Uniformity of water Distribution in drip Irrigation Systems
Irrigation is the artificial application of water to an area where it is needed. Sources of irrigation water includes rivers, lakes, dams, shallow wells and boreholes. Irrigation enables all year round crop production and also enables production in areas which would otherwise be considered unsuitable for agriculture due to inadequate rainfall. Irrigation substitutes or supplements natural supply with the purpose of increasing productivity in regards to both yields and quality of yields.
There are different types of irrigation systems including surface or flood irrigation, sprinkler and drip irrigation. Drip irrigation though capital intensive in the initial set up stage is becoming increasingly popular. Though drip irrigation presents numerous advantages over other types of irrigation, its growing popularity is most likely largely driven by the increasing need to conserve water. With a good design, up to 95% efficiency can be achieved. It is however important to point out that such near perfect levels of efficiency are achieved at a much higher cost and often one must strike a balance between uniformity and cost. Drips apply water in slow controlled rates and the water drips directly to the root zone without wetting the areas in between the crops and without wetting the plant canopy. Water is delivered by gravity from a raised platform or pumped directly from source through a series of pipes, filters and valves that eventually lead to drip laterals containing emitters that discharge the water at controlled rates in pre-determined spacing. The conveyance and distribution pipes can be below or above the surface.
Water application uniformity: Irrigation water distribution uniformity is an important performance parameter that must always be considered during drip irrigation system design. To enhance crop production, irrigation systems should be designed to apply water as uniformly as possible with each plant getting nearly the same amount of water. Poor designs lead to under and over irrigated areas. Under irrigated areas usually suffer from moisture stress and to prevent this, farmers are then tempted to extend irrigation cycles or increase duration of irrigation leading to over irrigation on other areas. Over irrigation causes surface run-off, leaching of water and nutrients and water logging. This not only affects crop growth but also increases energy use and other operational costs.
One key aspect of achieving uniformity of distribution is to have balanced and sufficient pressure; to achieve this it is important to have adequate pressure at the source and to properly size the main lines, sub-main lines and laterals. Many drip systems I have encountered with uniformity and clogging problems often have very low source pressure compounded with poorly sized pipes, poorly sized irrigation blocks and drip laterals that are too long. Mostly, this is done in order to save cost and present a quotation that is as low cost as possible. In the long run however, this initial cost saving becomes expensive. It is also important to prevent clogging; this can be done using filters. There are different types of filters with the most common in small and medium scale production being screen and disc filters. It is also important to identify and fix leakages.
Such uniform discharge can only be achieved with good design. This is part of an irrigation system installed in Kimutwa, Machakos County by Ace Intergrated Services.
Clogging of emitters: Apart from the relatively high cost of initial set up, clogging of emitters is a drawback that has affected a number of farmers. Clogging risk is largely a factor of irrigation water quality and can be caused by physical, biological or chemical contaminants. Physical clogging which is the most common clogging issue that I encounter is caused by suspended inorganic and organic particles such as sand, silt, clay, plastic particles, animal debris and microbiological debris such as algae. Chemical clogging is brought about by dissolved solids when they interact with each other to form precipitates; experiments have shown that water qualities such as electronic conductivity, Calcium, Manganese and Magnesium content can increase clogging. Emitter clogging leads to suboptimal water application uniformity and can force farmers to apply more water than would otherwise be necessary which in turns means there will be inefficient use of energy.
The most effective clogging control measure is proper filtration. As already mentioned, screen and disc filters are the most commonly used filters in small and medium production systems. Screen type filter strainers are more affordable but less effective in comparison to disc filters especially when working with water of poor quality (high amount of suspended solids). Disc filters offer a reasonable compromise between reliability and cost.
With adequate pressure, physical clogging of drip systems can be prevented or managed through flushing. I have observed that many drip irrigation systems have very low pressure negating any self cleaning potential and even when flushing, the pressure is not sufficient enough to push all particles out.
The trickle effect when drip laterals are connected to the connectors. Emitters must be kept free of particles that can lead to clogging.
Cost of drip irrigation: The initial cost of drip irrigation installation is understandably higher than other irrigation methods; this has prevented many farmers from adopting drip irrigation. However, the advantages offered by drip irrigation makes it worth the investment. Such include high water utilization efficiency (water saving); high energy utilization efficiency (energy saving); lower irrigation labor costs (labor saving); reduced weed growth; low nutrient leaching leading to fertilizer saving; lower incidences of fungal diseases as a result of the crops maintaining a dry canopy; ease of operation and automation; ease of inter culture operations and ultimately improved yields. Cost of drip irrigation Installation can be managed through phased installation with more and more irrigation blocks being added with increased operations and as funds become available. Before costing any system, it is important to make an actual site visit to collect information on parameters that affect design such as slope, soil type, water quality, actual field dimensions etc. Indicative prices for various filed sizes are as below:
|Indicative prices for Drip Irrigation installation
|Quarter Acre with 1,500m of drip.
|Half Acre with 3,000m of drip
|One Acre with 6,000m of drip
|Two Acres with 12,000m of drip
|Five Acres with 31,000m of drip
The prices above are inclusive of all pipes, fittings, connectors, disc filtration system, trenching and installation cost but are exclusive of transport of materials from Nairobi to the farm, tank and tank tower.
Clifton Opala is the founder of Ace Intergrated Services an Agricultural Services Firm offering end to end solutions to farmers. The firm specializes in Construction of Greenhouses, Shade structures & other Farm Structures; Irrigation Systems Design and Installation; Farm planning, establishment & Management; Ground water identification & Drilling and Farmer Training. The firm also has capacity to design and conduct Baseline and Impact Assessment Surveys for Agricultural Interventions.