The agronomic design represents the first phase of the design procedure of any type of irrigation, with which the amount of water that the facility is to transport is determined, corresponding to the gross irrigation needs in times of maximum need. It is an important part in an irrigation project because if mistakes are made in the calculations of the agronomic design, they will later affect the hydraulic design.
The variables to consider are:
– Determination of water needs. The plant only uses a small part of the available water in its metabolic processes, the rest is lost by the transpiration of the plant itself and by evaporation in the soil, a phenomenon known as crop evapotranspiration (ETc). The amount of water to be supplied must be equal to the ETc in order to compensate for said losses. ET0 is the reference evapotranspiration, data that can be obtained from the closest meteorological stations of each province.
Kc is a coefficient specific to each crop, a fact that can be consulted in many references, one of which is FAO.
ETc = Et0 x Kc.
– Calculation of irrigation needs. To obtain the net irrigation needs (Nn), this result must be subtracted from the gains due to rain or effective precipitation (Pef).
No irrigation system is perfect, so the previous value is multiplied by the irrigation efficiency (Ea) of the system used to obtain the gross needs (Nb) of irrigation. It is considered an Ea of 90% in drip irrigation (and 75% in aspersion).
Nb = Nn x Ea.
– Frequency and time of irrigation. One of the advantages of drip irrigation is the saving of water, precisely because it is not necessary to wet all the land as it happens in the irrigation by flood. The area wetted by the dropper varies according to the flow rate, and the texture of the soil. The flow of the drippers will be 4 L / h (at lower flow rate, greater obstruction), and the approximate surface that wets a dropper is approximately 1.25 m in diameter, although this data varies depending on the texture of the dripper. floor.
To avoid calculations, we will use the tables of the integrated production regulations, designed for this purpose.
- Number of emitters per tree in drip irrigation. Age of the tree Clay Sandy Grainy 1 - 2 1 1 1 - 2 2 3 - 4 1 2 2 - 4 4 5 - 6 2 4 4 - 6 6 7 - 8 2 - 4 4 - 6 6 - 8 8 > 8 4 6 8 8 - 12
– Recommended irrigation frequency in localized systems. Type of soil Clayey Era Sandy Grainy
SPRING G- 2 V.P.S. G- 3 V.P.S. G
– DIARY G- 1-2 V.P.D.
SUMMER G- 3 V.P.S. G
– DAILY G- DAILY G- 2-3 V.P.D.
AUTUMN G- 2 V.P.S. G- 3 V.P.S. G-
DIARY G- 1-2 V.P.D. V.P.S.
– TIMES PER WEEK V.P.D.
– TIMES PER DAY G
– DRIP IRRIGATION SYSTEM MA
– MICROSPERSION IRRIGATION SYSTEM
– Calculation of the flow.
Finally, we calculate the necessary flow to supply our surface, multiplying the needs per plant by the number of trees. These data will serve us as a starting point when sizing all the components of the installation in the second part of the project; the hydraulic design.