Irrigation Systems
XYLEM [TREE INJECTION] IRRIGATION
Xylem irrigation (Figure 4.13) is the direct application of water with necessary chemi-cal agents into the xylem of the tree trunk using a series of injectors that depends on the age of the tree. Xylem irrigation is also called ultra micro, high frequency, tension, tree injection, or chemotherapy irrigation. There is no difference in the concept these names represent. The basic idea originated when various chemicals were injected into the internal circulatory system of tree. It is simple to inject water, fertilizers, mi-cronutrients, growth promoters, growth inhibitors, pesticides, trace elements, gases, precursors of flavors/color and aroma, and in general any substance valuable for the improvement of fruit quality. This system is in the experimentation stage and has not been evaluated commercially.
Figure 4.13. (a) Principle of tree injection irrigation.
Figure 4.13. (b) Tensiometer in a trunk tree.
Figure 4.13. (c) Diagram illustrating the tissue layers and their organization within monocot and dicot roots.
Advantages
Efficient use of water
1. No evaporation from the soil surface into the atmosphere.
2. No infiltration into the subsoil where roots are incapable of absorbing mois-ture.
3. No runoff.
4. No wetting of foliage.
5. Inhibits non beneficial consumptive use of water by weeds because the terrain is free of weeds.
6. One can irrigate the entire field up to edges.
7. Accurate quantity of irrigation water can be applied according to transpiration rate of the plant.
8. Overall water application efficiency can go up to 99%.
9. Savings up to 95% of water use can be achieved.
Plant response
1. Crop growth characteristics can be manipulated.
2. Better fruit quality and uniformity of crop is expected.
Root environment 1. Shallow root system.
2. Effective soil aeration.
3. Provision of required amount of nutrients.
Pest and diseases
1. Pesticides can be injected into the plant system.
2. Frequency of sprays can be reduced.
3. Reduction in incidence of insects and diseases.
4. Reduced application rates of pesticides.
Weed growth 1. It is a minimum.
2. No weeds in dry surface between trees.
Agronomical benefits
1. Irrigation activities do not interfere with cultivation, spraying, picking and handling.
2. Less inter-cultivation, soil crusting, and compaction problems.
3. No surface runoff.
4. No soil/water erosion due to irrigation.
5. Fertigation and chemigation are possible thus savings in energy and quantity.
6. Other necessary chemicals can be applied along with irrigation water.
Engineering and economical benefits 1. Significant savings in energy.
2. Cost is low compared to surface sprinkler and drip irrigation systems.
3. Pipe sizes are significantly smaller compared to pipe sizes in other irrigation systems.
4. Conveyance efficiency and water use efficiency can be increased up to 99%.
5. System can be installed in uneven terrains.
6. It requires constant discharges at low pressures.
7. Water and chemical use can be programmed with the crop response.
Disadvantages
1. May not be applicable in vegetable crops as it is more convenient to inject into tree trunks.
2. May not be used in monocot species as the xylem is not as differentiated.
3. Introduction of new substances can cause toxic effects just as a man can over-dose on drugs.
4. May cause fungus growth at the injection site.
5. Holes in tree trunk must be made to install injection tips thus causing physical injury to the plant.
Operational Problems
1. No information is available on number of injection sites, water application rates, dosages of various chemicals depending upon the age of the tree.
2. At what height and depth, should the injection points be located?
3. Injection tips can be easily clogged by gum, wax and resins of tree.
4. Effective cleaning agent needs to be found to avoid clogging of tips.
5. Algae formation in the injector lines.
6. Laterals may contain air [from the tree] and thus obstructing the flow.
7. Leakage of water at the contact point between the injector tip and tree surface.
8. Excess pressure might loosen the sealing agent [silicon] and may throw out the injection tip.
9. Expert advice is needed to locate xylem.
10. Chemigation might disturb the osmotic and electrical internal equilibrium in the plant.
11. Screening of pesticides and chemicals suitable for xylem irrigation.
12. Salts in excess of 300–500 ppm may require desalinization of water.
13. A clean, pure or soil water is necessary.
Principle of Operation
It is based on utilizing natural negative sap pressures within a plant to suction liq-uids and gases directly into the inner circulatory system, analogous to a human blood
transfusion. The technique is accomplished by placing an injection tip [e.g., a ceramic implant] directly in the xylem layer, the negative pressure area. Liquid or gas is then made available to the implant through a plastic tubing at very little or no pressure.
Fluids can then traverse in the plant in any direction. The roots of the plant continue to be nourished by the natural way, with sap, water and nutrients. The roots still seek moisture and grow down using a stimulus called geotropism.
Plants give off water through a process called transpiration. The amount of water a plant “throws off” and the amount it needs are two different situations. A well known
“Hill Reaction” is:
6CO2 + 6H2O + H2 = C2H12O6 + 6O2 (3)
Opposite of transpiration is called respiration. By careful measurement of the quantities of sugar synthesized in the leaves by unitary surface and time [10–15 mg of hexose/sq dm-hr], it is readily calculable what stoichiometric quantity of water is required under the same conditions [e.g., 50–80 ml for a period of 8 hrs considering a canopy surface from 8 to 10 sq. m]. This quantity is very approximate to the quan-tity of water consumed by xylem irrigation during the same period under the same conditions. Primary water uptake occurs only during photosynthesis or day light [12].
System modification: It is accomplished by simply placing the ceramic piece in the root zone of house or commercial indoor plants, nursery stock or almost any plant too small to receive an implant in the trunk. The same efficient use of water and nutrients are applicable but some of the metabolic engineering techniques [Modulation of the plant metabolism with the aim of obtaining better fruits by injection of substances such as promoters of color, bouquet, flavor, aroma, metabolites, enzymes or coen-zymes] may not be effective. Seeds for greenhouses can also be germinated and grown from an implant in the soil. The seed can actually be glued to the implant, then planted and grown through maturity. Tree crops can be raised with other irrigation systems and then xylem tips can be installed after first year of growth. Water usage of 40 ounces/
day on older trees, 5 ounces/day for grapes has been reported. This calculates to be approximately 0.05 gpm/acre of irrigation during 12 hours photosynthesis or 36 gal-lons/day/acre.
Description of Xylem Irrigation System
The system consists of a water resource, pump, chemigation system, filter, main line, sub main, laterals, and injection tips. The installation of injection tip should be done in the following manner:
1. Select the size of a ceramic tip.
2. Select the best location on the plant.
3. Bore a hole through the cambium layer approximately 1/4 diameter larger than the injector.
4. Use a sharp instrument to remove this plug of bark. It is important to bore past the phloem to cause leakage out of the plant.
5. Continue the bore into xy1em [sapwood] portion to the same dimension as length of ceramic portion of the injector. The hole should allow a snug fit.
6. Use an inert sealing agent [silicone] for sealing the injector to tree.
7. Hook water to be injected to the tip at a pressure of 1–8 ft of head. [Necessary pressure can be allowed by gravity, low pressure pump]. Very minute quanti-ties of chemical can be injected into the water stream using a plastic syringe [doctor’s needle].
Precautions for Xylem Irrigation System 1. Sterilize the drill bit.
2. Hole should allow a perfect fit.
3. Use a good sealing agent.
4. Water should be free from pathogens.
5. Use a pesticide to avoid fungal growth.
6. Injector site should be allowed to dry before starting irrigation.
7. No leakage can be allowed between the tree and tip, as it will break the suction.
8. High precaution is essential in determining dosage of the chemicals to avoid toxic hazards in the plant.
9. Any injection holes, which cannot be used, should be left open. They heal with time.
HYDROPONIC
The growth of plants without soil is known as hydroponics. From l925 to l935, ex-tensive work was done to modify the nutrient culture in the nurseries. In l930, W.F.
Gericke at the University of California, defined hydroponics as a science to cultivate plants without the soil use, but using inert materials such as sand and sawdust, among others. A nutrient solution with all the essential elements is added for good develop-ment of the plants. After World War II, the Air Force Wing of the United States used hydroponics to provide food to the troops and established the first hydroponics project of 22 hectares in Chofu-Japan. During the fifties, the commercial use of hydroponics expanded quickly to United States, Italy, Spain, France, England, Germany, Sweden, USSR, Israel, India, and others. This expansion continued in Australia, New Zealand, Africa of the South, Kuwait, Brazil, Poland, Singapore, Canada, Malaysia, the East and Center of Africa and other countries, during 1950–2000. Figures 4.14 and 4.15 show a typical hydroponics system. The ventilation, darkening of the roots and sup-port of the plant are key elements of the hydroponics. The nutrient solution is pumped to a PVC tube covered with a black polyethylene cover. The PVC tube is cut in half and the black polyethylene is placed on top to prevent the entrance of light. Holes are made at the top of the polyethylene tube through which plants grow in the nutrient solution, which flows at the bottom of the PVC tube. At the end of a crop, the system is dismantled and the tubes with accessories are washed with a chlorine solution.
Disadvantages are:
1. The high initial capital cost.
2. Incidence of diseases like Fusarium and Verticillium.
3. The problems with nutritional complexes.
Figure 4.14. Hydroponic system.
Figure 4.15. General components of a hydroponic system.
Advantages:
1. A greater efficiency in the regulation of nutrients.
2. Its availability in the regions of the world with no arable lands.
3. Efficient use of the water and fertilizers.
4. Easy and low cost of sterilization of growing medias.
5. A greater density of plants by area.
SUMMARY
The need for additional food for the world’s population has spurred rapid development of irrigated land throughout the world. Vitally important in arid regions, irrigation is also an important improvement in many circumstances in humid regions. Unfortu-nately, often less than half the water applied is beneficial to the crop – irrigation water may be lost through runoff, which may also cause damaging soil erosion, deep per-colation beyond that required for leaching to maintain a favorable salt balance. New irrigation systems, design and selection techniques are continually being developed and examined in an effort to obtain the highest practically attainable efficiency of water application.
• Filter, sand
BIBLIOGRAPHY
See bibliography Section 4.1 for the literature cited.
APPENDICES
Appendix 1. Drop-tube (Over head) irrigation System.
Appendix 2. Components of a drip irrigation system.