Effects Of Deep Sowing And Waterlogging At Seedling Stage On Wheat Growth And Yield In Rice-wheat System And Regulatory Effects Of Exogenous Substances

The rice-stubble soil has poor tillage,short tillage period,high water content,and a large amount of rice straw returning to the field,so it is difficult to guarantee the quality of wheat sowing,which detrimentally affects the growth and development of seedlings and restricts the yield formation.Too deep sowing and seedling waterlogging are two of the main factors restricting the formation of vigor seedlings,increasing yield and stable yield of wheat in rice stubble wheat area.How to improve the quality of sowing and cultivate vigor seedlings has become an important issue to be solved urgently in wheat production in the middle and lower reaches of the Yangtze River.In this experiment,Yangmai 25 was used as the test material to conduct field experiments in Yizheng and Jiangdu of Yangzhou in 2020-2021 and 2021-2022 respectively.The effects of different sowing depths(shallow sowing and deep sowing)and soil moisture(natural growth control and seedling waterlogging)on grain yield and its composition,seedling quality,photosynthetic production capacity,population quality,nitrogen accumulation and nitrogen metabolism enzyme activity were analyzed in order to clarify the restrictive factors and characteristics of vigor wheat seedlings.In the first year,the spraying experiment of exogenous substances was carried out in the experimental pot farm of Yangzhou University to explore the chemical control ways to promote the transformation of weak seedlings and ensure stable yield.The effects of spraying auxin(IAA),zeatin(ZT),6benzylaminopurine(6-BA),gibberellin(GA),2,4-epibrassinolide(EBR),spermidine(SP),Bihu(BH)and deionized water(CW)on seedling growth,yield and its composition were investigated under the two conditions of deep sowing and deep sowing+waterlogging.In the second year,the growth regulators and nitrogen were put into field production to elucidate the effects of sowing depth,soil moisture and other seedling influencing factors(shallow sowing,deep sowing and deep sowing+waterlogging)and regulation measures(spraying water,N,EBR and N+EBR,and using N fertilizer)on seedling growth,population quality,nitrogen accumulation and photosynthetic capacity,grain yield and its composition,in order to identify the regulation ways of EBR and N to achieve weak seedlings becoming strong seedlings,and provide reference for high-yield cultivation of wheat after rice.The main results are as follows:1.Deep sowing(～4 cm vs.～1 cm)significantly reduced the number of tillers per plant,basal stem diameter and shoot dry weight per plant by 11%～24%,11%～20%and 10%～36%at the beginning of overwintering.The number of tillers per plant,seedling height,number of secondary roots per plant and shoot dry weight per plant decreased significantly by 8%～9%,8%～10%,8%～12%and 18%～19%,respectively,after waterlogging(～20 d waterlogging compared with natural growth).Deep sowing reduced the accumulation of nitrogen and soluble sugar by 6%～30%and 15%～30%,respectively.After seedling waterlogging,the accumulation of nitrogen and soluble sugar decreased by 16%～20%and 12%～25%,respectively,resulting in a decrease in seedling quality.In addition,deep sowing and seedling waterlogging significantly reduced the number of stems and tillers at the jointing stage,resulting in insufficient final panicles,which was the main cause of yield reduction.Deep sowing and seedling waterlogging caused yield reduction by 4%～27%and 7%～8%,respectively.Deep sowing and waterlogging at seedling stage also significantly reduced the leaf photosynthetic area and SPAD value of flag leaves after anthesis.The lower net photosynthetic rate of flag leaves under waterlogging treatment resulted in the decrease of dry matter accumulation at main growth stages and after anthesis.At the same time,it reduced the activity of nitrogen-metabolism enzymes such as GS and GOGAT in flag leaves after anthesis,reducing the absorption of nitrogen by plants and the amount of nitrogen transport before anthesis.This ultimately inhibited the ability of nitrogen absorption and utilization,leading to the decrease of grain weight and grain nitrogen accumulation.Compared with the single stress of deep sowing or waterlogging at seedling stage,the seedling growth,population quality and yield were further reduced under deep sowing combined with waterlogging stress at seedling stage,and the grain yield decreased by 8%～41%.The results indicated that the deep sowing and waterlogging stress at seedling stage could cause weak seedling growth of wheat after rice,inhibit seedling tillering ability,reduce the level of sugar and nitrogen metabolism and the accumulation of photosynthetic products.Finally,the subsequent growth and development of plants was impacted,resulting in insufficient population and reduced growth.Therefore,seed shallow sowing(～1 cm)can be used to deal with waterlogging stress and ensure seedling growth quality in high rainfall areas at seedling stage.2.Spraying growth regulators after deep sowing and deep sowing+waterlogging could increase grain yield by 1%～38%and 5%～59%,respectively.Spraying ZT and EBR under deep sowing showed the significant effect on seedling quality and yield.The grain yield could reach the level of suitable sowing depth+natural growth.Spraying ZT could synergistically improve the level of carbon and nitrogen metabolism in plants,and spraying EBR could maintain high level of nitrogen metabolism,which was helpful to improve tillering ability,promote the accumulation of photosynthetic substances.Although spraying EBR after deep sowing+waterlogging could improve the level of carbon and nitrogen metabolism and the tillering ability and photosynthetic production.The recovery effect was significant,which would still reduce the yield of wheat compared with natural growth.Therefore,ZT or EBR can be recommended for deep sowing wheat to improve seedling quality and increase yield.Spraying EBR can improve the growth quality of deep-sowing and waterlogging wheat seedlings and promote yield formation.3.Under the condition of deep sowing,spraying N,EBR and N+EBR could significantly increase the accumulation of nitrogen and soluble sugar in the shoots of seedlings,and effectively improve the growth quality of tiller number,secondary root number and dry matter accumulation of seedlings.The number of tillers at jointing stage was significantly increased.The leaf area index and dry matter accumulation at key growth stages were increased.At the same time,the leaves were found to have the higher photosynthetic rate and nitrogen metabolism enzyme activity,facilitating the accumulation of carbon and nitrogen substances.This increased the number of spikes and stabilized the yield of single spike,thus significantly improved grain yield and grain nitrogen accumulation.Under the condition of deep sowing+waterlogging,only spraying EBR and N+EBR had significant remedial effects on seedling quality improvement and grain yield.Spraying EBR promised remediation by increasing the number of spikes,while spraying N+EBR increased the number of grains per spike on the basis of stabilizing the number of spikes.In addition,further experimental results showed that spraying N+EBR also helped to improve seedling root activity and improve seedling leaf hormone levels.In summary,the growth and yield reduction of weak seedlings caused by deep sowing and deep sowing+waterlogging could be alleviated by spraying EBR or N+EBR at seedling stage,which could promote the growth and physiological recovery of subsequent groups and achieve high and stable yield.The effect of exogenous regulatory substances on seedling growth and grain yield under shallow sowing was not significant.The results further showed that the quality of seedlings directly affected the subsequent growth and development of wheat,and ultimately affected the yield.