Blue dye trial uncovers water flow below the soil surface

Department of Agriculture and Food development officer Rohan Prince said a trial using dye to track water spread had highlighted the difficulties in predicting what was happening below the soil surface and why it was so important to take a look.

“What was predicted by some available computer programs over estimated the spread and underestimated depth the water travelled in these coarse sandy soils,” he said.

The trial looked at 30 different combinations including application rate, dripper spacing and volume of water applied in the first trial of a new project to develop good practice for drip irrigated tomatoes grown on sand.

The information from the dye trial will be used to choose combinations of dripper spacing and flow rate to be tested in a production trial which will be planted in late October at the department’s Medina Research Station.

Mr Prince said by knowing the area of water spread beneath the crop, he hoped water application could be better matched to crop requirements.

“This will help reduce excess drainage while also keeping the nutrients in the root zone and delivering increased profits for growers,” he said.

“Depth of water from the most common drip tape used by growers in the Carabooda area had reached 30 cm after just half an hour or 0.5 L of water applied but had not met between the drippers.

“This may indicate that spacing of drippers and the timing and frequency of irrigation are particularly important.”

Mr Prince said this was very useful information not only for growers, but for drip manufacturers.

“Both recognise the importance of this work and have very supportive of these trials,” he said.

Drip irrigation supplier Dave Norman said the information would be useful when giving advice to growers when selecting the spacing and flow of drippers to use on there farm and would help growers continue to use water as wisely as possible.