Relationship Between Rice Ratooning Ability And Canopy Indices At Grain-filling Stage Of Main Crop

As a resource efficient and economical cultivation mode,ratoon rice has the advantages of time-saving,labor-saving,water-saving,fertilizer saving and high economic benefits.The unstable ratooning rate and high hill-missing rate in the ratooning season lead to unstable yield,which is a headache problem restricting the development of ratoon rice in Guangdong as well as in South China.The grain-filling stage of the main crop rice is the key stage affecting the ratooning ability.Improving the yield and its stability of ratoon rice through improved cultivation of main crop rice（especially during grain-filling stage）is of great significance to the production of ratoon rice in South China.The field experiment was conducted at Dafeng Experimental Base of Guangdong Academy of Agricultural Sciences in 2021.Meixiangzhan 2,a high quality rice variety widely used in Guangdong,was arranged in a randomized complete block design with six treatments consisting of two planting densities and three nitrogen management regimes.The planting density was 30 cm×13.3 cm（conventional,D1）and 25 cm×13.3 cm（increased density,D2）,and the nitrogen management was 75 kg N ha^-1 panicle fertilizer（N1）,75 kg N ha^-1 basal and tiller fertilizer（N2）and 75 kg N ha^-1 panicle fertilizer+75kg N ha^-1 basal and tiller fertilizer（N3）.During the harvest of the main crop rice,each treatment was split into low-stubble and high-stubble treatments.Leaf area index（LAI）,aboveground biomass,leaf SPAD value,root bleeding,light transmission ratio（LTR）at heading（HD）,15 days after heading(HD₁₅)and maturity（MA）,grain yield and yield components of main crop rice were measured.The ratooning ability as indicated as grain yield,maximum rationing rate,and final ratooning rate of ratoon rice were investigated.The main results are as follows:1.Planting density and nitrogen management had significant effects on the population indices at grain-filling stage,grain yield and ratooning ability of the main crop.Grain yield of main crop rice ranged from 5.85 t ha^-1to 7.25 t ha^-1,and was from 4.07 t ha^-1 to 4.79 t ha^-1 for low stubble and from 2.53 t ha^-1 to 2.98 t ha^-1 for high stubble ratoon rice,respectively.The maximum ratooning rate was 148.9%～222.4%for low stubble and116.7%～178.7%for high stubble ratoon rice.There were significant differences among plant density and N application treatments in canopy indices during grain-filling stage of the main crop,such as light transmission ratio（LTR）,root vigor,stem and sheath weight per stem,SPAD attenuation index,etc.2.The ratooning ability correlated closely with canopy indices at grain-filling stage of main crop.For low stubble ratoon rice,the grain yield and maximum ratooning rate were positively correlated to LTR（P<0.05）and root vigor（P<0.05）at HD,HD₁₅and MA,and positively correlated to stem and sheath weight per stem（P<0.05）at HD and MA of main crop rice.For high stubble ratoon rice,the grain yield was only positively and significantly correlated to LTR at MA,root vigor at HD and HD₁₅,the stem and sheath weight per stem at HD of main crop rice.The maximum ratooning rate was only positively and significantly correlated to LTR at HD₁₅,root vigor at MA,the stem and sheath weight per stem at MA of main crop rice.3.The low stubble and high stubble ratooning ability were negatively and significantly correlated to SPAD attenuation index at late grain-filling stage of main crop,with correlation coefficients being-0.444*（P<0.05）and-0.523**（P<0.01）.However,it was not significantly correlated to SPAD attenuation at early grain-filling stage of main crop（P>0.05）.Our results suggest that the light transmission ratio,root vigor,SPAD attenuation,stem and sheath weight per stem at grain-filling stage of the main crop rice could be used as indicators of ratooning ability of rice.The ratooning ability and grain yield of ratoon rice could be increased through enhancing light transmission ratio under a wide-row and narrow-plant spacing,by enhancing root vigor under alternate drying and wetting irrigation,by delaying leaf senescence with additional nitrogen application at late grain-filling stage.The results could be of practical value in stable and high-yield cultivation of ratoon rice in South China.