Precision irrigation

SENTEK

Meteobot® Pro weather station can be equipped with the Drill&Drop soil probes of the leading Australian manufacturer – Sentek. They show the soil water content every 10 cm depth – e.g. at 10, 20, 30, … down to 120 cm. The water content is displayed in litres (mm) per square meter. This way you have information how much water you have available in the soil at any given moment.

Sentek sensors are especially suitable for deep rooted crops – for example, corn, irrigated with pivot (or other sprinkler-type) systems.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Sentek uses as a “sensor” the root of the plant. On the following chart you can see how the soil water content drops steeply during the day and gradually during the night. The reason for that is that during the day the plant “pumps” water from the ground and evaporates it through the leaves. This does not happen during the night. That is why the chart looks like stairs whenever the soil moisture is within the optimal range.
When the soil dries so much that plants cannot extract water from it any more, the chart goes straight and levels out. This is exactly the moment when another irrigation is necessary. When the soil is saturated, plants cannot use water from it in an optimal way and the chart is flat. This way you can see when to irrigate – when soil moisture drops below the lower limit, under which plants get stressed. In the case on the next chart, this means one irrigation every 11 days.

How much to irrigate?

Sentek sensors measure soil water content at every 10 cm depth. This way you see how much water is necessary to provide optimal soil moisture down to the depth of the roots at the current moment. On the following chart you can see soil water content from 0 to 60 cm depth:

• Optimum water take-up – from 2nd to 13th day after irrigation
• Above 280 l/m2 in the soil layer (0-60 cm) – too much water
• Between 280 and 220 l/m2 – optimum water take-up
• Below 220 l/m2 – not enough water and danger of drought

This means that the crop has to be irrigated with about 60 l/m2.

EVAPOTRANSPPIRATION

If, for any reason, the installation of soil moisture sensors in unpracticable in your case, your Meteobot® can be equipped with a solar radiation sensor. By taking into account solar radiation data, as well as temperature, air humidity and wind, Meteobot® calculates how much water is evaporated from the soil and transpired by the plants every day (so called “evapotranspiration”) by using FAO Penman-Monteith equation. When you know the water losses from the soil for a certain period, you can find out how much you need to irrigate (e.g. 5 days x 4 liters evapotranspiration per day = need for 20 liters of irrigation).

 

WATERMARK Soil Moisture Sensor

In use since 1978, the patented WATERMARK sensor (PN: 200SS) is an electrical sensing device that is buried in the active root zone to measure soil water tension.

The sensor consists of corrosion resistant electrodes embedded within a specialized granular matrix. Water in the soil exchanges with the sensor matrix, providing a measurement of centibars (or kPa) of soil water tension. It requires no site calibration or maintenance and it’s durable and reliable for harsh soil conditions.

In Meteobot® mobile app the soil moisture measured by Watermark sensor is presented as percentage from the full soil capacity to accummulate water which is more understandable for farmers (0-70 % – dry (red sector), 70-90 % optimal soil moisture (green sector), 90-100 % waterlogged soil (blue sector)). The graph of soil moisture can be combined with the historical data for precipitation events: