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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 Li2In 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/vegetarian/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). 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.
a)
b)
c)
d)
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. 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.
a)
b)
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. 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.
a)
b)
c)
d)
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. 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, granular matrix sensors (modified gypsum blocks), time domain reflectometry probes (TDR), and dielectric probes ( Fig. 5 and Fig. 6 ). 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.
Figure 6. Granular matrix sensors or tensiometers should be installed in stations of two (one unit at the 6-in depth, the other at the 12-in depth) between actively growing plants. 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. 7 ). 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. 8 ). Without a maintenance plan, the risk of complete emitter clogging and crop loss becomes real.
a)
b)
Figure 7. 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.
a)
b)
Figure 8. Accumulation of precipitates around a drip-tape emitter (8.1) may result in an uneven water distribution pattern (8.2). 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 Web Sites
North Florida Research and Education Center - Suwannee Valley: http://nfrec-sv.ifas.ufl.edu/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.nhq.nrcs.usda.gov/BCS/nutri/manage.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/AE021Basic 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/AE080Injection 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/AE042Media 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/AE066Design 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/AE049Using 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/CV009IFAS 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. Please visit the EDIS Web site 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 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
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