Technical Library: Irrigation

Many kinds of irrigation systems for horticultural and agronomic crops – fruit, grains, vegetables, timber, and oil – are available in Asia. With so many designs and components to choose from, however, deciding which system will do the job properly at the lowest cost and still yield the greatest benefit is difficult. To get the most from an irrigation system, no matter how large or small, certain guidelines should be followed.

Soil Sampling. Soil samples should be analyzed to determine soil texture, pH, capillarity, water infiltration, and water-holding capacity.

Crop Information. A professional horticulturist or agronomist can use information regarding the crop and its demand for water in the dry season to recommend an appropriate irrigation system. Irrigation companies ordinarily consult professionals who provide these services at no cost to the buyer or grower.

Water Supply. The water supply is probably the most important determinant of irrigation system performance. If the water is not clean, some types of irrigation equipment may not function well without filtration. Even some mini-sprinklers require filtration of the irrigation water if the water is very dirty. In the case of drip irrigation, very clean water and special sand filters coupled with screen filters are necessary. If the water used is surface water, algae and bacteria may build up in the irrigation pipes and clog the small water outlets. When using drip irrigation, it is always a good idea to prevent future clogging by buying the best filtration device available, along with a water treatment chemical that will kill algae and bacteria as they enter the system.

Amount of Water Needed. Two common mistakes are applying too much water and applying too little water over too large an area. Too much water can cause as much harm to the crop as too little water. Plant roots need oxygen to live and grow strong. If too much water is applied, oxygen is forced out of the soil and the plant roots soon die, reducing yields and quality. This effect may not be noticeable or may be confused with effects of weather, insect damage, or nutrient deficiencies. Too little water over a large area does not benefit the plant and may even cause damage to the plant from salt accumulation. It is not necessary to wet a large area for each tree. Growers should consult experts who can design a system that will deliver the best amount of water for particular crops.

Devices for measuring water in the soil should indicate how much water the soil has in storage and the best time to irrigate. Previously, vacuum and water-filled tubes called tensiometers were used, but they required too much maintenance. Modem farms use electrical conductivity blocks that are inexpensive, require no maintenance, and give information instantly with a digital meter.

Type of System. Irrigation costs rise every year. Pumping costs are driven up by increasing fuel prices. Maintenance and replacement costs continue to climb. Installing a well-designed and high quality irrigation system that will last for many years with little or no maintenance makes good economic sense. Irrigation equipment that requires manual cleaning and adjustment is cheaper than automated equipment, but often is not cost-effective because automated equipment usually works on hydraulic principles that are difficult for people to duplicate. Modern irrigation systems are designed for automatic valve adjustment and switching, filter cleaning, injection of fertilizers and chemicals, and flushing of the irrigation pipes. All these features save far more money than they cost, through more efficient use of water, fuel, labor, chemicals, fertilizers, and time. As with saving money in the bank, the day-to-day effects are difficult to see, but they add up quickly.

Some useful hints regarding irrigation systems in the tropics follow: