The Current Scenario
Water is a finite and vulnerable resource, which is essential for sustaining life, and for the development of the environment. Currently, of all the water taken from nature, 80% is used for irrigated agriculture, 12% for industrial processes, and 8% for human consumption. Of the total volume used for agriculture, only a small portion is effectively used for the crops. The rest is lost through defects in the irrigation equipment, negligence in the operations, or simply through poor management of the water used for this purpose.
The high electricity subsidies used for agriculture, when used during the night, leads users of irrigation in intensive agriculture to apply large amounts of water during this period, in the hope that the soil will retain it until it is used by the crops. In reality however, this does not occur, due to the porosity of the soil, which drains most of this water away before the start of the solar irradiation that promotes photosynthesis and generates the necessary energy for the circulation of water and nutrients inside the plants. Furthermore, there is a habit of irrigating crops during the night in the mistaken belief that the water will not evaporate, and that because the soil is cooler, more water will be saved.
Therefore there is unnecessary consumption of drinking water by irrigated agriculture.
To make matters worse, it is observed that water used in excess by irrigation promotes the lixiviation of the nutrients in the soil, contributing to the processes of desertification which currently affects 20% of the earth’s irrigated area. Added to this is the fact that this excess water now contains high levels of fertilizers and pesticides, which contaminate the underground reserves of drinking water.
In response to this issue, an intelligent system has developed in Brazil, for controlling the use of water in irrigation. The Sistema Fotossíntese (Photosynthesis System) uses phenomena and reactions occurring in nature, to control the use of water in such a way that it only allows the necessary amount of water to be removed from the environment, and at the right moment for the crop which is being irrigated. The operation of the Sistema Fotossíntese is based on three principles which are essential to plant life, namely:
- Photosynthesis,
- The Dynamic of the Water in the Soil
- Intelligent Irrigation.
The Parameters
Photosynthesis
Photosynthesis is a highly complex phenomenon. With the indispensable help of energy from sunlight, and chlorophyll, sugars (glucose), carbon hydrates (amide) and other substances are processed in the leaves and green parts of a plant, using CO2 (carbon dioxide) which comes from atmospheric air that penetrates the plant through the stomata, and H2O (water), which comes from the roots. See Figure 1.
Figure 1. Photosynthesis Process
The stomata (stoma = mouth) are tiny openings located mainly at the edges of the leaves. These pores open when there is sufficient light, to enable CO2 to enter the leaf and release the water vapor from transpiration. The stomata close when there is insufficient light, or when the plant runs the risk of drying out because not enough water is reaching the leaves. If they are closed, the growth mechanisms do not function and the plant does not grow; if they remain open for a long time, the plant grows more. The stomata are not binary elements, so intermediate states of opening are possible (Julio Guri, Barcelona-Spain. 2000).
Dynamic of the water in the soil
The water and mineral salts are in constant movement in the soil. These migrate from the lower gradient zones to higher gradient zones, until they reach an equilibrium. Thus, during the hotter hours of summer days, the roots extract water and nutrients from the soil around them, while at night, when they stop absorbing water, the soil tends to become uniform again, to balance the concentration gradients.
Thus, we can say that it is the plants that promote the movements of water and nutrients in the soil, with gravity, surface tension, evaporation and condensation, hydraulic pressures and friction controlling the movements of the water in the soil.
These factors depend on two important pieces of information:
- Ferti-irrigation should be carried out at the end of the afternoon because, as plants stop absorbing water from the soil at night, there will be sufficient time for the movements of the nutrients in the soil to equilibrate themselves, spreading the fertilizers better.
- Irrigation, if the selected system allows, is more efficient at the start of and during the photosynthetic processes, and before the peak sunlight hours, since these avoid temporary water exhaustion in the root zone.
Intelligent Irrigation
An irrigation is considered intelligent when the available water is managed in such a way as to maintain the moisture of the soil at an optimum level, without harming the environment.
If the moisture is not maintained at optimal levels, one of two things may occur:
- In excess: If there is no limit on available water, we stop irrigating areas with the same availability.
- Lacking: The plants do not grow to their full potential.
To ensure good control of the moisture in the soil, equipment is needed which indicates the values obtained and the irrigation programs based on these controls. Based on an efficient control of moisture, we see that irrigation cycles vary considerably in terms of space and time, as do the quantities of water to be made available for each cycle.
Conventional irrigation is characterized by a defined, regular cycle, with a fixed, pre-determined quantity of water to be used, and these parameters are defined by the average usage forecast for the crop. This procedure leads to a lack of moisture during peak transpiration hours, and excess water during the periods with less transpiration.
Intelligent irrigation liberates differentiated quantities of water, with intervals between the cycles and different cycle times for each occasion.
The key to intelligent irrigation is to obtain constant moisture content during the critical periods of plant absorption.
The Contribution
Photosynthesis Project
Consubstantiating this reality, and the parameters above, the Sistema Fotossíntese (Photosynthesis System) was developed, which consists of a programmable microprocessor, aided by an Osmotic Soil Moisture Sensor, which acts by osmosis according to the permeability of each type of soil; a Light Sensor, which identifies the start of the processes of photosynthesis in the plants, and a Rainwater Sensor which prevents the application of water during rainfall.
This system is designed to enable the Automation and Management of Irrigation, and ensure that water is applied in ideal quantities, and at the right moment, for the crop being irrigated, preventing unnecessary use of water by irrigation systems and providing greater efficiency per drop of water used.
The System can also be used for the Protection of Underground Spring Waters, identifying contaminating infiltrations before they reach and contaminate the water table.
For this purpose, it has a Software program which processes the digital signals emitted by the sensors through the microprocessor, adjusting the water consumption by the Irrigation systems to the water needs of the plants during periods with solar irradiation, according to the conditions of soil moisture in the absence of rain.
The Software manages the information which comes from the Light and Soil Moisture, and Rainwater sensors. These signals are received by the microprocessor, which activates or deactivates the Irrigation Valves.
The System has digital outlets for remote monitoring and enables the activation of the motor pump apparatus for ferti-irritation and/or pressurization of the irrigation systems.
With these characteristics, the System prevents consumption of water for irrigation during periods when there is no solar irradiation to provide the energy needed for photosynthesis and the circulation of water and nutrients to the inside of the plants. Because at this moment, the plants need to breathe through the porosity of the soil, and the water impedes this respiration and contributes to speeding up the lixiviation of the nutrients in the soil. Also, it does not allow the application of water to exceed the capacity of the field, thereby preventing exhaustion and water deficit of the roots.
The technological differential of this System is that promotes an interaction between the application of the water by the irrigation systems and the occurrence of solar irradiation which promotes photosynthesis, the moisture conditions of the soil, and the presence of rain.
The Figure 2 illustrates the Photosynthesis System.
Figure 2. Photosynthesis System
The Benefits
- Reduction of Water and Energy Consumption in Irrigation
- Increase in Productivity of the Water in the Field
- Improvement in Quality of Agricultural Production
- Avoids Saturation of the Soil
- Avoids Deficit and Water Exhaustion of the Roots
- Avoids Lixiviation of the Nutrients in the Soil
- Avoids Salinization and Desertification of Arable Areas
- Protects the Underground Springs
See Appendix
