It is an irrefutable fact that water must be used sparingly in South Africa and across the rest of the continent. South Africa is a water-scarce country and the recent disastrous droughts reminded us yet again of the necessity for extremely efficient water use. Drip irrigation technology enables more efficient water use and water conservation. According to Willem Botha, marketing manager of Netafim South Africa, there are new trends in drip irrigation that further improve on these advantages.

Lees dit in Afrikaans.

“Low-delivery drippers are increasingly being used and improved technology is constantly available. We had started out with drippers featuring delivery rates of 4ℓ/h; we are now working with drippers that have average delivery rates of 2,3, 1,6 and even as low as 0,7 and 0,4ℓ/h. We now define low-delivery drip irrigation as irrigation systems where drippers with delivery rates of 1ℓ/h and lower are used,” says Botha.

Examples of low-delivery drippers.

From this technology has flowed the concept of continuous irrigation. According to Botha, continuous irrigation can be described as low-delivery drippers being used to irrigate at a very low level over a longer period of time. He explains that experience with traditional drip irrigation has proven that water delivery with these drippers is too fast and too deep. “This led to the requirement for short irrigation periods with regular intervals. This practice in turn made uniform water delivery impossible and often caused waterlogged subsurface soil. In general, the system could not function accurately and efficiently.”

Benefits outlined

Advantages of low-delivery drip irrigation include better depth management, improved water distribution, the possibility of longer irrigation periods and a resulting better soil-water-air ratio. “No system is ever without possible disadvantages. Low-delivery drip irrigation systems make meticulous maintenance a necessity and require that the drip lines are flushed out more often and various maintenance activities be done more regularly. Due to a smaller cross-section of the flow path, low-delivery drip irrigation systems require finer filtration grades.”

However, the good far outweighs the bad. “To mention only a few positive results

  • We can irrigate larger areas simultaneously.
  • It is easier and simpler to automate the system.
  • Managing the system is less complicated.
  • We can better utilise certain problem soil areas.
  • It allows us to follow certain strategies, such as continuous irrigation.

“This makes the system much more accurate and efficient. Modern farming is all about precision and ever-efficient production. Low-delivery drip irrigation technology and concepts such as continuous irrigation will assist greatly in reaching these goals.

“From an agronomic perspective, the advantage of these technologies is better distribution of water below the dripper, which leads to a larger wetted area from which the plant can extract water. The greatest advantage of this is that areas with sandy or rocky soils with low water retention capacity and poor water distribution can now be better utilised as water is delivered at a very low rate, allowing proper lateral distribution before deep penetration occurs due to gravity.”

Another key advantage of low-delivery drip is that in cases where fertiliser is distributed through the irrigation system, fertiliser leaching is prevented. When practising continuous irrigation, it is recommended that the central chemical dosing is planned from the start.

Continuous irrigation

The greatest advantage of low-delivery drip technology is that it makes continuous irrigation possible by lowering the flowrate of water through the system to such an extent, that irrigation can be done over a longer period. Botha explains the concept: “Continuous irrigation is where the application rate of the irrigation system is balanced with the maximum daily water use over the total consumptive period of the crop. This is achieved by using only one irrigation shift with the aim of applying the water within a 14-hour period.”

A system that applies continuous irrigation has the following attributes:

  • It is designed to achieve a flowrate between 2,5 and 3,5m3/h.
  • Drippers with a delivery rate of 0,7 or 1,0ℓ/h are used.
  • Dripper spacing can be between 0,8 and 1,2m.

In order to achieve optimal aeration conditions, drippers are spaced wider than normal so that the outside perimeters of the wetted area underneath the adjacent drippers do not come into contact. It is vital that only one setup is used, which means that the entire farm or development can be irrigated simultaneously.

The system is designed in such a manner that one irrigation shift can be completed in less than 14 hours. “With previous technology, we had to irrigate five to six times a day for short 10 to 15 minute periods. You can now irrigate continuously for 14 hours. This makes management easier and improves accuracy.”

Botha explains that a crop’s water demand will typically follow a bell curve over the consumptive period of the day, while water application will remain constant. This entails an oversupply of water early and late in the day and an undersupply during the peak water consumptive period of the day. “The wetted soil volume compensates for this with a buffer for shortages.”

Crop water demand versus irrigation application rate.

Two-zone scheduling

As mentioned, irrigation management practices must be adapted to new technology. This includes the adaptation of scheduling practices. According to Botha, irrigation scheduling focuses on a two-zone strategy. “This means that two different soil depths are managed. Firstly, the root zone is managed. This is the soil depth where 80% of the roots occur. This zone will be irrigated daily according to the crop’s water demand.” The irrigation can be continuous or scheduled according to an Eskom programme, where it is interrupted to irrigate only during low-cost electricity usage times.

The second zone is the buffer zone. This is the deeper zone below and located at the perimeter of the root zone. “Theoretically, a plant will extract more water during a certain period than delivered to the root zone in that period. This means that it will start to extract water from the buffer zone, thereby causing this zone to become dryer.”

Botha explains that if the buffer zone’s water content reaches a certain level, it will have to be replenished. This process is called technical irrigation and will be done outside the main 14-hour irrigation shift, which means that the remaining hours of the day would have to be used for this.

To manage these zones accurately, soil water measurement is a necessary part of scheduling. The farmer has to understand the measurements and must be able to refer back to the field conditions. It is therefore important that the value of the measurement and the true soil circumstances are calibrated.

For more information contact Netafim’s irrigation and agronomy experts to learn more about how they can help you grow more with less.

021 987 0477 • infoza@netafim.com • www.netafim.co.za

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