|  |
Injection of Chemicals Into Irrigation Systems: Rates, Volumes, and Injection Periods 1
G.A. Clark, D.Z. Haman and F.S. Zazueta2Irrigation systems can be used to transport soluble chemicals to the crop. Depending on the type of irrigation system, chemicals may be applied to the root zone, the aerial part of the plant, or both. The process of chemical transport using the irrigation system is referred to as chemigation. Specific terms may be used to refer to specialized applications of chemigation, such as nematigation and fertigation.
Irrigation systems designed or adapted for chemigation require specialized equipment for the injection of the chemical solution into the irrigation system at a controlled rate. Several injection methods are possible and are discussed in detail in other publications (Nakayama and Bucks, 1986; Smajstrla et al., 1987; and Yeager and Henley, 1987). The cost, accuracy, reliability, and longevity of the equipment varies greatly among manufacturers.
It is important to select adequate equipment, maintain it regularly, and properly operate it to insure a successful chemigation system. New irrigation system designs must consider which chemicals are to be injected while selecting the system components to insure compatibility. Uniformity of chemical application cannot exceed that of the irrigation system. Therefore, it is very important to have a well designed and well maintained irrigation system to provide the greatest potential for a high level of application uniformity. When existing irrigation systems are to be adapted for chemigation, they should be thoroughly examined for uniformity of application as well as compatibility of the chemicals to be injected with existing components.
Water quality is another factor to consider in the design or adaptation of an irrigation system for chemigation. Some water supplies require chemical amendment to prevent bacterial growths or chemical precipitants from clogging the system. This publication will concentrate on the management aspects of chemigation and how chemigation influences other aspects of irrigation management.
Chemical Mixtures and Injections
Chemicals may be applied as a precisely managed level of concentration or as a bulk mass of chemical with possibly varying concentration levels. Concentration management requires a precise injection system and is more involved than bulk injection. The injection system must be specifically calibrated for the irrigation system it is to be operated on and under the operating conditions that will exist when chemicals are to be injected. Variations in operating pressure, system flow rate, and at times even temperature can influence the calibration of the system. Bulk injection simply involves the injection of a desired volume or amount of chemical into the system. The injection rate does not need to be precisely controlled. However, it should not be damaging to any part of the system or crop, should not exceed manufacturers' recommended application rates, and should apply the chemical in a time period which does not result in over-irrigation or leaching of previously applied chemicals.Concentration Mixtures of a Stock Solution
Some chemical applications require that a certain concentration level be maintained for proper use of that chemical in that situation. Concentrations are generally expressed in parts per million (ppm), which is not a convenient term for mixing purposes. Chemicals may be supplied in dry form or liquid form; however, the end result is a liquid mixture of a desired concentration. The following equation can be used to determine the mass of chemical required to achieve a particular ppm level. ( Equation 1 )
This provides the mass of actual chemical that must be dissolved per 100 gallons of water. For example, a 200 ppm concentration level of nitrogen as a fertilizer solution will require as shown in Equation 2 :
Equation 1.
This is pounds of actual nitrogen required and not pounds of fertilizer mix as either a dry or liquid source.
Equation 2. Many chemicals are supplied as either a percentage by weight of a dry or liquid mixture. Therefore the mass of chemical mixture required will depend on the concentration of raw chemical in the mixture. Equation 3 can be used to determine the mass of chemical mixture required to provide the necessary level of raw chemical.
where
Equation 3. M(mixture)=the required mass of chemical mixture (lb.),
M x =the desired mass of chemical X (lb.), and
%X=the percentage of chemical X in the mixture.
If in the above example a 16-4-8 (N-P 2 O 5 -K 2 O) dry fertilizer mix was used, then the required mass of fertilizer mix for 100 gallons of solution is shown in equation 4 :
Therefore 1. 1 pounds of 16-4-8 fertilizer source mix are required to supply 0.17 pounds of nitrogen.
equation 4. Table 1 combines both Equations (1) and (3) to provide the mass of chemical mixture (for example, fertilizer mix) to add to 100 gallons of water to obtain a certain ppm level for the desired chemical. An example using Table 1 is included in the Appendix.
It is important to remember that the A-B-C analysis of a fertilizer label refers to the nitrogen (N), phosphorus oxide (P 2 O 5 ), and potash (K 2 O). Therefore only 44% of the B factor (P 2 O 5 ) refers to actual phosphorous (P), and only 83% of the C factor (K 2 0) refers to actual potassium (K). Equation (3) can be slightly rearranged to solve for M x based on M(mixture), and used to determine the mass of actual P or K contained in a fertilizer mix. For example, in 50 pounds of 16-4-8 fertilizer the mass of P 2 O 5 is shown in Equation 5 :
Similarly, the mass of actual P is shown in Equation 6 :
Equation 5.
Therefore 50 pounds of a 16-4-8 fertilizer mixture contains only 0.88 pounds of actual P. The same procedure can be used to determine that the amount of actual K is 3.32 lbs.
Equation 6. When chemicals are supplied in liquid form, it is more convenient to measure volumes rather than masses or weights. This requires the specific density or specific weight (S x ) of the liquid mixture such as pounds of chemical per gallon of liquid. This property should be provided by the manufacturer or chemical supplier and can be used to simply convert from required lbs. to required gallons. For example a liquid fertilizer provided as a 4-0-8 solution has 4% nitrogen by weight. However, the amount of nitrogen is not known unless the specific weight of the chemical (fertilizer) solution is known, such as 9.6 lb. per gallon. As was previously mentioned, this value varies among chemical mixtures and should be on the chemical label, but may be obtained from the chemical supplier.
Concentration Injection Rates
The previous section described the procedure for mixing particular concentrations of a stock solution. However, many systems will have flowing water with a requirement to maintain a desired concentration of a chemical in that system. This requires injecting a supply mixture at the proper rate to maintain the desired concentration level. The following equation or Tables 2 and 3 can be used to determine the injection rate necessary to maintain the desired concentration of a chemical X. ( Equation 7 )
where
Equation 7. Q i =Injection rate in gallons per minute (gpm),
Q w =Water supply flow rate (gpm),
8.3=Specific weight of water (lb./gal.),
ppm x =Desired ppm level of chemical X,
%X=Percentage of chemical X in the stock solution, and
S x =Specific weight of the stock solution mix (lb. /gal.).
For example, chlorine is to be injected to provide 10 ppm of free chlorine into a micro-irrigation system which has a system flow rate of 550 gpm. ( Equation 8 ) The chlorine stock solution contains 5% free chlorine (sodium hypochlorite source, NaOCl) and has a specific weight of 9.1 lbs. per gallon. Therefore,
Therefore, the injector should be set to provide 0.10 gallons per minute of stock solution into the irrigation system in order to maintain an injected free chlorine level of 10 ppm. The actual ppm of free chlorine throughout the system will depend on how much free chlorine is used by organics in the water supply and in the irrigation system.
Equation 8. If the specific weight of the chemical is close to that of water, Equation (7) can be simplified. The simplified approximation to Equation (7) is shown in Equation 9 :
where
Equation 9. Q i = Injection rate in gallons per minute (gpm),
Q w = Water supply flow rate (gpm),
ppm x = Desired ppm level of chemical X, and
%X = Percentage of chemical X in the stock solution.
In repeating the above chlorine example we get as shown in Equation 10 :
This result is consistent with the previous example. In most cases, Equation (9) may be used. However, if greater accuracy is needed, then use Equation (7). Some injectors are operated to inject on a gallons-per-hour (gph) basis. Therefore, the injector rate determined above must be converted using Equation 11 :
Equation 10.
For example, a flow rate of 0.10 gpm is equal to a flow rate of 6.0 gph.
Equation 11. Injection Volumes and Periods
In the field, flushing velocity can be determined by measured the flow rate during flushing and comparing it with the required minimum values given in Table 1 . Flow rate can be measured by recording the time required to collect a given volume of flush water in a graduated cylinder or other graduated container.Table 2 shows flow rates in gallons per minute (gpm) based on the time required to catch a specified number of gallons. Example: when flushing a 2-inch PVC manifold pipeline in a drip-irrigation system, a grower uses a graduated tank and collects five gallons of water in 20 seconds. This is a flow rate of 15gpm. From Table 1 , the minimum required flow rate for effective flushing of a 2-inch pipeline is 12gpm, therefore the measured flow rate of 15gpm is adequate.
If the flow rate was inadequate, the grower would need to increase it by shutting off flow to other sections of the irrigation system and directing it to this manifold for the flushing operation. This could be done with manual valves used only during flushing. Irrigation system designers should take this need into account when systems are planned and installed.
As another example, in a microsprinkler-irrigated citrus grove, a grower flushes thirty 1-inch PE lateral pipelines at one time. A flow rate of 2.0gpm is measured at the end of each lateral. From Table 1 , a minimum flow rate of 2.7gpm is required to obtain a flush velocity of 1fps, and double this rate (5.4gpm) is recommended for microsprinkler systems. Therefore, the measured flushing velocity is inadequate, and something must be done to increase the discharge rate per lateral. This can be done by simply closing some of the flush valves and flushing fewer laterals at once. The grower should close flush valves until the required flow rate is obtained from the remaining open valves.
In most cases, growers will need to follow this trial-and-error field procedure to calibrate their systems. The number of laterals in a system that can be flushed at the same time depends on many factors, and the easiest way to determine it is to measure it for each irrigation zone by opening and closing flush valves until the required minimum flow rate is obtained. Note: higher velocities than those shown in Table 1 can be used and will be more effective, but values smaller than these should not be used.
In some systems, frequent flushing is required due to poor water quality. This can be done by installing an automatic flush valve on each lateral. These valves are typically normally open valves that close at low pressures (1-3psi) or after a certain time of operation or amount of water has been discharged. Thus, the first surge of water in each lateral is discharged through the valve, carrying debris with it. This approach is effective in many cases, but may not always be adequate since the valves may not always provide the required flush velocity or duration, especially as water quality changes during the year. Thus, it may still be necessary to periodically manually flush these systems.
Summary
Information pertaining to the injection of chemicals into irrigation systems was discussed in terms of concentration injections, bulk injections, quantity of chemicals to be injected, injection system calibration and injection periods. The information was provided to assist irrigation system designers and operators with the chemigation aspects of irrigation system design, scheduling and management.TABLE EXAMPLES
(0.025 gpm/100 gpm) (400 gpm) = 0.10 gpm .
- How much 10-10-10 soluble fertilizer mix is required to mix with water to make a 100 ppm solution of actual nitrogen? From Table 1 a value of 0.83 lb of soluble fertilizer is required per 100 gallons of water (solution) to provide a 100 ppm solution of nitrogen.
- Chlorine is to be injected into an irrigation system which has a water delivery (supply) rate of 400 gpm. The chlorine stock solution contains 8% of "free" chlorine. What stock solution injection rate is necessary to provide 20 ppm of "free" chlorine to the irrigation supply water? Table 2 (or Table 3 ) indicates that to provide a 20 ppm concentration level with an 8% stock solution, approximately 0.025 gpm (1.50 gph) of stock solution injection is necessary per 100 gpm of water delivery rate. Therefore, a 400 gpm water delivery rate requires a stock solution injection rate of:
or
(1.50 gph/100 gpm)(400 gpm) = 6.0 gph .
Therefore injecting an 8% stock solution of chlorine at 0.10 gpm (6.0 gph) into an irrigation system with a system flow rate of 400 gpm will provide approximately 20 ppm of "free" chlorine into the system.
The required amount of fertilizer is:
- A vegetable field is to be fertigated (have fertilizer injected) on a weekly basis with three pounds of nitrogen (N) per 1000 feet of plant bed per week. The field is 25 acres in area with 6000 bedded feet per acre. What size of feeder tank is necessary to hold the required volume of fertilizer mixture if the mixture is a 4-0-8 solution with a specific weight of 10 lb/gal?
=(3 lb/1000 ft) (6000 ft/acre) = 18 lb/acre
=(18 lb/acre) (25 acres)
= 450 lb of N per week.
Table 4 is used to determine the amount of chemical (nitrogen) per gallon of solution. A 4-0-8 solution of fertilizer (S x = 10) has 4% nitrogen.
From Table 4 read the actual amount of N as 0.40 lb per gallon of solution.
Next use Table 5 to determine the required volume of mixture. For a 0.40 lb/gal chemical (nitrogen) density and 450 lb requirement, read 1125 gallons of fertilizer mixture required. Therefore, the supply tank must have a minimum capacity of 1125 gallons to hold the weekly supply of fertilizer.
References
Ingram, D., and B. Hoadley. 1986. Chemical Injection for Drip Irrigation in the Woody Ornamental Nursery. Ornamental Horticulture Commercial Fact Sheet OHC-6. IFAS, Univ. of Florida, Gainesville, FL.Kovach, S.P. 1984. Injection of Fertilizers into Drip Irrigation Systems for Vegetables. IFAS Circular 606, Univ. of Florida, Gainesville, FL.
Nakayama, F.S., and D.A. Bucks. 1986. Trickle Irrigation for Crop Production: Design, Operation, and Management. Elsevier. Amsterdam. 383 p.
Smajstrla, A.G., D.S. Harrison, W.J. Becker, F.S. Zazueta, and D.Z. Haman. 1985. Backflow Prevention Requirements for Florida Irrigation Systems. Bulletin 217. IFAS, Univ. of Florida, Gainesville, FL.
Smajstrla, A.G., D.Z. Haman, and F.S. Zazueta. 1986. Chemical Injection (Chemigation): Methods and Calibration. Agric. Engr. Ext. Report 85-22 (revised). IFAS, Univ. of Florida, Gainesville, FL.
Yeager, T.H. 1986. Fertigation Management for the Wholesale Container Nursery. IFAS Bulletin 231. Univ. of Florida, Gainesville, FL.
Yeager, T.H. and R.W. Henley. 1987. Techniques of Diluting Solution Fertilizers in Commercial Nurseries and Greenhouses. IFAS Circular 695. Univ. of Florida, Gainesville, FL.
Tables
Table 1.
Table 1. The mass (lb) of chemical mixture (i.e., fertilizer mix) to add to 100 gallons of water for different ppm level solutions. PPM Level
Percent Analysis of the Mixture 5 10 15 20 25 30 40 50 (lb per 100 gallons) 10 0.17 0.08 0.06 0.04 0.03 0.03 0.02 0.02 20 0.33 0.17 0.11 0.08 0.07 0.06 0.04 0.03 30 0.50 0.25 0.17 0.12 0.10 0.08 0.06 0.05 40 0.66 0.33 0.22 0.17 0.13 0.11 0.08 0.07 50 0.83 0.41 0.28 0.21 0.17 0.14 0.10 0.08 60 1.00 0.50 0.33 0.25 0.20 0.17 0.12 0.10 70 1.16 0.58 0.39 0.29 0.23 0.19 0.15 0.12 80 1.33 0.66 0.44 0.33 0.27 0.22 0.17 0.13 90 1.49 0.75 0.50 0.37 0.30 0.25 0.19 0.15 100 1.66 0.83 0.55 0.41 0.33 0.28 0.21 0.17 200 3.32 1.66 1.11 0.83 0.66 0.55 0.41 0.33 400 6.64 3.32 2.21 1.66 1.33 1.11 0.83 0.66 600 9.96 4.98 3.32 2.49 1.99 1.66 1.24 1.00 800 13.28 6.64 4.43 3.32 2.66 2.21 1.66 1.33 1000 16.60 8.30 5.53 4.15 3.32 2.77 2.07 1.66
Table 2. Chemical injection rate expressed in gpm of injection rate per 100 gpm of irrigation system flow rate for different desired concentration levels (ppm) and different stock solution concentration levels.1 Desired PPM
Level
Percent Analysis of the Chemical in the Stock Solution 4 8 12 16 20 30 40 50 (gpm of injection per 100 gpm of irrigation rate) 10 0.025 0.013 0.008 0.006 0.005 0.003 0.003 0.002 20 0.050 0.025 0.017 0.013 0.010 0.007 0.005 0.004 30 0.075 0.038 0.025 0.019 0.015 0.010 0.008 0.006 40 0.100 0.050 0.033 0.025 0.020 0.013 0.010 0.008 50 0.125 0.063 0.042 0.031 0.025 0.017 0.013 0.010 60 0.150 0.075 0.050 0.038 0.030 0.020 0.015 0.012 70 0.175 0.088 0.058 0.044 0.035 0.023 0.018 0.014 80 0.200 0.100 0.067 0.050 0.040 0.027 0.020 0.016 90 0.225 0.113 0.075 0.056 0.045 0.030 0.023 0.018 100 0.250 0.125 0.083 0.063 0.050 0.033 0.025 0.020 200 0.500 0.250 0.167 0.125 0.100 0.067 0.050 0.040 400 1.000 0.500 0.333 0.250 0.200 0.133 0.100 0.080 600 1.500 0.750 0.500 0.375 0.300 0.200 0.150 0.120 800 2.000 1.000 0.667 0.500 0.400 0.267 0.200 0.160 1000 2.500 1.250 0.833 0.625 0.500 0.333 0.250 0.200 1. (Caution: these values assume a stock solution specific weight equal to water. If necessary, these numbers may be adjusted by multiplying by the ratio of the specific weight of the chemical solution to the specific weight of water.)
Table 3. Chemical injection rate expressed in gph of injection rate per 100 gpm of irrigation system flow rate for different desired concentration levels (ppm) and different stock solution concentration levels.1 Desired PPM
Level
Percent Analysis of the Chemical in the Stock Solution 4 8 12 16 20 30 40 50 (gph of injection per 100 gpm of irrigation rate) 10 1.50 0.75 0.50 0.38 0.30 0.20 0.15 0.12 20 3.00 1.50 1.00 0.75 0.60 0.40 0.30 0.24 30 4.50 2.25 1.50 1.13 0.90 0.60 0.45 0.36 40 6.00 3.00 2.00 1.50 1.20 0.80 0.60 0.48 50 7.50 3.75 2.50 1.88 1.50 1.00 0.75 0.60 60 9.00 4.50 3.00 2.25 1.80 1.20 0.90 0.72 70 10.50 5.25 3.50 2.63 2.10 1.40 1.05 0.84 80 12.00 6.00 4.00 3.00 2.40 1.60 1.20 0.96 90 13.50 6.75 4.50 3.38 2.70 1.80 1.35 1.08 100 15.00 7.50 5.00 3.75 3.00 2.00 1.50 1.20 200 30.00 15.00 10.00 7.50 6.00 4.00 3.00 2.40 400 60.00 30.00 20.00 15.00 12.00 8.00 6.00 4.80 600 90.00 45.00 30.00 22.50 18.00 12.00 9.00 7.20 800 120.00 60.00 40.00 30.00 24.00 16.00 12.00 9.60 1000 150.00 75.00 50.00 37.50 30.00 20.00 15.00 12.00 1. (Caution: these values assume a stock solution specific weight equal to water. If necessary, these numbers may be adjusted by multiplying by the ratio of the specific weight of the chemical solution to the specific weight of water.)
Table 4. The mass (lb) of active chemical contained per gallon of stock solution (Smx) for different combinations of specific weight and chemical concentration. SpecificWeight (lb/gal)
Percent Concentration of the Active Chemical 4 8 12 16 20 30 40 50 8.0 0.32 0.64 0.96 1.28 1.60 2.40 3.20 4.00 8.5 0.34 0.68 1.02 1.36 1.70 2.55 3.40 4.25 9.0 0.36 0.72 1.08 1.44 1.80 2.70 3.60 4.50 9.5 0.38 0.76 1.14 1.52 1.90 2.85 3.80 4.75 10.0 0.40 0.80 1.20 1.60 2.00 3.00 4.00 5.00 10.5 0.42 0.84 1.26 1.68 2.10 3.15 4.20 5.25 11.0 0.44 0.88 1.32 1.76 2.20 3.30 4.40 5.50 11.5 0.46 0.92 1.38 1.84 2.30 3.45 4.60 5.75
Table 5. Required volume (gal) of chemical mixture to provide a desired level of an active chemical for different concentrations (lb/gal) of the chemical in the stock solution from Table 4. Mass of Chemical Desired(lb)
Smx Mass of Chemical (lb) per gallon of Stock Solution 0.2 0.4 0.6 0.8 1.0 2.0 3.0 4.0 (gallons of stock solution) 20 100 50 33 25 20 10 7 5 40 200 100 67 50 40 20 13 10 60 300 150 100 75 60 30 20 15 80 400 200 133 100 80 40 27 20 100 500 250 167 125 100 50 33 25 150 750 375 250 188 150 75 50 38 200 1000 500 333 250 200 100 67 50 250 1250 625 417 313 250 125 83 63 300 1500 750 500 375 300 150 100 75 350 1750 875 583 438 350 175 117 88 400 2000 1000 667 500 400 200 133 100 450 2250 1125 750 563 450 225 150 113 500 2500 1250 833 625 500 250 167 125
Footnotes
1. This document is BUL250, one of a series of the Agricultural and Biological Engineering Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date May 1998. Reviewed December 2005. Visit the EDIS Web Site at http://edis.ifas.ufl.edu.2. G.A. Clark, Assistant Professor, Extension Irrigation Specialist, Gulf Coast Research and Education Center, Bradenton, FL; D.Z. Haman, Associate Professor and F.S. Zazueta Assistant Professor, Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, 32611.
The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other extension publications, contact your county Cooperative Extension service.
U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Larry Arrington, Dean.
Copyright Information
This document is copyrighted by the University of Florida, Institute of Food and Agricultural Sciences (UF/IFAS) for the people of the State of Florida. UF/IFAS retains all rights under all conventions, but permits free reproduction by all agents and offices of the Cooperative Extension Service and the people of the State of Florida. Permission is granted to others to use these materials in part or in full for educational purposes, provided that full credit is given to the UF/IFAS, citing the publication, its source, and date of publication.