Research Findings |
Analysis |
A wide range of inflow rates could have equivalent irrigation performance on all modelled soil types and crops provided the appropriate inflow duration was used. |
Irrespective of the crop, no substantial irrigation performance improvements were achieved on more permeable Group 2 soils by increasing bay inflow rates above the current recommended rate of 0.2 Ml/d/m of bay width, provided that both the inflow duration and the irrigation deficit were appropriate for the inflow rate adopted. |
For example, on a permeable soil growing lucerne, an inflow rate greater than 0.2 Ml/d/m can reduce deep drainage below the crop root zone for crop water deficits of less than 70 mm, but generate substantial irrigation runoff to achieve satisfactory requirement efficiency at crop water deficits greater than 90 mm. |
On less permeable Group 3 soils no substantial performance improvements were achieved, irrespective of the crop or the crop water deficit, above an inflow rate of 0.1 Ml/d/m, provided that the appropriate inflow duration was selected. Deep drainage could be slightly reduced by using inflow rates of 0.2 Ml/d/m. |
The reasons for this were the low final infiltration rate and very slow rate of surface water drainage, causing long durations of ponding that inflow rate did not substantially influence. |
No productivity differences that could be attributed to inflow rate were measured on any site. |
While there may be other reasons for adopting higher inflow systems, such as time and labour savings, the message we are able to deliver to industry as a result of this project is to not assume water and productivity benefits when assessing investment in infrastructure to achieve bay inflows greater than 0.2 Ml/d/m. |