NC1186: Water Management and Quality for Ornamental Crop Production and Health
(Multistate Research Project)
NC1186: Water Management and Quality for Ornamental Crop Production and Health
Duration: 10/01/2015 to 09/30/2020
Statement of Issues and Justification
Water conservation and quality are top national and regional priority issues in agriculture. The issues of water scarcity and water security were highlighted in recommendations by the Water Working group of the nation’s Land-Grant Institutions to the US Department of Agriculture in August 2014, entitled “National Initiative on the Improvement of US Water Security”. Water management issues, specifically irrigation scheduling, salinity and production runoff water quality, and urban surface and storm-water management are topics of major concern to ornamental producers, landscape and ecosystem service providers, and urban environment managers. Climate change may influence rainfall patterns, annual snowpack, and the frequency and severity of drought events. Drought, urban competition for water resources, regulations that mandate lower environmental impacts and increasing legislation at state and county levels increase the need for both agriculture and urban sectors to manage water more effectively. This includes the use of alternative water sources that can be inferior quality to fresh water. Challenges exist regarding sufficient quantities of appropriate quality water sources and the impact of green industry management practices on the quality of surrounding water resources in all regions of the US.
Irrigation use accounts for 62% of freshwater (surface and ground water) resource use in the US (Kenny et al., 2009). More than 55.4 million acres of land were irrigated in the US in 2013, of which 72% were irrigated by sprinkler and micro-irrigation systems (USDA-NASS, 2014). Most field producers of nursery stock use irrigation at some point during the growing season. Many field producers use low-volume irrigation and some use such systems to deliver soluble fertilizers. While supplemental irrigation is beneficial in field production, frequent (most often daily) irrigation is essential for container production both in nurseries and greenhouses. Container substrates need to be well drained and container volume limits the amount of available water, resulting in frequent irrigation and high water use. For example, in Florida, container nurseries annually apply 56 to 120 inches per year in addition to the 40 to 50 inches of average annual rainfall. Over 75% of nursery crops in 17 of the major nursery producing states were grown in containers (USDA, 2007) and thus require irrigation. Almost all greenhouse crops are produced in containers.
Frequent irrigation along with high fertilizer and pesticide use can lead to significant movement of agricultural chemicals and pathogens in runoff water that transports them to containment ponds and/or off-site into groundwater or surface water (Camper et al., 1994; Hong and Moorman, 2005; Warsaw et al., 2009b; Wilson and Foos, 2006; Wilson and Boman, 2011). Irrigation water management is a key component in the nutrient management of ornamental crop production and in reducing the impact of runoff water on local water systems (Tyler et al., 1996; Lea-Cox et al., 2001; Ross et al., 2002; Warsaw et al., 2009b). Emerging constraints on water use and quality means that the green industries need to find ways to manage water without detracting from production schedules and crop quality. Precision water management and resource efficiency were rated at the top of the issue/need/concern list developed at the joint USDA, ARS, NASA and NSF workshop Engineering Solutions for Specialty Crop Challenges (USDA, 2007). Furthermore, the United States Environmental Protection Agency (EPA) is enforcing federal legislation requiring states to implement Total Maximum Daily Load (TMDL) programs for watersheds (Majsztrik et al., 2013).
A multi-state, multidisciplinary research and extension group is necessary to address the water quantity, quality and plant production issues in green industry. During the first 5 years of the NC1186 group, we have fostered collaborations among a team of research and extension specialists that have created research and outreach programs that have advanced the scientific understanding not only of irrigation and runoff water management and quality, but also substrate, nutrient and pathogen management to optimize ornamental crop production. In one specific example, an interdisciplinary SCRI group that includes a number of NC-1186 members, developed an advanced monitoring and control capability for field, container-nursery and greenhouse producers using wireless sensor networks (Lea-Cox et al., 2013). In addition, this group helped develop a national SCRI planning grant (White et al, 2013) that has led to a successful national SCRI funded proposal in 2014 (White et al, 2014). During the next 5 years, this project will address management strategies for anticipated decreasing availability and quality of water for irrigation use in the green industries. Water conservation methods, improved nutrient management practices will be used to reduce the amount of water used and potential contamination. The project will also investigate methods to reduce or remediate production impacts on water quality in order to safely reuse water in production or return water to the surrounding water systems with respect to agrichemicals, abiotic and biotic, substrate and nutrient management environmental, economic and social benefits. In addition, we plan to target urban environmental situations, specifically building on green roof stormwater runoff models developed by Starry et al. (2014), using the same wireless sensing technology developed by the above mentioned SCRI team (Lea-Cox et al., 2013). The following sections provide more detailed explanations of the issues and justification for the three main sections of this project, namely water sources and quality, irrigation management, substrate and nutrient management.
Water sources and quality
There are four primary water sources available for ornamental production: groundwater, surface water, reclaimed water, and recycled tailwater from runoff. All of these water sources can have quality issues that require management before they can be used for plant production. Groundwater is being contaminated by infiltration of contaminants from nearby industrial, urban, and agricultural operations. In other regions of the U.S., groundwater is impaired by natural geological features, making water alkaline, sodic, and/or saline. Surface water is even more vulnerable to contamination since it has no protective over-layer of soil. Reclaimed water, which is wastewater or sewage that has been treated with conventional wastewater treatment processes or other processes, is being used in various parts of the country to irrigate specific agricultural crops. While reclaimed water offers a water source that can be available when other water sources are limited, there are drawbacks to using this water source. Plant producers therefore must develop new technologies to remove harmful contaminants when necessary, modify horticultural practices, and/or develop or choose crops which are more tolerant of lower quality water.
In many areas of the country, ornamental producers have begun recycling tailwater and stormwater runoff from their facilities. This process can save money, especially for larger operations, since fertilizers in the runoff are re-utilized. However, runoff water may contain pesticide residues and nitrates (Briggs et al., 2002; Riley et al., 1994; Willis, 1982; Warsaw et al., 2009a; Wilson et al., 2006, 2011). Phytotoxicity problems may result when recycled water contains either pesticides with medium to high water solubilities or one pesticide is extensively used and the recycled water is applied to plants sensitive to that pesticide (Bhandary et al., 1997). Herbicide contamination levels of 1 to 10 ppm for short durations were found to be detrimental to growth and quality of several ornamental crops (Bhandary et al., 1997; Fernandez et al., 1999). Other drawbacks of recycling include the need for adequate infrastructure to collect, capture and treat irrigation water runoff. However, in areas such as California, recycling of tailwater has been practiced since the 1970s (Skimina, 1986).
Container-nursery production creates the largest challenge to managing runoff water. The volume of water used and amount of runoff generated is much less for field production but issues are similar and still can have a major impact on water resources. Runoff of rain and irrigation water is an important avenue for the movement of agrichemicals from production sites into nearby receiving water bodies (Bjorneberg et al., 2002; Latimer et al., 1996; Taylor et al., 2006). Assessment and management of runoff plays a critical role in minimizing environmental impacts of ornamental plant production operations.
Runoff can be substantially reduced by precision irrigation management (Warsaw et al., 2009b). Capturing, treating and recycling runoff water is an alternative option. Many larger greenhouses have addressed the issue of runoff by using closed recirculating irrigation systems, such as ebb-and flood floors. Although subirrigation systems can virtually eliminate runoff from greenhouses, they are cost-prohibitive for many producers. Many of those producers have also identified pathogen management as their top concern in using recycled water (White et al, 2013).
Plant pathogens in irrigation water were recognized almost a hundred years ago as a significant crop health issue (Bewley and Buddin, 1921). Plant pathogens threaten the sustainability and profitability of the ornamental plant industries as much as water shortages. Recycling irrigation conserves water, but it may also spread pathogens from a single point to an entire enterprise and from a single farm to other facilities sharing the same water resource (Hong et al., 2008a,b,c). This could result in severe losses of both crop and consumer confidence. At least 17 Phytophthora species, 26 of Pythium, 27 genera of fungi, 8 species of bacteria, 10 viruses, and 13 nematode species have been detected from water sources (Hong and Moorman, 2005). Among those pathogens are the sudden oak death (SOD) pathogen, and Ralstonia solanacearum, one of the USDA select agents under the Agricultural Bioterrorism Protection Act of 2002. Thus, there is an urgent need to assess the waterborne pathogen risk and develop mitigation strategies.
Restrictions or timing of irrigation to conserve water may also decrease crop health due to coincidence of irrigation and ideal conditions for disease development. These issues have increased greatly in degree of impact and it will continue to be a problem with the increasing dependence on alternative irrigation water sources (Hong and Moorman, 2005).
Ideally, only the amount of water used through evapotranspiration is replenished when irrigating with good quality water. Applying water in excess of evapotranspiration can lead to reduced growth and nutrient loss (Tyler et al., 1996; Warsaw et al., 2009a, 2009b). However, irrigation system uniformity and efficiency are always less than 100% and result in wasted water. Manual versus automated irrigation systems and more importantly how irrigation decisions are made, also affects irrigation water use efficiency. Water quality and quantity issues affect irrigation management decisions: when water with high soluble salts is used for irrigation, a high leaching fraction may be required to prevent the buildup of excess salts in the substrate. Conversely, alkaline water should be applied at the lowest possible rates to minimize effects on substrate pH. Either of these scenarios can lead to nutrient management problems, a longer production cycle and more water used over the extended cycle (Beeson, 2006).
Over-application of water is both an inefficient use of water and is the main cause of fertilizer runoff (Warsaw et al., 2009a). State laws have been passed that regulate the amount of runoff from all forms of agriculture (Lea-Cox and Ross, 2001). Excessive irrigation may also result in anaerobic conditions in the root zone possibly resulting in: 1) a root systems more susceptible to pathogens (Powell and Lindquist, 1997); 2) dissemination of pathogens from production areas, potentially leading to contamination of irrigation ponds; 3) nutritional problems due to denitrification and effects on root physiology and soil/substrate pH; 4) leaching of water, nutrients, pesticides, and herbicides from production areas posing a threat to water quality, and 5) excessive stem elongation, reduced plant quality and increased shipping costs.
Substrate and nutrient management
Nursery producers purchase or create unique soilless substrate mixtures by combining two or more components. The majority of components are regional and based on available resources. Mixtures are dominantly comprised of organic materials (e.g. Sphagnum peat, bark) with lesser amounts of inorganic materials (e.g. perlite, coarse sand). Open-air container operations dominantly use bark as the base component mixed with other organic and inorganic materials to create a multitude of possible substrates with varying physical and chemical properties. Yeager and Newton (2001) reported that at a hands-on workshop in Hillsborough County, FL, of the 40 soilless substrates samples provided by containerized nursery operations brought for analysis, 26 were unique and comprised of 16 different components. Similarly, Blythe and Merhaut (2007) documented the relatedness of 127 different substrates commonly used by nursery growers in California which consisted of 11 organic and inorganic components. The aforementioned papers illustrate the broad number of substrate components and virtually unlimited number of combinations that nursery growers utilize to produce containerized crops within the United States; each believed to hold the optimal physio-chemical properties to yield the best crop for a given region or management style.
The manner in which scientists approach evaluation of substrates has been evolving over the past three to five years. Scientists are beginning to evaluate more dynamic physical properties over traditional static properties. Scientists are moving from evaluation of “the best fertilizer” for a particular crop to studying crop nutrient needs in order to increase nutrient use efficiency. Furthermore, a new push is being made to better understand how the economic sustainability of new and traditional substrates affects their adoption and use by the nursery industry. Substrate scientists in this group will collaborate on new and emerging techniques to quantify and evaluate the complex system of substrates, and how substrate components affect dynamic chemical and physical properties, as well as the economic sustainability of those substrates.
Related, Current and Previous Work
Water sources and quality
Majsztrik et al. (2011) provided a comprehensive review of the various issues surrounding water and nutrient management in the production of container-grown ornamentals in the US. In a recent survey, over 75% of nursery crops in 17 states were grown in containers and require irrigation (USDA, 2010). White et al. (2013; all collaborators within NC1186), facilitated by a SCRI Planning Grant (NIFA Project # 2011-51181-30633 “Containment, Remediation, and Recycling of Irrigation Water for Sustainable Ornamental Crop Production”), distilled results from (1) a national survey and (2) round-table discussions held with greenhouse and nursery growers in five regions throughout the US, which helped the research team clearly define the objectives of this project. Survey results provided a broad characterization of current water use practices in the green industry, against which future changes in water management and handling practices and impacts of the proposed project can be assessed. Frequency analysis of collated round-table discussion responses indicate that the primary barriers limiting adoption of recycling practices or use of alternative water resources include: (1) concerns related to presence of pathogen, pesticide, and nutrient contaminants which could negatively impact crop growth and subsequent economic sustainability; (2) lack of reliable (scientifically derived) estimates of costs and benefits, return on investment, and efficacy of treatment technologies to manage specific contaminants; and (3) lack of infrastructure for retaining or treating runoff, whether due to geographical (land-limited), environmental (limited precipitation), or practical (high water table) constraints. Grower decision-making is therefore often based on incomplete information, and sometimes the ultimate decision is to do nothing rather than implement a practice without adequate assurance of success and return on investment.
A newly funded USDA-NIFA-SCRI project “Clean WateR3 - Reduce, Remediate, Recycle – Enhancing Alternative Water Resources Availability and Use to Increase Profitability in Specialty Crops”, was a direct outcome of this planning grant. All co-PI’s are active NC1186 members. The broad objectives of this five-year SCRI national project is to help nursery and floriculture crop producers obtain and retain sustainable, alternative sources of water, to decrease dependence on potable water and to enhance their long-term economic viability. The project will (1) develop and publish an online decision support system (system-wide model) to aid growers with identification and implementation of innovative technologies to recycle water for reuse or release from containerized crop production systems; (2) reduce contaminant loading into recycled water sources by (a) installing treatment technologies and (b) managing production inputs to reduce pathogen and agrichemical presence; (3) identify and develop biological and physical treatment technologies that (a) effectively remediate pathogen, pesticide, and nutrient contaminants and (b) integrate into existing operations with negligible reductions to production area and minimal energetic or chemical inputs; and (4) effectively communicate project outputs to stakeholders to encourage adoption of defined practices to reduce, remediate, and recycle production runoff.
Another multi-state outreach project that has been developed by members of the NC1186 group is the on-line Green Industry Knowledge Center for Water, Nutrient and Plant Health Management (http://www.waternut.org/moodle). Twenty five in-depth learning modules provide research-based best management practices for substrate, irrigation, surface water, nutrient and crop health management for nursery and greenhouse environments (Lea-Cox et al., 2008b). We plan to revise and add modules to this knowledge center, to provide a wider range of water management information, tools and advanced technology to ornamental producers nationwide.
An additional group of NC1186 members in Texas and Ohio have been funded by USDA-ARS (FNRI) on “Alternative irrigation water sources for sustainable nursery production and urban landscapes”. Their objectives are to evaluate the long-term ecological effects of irrigation with reclaimed water and graywater on nursery and greenhouse crops and landscape plants, comparing these sources to municipal potable or high-quality water sources. All these projects will fully support the specific NC1186 project objectives (detailed below), and will continue to foster and promote collaborations and knowledge gain among NC1186 members.
Different approaches have been used in the past to develop more efficient irrigation practices. Irrigation systems are primarily dependent upon good design and continued maintenance (Ross, 2008b, c). However, the critical issue for most growers is scheduling irrigations, which is a complex daily decision often based upon subjective techniques (Lea-Cox et al., 2009). When controlling irrigation based on real-time measurements, the first decision for a grower is whether to use a measure of plant water status or the water content of the substrate/soil, to measure plant water availability. Both approaches have advantages and disadvantages.
In principle, controlling the water status of the plant may allow for more direct control of the physiology and growth of the plants. Leaf temperature, leaf reflectance, leaf/stem water potential, and stem diameter have all been used as indicators of plant water status. Leaf temperature measurements can be used to determine the crop water stress index (CWSI), which can then be used to control irrigation. Prenger et al. (2005) found that irrigation was reduced by approximately 50% when based on CWSI as compared to using a timer.
However, Jones (2004; 2008) argued that measurements of soil water status are better suited for irrigation control than plant water status, in terms of cost and ease-of-use. In the case of measuring substrate/soil moisture, the first decision to be made is whether to measure volumetric water content or matric potential. Tensiometers have long been used to measure the matric potential of soils and soilless substrates (Lieth and Burger, 1989). Although tensiometers have proven to be valuable research tools, they are difficult to use in soilless substrates and some soils due to poor contact between the ceramic tip and the soil or substrate. These problems, and the need for routine maintenance, have limited the use of tensiometers in commercial container-production in soilless substrates. In recent years, several new soil moisture sensors have become available. These new sensors determine the volumetric moisture content by measuring the apparent dielectric constant of the substrate and have been successfully used in automatic irrigation system (Nemali and van Iersel, 2006, 2008).
Although it is currently possible for growers to control irrigation using soil moisture sensors, it is important to develop systems that allow growers to easily collect, store, and analyze the data from these sensors. The SCRI-MINDS team (Lea-Cox et al., 2013) developed advanced wireless sensor networks (Fig. 1, see attachment) that can be used to both monitor and control irrigation events throughout a greenhouse or nursery. A major accomplishment of this project was the development of a fully functional commercial wireless sensor network (WSN) system (PlantPointTM), which will be available in early 2015 (Decagon Devices, Inc, Pullman, WA). In summary, sensor data is transmitted to a central computer, from where soil moisture sensor-based information can be monitored and irrigation set-points can be adjusted as needed. Node-based “local control” of irrigation using nodes and sensors connected to latching solenoids in the field has eliminated the need for external power sources (Fig. 1). Using wide area sensor networks, the SCRI-MINDS team were able to go beyond the measurement of a single variable, such as soil/substrate moisture, by integrating them with other environmental variables including water inputs (rainfall, irrigation volumes), electrical conductivity (salt accumulation), light, soil and air temperature, relative humidity and wind speed/direction.
The SCRI-MINDS team developed both threshold-based (i.e., irrigation controlled by soil moisture set-points) and model-based approaches to provide quantitative, real-time methods for scheduling irrigation, based on plant water requirements. The use of wireless sensor networks (WSN’s) realizes significant (40-70%) savings in water use (Belayneh et al., 2013; Chappell et al., 2013) that benefits commercial specialty crop producers by reducing production times and improving yield, thereby leading to significant economic benefits, both private (Lichtenberg et al., 2013; Majsztrik et al, 2013) and public (Majsztrik, Price and King, 2013). Both threshold- and model-based irrigation scheduling provide efficient and effective ways to improve water and nutrient management for crops monitored by sensors or for which key empirical (Belayneh et al., 2013; Chappell et al., 2013; van Iersel et al., 2013; Warsaw et al., 2009a,b) or physiological (Bauerle and Bowden, 2011; Barnard and Bauerle, 2013) parameters are known. This WSN technology has been tested on number of species in nursery and greenhouse operations, and green-roof installations (e.g., Barnard and Bauerle, 2013; Kim et al. 2011; van Iersel et al. 2013; Starry, 2013).
However, the current WSN approach to automated irrigation control relies on intensive monitoring, using large numbers of weather and/or soil moisture sensors. This makes it difficult and expensive for specialty crop producers to implement this technology on a large scale, especially in situations where a wide variety of different crops is produced. To do this, we need to investigate different strategies for scaling up sensor networks, to maximize ease-of use and return on investment, but to minimize the complexity and cost of sensor networks. To scale-up WSN technologies, stakeholder-friendly methods for categorizing plants into irrigation functional groups (IFGs) are needed to schedule irrigation events for a broad range of specialty crops/cultivars. One solution is to use small scheduling blocks with indicator plants that are representative of IFGs. Small numbers of indicator species can be densely sensed with substrate moisture sensors and electrical conductivity (EC) sensors to determine plant water use and nutrient availability. Plants in normal production areas will be grouped into irrigation zones by IFG. Water and nutrient-management decisions from the densely-sensed scheduling block can then be easily scaled to production-sized blocks, where monitoring nodes can be placed to verify that those irrigation decisions are correctly made. With this approach, sensors will be concentrated in a designated area for easier installation and maintenance. These scheduling blocks will also have space for plants of unknown IFGs, for IFG determination. This same approach could be taken with many plant species, including horticultural food crops.
Urban Storrmwater Management: Green roofs are primarily used to reduce the immediate effects of any rainfall event, by absorbing (retaining) the first inch of a rainfall event. This reduces the effect of this stormwater (peak runoff) running off into surrounding streams, or in the event of a city, excess stormwater overflowing into combined sewer outlets (CSO’s) which then dump untreated sewage into local streams and rivers. Green roofs are usually designed to mitigate the first 1.2 inches of any rainfall event, which in Mid-Atlantic region, typically translates into complete capture of the rainfall for 50 to 70% of all events, dependent on year to year rainfall totals and intensity (Starry, 2013). This has a large benefit on reducing the impact of rainfall on combined sewer outfalls (CSO’s) to the Chesapeake Bay. This is the primary reason that cities like Washington, DC with large CSO Districts are now managing storm water runoff through a combination of regulations (impervious surface fees) and incentives (rebates for green roof installation, reduction in yearly stormwater fees).
Green roofs are typically designed according to civil engineering standards, determined by curve numbers for predicting storm water runoff from a specific rainfall event, in inches per hour (Maryland Department of Environment, 2009). However, these runoff estimates are known to be inaccurate for green roofs, since they fail to take into account the many site-specific variables that determine green roof efficiency, as a combination of physical (aggregate layer depth, organic matter content) and biological components (e.g. plant type, coverage, age and health). Data have been collected over the past 10-15 years of runoff from various green roof installations throughout the US (and world), but estimates of efficiency still vary widely, since runoff is dependent on specific roof designs as well as antecedent moisture conditions on the roof. Starry (2013) developed a simple water-balance model that gathers the data from wireless sensor networks to predict stormwater runoff from roofs with varying design elements. We can therefore now cost-effectively monitor the performance of green roofs using wireless sensor control systems (WSCS), to quantify the efficiency of those green roofs to building managers and municipalities over weeks, months or years.
More importantly, we have the ability to use the control capability of advanced WSNs to automatically irrigate those green roofs only when plants are under water stress, and need water to maintain the health of the plant. This is likely to not only maintain the health of plants during periods of drought (even short term drought), but reduce maintenance labor costs (weeding and plant replacement), increase the diversity of plants that can be used for green roofs and likely increase the stormwater capacity of green roofs (since those plants have greater biomass and transpire more water than the succulent (water-conserving) species that are typically used in extensive green roof installations. Wireless sensor control systems have great potential and offer a number of advantages for the green roof industry.
Substrate and nutrient management
The manner in which substrate physical properties are evaluated is changing. Historically, static physical properties (air space, water holding capacity, total porosity and bulk density) have been used by scientists and growers alike to formulate substrates with “ideal” conditions (namely air and water capacity; Verdonck et al., 1978) for specific vessels with a given geometry. These are calculated utilizing porometer analysis (Fonteno and Bilderback, 1993) or moisture characteristic curves (Dane and Hopmans, 2002) and modeled to provide specific parameters for a given container geometry at a given point in time (Milks et al., 1989). New dynamic parameters that describe water, air and nutrient flux, transport gradients, and consumption are needed to assess and select soilless substrates for the 21st century and beyond to deal with increasing challenges facing producers (Caron et al., 2014). Specifically, there is a need for increased yield or biomass with limited resources, especially increasing water scarcity. Parameters, which deserve greater attention, include, but are not limited to, gas diffusion, hydraulic conductivity, and solute transport. These parameters will provide inferences into infiltration of oxygen and replacement of carbon dioxide from root respiration, water movement and connectivity, and both mineral nutrient and water availability as well as leaching during crop production. Much of the phenomena can be better understood via accurately measuring or predicting pore size distribution. More specifically, which pores are “allowable” (i.e. water transport is not hindered by capillary forces within the pore) or “accessible” (i.e. water and air can move to or from the pore) (Hunt et al, 2014). A portion of this information can be discovered via hysteric models, which are seldom utilized in horticultural substrates, in which the “ink-bottle” effect results in the observation of air or water entrapment; however, macro- and micro-pores remain immeasurable and poorly understood. Therefore, new tools (e.g. HYdraulic PROPerty analyzer; Schindler et al., 2010) and models (e.g. HYDRUS; Šim?nek, 2012) that utilize the Richards equation or in-situ measurements (e.g. Hoskins, 2014; O’Meara et al, 2014) must be employed to make inferences of these dynamic phenomena. Utilizing new methodology and tools will allow scientists to continue to assist crop producers that utilize soilless substrates to improve resource use efficiency.
Fertilizer available for plant uptake is a function of substrate chemical and physical and properties, and irrigation practices. There is a strong need for integrated assessments of the impact of substrate properties and fertilizer and irrigation practices during the course of plant production (Singleton et al, 2014). Depending on the type of substrate used, plant water use varies (Owen et al., 2007 and 2008; Kim et al, 2015) and plants require different amount of fertilizer to achieve the same amount of growth (Wright and Latimer 2007; Wright et al. 2008). Therefore, understanding the link between substrate properties, irrigation efficiency, and nutrient use is an important step to enhance plant productivity and to reduce crop water and fertilizer use.
To maintain profitable nursery crop production, costs of substrates relative to their actual impact on chemical and physical properties needs to be included in assessments. Costs of nursery substrates continues to increase with increasing costs of harvesting bark biomass and transporting it from lumber and paper mills to nursery producers. Research has been done to identify regional and sustainable alternatives to pine bark for use as the primary component in nursery substrates (Altland and Locke, 2011; Boyer et al., 2008; Fain et al., 2008, Jackson et al., 2010; Wright and Browder, 2005). Despite this work, market forces and grower comfort with pine bark as the primary component have resulted in the continued use of pine bark despite its increase in price. One area that has been explored only piecemeal is the cost and utility of the numerous amendments added to pine bark to create potting substrates. As mentioned previously, the number of amendments, their rates of incorporation, and all permutations of their combination are done with little knowledge of how those amendments actually affect the physical and chemical properties of the resultant substrates. While the costs of amendments are known, the value of the amendments to plant growth or their effectiveness in changing/improving substrate properties versus their cost is poorly understood.
Develop effective outreach programs which a) change behavior and implement best management practices, b) increase resource use-efficiency and minimize environmental impacts of practices, c) increase production efficiency and profitability and d) allow regulatory agency and public sectors to access baseline information which can be used for policy and other decision-making. Research results will be disseminated to the academic community through traditional means (e.g. peer reviewed journals, and extension programs) and also more novel web-based methods (knowledge centers, eXtension and social networks).
Regional water quality and plant health: Determine which water quality parameters limit ornamental plant production and determine how various secondary water sources in different regions of the U.S may be used in ornamental production.
Improved irrigation management: Determine the water requirements of a variety of ornamental plants and how these water requirements are affected by plant size and environmental conditions. Compare irrigation methods (e.g. overhead, spray stakes, drip irrigation, subirrigation) to determine how they affect total water use, plant growth and quality, and runoff water quality. Quantify reductions in water use, leaching, and runoff that result from more efficient irrigation techniques. Develop new and optimize existing methods to provide growers with real time information regarding the water requirements of their crops, including crop water use models and sensor networks that can be easily deployed in greenhouses and nurseries.
Urban stormwater runoff mitigation with green infrastructure: Quantify green roof efficiency and reductions in urban storm water runoff, to reduce combined sewer outfalls to receiving waters. Determine the economic impact of more efficient irrigation and water management practices (cost/benefit analyses).
Runoff and recycled water management: Continue to address research and extension needs related to improving runoff management by: (1) gathering comprehensive runoff-related information from the following sectors: a) growers, b) regulatory agencies, and c) university research and extension. Quantify the relative impacts of nursery runoff on surface water resources through detailed on-site investigations. Characterize critical control points within production systems and their influence on the presence and fate of pests, pesticides, and other agrichemicals (mineral salts) in production runoff, irrigation reservoirs, and other water sources. Develop chemical, physical, and biologically-based water treatment technologies to mitigate adverse effects of pesticides, salts, and pests in recycled irrigation water. Develop BMP guidelines for water recycling programs to minimize potential for negative effects on plant health by pests, pesticides, and mineral salts in recycled irrigation water.
Substrates and nutrient management: Assess physical and chemical properties of formulated media mixes and their impact on plant health, water use efficiency, and nutrient levels in leachates for a variety of plants considered of importance to various states/regions. Expand our knowledge of how formulated media mixes affect dynamic physical properties including hydraulic conductivity, cation and anion mass flow, and plant-water buffering. Develop BMP guidelines for substrate/amendment management practices.
MethodsThe methods outlined below are not clearly delineated areas; rather there is much overlap among these areas, which is necessary to assure that this project will integrate the most promising approaches. Each subsection of the methods will be coordinated by one of the project members identified at the annual meeting. Subsection leaders and project executive committee will accomplish coordination of methods to attain overall project objectives. The methods are listed in three sections: irrigation management, water sources and quality, and substrate and nutrient management. Water sources and quality Methods for Objective 1. i) We will combine modeled data and results of treatment technology studies into an online decision support system to guide grower selection of best management practices (e.g. installation of treatment technologies and adoption of water recycling practices) based on contaminants of concern, desired treatment levels, and economic factors. Methods for Objective 2 and Objective 5. i) We will systematically assess water quality parameters that influence plant growth, and categorize their potential impacts on plant production through plant screening trials. We will also assess regional water quality differences to begin tailoring recommended plant selections based on regional water quality parameters and water availability. ii) We will work with external collaborators to gather, collate, model, and interpret runoff-related water quality data from nursery and greenhouse operations across the US. These data will be combined with data characterizing critical control points in production systems. iii) We will identify, adapt, and monitor select filtration and chemically- and biologically-based treatment technologies to manage agrichemical, pesticide, and pest contaminants in recycle irrigation water. iv) We will develop a survey instrument to help identify nursery and greenhouse operations that utilize municipal reclaimed water, or other alternative, poor-quality water sources (like brackish, highly-sodic, saline, etc.) to irrigate their crops. v) We will assess plant responses to simulated recycled water or other alternative, poor-quality water sources and the substrate salt accumulation. vi) We will investigate responses of landscape plants to graywater irrigation in order to determine the long term effect of graywater irrigation on plants and soil. Irrigation management Methods for Objective 3. The efficiency of water applications depends greatly on how the water is delivered. A wide variety of irrigation systems are used in greenhouses and nurseries, ranging from recirculating sub-irrigation systems, to drip irrigation, to spray stakes, and to overhead sprinklers. In general, the more efficient irrigation systems are more expensive to install and maintain. There is little comprehensive information available on differences in water use among these different irrigation approaches, and even less information on their economics. i) We will determine how the irrigation method affects water use in greenhouses and nurseries. ii) Use environmental (weather station) data to determine the reference evapotranspiration, and combine this information with indicator species coefficients to estimate daily water use of indicator species. This can then be used to inform IFG-based irrigation schedules for growers. iii) Determine the costs and benefits of different irrigation systems and strategies. iv) Use soil moisture sensor and EC sensors to measure substrate water and nutrient status, to control irrigation and reduce nutrient leaching to a minimum. v) Measure plant responses to drying substrates and detect the early onset of drought stress to determine when irrigation is needed. Plant parameters to be measured could include changes in stem caliper, leaf temperature, leaf reflectance, stomatal conductance, and photosynthesis. vi) Quantify the effects of mild drought stress and plant anatomical, morphological, and physiological responses to determine how plant quality is affected. Methods for Objective 4. Soils and substrates: The benefits of efficient irrigation methods go beyond reductions in water use. Equally important are reduced leaching and runoff. Reduction in leaching and runoff of nutrients (and N and P in particular) need to be quantified. Since substrates differ in water holding capacity and ion exchange capacity, leaching and runoff is likely to be dependent on the physical and chemical properties of the substrate. Interactions between substrate properties and irrigation practices are therefore likely to affect leaching and runoff, and optimal irrigation practices may be substrate dependent. Thus, different irrigation methods will be tested in a variety of substrates, with various plant species (high vs. low nutrient-users) Runoff and pathogen management: In addition, we will investigate the systematic impacts of cultural practices and technologies (automated irrigation scheduling, deficit irrigation) on pathogen incidence, survival and pathogen loading in runoff water. The premise is that using precision irrigation techniques will significantly decrease water, agrochemical and pathogen loads running off from production areas. i) Determine threshold substrate moisture contents (sensor-controlled precision irrigation) to minimize daily irrigation runoff in two commercial nursery and greenhouse operations. ii) Investigate interactions between (i) and pathogen incidence and survival. iii) Determine whether (i) will also optimize root and plant growth. iv) Investigate increased or decreased fungicide effectiveness in combination with (i) and (iii). v) Quantify reductions in water and fungicide use in combination with (i) and (iii). Stormwater management: The validation and verification of Starry’s (2013) stormwater model will be associated with sensing commercial green roof installations. A green roof at NASA-Johnson Space Center (Houston, TX) was instrumented in February, 2014. Two other commercial roofs may be instrumented in 2015, one in Washington, DC and one in Portland, OR. These three roofs will provide opportunities for not only validation of the stormwater model but also calculating the efficiency of these green roofs with varying storm amounts and rainfall intensity. Methods for Objective 1. The benefits of any technology or practice depends upon how quickly and extensively they are adopted by industry, but follow two general pathways: i) Private Benefits will include those that accrue to nursery and horticultural businesses because of the higher prices they may be able to receive because of higher product quality and because of cost savings associated with increased resource use efficiency and other related reductions in input requirements. ii) Public Benefits will include those associated with reduced demand for water and reduced water discharges and related pollutant discharges and reduced energy use and air emissions. The value of some environmental improvements and related ecosystem services may be measurable directly using non-market valuation methods. The value of others may be imputed by examining the level of spending that is taking place elsewhere to achieve the same reductions in water use and water and air emissions. Substrate and nutrient management Methods for Objective 6. i) We will systematically assess static and dynamic physical properties of substrates with incremental rates of the most common amendments. New techniques will be shared and incorporated for measuring gas diffusion, hydraulic conductivity, and solute transport of substrates and their amendments. ii) We will develop an integrated substrate/nutrition/irrigation model for integrating substrate chemical and physical properties, crop nutrient requirements, and irrigation regime to maximize nutrient use efficiency and minimize nutrient leaching. To do this, we will start with a single crop, substrate, and fertilizer regime. We will attempt to use the latest published models for each of these systems in order to integrate them into a single model to guide irrigation and fertilizer delivery. The exact manner for doing this is currently unknown. We hope to use the collective experience of the group to formulate a high-risk, but high-reward strategy for integrating these fields for a unified system of nutrient and water delivery. iii) We will develop a sustainable-substrate matrix of the most common substrate components for nursery production along with their current market costs. We will populate the matrix with existing and new data on substrate chemical and physical properties. We will then offer a guide on how amendments both affect substrate properties and how those properties change in relation to their costs.
Measurement of Progress and Results
- Improved strategies for irrigation management, which reduce water and fertilizer use, while maintaining or improving plant quality.
- Guidelines for growers on the optimal irrigation approach for their operation.
- Presentations at grower meetings, symposia, colloquia, and workshops.
- Refereed journal publications for scientific community and extension articles and factsheets readily available for growers.
- Serve as a clearinghouse for articles and speakers from members to national and state trade journals, conferences, workshop and other presentations. Existing and new websites will be used to disseminate research results from this group.
Outcomes or Projected Impacts
- Increased profitability by reducing costs associated with irrigation (direct costs of water), reduced power use, savings on fertilizer cost, and labor savings.
- Reduced water and fertilizer use, energy and labor (increased resource use efficiency).
- Increased production (plant growth benefits).
- Large reductions in leaching and runoff of water and nutrients (environmental benefits).
- Conservation of water resources. Decreasing the amount of water used by ornamental growers will leave more water available for other uses.
- Improved water quality. Reducing runoff will help protect the water quality of ground and surface water throughout the U.S.
- Decreased carbon footprint of operations
- Greater understanding of the link between measured substrate properties and irrigation use efficiency
- Development of an integrated substrate/nutrition/irrigation model for crop management which will offer a new way of studying and growing crops
- A sustainable-substrate matrix will provide researchers and industry with a valuable tool for assessing the cost-benefit of substrate amendments. Economic sustainability has been increasingly stressed as an important component of research in agriculture. This matrix will provide a cornerstone to addressing the economic component of future research
- Knowledge on plant responses to recycled water and other alternative water sources can help nursery and landscape professionals and home owners to choose appropriate plants for landscapes where low quality water may be used
- Using recycle water or other alternative water sources for irrigating nursery crops and landscape plants can extend the supply of available freshwater for other beneficial use
Milestones(1):w ideas for determining impact of various water quality metrics and for measuring dynamic physical properties will be shared. A hypothetical model, integrating hydrology, irrigation application methodology, water quality, and treatment technology will be discussed and evaluated. Another model, integrating substrate properties, crop nutrient needs, and irrigation regime will be discussed and proposed. A sustainable-substrate matrix, composed of base substrates, amendments and rates, measurable responses, and economic costs will be proposed and agreed upon.
(2):Plant selection trials, water quality evaluation, and treatment technology evaluations will be carried out. Treatment technologies implemented at grower facilities. Validation of the model (hydrology, irrigation, water quality, and remediation efficacy) will be attempted and discussed. Data from the monitoring runoff at select grower sites will be used to populate the model. Website updated with data derived from research, preliminary models and case-studies published to support stakeholder adoption. Validation of the integrated substrate/nutrition/irrigation model will be attempted and discussed. Data from the sustainable-substrate matrix will be populated
(5):e model will be applied to cooperator nursery/greenhouse systems for validation. Data from these varied aspects will be developed into a peer-refereed extension publication for disseminating the information to the green industry. The integrated substrate/nutrition/irrigation model will be applied to cooperator nursery systems for validation. Data from the sustainable-substrate matrix will be developed into a peer-refereed extension publication for disseminating the information to the green industry.
Projected ParticipationView Appendix E: Participation
This group will deliver presentations at regional, national and international meetings. Examples of these meetings are Southern Nursery Association research conference, Annual conference of American Society for Horticultural Science, Cultivate (Formerly Ohio Florists Association Short Course), state grower association meetings, etc. Peer-reviewed publications and extension articles will be generated. In addition, existing and new websites will be used to disseminate information.
Altland, J.E. and J.C. Locke. 2011. Use of ground Miscanthus straw in container nursery substrates. J. Environ. Hort. 29:114-118.