| Rice-crayfish continuous production system offers high economic benefits and was ecologically friendly,which had expanded rapidly across many provinces of China in recent years.However,the high yield and excellent quality of rice-crayfish continuous cropping with machine-transplanted rice has been a difficult problem.The experiment was carried out in the experimental base of rice field comprehensive cultivation in Jiujie Village,Maba Town,Xuyi County,Huai ’an City in 2018 and 2019.Nanjing 2728,a japonica rice variety,and Taoyou Xiangzhan,a indica rice variety,both of which had high-quality taste,were selected as materials,and two mechanical transplanting methods were set up:mechanically transplanted carpet seedling(equal spacing,30 cm)and mechanically transplanted pot seedling(wide and narrow rows,row spacing 33 cm+23 cm).The plant spacing designs of mechanically transplanted carpet seedling were 11.5 cm,12.8 cm,14.4 cm,15.7cm and 16.7 cm,and that of mechanically transplanted pot seedling were 12.4 cm,13.8 cm,15.5 cm,16.8 cm and 17.9 cm.The paper aims to explore the effects of transplanting methods and specifications on yield formation,photosynthetic material production,lodging resistance and rice quality of Nanjing 2728 and Taoyou Xiangzhan,and to determine the best density for rice transplanting with excellent quality and high yield under rice-crayfish continuous cropping.The results can provide theoretical basis for rational allocation of row spacing of rice-crayfish continuous cropping in the Hongze Lake area.The main research results are as follows:1.Compared with mechanically transplanted carpet seedling,the yield of rice mechanically transplanted pot seedling increased significantly.The main reason was the increase of grain number per panicle.Under different transplanting methods,the rice yield increased at first and then decreased with the decrease of density.The yields of Nanjing 2728 and Taoyou Xiangzhan reached the highest value was obtained at 77.9 × 104 seedlings ha-1 and 42.6×104 seedlings ha-1.Compared with mechanically transplanted carpet seedling,the tiller dynamics of mechanically transplanted pot seedling showed a slow rise and decline trend.The peak seedlings time of Nanjing 2 728 was the 28th day after transplanting,and that of Taoyou Xiangzhan was the 21 st day after transplanting.The dry matter weight of population and single stem increased significantly at jointing stage,heading stage and mature stage of mechanically transplanted pot seedling.The leaf area index and photosynthetic potential of three main growth stages were higher,and the population growth rate and net assimilation rate increased.The trends of both varieties were consistent.Under the same transplanting mode,with the decrease of density,the panicle number,dry matter weight and leaf area index of rice in the main growth stages of both varieties showed a downward trend.The photosynthetic potential,population growth rate and net assimilation rate from sowing to jointing stage of Nanjing 2728 showed a similar trend,while the dry matter weight of single stem and net assimilation rate from heading to maturity showed an upward trend.The population growth rate and net assimilation rate from jointing stage to heading stage,photosynthetic potential and population growth rate from heading stage to maturity stage of Taoyou Xiangzhan increased at first and then decreased,while photosynthetic potential,population growth rate and net assimilation rate in other growth stages decreased with the decrease of density.2.Mechanical transplanting methods and planting specifications had great influence on lodging resistance of rice under continuous cropping of rice-crayfish.Compared with mechanically transplanted carpet seedling,mechanically transplanted pot seedling of two varieties significantly improved individual morphological indexes such as fresh weight of single stem,height of plant,height of center of gravity,leaf length and leaf area of three leaves on spike weight,and improved rice stem base morphological indexes such as stem thickness,wall thickness,dry weight per unit length of stem and leaf sheath,flexural strength and bending moment.The influence of mechanically transplanting methods mode on single factors such as long axis outer diameter,long axis inner diameter,short axis outer diameter,short axis inner diameter,section coefficient and bending stress were not significant.Lodging index was closely related to breaking moment and bending moment.Multivariate analysis of variance showed that the main factor that contributed to the decline of lodging index was the increase of breaking moment.With the decrease of density,the lodging index of both varieties with mechanically transplanting methods showed a downward trend,which was mainly due to the increase of stem diameter,wall thickness and plumpness of the base internode.As a result,the bending strength of the base internode was significantly improved and the lodging resistance was enhanced at lower density.3.Machine transplanting significantly affected rice quality.Compared with mechanically transplanted carpet seedling,mechanically transplanted pot seedling increased the head rice rate of Nanjing 2728 and Taoyou Xiangzhan,reduced chalkiness rate and chalkiness degree,and significantly improved the processing and appearance quality of both varieties,the amylose content showed a slight downtrend,and the taste value showed an upward trend.Mechanically transplanted pot seedling was beneficial to improving the cooking and taste quality of rice.The protein content of the same variety was less affected by the transplanting method and planting density.As to the influence on RVA characteristic value of starch,the peak viscosity,hot paste viscosity,disintegration value and final viscosity of mechanically transplanted pot seedling were higher than those of mechanically transplanted carpet seedling,while the reduction value and recovery value of both showed an opposite trend.Under the same machine transplanting mode,the reduction of planting densities was beneficial to improving the processing and appearance quality of both rice varieties,and the amylose and protein contents showed a downward trend,but the difference was not significant.With the decrease of density,the peak viscosity,hot paste viscosity,disintegration value and final viscosity of two varieties under both mechanically transplanting methods showed an upward trend,while the reduction value and recovery value showed a downward trend.The difference between similar densities was not significant,and the difference between high density and low density reached a significant level.To sum up,the optimum density for Nanjing 2728 carpet seedling was A2(30 cm×12.8 cm),and that for Taoyou Xiangzhan was A4(30 cm×15.7 cm).The optimum density for transplanting rice seedlings in Nanjing 2728 was B2((33 cm+23 cm)×13.8 cm),and that for Taoyou Xiangzhan was B4((33 cm+23 cm)× 16.8 cm).The yields of Nanjing 2728 in mechanically transplanted pot seedling were 4.4%and 5.1%higher than that in mechanically transplanted carpet seedling in 2018 and 2019 respectively,and the figures for Taoyou Xiangzhan were 7.9%and 8.7%.Meanwhile,mechanically transplanted pot seedling had a better effect on the processing quality and appearance quality of rice.Therefore,mechanically transplanted pot seedling(wide and narrow rows,row spacing 33 cm+23 cm)with 13.8 cm plant spacing for japonica rice varieties,as well as mechanically transplanted pot seedling(wide and narrow rows,row spacing 33 cm+23 cm)with 16.8 cm planting densities for indica rice varieties,which showed a bright application prospect,was beneficial to the high yield and good quality of rice under the continuous cropping of rice-crayfish. |
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