Effects Of Interaction Between Nitrogen Application Rate And Direct-sowing Density On Yield And Rice Quality Of Rice With Good Eating Quality

Field experiments were conducted in Diaoyu Town,Xinghua City,Jiangsu Province in 2017 and 2018.Nanjing 9108,a japonica cultivar with good eating quality,widely distributed in Jiangsu Province,was used as the experimental material.We designed four nitrogen application rates,namely N1(0 kg·hm-2),N2(150 kg·hm-2),N3(225 kg·hm-2),N4(300 kg·hm-2),and five direct-sowing densities,namely D1(90×104·hm-2),D2(180×104·hm-2),D3(270×104·hm-2),D4(360×104·hm-2),D5(450×104·hm-2).We explore the effects of interaction between nitrogen application rate and direct-sowing density on yield,yield components,photosynthetic production,dry matter production and rice quality,to determine the optimum density of mechanical direct-sowing rice under different nitrogen application rates and elucidate yield and quality formation characteristics of rice.It provides theoretical and technical support for high and stable yield and green production of mechanical direct-sowing rice.The main results are as follows:(1)The rice yield increased with the increase of nitrogen rate.Under the nitrogen application rate of Nl,N2,N3,the grain yield of rice was first increased and then decreased with the increase of direct-sowing density.Under these nitrogen application rates,the highest yield was obtained at the direct-sowing density of D4,D3,D2,respectively.Under the nitrogen rate of N4,the yield decreased with the increase of direct-sowing density,and the highest yield was obtained at the direct-sowing density of D1.The reasonable direct-seeding density under different nitrogen application rates could coordinate the number of productive panicle and the number of spikelets per panicle,thus obtaining a higher population of spikelets,which was conducive to high yield of rice.The mathematical model of quadratic saturated D-optimal design is used for further analysis.Under the nitrogen application rate of 0 kg·hm-2,150 kg·hm-2,225 kg·hm-2,300 kg·hm-2,the highest yield was obtained at the direct-sowing density of 372.51×104 hm-2,229.66×104 hm-2,158.24×104 hm-2,86.81×104 hm-2,respectively.In the range of 0?300 kg·hm-2 nitrogen application rate in this experiment,the highest yield was obtained at the nitrogen application rate of 300 kg·hm-2 matched with the direct-sowing density of 86.81×104 hm-2.(2)The direct-sowing density had no significant effect on the growth process of mechanical direct-sowing rice.With the increase of nitrogen application rate,there was no significant difference in the growth process of rice from sowing to jointing stage,and the heading stage and maturity stage were delayed correspondingly.The phenomenon of late ripening was observed under the application rate N4.With the increase of nitrogen application rate and direct-sowing density,the population number of tillers in rice showed an increasing trend in the critical period of mechanical direct-sowing rice.With the increase of nitrogen application rate,the percentage of productive tiller increased first and then decreased,and all reached the highest level at the application rate of N4.With the increase of direct-sowing density,the percentage of productive tiller of direct-sowing rice showed a decreasing trend.Suitable direct-sowing density at different nitrogen application rates was beneficial to increase leaf area index and photosynthetic potential of mechanical direct-sowing rice at middle and late growth stage,increase dry matter accumulation amount,crop growth rate and net assimilation rate from heading to maturity stage,and improve dry matter weight at maturity stage.(3)With the increase of nitrogen application rate,the milled rice rate and head milled rice rate of mechanical direct-sowing rice increased,and the amylose content decreased.With the increase of direct-sowing density,the milled rice rate and head milled rice rate decreased,and the amylose content increased.With the increase of nitrogen application rate and direct-sowing density,protein content of mechanical direct-sowing rice increased,glue eonsistency decreased,peak viscosity of RVA spectrum,trough viscosity,final viscosity and breakdown decreased,and setback increased.With the increase of nitrogen application rate and direct-sowing density,the appearance,stickiness,balance degree and taste value of rice decreased and its hardness increased.The taste value of N1 without nitrogen treatment was significantly higher than that of nitrogen treatment.Comparing with nitrogen treatment,the taste value difference between N2 and N3 nitrogen application rates was small,and the taste value of N4 with high nitrogen treatment was significantly reduced.(4)Under the premise of fine soil preparation and precise direct seeding to ensure full stand of seeding,the highest yield could be obtained by applying 300 kg·hm-2 nitrogen fertilizer combined with 86.81 ×104 hm-2 direct-seeding density.However,from the multiple perspectives of green production,cost saving and efficiency increase,high quality and yield,as well as the improvement of commercial and economic value of rice,225 kg·hm-2 nitrogen application rate combined with 158.24×104 hm-2 direct-sowing density,that is,reducing the nitrogen application rate appropriately with increasing the density appropriately,has a good application prospect.