To calculate the water balance, we are using several parameters depending on the soil and the rainfalls.
Soil
To calculate the TAW (Total Available Water) we are taking several parameters into account:
1. The soil type
2. Roots depths (by crop)
3. Stones percentage in the soil
Thanks to Rawls and Saxton equations we can calculate the Total Available Water in the soil from soil composition in terms of clay, sand, silt and organic matter.
These formulas provide two essential values; the field capacity and the wilting point. The difference between these two values is the TAW. Then, in order to reduce this value to a volume of soil explored by the roots, this first theoretical TAW value is multiplied by the root depth.
Stones are part of the soil but do not contribute in the same way to water retention. That’s why, at Sencrop, we take in account the percentage of stones in the soil to recalculate the TAW according to the real part of the soil that can contain water.
The result of these calculations is shown on the y-axis of the graph.
Rainfall
The rainfall shown in the report is the one registered by the Raincrop (same as the one displayed on the Dashboard).
However, in the calculation of the water balance, we are only taking efficient rainfalls into account.
Different rules exist regarding efficient rainfalls (the ones that actually reach the roots of your crops).
We use the ones implemented by the FAO:
For the months of June, July, August, September:
We considered an isolated rain the phenomenon that is not repeated in the following 24h. The continous rain is considered when it is repeated at least, every 24h.
An isolated rainfall of less than 5mm is considered as not significant.
An isolated rainfall of 5 to 12 mm is considered 50%.
Isolated rainfall of more than 12 mm is considered 100%.
Continuous rainfall of more than 5 mm is considered 100% except for the first 5 mm.
For all other months:
An isolated rainfall of less than 5mm is considered at 50%.
Isolated rainfall of 5 to 12 mm is considered at 80%.
Isolated rainfall of more than 12 mm is considered at 100%.
Continuous rainfall of more than 5 mm is considered at 100% except for the first 4 mm.
When does my water balance start?
By default, the start date of your water balance is set on January 1st.
However you can change the start date of the water balance directly in the app.