Optimizing the working performance of a pollination machine for hybrid rice

Highlights

• An impact pollination machine was developed for hybrid rice cross-pollination.

• The impact device was simulated and optimized using MATLAB.

• Harvest speed, impact frequency and impact height significantly affect efficiency.

• The pollen quantity by 80% under optimized parameters.

Abstract

Pollination is the key process in seed production of hybrid rice; however, the low level of mechanization and the lack of pollination equipment have restricted pollination efficiency. Therefore, a mechanical impact pollinator with a power chassis, a lifting unit, and an impact device was developed for hybrid rice cross-pollination. The impact device installed with a reciprocating leading screw mechanism for power transmission was tested by simulating the impact device's movement using MATLAB software to optimize its mechanical structure. The major working parameters of the impact pollinator were optimized using an orthogonal design based on the actual planting pattern of hybrid rice. The impact height, impact frequency, and harvesting speed of the machine were designed as experimental factors, and the pollen amount was calculated as the evaluation index. The results showed that the pollen amount was significantly influenced by the harvest speed, impact frequency, and impact height, and the optimized working parameters were 0.8 m·s⁻¹, 2.5 Hz, and −20 cm accordingly. Compared with the commonly used artificial auxiliary pollination method with rope, the impact pollination machine with optimal working parameters increased the pollen quantity by 80% and the setting percentage by 36% in the verification test. This study provides a reference for the design and testing of an impact machine for hybrid rice.

Introduction

Rice (Oryza sativa L.) is one of the most important dietary staples and feeds more than half of the world's population (Li et al., 2019). To meet the growing food demand under the background of an increasing global population, 28% greater rice yield is expected in the following three decades (Alexandratos and Bruinsma, 2012). Nevertheless, rice production is predicted to decline significantly under the background of global warming (Chen et al., 2020). One of the key factors in achieving high yields of hybrid rice seeds is to improve the pollination rate, as inadequate pollination could significantly limit seed production (Larson and Barret, 2000, Chamer et al., 2015). However, the pollination of rice is a very sensitive process that is highly dependent on weather conditions, especially wind (Matsuia et al., 2020). Therefore, sufficient and well-distributed pollination is essential to obtain a high rate of cross-pollination, thereby improving the yield and quality of hybrid rice.

Manual pollination is the traditional pollination technique widely accepted by farmers in Asian countries due to its high feasibility. However, it is very time-consuming and labor-intensive with low efficiency. Moreover, manual pollination with rope lacks the transmission capacity to transmit pollen farther and therefore cannot meet modern hybrid rice seed production requirements on a large scale. Recently, mechanical pollination has received greater popularity by the modern farming industry. It has evolved from the early method of simple collecting, storing, and spraying pollen to pneumatic and collision approaches (Wang et al., 2013a, Wang et al., 2013b, Wang et al., 2013c, Li et al., 2014). Pneumatic mechanical pollination uses wind turbines to generate directional and quantitative airflow to move pollen to maternal plants with the help of airflow (Fang et al., 2014). For collision pollination, the impact device shakes off the pollen from the paternal plants, and the pollen flies to maternal plants using inertia by simulating the traditional manual pollination method using double short rods.

Effects have been made to improve the pollination efficiency of various mechanical pollinators for hybrid rice. For example, Wang et al. (2015) simulated the flow field distributions of the pollination tube in two machine types, the air-blow hole type, and air-blow nozzle type, using computational fluid dynamics (CFD) technology, indicating that the flow field distribution of the air-blow nozzle type was more uniform. Huang (2013) analyzed the basic principle and function of collision pollination by establishing a theoretical experimental model, suggesting that the collision position and velocity were more significant contributors to the pollination efficiency than the collision angle. Li et al. (2015a) optimized the parameters of a pneumatic pollination jet pipe and studied the effects of nozzle diameter and nozzle thickness on the distribution uniformity of pollen, which consequently reduced the uneven degree (variance) of pollination pollen distribution to 1.33. Furthermore, Li et al. (2015b) suggested that the optimal position of the jet pipe was 10 cm above the collision rod. However, the optimized parameters and the experimental model were not validated in field production.

Nevertheless, the mechanical pollination methods in the aforementioned literature have many limitations, such as the nonuniformity of the pneumatic mechanical pollination (Liao et al., 2011, Yao, 2013) and severe structural damage to the plant using a collision pollinator due to the combination of air blowing and collision (Wang et al., 2013a, Wang et al., 2013b, Wang et al., 2013c, Tang et al., 2012). Furthermore, the majority of these methods remain in the theoretical stage and lack a physical prototype. Therefore, a new pollination machine is urgently needed to overcome these disadvantages. In this study, a hybrid rice impact pollination machine was designed by imitating pollination with double short rods. Since the impact device is the core component of the pollinator that significantly affects the work efficiency of the machine, the movement locus of the impact device was analyzed using MATLAB software. The impact pollinator's harvest speed, impact height, and impact frequency were selected as the influencing factors, and the pollen amount was set as the evaluation index to study the diffusion rule of the pollen and optimize the working performance (Huang, 2013). Subsequently, a verification test was carried out to evaluate the working performance of machinery pollination compared with traditional pollination.