6 Operating the Irrigation System
6.1 COMPLETING THE PRE-SEASON CHECKS
Before beginning any irrigation, pre-season checks should be carried out. These should include:
- Calibrating equipment. Check flow measuring equipment, soil moisture monitors, pump rating etc. to ensure the equipment is performing to specification;
- Application depth checks. Using a rain gauge or similar device, check the depths that the irrigation system is applying. This may need to be carried out a few times each season to establish how depths change with climatic conditions;
- Checking uniformity of application. While checking application depths, check the uniformity of application for the irrigation system;
- Recording baseline information such as paddock sizes, crops, and soil water holding capacities.
6.2 IMPLEMENTING THE PLAN
The irrigation strategy planned at the start of the season should then allow you to decide when and where to irrigate, and how much water to apply.
Operating the system is, in effect, carrying out the plan. It is the "DO" part of the plan-do-monitor-review process described in Section 1.2.
6.3 USING INDICATORS TO MONITOR PROGRESS
Monitoring progress towards meeting your goals and determining whether or not your irrigation strategy is performing to expectations requires you set performance targets and measure whether you are moving towards those targets.
The indicators recommended in LE Report No 2720/1 have been developed for this purpose.
The indicators have been divided into four groups for convenience, (economic, environmental, soil health, and social indicators) and are summarised in Tables A, B, C and D respectively. A summary of the information needed to be recorded, and the equipment needed to record the information is also given in the tables. The soil health indicator is an aggregation of a number of soil properties, and although it is an environmental indicator, it has been listed separately for clarity. All of the indicators are essentially seasonal indicators, but for some of them, daily information must be recorded to obtain the seasonal values.
| Indicator | Task | Equipment/Information Needed |
| Annual net operating profit after tax ($). | Record profit from financial records. | Financial records/accounting system. |
| Profit per unit of water used ($/m3). | Record profit and total seasonal water use. | Water use records. Financial records. |
| Production/unit of water used (tonnes of each crop produced per m3 of water applied to that crop). | Record production of each crop and water applied to each crop in the season. (Refer to Note 1) | Daily water use records, seasonal production records. |
| Quantity produced/hectare for each crop (t/ha) (tonnes/ha for each type of crop). | Record production of each crop. | Production records. |
| Quality of produce (% at each grading level). | Record the different grades of crops produced. | Appropriate measure of quality (e.g. high/low grade product). Record sheet. |
| Annual energy used to operate irrigation system (kWh). | Record the amount of energy being used by the irrigation equipment from irrigation electricity meters. | Electricity meter readings for irrigation pumps. |
| Energy used per volume of water pumped (kWh/m3). | Use annual energy use and total seasonal water use from above. | Electricity meter readings and water use records. |
| Labour units per irrigated area (hours per hectare). | Record time spent on irrigation annually. | Daily record sheets. |
Note 1 - Flow measurements
Because it is important to measure the productivity per unit of water for each crop, the daily irrigation flows need to be proportioned between paddocks. If there is only one irrigator operating, the flows onto the farm can be calculated using water meters or electricity usage. However, if there are two or more irrigators operating from a single pump, the best way to obtain the volumes applied to each crop is from water meters on each irrigator. Otherwise, it is not easy to assign volumes to each crop, particularly if the irrigators are not identical or are run at different speeds.
A paddock is defined as an area containing the same crop, the same soil type and watered in the same irrigation setting.
| Indicator | Task | Equipment Needed |
| Resource consents obtained and complied with. | Record consent applications and outcomes. | |
| Daily volumes of
irrigation water flow onto farm for each crop (m3)
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Note 2 - Soil moisture measurements
- Most of the decisions relating to daily irrigation decisions require soil moisture to be measured in each paddock. For the purposes of irrigation management, two areas can be considered part of the same paddock if they contain the same crop and soil types, and are watered on the same day.
- There is some opportunity to reduce the number of soil moisture readings that are required to properly manage the whole farm. If two or more paddocks contain the same crop on the same soil type, then only one paddock needs to be monitored to determine how much water the crop is using. This water-use information can be used to determine soil moisture levels in the other paddocks. Furthermore, crop factors can be used to relate the water uptake by one crop to that of other crops on the same soil type.
| Indicator | Task (Refer to Note 3) |
Equipment Needed |
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Note 3 - Soil monitoring
Soil monitoring should be undertaken in the same place at the same time each year. Samples should be collected from every different soil type on the farm, and areas growing different crops. Usually, a ‘z’ shaped path is walked through a paddock, with samples taken every 10 m or so. The samples are then mixed thoroughly, and a portion sent to a suitably registered laboratory for analysis.
Refer to Appendix III.
Note 4 - Water quality monitoring - Lysimeters (effluent irrigation only)
Samples taken for water quality analysis need to be collected carefully to eliminate chance of contamination by other sources. The sample bottles must be clean and sterile, and depending on the type of analysis required, may need preservative or chilling to stop the composition of the water changing on the way to the laboratory. Samples usually need to be sent to the laboratory as soon as possible after collection. Remember to label the samples carefully - place, date, time. Sampling for nitrate requires that the sample be kept at 4 °C, and is analysed within 48 hours.
| Indicator | Task | Equipment/Information Needed |
| Abatement notices. | Retain abatement notices, and record date, time and date of incident. |
6.3.1 Determining Baseline Indicators
Before the first irrigation season that the indicators are going to be used to monitor progress, it will be necessary to determine indicators to provide baseline values for comparison later. These baseline indicators may require information from the previous season in order to calculate them.
The information sheets given in Appendix I can be used to record these indicators.
6.3.2 Obtaining Daily Information
These are the indicators that require daily flows, drainage, surface ponding and for effluent irrigation, nitrogen leaching to be measured. Nitrogen leaching is based on lysimeter readings, and need not be measured daily.
Appendix II contains a form, which we suggest farmers fill in on a daily basis, so that these indicators can be calculated. The information required to do this is:
- dates;
- daily rainfall;
- soil moisture readings;
- irrigation depth applied (based on checks of application depth);
- hours of irrigation;
- notes on any obvious surface runoff or ponding;
- labour hours.
6.3.3 Determining End of Season Indicators
At the end of the season, the indicators listed on the information sheet in Appendix I should be recalculated so that they can be compared with the previous seasons values.
Contact for Enquiries
MAF Information Services
Pastoral House
25 The Terrace
PO Box 2526
Wellington, NEW ZEALAND
Fax: +64 4 894 0721
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