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Precipitation: Natural rainfall occurring during the growing season.
Irrigation: the process of manually or mechanically applying controlled amounts of water to the land.
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The above graph shows how plants transpire more as they mature. The increase in evaporation during the same period is likely due to higher temperatures.
Taken together
Below we can see a commercial offering showing what such a “water balance” system might look like.
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On the x-axis we have time and on the y-axis we see the amount of moisture in the soil. As we might expect, several points on the y-axis denote the important levels (or derivatives of the levels) we discussed above:
Teal: Refill, AKA field capacity
Yellow: Safety, a point sufficiently proceeding the wilting point such that a farmer can schedule and perform irrigation before the crop becomes stressed and begins to wilt.
Red: Crop stress, AKA wilting point, where permanent losses to yield begin.
Brown: Permanent wilting point, where crops effectively have no access to moisture and die.
While this dashboard doesn’t explicitly show the reasons that soil moisture decreases over time, we can safely assume the four factors described in the previous section are the culprit. Indeed, we could likely correlate particularly hot or windy days with particularly precipitous drops in available water levels. Furthermore, based on when significant decreases in soil moisture begin (despite continued precipitation), we can assume the crop was planted in late April and shortly thereafter began actively evapotranspirating at an increasing rate until mid-Fall where the crop transitioned to a less active growth stage.
On the “filling the bucket” side of things, we see:
Dark blue: Rainfall events
Light blue: Irrigation events
As we might expect, the irrigation events clearly show a spike in soil moisture levels. Precipitation is a bit more muted but clearly serves to maintain high soil moisture prior to the growing season (where ET surpasses natural recharge from precipitation).
Modeling the state of the bucket and future water needs
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