield of both types of hybrid rice were highly significant,and the N2D1treatment of two-series hybrid rice Jingliang You 534 had the highest yield,reaching 12,364kg/hm~2,9,801 kg/hm~2 and 10,280 kg/hm~2 in three years,respectively.In terms of yield components,the higher yield of the two-series hybrid rice came from the higher adequate number of spikes and grains in 2019-2021.The interaction between density and N application significantly increased the number of spike grains and thousand-grain weight.Regular N application at the same density effectively increased spike size and grain weight.In contrast,further incremental N application did not consistently increase spike size and grain weight and even decreased spike size and grain weight at higher densities.2.The differences between the leaf length,leaf width,and leaf angle of the two-series hybrid sword leaf,inverted second leaf,and inverted third leaf were lower than those of the three-series hybrid rice among different types of varieties.Compared with the three-line mixed rice Yixiang You 2115,the two-line hybrid rice Jingliang You 534 had a smaller leaf area,more upright leaves(shorter leaves and smaller leaf angles),and a more compact plant shape,and could maintain a compact population structure even with increased nitrogen application and population density.Density and nitrogen application significantly affected the plant leaf morphology of both types of hybrid rice.With increasing planting density,the leaf length and leaf width of both varieties gradually increased,but the leaf angle of three-line mixed rice Yixiang You 2115 was smaller at high density than at low density;with increasing nitrogen application,leaf length,leaf width,and leaf angle of both varieties gradually increased,showing N2>N1>N0.3.Density and nitrogen application significantly affected the photosynthetic performance of different rice varieties.Density significantly affected the photosynthetic production characteristics of both types of hybrid rice.Under D1 density,both types of hybrid rice showed superior population quality and photosynthetic performance,relying on excellent leaf morphology,which was conducive to post-flowering dry matter accumulation and yield improvement.Under the conventional N application,both two-and three-line hybrids showed suitable leaf area,good light exposure in the upper trifoliate leaves,high net photosynthetic rate,and slow green leaf senescence during the fruiting period,which was conducive to the accumulation of post-flowering group dry matter and could maintain a compact group structure and good light exposure despite the increase in N application and group density,thus ensuring better post-flowering photosynthetic production capacity and achieving higher The seed yield was high.The canopy PAR transmission rate of the two-series hybrid rice Jingliang You 534 was significantly higher than that of the three-series hybrid rice Yixiang You 2115.The canopy PAR transmission rate gradually decreased,and the PAR interception rate gradually increased with planting density and N application.4.Nitrogen application,density,and N-density intercropping greatly affected rice’s single-plant growth and population dry matter accumulation and translocation.Compared with the N1 treatment,the N2 treatment had a larger dry matter spike allocation ratio,post-flowering dry matter accumulation ratio,and dry matter translocation and contribution to seeds,while increasing density increased dry matter transfer but reduced spike allocation ratio,post-flowering dry matter accumulation ratio,and dry matter translocation and contribution to seeds.Under N2D1 of N-density intercropping,the two types of hybrid rice had more post-flowering dry matter accumulation,higher transformation rate,higher contribution ratio,higher dry matter spike share,and the highest population dry matter accumulation reached18.39 t/hm~2.5.Nitrogen application,density,and N-density intercropping all significantly affected root biomass and crown ratio.The root biomass and root crown ratio of three-line hybrid rice were higher than those of two-line hybrid rice.The root biomass was highest under the treatment of incremental nitrogen application,and there was no significant difference in root biomass between different densities.In terms of rice root morphological indexes,variety,nitrogen application,and density and their interactions had significant effects on total root length,root diameter,total root surface area,and total root volume;aboveground and root biomass of three-line hybrid rice Yixiang You 2115 were 24.5%and 56.8%higher than that of two-line hybrid rice Jingliang You 534,respectively.With the increase of N application,the aboveground and root biomass gradually increased in different treatments,among which N2 was the highest;with the increase of planting density,the aboveground biomass under different treatments showed an increasing trend.6.Density and N-density intercropping had essential effects on nitrogen accumulation and utilization in different types of rice.Nitrogen accumulation was highest in N1D2,followed by N1D1.Conventional N application effectively promoted N use by rice plants.It significantly increased the N harvest index and N rice grain production efficiency compared with incremental N application.In contrast,rice plants’N harvest index and rice grain production efficiency decreased under incremental N application.Nitrogen accumulation in all organs and whole plants of two-series hybrid rice was higher than that of three-series hybrid rice.Nitrogen accumulation in all organs increased with increasing nitrogen application,and N1 and N2 treatments were significantly higher than those without nitrogen application.There was no significant difference in the amount of nitrogen translocation,rate of nitrogen translocation,and increase of nitrogen in the spike between different densities of rice stem sheaths and leaves.Overall,the two-series hybrid rice Jingliang You 534 had a higher yield,superior population quality,photosynthetic performance,root biomass,root-to-crown ratio,and nitrogen use efficiency the N2D1 treatment.In contrast,the three-series hybrid rice Yixiang You 2115 performed better in the N1D1 treatment. |
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