Effects Of Densities On Photosynthetic Characteristics And Yield Of Different Maize Varieties

Increasing planting density is one of the key measures to improve maize yield.Photosynthetic characteristics are important basis for crop yield,however dense planting leads to changes on population light environment,affect photosynthetic characteristics,and induces high risk of kernel abortion and plant lodging.Understanding the response patterns of different spike type maize hybrids photosynthetic characteristics and yield to density can provide theoretical basis and technical support for dense planting and high yield.Here,two maize hybrids Shaandan609（medium-spike）and Yuyu22（large-spike）were used as materials.The studies were carried out with four planting densities:6.0×10⁴plants/hm²（D1）,7.5×10⁴plants/hm²（D2）,9.0×10⁴plants/hm²（D3）,10.5×10⁴plants/hm²（D4）at the Northwest A&F University Maize Experiment and Demonstration Station in Yulin City,Shaanxi Province from 2020 to 2021 years.The results reveal the effects of photosynthetic characteristics,grain development and filling,plant lodging,and yield in different maize varieties due to different planting density.The detailed results are as follows:1.Increasing planting density can increase significantly maize yield within a certain range,but there are differences in the optimum planting density of different corn varieties.Shaandan609 and Yuyu22 had highest yields when the density was9.0×10⁴plants/hm²（17 640.02 kg/hm²）and 7.5×10⁴plants/hm²（16 493.56 kg/hm²）,respectively.Due to optimal yield,the total yield of Shaandan609 is 6.95%higher than that of Yuyu22.When the density increased by 1×10⁴plants/hm²,the number of effective panicles per unit area of Shaandan609 and Yuyu22 increased on average by14 081 ears and 13432 ears,the number of grains of per ear decreased by 55.3 grains（10.98%）and 64 grains（17.84%）,and the 100-grain weight decreased by 6.64%（1.46g）and 9.06%（1.6g）.The Yuyu22 had a lower decrease for number and grain number compared with Shaandan609.2.With the increase of planting density,the leaf area index and photosynthetic product accumulation of two different maize cultivars were increased,however the photosynthetic rate of ear leaves were decreased.At silking stage,the average leaf area index and photosynthetic rate of ear leaves in Shaandan609 were 5.74 and 24.7μmol·m^-2·s^-1,and those of Yuyu22 were 5.88 and 23.86μmol·m^-2·s^-1.Compared with Yuyu 22,the Shandan609 had a smaller leaf area index（5.74）,higher photosynthetic rate(24.7μmol·m^-2·s^-1),and better group light environment.After densification,the leaf senescence process of Shaandan609 progressed relatively slowly,maintaining a large green leaf area and high material transport rate.The aging rate of Shaandan609was 0.88%/d,while Yuyu22 was 0.94%/d.When the density of Shaandan609 was9.0×10⁴plants/hm²,the total material transport rate and the late leaf transport rate were 18.24%and 17.48%,respectively.By contrast,when the density of Yuyu22 was7.5×10⁴plants/hm²,the total material transport rate and the late leaf transport rate were16.84%and 11.48%,respectively.3.Increased planting density affected the process of tassel differentiation in maize.The anthesis-silking intervall（ASI）of Yuyu22 and Shaandan609 were prolonged by 0.93-3.5d and 0.76-2.95d,respectively.Compared with Yuyu22,the anthesis-silking intervall（ASI）of Shaandan609 was shortened by 0.17-0.55d.Under the same density,The number of florets per panicle,silking number and abortion rate of Yuyu22 were 4.29%,1.71%and 33.5%higher than those of Shaandan609,and lower rate of fertility and fertilization by 4.57%and 4.93%.It can be seen that although Shaandan609 has a small number of florets,the interval between flowering and silking was shorter,the synchronization was better,of which is easier to stabilize the number of grains per panicle.In addition,compared with Yuyu22,the maximum grain filling rate(G_max)of Shandan609 was 0.11g/d higher,and the growth amount(W_max)at the maximum grain filling rate was 0.04g less;the maximum grain filling rate days(T_max)and the grain filling duration（P）3.43d early and 4.43d long,thus ensuring the grain filling of Shandan609 in the late stage.4.Increasing planting density result in an increase of plant lodging rate.After densification,the lodging rate of Yuyu22（2.89%）is higher than that of Shaandan609（1.25%）.Compared with Shaandan609,the plant height,ear height and ear position coefficient of Yuyu22 were increased by 6.8%,9.79%and 4.76%;the third internode length and stem thickness coefficient were increased by 27.13%and 40.97%;the stem thick and less moment of inertia of section were decreased by 7.68%,9.10%and29.59%.The moment of inertia was decreased by 7.68%and 29.59%,and the same trends were observed between the 4th and 5th knots with the same variation pattern of the sections 4 and 5 show.The stem puncture strength of Shaandan609(57.18N·mm^-2)was higher than that of Yuyu22(53.67 N·mm^-2)by five times.It can be seen that Shaandan609 has better internode characters and stronger lodging resistance.In summary,close planting synergistically improved the photosynthetic characteristics and yield of maize varieties.Compared with Yuyu22,the Shaandan609had better population photosynthetic characteristics,higher accumulation and transportion rate of photosynthesis pruduction,shorter anthesis-silking interval（ASI）,well ear development,which causes a stabler grain number,higher filling rate,lower grain weight change,shorter and thicker stem internodes,higher puncture intensity and loding resistance.When the density increased to 9.0×10⁴plant/hm²,the Shaandan609 obtained a highest yield（17 640.02 kg/hm²）,which is 6.95%higher than that of Yuyu22 with the optimum yield.