Trickle irrigation – is it the way to go for potato growers?
26 June 2007 - Is trickle irrigation the answer in terms of water efficiency?
Water resources are under severe pressure as demand from a range of sectors rises. It is becomingly increasingly important that growers are able to demonstrate the efficient use of water for irrigation, especially as part of the abstraction licence renewal process. Efficient irrigation is all about placing the correct amount of water at the right time to ensure maximum utilisation by the crop and minimal wastage. Trickle irrigation uses lower application rates and volumes of water compared to overhead systems (although water has to be applied more frequently) so does this mean that trickle irrigation could be the answer in terms of water efficiency?
It is true that trickle irrigation has the potential to be more water efficient than overhead systems, there are no evaporative losses from the spray and no surface water losses if the tape is buried. Water can also be placed exactly where it is needed to be utilised by the crop, overhead systems will apply water to a whole area including bare soil and weeds.
In arid conditions trickle irrigation has been proven to increase the efficiency of water use; however within the UK where irrigation is used to supplement rainfall the results are less impressive.
Trickle irrigation requires soil to be kept wetter around the emitter and it is essential that cracks in the soil do not develop as this would hinder the movement of water. Therefore a trickle system will have to be restarted sooner after rainfall to maintain the soil moisture and will be using water when an overhead system will not be. The need for this earlier application of water leads to less efficient use of the rainfall as the field is being held closer to field capacity resulting in losses through drainage.
The management of trickle irrigation varies greatly to an overhead hose reel system. There is no extra work involved in applying more water as trickle irrigation can be easily turned on and off and this can lead to slight over irrigation as a precaution. Over irrigation on a trickle system isn't always easy to spot as the water will simply drain away. Over irrigation with a hose reel is far more noticeable and less likely due to the labour required with an extra hose reel move.
The monitoring and maintenance of trickle systems is more difficult, particularly in potato crops where the tape is buried. Blocked emitters are not easily spotted and damaged tape caused by rodents or by an over zealous hand fork will cause significant problems!
For a potato grower, particularly those growing for the prepack market it is not only the water efficiency that may attract them to trickle but also the potential quality and yield benefits. As the soil is kept constantly moist with the 'little and often' approach water stress on the crop can be avoided and will therefore promote plant growth and potentially higher yields. On scab prone crops such as Maris Piper where higher prices will be paid for top quality prepack product trickle irrigation plays a huge part in achieving a blemish free sample.
If water application is properly managed the skin finish and uniformity of crops can generate significantly higher returns to the grower, however this will only pay off if water is applied at the correct time. Growers who miss the critical application window at tuber initiation could be left with an average crop with above average costs attached to it (£350/ha for trickle irrigation). The additional cost and management time linked to trickle irrigation means that growers are taking a certain amount of risk when deciding at planting time on whether or not to trickle irrigate a crop. In years when rainfall and growing conditions are optimal and a majority of growers manage to achieve uniform crops with a good skin finish a trickle irrigated crop is unlikely to be worth significantly more, however if the management and scheduling in the more challenging seasons is correct a sizeable premium can be generated.
There is no doubt that trickle irrigation can provide benefits in terms of water saving, yield and quality while opening the door for other management techniques such as the potential for fertigation. However in order to achieve any of the above there is a very real need for high uniformity, accurate scheduling and significant attention to detail (including land type and variety choice). The system is expensive and requires a concerted management effort in order to maximise its potential. The key message for irrigators regardless of the system they employ is to minimise wastage, maximise crop utilisation and choose a system that is both environmentally and commercially suited to your situation. More information on efficient irrigation can be found in the document 'Save water and money - irrigate efficiently' which can be downloaded from the UK Irrigation Association website or from the policy section of NFU online.
