4.3 Strategies to Increase Crop Irrigation Efficiency
4.4 Strategies to Manage Nursery Runoff
4_Irrigation-Systems-for-Plant-Production
6d - Definint Greywater, Blackwater and Clearwater PUBLIC DOMAIN
6d - III. Strategies to Manage Nursery Runoff COPYRIGHTED
6d - II. Strategies to Increase Nursery Crop Irrigation Efficiency COPYRIGHTED
6d - Irrigation Scheduling COPYRIGHTED
6d - I. Water Use in Nursery Production COPYRIGHTED
6d - Nursery Irrigation COPYRIGHTED
6d - Strategies for Efficient Irrigation Use COPYRIGHTED
Exercise 6a Irrigation Systems
Exercise 6b Nursery Design
Irrigation Systems for Plant Production
Overview
Title image used with permission from "Water Use in Nursery Production" by A. Fulcher & T. Fernandez, University of Tennessee Extension. Copyright © UT Extension.
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Introduction
Lesson Objectives
Evaluate the sustainable use of irrigation systems for a variety of plant production systems.
Determine the role of water balance, surface evaporation, and crop coefficient in determining irrigation needs.
Explain the use of drip emitters, drip line, spray, micro spray, and grey water in sustainable irrigation design.
Key Terms
crop coefficient - the calculation performed to estimate water use for a specific crop, sometimes at a particular growth or developmental stage; ratio of evapotranspiration of a specific crop relative to potential evapotranspiration
deficit irrigation - applies less water than a crop needs for full development
drip irrigation - supplies water at a low flow rate from a thin plastic tube so that only the soil above the root zone is moistened
evaporation - the change of a liquid to a vapor; in irrigation, this process occurs when liquid water on the soil surface becomes vapor
evapotranspiration - the combination of water loss due to evaporation from the soil surface and transpiration from the plant
microemitters - irrigation emitters that apply a small volume of water at low-flow rates to individual containers
microspray - the most common type of microemitter in nursery production; sprinkler heads are mounted on a stake in the container
sprinkler irrigation (or spray irrigation) - delivers water as a fine spray over the growing surface; this method is easy and relatively affordable to set up but is not efficient, because a lot of water lands between plants (also referred to as overhead irrigation)
water balance calculations - used to estimate soil or substrate moisture status and are calculated as the difference between water applied to the plant (irrigation and precipitation) and water lost through evapotranspiration
Water Use in Nursery Production
Used with permission from "Water Use in Nursery Production" by A. Fulcher & T. Fernandez, University of Tennessee Extension. Copyright © University of Tennessee Extension.
Water is essential to plant life and is a critical input to nursery crop production. For plants, water is used in temperature regulation, as a carrier for nutrients and plant hormones, and is the hydraulic force behind growth. Water is taken up by plant roots and is lost to the environment through the stomates and the leaf cuticle. A water deficit can negatively affect plant growth, plant health and the amount of time needed to grow a crop to a marketable size.
Irrigation can shorten the production period for field nursery crops and increase quality, which has a positive impact on nursery profitability. Because the nursery industry has shifted from primarily field-produced crops to container-produced crops, the need for irrigation is increasing. Over 75 percent of nursery crop value (gross farm gate) in 17 of the major nursery producing states is currently grown in containers (USDA 2009). Container nursery production is not possible without the use of irrigation (Figure 6.4.2).
The demand for fresh, high-quality water is increasing across the U.S. and the world. In eight of the 10 most populous states and in the top 10 nursery-producing states (based on farm gate value), competition between human, industrial and agricultural water use is becoming a major issue. Most wholesale nurseries require relatively large amounts of water for irrigation (Figure 6.4.3). A container nursery with 70 percent of the land in production under overhead irrigation could use between 14,000 to 19,000 gallons of water per acre per day during the peak growing season.
Scientists and industry leaders anticipate that there will be less water available for agricultural production in the future. U.S. municipalities in California, Delaware, Florida, Maryland, Michigan, North Carolina, Oregon and Texas already have responded to competition for water and/or concerns regarding water quality and runoff by creating legislation to monitor or regulate irrigation practices (Fernandez et al. 2009). Growers and researchers are exploring novel ways to alleviate this concern.
Nurseries have two main strategies for alleviating competition for water: improved irrigation efficiency and use of alternative, possibly lower-quality water from nontraditional sources. Many practices can improve efficiency, including irrigation scheduling, refining irrigation volume, irrigation system selection and delivery, substrate composition, plant spacing, and plant grouping within irrigation zones. The ability to use lower-quality alternative water sources depends on the type and quantity of contaminants in the source water and the sensitivity of specific species to those contaminants.
Overhead irrigation is commonly used to produce small containers (5 gallon and smaller). Inefficient application can occur easily with overhead irrigation due to a lack of delivery uniformity, which can be caused by inappropriate system design or clogged or damaged emitters (Figure 6.4.4). This leads to over- or under-irrigation of part or all of the target crops. In addition to poor delivery uniformity contributing to inefficient irrigation application, container spacing plays a substantial role in application efficiency. Up to 80 percent of overhead irrigation misses the intended target depending on pot spacing (Gilliam et al. 1992). The potential consequences of inefficient irrigation include wasted water; increased nutrient and pesticide leaching (removing nutrients and pesticides from the foliage, root zone and production surfaces); increased water runoff and movement of contaminants in runoff; increased biotic and abiotic stresses; reduced plant growth; increased plant death; and increased production duration (Figure 6.4.5). The potential consequences of under-irrigation include the latter four.
Water is necessary for industrial, municipal and agricultural purposes. Nursery crop production, especially container production, is dependent on water to grow healthy crops in a reasonable time period. Nursery crop production is often located in or near populated regions of the U.S., which can create competition for water. Growers can use several strategies covered here and in the [following sections] to increase irrigation efficiency and manage nursery runoff.
Strategies to Increase Crop Irrigation Efficiency
Used with permission from "Strategies to Increase Irrigation Efficiency" by A. Fulcher & T. Fernandez, University of Tennessee Extension. Copyright © University of Tennessee Extension.
Nursery irrigation management is a major concern for many nursery producers, especially container producers... Because irrigation is so critical to container production and most of the water associated with nursery production is applied to container plants, strategies are discussed largely in the context of container production.
Growers must make many irrigation management decisions on a daily basis, including when to irrigate, how much water to apply, which plants to irrigate and how to maximize efficiency. They also must plan for and manage water supplies in order to meet local and state water regulations (Figure 6.4.5). Increasingly, competition for water resources is affecting how these decisions are made.
Creating more efficient water-use systems can ease competition for water. Many factors contribute to overall irrigation system efficiency. Irrigation application efficiency is the proportion of total water applied that is intercepted and retained by the container (or root zone in the field). Water loss to excessive leaching, evaporation, wind, container spacing, canopy shedding and poor irrigation system design can decrease irrigation application efficiency dramatically, whereas recovery and reuse of surface water runoff and subsurface flow can increase irrigation application efficiency. Enhancing irrigation efficiency often increases crop water use efficiency.
Scheduling Irrigation
Scheduling irrigation applications has been the focus of much agricultural research. Scheduling can be relatively static and arbitrary, substrate/soil moisture-based, or plant-based.
Static
The conventional container production practice is to irrigate once per day by automatic timers or manually. Historically, these irrigation events were scheduled to begin predawn to minimize losses due to wind and evaporation and so that most irrigation would occur before employees arrived. However, applications are made commonly during daylight hours due to the number of hours needed to deliver water to the entire nursery every 24 hours. The time that irrigation begins may be the same time every day using timer-based irrigation or may be completely arbitrary (i.e., when an employee remembers and has time to turn on the irrigation). With static irrigation, application is not linked directly to plant or substrate moisture status. Irrigation is not adjusted often for changes in evaporative demand due to weather changes, but rather is limited to gross changes when the seasons change. A simple way to save water when using timer-based irrigation scheduling is to install a rain gauge that will prevent irrigation from being applied if a set amount of rainfall occurs.
Substrate Moisture-Based
Substrate moisture measurements consist of either substrate water potential or substrate moisture content and generally rely on moisture probes (Figure 6.4.6) or gravimetric (weight) measurements. Tensiometers reflect actual water potential but are difficult to use in coarse nursery substrates and may require regular maintenance. Some companies are now developing tensiometers that are better suited for container substrates. Capacitance probes and gravimetric techniques measure substrate water content. They do not reflect water potential and, thus, the actual availability of water. Advantages of using substrate moisture-based irrigation include the fact that it can reflect root-to-shoot signaling in response to substrate moisture conditions and can be relatively easy to automate.
Determining how to position a substrate moisture probe is challenging. Scientists are still investigating the ideal probe number per container, number of containers with probes per crop, probe orientation and probe placement within containers. However, studies at nurseries have shown that a very small number of probes involving modest financial investment can be effective in reducing water use without sacrificing plant quality or time to produce a crop. A universal substrate moisture level on which to base irrigation (irrigation set point) would facilitate adoption of this technology but may not be likely due to the variability in types of substrates used by the industry. Therefore, growers will need to do some in-house experimentation to develop irrigation set points. The set point may be affected by crop species, container size, temperature, root system size/time in current container, substrate and where the probe is placed in the container.
Plant-Based
Plant-based irrigation systems, such as leaf temperature-based, allow for environmental influence but do not account for root-to-shoot signaling and are challenging to automate. Plant- based systems can respond to the physiological changes that occur directly due to changes in plant water status, which make them very appealing to researchers and practitioners alike. However, this response can be a disadvantage for conservative irrigation schedules in certain environments, because low plant water status induced by extreme mid-day conditions could trigger irrigation when substrate moisture is not limiting. Leaf temperature, plant water potential and stem diameter fluctuations are some of the plant-based techniques that have been used to gauge water loss in horticultural crops (Figure 6.4.7). Plant- based systems are not automated easily or widely commercially available at this time.
Irrigation Volume
The approaches mentioned above address only when to irrigate. Other approaches are needed to determine how much water to apply. Growers commonly aim to apply 0.75 to 1 inch of irrigation water daily in the summer by irrigating for a set time period. However, determining irrigation volume by a time period can lead to errors in application. Research shows that due to variation in output (e.g., water pressure) and distribution, application volume based on a time period can result in excess or inadequate irrigation. For example, nurseries expecting to apply 1 inch of water in an hour may actually apply just 0.3 inch in 60 minutes, while other nurseries apply as much as 1.3 inches. Over the course of a season, the amount of water applied within one irrigation zone in a 60-minute period can vary as much as half an inch. Therefore, it is important to determine irrigation system application rates by measuring them periodically.
Several methods can be employed to determine how much water to use to prevent applying an excessive or deficient volume of water. Irrigation volume can be based on the container leachate. Leaching fraction is the percentage of water applied that leaches or drains out of the container.
A leaching fraction of 10 percent or less, allows for water and nutrient conservation. When irrigating at low leaching fractions (<10 percent), it is important to monitor substrates for soluble salts during production, especially during periods of low rainfall, as they can build up.
Water balance calculations are used to estimate substrate moisture status and are calculated as the difference between water applied to the plant, both through irrigation and precipitation, and water lost through evapotranspiration. Evapotranspiration is affected by many factors, including solar radiation, humidity and mulch layer. Using an evapotranspiration model presents several challenges. For instance, evapotranspiration models are often complex, requiring that several variables be measured. A weather station and datalogger must be located on-site. Additionally, a crop coefficient must be derived empirically for every species, perhaps even at the cultivar level and possibly for different stages of development, container sizes, plant (crop) size and spacing.
Daily water replacement is a practical way to approach water balance calculations. Daily water use measures how much water is lost during each 24-hour period and applies, or replaces, that volume of water minus rainfall. Daily water use measurements may be made by measuring weight or using probes to measure volumetric water content every 24 hours.
Irrigation System: Delivery
Overhead (sprinkler) irrigation is commonly used for plants in 5-gallon and smaller container sizes. The water is delivered by sprinklers mounted on risers on rectangular, square or triangular patterns throughout the container pad. While overhead sprinklers are easy and relatively affordable to set up, they are not efficient, because a lot of water lands between containers (Figure 6.4.8). As linear spacing between plants increases, irrigation efficiency decreases considerably, with as little as 35 percent efficiency even at close spacing (half a container diameter).
Microemitters (used in drip irrigation) are emitters that apply a small volume of water at low flow rates, generally to individual plants. Microemitters are often used for 7-gallon and larger container sizes (Figures 6.4.9 and 6.4.10). Microemitters include microsprinklers, drippers and bubblers. Microsprinklers, commonly called “spray stakes” [or “microspray”] are the most common type of microemitter in nursery production. Sprinkler heads are mounted on a stake in the container. The sprinkler head/ stake assembly is connected to the lateral line by a small diameter (1/4”- 1/8”) flexible tube called spaghetti tubing. Drip emitters and bubblers are not used often in nursery production because they do not apply the water to the surface of the substrate evenly, a problem that compounds the larger the container size. Also, the single-point delivery of a drip emitter can lead to water channeling through the bark substrate due to its coarse nature.
Microemitters are very efficient; when properly installed, they apply water to the root system with no overspray or wasted water. However, the particular spray patterns, placement in the container and juxtaposition to the trunk can affect the distribution of water. Two or more emitters can be used to apply water more evenly and/or to increase the amount of water applied in a given amount of time, especially for very large containers. Microirrigation systems have small orifices that can clog easily. Appropriate filtration as well as regular maintenance and cleaning are required.
Ebb-and-flow is a subirrigation technique that is used most commonly in floriculture production. An ebb-and- flow irrigation system floods the production floor, or bench, periodically, slightly submerging the base of containers for a short period to allow the substrate to absorb water by capillary action. A significant investment in infrastructure is required to develop an ebb-and-flow irrigation system. Typically, the irrigation water is captured and sanitized for reuse, making it a highly efficient system. A controlled water table (CWT) also is a form of subirrigation and requires specialized infrastructure. A CWT delivers water to plants via a capillary mat that pulls water from a reservoir (trough) at the edge of the bench. Like ebb-and-flow, CWTs are used most often in floriculture. CWTs are very efficient but do require some maintenance. Microemitters, ebb-and-flow systems and controlled water tables can be used to fertigate as well as irrigate.
Water-Conserving Strategies for Nurseries
Strategies to reduce water consumption in nurseries include grouping plants by relative water needs and container size and using cyclic irrigation. Grouping plants by perceived irrigation needs (high, medium, low) into irrigation zones is a common strategy employed by growers. Grouping plants by water needs along with proper spacing can reduce water consumption tremendously. Another conservative irrigation strategy is cyclic irrigation, in which the total daily volume of irrigation water is applied in multiple irrigation events with a minimum of one hour between irrigation events. Using cyclic irrigation can reduce runoff by 30 percent, compared with conventional continuous irrigation. Using amendments, such as calcined clay, to increase the substrate water-holding capacity also can reduce water use.
Growers have many options for increasing water-use efficiency in the nursery. These include refining irrigation scheduling, irrigation volume and irrigation delivery. The Extension publication, “W 280: Part III. Strategies to Manage Nursery Runoff,” discusses the significance of runoff from nursery production facilities, as well as strategies for minimizing and mitigating runoff.
Strategies to Manage Nursery Runoff
Used with permission from "Strategies to Manage Nursery Runoff" by A. Fulcher & T. Fernandez, University of Tennessee Extension. Copyright © University of Tennessee Extension.
“Water Use in Nursery Production,” discussed the importance of and competition for water use in nursery production. “Strategies to Increase Efficiency” covered techniques that growers can use to refine scheduling (volume and timing) and delivery of irrigation water. This final [section] discusses the significance and causes of nursery irrigation runoff and offers strategies to manage runoff.
As discussed in [the first section], irrigation can contribute to nursery runoff. While growers generally aim to apply 1 inch of water per day, field studies show that growers actually apply as little as 0.3 and as much as 1.3 inches per day. The greater the volume of water applied, the greater the potential for runoff. Runoff, or more precisely, surface runoff, is defined as water moving over the surface of saturated soil. Runoff can cause erosion and carry pathogens and pollutants, such as pesticides, petroleum products, soil, fecal contaminants and nutrients that may contaminate ground and surface water. Agricultural runoff and its link to eutrophication in surface waters led to legislative action affecting agriculture producers in recent years, including the Neuse River watershed in North Carolina and the Chesapeake Bay (Figure 6.4.11).
Erosion
Erosion is a serious threat to agriculture and contributes to reduced soil productivity. Moving water is often a culprit of erosion, because it concentrates as it moves, following the path of least resistance. Field and container producers may experience gully erosion (i.e., erosion by water moving so forcibly that it creates a furrow or gully) (Figure 6.4.12). Sheet erosion occurs when water moves over the ground as a sheet, dislodging soil particles without creating a gully.
Erosion Prevention Measures
Reducing the runoff from nurseries can minimize or eliminate the displacement of soil and the contamination of water. Refining irrigation applications so that excess water is not applied is one strategy to prevent runoff. However, even with sophisticated irrigation scheduling, heavy rain, even when infrequent, is sufficient to cause erosion. Erosion can be prevented or reduced by a number of techniques that slow the flow of stormwater, water that collects on land due to rain events. It includes runoff from impervious surfaces, such as roads, parking lots, compacted soil and roofs.
There are many best- management practices and techniques that may be used to minimize the effects of stormwater runoff and erosion, including contour plantings, filter strips and constructed wetlands. Contour plantings can be used to reduce erosion in hilly areas (Figure 6.4.13). This practice is accomplished by placing rows of plants perpendicular to the slope of the land, forming a barrier to surface runoff and slowing the movement of water. Filter strips are plantings that are placed strategically to intercept sheet flow runoff. Filter strips slow the water and can trap soil particles and contaminants before entering surface water. The benefits of filter strips are marginalized when sheet flow becomes concentrated and water flow is diverted from the full filter strip. In some cases, land may be too hilly to grow crops without risking erosion.
Constructed wetlands are artificially created wetlands that can serve many purposes (Figure 6.4.14). They can reduce erosion by slowing surface drainage, as well as remove nutrients, pathogens and heavy metals from stormwater runoff. Wetland vegetation and saturated soils provide a substrate on which microorganisms can live. Microorganisms are a key component of wetlands. They serve a critical function in changing and breaking down contaminants. Wetland plants filter water, stop the movement of sediment particles and allow sediments to settle before the flow is discharged into streams.
Stormwater Basins
Growers may have a need for two types of stormwater basins: retention basins and detention basins. A retention basin (wet basin) is designed to retain water in a permanent pool. Retention basins can be used to capture, contain and treat nursery effluent from irrigation and excess rainfall so that it remains on-site, protecting fresh water supplies (Figure 6.4.15). Retention basins are often lined with a polyethylene liner to avert runoff from infiltrating the soil and, thus, prevent it from being available for irrigation. Annual maintenance of basins includes removal of excess vegetation and sediment. A detention basin (dry basin) is dry during many months of the year, refilling only during peak rainfall events. Detention basins are designed to hold stormwater temporarily and release it slowly over time, which decreases water velocity and, therefore, erosive energy on stream banks.
Smaller nurseries and those with only one grade (i.e., nearly level) often need only one basin, although an additional sedimentation basin can improve water quality if the water will be recycled. Sedimentation basins should be designed to allow periodic cleaning to remove sediments that have accumulated. Larger nurseries and nurseries with multiple gradients need more basins. Impervious concrete runways or vegetated waterways can be used to direct water from the production area to the basin without contributing to erosion.
Conclusion
Nursery runoff can be caused by excessive irrigation, poor production area design and heavy rainfall. Runoff can lead to environmental concerns since it can carry biological and chemical contaminants; nursery effluent can contain pesticides, petroleum products, pathogens and nutrients and can cause erosion. Numerous strategies can be used to decrease nursery runoff and slow or prevent erosion. Retention basins can be used to capture runoff and provide a source of irrigation water while protecting nearby rivers, streams and groundwater.
Dig Deeper
"Greywater Systems" by R. Brain, J. Lynch, K. Kopp, J. Adams, O. Rogers, Utah State Extension is in the Public Domain
"Irrigation Scheduling: The Water Balance Approach" by A.A. Andales, J.L. Chávez, T.A. Bauder, Colorado State University Extension. Copyright © Colorado State University Extension. Used with permission.
“Nursery Irrigation: A Guide for Reducing Risk and Improving Production” by W. Yeary, A. Fulcher, B. Leib, University of Tennessee Extension. Copyright © University of Tennessee Extension. Used with permission.
"Strategies for Efficient Irrigation Water Use" by C.C. Shock, B.M. Shock, & T. Welch, Oregon State University Extension Service. Copyright © Oregon State University. Used with permission.
Unit 6 Lab Exercises
Exercise 6a: Irrigation Systems
Students design and evaluate the efficiency of various irrigation methods. This exercise helps students understand different types of irrigation systems and their applications in agriculture.
Exercise 6b: Nursery Design
Students plan and design a nursery, including layout considerations and plant selection. It aims to teach students the principles of effective nursery management and design.
Attribution and References
Attribution
Material used with permission from the "Sustainable Nursery Irrigation Management Series" A. Fulcher & T. Fernandez, University of Tennessee Extension. Copyright © University of Tennessee Extension.
Title image by Amy Fulcher, used with permission from "Water Use in Nursery Production" by A. Fulcher & T. Fernandez, University of Tennessee Extension. Copyright © University of Tennessee Extension.
References
Beeson, R.C. (2006). Relationship of plant growth and actual evapotranspiration to irrigation frequency based on management allowed deficits for container nursery stock. Journal of the American Society for Horticultural Science, 131:140-148.
Beeson Jr., R.C., M.A. Arnold, T.E. Bilderback, B. Bolusky, S. Chandler, H.M. Gramling, J.D. Lea-Cox, J.R. Harris, P.J. Klinger, H.M. Mathers, J.M. Ruter, & T.H. Yeager. (2004). Strategic vision of container nursery irrigation in the next ten years. Journal of Environmental Horticulture, 22:113-115.
Beeson, R. & G. Knox. (1990). Analysis of efficiency of overhead irrigation in container production. HortScience. 26:848-850.
Buxton, J., J. Pfieffer, & D. Slone. (2010). Controlled water table irrigation of container crops. University of Kentucky publication HO-84.
Fare, D., C. Gilliam, & G. Keever. (1994). Monitoring irrigation at container nurseries. HortTechnology. 2:75-7.
Fernandez, T., J.D. Lea-Cox, G. Zinati, C. Hong, R. Cabrera, D. Merhaut, J. Albano, M. van Iersel, T.H. Yeager, & D. Buhler. (2009). NCDC216: A multistate group for water management and quality for ornamental crop production and health. Proceedings of the Southern Nursery Association Research Conference, 54:35-38.
Haman, D.Z., A.G. Smajstrla, & D.J. Pitts. (2002) Efficiencies of irrigation systems used in Florida nurseries. University of Florida Bulletin BUL312. Retrieved from http://edis.ifas.ufl.edu/pdffiles/AE/AE08700.pdf
Howell, T. (2003). Irrigation efficiency. Encyclopedia of water science. Marcel Dekker, Inc., New York, New York.
Gilliam, C.H., D.C. Fare, & A. Beasley. (1992). Nontarget herbicide losses from application of granular ronstar to container nurseries. Journal of Environmental Horticulture, 10:175-176.
Majsztrik, J., A.G. Ristvey, & J.D. Lea-Cox. (2011). Water and nutrient management in the production of container-grown ornamentals. Horticultural Reviews, 38:253-297. John Wiley and Sons, Hoboken, New Jersey.
Owen Jr., J.S., S.L. Warren, T.E. Bilderback, & J.P. Albano. (2008). Phosphorus rate, leaching fraction, and substrate influence on influent quantity, effluent nutrient content, and response of a containerized woody ornamental crop. HortScience. 43(3):906-912.
Ross, D.R. (1994). Reducing water use under nursery and landscape conditions. Recycling and resource conservation: A reference guide for nursery and landscape industries. Nurserymen’s Association, Inc., Harrisburg, Pennsylvania.
Turral, H., J. Burke, & J.-M. Faurès. (2011). Climate change, water, and food security. Water Reports, No. 36. Food and Agriculture Organization of the United Nations, Rome. Retrieved October 4, 2011 from http://www.fao.org/docrep/014/i2096e/i2096e.pdf.
U.S. Department of Agriculture. (2008). 2007 Census of Agriculture, Washington, D.C.
Van Iersel, M., R.M. Seymour, M. Chappell, F. Watson, & S. Dove. (2009). Soil moisture sensor-based irrigation reduces water use and nutrient leaching in a commercial nursery. Proceedings of the Southern Nursery Association Research Conference 54:17-21.
White, S.A., M.D. Taylor, R.F. Polomski, & J.P. Albano. (2011). Constructed wetlands: A how to guide for nurseries. Retrieved from http://www.clemson.edu/extension/horticulture/nursery/images/cws_howtoguide_small.pdf
Wilson, P.C., & J.P. Albano. (2011). Impact of fertigation versus controlled-release fertilizer formulations on nitrate concentrations in nursery drainage water. HortTechnology. 21:176-180.
Wilson, S. & S. von Broembsen. (2017). Capturing and recycling irrigation runoff as a pollution prevention measure. Oklahoma State University BAE-1518. Retrieved from http://osufacts.okstate.edu/docushare/dsweb/Get/Document-7408/BAE-1518web.pdf
Yeager, T., T. Bilderback, D. Fare, C. Gilliam, J. Lea-Cox, A. Niemiera, J. Ruter, K. Tilt, S. Warren, T. Whitewell, & R. Wright. (n.d.). World Water Council. Retrieved from http://www.worldwatercouncil.org/index.php?id=25..
Yeager, T., T. Bilderback, D. Fare, C. Gilliam, J. Lea-Cox, A. Niemiera, J. Ruter, K. Tilt, S. Warren, T. Whitwell, & R. Wright. (2007). Best management practices: Guide for producing container-grown nursery crops. Southern Nursery Association,
Atlanta, Georgia.
Yeager, T., R. Wright, D. Fare, C. Gilliam, J. Johnson, T. Bilderback, & R. Zondag. (1993). Six state survey of container nursery nitrate nitrogen runoff. Journal of Environmental Horticulture, 11:206-208.