If trickle irrigation systems are to continue to operate properly without serious blockage of the fine water outlets, some periodic maintenance is necessary. Generally this maintenance consists of cleaning filters, flushing the system, and chlorination of the system.
Cleaning Filters
All filters should be cleaned at the start of a season, and then periodically from there onwards. The frequency of which has to be determined by individual circumstances. Mesh filters need to be periodically dismantled and the mesh cleaned and inspected even if a back flushing system is fitted. The housing of the filter should also be cleaned out at the same time. Sand filters need to be back flushed until completely cleaned and then the flushing water run through the by pass until clean water appears. Self cleaning filters need to be frequently inspected to see that they are operating properly and the mesh is still intact.
Flushing the System
Flushing removes accumulated deposits from the system and greatly reduces the likelihood of blockages. Flushing should always be continued until the water runs clear.
Use of Chlorine
Chlorine is an oxidising agent which kills bacteria and disintegrates organic matter. Used at heavy doses it can help to disperse deposits formed in the pipes and tubes, and to free blocked outlets. Alternatively it can be used at frequent intervals, or continually bled into the irrigation system at low dose rates to prevent the development of problems. Liquid Sodium Hypochlorite, which contains 10% chlorine, is a preferred source.
Chlorination In Doses
Strong doses of chlorine of 500 ppm are used to disperse any bacterial slime and other accumulated organic sediment within the pipes and tubes. This high rate is only usually used at the beginning of the season before the system is used. It is usual to leave the system full of the chlorine solution for 24 hours and then flush with clean water. During the growing season, periodic sterilisation of the system to prevent the redevelopment of bacterial slimes is usually necessary. For this purpose a 10 ppm dose of chlorine is injected into the system at the end of an irrigation pipe and left in the pipes until the system is used again. Whenever chlorine is added, the pump should be run after the chlorine application, so that it is free of the chemical. This is because chlorine is corrosive to metals.
Continuous Chlorination
This is probably the best, and the simplest method of avoiding blockages in a trickle irrigation system. Once installed, a continuous injection system operates without any attention, other than occasionally filling the chlorine container. This method is useful where a problem source of water is being used such as a river or dam water. The required rate will depend on pump capacity and water quality. The rate of injection should be adjusted so that 1 to 2 ppm of chlorine is detectable at the end of the line furthest from the pump.
Water Quality Maintenance
The main concern with water quality is the level of salinity. Salinity in irrigation areas throughout Australia has been the cause of severe environmental and economic degradation. This has been due to short sighted irrigation policies that were put into place without realisation of the problems that would occur at a later date. As salinity levels rise in an area the productivity potential falls. In extreme cases of salinity all plants receive toxic levels of salinity which limits plant growth and desertification eventuates.
The level of salinity in water can be measured by testing for electrical conductivity (EC). There are a number of EC meters that are used to test salinity on the market, which are adequate. Generally, a low EC reading indicates clean water. They can be used to measure how many nutrients can be added to a soil before it becomes over fertilised. EC meters are usually used in conjunction with pH meters.