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Publication #HS917

Drip Irrigation: The BMP Era - An Integrated Approach to Water and Fertilizer Management for Vegetables Grown with Plasticulture1

Eric Simonne, David Studstill, Bob Hochmuth, Teresa Olczyk, Michael Dukes, Rafael Munoz-Carpena and Yuncong Li2

In Florida, plasticulture is currently used on approximately 60,000 acres of vegetable (mainly tomato, bell pepper, eggplant, strawberry and watermelon). The Florida drip irrigation school is a one-day educational program offered by the Institute of Food and Agricultural Sciences at the University of Florida focusing on drip irrigation. Through talks, hands-on demonstrations and discussions, the goal of this program is to teach and help vegetable growers better manage fertilizer, water and fumigant applications through drip systems and to prepare them for the BMP era. This program involves county and state-wide Extension faculty and researchers, and members of the irrigation and fertilization industries.

Additional Florida Drip Irrigation Schools are being scheduled regularly thoughout Florida. These programs are offered at no charge, but require pre-registration. Contact your local Extension office to find out when the next drip irrigation school will be offered in your area or check announcements in the Vegetarian newsletter at http://www.hos.ufl.edu/newsletter/vegetarian.htm

This article presents a summary of the information discussed on fertilizer management, irrigation scheduling, and drip system maintenance and troubleshooting. A list of additional references is also included.

Total Maximum Daily Loads (TMDL) and Best Management Practices (BMP): The Basics

As the development of TMDLs and BMPs for vegetables grown in Florida takes place, growers are eager to find out how this process will affect their operations. TMDLs and BMPs have their origin in Federal and State legislations (Table 1). A TMDL is the maximum amount of a pollutant a water body can receive and still meet its water quality standards. BMPs are specific cultural practices that aim at reducing the load of a specific compound, while maintaining economical yields (Table 2). Growers will benefit three ways from having a documented BMP plan. They will be offered (1) a waiver of liability from reimbursement of costs or damages associated with the evaluation, assessment, or remediation of nitrate contamination of ground water (F.S. 376.307); (2) a presumption of compliance with state water quality standards [F.S. 403.067 (7)(d)]; and, (3) an oportunity to receive cost-share reimbursement for implementation of selected BMPs [F.S. 570.085(1)].

The BMPs applicable to vegetable production will be included in the Agronomic and Vegetable Crop Water Quality and Water Quantity BMP Manual for Florida for row crops and vegetables, which is under development. BMPs are 1-to-3 page long chapters that include a working definition of the topic, list specific things to do (BMPs) as well as things to avoid (pitfalls), and present existing applicable technical criteria together with additional references. As the new legislative mandate for Florida agriculture, the BMPs largely embrace IFAS fertilization and irrigation recommendations.

Principles of Fertilization Management in the BMP Era

Fertilization principle 1. With plasticulture, think in terms of rows Y and not in terms of field surface for irrigation and fertilization. For bare ground production of vegetables, fertilizer and irrigation rates are typically expressed in lbs/acre and gallons/acre, respectively. However, when vegetables are grown with plasticulture, the number of linear feet of beds in an acre becomes more important than the actual surface of the field. Growers should think in terms of lbs/100 linear bed feet (lbf) for fertilization injections and gallons/100 lbf for irrigation, and take into account the bed spacing. Typical bed spacings are used in the IFAS fertilization recommendations for plasticulture (Table 3).

Fertilization principle 2. Plants need all the essential nutrients. Sixteen essential mineral elements are recognized as the essential elements. Carbon (C), hydrogen (H), and oxygen (O) are supplied by air and water. Nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S) are the macronutrients. Boron (B), chlorine (Cl), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), and zinc (Zn) are the micronutrients. All these elements are essential because (1) vegetable crops cannot complete their life cycle without all of them, (2) typical deficiency symptoms appear when one is not available, and symptoms disappear upon the application of the deficient element, and (3) each element has a specific metabolic role. The overall success of a fertilizer program is determined by the essential element which is provided in smallest quantity (limiting factor). Adequate fertilization together with soil nutrient reserves should provide all these elements in adequate quantities, thereby ensuring that mineral nutrition is not limiting vegetable growth and yield.

Fertilization principle 3. Soil test and follow the recommendation. The only scientific method to apply fertilizer to vegetables is to use a calibrated soil test. A soil sample has to be recent, representative, and large enough to ensure valid results. The soil test recommendation has to be understood, and properly implemented. Typically, 20% to 50% of N and K2O, and 100% of P2O5 and micronutrients are applied preplant. The remaining 50% to 80% of N and K2O are injected through the drip system. A fertilizer program may be simply designed from IFAS recommendation using a spreadsheet format (Fig. 1). Correctly implementing soil test results is essential in increasing nutrient management to a level acceptable in the BMP era (Table 4).

Figure 1. 

Sample spreadsheet for designing a fertigation program for a 1-acre watermelon field planted on 8-ft centers. Beginning with soil-test results (top section), this worksheet that uses IFAS recommendations provides a weekly schedule for fertigation with liquid 8-0-8 (right column).


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Some growers do not believe that economical vegetable yields can be produced with IFAS fertilizer recommendations. Fertilizer recommendations are based on multiple trials and correspond to the fertilizer rates above which no yield response is likely to occur. IFAS fertilizer rate may not be optimal if excessive irrigation is applied. In this case, the solution is to adjust irrigation management, rather than increasing fertilizer rates. Fertilizer applications in excess of the recommended rate should not be made on a routine basis, but only when exceptional circumstances (leaching rain) occur or based on the results of petiole sap test and/or foliar nutrient analyses. IFAS definition of a leaching rain is 3 in. of rain in 3 days or 4 in. of rain in 7 days.

Fertilization principle 4. Monitor crop nutritional status and discover how healthy the vegetable plants are. The nutritional status of vegetables may be monitored with sap test or foliar analysis early in the season (from transplanting to fruit set). A representative sample for petiole and leaf analysis should be made with at least 20 leaves selected randomly throughout the field from most recently, fully mature leaves. For sap analysis, blades should be carefully separated from the petiole and discarded. Fig. 2 shows how to collect sap and perform a reading. For leaf analysis, the sampled part should be the blade and its petiole attached.

Figure 2. 

Sap testing for vegetables involves separating the petiole from the leaf blade, (2.1) calibrating the nitrate (NO3-N) and potassium (K) ion specific electrodes (Cardi meter shown here) with standard solutions, (2.2) extracting the sap, (2.3) collecting the sap from the press, and (2.4) placing a droplet of sap on the electrode. A hydraulic press may be needed only when few petioles are available or when petioles contain little sap as may occur with strawberry. In most cases, a garlic press will be an adequate tool to extract the sap. Readings should be compared to published sufficiency ranges.


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Figure 2. 

Sap testing for vegetables involves separating the petiole from the leaf blade, (2.1) calibrating the nitrate (NO3-N) and potassium (K) ion specific electrodes (Cardi meter shown here) with standard solutions, (2.2) extracting the sap, (2.3) collecting the sap from the press, and (2.4) placing a droplet of sap on the electrode. A hydraulic press may be needed only when few petioles are available or when petioles contain little sap as may occur with strawberry. In most cases, a garlic press will be an adequate tool to extract the sap. Readings should be compared to published sufficiency ranges.


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Figure 2. 

Sap testing for vegetables involves separating the petiole from the leaf blade, (2.1) calibrating the nitrate (NO3-N) and potassium (K) ion specific electrodes (Cardi meter shown here) with standard solutions, (2.2) extracting the sap, (2.3) collecting the sap from the press, and (2.4) placing a droplet of sap on the electrode. A hydraulic press may be needed only when few petioles are available or when petioles contain little sap as may occur with strawberry. In most cases, a garlic press will be an adequate tool to extract the sap. Readings should be compared to published sufficiency ranges.


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Figure 2. 

Sap testing for vegetables involves separating the petiole from the leaf blade, (2.1) calibrating the nitrate (NO3-N) and potassium (K) ion specific electrodes (Cardi meter shown here) with standard solutions, (2.2) extracting the sap, (2.3) collecting the sap from the press, and (2.4) placing a droplet of sap on the electrode. A hydraulic press may be needed only when few petioles are available or when petioles contain little sap as may occur with strawberry. In most cases, a garlic press will be an adequate tool to extract the sap. Readings should be compared to published sufficiency ranges.


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Principles of Irrigation Scheduling in the BMP Era

Irrigation scheduling is knowing when to start irrigation and how much to apply, in a way that satisfies crop water needs, conserves water, and does not leach mobile nutrients. Irrigation scheduling requires (1) a target water volume, (2) guidelines on how and when to split irrigation, (3) a method to account for rainfall, and (4) a practical method to monitor soil moisture.

Irrigation principle 1. Irrigation amount must reflect crop water use, no more, no less. Irrigation amounts may be estimated using historical weather data, climatic measurement in real-time, class A pan evaporation, atmometers, and empirical amounts (Table 5, Fig. 3). Empirical values have the advantage of being simple. However, they often result in excessive irrigation early in the season, and insufficient ones later in the season. This method alone (without monitoring of soil moisture) is unlikely to be part of the BMPs.

Figure 3. 

Tools and techniques available to estimate evapotranspiration and irrigation needs: (3.1) weather data may be simply downloaded from a small automated weather station to calculate reference evapotranspiration (ETo) and (3.2) water loss in the reservoir of the atmometer mimics ETo.


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Figure 3. 

Tools and techniques available to estimate evapotranspiration and irrigation needs: (3.1) weather data may be simply downloaded from a small automated weather station to calculate reference evapotranspiration (ETo) and (3.2) water loss in the reservoir of the atmometer mimics ETo.


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Irrigation principle 2. Irrigation amount should not exceed soil water holding capacity. Otherwise, water is wasted and mobile nutrients are leached. How far water moves down the soil profile is a rather abstract concept because it is not visible. However, it is possible to visualize soil water movements by using colored dyes (Fig. 4). Wetting patterns are affected by soil type, irrigation amount, and emitter spacing (Table 6). In the sandy soils of Hillsborough and Hendry counties, the wetting front reached maximum rooting depths at irrigation rates nearing 80 gallons/100ft.

Figure 4. 

Soluble blue dye may be used to visualize wetting patterns and understand how irrigation volume affects water movement in the bed. For short irrigation times (1 hour) a more even water distribution pattern may be expected with a 4-in emitter spacing (4.1) than with an 12-in emitter spacing (4.2). Flow rates were 33 gal/100 ft/hr for the 4-in emitter spacing, and 30 gal/100ft/hr for the 12-in emitter spacing. The presence of an impermeable clay layer at the 10-in depth (in Gadsden county) resulted in lateral movement as shown in (4.3) where the blue dye is in the alley (between the 3rd and 4th bed from the right) after 6 hours of irrigation delivering 180 gal/100ft. The presence of water and soluble nutrients in the row middles will likely promote weed growth. Wetting patterns in the very compacted beds used for strawberry production in Hillsborough county are rectangular which corresponds to an increase in lateral water movement as shown in (4.4) after a 6-hr irrigation that delivered 144 gal/100 ft with a 12-in emitter spacing.


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Figure 4. 

Soluble blue dye may be used to visualize wetting patterns and understand how irrigation volume affects water movement in the bed. For short irrigation times (1 hour) a more even water distribution pattern may be expected with a 4-in emitter spacing (4.1) than with an 12-in emitter spacing (4.2). Flow rates were 33 gal/100 ft/hr for the 4-in emitter spacing, and 30 gal/100ft/hr for the 12-in emitter spacing. The presence of an impermeable clay layer at the 10-in depth (in Gadsden county) resulted in lateral movement as shown in (4.3) where the blue dye is in the alley (between the 3rd and 4th bed from the right) after 6 hours of irrigation delivering 180 gal/100ft. The presence of water and soluble nutrients in the row middles will likely promote weed growth. Wetting patterns in the very compacted beds used for strawberry production in Hillsborough county are rectangular which corresponds to an increase in lateral water movement as shown in (4.4) after a 6-hr irrigation that delivered 144 gal/100 ft with a 12-in emitter spacing.


[Click thumbnail to enlarge.]
Figure 4. 

Soluble blue dye may be used to visualize wetting patterns and understand how irrigation volume affects water movement in the bed. For short irrigation times (1 hour) a more even water distribution pattern may be expected with a 4-in emitter spacing (4.1) than with an 12-in emitter spacing (4.2). Flow rates were 33 gal/100 ft/hr for the 4-in emitter spacing, and 30 gal/100ft/hr for the 12-in emitter spacing. The presence of an impermeable clay layer at the 10-in depth (in Gadsden county) resulted in lateral movement as shown in (4.3) where the blue dye is in the alley (between the 3rd and 4th bed from the right) after 6 hours of irrigation delivering 180 gal/100ft. The presence of water and soluble nutrients in the row middles will likely promote weed growth. Wetting patterns in the very compacted beds used for strawberry production in Hillsborough county are rectangular which corresponds to an increase in lateral water movement as shown in (4.4) after a 6-hr irrigation that delivered 144 gal/100 ft with a 12-in emitter spacing.


[Click thumbnail to enlarge.]
Figure 4. 

Soluble blue dye may be used to visualize wetting patterns and understand how irrigation volume affects water movement in the bed. For short irrigation times (1 hour) a more even water distribution pattern may be expected with a 4-in emitter spacing (4.1) than with an 12-in emitter spacing (4.2). Flow rates were 33 gal/100 ft/hr for the 4-in emitter spacing, and 30 gal/100ft/hr for the 12-in emitter spacing. The presence of an impermeable clay layer at the 10-in depth (in Gadsden county) resulted in lateral movement as shown in (4.3) where the blue dye is in the alley (between the 3rd and 4th bed from the right) after 6 hours of irrigation delivering 180 gal/100ft. The presence of water and soluble nutrients in the row middles will likely promote weed growth. Wetting patterns in the very compacted beds used for strawberry production in Hillsborough county are rectangular which corresponds to an increase in lateral water movement as shown in (4.4) after a 6-hr irrigation that delivered 144 gal/100 ft with a 12-in emitter spacing.


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Theoretical highest irrigation amounts can be simply calculated based on the soil physical properties. For a soil where the wetting width is 12 inches (6 inches each side of the drip tape), assuming a 0.75 in/foot soil water holding capacity and allowing a 50% soil water depletion, the theoretical largest water amounts that can be stored in the soil are 24 gal/100 ft within the top 12 inches, 36 gal/100 ft within the top 18 inches, and 48 gal/100 ft within the top 24 inches. These numbers can be used as guidelines. Actual amount that can be applied in one irrigation also depends on the rate of crop evapotranspiration, number of drip tapes, and soil type. The difference between observed (Table 6) and theoretical maximum water holding capacity may be due to bed compaction and wetting widths greater than 12 in. Irrigation greater than the maximum water holding capacity is likely to leach mobile nutrients below the root zone. This is why irrigation, fertilization, BMPs and TMDLs are tied together.

Irrigation principle 3. Rainfall contributes little to replenish soil moisture because of the plastic mulch. Several IFAS fertilizer recommendations for bare ground production allow for additional N and K fertilizer after leaching rains. Leaching rains are defined as three inches of rain in three days, or four inches in seven days. However, it would take less rain to leach through the soil profile in the coarse soils found in South Florida. Since the plastic mulch protects the bed from rainfall, there is no need to apply additional fertilizer after a leaching rain. However, when the field gets flooded, mobile nutrients may be leached out of the root zone or carried out of the field through surface run off. The need for additional fertilizer may be assessed after field drainage by monitoring sap tests levels of nitrate and potassium. Another consequence of using the plastic mulch is that an irrigation may be still needed after a small rain. Soil moisture measurements may be used to assess the need for additional irrigation.

Irrigation principle 4. Monitor soil moisture level daily to discover how much water stress the crop is exposed to. Soil moisture may be reported in terms of soil water tension (SWT) or volumetric water content (VWC). SWT represents the suction force that is necessary to free soil water from the soil attraction. The higher the value of SWT, the greater is the force needed. In some publications, SWT values are reported as negative values. The negative (-) sign is there to reflect the fact that the attraction is generated by the soil particles and therefore the plant has to spend energy to absorb water. SWT may be expressed in atmospheres (atm), bar (b), or kilo Pascals (kPa; the international unit). The conversion between units is 1 atm = 1.013 b = 101.3 cb = 100 kPa. The recommended range for vegetable production is to maintain SWT between 6 to 8 cb (field capacity) and 15 cb. Vegetables may tolerate SWT up to 25 cb without yield reduction on loamy soils. However, sandy soils with SWT above 15 cb may be difficult to re-wet. On the other hand, VWC represents the volume of water present in a volume of soil. VWC for sandy soils range between 14% and 18%, whereas it may reach 38% in clay soils. Instruments available for routine monitoring of soil moisture for vegetable crops are tensiometers, time domain reflectometry probes (TDR), and dielectric probes (Fig. 5). Table 7 summarizes a comparison of these instruments in terms of cost, accuracy, response time, preparation, installation, management, and durability.

Figure 5. 

Soil moisture measuring tools currently available for vegetable crops.


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Irrigation principle 5. Keep irrigation records daily. Vegetable growers are required to keep pesticide records. Fertilization records are usually kept in relation to soil testing and implementing the recommendations. However, vegetable growers seldom document their irrigation practices. For example, a daily log could contain soil moisture measurements (SWT or VWC) at selected depths, rainfall, an estimate of weather demand for water (evapotranspiration), and irrigation amount (gallons/field or duration of irrigation). Most growers who are already keeping irrigation records find them to be a useful management tool. It is likely that the documentation requested to support a BMP plan will include irrigation records, at the farm level and possibly at the field level.

Drip System Maintenance and Troubleshooting

Application uniformity of 85% to 95% is expected from a new, well-designed drip irrigation system (Fig. 6). As the irrigation system is used for water and fertilizer applications throughout the growing season, the application uniformity may remain the same if the system is well managed, but will most likely decline with time. A comprehensive maintenance plan will reduce the adverse effects of the agents that reduce application uniformity: small solids in suspension, organic matter, micro-organisms, and chemical residues on application uniformity (Fig. 7). Without a maintenance plan, the risk of complete emitter clogging and crop loss becomes real.

Figure 6. 

Uniform growth and yield may be expected with drip irrigation (7.1) as shown here with strawberry. When the drip tape is not placed in the center, one row may be taller than the other (7.2) as shown here with bell pepper.


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Figure 6. 

Uniform growth and yield may be expected with drip irrigation (7.1) as shown here with strawberry. When the drip tape is not placed in the center, one row may be taller than the other (7.2) as shown here with bell pepper.


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Figure 7. 

Accumulation of precipitates around a drip-tape emitter (8.1) may result in an uneven water distribution pattern (8.2).


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Figure 7. 

Accumulation of precipitates around a drip-tape emitter (8.1) may result in an uneven water distribution pattern (8.2).


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Every vegetable grower who uses drip irrigation should recognize that PREVENTION IS THE BEST MEDICINE in drip system maintenance. A maintenance plan should include (1) a filtration system, (2) chlorination and acidification, (3) flushing, and (4) regular observation of irrigation system components (Table 8 and Table 9).

References and Additional Readings

Related Websites

North Florida Research and Education Center - Suwannee Valley: http://nfrec.ifas.ufl.edu/publications/svreports.shtml [September 2011]

Horticultural Sciences Department: http://www.hos.ufl.edu

Florida Department of Environmental Protection: http://www.dep.state.fl.us/water

Suwannee River Water Management District: http://www.srwmd.state.fl.us/

Small Scale Irrigation for Arid Zones (FAO): http://www.fao.org/docrep/W3094E/w3094e00.htm#TopOfPage

Crop Evapotranspiration - Guidelines for Computing Crop Water Requirements - FAO Irrigation and Drainage Paper 56: http://www.fao.org/docrep/X0490E/X0490E00.htm

University of Florida Extension Soil Testing Laboratory: http://soilslab.ifas.ufl.edu/#ESTL

NRCS Nutrient Management homepage: http://www.nrcs.usda.gov/TECHNICAL/nutrient.html

General Irrigation

Soil Plant Water Relationships, D.Z. Haman and F.T. Izuno, Circ. 1085, Fla. Coop. Ext. Ser., IFAS, Univ. of Fla. http://edis.ifas.ufl.edu/ae021

Basic Irrigation Terminology, F.T. Izuno and D.Z. Haman, Fact Sheet AE-66, Fla. Coop. Ext. Ser., IFAS, Univ. of Fla. http://edis.ifas.ufl.edu/ae115

Principles and Practices of Irrigation Management for Vegetables, E.H. Simonne, M.D. Dukes, D.Z. Haman, pp.31-37, In: D.N. Maynard and S.M. Olson (eds.) Vegetable Production Guide for Florida, Univ. of Fla, Gainesville, FL.

Drip System Maintenance

Treating Irrigation Systems with Chlorine, G.A. Clark and A.G. Smajstrla, Circ. 1039, Fla. Coop. Ext. Ser., IFAS, Univ. of Fla. http://edis.ifas.ufl.edu/ae080

Injection of Chemicals Into Irrigation Systems: Rates, Volumes, and Injection Periods, G.A. Clark, D.Z. Haman and F.S. Zazueta, Bul. 250, Fla. Coop. Ext. Ser., IFAS, Univ. of Fla. http://edis.ifas.ufl.edu/ae116

Causes and Prevention of Emitter Plugging in Microirrigation Systems, D.J. Pitts, D.Z. Haman and A.G. Smajstrla, Bul. 258, Fla. Coop. Ext. Ser., IFAS, Univ. of Fla. http://edis.ifas.ufl.edu/ae032

Drip System Components

Micro-irrigation on Mulched Bed Systems: Components, System Capacities, and Management, G.A. Clark, C.D. Stanley, and A.G. Smajstrla, Bul. 245, Fla. Coop. Ext. Ser., IFAS, Univ. of Fla. http://edis.ifas.ufl.edu/ae042

Media Filters for Trickle Irrigation in Florida, D.Z. Haman, A.G. Smajstrla, and F.S. Zazueta, Fact Sheet AE-57, Fla. Coop. Ext. Ser., IFAS, Univ. of Fla. http://edis.ifas.ufl.edu/wi008

Screen Filters in Trickle Irrigation Systems, D.Z. Haman, A.G. Smajstrla and F.S. Zazueta, Fact Sheet AE-69, Fla. Coop. Ext. Ser., IFAS, Univ. of Fla. http://edis.ifas.ufl.edu/wi009

Principles of Micro Irrigation, D.Z. Haman and F.T. Izuno, Fact Sheet AE-24, Fla. Coop. Ext. Ser., IFAS, Univ. of Fla. http://edis.ifas.ufl.edu/wi007

Chemical Injection Methods for Irrigation, D.Z. Haman, A.G. Smajstrla and F.S. Zazueta, Circ. 864, Fla. Coop. Ext. Ser., IFAS, Univ. of Fla. http://edis.ifas.ufl.edu/wi004

Measuring Pump Capacity for Irrigation System Design, A.G. Smajstrla, D.Z. Haman and F.S. Zazueta, Circ. 1133, Fla. Coop. Ext. Ser., IFAS, Univ. of Fla. http://edis.ifas.ufl.edu/ae067

Florida Backflow Prevention Requirements for Agricultural Irrigation Systems, A.G. Smajstrla, D.S. Harrison, W.J. Becker, F.S. Zazueta, and D.Z. Haman, Bul. 217, Fla. Coop. Ext. Ser., IFAS, Univ. of Fla.

Drip System Design

Water Hammer in Irrigation Systems, G.A. Clark, A.G. Smajstrla, and D.Z. Haman, Circ. 848, Fla. Coop. Ext. Ser., IFAS, Univ. of Fla. http://edis.ifas.ufl.edu/ae066

Design Tips for Drip Irrigation of Vegetables, D.Z. Haman and A.G. Smajstrla, Fact Sheet AE-260, Fla. Coop. Ext. Ser., IFAS, Univ. of Fla. http://edis.ifas.ufl.edu/ae093

Efficiencies of Florida Agricultural Irrigation Systems, A.G. Smajstrla, B.J. Boman, G.A. Clark, D.Z. Haman, D.S. Harrison, F.T. Izuno, D.J. Pitts and F.S. Zazueta, Bul. 247, Fla. Coop. Ext. Ser., IFAS, Univ. of Fla. http://edis.ifas.ufl.edu/ae110

Field Evaluation of Microirrigation Water Application Uniformity, A.G. Smajstrla, B.J. Boman, D.Z. Haman, D.J. Pitts, and F.S. Zazueta, Bul. 265, Fla. Coop. Ext. Ser., IFAS, Univ. of Fla. http://edis.ifas.ufl.edu/ae094

Flushing Procedures for Microirrigation Systems, A.G. Smajstrla and B.J. Boman, Bul. 333, Fla. Coop. Ext. Ser., IFAS, Univ. of Fla. http://edis.ifas.ufl.edu/wi013

Irrigation Scheduling

Microirrigation in Mulched Bed Production Systems: Irrigation Depths, G.A. Clark and D.Z. Haman, Fact Sheet AE-49, Fla. Coop. Ext. Ser., IFAS, Univ. of Fla. http://edis.ifas.ufl.edu/ae049

Using Reference Evapotranspiration Data, G.A. Clark, Fact Sheet 251, Fla. Coop. Ext. Ser., IFAS, Univ. of Fla. http://edis.ifas.ufl.edu/AE073

Scheduling Tips for Drip Irrigation of Vegetables, D.Z. Haman and A.G. Smajstrla, Fact Sheet AE-249, Fla. Coop. Ext. Ser., IFAS, Univ. of Fla. http://edis.ifas.ufl.edu/ae092

Alternatives of Low Cost Soil Moisture Monitoring Devices for Vegetable in South Miami-Dade County. R. Muñoz-Carpena, Y. Li and T. Fact Sheet AE-230, Fla. Coop. Ext. Ser., IFAS, Univ. of Fla. http://edis.ifas.ufl.edu/ae230

Using Tensiometers for Vegetable Irrigation Scheduling in Miami-Dade County, T. Olczyk, Y. Li, and R. Munoz-Carpena, FactSheet ABE 326, Fla. Coop. Ext. Ser., IFAS, Univ. of Fla. http://edis.ifas.ufl.edu/tr015

On-farm Irrigation Scheduling for Vegetables Using the Watermark Soil Moisture Sensor, E. Simonne, A. Andreasen, D. Dinkins, J. Fletcher, R. Hochmuth, J. Simmons, M. Sweat, and A. Tyree, Proceedings of the 2001 Florida Agricultural Conference & Trade Show, Lakeland FL, October 2-3, 2001, pp. 17-22.

Basic Irrigation Scheduling in Florida, A.G. Smajstrla, B.J. Boman, D.Z. Haman, F.T. Izuno, D.J. Pitts and F.S. Zazueta, Bul. 249, Fla. Coop. Ext. Ser., IFAS, Univ. of Fla. http://edis.ifas.ufl.edu/ae111

Irrigation Scheduling with Evaporation Pans, A. G. Smajstrla, F. S. Zazueta, G. A. Clark, and D. J. Pitts, Bul. 254, Fla. Coop. Ext. Ser., IFAS, Univ. of Fla. http://edis.ifas.ufl.edu/AE118

Trickle Irrigation Scheduling. I: Duration of Water Application, A.G. Smasjtrla, D.S. Harrison, and G.A. Clark, Bul. 204, Fla. Coop. Ext. Ser., IFAS, Univ. of Fla.

Potential Impacts of Improper Irrigation System Design, A.G. Smajstrla, F.S. Zazueta, and D.Z. Haman, Fact Sheet AE-73, Fla. Coop. Ext. Ser., IFAS, Univ. of Fla. http://edis.ifas.ufl.edu/ae027

Tensiometers for Soil Moisture Measurement and Irrigation Scheduling, A.G. Smajstrla and D.S. Harrison, Circ-487, Fla. Coop. Ext. Ser., IFAS, Univ. of Fla. http://edis.ifas.ufl.edu/ae146

Tensiometer Service, Testing and Calibration, A.G. Smajstrla and D.J. Pitts, Bul. 319, Fla. Coop. Ext. Ser., IFAS, Univ. of Fla. http://edis.ifas.ufl.edu/ae086

Nutrient Management

Commercial Vegetable Fertilization Principles, G.J. Hochmuth and E.A. Hanlon, Circ. 225-E, Fla. Coop. Ext. Ser., IFAS, Univ. of Fla. http://edis.ifas.ufl.edu/cv009

IFAS Standardized Fertilization Recommendations for Vegetable Crops, G.J. Hochmuth and E.A. Hanlon, Circ. 1152, Fla. Coop. Ext. Ser., IFAS, Univ. of Fla. http://edis.ifas.ufl.edu/cv002

Plant Petiole Sap-testing for Vegetable Crops, G. Hochmuth, Circ. 1144, Fla. Coop. Ext. Ser., IFAS, Univ. of Fla. http://edis.ifas.ufl.edu/cv004

Fertilizer Application and Management for Micro (Drip)-irrigated Vegetables, G.J. Hochmuth and A.G. Smajstrla, Cir. 1181, Fla. Coop. Ext. Ser., IFAS, Univ. of Fla. http://edis.ifas.ufl.edu/cv141

Soil and Fertilizer Management for Vegetable Production in Florida, pp.3-14, Simonne, E.H. and G.J. Hochmuth, In: D.N. Maynard and S.M. Olson (eds.) Vegetable Production Guide for Florida, Univ. of Florida, Gainsville, FL.

Tables

Table 1. 

A brief legislative history of the Best Management Practices (BMP).

Year

Origin

Legislation

Public law #

1948

US Congress

Water Pollution Control Act (WPCA)

89-234

1965

US Congress

Amendment to the WPCA created fed. approved water quality standards for interstate waters. Name changed to Water Quality Act

89-234

1972

US Congress

Amendment 303(d) to WQA introduced Total Maximum Daily Loads (TMDL). Name changed to Federal Water Pollution Control Act (FWPCA)

92-500

1977

US Congress

FWPCA amended to introduce BMP development and renamed Clean Water Act

95-217

1987

US Congress

Amendments 304(1) and 319 introduced the development of numerical rather than qualitative water quality criteria. New name: Water Quality Act

100-4

1987

Florida Legislature

The Florida Surface Water Improvement and Management (SWIM) ACT created a program which focuses on preservation of the state's water bodies that were in good condition, and restoration of some of its most significant water bodies.

373.451 - 373.4595

Table 2. 

Driving forces behind the vegetable BMPs.

BMPs are meant to be

Comments

Educational

Through teaching and demonstration, the BMP process aims at raising the level of nutrient and irrigation management of growers.

Economically sound

BMP implementation is not aimed at reducing production or crop value.

Environmentally robust BMPs are tools to achieve the TMDLs and therefore reduce nutrient discharge.
Based on science Only science-based information will separate the facts from the perceptions.
Table 3. 

Typical bed spacing used in vegetables production and corresponding linear bed feet per acre. This spacing is used for fertilizer recommendations. When a different bed spacing is used, fertigation should be adjusted accordingly.

Bed Spacing

Vegetable Crop

Linear Bed Feet in One Acre

4

Strawberry, lettuce

10,890

5

Muskmelon

8,712

6

Bell pepper, tomato, eggplant, cucumber, summer squash, cabbage, broccoli, cauliflower

7,260

8

Watermelon

5,445

Linear bed feet per acre are calculated by dividing 43,560 sq-ft per acre by the bed spacing.
Table 4. 

Levels of fertilizer and water management and corresponding fertilization and irrigation practices for vegetables.

Management Level

Nutrient Management

Irrigation Management

0 - None Guessing Guessing
1 - Very low Soil testing and still guessing Using the "feel and see" method
2 - Low

Soil testing and implementing 'a' recommendation (not sure about how to correctly implement IFAS recommendations)

Using systematic irrigation for the entire growing season based on irrigation time (for example, three hours per day) and not water volume applied
3 - Intermediate Soil testing, understanding IFAS recommendations, and correctly implementing them

Using a soil moisture measuring tool to start irrigation

4 - Advanced Soil testing, understanding IFAS recommendations, correctly implementing them, and monitoring crop nutritional status

Using a soil moisture measuring tool to schedule irrigation and apply amounts based on a budgeting procedure

5 - Recommended

Soil testing, understanding IFAS recommendations, correctly implementing them, monitoring crop nutritional status, and practice year-round nutrient management and/or following BMPs

Adjusting irrigation to plant water use, and using a dynamic water balance based on a budgeting procedure and plant stage of growth, together with a soil moisture measuring tool and/or following BMPs

Table 5. 

Comparison of methods available for determining crop water use and their adoption level by the vegetable industry in Florida. Although the most promising method uses real-time potential evapotranspiration data, empirical methods are most commonly used by the industry.

Method

Principle

Advantages

Limitation

Level of Adoption by Industry

Historical potential evapotranspiration

Weather data from the past 30+ years are averaged to estimate ETo

IFAS recommended method

Crop water use (ETc) simply calculated as ETc=Kc x ETo, where Kc is the crop coefficient

Year to year variability may be +/- 20% of the historical average

Most Kc values available are for bare-ground production

None

Real time potential evapotranspiration

ETo is computed daily using site-specific, current weather data

Data more available as the FAWN system expands

Increasingly attractive as the cost of small, on-farm weather stations keeps decreasing

Crop water use (ETc) simply calculated as ETc = Kc x ETo, where Kc is the crop coefficient.

Variable Kc allows daily irrigation adjustment depending on crop age and weather demand.

Likely to be part of BMPs

Most Kc values available are for bare-ground production

Currently limited, but with real potential

Class A pan evaporation (Ep)

ETo is related to water loss from a free water surface

Crop water use (ETc) simply calculated as ETc = CF x Ep, where CF is the crop factor.

For practical purposes, CF and Kc can be inter-converted

Principle can be used with pans other the expensive class A pan

Variable Kc allows daily irrigation adjustment depending on crop age and weather demand

Possible alternative BMP method

Most CF values available are for bare-ground production

Old method that was not adopted widely

Virtually unused; should be replaced by the method above

Atmometers

Water loss from a ceramic plate with a canvas cover mimics ETo

Simple principle: water loss from a small surface closely estimates ETo

Units are rather inexpensive

Calibration data usually not available

None

Empirical methods

Rely on experience and individual knowledge to estimate irrigation needs

Simple to implement

Most farmers' favorite

Based on experience, rather than science

Typically results in over-irrigation early in the season, and sometimes under-irrigation during peak demand periods

Likely to be insufficient in the BMP era

Industry standard

Table 6. 

Effect of irrigation amount on water movement in three vegetable growing areas of Florida. Increasing irrigation volume increases vertical downward movement at a faster rate than the lateral movement. Emitter-to-emitter coverage (length) was reached after 3 hours with 12-in emitter spacings, while it was reached in only one hour with 4-in emitter spacing.

Irrigation volume (gph/100 ft)

Irrigation Time (hr)

Vertical depth (in)

Width (in)

Length (in)

Vertical depth (%)

Width (%)

Length (%)

Hillsborough County - 12-in emitter spacing drip tape (27 gal/100ft/hr)

27

1

9

11

10

66

25

83

54

2

12

15

11.5

73

38

92

81

3

14

16

11

97

43

100

108

4

13

17

11

97

51

100

162

6

17

20

12

110

54

100

216

8

17

22

12

110

64

100

Hendry County - 18-in emitter spacing drip tape (24 gal/100ft/hr)

12

0.5

7

6

6

50

17

33

24

1

9

7

7

61

19

39

36

1.5

10

9

8

68

23

43

48

2

10

9

8

68

24

46

72

3

12

10

11

80

26

59

96

4

17

9

14

115

25

80

144

6

15

10

10

102

28

80

192

8

13

10

9

100

28

80

Gadsden County - 4-in emitter spacing drip tape (33 gal/100ft/hr)

33

1

6

8

4

60

22

100

66

2

8

12

4

80

33

100

132

4

7

20

4

70

56

100

198

6

8

23

4

80

64

100

Vertical depth (V) = vertical length from the top of the bed to the bottom of the blue ring; Vmax = 15 in, except in Gadsen co. where a clay layer was found at the 10-in depth). Width = Hortizontal length perpendicular to the bed axis at the widest point of the wetting bulb; Wmax = bed width = 36 in at all three locations. Length = Horizontal length parallel to the bed axis at the widest point of the wetting bulb; Lmax = emitter spacing.
Table 7. 

Comparison of soil moisture measuring devices available to vegetable growers. While cost of the unit is always an issue, adoption of these techniques has been mainly determined by maintenance, reliability and dedication issues.

Point of comparison

Tensiometer

Granular Matrix Sensor (GMS)

Dielectric probe

Time Domain Reflectometry (TDR) probe

Principle of operation

Direct measurement of soil suction: changes in moisture in a porous cup in equilibrium with the soil can be expressed as changes in air pressure inside the cup

Indirect measurement of soil suction: in saturated saline condition, electrical conductivity is a function of soil moisture tension

Indirect measurement of water content: the soil dielectric constant depends on soil moisture and can be measured as an electrical signal (in volts)

Indirect measurement of water content: the soil dielectric constant depends on soil moisture and can be measured as an the speed of travel of wave signal (in seconds)

Unit reported to user

Soil water tension (cb or kPa)

Soil water tension (cb or kPa)

Volumetric water content (%)

Volumetric water content (%)

Cost for a complete operating unit

$70-110

$400-480

($40 for 2 GMS blocks, $400 for reader)

$525 ($150 for sensor, $375 for reader)

$585 ($260 for sensor, $325 for reader)

Life span

Several years

Few years for sensors, many years for reader

Many years

Many years

Fragility and risk of damage

Very high

Low to very low

Low

Very low

Set-up

Involved

Minor

Minimal

Minimal

Maintenance

High, very important

None

None

None

Time needed for equilibrium with soil (first reading)

Few hours

Few hours

Instantaneous

Instantaneous

Change in moisture reading in response to change in soil moisture

Fast

Fast for fine textured or well compacted soils, but slow for coarse-textured soils

Immediate

Immediate

Need for calibration

No (only adjustment)

Yes

Yes

No (yes)

Table 8. 

Components of the maintenance-is-best-medicine program for drip irrigation.

Component

Description and Comments

Few Do's and No-no's!

Filtration

Use 200-mesh filter or equivalent when ground water is used

Consider media filters when surface water is used. Angular sand particles should be used.

Centrifugal sand separators may be used where inorganic particle levels greater than 50 ppm are present

Do not remove or by-pass filters when they are clogged.

Clean filter regularly

Chlorination

Hypochlorus acid (HOCl) is the chemical that controls bacterial growth

HOCl may react with iron and create a precipitate [Fe(OH)3]

More Cl is in the active HOCl form at lower pH:

90% at pH = 6.5

50% at pH = 7.5

20% at pH = 8.0

Inject enough chlorine to detect 1 ppm Cl at the end of the line

See references on detailed chlorination procedure

Do not place chlorination point after filter. Instead, place it before, so that precipitates may be filtered out

Do not skip chlorination

When well done, chlorination will not damage the crop

Do handle chlorination products with care

Acidification

Sulfuric (H2SO4), hydrochloric (HCl) and phosphoric (H3PO4) acid are the acids most commonly used.

Do run a trial-test in a 55-gal drum to determine the amount of acid needed

Do not ignore the risks of cross precipitation with calcium (Ca) when H2SO4 or H3PO4 are used

Do handle acids with care

Flushing

Water velocity and pressure may be increased to 1 foot/sec at the end of laterals and pressure may be increased from 8-10 psi to 12 to 15 psi for flushing

Self-flushing valves allow for flushing at every irrigation, although usually these valves do not provide flushing long enough and not at the 1 ft/sec rate

Consider flushing every 2 to 3 weeks

After system is installed, allow for thorough flushing as soil materials are likely to be introduced in the system; then tie the ends

Do not use self-flushing valves in situations where the system pressure is too low; they may never close

Observation

Regularly look for leaks and system malfunctions

Measure water volume delivered, water travel time, and pressure changes regularly

Observe crop growth pattern

Do not assume that everything is working properly!

Be on the lookout

Keep record of benchmark operating values

Table 9. 

Observation component of the prevention-is-best-medicine maintenance program: possible drip irrigation system checks and frequency during the growing season.

What to check?

How often?

Compared to what?

What to look for?

Possible Causes

Pump flow rate and pressure, for each irrigation zone

Weekly

Design, benchmark flow rate and pressure, or water travel time (using dye)

High flow and/or low pressure

Low flow and/or high pressure

No flow, no pressure

Leaks in pipelines or laterals

Flush valves remain open

Open end of laterals

Closed zone valves

Pipeline obstruction

Tape clogging

Pump malfunction

Well problems

Broken well shaft

Drop in water level

Pressure difference across filter

At each irrigation

Manufacturer specifications

Exceeds or is close to maximum allowable pressure difference

Filter becoming clogged

Obstruction in filter

Sudden change in water quality

Operating pressures at ends of laterals

Monthly, unless other checks indicate possible clogging

Benchmark pressures

High end pressure

Low end pressure

Possible clogging

High system pressure

Obstruction in tape

Broken lateral

Leaks in laterals

Low system pressure

Water at lateral ends and flush valves

Bi-weekly

Water source

Particles in water

Other debris

Broken pipeline

Missing filter screen

Hole in filter screen

Tear in filter mesh

Particles smaller then screen

Filter problem

Chemical/fertilizer precipitation

Algae growth

Bacterial growth

Overall pump station

Weekly

Manufacturer's specification and values at startup

Leaks, breaks, engine reservoir levels, tank levels

Mostly mechanical

Injection pump settings

Weekly

Calibrating setting at startup

Reduced injection rate

Injector clogged with debris (check filter)

Precipitates in the fertilizer (check fertilizer compatibility)

Precipitation between high- calcium water and phosphates or sulfates in fertilizer

Overall system

Weekly

System at startup

Discoloration at outlets or ends of laterals

Leaks in tape

Wilting crop

Indicates possible build up of minerals, fertilizer, algae, and/or bacterial slime

Pest or mechanical damage

Tape off fittings

Tape blow out from high pressure

Insufficient irrigation and/or high crop transpiration rate

Tape clogged, obstructed or broken

Root disease (bacterial and/or fungal soil born diseases, nematodes)

Footnotes

1.

This document is HS917, one of a series of the Horticultural Sciences Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Publication date: March 2003. Reviewed August 2011. Please visit the EDIS website at http://edis.ifas.ufl.edu.

2.

Eric Simonne, assistant professor, David Studstill, biologist, Horticultural Sciences Department; Bob Hochmuth, extension agent IV, NFREC-Live Oak; Teresa Olczyk, extension agent II, Miami-Dade County; Michael Dukes, assistant professor, Agricultural and Biological Engineering Department; Rafael Munoz-Carpena, assistant professor, Agricultural and Biological Engineering Department, Yuncong Li, assistant professor, Soil and Water Science Department, TREC-Homestead, 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 UF/IFAS Extension publications, contact your county's UF/IFAS Extension office.

U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.