Irrigation Management

The knowledge about the actual evapotranspiration, the water balance, and the results of the soil moisture makes irrigation more efficient. Using these values you can show when irrigation has been and done and at the same time reduce water use and save energy also. Receive an alarm SMS from the iMetos and it tells the irrigator when to start and stop the Irrigation system!

• Evapotranspiration and the respective crop factor show exactly how much water your crop actually needs.

• The water balance shows you, how much water has been taken from the soil and how much has been re-filled through to rain and irrigation

• The water tension (suction) gives you an indication how good the water in the soil is available for your plants.

• The water capacity tell us, what is the percentage of water in the soil

All these methods tell you how much you should irrigate. All these methods do this in a very specific way. Using the Evapotranspiration and the phenological stage (crop factor) model you precisely estimate how much water the plant does really need. Using that method you do not need to add a sensor to every single plant or crop. The Evapotranspiration value (ET) is valid for a bigger area with the same or similar climatic conditions – just knowing what crop and what phenological it is - the water uptake is automatically adjusted to your specific crop.

Water tension (suction) in the soil can be measured with 3 types of sensors: Tensiometer, Watermarks and MPS-1 Sensors. Water tension is a very practical value to estimate the irrigation needs of a crop. For many cultivation simple rules applies to estimate when and how much water based on the tension should be irrigated. In potatoes the following rule of thumb applies: hold you crop till flowering in a water tension level between -20 to -40 cBar – with this strategy you avoid potato scab. After flowering you can keep the crop drier – from now on you can let the water tension levels go to -60 cBar. For Apple trees: you can simple keep them in a range between -20 and -80 cBar. In the same way or similarly you also irrigate your cherries. Before harvest you should look that they should be drier: around -40 cBar and you should keep them around -20 to -40 or maximum till -50 cBar to avoid the risk of splitting. In any case you should not let the water tension down to less than -20 cBar because of the risk of splitting. Shallow rooted plants and vegetable you should be kept between -20 and -40 cBar.

Soil WaterTension:

Principle of water tension – for that topic we offer currently 3 types of sensors: Tensiometer, Watermarks and MPS-1 Sensors. Tensiometer are tubes filled with water and a ceramic tip on the bottom (in the soil) in which the inside tube pressure is distributed into the soil. The relevant water suction is measured digitally through a pressure transducer and communicated to the data logger. Tensiometer are very accurate but measure only to a suction of about -850 mBar (-85 cBar) and if the suction goes beyond that value the tensiometer is sucked out and stops working. For that reason we suggest that sensor only for application in vegetable crops.
Watermarks are a very good and cost effective alternative to tensiometer as they are maintenance free and can work many years without problems. They work reliably and good in medium and heavier soils. They do similar good job for practical irrigation management than the proven good old tensiometer. Watermarks are a special form of gypsum blocks which have a reliable resistance change. The measuring range is between 10 and -200 cBar.

Decagon is producing the MPS-1 Sensorto measure suction. The sensor is based on a capacitance measuring part which is measuring the water tension in between two ceramic plates. The water content inside the ceramic plates has again a close relation to suction in the soil. The advantage of the sensor is that it can measure suction from 15 to -500 cBar which is high enough also to be used in regulated deficit irrigation methods (RDI).

Soil Water Content

Soil water content in percentage of soil volume can be measured with capacitance sensors. Here we offer two types of sensors. For economic reasons we support sensors which work on the principle of „Frequency Domain Reflectrometry" (FDR). 10HS, EC5 and 5TE are single sensor solutions from Decagon. The sensor 10HS is suitable very good to open field application. The sensor EC5 is designed more for pot plants and soil less applications. The sensor 5TE measures apart from soil moisture also soil temperature and electric conductivity in the soil. With this sensor we can show also the movement of nutrients within the soil profile.

AquaSpy and SENTEK profile probes measures the soil moisture in the vertical profile with 5-15 single sensors (50 cm to 150 cm length). They are very useful if the topic is to verify the soil moisture changes in the whole profile in order to get from this information better nutrition and irrigation schemes.
How much and when to irrigate:

Soil water content in percentage of soil volume can be measured with capacitance sensors. To get the from the volumetric soil water content the decision when and how much to irrigate you need either the wet sieving of the soil to calculate from that the soil physiological parameters or longer measurement series during the growing season. The second solution is easier to get as after a series (some weeks) of measurement the agronomic thresholds are a result of it. Out of these measurements you can see how the plant is changing the water uptake over time. Water stress is reducing the ability to uptake water and out of this the onset of water stress can be seen easily. On the opposite side if the soil is too wet you can easily see the water distribution as water is moving through the force of gravity.
IRRIMETis the water balance and field management program. iMETOS weather stations are supplying the base values for the calculation of the reference Evapotranspiration (ETo) based


Created by system. Last Modification: Friday 18 of May, 2012 14:10:15 GMT by Lena.