Effects Of Planting Density And Supplemental Irrigation Amount On Souce-Sink Relationships And Water-Nitrogen Utilization Of Winter Wheat Under Ridge-Furrow Mulching

The shortage of agricultural water resources and low water-nitrogen use efficiency are two important factors limiting the development of agriculture in northwest China.It is important to further improve water and fertilizer productivity and promote stable crop yield growth and sustainable agricultural development by planting density regulation,planting pattern optimization and supplemental irrigation.In this study,a two-year filed experiment was conducted on winter wheat（Xiaoyan 22）from October 2020 to June 2021 and from October 2021 to June 2022 at the Irrigation Experiment Station of the Key Laboratory of Agricultural Soil and Water Engineering,Ministry of Education,Northwest A&F University in the sub-humid and drought-prone regions of northwest China.Two cultivation modes（R:ridge-furrow cultivation,F:traditional flat planting）,three planting densities(D₁:2400,000plants ha^-1,D₂:3600,000 plants ha^-1,D₃:4800,000 plants ha^-1)and two supplemental irrigation levels(I₀:no irrigation,I₆₀:30 mm of supplemental irrigation during the overwintering and regreening stages)were set up to investigate their effects on the growth,physiological characteristics,source-sink relationships,grain yield and its components,water-nitrogen use efficiency and economic efficiency of winter wheat.Based on the results of this study,the suitable combination of planting pattern,planting density and supplemental irrigation for winter wheat in this region was proposed.The main results of the study were as follows:（1）The effects of planting density and supplemental irrigation on the growth of winter wheat under ridge-furrow mulching were clarified.The growth advantage of winter wheat under ridge-furrow planting and supplemental irrigation was evident,with R and I₆₀ significantly increasing the plant height of winter wheat by 6.1%and 5.8%,respectively.The plant height increased with increasing planting density,ranging from 6.3%to 14.4%.R and I₆₀ increased leaf area index by 4.8%and 4.6%relative to F and I₀.Leaf area index under D₃ was significantly higher than D₁（20.5%increase）and D₂（11.3%increase）.Leaf area index reached maximum values at flowering and plucking stages during 2020-2021 and 2021-2022,respectively,and then began to show a decreasing trend.Aboveground biomass increased with increasing planting density and followed an s-shaped growth curve.Aboveground biomass increased by 8.3%and 8.0%under R and I₆₀ conditions,respectively.（2）The effects of planting density and supplemental irrigation on leaf physiology of winter wheat under ridge-furrow mulching were revealed.Different planting patterns,planting density and supplemental irrigation had significant effects on the relative chlorophyll content of winter wheat in both growing seasons.The relative chlorophyll content showed a trend of increasing and then decreasing from the nodulation to the maturity stage.Compared with F and I0,R and I₆₀ significantly increased the relative chlorophyll content（5.0%and 6.4%）,net photosynthetic rate（19.8%and 11.7%）,maximum quantum yield of PSⅡ（5.2%and 2.4%）,energy conversion efficiency of PSⅡ（4.1%and 1.5%）,and effective quantum yield of PSⅡ（12.2%and 9.5%）.Relative chlorophyll content and photosynthetic fluorescence parameters were negatively correlated with plant density,and with increasing density,relative chlorophyll content,net photosynthetic rate and fluorescence parameters showed a decreasing trend.（3）The effects of planting density and supplemental irrigation on the source-sink relationships of winter wheat under ridge-furrow mulching were investigated.Both source activity and sink activity of winter wheat showed a trend of increasing and then decreasing.Source activity reached a maximum around 170 days after sowing and then began to decline rapidly.The maximum source activity appeared before sink activity,while sink activity started to increase rapidly towards the end of source activity.Source growth and source activity increased with increasing planting density.sink activity in 2021-2022 was17.5%higher than in 2020-2021.R increased sink/source by 6.2%and 3.3%in 2020-2021and 2021-2022,respectively,compared to F Similarly,supplemental irrigation(I₆₀)improved the sink/source ratio by 6.5%.Under the same cultivation pattern and supplemental irrigation level,D₃ and D₂ reduced the sink/source ratio by 36.5%and 21.8%,respectively,compared to D₁ and 18.9%for D₃ compared to D₂.（4）The effects of planting density and supplemental irrigation on the yield and water-nitrogen use efficiency of winter wheat under ridge-furrow mulching were elucidated.At the same planting density,R and I₆₀ increased grain yield by 10.4%and 13.5%,respectively,and the effective number of spikes per unit area increased by 3.7%and 4.6%,the number of seeds per spike increased by 5.2%and 5.0%,and the thousand grain weight increased by 3.1%and 3.3%.The number of spikes increased with planting density,and the number of spikes in D₃ increased by 20.1%and 8.8%compared with D₁ and D₂,respectively.The yield of winter wheat under ridge-furrow cultivation increased and then decreased with increasing planting density.The maximum grain yield(7383.5 kg ha^-1 and 8577.4 kg ha^-1),water use efficiency(20.03 kg ha^-1 mm^-1 and 21.77 kg ha^-1 mm^-1),nitrogen fertilizer use efficiency（36.92 kg/kg and 42.89 kg/kg）and economic efficiency(8656 CNY ha^-1and10517 CNY ha^-1)were obtained under the RI₆₀D₂ combination for both winter wheat yields.（5）The optimal combination of planting pattern,planting density and supplemental irrigation for winter wheat were proposed.Based on a comprehensive analysis of winter wheat growth and physiology,yield,water-nitrogen use efficiency and economic efficiency based on principal component analysis,the combination RI₆₀D₂ ranked the first,indicating that ridge-furrow mulching combined with a planting density of 3600,000 plants ha^-1and supplemental irrigation of 60mm was an optimal combination for winter wheat in the sub-humid and drought-prone regions of northwest China.