Pulse drip irrigation

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One of two pulsing impact sprinkler at The Crescent Grange in Broomfield, Colorado providing 5000 sq. ft. of coverage of their Permaculture garden. The sprinklers were run continuously delivering 5 second pulses per minute for the first twelve days to germinate the seeds. Thereafter it was gradually cut back to 8- to 10-hour watering periods three times a week.

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Landscaping in sand with in situ seed germination. A one gallon per hour drip flow controller feeding an eighty-two foot drip line with check valves comprising eighty-two drip points along its length so each drip point is putting out about 1/82 gallons per hour.

Crimson clover sprouts grown on 1/8" urethane foam mats and flagstone. Four micro-sprinklers cycle pulsing continuously over a 7 day period, each putting out about 1/2 gallon per hour. The four micro-sprinklers were each fitted with an LPD to keep the lines fully charged between pulses.

Pulse drip irrigation is a scalable low-flow irrigation technique that allows for close management of water usage and can be employed with either drip or sprinkler irrigation devices and extend conventional low-flow irrigation systems to ultra-low micro-irrigation levels. Pulse irrigation is common in locations such as Israel where water conservation is a priority.

Pulse drip irrigation systems operate by passively letting water flow into a reservoir at a controlled rate to steadily build pressure within the pressurized reservoir. When the pressure in the reservoir reaches some predetermined pressure level the valve on the reservoir opens and a portion of the fluid contained within the reservoir is forcefully discharged. While the fluid is discharging the pressure within the reservoir decreases. When the decrease in water pressure reaches a predetermined level the valve closes to resume the charging phase. The charge-discharge cycling will continue as long as the flow rate coming in through the inlet is less than the expel rate passing out through the outlets while the valve is open. A device called a drip flow controller is placed at the inlet for this purpose to regulate the flow into the inlet.

Low-flow pulse systems can be left operating continuously without overwatering. Constant and frequent irrigation applications have been cited as one way to reduce water demand. Some literature also cite the benefits of small frequent watering applications to reduce water stress on plants.

Low-flow application rates can grow in different mediums. The water can be applied slowly enough to match the water assimilation rate and prevent water loss from percolation or run-off. Mineral nutrients added to mediums with a high void content such as coarse grained sand will provide more oxygen to roots than ordinary soil and share some of the advantages with aeroponics. Sand also has a low water retention potential that makes it easier for plants to extract water by expending less energy due to the sand's relatively large particle size, which consequently does not bind very well to water. This increases the plant's water-use efficiency. Sand is also inhospitable to pathogens that can attack roots.

Advantages

Pulse drip irrigation has many advantages for drip and sprinkler systems:

• No run off on heavy soils.
• No leaching or water loss in sandy soils.
• Water can be applied efficiently on shallow soils and in hilly areas.
• Intermittent operation of sprinklers and foggers can provide evaporative cooling for temperature control.
• Reduce the size of growing containers in greenhouses due to very low discharge rates.
• Low flow inputs reduce supply system costs because smaller conduits and lower capacity pumps would be needed.

Disadvantages

• The additional expense of buying and maintaining a pulse drip system to a pre-existing irrigation system.
• The system requires a minimum of 25 psi water pressure to run efficiently.
• Maintaining the integrity of a pressurized water supply is of critical importance. Leaks in the piping can run up substantial costs due to the long duration of the watering periods.
• Close attention to the watering cycles is needed to avoid salinity build up in the soil. Light watering can leave salt residues behind as the water evaporates and leave little added moisture to the soil.
• The additional expense of leak prevention devices (LPDs) are recommended to be fitted at each watering distribution point along the system to insure even distribution of water. If the discharging conduits are allowed to drain between pulses most of the water will preferentially flow to those at the beginning of the line.