Case Study – Tomatoes


  • Hornet: 40cm probe
  • Soil Type: Deep sand soil
  • Crop: tomatoes
  • Location: North of Perth Western Australia
  • Irrigation type: Drip line (pressure compensating)

The graph below shows four lines each representing mm of moisture at 4 depths below the crop during mid-February 2013.. The different coloured lines represent the 4 sensors down a 40cm probe. Blue is moisture in the top 10cm, green top 20cm, red top 30cm and blue top 40cm sensor.

The horizontal lines are lines placed on the graph to assist in irrigation decision making. The full point represents filed capacity at 10cm (this is the point where the soil is unable to hold any more water).

Tomato case study graph

The refill point represents the level at which soil moisture needs replenishing. The stress point is where the moisture in the soil may start impacting on plant growth.

Each peak represents an irrigation event.This graph shows that the crop is consistently being overwatered. At every event the water rapidly flows down the profile and is more than likely leached out below the root zone. Watering was applied on average 3 to 4 times per day depending on the weather.

Watering occurred at around midnight, 6am, 2pm and sometimes 5pm. The amount applied at each watering was aound 2-3mm or 8-11mm per day.

For this deep sand it would be better to drop a watering (the midnight one) and see the result and if necessary drop the late afternoon watering. Unnecessary waterings especially midnight leads to over watering and leaching of nutrients. The aim is to keep the 10cm moisture levels tracking well within the full point and refill lines.

Crop benefits from using the Hornet – Less water being used, Lower pumping costs, lower fertiliser costs and higher crop yields.