Quantitative Analysis Of Leaf Longevity On Spring Maize

The leaf longevity is the photosynthetic active duration of green leaf,which is a key factor affecting the photosynthetic productivity.The quantitative evaluation the effects of canopy leaf longevity is of significance for maize plant growth and yield formation.This method on different planting densities and nitrogen application rates plays an important role in guiding crop nitrogen management.The experiments were conducted in the experiment station of Institute of Crop Sciences,the Chinese Academy of Agricultural Sciences,Gongzhuling,Jilin province in 2015–2018.The treatments cultivar were Xianyu 335 and Zhengdan 958.Seeds were planted manually at two densities of 37,500plants hm^-2 and 67,500 plants hm^-2.Nitrogen levels consisted of a fertilized condition of 300 kg N hm^-2,a fertilized condition of 150 kg N hm^-2 and a control with no added N,which were set for each density.We commence the quantitative analysis of leaf longevity on spring maize.The main results are as follows:Firstly,the maize leaf longevity model was established by Gaussian function???with 2015 and 2016 text data,and validated with 2017 and 2018 data.The physiological significance of model parameters was specified.By further analyzing,five turning points were definitely well fitted to establish this model,which greatly simplified the data requirements for developing this model and the possibility of using this model to group the maize leaves was discussed.Secondly,the applicability of the Gaussian function to simulate the leaf longevity was verified at different planting densities and nitrogen application rates and its influencing factor was quantified.When the planting density increased from 37,500 plants hm^-2 to 67,500 plants hm^-2,the leaf longevity of each 1000 plants hm^-2 decreased by 33-63°C d,the maximum in 6-8 leaves,which decreased by 7-15%;the leaf longevity of each 1 kg N hm^-2 increased by 18-25°C d,the maximum in 6-8 leaves,which increased by 22-32%,when the nitrogen application rate increased from 0 kg N hm^-2 to 150 kg N hm^-2;the nitrogen application rate increased from 150 kg N hm^-2 to 300 kg N hm^-2,leaf longevity of each 1 kg N hm^-2 increased by 3-6°C d,the maximum in 6-8 leaves,which increased by 3-6%.Finally,the high-density rapid monitoring of SPAD readings can fully reflect its temporal and spatial dynamic.The SPAD readings test data obtained in 2017 and 2018 showed that the increased first and then decreased during the growth period.The further based on the rational function???fitting the dynamic change of SPAD readings during the growth period of single leaf.The 3D model of SPAD readings was established based on the visible GDD of each leaf and the effect of planting density and nitrogen application rate on leaf SPAD reading was clearly analyzed.When the plant density was increased,the green color became shallower.And increasing the nitrogen fertilizer under high planting density conditions,the green color became darker and the duration was prolonged.The rate of decline of SPAD reading in the reproductive growth was delayed,and the leaf longevity was prolonged.