INTELLIGENT IRRIGATION

The Plant

We can consider the plants as being a thermal machine. The energy is supplied by the sun and is used by the plants to perform the chemical processes of the photosynthesis, synthesizing the organic matter of the plants through the conversion of the carbon oxide in the air and the chemical elements in solution that are absorbed by the roots.

The energy is also used to absorb the water and the nutrients from the soil by the plant. The sun makes the leaves breath, what causes water disequilibria in the tissues of the plant, and consequently results in the absorption of the solution of the soil to get back to a state of equilibrium.

Only a fraction of the water that is "pumped" by the roots is used in the formation of the plant tissues. A larger amount is used to remove from the soil the chemical products that the plant needs. Hence, a soil that has sufficient amounts of nutrients requires smaller amounts of water.

In case there is an excess of nutrients in the soil and little water, the solution in the soil will be more concentrated than that in the plants, and the plant will be killed by the osmotic pressure of the soil, which will remove the water from the plants. If, on the other hand, there is an excess of water and too much nutrients, the plant will absorb large amounts of water without, however, obtaining all the nutrients that it needs and, therefore, exhibits reduced growth.
The equilibrium among the nutrients, the air and the water in the soil is vital for obtaining good crops.

Movement of the Water in the Soil

The water and the minerals are in constant movement in the soil. They migrate from the zones of smaller gradient to the zones of large gradient, until they reach a condition of equilibrium. Therefore, during the hotter hours of summer days, the roots extract water and nutrients from the soil around it, while at night, when they stop absorbing water, the soil tends to get homogeneous again, in order to balance the concentration gradients.

Hence, we are led to say that the plants are the driving force for the movements of the water and the nutrients in the soil, whereas gravity, surface tension, evaporation and condensation, as well as the hydraulic pressures and friction control the movements of the water in the soil.
In general, gravity and surface tension force an equilibrium: while the force of gravity forces the water down, the surface tension forces the water to stay where it is, and even to go up.
In this way, when the roots absorb the humidity of the soil, they cause a difference in gradient, and the water in the surrounding regions migrates to recover the homeostasis of the system, causing a directing of the humidity to the zone of the roots. This movement is slow and is usually much slower than the extraction of the water by the roots.
In this sense, we can have, temporarily, during the hours of peak perspiration, a lack of humidity in the radicular zone, even tough the area in the surroundings may seem humid.

With this, it can be said that a good irrigation system must always start whenever the radicular zone is susceptible to entering in a state of temporary stress, what usually takes place during the hours of peak heat.
From these factors, two important information may be inferred:
1) The fertilization and irrigation should be performed at the end of the afternoon, because, as the plants stop absorbing water from the soil at night, there will be enough time for the movements of the nutrients in the soil to lead to a state of equilibrium, distributing the fertilizers in a better way.
2) The irrigation, if the system that was chosen allows it, is more effective during the hours of peak sunlight, as it avoids temporary stresses at the radicular zone.

An intelligent Irrigation
Irrigation is intelligent when it handles the water that is available in such a way as to maintain the humidity of the soil at an optimum level.
In case the humidity is not maintained at optimum levels, there are two alternatives:
a) In excess: If there is a limitation on the amount of water that is available, we leave more areas without irrigation for a given availability of water.
b) In absence: The plants do not develop its entire potential.
In order to obtain a good control of the humidity of the soil, it is necessary to have devices that are capable of indicating the values that are obtained and the programs of irrigation that are based on these controls. Starting from an efficient control of humidity, we will see that the irrigation cycles will vary considerably as a function of space and time, as well as will vary the amounts of water that are to be made available per cycle.
The conventional irrigation is characterized for having a defined watering cycle, with a fixed and predetermined amount of water that is to be used, these parameters being defined by the average of the consumptions expected for the given culture. This procedure causes a lack of humidity during the peak hours of perspiration, and an excess of water during the periods in which the perspiration is smaller.
The intelligent irrigation is characterized by the release of different amounts of water with intervals between the cycles and different durations for the cycles in each occasion.
The key to an intelligent irrigation is to have greater humidity during the critical periods of absorption by the plants.
Determination of the Programs of Irrigation

Theoretically, the ideal system and program are to supply water and nutrients to the plant, directly to their radicular zone, at the exact moment that it needs it, and according to the same rate that it is consuming it.
All irrigation systems have a minimum time and a maximum time of irrigation:

• The minimum time is the time that it takes for the water to effectively reach the radicular zones.
• The maximum time is the time that the water takes to reach immediately below the radicular zone (percolation), at the closest neighboring areas.

To any system of irrigation, it may be introduced control methods for performing an intelligent irrigation.
By using sprays during the hours of peak sunlight, up to 80% of the water fed may be lost due to evaporation. The water reaches the leaves, and starts evaporating right there. Additionally, the soil is hot and the sun that is falling right onto the water on the soil can evaporate it faster than it is capable of infiltrate the soil.

The localized irrigation tends to have small minimum irrigation time irrigation, because the water has only to fill the pipeline in order to be effective in the soil.
A common error incurred in localized irrigation is to have long periods of irrigation, with a low frequency. On the contrary, it is better to have short periods of irrigation, occurring more frequently.
The amount of water to be used must also be larger than the velocity of infiltration, because by doing so the water will also go to the sides. If an analogy is made with a dripping faucet, it is expected that the water wet a small circle and infiltrate into the soil. However, if a bucket is placed under the same faucet, and if when the bucket is full the content is overflowed, a humid zone will be formed, that will be much larger and less deep.