To estimate when irrigation is needed, it is useful to know the soil moisture content of your plots. Inagro tested IrriWatch (from Hydrosat) last year. This platform estimates the soil moisture content using satellite images and crop models.
We already shared some initial results last year. Now we can share the analysis of five fields: two potato plots, a spinach plot and two chicory plots. For these plots, we purchased an IrriWatch subscription, installed a soil moisture sensor (Pessl Instruments) and regularly took soil moisture samples.
Weather station-style soil moisture sensors from Pessl Instruments being prepared for field deployment.
Sensors measure different parameters
Our sensors measure, just like a weather station, air temperature, precipitation and relative humidity. In addition, they also measure the soil temperature, soil moisture content and suction tension in the soil. At Inagro, we mainly use these sensors to monitor precipitation and to see trends in the soil moisture content. Is the soil moisture content falling or rising? To obtain accurate results, correct installation is essential. The soil must fit nicely around the sensor and must be clean.
In addition, the sensors must be maintained, we regularly replace broken parts and have the software updated.
The IrriWatch platform has no maintenance costs, prevents repairs and excludes possible incorrect installations. You buy an annual subscription and receive new maps daily for the entire period. With sensors, you receive up-to-date information about the condition, while with IrriWatch you are always a day behind and only receive yesterday’s data. But there is also a major advantage: you receive a soil moisture map of the entire plot and can thus see the field variability.
IrriWatch versus sensors
We collected a mixed sample from a specific zone from each potato field and the spinach plot and determined the soil moisture content in the lab. We also placed the soil moisture sensors in those zones. It is striking that the results of the sensors and IrriWatch show completely different trends on the potato plots. For the spinach plot, we do see similar trends. The soil moisture content at IrriWatch corresponds better with the values measured in the soil moisture samples than with the values of the sensor.
Comparing soil moisture data from sensors, IrriWatch, and lab-analyzed soil samples across two potato plots and one spinach plot.
We checked whether the field variability of IrriWatch corresponds with reality by collecting a few samples at specific points in the chicory plots.
- On the first chicory field, the first two IrriWatch images show a strikingly wet spot, which is also visible in the results of the soil moisture samples.
- On 14 October (image on the right), we see that the soil moisture samples again indicate a high soil moisture content at this specific spot, while the IrriWatch image does not confirm this. Map of chicory plot 6 June, map of chicory plot 12 September, map of chicory plot 14 October.
Soil moisture sample points on the chicory plot indicating high moisture content at a specific location.
- On the other chicory plot, we see no major differences in the soil moisture content according to IrriWatch on 23 July (values vary between 16 and 19 percent, image on the left). According to the platform, the sample in the west of the field should be in a slightly wetter zone, but it is actually lower than the other samples.
- On the image of 11 September (middle) we see that the soil moisture content of the samples falls within the same range as on the IrriWatch image.
- From autumn onwards, we have noticed an underestimation of the soil moisture content on the IrriWatch images in both chicory fields (image on the right).
Soil moisture content on 23 July, Soil moisture content on 11 September, Soil moisture content on 14 October.
Graph visualizing soil moisture content from IrriWatch imagery alongside lab-analyzed soil samples.
IrriWatch closer to correct values
A sensor offers a good option for monitoring precipitation, temperatures and trends in soil moisture content. However, these small-scale tests show that the soil moisture values often deviate from other measurement methods. The soil moisture content indicated by IrriWatch corresponds better with the values we obtained in the lab. However, the time trends do not always correspond consistently. Large variations in soil moisture content within a field were clearly visible on the IrriWatch maps. However, for smaller differences, the field variation does not always correspond to the sample results.
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