NC_old1186: Water Management and Quality for Ornamental Crop Production and Health

(Multistate Research Project)

Status: Inactive/Terminating

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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).


Irrigation Management


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.
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