# Irrigation System for a Roller-Type Onion Pot Seeding Machine
## 1 Introduction  
As the consumption of onions has been increasing worldwide, the onion cultivation area has increased by about 4 times, from 2,403,700 ha to 9,464,473 ha, from 1994 to 2014. In addition, onion production has more than doubled, from 38,902,195 tons to 88,694,456 tons for the same period [1]. As the demand for onion is expected to grow continuously in the future, cultivation methods that can improve the efficiency and productivity need to be researched.  
In China, the global leader in onion production, onions are seeded and cultivated in pot trays and then transplanted to the field [1, 2]. The production per unit cultivation area as of 2014 is 22.19 t/ha. In India, the second-largest producer of onions next to China, onion seeds are directly sown and cultivated in the field by manpower [3]. The production per unit cultivation area as of 2014 is 16.12 t/ha. In order to increase the production efficiency, a preferable method is to cultivate high-quality seedlings in pot trays and transplant them to the field.  
The mechanical pot-seeding machines are suitable for sowing onion seeds in pot trays efficiently, because they consume less manpower and demonstrate a high work capacity [4]. They are classified into the roller type and the vacuum nozzle type, depending on the operating method. The roller type is more suitable for general use in various countries including developing countries, because it is less expensive and more durable than the vacuum nozzle type [5, 6]. However, it has a disadvantage that the watering should be performed after sowing by manpower because it does not comprise an irrigation system. Watering by manpower cannot produce uniform irrigation, and the germination period may be long, if sufficient water is not supplied earlier after sowing [7, 8]. Therefore, it is necessary to develop an irrigation system capable of uniform watering in order to eliminate manpower and improve the germination conditions.  
In agricultural applications, the irrigation systems are typically categorized into three types: sprinkler, drip, and spray type. The sprinkler type is used to supply a large quantity of water in a short time. Therefore, this type is mainly used in the greenhouses to control the temperature and humidity. The spray type can irrigate a specific area uniformly. The water is sprayed through the nozzle installed to the high-pressure spraying device, and mobile watering is possible by the rail andtraction device. The drip type supplies water by dropping an appropriate amount of water. Among all the types, it uses the smallest amount of water, and location-specific watering is possible even at a low pressure. This can prevent the loss of soil and fertilizer caused by high watering pressure. The spray and drip types have been used in the irrigation system of pot-seeding machines of various vegetables (except for onion). The spray type is especially used for nursery plants in a large facility, due to its characteristics of uniform irrigation on a relatively large area [9]. The drip type is mainly used for small-size mechanical pot-seeding machines because of the low water usage [10].  
In this study, we developed a highly effective drip-type irrigation system for the roller-type onion pot-seeding machine. The system has a sufficient and uniform watering when seed positions do not change and bed soil loss does not occur. Also, it is small and modular, so that it can be easily attached to and detached from the existing roller-type onion pot-seeding machines, for usability.