How to Measure Crop Water Use Directly.


The Implexx Sap Flow Sensor can be used to directly measure crop water use. The sensor is installed into crops and connected to a data logger or internet enabled device. The Implexx Sap Flow Sensor measures crop water use every 10 to 15 minutes. It is possible to track crop water use throughout the day or via daily sums.


Why measure crop water use directly?

The Implexx Crop Water Use Forecast provides an estimate of what may occur in the future. The Implexx Sap Flow Sensor is an estimate of the crop water use that most likely occurred. One is an estimate of future crop water use, whereas the other is an estimate of the present or past crop water use.

The information from the forecast and sap flow estimates can be used in combination for irrigation management.

If the crop water use estimated from the sap flow measurement is significantly lower than the forecast estimated crop water use, then it is possible that the crop is experiencing soil moisture deficit and additional irrigation may be required.

Another interpretation may be that the crop is under some other stress. For example, the crop may have a lack of, or too much, nutrients or it may be affected by fungi or disease.

By combining information from a crop water use forecast and measured crop water use, a deeper understanding of crop behaviour or status can be gained.



How to use the Implexx Sap Flow Sensor for irrigation management



How does the Implexx Sap Flow Sensor work?

The Implexx Sap Flow Sensor, also known as a crop water use sensor, is installed into plants and trees. The sensor consists of three needles – a top and bottom temperature needle with a heater needle in the middle. The temperature sensors measure a change in temperature following a short duration heat pulse of 3 seconds. A large change in temperature indicates rapid, or high, sap flow and a small, or no change, in temperature indicates slow or zero sap flow. The temperature changes are carefully calibrated for total plant water use, or crop water use, via a series of intensively researched, highly accurate equations and algorithms.



Litres, gallons, millimetres and inches

When crop water use is estimated from different sources, the data will likely be presented in different units of measurement.

The Implexx Crop Water Use Forecast presents data in metric units as millimetres per day or imperial units as inches per day.

The Implexx Sap Flow Sensor presents data in metric units as litres per hour or litres per day.

The data can be converted and interchanged so interpretation can be made on the same units of measurement. Here are the conversions:

Millimetres (mm) = Litres / Area

Millimetres = 25.4*Inches

Inches = 0.0394*Millimetres

Area is the tricky parameter in these conversions. Area must be carefully defined otherwise confusion, and misinterpretation, over data can easily be made.

For example, 1 mm (millimetre) of rainfall is defined as 1 litre of water per 1 m2 of ground. However, the Area parameter used in crop water use (also known as total sap flow or transpiration) may be canopy projection area, planting density, irrigation (dripper) area, basal trunk area, sapwood area, or total leaf area. There is no wrong use of these Area parameters and they all have their own importance. But these different definitions of Area are all defined as crop water use, transpiration, or crop evapotranspiration and the interpretation of the results will be vastly different. Therefore, when converting from millimetres or inches to litres, the Area must be carefully and consistently defined for meaningful analysis.



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