Effects Of Sowing Date And Regulation Measures On Wheat Seedling Growth

The experiment was carried out in two wheat growing seasons of 2019-2021 at the Beijing Experimental Base of the Institute of Crop Sciences,Chinese Academy of Agricultural Sciences.Two winter wheat cultivars Zhongmai8 and Hangmai501 with different tillering ability were selected as experimental materials.Four sowing dates were set: early sowing on September 25(J),appropriate sowing on October 5(S0,control),appropriate late sowing on October 15(S1),and later sowing on October 25(S2).Before winter,the film mulching(F)and supplementary application of nitrogen fertilizer(N)to S1 and S2 was taken as the regulated measures.The experiment focused on the effects of sowing date and regulated measures on population quality,individual characters and their physiology at the seedling stage,so as to provide theoretical and technical references for achieving strong seedlings before winter.The main results are as follows:1.Sowing date had different effects on the accumulated temperature,emergence days,population quality,individual growth and their physiological changes of wheat before overwintering.With the sowing date delayed,the accumulated temperature before winter,total number of population,CGR,NAR,dry matter weight,PNA,and number of tillers per plant,LAR,LAI,leaf age,and accumulated temperature requirements from 1N to 3N decreased gradually,the chlorophyll a/b value and leaf thickness increased,and the growth process of tillers accelerated.Under suitable sowing conditions,RGR,NAR,LAR and SLA and soluble sugar content at seedling stage of population before winter were higher than those of early sowing and late sowing.The total number of stems and tillers,the number of,tillers per plant and the leaf age of the population were slightly higher than those of traditional strong seedling standard in Beibu Winter Wheat area,and the date of appropriate sowing was the most suitable sowing dates close to the strong seedling standard among the four sowing dates.2.Under the condition of late sowing,film mulching and supplementary nitrogen fertilizer had different regulating effects on the growth of wheat seedling before winter.Under proper late sowing conditions,film mulching could increase accumulated temperature before overwintering,total stem number of population,CGR,RGR,LAI,PNA,tillers per plant,soluble sugar content of main organs(stems and leaves,tiller nodes,roots)and IAA/ZR value.The total stem number of population and the tillers per plant reach the standard of strong seedlings before winter.In addition,Film mulching increased the accumulated temperature from 1N to 3N.Under the condition of too late sowing,film mulching mainly increased the temperature and the accumulated temperature before winter,significantly increased the total number of stems,tillers per plant,LAR and the dry weight of leaves,decreased the leaf thickness and increased NR activity and the ratio of dry weight of 1N and 2N to the main stem.However,the effects of nitrogen supplement on the population quality and individual characters of late sowing wheat were not obvious,but it was beneficial to improve NR and GS activities of the main stem and tillers.At the same time,there were significant differences in terms of individual characters,LAI,PNA and nitrogen metabolism enzyme activities between the two different cultivars with different tillering ability in response to late sowing.In general,the adaptability of Zhongmai8 to late sowing(decrease of accumulated temperature)was lower than that of Hangmai501,and the effect of film mulching(warming)on Zhongmai8 was greater than that of Hangmai501.3.The evaluation results of late sowing seedlings showed that under the condition of suitable sowing,the tested cultivars had the best seedlings before winter,and the comprehensive evaluation of population and individual quality was the highest.Under the condition of late sowing,there were more differences in the seedling situation of each treatment before winter.For Zhongmai8,a multi-spike cultivar,had better seedling situation under the condition of late sowing + film mulching,but weaker seedling situation under proper late sowing,too late sowing and too late sowing + supplementary application of N fertilizer;and for Hangmai501,a large spike cultivar,had better seedling situation under the condition of proper late sowing,proper late sowing + supplementary nitrogen fertilizer,proper late sowing + film mulching,and too late sowing + film mulching,but had weaker seedling situation under too late sowing and too late sowing + supplementary application of N fertilizer.Besed on the results of two years experiment,when the average daily temperature is 15-17 ℃,it is the optimum sowing time for wheat in the experimental area.Under proper late sowing conditions,the comprehensive quality of wheat population and individuals before winter could be improved by film mulching,and promote wheat to reach the traditional strong seedling standard of " total five tillers(three large and two small),ten roots and six leaves" before overwintering,laying a seedlings foundation for highyield.