Over the years, experiences and studies have determined that the most important aspect for agricultural production is water. During the last decade, this vital element has decreased considerably due to a prolonged drought that now affects the entire surface of Chile. For all these reasons, we consider it essential to know how and how much we are watering. One of the things that a farmer must be clear about is how much water his equipment delivers. For this, there are many tools to measure soil moisture, moisture tension, water movement in the plant, etc.
But if we do not know what our equipment should really deliver and if it is actually delivering it, we will start with a very poor foundation to be able to use this type of more sophisticated or detailed tools, this is why we must initially know how many millimeters our equipment delivers, for this we must initially know how to obtain the instantaneous precipitation of our technical irrigation equipment.
One of the most common mistakes in our fields is to determine irrigation hours based on what we already have or on the experience of someone we know; but we usually do not notice if there are variations in the distance between rows or in the distance of the drippers or the flow of the latter.
We will try to explain in an easy and practical way the basic parameters that will allow us to have knowledge of the capacities and differences of our technological irrigation systems, this with very simple formulas to apply.
1.- Instantaneous precipitation of our system (mm/hour) mm/hour = emitter flow rate (l/h) x number of laterals Spacing between rows (m) x distance between irrigation emitters (m)
Example, cherry trees planted at 4.0 x 2.0 m with a double-line drip irrigation system, with 2.1 l/h emitters spaced 0.4 m (40 cm) apart
mm/hour = 2.1 l/h x 2 irrigation lines = 2,625 mm/hour
(4.0 m x 0.4 m)
That is, in this simple example, for every hour of irrigation our equipment is able to apply 2.62 mm of water per hectare, this is equivalent to 26.2 m3 per hour per hectare.
2.- Capacity of my irrigation equipment (mm/day), to make this calculation I consider how many millimeters my irrigation equipment can apply daily by irrigating all sectors on the same day, this regardless of the frequency or the way of irrigating each field.
mm/day = Instantaneous Precipitation (mm/h) x 24 hours (day)
Number of sectors in my team
Example, following the same data already mentioned in point 1.- we will add that our equipment is designed with 6 irrigation sectors
mm/day = 2.625 mm/h x 24 hours = 10.50 mm/day
6 (sectors)
If I wanted to calculate the capacity of my equipment in less hours, for example 22 hours, it is as simple as modifying the hours in the previous equation
mm/day = 2.625 mm/hx 22 hours = 9.63 mm/in 22 hours
6 (sectors)
If I wanted to calculate how many millimeters I applied when I determined a certain amount of hours, we just have to multiply the instantaneous precipitation by the hours watered, in our example, if I watered for 12 hours it would be
Mm applied in 12 hours of irrigation = 2.625 mm/hx 12 hours = 31.50 mm/in 12 hours
3.- Water supply (m3/hol/sec), how much water should we have in our field to supply the water requirements of our irrigation equipment.
m3/h = Instantaneous precipitation (mm/h) x area of the sector x 10 (constant)
Example, following the same data above, assuming that it is a 24 ha field and assuming that one sector has 4.3 ha
m3/h = 2,625 mm/h x 4.3 ha x 10 = 112,875 m3/h
To transform from m3/hal/sec you just have to divide by 3.6 (this is because 1 m3 is equivalent to 1,000 l and 1 hour is equivalent to 3,600 sec)
l/sec = M3/h = 112.875 = 31.35 l/sec
3.6 3.6
Once you have this information clear, your second step will be to check if your irrigation equipment is actually delivering the flow rate for which it was designed.
