Abstract:
Abstract: Rice is the staple food for more than half of the global population, and the rice production, especially planting, needs a lot of labor force, material and financial resources. At present, the rice mechanized planting level is low in China. According to statistics, the mechanization level of rice planting in China was only 44.45% in 2015. The main ways of planting are artificial seeding and transplanting. The mechanization of rice direct seeding technology mainly includes mechanical seeding, mechanical drilling, and hill-direct-seeding. Compared to mechanical transplanting, mechanical direct seeding can avoid the process of raising rice seedlings, reduce the input of prophase cost, and does not affect yield. It is expected to be the developing trend in mechanized rice planting in the future. Normally, it is difficult to control the precision of mechanical sowing and mechanical drilling. This leads to uneven seedling distribution and affects the growth and field management of rice. In recent years, due to the increase of labor cost, the cost of rice planting has also increased. It is imperative to develop the mechanized planting of rice. The mechanization of rice direct seeding can eliminate rice seedlings process and save the labor and material consumption. Super hybrid rice has stronger tillering ability than ordinary hybrid rice. By using direct seeding technology, the high yield population structure can be formed with only 1-3 seeds per hill. The pneumatic rice precision direct seeding technique is a combination of machinery and air flow. This technique has the advantages of high seeding precision, low seed damage rate, and strong adaptability and can satisfy the seeding demands of many kinds of seeds. However, existing pneumatic seed metering devices are mainly for soybean, corn, wheat, rape and other crops. Seed metering devices have been widely used in actual production, and theoretical research is also relatively mature. In this study, the relationship between emergence rate in the field and seeding precision are studied with the pneumatic rice direct seeder seeding super hybrid rice. The relation formula between the germination rate of rice seed and the precision of seeding was established. The field experiments were conducted using pneumatic rice seeder with 10 seed metering devices. 3 kinds of super hybrid rice, which named "Y-2 You", "Chao you 1000" and "Wu feng you 615" respectively, were selected as the research objects. The tests of germination rate in the laboratory and the precision of seeding in the field were carried out. The germination rate was 94%, 91% and 92%, respectively. The seeding qualified rate (the probabilities of 1-3 seeds per hill) was 94.98%, 95.07% and 95.21%, respectively. The probability of empty hill was 1.78%, 2.03% and 1.95%, respectively. The relation formula established in this study was used to calculate theoretical seedling survival rate. The theoretical seedling survival rate were 96.85%, 95.79% and 96.07%, respectively. The actual seedling survival rate in the field were 94.22%, 93.94% and 93.76%, respectively, which were lower than those calculated by theoretical calculation. The main factors that affect the seedling survival rate in the field were analysed. In order to improve the seedling survival rate in the field, 1) the precision of seeder should be further improved, the probability of empty hill and the probabilities of 1 seed per hill should be reduced, and the probabilities of 2 seeds per hill in the agricultural machinery should be increased, 2) the germination rate of rice should be further improved in the agronomy. The results of this study provided a basis for the application of the pneumatic seed metering technology to the precision direct seeding of super hybrid rice.