Effects Of Planting Density On Growth And Lodging Resistance Of Broomcorn Millet Under Furrow-ridge Rainwater Regime

In the arid and semi-arid areas of northwest China,water resources are scarce,the climate is dry and cold,and the land is barren.Millet has the characteristics of barren resistance,heat resistance and drought resistance.It is a pioneer crop with stress resistance.At the same time,it has the characteristics of short growth period.It is the main multiple cropping and disaster relief crop in arid and semi-arid areas of northern China.In recent years,with the significant improvement and application of film mulching,ridge and furrow rainwater harvesting,straw mulching,rainwater harvesting and limited supplementary irrigation in arid areas,ridge and furrow rainwater harvesting planting mode has been widely used in agricultural production in arid and semi-arid areas.The furrow ridge rainwater harvesting planting mode can effectively reduce the invalid evaporation of soil moisture,and has a good application effect in water retention and heat preservation.In order to further improve the rain-harvesting planting mode,this study took the broomcorn millet variety’Yumi No.2’as the test material,and carried out in Yulin small grain test demonstration station of Northwest A&F University from 2021 to 2022.The experiment adopted a two-factor randomized block design,set up three cultivation methods,and used the traditional flat as the control（TP）.Two rain-harvesting planting modes with different furrow-ridge ratios were adopted.The furrow-ridge width ratios were 40 cm∶40cm（RF40）and 40 cm∶80 cm（RF80）,respectively.Three different planting densities（L:450,000 plants/hm²,M:750,000 plants/hm² and H:105,000 plants/hm²）were set up.Through field experiments,the effects of planting density and ridge-furrow rainwater harvesting on soil moisture,growth status,lodging characteristics,photosynthetic characteristics,water use efficiency and yield of broomcorn millet farmland were compared and analyzed.The main conclusions are as follows:Ridge-furrow rainwater harvesting planting can increase the soil water content,soil water storage,water consumption and water consumption intensity of broomcorn millet in each growth period.The increase of rainwater harvesting planting treatment in dry years was greater than that of traditional flat planting treatment.The soil moisture content will gradually decrease with the increase of planting density;water consumption and water consumption intensity will increase with the increase of planting density.The water consumption and water consumption intensity of rainfall harvesting planting were significantly higher than those of traditional flat planting,and the water consumption and water consumption intensity of RF（40）treatment were the highest.The plant height,stem diameter,leaf area per plant,dry matter above ground,total root length,total volume,total surface area,average diameter,breaking resistance and lodging resistance index of broomcorn millet were significantly increased by furrow ridge rainwater harvesting planting compared with traditional flat planting,and the value of gravity center height/plant height was significantly reduced,thus significantly reducing stem lodging rate,root lodging rate and total lodging rate.The barycenter height/plant height of high-density planting was significantly higher than that of medium and low density treatments,while the breaking resistance and lodging resistance index were significantly reduced,resulting in a significant increase in stem lodging rate,root lodging rate and total lodging rate.The relative chlorophyll content,leaf relative water content,net photosynthetic rate,transpiration rate,stomatal conductance and intercellular CO₂ concentration of broomcorn millet were significantly higher than those of traditional flat planting.This shows that the increase of net photosynthetic rate during the filling stage of drought years is greater,and the difference of crop filling is greater.Compared with traditional flat planting,furrow and ridge rainwater harvesting planting also reduced the initial fluorescence of broomcorn millet leaves and increased the maximum fluorescence of dark reaction,which led to the increase of variable fluorescence,thus significantly improving the maximum photochemical efficiency of photosystem II and the potential activity of photosystem II in broomcorn millet leaves.Under the same cultivation method,the relative chlorophyll content,leaf relative water content,net photosynthetic rate,transpiration rate,stomatal conductance and intercellular CO₂ concentration of high-density planting were lower than those of medium and low-density planting.High-density planting also increased the initial fluorescence,reduced the maximum fluorescence and variable fluorescence,resulting in a decrease in the potential activity and maximum photochemical efficiency of photosystem II,and the leaves were damaged more seriously in drought years.The water use efficiency of furrow ridge rainwater harvesting planting was significantly higher than that of traditional flat planting,and the increase in drought years was higher than that in normal years.The water use efficiency of broomcorn millet under medium density planting is higher than that under high and low density planting.The light energy interception rate of high density treatment was significantly higher than that of medium and low density treatment,but the light energy utilization efficiency of high and low density treatment was significantly lower than that of medium density treatment.The grain yield of broomcorn millet was significantly higher than that of traditional flat planting.Rain-harvesting planting and planting density had significant effects on grain weight,1000-grain weight and grain yield.The 1000-grain weight and grain yield of high density planting were significantly lower than those of medium and low density treatments.There was no significant difference in 1000-grain weight between medium and low density treatments,while the grain yield of medium density treatment was higher than that of low density treatment.In all treatments,under the medium density treatment,the water use efficiency,light energy use efficiency and grain yield of the ridge-furrow planting treatment with a ridge-furrow ratio of 40:40 were the highest.In summary,the suitable planting density of broomcorn millet under ridge-furrow rainwater harvesting planting mode is 750,000 plants/hm².This density combined with 40:40 ridge-furrow ratio ridge mulching planting method can improve the growth and development status,water and light energy utilization efficiency and grain yield of broomcorn millet.Therefore,this model is a rainwater harvesting and water-saving technology suitable for broomcorn millet planting in the semi-arid Loess Plateau of Northwest China,and has the value of popularization and application.