Experimentation Research and Design of Circular Tube Slit Pneumatic Precise Wheat Seed-metering Device

In order to solve problems that traditional mechanical wheat seed-metering device has defects such as poor seeding uniformity and consistency, instability and high seed-injuring rate, a kind of pneumatic wheat precision seed-metering device is designed. The seed-metering device with internal and external circular tube grip seeds in vertical slit of the external circular tube by the negative pressure of the internal circular tube. We optimized slit width, rotating speed and negative pressure of the seed-metering device by the orthogonal experiment. In the field, we did contrast experiment through contrasting the existing mechanical seeder for wheat and measured and analyzed seeding uniformity, seedling emergence rate, consistency of each line seeding quantity, stability of total seeding quantity and rate of damaged seeds of the seed-metering device. The experiment data shows its each seed distance variation coefficient increases more 20% than current domestic mechanical wheat seed-metering device and its seeding uniformity gains obvious improvement.


INTRODUCTION
Wheat precision seeding technology promotes its output and quality, being significant to stable and high yield (Zheliang et al., 2012;Ruixue et al., 2009).It requires precise, quantitative and even seeding, so that each wheat plant obtains equal nutrient area and place, sufficient water and fertilizer for effective tiller (Feng and Liu, 2004).As for precision seeding, wheat dropping distance evenness is hardest controllable.Dropping distance evenness depends on uniform seed flow.Seed metering, seed charge and touchdown have effects on seeding evenness in the seed trench, of which seed metering of the seed-metering device uniformity plays a leading role (Junfeng et al., 2001;Liao et al., 2012;Liu and Zhao, 2008;Zhao et al., 2011).
Presently wheat field seeding mainly uses mechanical wheat seeder, having high rate of damaged seeds and unstable seeding quantity (Zhao et al., 2005;Hui, 2003;Liu et al., 2011Liu et al., , 2009)).The new type pneumatic precision seed-metering device does not damage seeds and is tolerant to seeds geometry for precision seeding (He and Qiu, 2001;Huo et al., 2003;Wang, 2006).In USA, Australia, Canada and France it researched and applied pneumatic precision seeding machines, of which air flow first-order distributive central type seed metering system is mostly applied to grain drills, but is not applied in China due to high cost (Zheng, 2007;Sun, 2003).New type wheat precision seeding seed-metering device with combined suckers developed by China Agricultural University, small type pneumatic wheat precision seeding sample machine developed by Wheat Engineering Research Center in Shandong Province and twin-disk pneumatic precision seeding machine developed by Hui (2003) in Shandong Agricultural University, all of them have some defects and have no products in the market (Liang et al., 2001;Jun et al., 2000;Hui et al., 2002).Therefore it is necessary to develop new type wheat precision seeding machine.
Traditional mechanical wheat seed-metering device has poor seeding uniformity and consistency, instability and high seed-injuring rate, which cannot match the wheat precise seeding agronomic requirements.In this study, a type of circular tube slit pneumatic precise wheat seed-metering device is designed to solve the problem.In addition, it compares with present mechanical wheat seeder by field seeding test and seedling emergence rate to evaluate the effect of the pneumatic seed-metering device for sowing.

METHODOLOGY
Structure and operation principle seed-metering device: Seed-metering device structure: This seed-metering device performs seed metering through straight slit based on suction principle, being composed of 13 Seed-metering device operation principle: As the wheat seeder operating in the field, driven by land wheel, it rotates seed-metering device through chain drive.Negative pressure airflow of the blower passing gas tube and air hole in internal circle tube generates negative pressure in external circle tube and generates vacuum suction at the slit.Each slit sucks one circle of wheat seed.Rotating to seed falling plate, seeds fall into seed receiver box blocked by seed falling plate and accomplish seed metering.Seed protection board may ensure no leakage sowing except for the slit.Mixing wheel at the bottom of the seed box constantly stirs bottom wheat seeds, being in favor of uniform suction of wheat seeds.The operation principle is illustrated in Fig. 2. Seed suction performance is illustrated in Fig. 4.

SEEDER FIELD TEST AND ANALYSIS
Taking straight slit pneumatic wheat seed-metering device as the key part, twelve-row equidistant wheat precision seeding machine is manufactured.It performed field seeding test in national project for food production test area in Shenzhou City of Hebei Province.The test selects two adjacent lands with commonly equal soil features, equal fore-rotating crops and the same seeding period, uniform field management.It makes seeding contrast test by commonly used mechanical wheat seeder (2BXF-12 disc type wheat seeder) installing mechanical external Geneva wheel seed-metering device and straight pneumatic wheat seeder.It seeds in two adjacent plots by the same seeding quantity (180 kg/ha) with the operation speed 3.5-3.7 km/h and checks seedlings within fifteen days after the seeding.

Results of other performance tests:
Comparing each performance parameter in the test with normal data shown in GB-9478-88 Grain Drills Test Method, it finds that variation coefficient qualified standard of seed metering amount per row uniformity is less than or equal 6.0%, test result of this machine is 3.0%; variation coefficient qualified standard of total seed metering quantity stability is less than or equal 1.3%, test result of this machine is 0.8%; variation coefficient qualified standard of seeding uniformity is less than or equal 45%, test result of this machine is 25.3%; qualified standard of rate of damaged seeds is less than or equal 0.5%, test result of this machine is 0.25%.It shows that all performance indexes satisfy the national standard.

CONCLUSION
Compared with present mechanical wheat seeder, straight pneumatic wheat seeder in this research topic has high seeding uniformity, low rate of damaged seeds, seldom seedling missing and seedling-less ridges.It proves that straight pneumatic wheat seedmetering device satisfies precise less seeding technology.
The wheat individual tiller by this precision seeding machine seeding is doubled, averagely four to seven tillers (presently seeder's wheat individual having one to three tillers), with evenly seeds distribution, less basic seedling and more individual tillers.Therefore the individual has sufficient nutrition, large area of illumination, strong wheat seedling and developed roots, as well as high capacity of lodging resistance, all of which ensure high and stable yield of wheat.

Table 1 :
Comparative analysis of seeding uniformity

Table 2 :
Comparison of seedling emergence rate of two kinds of wheat seeder Testing pneumatic precise wheat seeder