Effects Of Sowing Date And Density On Yield And Quality Formation Of Insect-resistant Cotton Under Filmless Cultivation

The experiment was carried out at Science and Technology Demonstration Park of the Dezhou Academy of Agricultural Sciences,cotton test base of Shandong Agricultural University in 2018 and 2019.The experiment was in split-split plot design with filmless cotton in main plot,sowing time in subplot and density in deputy subplot.The film mulching pattern includes cotton under common polyethylene plastic film-covered（CF）and filmless cultivation（NF）.Sowing date respectively includes April 20th（S1）,April 30th（S2）and May10th（S3）.The planting density includes three planting densities of 5.25×10⁴ plants hm^-2（D1）,6.75×10⁴plants hm^-2（D2）,and 8.25×10⁴plants hm^-2（D3）.This experiment studys the influences mechanism of sowing date and density on filmless cotton from aspects of cotton growth and development,photosynthetic performance,quality and yield to study on suitable sowing date of filmless insect-resistant cotton.The main findings are as follows:1 Effects of sowing date and density on growth and development of filmless cotton.Compared with film-covered cultivation of insect-resistant cotton,the growth process of filmless insect-resistant cotton was delayed in the two years,and the squaring stage in 2018was 4-5 days late,and 9-10 days late in 2019.Compared with film-covered cultivation,plant height,number of fruit nodes,and number of fruit branches decreased by 29.01%-29.85%,42.73%-46.07%,and 26.85%-27.04%of filmless insect-resistant cotton on June15,the height difference of the first fruit branch was not significant.Late sowing slowed down the cotton growth process and prolonged the growth period.As the density increased,the plant height and the height of the first fruit branch increased,and the total number of fruit nodes,and fruit branches decreased.2 Effects of sowing date and density on photosynthetic performance of filmless cotton leaves.Compared with film-covered cultivation,SPAD,P_n,and G_s of functional leaves were significantly reduced under filmless cultivation conditions.There was no significant difference in C_i and T_r.No significant difference was found in SOD in functional leaves at each leaf age,but POD activity was significantly reduced.The performance of the donor and recipient were weakened,and the performance index were reduced.With sowing date delaying,SPAD,P_n,G_s decreased,C_i and T_r increased during every period.With density increasing,SPAD,P_n,G_s,T_r in functional leaves decreased and C_i increased in each period.There were no significant differences in donor-side parameters,accepted-side parameters,PI_abs,and?_o.Increasing density led to poor light conditions,weakened leaf physiological performance,which resulted in lower SOD,POD activity,higher malonaldehyde content.3 Effects of sowing date and density on the spatiotemporal distribution of filmless cotton.In each treatments,the ratio of boll was highest in summer boll,followed by autumn boll,and lowest in pre-summer boll.Compared with film-covered cultivation,the proportion of boll of pre-summer boll and summer boll was reduced,and the proportion of boll autumn peach was increased,while that of summer boll increased in 2019.The proportion of bolls at the basic inner branches,the basic outer branches and the middle inner branches had a tendency to decrease,however,that of middle outer branches,upper branches showed opposite trend.With the sowing date was delayed,the proportion of bolls in pre-summer boll decreased,which was increased in summer bolland autumn boll.The proportion of boll in the base inner branches and the middle inner branches had a tendency to decrease with the delay of the sowing date,while the other parts of branches increased.The trend of the two-year test results was basically the same.With density increasing,the proportion of pre-summer boll and autumn boll decreased in 2018,and summer boll increased.In 2018,the proportion of boll in the upper outer branches had a trend of D3>D1>D2.However,it had no significant effectes on the proportion of bolls in other parts of branches.In 2019,the proportion of pre-summer boll increased,and the proportion of summer boll and autumn boll decreased.The proportion of inner boll in the base branches significantly increased with increasing density in 2019,which was,otherwise,significantly decreased in other parts of branches.Compared with 2018,due to the impact of climatic conditions,cotton grew early in 2019,which resulted in the number of pre-summer boll increased,and the number of autumn boll decreased.4 Effects of sowing date and density on fiber quality of filmless cotton.The fiber length of autumn peach was highest,followed by summer boll,pre-summer boll least.The micronaire value of summer boll was highest,followed by pre-summer boll,autumn peach least.The fiber uniformity,fiber strength,and fiber elongation of summer boll was highest,followed by autumn peach,pre-summer boll least.The fiber length,fiber uniformity,fiber strength,and fiber elongation of inner part of the basic fruit branches were significantly lower than that of the other parts of fruit branches.There was no significant difference in cotton fiber length,micronaire value,uniformity,and elongation of each treatment.Under filmless cultivation conditions,the fiber specific strength at different sowing dates of D1 was hightest,followed by D3,D2 lowest,while that of film-coveredcotton had no significant difference.5 Effects of sowing date and density on yield and its constituent factors of filmless cotton.The seed cotton yield in each treatment was highest in summer boll,followed by autumn boll,and lowest in pre-summer boll.In 2019,seed cotton yield of pre-summer boll was higher than autumn boll.Compared with film-mulching cultivation,the seed cotton yield of pre-summer boll and summer boll of filmless cotton decreased,and the seed cotton yield of autumn peach increased.With the sowing date was delayed,the seed cotton yield of pre-summer boll decreased,which was increased in summer bolland autumn boll.Seed cotton yield of boll increased in 2019,while that of autumn boll declined.There were no significant difference between treatments.The trend of the two-year test results was basically the same.Compared with film-covered cultivation,the number of bolls cottonin filmless cultivation decreased by 5.26%-14.15%,the weight of single boll decreased by 5.42%-8.33%,resulting in a 10.36%-21.27%decrease in seed cotton yield and 11.80%-20.66%decrease in lint yield.When the sowing time was late,the single boll weight,boll number per plant,group boll number,lint percent,seed cotton yield,and lint yield were all reduced.With the density increasing,the single boll weight,the number of bolls per plant,and lint percent decreased,and the number of bolls,seed cotton yield,and lint yield increased.The number of bolls has the largest effect on the difference in yield,followed by the single boll and the smallest lint percent.In 2018,the seed cotton yield of CFS1D3 was maximum,followed by CFS2D3 and NFS1D3 with no significant difference.In 2019,the yield of seed cotton under film-mulching cultivation was significantly higher than that of filmless cotton,and the yield of seed cotton for CFS2D1,CFS2D2,and CFS3D3 were higher than other treatmens.The seed cotton yields of NFS1D2,NFS1D3,NFS2D1,NFS2D2,and NFS2D3 were higher of filmless cotton.In 2018,the ratio of three peaches was reasonable,and the quality and yield of bolls were higher.However,the early cotton production in 2019 increased the proportion of pre-summer peache and the yield of seed cotton,which resulted in reduce ofthe final quality and yield significantly.Therefore,early sowing（April 20th）and highdensity(8.25×10⁴ plant hm^-2)cultivation measures can make filmless cotton to achieves atisfactory production that does not significantly reduce.