Designing a Fully Automated Irrigation System for a Large Scale Cultivation

K.U.Wijayasekara ,B.Sc.Eng (Hons), A.S.Maxworth, B.Sc.Eng (Hons)

Introduction

Sri Lanka, from the ancient history was mainly dependent on agriculture. Nowadays the cultivations are done mainly for the commercial purposes than consumer purposes. The area which is used for these cultivations are generally situated in the dry zone of the country where the rain fall is highly limited. In the ancient history, the kings who ruled the country have built reservoirs with huge capacities to store water. Those tanks are still in use to supply water for the Paddy cultivations in Sri Lanka.

For large scale farms which are situated at the dry zone of the country needed a proper method to establish a continuous supply of water for their cultivations. The obvious solution was to building a small tank within the premises to store water. After the establishment another issue arose when supplying water to the cultivations. Since water is essential for plants a requirement of a properly deigned irrigation system was mandatory.

The commonly used method was the drip irrigation method which was controlled manually. Figure 1 shows the positioning of the drip holes. This type of a system is completely operated by a person depending on the experience he or she has about the wetness of the soil.

Fig 1: locations of the drip holes

That method introduces a high amount of labor cost. And the amount of time that the water is being applied to plants varies with the person who operated the system. Also the amount of water that should be applied differs between cultivations and the growth stage of the plant. Supplying the precise level of water which is needed for the plants cannot be guaranteed.

Therefore the manually operated system has high probability of introducing errors to the supply of water.

That issue led to the fact that there should be a fully automated irrigation system for the large scale farms.

Design

A manually controlled system can be expressed as an open loop system (fig 2) where there is no feed back path. When the supply was done for a particular amount of time the operator will disconnect the supply.

Fig 2: Open loop system

The fully automated system can be viewed as a closed loop (fig 3) system where there is at least one sensor to detect the moisture content of the soil near the roots of the plant. Depending on the output of the sensor the values can be opened and closed automatically.

Fig 3: Closed loop system

A general automated system consists of sensors and actuators. Sensors to measure soil moisture, temperature, rain fall and pressure are used within the system. And the actuators such as pumps, valves and flow rate controllers are also used. The sensors can be placed within the land area with random distances apart to get an accurate measurement. To process the readings of the sensors a processing unit can be used and should be programmed to set the threshold values accordingly.

Figure 4 below indicated the implementation of the system with a controlling interface to control the performance of the actuators.

Fig 4: implementation of the system with basic sub units

Implementation

Figure 5 below shows the water application cycles for a manually operated irrigation system and for an automated system. Manually operated unit is supplying water when the water level of the plant reaches the threshold value. But the automated system supply water when the water level of the plant goes down a particular high value.

Fig 5: (left) Water application cycle for manually controlled unit (right) water application cycle for an automated unit

Discussion

Whenever cultivation is done in a dry zone an irrigation system is needed. By automating the irrigation system, the operation labor cost can be minimized and a precise supply of water can be established with modern science and technology.

Figure 6 below shows the design of the fully automated irrigation system for large scale cultivation.

Fig 6: Fully automated irrigation system design