Mechanism And Regulation Of Mechanized Tillage And Sowing Methods Effecting On Seedling Quality And Grain Yield Formation Of Wheat In Rice Stubble

The rice-wheat rotation area is rich in temperature,light resources and natural precipitation,making wheat good production potential and comparative advantages.However,due to the problems of heavy soil,improper treatment of rice-straw returning,and wet soil during plowing and sowing,the quality of sowing and seedlings are difficult to improve,which has become the main constraint limiting wheat production.How to achieve "sufficient seedlings,uniform seedlings,and strong seedlings" through efficient,precise,and highquality mechanized tillage and sowing operations and the regulation of supporting agronomic measures to build high-yielding populations,and ultimately achieving the goal of green,highquality and efficient production of rice stubble wheat,is still the focus of current research.In this study,three types of tillage(plow tillage followed by rotary tillage,rotary tillage,and notillage)and ten mechanical sowing methods were tested in 2017-2021 at Jintan,Hanjiang,Yizheng,Sihong,and Suining ecological sites under full rice straw return condition.The differences in soil physical and chemical properties,root and aboveground growth between plow tillage followed by rotary tillage and no-tillage were analyzed to investigate the mechanism of strong seedling formation.We investigated the differences in the physiological characteristics of individual and group growth,yield,and composition at key growth periods among different seedling quality types in wheat,aiming to elucidate the mechanisms of strong seedling formation and its achievement of high yield.A combination of drone image recognition,field agronomic trait surveys,and data simulations was utilized to explore differences and mechanisms in agronomic traits,radiation use,and grain yield among different uniformity seedling populations.The differences in sowing quality,seedling quality,grain yield and quality,and nitrogen efficiency of different tillage and sowing methods were analysed to clarify the mechanized tillage and sowing technology process and recommended implements for different soil types and soil moisture conditions.In addition,the trials on the application of basal and tiller fertilizers were conducted to propose fertilization techniques for strong seedlings and high yields in conjunction with mechanized tillage and sowing.This study will help to provide theoretical and technical support for green,high-quality and efficient,large-scale mechanized production of rice stubble wheat.The main results are as follows:1.Field experiments were carried out at two sites,located in Jiangsu Province,China,during two wheat growing seasons,to assess the effects of plow tillage followed by rotary tillage and no-tillage on soil physical and chemical properties,wheat seedling growth,grain yield,and spike amounts and quality.The results indicated that with the reduction in soil mixing,soil bulk density was higher in no-tillage than in plow tillage followed by rotary tillage,which helped to maintain moisture in dry soil.In soils with high water content,in notillage,when the wheat field was subjected to waterlogging stress,the drainage decreased to deeper soil possibly due to reduced infiltration and higher evaporation of surface water.The diurnal variation in soil temperature decreased in no-tillage,and when the soil was cold,notillage helped to insulate soils at 0-25 cm.Compared with plow tillage followed by rotary tillage,the contents of available nitrogen and phosphorus increased at 0-20 cm in no-tillage.Root number,biomass,activity,and nitrogen content of wheat seedlings at 0-20 cm were also higher in no-tillage than in plow tillage followed by rotary tillage.Compared with plow tillage followed by rotary tillage,wheat seedlings under no-tillage also had more culms,leaf area,and photosynthetic product at the beginning of the overwintering stage.Therefore,in regions with high rainfall,compared with plow tillage followed by rotary tillage,no-tillage provided an improved physical and chemical condition,including the coordinated ability of drainage in wet and water retention in dry,the insulation and decreased diurnal variation in soil temperatures in cold,and the rich nutrient content in the top layer.The favorable soil hydrothermal and nutrient environment might contribute to a larger and more active surface root system,and by increasing seedling vigor,in particular,producing more early tillers,the spike number per plant increased.The average yield of wheat under no-tillage was 15.8%higher than that under plow tillage followed by rotary tillage.2.The different seedling quality types were constructed through tillage and sowing experiments at many sites for many years in rice-wheat rotation.The differences in seedling physiological characteristics,individual and population characteristics at key growth stages.grain yield,and its components were explored among different seedling types of wheat.The results showed that high tiller number per plant,leaf area,dry matter weight,nitrogen content,and NR,GS,GOGAT,and Rubisco activities of the leaf at the beginning of overwintering were beneficial for the improvement of grain yield.The cluster analysis was carried out using the number of tillers per plant,leaf area per plant,dry matter weight per plant,and nitrogen content as indicators.The results of cluster analysis were as follows:Type I with synchronously emerging of the tiller with leaf,strong single plant(large leaf area and biomass),and dark green leaves(high nitrogen content).Type Ⅱ with basically synchronously emerging of the tiller with leaf,weaker single plant.and dark green leaves.Type Ⅲ with tillering vacancy,weak single plant,and light green leaves.Compared with type Ⅱ and Ⅲ,type Ⅰ showed significantly higher activities of leaf nitrogen metabolism enzymes and Rubisco enzymes,which increased plant nitrogen content and photosynthetic productivity.The activities of the enzymes associated with nitrogen metabolism in leaves of strong seedling-type wheat were high before winter,and the capacity was strong,which promoted the increase of plant nitrogen content.At the same time,the activity of ribulose bisphosphate carboxylase in the leaves was high,and the photosynthetic capacity is enhanced,which promoted the biomass of a single plant.Therefore,synergistic improvement of nitrogen metabolism and photosynthetic productivity is the physiological basis for wheat strong seedlings formation.Strong seedling type wheat had a high tiller number,dry matter weight,nitrogen content,and accumulation per plant from booting to maturity.After flowering,the leaf area per plant of this type of wheat was large,and the photosynthetic capacity and antioxidant capacity of flag leaf were significantly higher,which was conducive to delaying senescence and transporting nitrogen nutrition to grain.Thus,strong seedling type wheat facilitates the formation of robust individual characteristics and significantly increases the yield per plant and per spike.At the same time,the population of strong seedling type wheat showed higher tiller number,leaf area index,and dry matter accumulation,and had significantly higher leaf area index from booting to milk stage,larger population photosynthetic area,and stronger matter and nutrient production capacity.The strong seedling type wheat had a higher accumulation of photosynthetic products and nutrients at maturity.During the whole growth period,strong seedling type wheat is beneficial to form robust individuals and constructing suitable larger population,and improve grain weight per spike based on maintaining the number of spikes.The grain yield of strong seedling type wheat was 18.4%higher than that of weak seedling type.3.The effects of seedling uniformity on grain yield,light energy utilization,and dry matter accumulation of wheat under drilling and broadcasting were studied by using UAV image recognition and field investigation methods through data fitting and uniformity population construction.The results showed that grain yield and the stability of wheat increased with the increase of seedling uniformity under drilling and broadcasting.The grain yield of drilling sowing and broadcast sowing was affected by uniformity to different degrees.For every 0.5 increase in seedling uniformity,the single spike yield increased by 11.46%and 1.16%,and the grain yield increased by 13.73%and 2.11%under the drilling sowing and the broadcast sowing,respectively.It shows that seedling uniformity under drilling sowing has greater potential to affect yield,and drilling sowing has greater room for improvement than broadcast sowing.With the increase of basic seedling number,the yield potential of high seedling uniformity of wheat sown in the drilling was close to that of broadcast.The coefficients of variation of population-stem number from jointing to anthesis and earing percentage of tillers with high seedling uniformity were low,which is conducive to improving the stability of spike number within the population.At the same time,the neat stem group resulted in a canopy structure more reasonable,and a low light penetration rate in the lower part of the canopy at anthesis.It was indicated that the overall light energy interception area is large,while the relative chlorophyll content of the group is more stable and the group photosynthetic production capacity is stronger,which is conducive to the potential of the group photo synthetic accumulation and the improvement of photosynthetic material production capacity to increase the yield per spike.Wheat planting should be based on the premise of suitable and higher basic seedlings,ensuring the sufficient number of ears,maximizing the uniformity of seedling distribution,and giving full play to the light use efficiency of a uniform population after flowering,to achieve stable and high yield.4.The ecological and soil environment of the rice stubble wheat area is complex,and the responses of mechanical tillage and sowing methods are varied,so the ecological conditions of the experimental sites were divided according to different soil textures and soil moisture conditions.The sowing quality,seedling quality,nitrogen use efficiency,grain yield,and grain quality under different soil properties and soil moisture with mechanical tillage and sowing methods were investigated as well.The results showed that plow tillage followed by rotary tillage was easier to achieve the improvement of grain yield for the same amount of seeding and sowing quality than rotary tillage and no-tillage when the sandy loam,loam,clay loam,and loamy clay were dry or partially dry.In sandy loam and clay loam,wheat seedling quality.nitrogen efficiency,and grain quality could be improved by plow tillage followed by rotary tillage under suitable soil moisture or drought conditions.In clay soil,no-tillage was more likely to produce a high yield for the same amount of seeding and different moisture.Although the depth of rotary tillage was shallow,the use of a straw to cover seeds could improve the sowing quality in clay soil.In loam,loamy clay,and clay soil,the no-tillage method was selected under the condition of wet soil moisture,although the emergence rate was reduced.the sowing depth was shallow and the emergence was fast,which promoted the healthy growth of individual plants.No-tillage achieved high yield under the same basic seedling conditions,regardless of soil type or moisture content.At the same time,no-tillage was conducive to improving nitrogen efficiency under the conditions of sticky soil and over-wet soil moisture,and achieved a simultaneous improvement of grain quality and nitrogen efficiency under the conditions of partial dry soil moisture.The mechanical sowing(S7,S8,and S9)facilitated better sowing and seedling quality than manual sowing(S10),thus giving the highest yield for the same amount of seeding.Mediumsized seeders(S4,S5,S6,S7.S8,and S9)had stable seeding quality and strong tillering ability compared with small-sized seeders(S1,S2,and S3),which could be beneficial for the simultaneous improvement of grain yield and nitrogen physiological efficiency under the same basic seedling conditions.Medium-sized seeders wide strip sowing adapted to clay and sandy loam soils with different soil moisture,its sowing depth was reasonable,uniformity of sowing depth seedling emergence rate was high,which could steadily improve seedling quality,grain yield and quality,and nitrogen efficiency.Medium-sized seeders drilling sowing and broadcast sowing were suitable for clay loam partial dry soil moisture and clay loam soil drought after sowing under rainy conditions,respectively with high uniformity of seedling emergence,which improved both grain yield and nitrogen utilization rate.Small-size seeders broadcast sowing was suitable for loam and loamy clay soil,with shallow sowing depth,high seedling emergence rate,and seedling quality,which simultaneously improved grain yield,nitrogen absorption and utilization capacity,and grain protein content.The sowing quality,seedling growth,grain yield,and grain quality of tillage and sowing combinations were also affected by soil type and soil moisture.The adaptability of mechanized tillage and sowing methods under different ecological conditions had both similarities and differences.And it is necessary to further study the regional maturation of mechanical tillage and sowing technology according to the differences in soil type and soil moisture.5.Three basal fertilizer application methods were set up under plow tillage followed by rotary tillage:application of base fertilizer before sowing,application of base fertilizer before rotary,and application of base fertilizer before ploughing.Compared with application of base fertilizer before rotary and before ploughing,application of base fertilizer before sowing improved the ability of surface roots to absorb nitrogen from fertilizer and soil during the overwintering and maturity stage,improved the utilization efficiency of basal nitrogen,and increased the accumulation of nitrogen in both grain and vegetative organs.In addition,the application of base fertilizer before sowing increased the number of tillers at the beginning of the overwintering period of wheat,resulting in a more productive single plant and a higher number of stem tillers in the group,which facilitated the formation of full spikes,and the high leaf area index promoted photosynthetic material production.Four tillering fertilizer application methods were set up under plow tillage followed by rotary tillage,and rotary tillage:tillering fertilizer was applied at 4.5-leaf stage as the control,advanced to 1.5-leaf stage,advanced to 3-leaf stage,and increased 10%nitrogen fertilizer at 3-leaf stage after fertilizer applied at 4.5-leaf stage.Under the same amount of the tillering fertilizer,the fertilizer was applied to the 1.5-leaf stage and the 3-leaf stage of the wheat in advance promoted the early growth and rapid development of seedlings.Among them,the application of tiller fertilizer in advance to the 3-leaf stage achieved strong individuals at the beginning of overwintering,significantly improved the number of tillers and leaf area index of the wheat population from the beginning of overwintering to the flowering stage,to form sufficient spikes,expand the photosynthetic area,which could facilitate the improvement of material production capacity in the whole growth period.Under the normal application of tiller fertilizer at 4.5-leaf stage combined with 10%fertilizer application at 3-leaf stage,the seedling quality and grain yield were the best,which could be used as a response measure under the condition of poor seedling quality or stress under ploughing.The basal fertilizer and tillering fertilizer significantly regulated the growth of wheat under ploughing and rotary tillage,formed strong seedlings before winter,helped to expand the population in the whole growth period,and achieved the purpose of strong seedlings and high yield by synergistically increasing the number of spikes and grain number per spike.To achieve a high and stable yield of wheat,sufficient seedlings are the foundation,strong seedlings are the key,and uniform seedlings are the guarantee.On the premise of high-quality straw returning,according to different soil moisture and soil types,determine the tillage method and select the appropriate sowing amount,improve the seedling quality by adjusting the fertilizer application,especially the application of basal and tillering fertilizer,improve the seedling uniformity by using medium-seeders with good stability broadcast sowing or wide strip sowing,which could achieve high yield,stable yield and high efficient mechanized production of wheat in rice stubble.