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THE NCSU HORTICULTURAL SUBSTRATESLABORATORY

Douglas A. Bailey

Each day we are facing newchallenges in floriculture. Mostgrowers are very aware of thecurrent emphasis beingplaced on water quality,waterconservation, and the

reduction of runoff from

agricultural industries.Another issue that reaches

beyond floriculture andaffects society as a wholeis solid waste managementand waste productutilization. Here at N.C.

State, these issues are beingaddressed in an inimitable

fashion. Faculty within theDepartment of Horticultural Sciencehave combined their expertise and formed apowerful research unit, the HorticulturalSubstrates Laboratory.

Creation of the Horticultural Substrates

Laboratory

For some time, the Department hashoused experts in horticultural substrates (forthose of you like myself who are behind thetimes, "growth medium" is passe' and"substrate" is the correct termfor the "stuff'around your plant roots): Dr. Bill Fonteno hasbeen specializing in physical properties ofhorticultural substrates, particularly the mixesused in floriculture; Dr. Ted Bilderback alsoresearches physical aswellaschemical propertiesof substrates, primarily for use in containernursery production of ornamentals; Dr. StuWarren has expertise in amending native soilsfor landscape use and is also involved with

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fertilization practices in the landscape and innursery production; and Dr. Paul

c^tlBSTi? Nelson is renowned as aleadingZ> **.7V authority in floriculture crop

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O

nutrition and has a greatinterest in pursuingalternative fertilization

practices for plantproduction. These four

faculty members areassisted in the horticultural

substrates laboratory byfour technicians and three

graduate students. This coreof researchers banded

together, integrating thestrengths of each program into a

center of excellence for substrates

research. Though in its infancy, the interactionworks well; sharing offacilities, sometimes labor,and a constant dialogue of shared ideas allowsthe group to address issues that no one membercould approach alone.

Grower Issues and Research Goals

Any plant/water/fertilizer issue that isrelated to the below ground portion of a crop isa concern of the substrates research group. Theissues being addressed and the correspondingresearch goals can be broken into two groups,those relating to physical properties ofa substrateand those relating to chemical properties of asubstrate.

Chemical properties of a substrate areconcerned with plant nutrition, fertilizationpractices, andnutrientretentionin thecontainer.In the past, most chemical properties researchdealt with these issues without addressing how

* NCSU ^

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physicalpropertiesofthe substrateaffectedplantnutrition. It is hard to separate physical fromchemical properties because they are sointerrelated. Forexample, wateringhabits (basedon drainage and water holding of a substrate)drastically affect nutrient levels in the substratesolution.

The physicalpropertiesofa substrate areequally important to growers, yet are lessunderstoodthan chemicalproperties. A substrateis needed to supply anchorage for the plant,moisture and oxygen to the roots, and to serve asa reserve for plant nutrients. Physical propertiesdictate how rapidly the containerwill drain, howoften watering is needed, and to a certain extent,how available nutrients will be to plants.

So what are the issues being addressedby the substrates laboratory? How are thehorticulture industries—floriculture production,nursery production, and landscapemanagement--benefiting from the projects? How is society ingeneral benefitingfrom this work? Listed beloware two major issues and what is being done totackle the problems involved.

Water quality/water conservation/runoff/groundwater contamination. It isonlya matter of time until growers will be forced tochange their fertilization and irrigation habits.

The amount ofwater used in production and thequantityof fertilizerrunningoutof thecontainerafterawateringmustbereduced. In the simplestterms, the goal is to keep the nutrients in thecontainer, reduce the amount that escapes intothe environment, andreducewateruse in general.

Paul Nelson's research targets nutrientuptake efficiency as a major goal (Figure 1).Part ofPaul's research has immediate and direct

application for the industry. The applicationsportion of Paul's program attacks die nutrientrunoff problem using three different strategies:1) Develop slow release fertilizers that willsupply constant, uniform, low levels of plantnutrients. Slow release fertilizers are currentlyavailable,but theydo notrelease as uniformlyasrequiredtoprevent"peaksandvalleys"innutrientconcentrations in the substrate solution. Plant

roots really do not require 200 ppm nitrogen. Ifwe could supply 14 ppm N (1 mmol) constantlyto the roots, never allowing the concentration atthe root surface to drop below 14 ppm N, thecrop could draw ample nitrogen for growth. Dr.Nelson's lab group is involved in evaluatingnutrient sources that may supply ample nitrogenuniformly over the entire production time of acrop (~12 weeks, as for pot mums). Some of thematerials being evaluated include composted

NUTRIENT UPTAKE EFFICIENCY

FUNDAMENTALS!

ESTABLISH DYNAMC

BOUNDARIES OF

RMZOSPHERE

INCREASE NUTRIENT

RETENTION IN THE

RMZOSPHERE

(AEC.CEC)

RELATE NUTRIENT

AVAILABILITY

FLUXES TOUPTAKE KINETICS)

CROSSUNK

PROTEINS

IAPPUCATIONS1

DEVELOP SLOW-

RELEASE NUTRIENT

SOURCE FOR LOW

CONSTANT LEVELS

SEEK SLOWLY

MNERAUZED

NUTRIENT SOURCES

EXTEND RMZOSPHERE

BOUNDARIES

| ENCAPSULATION|

Figure 1. Organizatonal diagramfor Dr. Paul Nelson's nutrition research program.

Figure2. Dr. Paul Nelsonandtechnician NancyMingisare measuring nitrogen releasefromexperimental slow-releasefertilizers.

poultry litter, bacteria, yeasts, and feather meal(Figure 2). These naturally occurring forms ofnitrogen are slowly broken down by nitrifyingmicrobes in the substrate. As the organicnitrogen is "mineralized", it becomes availablefor plant growth. Another class of slow releasefertilizers being developed are complex proteinmolecules that contain high levels of nitrogen.As the proteins are broken down in the substrate,the nitrogen becomes available for plant use.The third group of slow release materials ofinterest to Dr. Nelson is microencapsulatedmineral fertilizers. 2) Increase nutrientretention in the rhizosphere. First, a definitionfor rhizosphere: the rhizosphere is the portion ofthe substrate within a container from which

roots can draw nutrients and water. A largeportion of the container volume may holdfertilizer and water, but if the roots cannot pullthe moisture and the nutrients from that area,then it is not part of the rhizosphere. One wayDr. Nelson's group hopes to increase nutrientretention is to increase the cation and anion

exchange capacity (CEC and AEC) ofsubstrates.This involves evaluating differentmaterials usedin the substrate mixes and noting whichcomponents "hold" the most nutrients. If morenutrients are retained, less can leach out thebottomof the pot. 3) Extend the boundaries of

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the rhizosphere. As mentioned above, only aportion of the container volume is tapped byroots, and a large portion of the nutrients andwater in the pot are not available to the plant.How can plants utilize these unavailablenutrients? Aswatermoves throughthesubstrate,it carries nutrients with it. The nutrients outsidethe rhizosphere would be available, if we couldincrease the lateral movement of water into the

rhizosphere andtowards theroots. This is a goalbeingaddressedbyDr. Nelson's group aswellasDr. Fonteno's research group.

Bill Fonteno has been researchingphysicalpropertiesof substrates for manyyears.His work has led to standard procedures that areused to test the air and water status of mixes

produced by many ofthe substrate manufacturerstoday (Figure 3). The procedures developed inhis laboratory have reduced the turnaround timefor physical properties testing from 3 weeks to48 hours, allowing for quicker response to

Figure 3. Dr. Bill Fonteno and technician Beth Hardenare measuring drainage, aeration, container capacity,and total porosity ofgreenhouse substrates.

manufacturers and growers. Bill is continuingthis research into standardization of physicalproperties testing. Another portion of Bill'swork deals with reducing fertilizer runoff. Twoapproaches are being taken to reduce runoff andincrease nutrient efficiency: 1) Redesign mixes

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to reduce the amount of water that drains

from the container. Many of our mixes arevery "loose", and water drains out very rapidly.A well-drained substrate allows growers to be"heavy with the hose", watering more often andleaching with every watering withoutoverwatering the plants. We must change ourwatering habits and reduce the amount of waterrunning out the bottom of the pot. Recently, Dr.Jay Holcomb from Penn State University wasvisiting Bill's lab to become better acquaintedwith physical properties testing procedures. In agroup discussion of substrates and runoff

couldbeincreased, then the nutrients heldoutsidethe rhizosphere could become available to plantroots. Lateral movement of water through asubstrate is calledunsaturatedconductivity. Thisphysical property of a substrate has not beenaddressed in the past. Increasing lateralmovement of water and nutrients in a container

has not been a goal in the past. As a matter offact, unsaturatedconductivity has been sacrificedin order to increase substrate drainage. Lateralmovementof water isimportant toplantnutrition,andpart of Bill's research efforts are addressingways of increasing unsaturated conductivity in

substrates. Not only would anincrease in lateral movement of

water expand the rhizosphere, itwould result in more uniform

moisturedistribution in thecontainer

reducing the number of pockets oftoo much and too little moisture in

the substrate.

The topic of water qualityand reducing runoff is difficult toseparate from irrigation systemsresearch. Subirrigation and closedsystems such as ebb and flowbenches are one alternative to

nutrient runoff and excess water

use. Bill Fonteno, Roy Larson, andmyself are examining differentirrigation systems-tube systems,tray systems, and ebb and flow—forpoinsettia and bedding plant

production (Figure 5). This research will helpoffer design alternatives to traditional watering/fertilizing strategies that use tube deliverysystems.

The greenhouse industry is not the onlyfacet of horticulture concerned with nutrient

runoff. The nursery producers are alsoreevaluating their fertilizer procedures. Dr. TedBilderback's research efforts are centered around

keeping nutrients in the container in an outdoornursery situation. A container nursery does nothave the luxury of a greenhouse in having total

Figure 4. Attenders at a horticultural substrates briefing meeting heldthis summer included (L-R) Paul Nelson, Bill Fonteno, Ted Bilderback,Penn State graduate research assistant Noreen Khoury, Penn Statevisitingprofessor Jay Holcomb, and NCSU undergraduate researchassistant Jerome Brewster.

problems, the above point wasmade—greenhousemixes must"tighten up" and growers must reducetheir watering (Figure 4). Jay made an importantobservation that each of us must accept: "This(changes in greenhouse substrates and wateringhabits) is a major philosophical change in howwe grow plants." Growers will have to relearnhow to water theirplants. Dr. Fonteno's researchefforts in greenhouse mix design are crucial forrunoff reduction. 2) Increase the amount ofunsaturated conductivity in substrates. Asmentioned above, if lateral movement of water

Figure5. Irrigationsystemsare being testedbyBill Fonteno, RoyLarson, and Doug Baileyfor beddingplant and poinsettia production.

control overwatering. Nurseries must stick with"loose" mixes to prevent water logging duringheavy rain periods. This enhances the need forincreased nutrient retention in the nurserysubstrates. Ted has been testing slow releasefertilizers, and he has been evaluating substratecomponents that resist/reduce nutrient leaching(Figure 6). R-obably the biggest leachate problemin nursery production is phosphate loss. Ted'sapproach to phosphate retention in media issimilar to one of Paul Nelson's-increase the

nutrient retention ofa substrate by increasing thecation and anion exchange capacities. Moreanion exchange sites for phosphate in thesubstrate means less will flow out the bottom of

Figure 6. Dr. TedBilderback andtechnician MaryLorscheiderare determining nutrient levels incontainer leachates and nursery irrigation runoff.

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the container. In our groupdiscussion with Jay Holcomb, Tedcommented: "in today's bark-basednursery mixes, anion exchangecapacity is a mute point, but that ischanging rapidly." Again, thesubstrate laboratory group isaddressing basic chemical andphysical properties of substrates tosolve grower problems.

Dr. Stu Warren also deals with

nutrition of containerized nurserystock, magnesium availability inparticular. Magnesium leaches veryrapidly from nursery mixes,resulting in magnesium deficiency

during the second year ofgrowth. Stu is analyzingsources of magnesium that are more resistant toleaching than the magnesium released fromdolomitic limestone, the traditional source of

Mg used today. The most promising materialStu has worked with is the mineral olivine

(MgFeSi04). Olivine breaks down slowly,releasing enough Mg to supply the plantthroughout the production cycle. Stu and Tedare evaluating yard waste and poultry littercomposts as slow release sources of phosphatefor nursery production as a cooperative project.Composted materials may help increase nutrientretention by increasing CEC and AEC as well asserve as a source of plant nutrients. Stu and Tedare also looking at calcined clays as anamendment for nursery substrates. Calcinedclays can increase the CEC of the mixes and alsoincrease water holding capacity to reduceirrigation needs.

The horticultural substrates laboratory isaddressing water quality issues from many anglesfor many industries. But this is not the only issuethe laboratory is researching. Equally importantto both growers and society is the issue of solidwaste management.

Horticultural Uses of Solid Waste

Materials. The increasing problem of solidwaste management affects each of us in our

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personal as well as professional lives daily. Theproblem is intensifying and society must beprepared with alternatives to landfill disposal.In case you were unaware, you should know thatbeginning January 1, 1993, it will be illegal toplace any yard trash or plant material in a NorthCarolinalandfill. Currently, items such as leavesand yard debris (including plant material fromhorticulture industries) account for -30% of thevolume of North Carolina landfills. Where will

this material go in 1993? Where will you placeyour poinsettia stock after you have taken all thecuttings you need? This area ofwaste utilizationis being addressed by the horticultural substrateslaboratory. For example, Mecklenburg Countyhas already contacted the members of thesubstrates laboratory group in regards tocomposting the large amounts of debris createdlast year by hurricane Hugo.

We are fortunate at N.C. State to alreadyhave in place a strong program in agriculturalwaste management. Dr. L.M. (Mac) Safley ofBiological andAgricultural Engineering has beenresearching composting procedures for sometime. The engineers have the compostingtechnology; the horticultural substrateslaboratory have substrates technology. The twoareas are being meshed to form alternative usesfor the large volumes oforganic waste generatedby society. Stu Warren is working on theutilization of composts in the landscape (Figure7). Compost products are an excellentamendment for landscape use as well as ingreenhouse and nursery production substrates.The trendofusing waste materials in greenhousemixes can already be seen; materials—rice hulls,peanut hulls—are being used commercially insubstrates with good results. Stu Warren andTed Bilderback are cooperating on the use ofcompost materials in nursery container media asnutrient sources (mentioned above) as well as analternative use for solid waste materials. Bill

Fonteno is measuring the physical properties ofsubstrates containing composts and otheralternative substrate components. In the past,

Figure 7. Dr. Stu Warren (right) andtechnicianWilliam Reece are measuringplant growth responses tocompost incorporation intosubstrates.

this type of research was based on growingplants in a mix and evaluating growth. Thisapproach took years; many species need to beexamined with this approach and each croptakes time. Now that Bill's lab has standard

testing procedures, the approach is one ofmatching a setofphysical and chemical propertystandards. This approach takes only about 6months when evaluating a substrate mixture.The trend is away from worrying aboutingredients. Ingredients are not the issue-properties are. Another solid waste projectinvolves Paul Nelson's work with bacteria as a

nitrogen source for plants. Pharmaceuticalcompany waste products include dead bacteriaand other microbes that cannot be placed in landfills. Paul is using these materials as nitrogensources for our industry. In many areas offloriculture technology, universities fall behindthe industry with respect to state-of-the-artfacilities and equipment. Composting and wasteutilization is one area where we are a forerunner.

Benefits of the Horticultural Substrates

Laboratory

In a time when agriculture is beingcriticized for environmental pollution, we areattempting to increase water quality, and we arestanding on the edge of an era when we will

N.C. Flower Growers Page 27

become an essential userof society's waste products (talk about environmental stewardship!) Thehorticultural substrates groupisresearching realissues ofrealconcern forourindustry; waterqualityand solid waste utilization being emphasizedmost. Approached by individualprograms,progressin these areaswouldbe slow. However, with thecooperative additive effortscurrently underway,perhaps the general public will gain a better appreciation for horticulture in the very near future.

N.C. FLORICULTURE NEWS

• The 43rd annual North Carolina Commercial

Flower Growers' Short Course and Trade Fair

will be held September 23-25 at the MissionValley Inn in Raleigh, N.C. Please make plansnow to attend.

• Nominations are now open for NCCFGAsecretary, treasurer, vice president, and for threepositions on the boardofdirectors. Please contactBilly Hardin at (919) 622-3035 if you would liketo submit a nomination. Nominations will also

be taken from the floor during the Short Coursein September.

• Susan Rollins is heading the decorationscommittee for the Short Course, and yourparticipation and assistance is requested. Pleaseplan on bringing plant materials to decorate theconference room and trade fair area. Contact

Susan at (919) 851-6821 if you have anyquestions.

• Thanks to all who assisted with or attended

this year's bedding plant field day. The eventwas well-received with over 200 participantsin the garden tours and afternoon sessions. Ifyou missed this year's field day, please planon attending next year in late July.

• Congratulations to Robert Milks, VanWingerden International, Inc., Fletcher, N.C;Bill Fonteno and Roy Larson, North CarolinaState University, Raleigh, N.C, for beingchosen as co-recipients of the Alex LaurieAward presented at the 1990 International

Floriculture Industry Short Course (formerly theOhio Short Course). The authors received theaward for their article entitled "Hydrology ofHorticultureSubstrates: III.Predicting AirandWater Content ofLimited-Volume Plug Cells."The article appeared in the January 1989 Journalof the American Society for HorticulturalScience.

• Plan on attending one of the two Paul EckePoinsettia Clinics to be held in N.C. duringOctober. The clinics will be held MondayOctober 22 at the Wake County Agr. Ext. Officesand also Tuesday October 23 at the MecklenburgCounty Agr. Ext. Offices. The clinics are freeand no preregistration is needed. The NCCFGAwill be sponsoring complimentary refreshmentsat each. Call Doug Bailey at (919) 737-3321 ifyou have any questions.

Congratulations to (L-R)RoyLarson, RobertMilks,andBill Fontenofor being awardedthe1990 AlexLaurieAwardfor themostoutstanding researchpaperpublished byASHS in1989.