Irrigation Reasonable Use Database

Introduction

The irrigation water requirements database accessed by this webpage was developed by computer simulating the operation of irrigation systems using Aqualinc’s irrigation calculator “IrriCalc”. This model simulates the day-to-day operation of farm/orchard/vineyard irrigation systems. IrriCalc uses daily climate data (from 1 July 1972 onwards), along with soil, crop and irrigation system data, to calculate a daily soil water balance using methods described in FAO Irrigation and Drainage Paper 56. Irrigation water requirements are greatly influenced by the type of irrigation method used and how it is managed.

The irrigation water requirements presented here are based on the assumption that Good Management Practice is applied. Good Management Practice depends on the combination of irrigation method, soil and crop chosen for a particular land-holding. It aims to maximise production and achieve the highest level of irrigation system efficiency that is reasonably achievable for the chosen irrigation method and soil. Lower irrigation water use than is presented here can be achieved by, for example, applying a more aggressive deficit irrigation management strategy. If you wish to investigate the benefits of using alternatives to Good Management Practice please contact John Bright, Aqualinc.

There are five steps to obtaining information on the irrigation requirements of the crops you irrigate, or plan to.

Step 1: Specify the location of your property.
The red marker shows the location currently specified. When the website page loads, the red marker is located near Blenheim – roughly the middle of New Zealand. There are three ways to move the location of the red marker to your property.

1. Click on the location of your property on the on-screen map.
   To do this accurately you will need to enlarge the on-screen map. Hold down the CTRL key on your keyboard and, while this is held down, use the scroll wheel on your Mouse to zoom in (enlarge the map) or zoom out. Alternatively use the + and – buttons at the bottom right hand side of the screen to zoom in or out. To reposition the map back into the centre of the webpage, hold down the left button on your Mouse and drag the hand-shaped pointer around the screen.
   To accurately locate your property you may find it helpful to switch from Map view to Satellite view.
   When you have enlarged the map sufficiently to see where your property, click on its location using the left button on your mouse. This will move the red marker to that location.

2. Enter your address and then click on the Locate button.
   Delete any text or numbers in the box beside the 1, type in your street address and click on the Locate button. This will move the red marker to that address. You can use more than one of these options, in any order, to home-in on the location you want. For example, use option (b) first and then (a). Once you have specified the location of your property, the map should show that the red marker is on your property.

Step 2: Select your crop.
You select the crop by opening up the drop-down list in the box to the right of the 2. Click (left button) on the downward (V) pointing arrow on the right hand end of the box. This opens up the list. Move the pointer to highlight the crop you want and Click (left button) on it. If a crop is listed twice and your property is in Hawkes Bay, use the crop with the HB label (e.g. HB-Apples). Selecting the other option (Apples) will result in the message “There is no data available for the crop and soil combination selected for the site – see User Guide”.

Step 3: Select Plant Available Water (PAW).
Irrigation requirements depend on the capacity of the soil to store Plant Available Water (PAW). This can vary from property to property, and within a property. When you specify the location of your property, the website looks in its database for the soils most likely to be found in your area, and the associated PAW. The database is derived from soil map information that is publically available from Manaaki Whenua Landcare Research’s S-Map and Land Resource Information System products. The webpage provides 3 ways of selecting which Plant Available Water value to use for your property – or multiple values. For all options, the default area (ha) of each PAW is 1. This needs to be altered to the correct number of hectares irrigated for each of the required PAW values. You can enter a different area by deleting the current value, typing in the value you want, and pressing the Enter key. The three different options for selecting PAW are detailed below:

1. Most likely PAW in this area.
   When you select this option the website chooses the PAW value that has the highest likelihood in your area. The PAW value and the Likelihood value is shown. To the right of these numbers is a box for entering the area to be irrigated (in hectares). By default this is 1.

2. User specified PAW’s
   When you select this option the website displays the PAW values that are likely to be present in your area, the Likelihood value and the default area (1ha) for each of them on your property. They are ordered according to their Likelihood value. Up to five PAW values will be displayed. If there are less than five likely PAW values there will be unused boxes indicated by the text ‘PAW’. While the soil maps and associated data used are the best available at catchment scale, the land-owner may have access to very farm-specific information – as a result of on-site soil sampling and analysis, for example. Option (b) provides the ability for farm-specific PAW data to be used. It does this by allowing the user to select a PAW value ranging from 30mm to 200mm, and so over-ride the default values the website presents. The PAW values on any line can be changed by clicking on the V arrow on the right hand end of the PAW box to bring up a list of all the available PAW options, and the option of clearing the current PAW from that line. Move the cursor using your Mouse to highlight the option you want to select. Press on the left Mouse button to make the selection.

3. Likelihood Weighted
   This option uses the soil PAW’s most likely to be present in your area, up to a maximum of five, and weights the irrigation requirements values according to the likelihood of each. For example, if the likelihood value for a PAW of 70mm is 60, and for a PAW of 120mm is 40, then the irrigation requirements are calculated assuming 60% of the Total Area irrigated has a PAW of 70mm and 40% of the Total Area irrigated has a PAW of 120mm. With this option the user can enter the Total Area irrigated, only, and not the area for each individual PAW. The irrigation requirements information on the right of the webpage is shown on a per hectare basis, and for the total area. The area values you enter scale the per hectare results to produce the Total Area result. If, for example, the System Capacity is shown as 0.61 (l/s/ha) and you have entered irrigated area(s) that gives a Total area of 100 ha, then the System Capacity for the Total Area will be 61 l/s.

Step 4: Select Irrigation Method.
One or more irrigation method is assigned to each Crop type, based on current good practice. If pasture is selected, for example, the available Irrigation Methods are “Centre pivot” and an “80% Efficient irrigator”. For most orchard crops the only irrigation method provided for is “Micro/Drip”. The irrigation requirements for each combination of Crop, soil PAW and Irrigation Method are based on current Good Management Practice. This assumes that decisions on when to irrigate and how much to apply are based on soil moisture levels that are regularly measured or estimated.

Step 5: Fetch Data.
Once you have completed Steps 1 to 4, click on the Fetch Data button to obtain the Irrigation Requirements information. A blue progress bar should cross the webpage from left to right, along the bottom of the dark blue box containing the Steps 2,3,4 and 5. If the webpage appears to have frozen you will need to Refresh the webpage. This can happen if the webpage is left open for a while with no user input. The irrigation requirements are presented as statistics that are relevant to the planning, design and consenting of irrigation systems in New Zealand. The main webpage shows the information normally required for planning, design and consenting in your region. More irrigation requirements data is shown by clicking on the “Detailed Results” button. Note that this is where you must look for seasonal irrigation volumes that meet needs 95% of the time. The main webpage currently shows the 90% value. The irrigation requirements shown are based on the assumption that the crop you selected can be grown and irrigated at the site you selected. Constraints such as topography and crop-specific climate requirements such as growing degree days or number of frost-free days are not currently taken into account. Irrigation requirements may be less than those shown on this website if your soils are slow draining, or if the water table is close enough to the crop root zone during summer to meet some (or all) of the crop’s water need most years. Fetching the irrigation requirements data for some combinations of location, crop and soil will produce the message: “There is no data available for the crop and soil combination selected for the site.” This occurs for one of two reasons.

1. There is no data available for the crop and soil combination selected for the site. For example, selecting “Apples” for a Hawkes Bay site will produce this result. Selecting “HB-Apples” will avoid this message. Selecting “HB-Apples” in another region will produce the same message. In that case select “Apples”.

2. The average annual irrigation water use for the crop and soil combination selected for the site is so low that irrigation is unlikely to be economic. If you get this message but you think that irrigation is or will be economic, please contact Aqualinc.