Water, we can’t live without it, and it’s even more important at this time of the year when the supply becomes more limited. Irrigation NZ North Island Project Manager Kate Jefferd writes of some of the important technical aspects to consider when irrigating this summer

Many water users should be familiar with the term SMART irrigation – Sustainably Managed, Accountable, Responsible, and Trusted Irrigation.

Getting these right can help play a critical role in both overall profitability and crop production, not to mention water savings and reduced power costs. In an increasingly tougher regulatory setting, reducing your farming footprint by applying water in the right place at the right time (avoiding over application and runoff or leaching) offers a promising start. Justified irrigation allows for accuracy and precision for when water is applied, as well as how much, and how often.

The three components to SMART irrigation are: an irrigation system applying water efficiently; the use of water is justified; irrigators can show evidence of the above and are accountable for their performance and actions.

Applying water efficiently – how?

How evenly water is being applied across an irrigation system and to what depth, is a measure beginning to be captured as part of farm plans requirements.

Generally it has been a voluntary action in the form of ‘bucket testing’, giving peace of mind that your irrigation system is performing as it should, or whether any major or minor problems need resolving. Bucket testing considers ‘technical efficiency’ and is determined by user inputs such the length of your irrigator and the type of system it is.

These inputs are entered into the bucket test app, which will advise how many buckets to lay out, and over what spacing. Results tell of ‘distribution uniformity’, how evenly water is being applied along the system, and application depth, how close is your actual ‘measured depth’ on the day of the test, compared to your assumed ‘target depth’ (in mm).

Whether or not irrigation efficiency is something you are required to test for (usually by a qualified assessor), a basic test can be done yourself with the right equipment at hand, and a spare 30 minutes. Knowing what you have invested in is paying its way in good performance, is a no brainer.

Use of soil moisture technology – and trusting this technology

The increased investment in precision irrigation infrastructure and control systems, coupled with a need for irrigators to be more accountable for their water use and nutrient loss, is resulting in an increase in the adoption of soil moisture monitoring.

However, the use of soil moisture monitoring within irrigation decision making is not a simple task. Irrigators must choose the right equipment for their soil, land use activities and irrigation system type. This sits alongside locating, installing and calibrating (if necessary) soil moisture monitoring systems correctly to ensure they accurately inform irrigation decisions.

Accessing, managing and understanding the measured data is also important to the water scheduling process.

Tools and technologies for efficient water use

Soil moisture monitoring allows a greater understanding of the relationship that water has with plant growth. Soil moisture monitoring does not simply mean measuring how wet or dry a soil is, it can enhance water management strategies to improve crop yield and quality potentials.

The simple answer to this question is with upmost care. All sensors, with the exception of a neutron probe, rely on ‘good sensor-soil contact’ for accurate results.

Quality sensors come with detailed instructions for their successful installation, and provide specialised installation tools, augers for example. Some sensors, particularly those that require significant soil disturbance during installation, recommend only experienced service providers install them.

Down the soil profile

Changes in soil type, different soil horizons (layers), and plant rooting depth are the two key considerations for determining the number and location of sensors down the profile. Sensors should be located within a soil horizon and avoid crossing the boundary between them. If multiple thin horizons exist, then the most significant horizons should be selected.

For permanent crops (trees and vines), depending on the number of soil horizons and the crop’s plant rooting depth, three to five sensor points should be placed in the root zone (ideally one every 200mm), with the bottom sensor located just below the root zone to detect drainage.

In annual and shallow rooted crops, depending upon the number of soil horizons and plant rooting depth, two to four sensor points should be placed in the root zone (ideally one every 100mm), with one located just below the root zone to detect drainage.

For pasture, depending upon the number of soil horizons and plant rooting depth, two to four sensor points should be placed in the root zone (ideally one every 100mm), again with one located just below the root zone to detect drainage. The depths at which the sensors are placed depends on the soil horizons and crop root depth. However, in general:

  • The first soil sensor is installed closest to the surface, usually between 100–200mm. The 100mm depth is frequently used if the sensor also records soil temperature as this is the standard measurement depth. Soil moisture readings from this sensor fluctuate greatly which make irrigation decision making difficult if based on this sensor alone.
  • The second soil moisture sensor is installed at mid-depth (300–400mm). Soil moisture readings from this sensor are more stable and important in scheduling irrigation. This depth is focused upon the rooting mass.
  • The third soil moisture sensor is installed at a deeper depth (500–900mm). Soil moisture readings from this sensor change slowly and are a good indicator of whether the irrigation strategy is adequate.

If the line trends up or remains flat over the season, over-irrigation is occurring. If the line has a slight downward trend then irrigation is being well managed. A sharply declining line means under-irrigation is occurring.

You don’t know what you don’t measure

Quality data can only be collected by what is first measured – it is then essential that was is measured is in fact accurate, in order to gain any proper value.

Despite being a matter of compliance from regional councils, water use information and record keeping should be seen as much of a benefit as it is cost. For many, it already is, and has been for a long time. Having records on hand is not only a teller for staying under consent limits and set allocations, but contributes to management decisions around when to start and stop irrigation.