An important part of irrigation planning and operation is understanding how hard a person must work to apply the required amount of water to the crop in the field.
On large commercial farms, a single labourer could be used to control an irrigation area of up to 40 hectares. Labour intensive systems could, however, require two to three labourers per hectare to properly irrigate the field. Labour usage is important regardless of the size or type of irrigation system used.
A commercial farmer must understand the cost implications of maintaining a labour team merely to operate the irrigation system. For a small-scale farmer who only irrigates a small area, it is equally important to understand how much time will be spent each day to operate the irrigation system and if there is enough time left to schedule other important activities such as weeding, spraying for pests, harvesting and marketing.
A farmer who, for example, grows kiwi fruit on a vine and harvests at regular intervals throughout the fruiting season will still need to continue irrigating, weeding and performing other normal farming operations throughout the harvest period. Therefore, a farmer must know how much time is needed to perform each task and plan a schedule for daily activities.
For a large-scale or commercial farmer, labour usage would typically be indicated in terms of the number of people needed to irrigate a 10 hectare block, or the entire system. This will impact directly on the labour component of running costs for the system and on the availability of labour to perform other tasks.
Labour requirements have a different implication for the market gardener or small-scale farmer. It is important to schedule all tasks and activities for the day. Labour requirements will more typically be expressed in terms of the amount of time normally needed for one person to irrigate one hectare when crop water demands are at a peak. This, in turn defines the time available for other tasks.
Every irrigation system needs regular maintenance. How complex or difficult maintenance tasks are likely to be, the amount of labour (with different levels of skill) that is needed to perform these tasks, the cost of equipment and spare parts, the frequency of maintenance operations and the availability of technical support can each make a big difference to the viability of an irrigation system.
Maintenance is important. Poor maintenance will allow an irrigation system to degrade. Water distribution and irrigation efficiency will suffer.
A typical maintenance task is the regular checking of sprinkler nozzles for wear. If a nozzle is worn, more water will escape from the nozzle at normal operating pressures. The distribution pattern of water around the sprinkler will change. Less water will be available to other sprinklers in the system. The pump will not work as efficiently. Energy costs will increase, irrigation efficiency will drop and crop production will decrease.
Regularly check sprinkler nozzles for wear and replace worn nozzles with new nozzles of the correct size and type. Each type of irrigation system will naturally have a list of maintenance operations that must be carried out on a routine basis to ensure that the system continues to function correctly.
It is important that each irrigation farmer should have an operations manual for his system that details maintenance tasks, and a toolbox that contains all the tools and equipment needed to perform routine maintenance tasks. A farmer should also maintain a contact list of people who can be approached for advice or assistance with specific problems that may be encountered when operating the system.
Next month we shall look at scheduling water use.
This series is published with acknowledgement to the ARC Agricultural Engineering for the use of their manuals. Visit www.arc.agric.za for more information.