Optimising the nutrition of containergrown hardy nursery stock study tour

Transcription

1 Optimising the nutrition of containergrown hardy nursery stock study tour PCS, Destelbergen, Ghent, Belgium and surrounding local HNS nurseries 6 and 7 July 2016

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3 Study tour programme Wednesday 6 July Meet in the car park at Oakover Nurseries Plant Centre, Potters Corner, Maidstone Road, Hothfield, Ashford TN26 1AP Depart Ashford and travel to Dover for the ferry crossing to Dunkirk Ferry crossing. Breakfast on ferry Arrive at Dunkirk, travel to C. Verhelst-Verplancke Nursery. This nursery specialises in the propagation and production of both container- and field-grown trees and shrubs. They have experience with plant sap measurements to monitor the nutritional status of plants, use compost tea for disease control and manufacture their own growing media. Travel direct to PCS, Destelbergen Arrive at PCS, Destelbergen. View the project work undertaken as part of project HNS 193 and discuss the issues of on-site nutrient monitoring. Other related trials at the station will also be available for viewing. Lunch at the station, then travel to Luc Dierick Nursery Arrive Luc Dierick Nursery. This nursery specialises in the production of laurels. The nursery collects and recirculates both rain and irrigation water, filters the water via a sand filter and uses both CRF and liquid feed fertilisers to provide plant nutrition. Travel to hotel Arrive at Ibis Ghent Centrum Opera hotel in Ghent. Thursday 7 July Breakfast, room payment and depart Ibis hotel in Ghent Arrive at Eric Boterdaele Floristry. This nursery produces a specific range of containergrown shrubs for winter troughs, pots and gardens, it recycles water and undertakes ecological footprint monitoring via the MPS certification scheme. Travel to Willy De Nolf Nursery Arrive at Willy De Nolf Nursery. This 26 ha nursery and cash carry produces a wide range of container-grown trees, conifers, shrubs and herbaceous plants. It extensively uses a loose fill bark mulch to achieve weed control on the nursery Lunch Arrive Devriese-Luyssen Nursery. This nursery specialises in the production of Laurus nobilis and Lagerstroemia (crepe myrtle). The nursery collects and recirculates both rain and irrigation water and filters the water via an iris bed Depart nursery and travel back to Dunkirk for ferry crossing back to Dover Ferry crossing. Evening meal on ferry Arrive at Dover and travel onto Ashford Arrive at Oakover Nurseries Plant Centre car park, disembark coach and collect cars for onward journeys. UK time Belgium time

4 Lunch-workshop KEEP TRACK OF YOUR PLANT NUTRITIONAL STATUS Wednesday 6 July 2016 at 13h00 PCS Schaessestraat 18, 9070 Destelbergen, Belgium Nowadays there are various techniques and devices to monitor plant s nutritional status quickly and easily. During a lunch-workshop you will learn what these new techniques have to offer, how to use them and how to interpret their readings. Flemish growers will also attend this workshop. Programme Indoor session with sandwiches: 13h00 13h20 13h35 Keep track of your plant nutritional status John Adlam (Dove associates) NutrHONS plant trial Neil Bragg (Bulrush) Detection of plant stress with sensors Bert Schamp (PCS) Outdoor session: This workshop is organised within the project Nutrient management in hardy nursery stock, financed by the Agriculture and Horticulture Development Board 13h50 14h10 14h40 Demonstration of sampling techniques and pieces of equipment being used in the NutrHONS project Verónica Dias (PCS) Nutrient management trials at PCS tour Bruno Gobin, Sandy Adriaenssens and Dominique Van Haecke (PCS) Drinks

5 PCS Ornamental Plant Research Organisation The creation of PCS in October 1988 marked a new era in the history of cultivation of ornamental plants in Belgium. PCS was an amalgamation of the Experimental Gardens for Floriculture, Nursery Stock and Cut Flowers and the Research Station for Horticulture BVO, all of which were non-profit associations. Since 1 January 2005, the activities of the different unities are brought together in one entity: PCS n.p.a. Ornamental Plant Research is situated in Destelbergen, right in the heart of the growing region for ornamental plants, which strengthens its function as a research and information centre for ornamental horticulture. Policy The professional sector and consultancy services are closely involved in the functioning of the centre, resulting in an optimal interaction between research, information and practice. Each year the programmes of the practical research are worked out in technical committees consisting mainly of growers, but also attended by researchers and consultants. The current problems are introduced via various culture workgroups. For the new programmes of the scientific research, the proposals and activities of the culture workgroups are also taken into account, but mainly researchers decide on the exact structure of the research. Activities PCS Ornamental Plant Research has the expertise and facilities to carry out applied scientific research and more practice-oriented research. At both levels the research is done thematically. Important research themes are the optimization of culture methods, growth and flowering regulation, use of energy, quality and post harvest properties of ornamental plants and research for practical utility. In the present research, environmental protection has become a very important theme. This includes trials in closed culture systems, in which water and fertilizers are recycled, so that nothing can leach into the subsoil. The minimization of use of chemical products is also a central issue in the theme of plant protection. Integrated control is an important aspect of this research. In this context, PCS developed an observation and warning system for pests and diseases in nursery stock and has also a program for guided control in glasshouse cultures. Within PCS, there is also an important engagement to information and education activities. The transfer of knowledge is realized by the publication of results in professional journals and the organisation of study meetings, lectures, visits, etc. Funding The operating costs of the Centre are financed by government and industry. The most important funds are given by the Flemish Community, IWT (Institute for the Promotion of Innovation by Science and Technology in Flanders), the Province of East Flanders, the Provincial Chamber of Agriculture of East Flanders, Boerenbond (the Belgian Farmers Union), AVBS (the Belgian Ornamental Growers Federation), KMLP (the Royal Agricultural and Botanical Society organizer of the Floralies of Ghent), KBC Banking & Insurance and the voluntary contributions of growers. Schaessestraat 18 B-9070 Destelbergen T: +32 (0) F: +32 (0) E: info@pcsierteelt.be W:

6 HARDY NURSERY STOCK A picture of health New technologies are making it possible to monitor nursery stock crops routinely for nutrient status. An AHDB Horticulture project is beginning to come up with the baseline data that growers will need to interpret their test results, as Neil Bragg reports To gather crop nutrition data, plants are grown in specially designed units that can capture all the run-off from the containers for analysis Regularly monitoring the nutrient status of a nursery stock crop not only helps pick up problems before growth or quality suffer, it makes it possible to fine-tune nutrition for optimum crop performance and minimise nutrient run-off because supply is matched to crop demand. But until recently, nutrient analysis of the plant tissues themselves meant sending samples away for laboratory testing and the inevitable time lag in getting the results delays being able to address any problems that the analysis identifies. So growers have been looking for reliable on-nursery tissue analysis methods, as well as information to help them interpret the results in terms of what they mean for crop health and performance. A variety of techniques and pieces of equipment have become available over the last few years that claim to eliminate the need for laboratory testing. But what do they really offer? How easy are they to use and how confident can we be in the results? And where is the data to show what the nutritional status of a healthy crop looks like, so that growers can interpret their own analyses? To help answer those questions, the Hardy Nursery Stock Panel commissioned a project that started this spring to investigate ways of monitoring nutrients in crop tissue. One of the first steps is a review of existing research and other literature on methods of measuring plant growth and performance in relation to nutrient inputs, and on tissue nutrient analysis and PROJECT PROFILE HNS 193 Nutrient management in hardy nursery stock (NutrHONS) project Term: April 2015 to March 2018 Project leader: John Adlam Industry representatives: Nick Dunn, Chris Bowman, Ann McCann Location: Greenmount College, Northern Ireland; PCS Destelbergen, Belgium; commercial UK nurseries monitoring. This includes looking at data on the nutrient balance between plant uptake and losses due to leaching. The techniques that appear the most practical and useful for growers are being tested on a range of crops and at various locations in the UK and Europe. The results of the analyses from each are being compared with results from laboratory methods to judge their accuracy. By the time the work has finished, growers should have enough information on crop nutrient status and on the performance of the equipment to develop their own on-nursery monitoring schemes with their own mix of crops. The project is being co-ordinated by nursery stock consultant John Adlam of Dove Associates and the research partners are Northern Ireland s Greenmount College and Belgian nursery stock research station PCS Destelbergen, near Ghent. Trials are also being undertaken on commercial nurseries in the UK: Coles 20 AHDB Grower November 2015

7 hardy nursery stock Nurseries, Frank P Matthews and Osberton Nurseries will be testing the equipment over a wide range of crops. One advantage of collaborating with the research team at PCS Destelbergen is that they already have plenty of experience in working on the nutrient balance of nursery stock crops and have designed their own experimental equipment for measuring rainfall, irrigation, run-off and nutrient losses from a container, giving an accurate picture of nutrient availability to the crop. The results from these measurements are being used alongside the data collected from tissue and growing media analysis so nutrient uptake and loss can be calculated. By running our trials in both Northern Ireland and Belgium we can also capture any effects that might be a consequence of climate variation from north-west to southeast any nursery in the UK would fall somewhere within that range. The laboratory analyses, from samples of the collected run-off and of substrates and plant tissue, are being undertaken by NRM in the UK and the analysis data is being correlated by project partner Bulrush. FIRST SEASON TRIALS The aim of these initial trials was, as much as anything, to get a feel for the usability of the on-nursery nutrient testing kit that we d chosen from our literature review to make sure it could be used by our grower partners and to firm-up protocols so that each nursery would use each type of equipment in the same way. The trials were established by late April. From then on, we routinely sampled substrates and plant tissue for nutrient analysis and at the same time took measurements of growth extension. Measurements such as moisture content, ph and EC levels are being recorded using the kind of equipment that growers are already familiar with. Despite the high rainfall and poor light levels, particularly through July and August, we ve seen at both Greenmount and PCS Destelbergen, the trials have enabled us to start collecting the data that we ll be building up over the three years of the project. We chose four plants as our test subjects for the first year: buddleja, because it is fast growing and very responsive to fertiliser; Chamaecyparis pisifera Boulevard, because its A simple strip test for sap nitrogen content A hand-held sap nitrate meter This meter checks moisture and EC in growing media Using a smartphone app to read leaf colour foliage colour is sensitive to nitrogen; Viburnum tinus, because it s so widely grown, growth measurement and assessment are easy and the project team is familiar with it over many years of trials; and Skimmia japonica Rubella, a nursery shrub that produces plenty of foliage and which is also easy to assess for growth. We decided from the outset to use the same basic growing medium across all sites to eliminate any effects that might be due to differences in substrate. Obviously lime rates are dependent on crop species but the only other variable imposed as part of the trial was the rate of controlled release fertiliser. A standard 8-9 month product was used at 2, 4, 6 or 8g per litre. The on-nursery test methods we ve been looking at vary from very simple hand-held dipsticks for measuring sap nitrogen, to smartphone apps which relate leaf colour to nitrogen content. There are also various portable meters that make assessments of either tissue nitrogen content or leaf chlorophyll fluorescence as indicators of plant health. Most of the smartphone apps available have been designed for cereal agronomists and our trials should show whether their results can transfer to other crops. One of the main problems we have experienced so far is actually obtaining appropriate quantities of sap extracts to use with the hand-held devices. In the case of chamaecyparis, for example, the only way we could generate enough tissue sap exudate was by squeezing the tissue with pliers. As this first season draws to a close the project team will have enough information on the various techniques to decide which to carry forward to grower trials and whether others need to be considered. We have already decided not to pursue any further trials with the dipstick methods, as the colours already present in sap samples make it too difficult to distinguish or interpret the colour reaction on the test strip. We re likely to continue to work with the various forms of test meters and with the smartphone apps. And, as we go into the grower trials next year, we ll have correlated a huge data set from the laboratory results which will be of considerable help in understanding the nutrient uptake and losses from the growing media and crop species that we re studying. Some of the members of the Hardy Nursery Stock Panel have already seen the trials under way at Greenmount on a visit earlier this autumn and we are planning to arrange some trial open days for growers during the next phase of the work. ABOUT THE AUTHOR Bulrush horticulture director Neil Bragg is a partner in HNS 193, supporting project leader John Adlam November 2015 AHDB Grower 21

8 HNS 193 equipment outline Monitoring plant nutrient status has traditionally been done through soil nutrient and/or tissue analysis. Tissue analysis methods have been widely applied to plants due to their reliability in organic nitrogen determination, but they are time-consuming and destructive. Therefore, the focus of these studies is to test easy to use and non-destructive new tools designed for plant nitrogen (N) status estimation. This project has initially tested five different pieces of equipment that were affordable and easy to use. An additional leaf chlorophyll measurement device has been added in the second year. Nitrogen in plant sap The extraction of plant sap is a destructive method that includes the detachment of the main petiole of the leaves, cutting it into small pieces and press it using a garlic press. As petioles in ornamental plants are mostly very small in this trial leaf samples (including petiole) were used and leaf sap was analysed. Two pieces of equipment were used to measure the concentration of nitrate in leaf sap. Merck Nitrate test strip Nitrate test strips change colour when exposed to nitrate contained in the sample of plant sap. The colour can then be compared to a colour chart (subjective method) or be measured by a hand-held reflectometer. The Merck test strips used during this project were those for the detection of nitrate the Merckoquant NO 3. This test strip measures from 0 ppm to a maximum of 500 ppm NO 3. Merck test strips are quick, easy

9 to use and very cheap ( per 100 pieces). Quant strip tests measure in nitrates instead of nitrate-n, therefore readings must be divided by 4.43 to find the nitrate-n value. Horiba Laquatwin Nitrate kit cover both electrodes). For this piece of equipment, nitrate levels in plant sap are measured using a nitrate sensitive electrode. This compact nitrate sensor has an operational range from 23 to 2,300 mg/l and only needs a few drops of plant sap to generate a reading (enough to However, this technology does have some disadvantages: (1) It does not measure total N in plant tissue but only NO 3-N, (2) The presence of other ions such as chloride, bicarbonate or nitrite can affect measurements (b). 1 (3) Frequent calibration is also needed to maintain the accuracy of the sensor (every 5 samples) (4) Readings should be made in the shade since direct sunlight can affect the meter. Optical sensing methods The greenness of the leaves represents the amount of chlorophyll found in the chloroplasts. Leaf chlorophyll content can be used as an N status indicator, because this is an essential element in photosynthetic protein synthesis. Leaf chlorophyll content increases with N supply and decreases when N is limiting. 1 This has always been a problem with ion specific electrodes

10 atleaf+ The atleaf+ is a sensor that measures leaf Chlorophyll content in a similar way as a SPAD meter, but has the advantage of being cheaper. It is a non-destructive, handheld, lightweight and easy-touse, sensor. The device works by inserting the leaf into the aperture in the front of the sensor and clicking on the measure button. There are two LED emitters in the upper part of the aperture at two wavelengths, red at 660 nm and near infra-red (NIR) at 940 nm. Light filtered through the leaf is captured by a sensor below it which measures the absorbance of the leaf. The difference in transmission of the filtered wavelengths gives a measure of chlorophyll content in atleaf+ units. The sensor continues to sample the scanned area as long as the measure button is being pressed. An average value of the measurements will appear when the measure button is released. The device can measure leaves that are up to 0.1 in (2.5 mm) in thickness. Measurements can be stored and easily uploaded to a computer. According to literature this sensor is not very effective at collecting readings on leaves with small widths like conifers. Unlike SPAD that makes the measurements in a closed chamber which clamps over the leaf, and has a filter to clear other wavelengths in the light spectrum, the atleaf+ sensor takes measurements in an open aperture and has no filters. This is likely to affect the readings because: (1) the position of the leaf can vary (closer to the top part of the aperture or to the lower part) and (2) this aperture allows for light to reach the sensor diode and interfere with the reading.

11 Fieldscout Green Index App This App was developed to capture differences in greenness between corn leaves. The app captures images using the iphone digital camera and determines the DGCI (Dark Green Colour Index) of plant leaves (between 0 and 1). When purchasing this App, growers should also purchase a reference board which is used as a background when taking pictures of the leaves. The green and yellow discs present in this board are known colours (standards) used by the software to calibrate differences in light conditions; the pink background increases contrast and reduces noise, and the grey colour calibrates the white balance. Because N status is not the only factor that affects the greenness of the leaves (water stress, temperature, and cultivar also do) the DGCI readings taken in a field must be compared with readings taken in a high- N reference area. Recent studies show that DGCI is closely related to the N content in leaves as well as with SPAD readings.

12 Apogee MC 100 Hand-held chlorophyll meters typically provide a relative indication of chlorophyll in plant leaves. The Apogee model MC-100 chlorophyll concentration meter measures relative chlorophyll content and outputs an estimate of actual chlorophyll concentration in units of ρmol per m 2 of leaf surface. The MC-100 provides an alternative to destructive sampling techniques for determining chlorophyll concentration. It is less time consuming and labour intensive, and allows for leaves to be measured and monitored over an entire growth cycle. It also allows for rapid replicate measurements of the same leaf, or rapid measurement of multiple leaves. The MC-100 chlorophyll concentration meter includes custom coefficients to determine chlorophyll concentration for twenty-two different plant species. It also includes a generic equation for use with all plant species, where the equation was derived from the data from all twenty-two species measured. The MC-100 chlorophyll concentration meters consist of two light emitting diodes (one emitting red radiation and one emitting near infrared radiation) with paired detectors, liquid crystal display (LCD), operation buttons, 9 V alkaline battery, and signal processing circuitry mounted in a plastic housing. The meter also includes a USB port for data download to a computer and RS-232 port for use with GPS. The meter is handheld and designed for instantaneous, non-destructive, direct determination of leaf chlorophyll concentration. The meter measures the ratio of radiation transmittance from two different wavelengths (red and near infrared) and outputs chlorophyll concentration, which is calculated internally from the transmittance ratio measurement

13 and then displayed on the LCD. In our initial trials with this piece of equipment has proved to be very sensitive in identifying the colour change in leaves from the four different CRF rates. It is showing a change in colour before it is visible to the eye and may be capable of detecting nutrient deficiencies at an early stage. Electrical conductivity (EC) in substrate Monitoring the N present in the growing media through substrate analysis is a method widely applied in the hardy nursery stock industry. However, sampling growing media is labour-intensive, expensive, and growers have to wait for the results in order to be able to adjust fertilization regimes. Procheck and GS3 sensor probe The sensor GS3 from Decagon measures soil moisture, temperature, and electrical conductivity (EC) of the substrate. The probe has three steel needles that improve sensor contact in porous substrates such as peat or perlite. By measuring EC in the substrate solution, the sensor measures the total amount of salts dissolved in pore water. It does not give information on the amount of a specific nutrient. However since the majority of salts in the substrate are macronutrients, EC can be used as an indicator of the presence of macronutrients in the growing medium. This is proving to follow leaf tissue N levels well as an indicator of nutrient status.

14 Nutrient management in Hardy Nursery Stock HNS 193 (NutrHONS project) D J Adlam, Dove Associates N Bragg, Bulrush Horticulture Ltd Merck Nitrate test strip Equipment Nitrogen in plant sap Detection of nitrate NO 3 using a colour change in the strip tip

15 Equipment Nitrogen in plant sap Horiba Laquatwin Nitrate kit Detection of nitrate NO 3 using a nitrate sensitive electrode operating over the range 23 2,300 mg/l atleaf+ Equipment Optical sensing Measures chlorophyll content in the chloroplasts as an N status indicator Measures two different spectrums at 660nM and 940nM that are passed through the leaf in an open slot.

16 Equipment Optical sensing Refractometer Measures the degree of refraction in light caused by the nutrient levels in sap. The refractive index of a given sample varies with wavelength for all materials. This relation is nonlinear and is characteristic for every material. Some work done in Ireland shows that levels of plant nutrients in the sap can be identified by refraction. Apogee MC 100 Equipment Optical sensing Measures chlorophyll content in the chloroplasts. It measures two different spectrums at 653nM and 931nM that are passed through the leaf, within a closed chamber.

17 Field Scout Green Index App Equipment Optical sensing Measures leaf colour using an iphone or ipad. Equipment Electrical conductivity in the substrate Procheck with GS 3 sensor Measures soil moisture content, EC and temperature No specific nutrient information

18 Factsheet 05/05 Horticultural Development Council Hardy nursery stock HNS 43a-f, 95, 96, 96a and 98 Bradbourne House East Malling Kent ME19 6DZ T: F: E: Nutrition of container-grown hardy nursery stock By Susie Holmes and Andrew Hewson, ADAS This factsheet contains information on optimising the nutrition of container-grown hardy nursery stock. It collates the results of several HDC-funded projects on controlled release fertilisers and provides recommendations on supplementary feeding techniques and base fertilisers. It also covers the importance of ph, monitoring and water quality in relation to plant nutrition. Background The production of uniform, high quality container plants requires good nutrition in addition to the correct physical characteristics of the growing medium. For container-grown plants, excessive nutrient levels can be more damaging than low levels but either can result in plant losses or poor quality and failure to meet customer specifications. Quality assurance schemes also demand that growers use fertilisers in a responsible way in accordance with current legislation and Codes of Practice, such as The Groundwater Regulations 1998 and Nitrate Vulnerable Zones. In addition, container plants sold through the retail market must maintain an attractive appearance for several weeks in store before they are sold. The growing medium should therefore provide a gradual release of nutrients to maintain an acceptable shelf-life and avoid the plant becoming starved. Table 1 overleaf summarises the essential plant nutrients, their functions within the plant and symptoms of deficiency or excess. Fig 1 Interveinal chlorosis of young leaves often indicates iron deficiency ( lime induced chlorosis ) one of the most common nutritional deficiencies seen in container-grown nursery stock and usually associated with high ph of growing media

19 Table 1 Essential plant nutrients, their functions within the plant and symptoms of deficiency or excess Nutrient Function in plant Deficiency symptoms Comments Nitrogen (N) Protein formation. Uptake mainly as nitrate (NO 3 ), but also possible as ammonium (NH 4 ). General yellowing of leaves, starting on oldest leaves, poor growth. Excessive nitrogen is more likely than a deficiency and can be damaging, especially in the ammonium form. Phosphorus (P) Energy transfer. Root development. Purpling of older leaves, can be induced by cold and/or drought. Excess phosphorus causes chlorosis. Excess phosphorus is more likely than a deficiency and causes damage to sensitive plants eg Ericaeous, Cytisus. Potassium (K) Regulation of cell water content; enzyme systems. Interveinal yellowing/ necrosis starting for outer edge on older leaves. High levels of potassium depress magnesium uptake. Magnesium (Mg) Chlorophyll production. Interveinal chlorosis/ necrosis of oldest leaves. Magnesium deficiency is often related to poor root conditions. Sodium (Na) Similar to potassium. Dark green, dull foliage. Rarely deficient. Sulphur (S) Constituent of proteins, amino acids and vitamins. Chlorosis, similar to nitrogen deficiency. Rarely deficient. Calcium (Ca) Cell wall formation and cell division. Distortion of growing points, necrosis of leaf margins, low calcium often associated with low ph (acid conditions). Ca deficiency usually related to environmental conditions such as high humidity/poor ventilation when transpiration rates are low. Iron (Fe) Enzyme and chlorophyll production. Interveinal chlorosis of youngest leaves. Most common trace element deficiency seen in nursery stock when ph is too high. Manganese (Mn) Enzyme systems. Mottled chlorosis of middleaged leaves (deficiency often linked to high ph conditions). Excessive Mn levels from low ph or barks cause black spotting/ papery bark. Boron (B) Respiration, carbohydrate metabolism, cell division and differentiation. Internal browning of stems, lack of apical dominance. Boron toxicity usually only occurs if boron is applied where not needed. Copper (Cu) Enzyme systems/ photosynthesis. Poor leaf development. Rarely deficient. Zinc (Zn) Enzyme systems/auxin production. Pale, stunted plants. Rarely deficient. Molybdenum (Mo) Nitrogen reduction enzymes. Narrow strap-like leaves. Deficiency very rare.

20 Methods of providing plant nutrients There are four principal methods of providing nutrients to plants: 1. Controlled release fertilisers 2. Base fertilisers 3. Liquid feeds 4. Supplementary feeds. The method chosen is dependent on a number of factors including crop species grown, growth stage and marketing date, irrigation system and growing situation. Often a combination of systems is used, for example a low rate of base fertiliser plus a controlled release fertiliser. These are covered in detail in the following sections. 1. Controlled release fertilisers The majority of container nursery stock in the UK is grown with Controlled Release Fertilisers (CRF s), which provide nutrients gradually over a period of time, typically, for longer term crops, up to 18 months. Such fertilisers are also available with a shorter release period for single season and quick growing crops such as pot liners, and as medium term products for over-wintered container stock. Nutrient release is temperature controlled and so is generally in line with plant demand, thereby reducing leaching into groundwater. CRF s can also provide some shelf-life for plants once they have left the nursery. Nutritional programmes based on CRF s often incorporate other methods of supplying nutrients. For example, CRF s can be slow to start releasing nutrients, particularly early in the year when low temperatures prevail and so supplementing them with base fertilisers provides more immediate nutrition for newly potted material. Liquid feeding may also be used to provide additional nutrition, particularly when the CRF is running out. Product selection The following factors need to be considered when selecting CRF products to use on hardy ornamental nursery stock. Figs 2 & 3 CRF products release nutrients gradually over a period of time and generally in line with plant demand thus minimising leaching Time of potting Will plants be potted in spring/ summer or autumn/winter? Production timeframe What is the length of time before the next potting stage or the scheduled marketing period of the plants? Short term single season crops usually require different CRF products to longer term overwintered crops. Growth stage What is the growth stage of the plants eg cuttings, liners, finished plants? Species grown What is the vigour of the plant eg salt sensitive species (such as ericaceous crops and heathers), moderate vigour or fast-growing? Where a large number of species are grown, these are normally grouped according to their vigour and hence nutritional requirements. Different CRF products have different ratios of nutrients, allowing products to be matched more closely to the requirements of different crop types. For example, products with a lower nitrogen content and higher potassium release may be more appropriate where excessive vegetative growth is not wanted, (eg herbaceous perennials and some climbers). Crop management What type of irrigation system will be used? Lower rates of CRF are used with sub-irrigation systems, such as capillary sand-beds, compared to overhead irrigation systems. Is production taking place indoors or outdoors? Temperatures are higher under protection and the type and rate of CRF used must take this into account, especially for autumn potting under glass when lower fertiliser rates should be used. Controlled release fertiliser rates Table 2 overleaf summarises the main CRF products, their typical rates and suggested crop type.

21 Table 2 Summary of the main Controlled Release Fertiliser products, suggested crop type and rate range Typical use CRF type Example product (ratios are for N:P:K) Typical rate range kg/cu m Propagation with cells less than 5cm Mini granules Multicote Mini (19:6:11) Osmocote Mini (16:8:11) Spring-potted very short term perennials Very short-term Osmocote Exact 3-4 month (16:11:11) Plantacote Plus 4 (14:9:15) Polyon 4-5 month (14:14:14) Herbaceous perennials Herbs Alpines Heathers Short-term Multicote 6 (18:6:12) Osmocote Exact 5-6 month Low (15:8:10) Standard (15:9:9) High (15:10:10) Osmoctoe Exact 5-6 month High K Plantacote Plus 6 (14:9:15) Sincrocell 6 (14:9:14) General shrubs Climbers Conifers Shrub liners Medium term Multicote 8 (18:6:12) Osmocote Exact 8-9 month Standard (15:9:9) Lo start (15:8:10) Hi start (15:10:10) Plantacote Plus 8 (14:8:15) Polyon 6-8 month (19:6:12) Polyon 8 10 month Sincrocell 9 (14:8:14) Herbaceous perennials Alpines Heathers Medium term, High K Osmocote Exact 8-9 month High K Over-wintered liners Shrubs Trees Heathers Two-season, overwintered Osmocote Exact month Standard (15:9:9) Lo start (15:8:10) Hi start (15:10:10) Plantacote Plus 12m (14:8:14) Polyon (17:5:11) month Sincrocell 12 (14:8:13) Vitacote (18:6:12) Multicote 12 (15:13:15) 1.5 for heathers for liners for potting on Trees Specimen plants Long-term Osmocote Exact month (15:8:10) Plantacote Plus 16m (14:8:14) for salt-sensitive spp for vigorous spp./trees Notes: The product examples are not exhaustive and no criticism is implied of products not included. For several products there is now a range of ratios of major nutrients within each longevity type. For example, fast-start blends with more nitrogen and high K blends with less nitrogen and more potassium where excessive leafy growth is not wanted (eg for herbaceous plants). Manufacturers technical literature and recommended CRF rates should always be referred to. Reduced CRF rates are recommended for young plants/liners and for autumn potting.

22 Options for CRF application Mixing The fertiliser can be mixed evenly into the substrate. Uneven mixing will result in large differences in nutrient status between pots. Even mixing is particularly important for small pots use mini granules for small modules (less than 5cm in diameter) and pots (less than 7cm in diameter). Dibbling With this technique, the desired dose of fertiliser is dispensed or dibbled into each pot at the base of the drilled planting hole during machine potting. This approach allows changes in fertiliser rates to be made more easily, for example when potting species of different vigour one after the other. The rate of CRF used can also be reduced slightly (see manufacturer guidelines) with dibbling and it may, when coupled with careful water management and good nursery hygiene, help reduce moss and liverwort problems because the nutrients are not present in the top layer of substrate. 2. Base fertilisers For many spring-potted shrubs, a combination of a low rate of base fertiliser that releases nutrients over the first 4 8 weeks plus the appropriate rate of CRF is a good, cost effective system. Typical rates are kg/cu m of base fertiliser (eg a 14:16:18 or 12:14:24 compound horticultural grade fertiliser) with kg/cu m of a 12 month longevity CRF (see HDC projects HNS 43e and HNS 43f for detailed trial results). Reduced CRF rates are also used for liners, typically kg/cu m with 0.5 kg/cu m base depending on species. Base fertilisers applied at kg/cu m can also be useful to give a fast start to some crops, particularly in cooler geographical locations or times of potting when CRF nutrient release is slower. They are not always necessary for autumn/winter potted container stock and are usually omitted with Ericaceous and salt sensitive subjects. An appropriate rate of N:P:K base fertiliser can also be used to supply supplementary nitrogen required in media containing bark as an alternative to ammonium nitrate, which Fig 4 CRF dispensers can be used to dispense measured doses of fertiliser into the base of the drilled planting hole when machine potting Fig 5 Base fertilisers can be used in combination with CRFs for spring and summer potted container stock to provide immediate nutrition. They can also be considered as a form of supplementary nitrogen for crops grown in media containing bark at low rates, can be difficult to mix in evenly. For example, 1.0 kg/cu m of a 14:16:18 fertiliser would provide 140 mg/l nitrogen, which would be an adequate amount of supplementary nitrogen for a mix with 20-30% bark.

23 3 Liquid feeds If the appropriate rate and longevity of CRF has been used, liquid feeding should not be necessary. However, the use of liquid feeds may be useful if the CRF is running out, due to plants being kept on the nursery longer than anticipated or where excessive leaching of nutrients has occurred. Liquid feeds are particularly suitable for protected crops; they are more difficult to use on outdoor crops during wet weather. Systems using only liquid feed (no CRF) can work well for plants grown under protection, particularly specialist mono-cropping systems with capillary irrigation as this allows greater control of plant growth than a CRF system. However, plants grown solely with liquid feeding will have very little shelf life once they leave the nursery and feeding ceases. Liquid feeds can also be used to help to manipulate growth by using different ratios of nutrients in the feed (Table 3). For example, high nitrogen feeds used carefully during the growing season can provide a timely Table 3 Typical liquid feed ratios for shrubs and herbaceous plants and suggested growth stage use Feed ratio (N:P 2 O 5 :K 2 O) 1:1:1 3:1:3 or 4:1:4 3:1:6 Typical use boost to crop growth and colour. Similarly, the delivery of high phosphate feeds to rooted cuttings and plug plants prior to potting on will ease and speed establishment. With any type of liquid feed, the amount of nutrients applied can be varied either by adjusting the strength of the stock solution made up, or (more commonly) by adjusting the dilution of the stock solution when applied to the crop eg 1 in 100 is twice as strong as 1 in 200. There are also specialist feeds available for use with hard or soft irrigation water, the former containing phosphate in a form more available at higher ph s and the latter supplying extra calcium. 4 Supplementary feeding Where nutrient levels are low due to the CRF running out or where excessive leaching of nutrients has occurred over winter and liquid Young plant establishment when P demand higher Vegetative stages in spring/summer Lower N/higher K feed for flowering/later stage of growth in late summer/autumn feeding is not practical, plants can be top-dressed in the early spring using either short-term CRF s or compound fertilisers. Short-term CRF s Supplementary feeding with a short term CRF either top-dressed loosely onto the surface of the growing media or by the use of CRF plugs (clusters of prills) inserted into the growing media is more expensive than other options but useful for long term/high-value crops that may not be sold until later in the year. This should be done during March to allow sufficient time for nutrient release to take effect. Compound fertilisers Top-dressing with a compound fertiliser (eg N:P:K 10:10:10) will supply nutrients for up to six weeks and if the substrate is moist the nutrients will become available to the plant quickly. Nutrient release from organic based fertilisers is usually slower and will take a little longer. Fig 6 Dosatron systems are a popular, flexible, cost effective method of accurately supplying liquid feed to container plants Figs 7 & 8 Top dressing in March with compound fertilisers can supply nutrients to the plant quickly to boost spring growth

24 Application should be made just before the spring flush of growth (a few weeks earlier under protection). Application of a measured amount to each pot is more accurate and less wasteful than broadcasting over the bed. The rate of application will depend on the vigour of plants but 3g per 3 litre pot of a 10:10:10 compound fertiliser will supply 100 ppm of nitrogen and similar amounts of P and K. Lower rates are needed for salt-sensitive species to avoid the possibility of root damage. Compounds are available with a proportion of the nitrogen in slow release form (as methylene urea). Where top-dressing leaves granules lodged in plant foliage, overhead irrigation may be needed to wash the fertiliser into the substrate and hence prevent leaf scorch. Foliar feeding This is a useful means of providing crops with short-term nutrition to boost growth and colour. It can be particularly useful where crops are under stress and to improve the appearance and marketability of finished container stock. Some products are tank mixed with routine fungicide applications although product information and manufacturers recommendations should always be checked first. Trace elements The majority of CRF s contain trace elements. If CRF s do not contain trace elements then these are normally added as fritted trace elements (FTE). The standard rate of frit addition is 300 g/cu m. The two most common frits in the UK are 255 and 253a. The influence of ph on nutrient availability Major and minor nutrients are most available to plants within certain ph ranges. As a guide, for most peat-based potting media, a start ph of is preferred for general shrubs and for acid loving or Ericaeous spp. A ph below for non-ericaceous plants will cause problems due to insufficient calcium and excessive availability of elements such as iron, manganese, zinc and aluminium, causing toxicity. If the ph is too high (greater than ) many nutrients become less available, particularly iron, manganese and phosphorus. These effects are not so relevant for media based on more highly buffered materials; for example bark/green compost blends, where ph values of can still be satisfactory. Some Prunus and Malus species of fruit trees require a higher ph than general shrubs ( is recommended). The ph of own inhouse mixes should be checked on each batch before use and on new batches of bought in media (which should be within the target ph range specified). Lime rates As peat-based growing media have a naturally low ph, ground lime or magnesian lime is added to raise it to within the desired range. The rate of lime needed to raise the ph by 1 ph unit is usually in the range kg/cu m of peat although older peats generally require more due to their greater buffering capacity. Fig 9 Nutrients are most available to plants within certain ph ranges; a start ph of is preferred for ericaceous species such as Pieris Magnesian lime Magnesian lime (eg Dolodust ) is commonly used as all or part of the liming material for growing media. This contains magnesium carbonate as well as calcium carbonate and so is the major source of both magnesium and calcium for the plants. It is a safer way of adding magnesium than the use of magnesium sulphate (eg Kieserite). Kieserite can be useful however when used at modest rates where magnesium is required without increasing the ph, for example in some reduced peat/peat-free mixes. The rate of magnesian lime used in nursery stock growing media depends on several factors, most notably, the crop type (eg ericaceous/acid loving/general shrubs etc), the type and age of the bulk ingredients and, the alkalinity of the water used for irrigation (see water hardness below). As a general guide for growers wishing to mix their own growing media, rates of kg/cu m are widely used. However, it is advisable to routinely check the start ph of bulk ingredients particularly when switching between different suppliers/sources and, the alkalinity of irrigation water, amending lime rates accordingly. Water hardness When considering the ph of a growing medium, it is important to consider the bicarbonate level in the irrigation water. Hard water,

25 if it is not treated, may contain high levels of bicarbonate (eg over 300 mg/l) which will cause a gradual increase in the ph of the growing medium. It is worth checking irrigation water from time to time as water companies may switch between different water sources at different times of year. As some waters can have a high ph but a relatively low bicarbonate level, it is advisable that both components are checked rather than relying on ph alone. Some bore-hole supplies can be particularly hard and should be checked at least annually and preferably twice a year. If water intended for crop irrigation regularly has a bicarbonate level significantly above 200 mg/l, then acid dosing should be considered. Acidification of irrigation water Where irrigation water is only moderately hard (ie below 200 mg/l of bicarbonate) specialised acidic liquid feeds can be used to help overcome this, for example those containing urea phosphate. Alternatively, where liquid feeding is not routinely used or the water hardness is extreme (ie above 300mg/l bicarbonate), the water may be treated with concentrated acid, usually 60% nitric acid, to remove most of the bicarbonate (about mg/l of bicarbonate should be left). Fig 10 Acid dosing using specialist equipment is an effective way of neutralising the alkalinity of hard water supplies Specialist acid dosing equipment should be used for this with ph monitoring to ensure correct dosage. Acidification of a typical hard water containing around 300 mg/l bicarbonate would need about 300ml of 60% nitric acid per 1000 litres of water and this would also supply around 50 mg/l of nitrogen at every watering. IMPORTANT NOTE: Concentrated acids are very dangerous and all the relevant Health & Safety precautions should be followed when using them. Reduced peat and peat-free media The main fertilisers used for nursery stock were designed for peat-based substrates, which are naturally low in nutrients unless fertilisers are added. As growers move to the use of reduced peat and peat-free media, more products tailored to these types of media may become available, for example with different nutrient ratios or release patterns. In the interim, growers should adapt fertiliser types and rates as necessary. Materials such as bark, forestry brash or wood-fibre can be used with peat to maintain an open, well-drained growing media structure, particularly for outdoor, over-wintered container stock. Mixes with a large percentage of bark need slightly more nitrogen to counteract immobilisation. The standard recommendation for supplementary nitrogen addition for peat mixes with bark is 100g/cu m of ammonium nitrate per 10% bark. This should be modified according to base fertiliser use, other components of the substrate and plant species grown (with salt sensitive species it may be unnecessary). Mixes containing composted material can contain significant amounts of slower release nutrients and hence a lower rate of CRF may be satisfactory. Fig 11 Mixes containing a large percentage of bark will require the addition of supplementary nitrogen to counteract immobilisation

26 Monitoring crop nutrition Growers should be aware of plant nutrient deficiency and toxicity symptoms and monitor nutrition on a routine basis by checking foliage colour and taking samples for analysis. Substrate analysis for overall nutrient status Analysis of samples of both the unused growing medium and medium from growing crops is useful to monitor ph and nutrient status, particularly for new crops or after changes to growing media specifications. This is a useful check that specifications are correct and allows fine-tuning of nutrition. A minimal monitoring programme for spring potted over-wintered nursery stock should be one based on ph and nutrient analysis in midsummer, early autumn (total nutrients) and late winter/early spring (total nutrients). For protected crops where nutrient values may fluctuate more and for salt sensitive subjects, a more frequent programme of analyses may be necessary (eg at monthly or 6 weeks intervals), particularly for EC levels (see below). This can be especially pertinent where capillary watering systems are used as a gradual salt build up in pots and beds may occur. The overall nutrient status of a substrate sample can be broadly determined from the Electrical Conductivity (EC) which is a measure of the total salts in solution. EC is usually expressed by UK laboratories in micro-siemens (μs) per centimetre. Milli-siemens (MS) per metre is also sometimes quoted (500 μs/cm = 50MS/m). Care must be taken if comparing analyses from laboratories using different analytical methods. Monitoring available nutrients To obtain an indication of available nutrient levels within a substrate sample, water extraction is used (peat-based media only). Where CRF s are used, however, it must be remembered that the analysis will only measure nutrients in solution at the time of sampling. If nutrient release from the granules is balanced by crop uptake only low levels will be detected. Similarly, where significant slower release nutrient sources are present (eg in mixes containing green compost) this will underestimate the potentially available nutrients hence different extractants (eg calcium chloride + DTPA) are more appropriate. Monitoring remaining CRF nutrients Total water soluble nutrient analysis (analysis of a macerated sample of the growing medium) may be more helpful as it provides information on the percentage of the original nutrients still contained within the CRF granules. This can be particularly useful to assess total nutrient levels before the winter period and prior to supplementary feeding in spring. The major UK laboratories can carry out both types of analysis eg Direct Laboratories Ltd ( ) or NRM Ltd ( ). Use of on-nursery meters Hand-held nursery meters for measuring ph and EC are useful. They can be used for substrates but these need to be mixed with water to obtain a solution. The ratio of substrate and water used and dryness of the substrate can influence the results as well as the amount of shaking and time left before taking a reading. The best way of using such meters is to validate results against laboratory readings in the first stage of use and to make sure the probes are re-calibrated against standard solutions regularly. On nursery meters can be useful for regular monitoring of a new crop (for example once a month), batches of growing medium or to check the need for supplementary feeding in early spring. Table 4 Maximum suggested EC levels for hardy nursery stock and herbaceous species (peat-based media) Crop type EC (1:6 water extract), μs/cm Salt sensitive young plants, eg Ericaeous liners, rooted cuttings, plug plants 150 Other young plants, eg liners, bare-root herbaceous plants, alpines 300 Established herbaceous plants, shrubs Vigorous growing shrubs and trees Fig 12 Hand-held nursery meters for measuring ph and EC are useful for checking water and liquid feeds. They can also be useful when monitoring new crops and batches of growing medium or checking the need for supplementary feeding

27 Foliage analysis Foliage analysis can be useful for diagnosis of nutritional disorders, particularly suspected trace element deficiencies/toxicities for which substrate analysis is less easy to interpret. There is scope for using foliage analysis to monitor and hence manipulate plant growth for very specialist nurseries growing only one or two lines, particularly where liquid feeding is used. Data on normal nutrient levels in leaves of some of the common species is available in the final report for HDC project HNS 43f (ref. Appendix C). Care must be taken if comparing tissue analysis from laboratories using different analytical methods. Avoiding excessive nutrient levels High nutrient levels can occur if too much fertiliser is used or if crop uptake is reduced or when release from CRF granules is accelerated (eg during very hot weather). Outdoor crops do not usually have problems but nutrient accumulation can occur in protected crops, particularly on sub-irrigation systems, and this can cause root damage/poor growth. White deposits of salt crystals on the surface of the growing medium may indicate salt accumulation hence samples should be taken for analysis. If substrate analysis shows a high Electrical Conductivity (EC) all liquid feeding should cease and the growing medium flushed through with plain water. It is also good nursery practice to flush through sand-beds and capillary matting systems occasionally to remove salt build-up. Conductivity in water used for irrigation can also vary and should be checked at least once a year (mains supplies) and twice yearly where bore-hole supplies are used. Fig 13 Conductivity values in substrates should be regularly monitored; high salt levels can seriously damage crop growth and saleability as seen here where high conductivity has caused leaf scorch on rhododendron Action points Growing media preparation Draw up clear, written specifications for all growing media and nutritional programmes well in advance of potting. Take full account of crop species, crop growth stage and growing period, irrigation systems, growing system (eg outdoors/under protection), market requirements, production period and potting dates. Follow through with regular ph and nutrient monitoring of all substrates. Include fresh mixes. For peatbased media, aim for a start ph of for general potting and for Ericaceous/calcifuge subjects. Check lime additions and adjust accordingly; as a general guide, to raise the ph of peat by one unit requires kg/cu m of lime. Water hardness and ph Check water quality periodically, particularly for bicarbonates and conductivity. For moderately hard water (below 200 mg/l of bicarbonate) use acidic liquid feeds. Acidification with concentrated acid should be considered where water supplies are very hard (above 300 mg/l bicarbonate). CRF and base fertilisers Use a low rate ( kg/cu m) of base fertiliser with an appropriate rate of controlled release fertiliser eg 4.0 kg/cu m during the spring potting season for quick growth and balanced nutrition of general shrubs. Use extended release CRF s for slow growing, salt sensitive shrubs grown under protection (eg Pieris) or where plants are grown for 2 years in the same container. Use a high K CRF blend with less nitrogen and more potassium for crops prone to excessive leafy growth (eg vigorous herbaceous subjects). This also improves cold and disease resistance. Liquid feeding Under protection, use liquid feeding as necessary (often when CRF s are running out) to top up nutrient release from CRFs. Use high nitrogen feeds to boost crop growth and colour and high phosphate feeds to speed establishment of rooted cuttings and plugs. Reduced peat growing media Use bark, forestry brash or woodfibre with peat to maintain an open, well-drained growing media structure, particularly for outdoor, over-wintered container stock. Use supplementary nitrogen to counteract immobilisation by such materials if necessary (eg 1.0 kg/cu m of a 14:16:18 base fertiliser will provide sufficient supplementary nitrogen for media containing 20-30% bark). Trial alternative substrates to reduce peat consumption (eg herbaceous perennials respond well). Adapt fertiliser types and rates as necessary. Mixes with a large percentage of bark require more nitrogen to counteract immobilisation and may require changes to irrigation schedules.