Effects Of Planting Density And Irrigation Period On Population Structure And Canopy Photosynthetic Characteristics Of Winter Wheat

Improving wheat yields is an important way to ensure national food security.Canopy photosynthetic efficiency is a key factor in determining wheat yields,and population structure is the key to achieve high light efficiency in the canopy.This study was conducted during two winter wheat growing seasons in 2020-2022.Two-factor split-zone experimental design was used.Planting density is the main area.Four planting densities of 150×10⁴（D1）,300×10⁴（D2）,450×10⁴（D3）and 600×10⁴（D4）were set for basic seedlings per hectare.Irrigation period is the secondary zone.There were three irrigation periods in the first water period of spring,which were irrigated at spring 4 leaf（T4）,spring 5 leaf（T5）and spring 6 leaf（T6）appearing.The effects of planting density and irrigation period on wheat population structure and canopy photosynthetic characteristics have been systematically studied,in order to provide theoretical basis for research on high yield of wheat and technical reference for production management optimization.The results of this study showed that:1.The leaf area index（LAI）of each leaf layer,the total canopy LAI,the light interception rate of the flag leaf layer and its upper organs,and the total canopy interception rate can be increased by increasing the planting density during the filling period.However,the light interception rate and its decline rate in the lower and middle canopy organs were not significantly affected by planting density.The canopy photosynthetic rate（TCAP）and photosynthetic contribution of non-leaf organs were significantly higher under the medium-high density treatment compared with the low density treatment.In 2020-2021,TCAP under D2-D4 treatment was increased by 31.7%compared with D1 treatment.In 2021-2022,D3 and D4 treatments increased TCAP by 23.7%compared with D2,among which the photosynthetic rate of non-leaf organs was increased by 43.9%and its contribution to TCAP was increased by 8.4%.2.Postponing the irrigation period significantly reduced the area of the upper 3 leaves,increased light exposure in the top 2nd leaf and below leaves,and reduced the decline rate of LAI in the flag,top 2nd and top 3rd leaf layers.Compared with T4,the leaf area index of the flag leaf,top 2nd leaf and top 3rd leaf layers at anthesis stage decreased by 17.0%～44.2%,17.8%～31.1%and 2.4%～20.0%under T5 and T6,respectively.The light interception rate of the flag leaf and its upper organs decreased by an average of 26.4%,while the light interception rate of the top 2nd and top 3rd leaf layers increased by an average of 43.4%and 93.7%.The decline rate of LAI in the upper 3 leaves from mid to late filling stage was reduced by 32.8%,27.3%and 55.9%,respectively.3.Delaying irrigation could delay the decline of photosynthetic rate（Pn）for the upper 3 leaves,and it could improve the photosynthetic contribution of TCAP and non-leaf green organs under medium-high planting density.Compared with T4,the Pn of the flag,top 2nd and top 3rd leaves at mid-filling increased by 1.5%,0.7%and 60.4%under T5 and T6,respectively;and increased by 59.9%and 91.3%at late filling for the flag and top 2nd leaves,respectively.In 2020-2021,late irrigation treatments increased TCAP by 7.4%～37.8%under D2-D4 planting density.With an 11-day delay in sowing in 2021-2022,the late irrigation treatment increased TCAP by 14.2%under D4 planting density.Among them,the photosynthetic rates of the top 2nd leaves and below leaf layer and non-leaf organs were increased by 43.8%and 18.9%,respectively,and their contributions to TCAP were increased by 30.3%and 6.4%,respectively.However,the TCAP of late irrigation treatment under the minimum density in both years decreased due to low light interception rate.4.Increasing the planting density from 300×10⁴·hm^-2 to 600×10⁴·hm^-2 under the suitable sowing condition had less effect on the dry matter accumulation of wheat at pre-anthesis and post-anthesis.However,delayed irrigation was beneficial to increase dry matter accumulation in this density range.Ultimately,in 2020-2021,the highest yields were achieved under T5 and T6 treatments with 450×10⁴·hm^-2 basic seedlings（D3）,but not significantly different from yields under D2 and D4.In 2021-2022,the T6 treatment with 600×10⁴·hm^-2 basic seedling had the highest yield under 11-day late sowing conditions.In summary,under the higher planting density conditions in Hebei Province,delaying the spring irrigation period to the spring 5 leaf age or spring 6 leaf age is beneficial to increase canopy light interception rate and optimize vertical light distribution,improve photosynthetic contribution and canopy photosynthetic rate of green organs except flag leaves,and promote biological yield and seed yield.It can be used as the optimal management solution for the region.