Irrigation Efficiency at Robinvale

Wemen Vineyards at Robinvale, Victoria, are using sprinklers to irrigate wine grapes, with tile drains installed at 1.2 m depth to drain off excess irrigation water. They are recording the number of hours that water was pumped at each irrigation; the Neutron Probe is measuring the amount of water that actually reached the crop root zone at each irrigation; and a record is kept of the volume of water running out of the drains, on a scale from 1 to 10. The pipe has been marked off in 10 equal discharge volumes. The objective was to monitor the efficiency and effectiveness of each irrigation, and to graphically display the results.

The solution was to make four keydata entries, called EFFEC, HOURS, +EFFEC/HOURS and DRAIN on the Edit Site screen (Figure 1). EFFEC is the effective depth of water that reached the soil profile, as measured by the Neutron Probe; HOURS is the pumping time in hours; the ratio of EFFEC to HOURS will be a measure of the irrigation efficiency; and DRAIN is an arbitrary number from 1 to 10 . The actual units of the ratio will depend on pump capacity and area irrigated, but it will immediately give an indication of efficiency.

Figure 1 Edit Site Screen.

Each time an irrigation was posted to the readings screen (Figure 2), the pumping time (in hours) was also entered in the Irrigation column, in the Keydata HOURS row. The depth of water that actually reached the soil profile, after adjustment to get a reasonable ProbeDWU, was copied from the first row of the spreadsheet to the Keydata EFFEC row. After updating, the +EFFEC/HOURS was calculated by the Probe software.

Figure 2. Readings Screen.

Figure 3. Time Graph of Irrigation Efficiencies.

By selecting the +EFFEC/HOURS keydata row, and plotting a time graph of selected data, users could quickly see the efficiency of all irrigations in the season. However, in order to actually plot vertical bars for HOURS on the time graph a slight 'adjustment' was required. A 'dummy' estimate column was inserted immediately after each irrigation, and a value of "0" was inserted in the keydata rows in the (Est) columns before and after the irrigation. In this way, when the HOURS Keydata row was selected, vertical columns with a symbol at the top are drawn, on top of the normal Irrigation bars (Figure 3).

In this example, in 6 hours of pumping 30 mm was applied at a rate of 5 mm/hour, but only 17 mm was effective - a rate of 2.8 mm/hour. The difference is being lost in the pumping system, by evaporation, or by through drainage. An examination of the depth graphs will show the amount of drainage. In this case, pumping should have been for only 3.4 hours (17 mm at 5 mm/hour).

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