2.3.7.2 - How suitable is border-check irrigation for the soil types on my farm?
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Although border-check irrigation can be very efficient, there are situations where this is not the case. The performance of your border-check system will depend on a combination of soil type and the management and design of your system.
The findings of a recent DEPI research project investigating the impact of bay inflow rate on irrigation efficiency concluded that on medium to heavy soil types (Soil Groups 3 to 6) of northern Victoria, increasing bay inflow rate above 0.1 Ml/d/m bay width would not have substantial water saving benefits, provided the correct inflow duration was used.
On lighter soil types (Group 2 soils without a strong texture contrast to a heavy clay subsoil), the most appropriate inflow rate depended on the irrigation deficit. On a lucerne site with a deficit of 67 mm, increasing inflow rate to 0.4 Ml/d/m of bay width slightly improved potential irrigation performance by reducing deep drainage. The same site with a deficit of 95 mm could not meet irrigation requirement without excessive runoff unless ithe inflow rate was reduced to 0.1 Ml/d/m.
Border-check irrigation of a shallow rooted pasture on a Group 2 soil was found would cause substantial deep drainage irrespective of the inflow rate used. To substantially improve irrigation efficiency at this site would require either changing to a crop such as lucerne, or changing system to sprinkler irrigation.
Although border-check irrigation can be very efficient, there are situations where this is not the case. The performance of your border-check system will depend on a combination of soil type and the management and design of your system.
Runoff reuse systems prevent water escaping from the farm; these systems are now widely applied in the region. If you have a runoff reuse system, the main way water can be lost is by drainage below the rootzone. These losses are closely associated with soil types and infiltration behaviour.
Indicative annual deep drainage losses below the rootzone for a 20-irrigation season are shown in Table 2.8 below for a range of soils with different infiltration rates and for different irrigation application times. For properly designed border-check irrigation systems application times will be similar to inundation time. The data is from a lysimeter experiment at Tatura carried out in 2004/05 and desktop modelling.
Table 2.8 – Deep drainage losses under pastures for different soil types/infiltration rates and application times (ML/ha/yr)
Soil type | Infiltration rate (mm/hr) | 1.5 hr application time | 3 hr application time | 6 hr application time | 9 hr application time |
| Sand | 14 | 4.5 | 9 | 18 | 27 |
| Sandy loam | 5 | 1.5 | 3 | 6 | 9 |
| Medium clay | 2.5 | 1.0 | 1.5 | 3 | 4.5 |
| Heavy clay | <2 | 0.5 | 0.5 | 0.5 | 0.5 |
The information in Table 2.8 shows that very high deep drainage losses can occur on light soil types under poor irrigation management (i.e. excessive irrigation times). The data in Table 2.8 is only indicative and should be used with care. Soils can vary considerably over short distances, even in units that are mapped as uniform on the soil map. Only detailed (and expensive) field investigations can provide accurate information on site infiltration behaviour and percolation losses. If the potential water saving on your farm (e.g. as in Table 2.6) exceeds say 1 ML/ha, this indicates that either your border-check irrigation layout and/or management can be improved, or that border-check irrigation is inappropriate for your soil. If your soils are inappropriate for border-check irrigation, you should consider converting to sprinkler (e.g centre pivot irrigation).
Case study - The farm described in Table 2.6 has an average potential water saving of 2 ML/ha. The soil on this farm was a medium clay, and the farmer typically irrigated for 5 hours. From Table 2.8 deep drainage of 3 ML/ha/year would be expected for a medium clay and 6 hr application time. The farmer could save water by increasing the flow rate onto the bay and reducing the irrigation time. From Table 2.8, reducing the application time from 6 hours to 3 hours would reduce deep drainage from 3 to 1.5 ML/ha/year.
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