| Sowing is the start of agricultural planting and production,and also the basis for the growth,development and harvest of crops.The core link of sowing works is to build an appropriate seedbed soil structure,forming a favorable seedbed performance,and thus create a suitable environment and condition for seed germination and seedling growth.The good seedbed construction technique becomes one major direction of sowing technique research,and also a frontier domain for agricultural machinery and agronomy fusion/intersection.With the precision seeding technology,a predetermined quantity of qualified seeds is sowed into the preset sites of qualified soil.Then,a 3D space coordinate system consisting of column space,seed space(row distance)and sowing depth was formed,which saved the improved seeds,preserved soil quality and reduced work hours and field seedling homogeneity.This advanced multidisciplinary technology integrates agricultural machinery and agricultural arts,and has been widely applied into point sowing of row crops,including soybean,maize and cotton.The key procedures that influence precision seeding include seed metering,seed dropping,and seedbed construction.The use of an excellent seedbed environment can prevent seeds from soil-contact bounce displacement and improve the seed distribution homogeneity,deep seeding consistency,and emergence rate.Thus,an excellent seedbed is a key influence factor on the performance of precision seeders,and also a guarantee for the realization of precision seeding technology.In this study,we investigated the structure,functions and construction of excellent seedbeds and discussed the importance of suppression and furrowing for excellent seedbed creation.Through sunlight/greenhouse single-factor comparative tests,we detected how seed furrow suppression and suppression forces would affect the seedbed physical properties and soybean seedling.Then together with soil physical method,hanging water evaporation mechanism and soil agglomeration,we analyzed the test results and determined the ranges of seed furrow suppression forces that were suitable for soybean growth.It was found seed furrow suppression could affect seedbed soil temperature,water content,cone index,seedling time,seedling rate,seedling height consistency,root growth,and crest growth.Seed furrow suppression could reduce the changes of soil temperature along with air temperature.It most largely affected the water content at the 0-50 mm layer,and the water content modestly returned at this layer at the seedling stage.At the 0-150 mm layer,the average water contents after furrow suppression were all higher than the case of no suppression,indicating the seedbed soils could affect humidity protection.The soil cone index after seed furrow suppression was qualified for crop growth.Under a semiarid condition,the emergence rate after furrow suppression was significantly improved,the average seedling time was 0.79 day earlier,and the seedling height consistency was improved by 5.34% compared with the case of no suppression.Under different intensity of furrow suppression forces,the average seedling time changed in the order of 600 N<700 N<500 N.The deep seeding consistency,the emergence consistency,and the average seedling height were all improved as the furrow suppression force was enlarged within 500-700 N.It was found the physical properties of seedbed soil and the soybean seedling condition were all optimized at the furrow suppression force of 600-700 N.Based on the results of excellent seedbed construction,we proposed a scheme suitable for the ridge double-row planting in Northeast China.The seedbed construction effect was evaluated by using the index of backfill quantity.By analyzing the roles of V-shaped seed furrows,the molding mechanism,and the dynamics of furrow openers,we found four influence factors on seedbed construction,including pressure,furrowing angle,sowing depth and advancing speed.Orthogonal tests were conducted by using the Box-Behnken Design response surface methodology on Design-Expert to identify the optimal parameter combination for squeezing knife,which was a key part of furrow openers.The influences of these factors on backfill quantity changed in the order of pressure > furrowing angle > advancing speed > furrowing depth.The optimal parameter combination was pressure = 689.66 N,furrowing angle = 40.43°,advancing speed = 2.12 m/s,and furrowing depth = 51.62 mm.According to the conclusions of general part squeezing knives and in order to reduce seed bouncing displacement and soil disturbance and construct excellent seedbeds,we developed three types of furrowing devices with the functions of seed furrow suppression and furrow shaping,including a double V-shaped opener,a profiling sliding knife opener,and a rolling V-shaped opener.In particular,the squeezing knives of the double V-shaped opener designed with cissoidal blade curves could reduce the soil opening resistance and tilling resistance of squeezing knives.Moreover,the heart-shaped press plates and profiling press plates functioned simultaneously to retain soil and prevent weed congestion.The profiling sliding knife opener was capable of furrowing,pressing and profiling,which improved the sliding knife blades and profiling compacting wheels.The sliding knife blades were kept between the squeezing knives,which improved the passing rate of openers.The profiling compacting wheels,which were composed of middle compacting wheels and bilateral compacting wheels,acted at two sides of squeezing knives and were capable of solitary profiling,soil clod crushing and seedbed quality improvement.The rolling V-shaped opener designed with rolling vertebral squeezing knives and installed with notched cutting discs in the middle could improve the passing rate of the opener and were capable of material selection.Through soil bin and field comparative tests,we comparatively analyzed the three types of openers by single-factor full tests,including the indices of soil disturbing quantity,working resistance,furrow shape effect,deep seeding variation coefficient,seed transversal drift,variable coefficient of qualified grain intervals,and soil cone index.The effects of working speeds(1.6,1.9,2.2 and 2.5 m/s)on the real working performance and seed spacing uniformity were investigated when the squeezing knife angles and furrowing depths were both consistent.The three openers showed different characteristics.When the working speed was ? 2.2 m/s,the rolling V-shaped opener reached the most stable working status with the smallest soil disturbing quantity,traction resistance and vertical resultant force.During the field trials,the furrowing depth variation coefficient was least changeable with the working speeds.The smallest variable coefficient of qualified grain intervals helped to build excellent seed furrow shapes and an excellent seedbed environment,and was suitable for the high-speed working of soybean precision seeders.The soybean precision seeder was integrated with double-cavity seed metering devices,three-tray soil covering devices and suppression devices,and its working performance and the effects of the rolling V-shaped opener on soybean seedling were validated by complete machine field trials.When the working speed was 2.12 m/s and precision seed spacing was 9 cm,we selected four types of seeds with different sizes and carried out field trials with the indices of missed sowing,repeated sowing,seed damaged rate,seed spacing qualified rate and deep seeding qualified rate.Mathematic statistics via t-test showed that the seed damaged rate was 0.25%,and the average particle sizes of soybeanbean seeds did not significantly affect the average seed damaged rates of the soybean seeders designed here.The average seed missed rate was 5.35%,the missed rate was 8.15%,the seed spacing qualified rate was 86.5%,and the variation coefficient of seeding depth was 7.04%,indicating the complete machine working performance met the state-level standard.The field emergence effects with and without seed furrow suppression were compared through complete machine trials.Compared with the unsuppressed plots the plots loaded with 690 N showed the highest moisture content and an average soybean emergence rate of 5.4% higher to 83.20% and an emergence time of 0.71 earlier.It was validated that the V-shaped opener with the functions of seed furrow suppression and furrow shaping could improve the emergence consistency and emergence rate,reduce the emergence time and well protect humidity. |
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