Controlled-release Fertilizer Application Research Articles

Influences of Chemical Fertilizers and a Nitrification Inhibitor on Greenhouse Gas Fluxes in a Corn (Zea mays L.) Field in Indonesia

The influences of chemical fertilizers and a nitrification inhibitor on greenhouse gas fluxes (N(2)O and CH(4)) in a corn field in Indonesia were investigated using a closed chamber. Plots received 45+45 kg-N ha(-1) of nitrogen fertilizer by split applications of urea, a single application of controlled-release fertilizer (CRF-LP30) or urea+dicyandiamide (DCD; a nitrification inhibitor), and no nitrogen application (control). Cumulative amounts of N(2)O emitted from the field were 1.87, 1.70, 1.06, and 0.42 kg N(2)O-N ha(-1) season(-1) for the urea, CRF-LP30, urea+DCD, and control plots, respectively. The application of urea+DCD reduced the emission of N(2)O by 55.8% compared with urea. On the other hand, the soil acted as a sink for CH(4) in the CRL-LP30, control, and urea+DCD plots with value of -0.09, -0.06 and -0.06 kg CH(4)-C ha(-1) season(-1), respectively. When the viability of AOB (ammonia-oxidizing bacteria) and NOB (nitrite-oxidizing bacteria) were monitored, AOB numbers were correlated with the N(2)O emission. These results suggest that 1) there is a potential for reducing emissions of N(2)O by applying DCD, and 2) corn fields treated with CRF or urea+DCD can act as a sink for CH(4) in a tropical humid climate.

Studies on the Mechanism of Single Basal Application of Controlled-Release Fertilizers for Increasing Yield of Rice ( Oryza safiva L.)

This paper was to explore the mechanism of single basal application of controlled-release fertilizers for increasing yield of rice ( Oryza sativa L.). Pot trials and cylinder trials were carried out from 2002 to 2005 to study the influences of single basal application of 3 controlled-release fertilizers on the changes of soil available N, root development, senescence and lodging resistance at late growth stages. Results showed that at 30 days after fertilization, single basal application of controlled-release fertilizers coated with vegetal-substance (CRF1) and polymer materials (CRF3) increased soil available N to 12.0 and 147.9%, respectively, in comparison to split fertilization of rice-specific fertilizer (RSF1). Treatments of the two CRFs obviously benefited the development of root system, resulting in greater rice root weights with extensive distribution and higher root activity. In addition, the two CRF treatments, in comparison to RSF1, enhanced chlorophyll consents of the flag leaves to 9.5 and 15.5%, and soluble protein up to 89.7 and 108.0% respectively. Application of the two CRFs also made the base of rice stems strong and large, declined the proportion of shoot and root, increased root depth index. Though relatively low K rate, single basal application of the CRF3 coated with NH 4MgPO 4 could also promote the development of root system, enhance root activity and some physiological functions of flag leaves. Based on these results, it was concluded that major mechanisms for increasing rice yield by single basal application of the CRFs should be attributed to grater soil available N supply, superior development of root systems, better nutrient absorption capacity, slower senescence and enhancement of lodging resistance at late stages.

Effect of seed coat removal and controlled-release fertilizer application on plant emergence and vegetative growth of two citrus rootstocks

Introduction. The technology for citrus rootstock production through improved sowing methods and fertilizer inputs offers greater opportunity in the certified citrus plant production system. Our work evaluated the influence of seed coat removal and different con- trolled-release fertilizer concentrations on plant emergence and plant growth of two citrus rootstock cultivars. Materials and methods. Decoated and not decoated seeds of Rangpur lime (Citrus limonia Osbeck) and Swingle citrumelo (Citrus paradisi × Poncirus trifoliata (L.) Raf) were sown in 50-cm 3 tubes. Fertilizer concentrations were (0, 1, 2, 3, 4 and 5) kg·m -3 of controlled-release fertilizer (NPK 19-06-10) incorporated into the substrate. The experimental layout followed a randomized block design with 2 × 6 factorial (seed coat removal × fertilizer concentration) for each rootstock. Results and discussion. Seed coat removal resulted in faster plant emergence and higher dry weight for both rootstocks. Vegetative growth increased with controlled-release fertilizer concentrations. Brazil / Citrus / rootstocks / plant propagation / seeds / shelling / fertilizer application / emergence / growth

Overcoming Fe deficiency in guava (Psidium guajava L.) by co-situs application of controlled release fertilizers

Among micronutrient deficiencies, Fe deficiency is the most difficult nutritional disorder to prevent in the fruits of trees growing on calcareous soils. In this study, a pot experiment was carried out to evaluate the potential of co-situs application of controlled release fertilizers (CRF) in alleviating Fe deficiency and improving the growth of fruit trees growing on calcareous soil (pH 9.3). Guava (Psidium guajava L.) seedlings were used as test plants because of their sensitivity to Fe deficiency. Treatments consisted of the following: (1) broadcast application of readily soluble Fe, Zn, Cu, B and Mn fertilizers (Control) or (2) co-situs application of CRF containing N, P, K, Mg, Fe, Zn, B, Cu and Mn (Co-situs). For the Control treatment, CRF containing only N, P and K was used. Both treatments received the same amount of all nutrients. Plants were more chlorotic in young leaves under the Control treatment and the Fe content of young leaves was significantly (least significant difference [LSD0.05]) higher under the Co-situs treatment. Dry matter production of shoots under the Co-situs treatment was 5.2-fold higher than under the Control treatment, and the total accumulations of macro and micronutrients were much higher under the Co-situs treatment than the Control treatment. Total accumulations of N, P, K, Ca and Mg were 5.0, 4.1, 9.6, 3.2 and 2.2-fold higher, respectively, under the Co-situs treatment compared with the Control treatment, and Fe, Zn, Cu and Mn accumulations were 3.2, 4.1, 6.0 and 3.7-fold higher, respectively. Iron deficiency in guava seedlings was successfully alleviated by the co-situs application of controlled fertilizer, proving the high potential of this method in alleviating Fe deficiency in fruit trees growing on calcareous soils.

(59) An Examination of Irrigation Volumes and Controlled-release Fertilizer Application Methods and Rates to Reduce Nursery Container Leachate and Fertilizer Use

Plug-rooted liners of common ninebark [Physocarpus opulifolius (L.) Maxim.] were grown in 6-L nursery containers filled with 73% composted pine bark, 22% sphagnum peat moss, and 5% pea gravel (by volume). Plants were fertilized with Polyon (Nutryon) 17–5–12 (17N–2P–5K) 6-month controlled-release fertilizer at various rates (2.5, 4.5, 6.5, and 8.5 kg·m-3) pre-incorporated, topdressed, or dibbled (placed under the liner at potting). Plants were trickle-irrigated daily with low (0.4-L), middle (0.8-L), or high (2.0-L) volumes of water to maintain leaching fractions of <0.15, 0.25–0.35, or >0.60, respectively. Regression analysis indicated that growth of ninebark increased from 30 to 109 g/plant with increasing rates of incorporated fertilizer (mean over irrigation volumes), from 27 to 71 g/plant with topdress and from 59 to 103 g/plant with dibble. Electrical conductivity (EC, mean over five dates) of the leachate throughout the season was highest with dibble (0.85 dS·m-3), intermediate with incorporated (0.81 dS·m-3), and least with topdressed (0.76 dS·m-3). With low irrigation volumes, growth of ninebark increased from 42 to 81 g/plant with increasing rates of fertilizer (mean over methods), and from 39 to 105 g/plant with middle or high volumes (common regression curve). With low irrigation volumes, leachate EC increased from 0.74 to 0.94 dS·m-3 with increasing rates of fertilizer, and from 0.75 to 0.81 dS·m-3 with middle or high volumes.

Performance of Pot-Grown Seedlings of the Dipterocarp Dryobalanops lanceolata with Controlled-Release Fertilizer after Transplantation to the Shifting Cultivation Land in Sarawak, Malaysia

In the present study, the focus was placed on the survival, growth, nutrient status, and ectomycorrhizal formation of pot-grown dipterocarps treated with a controlled-release fertilizer or a chemical fertilizer when transplanted to abandoned shifting cultivation land. Either a chemical fertilizer (CF) or a 700-day controlled-release fertilizer (CRF) had been applied to Dryobalanops lanceolata seedlings at the rates of 0, 2, 5, and 10 g fertilizers per pot in the nursery of the Forest Research Station Niah (FRSN), Miri, Sarawak, Malaysia. The seedlings were cultivated for 18 months in the nursery, and then transplanted to abandoned shifting cultivation land around the FRSN. At 16 months after transplantation, the plants in the CRF treatments showed a good performance in terms of growth and survival ability, because of the sufficient amounts of nutrients accumulated in plants with a sound shoot form and high photosynthetic activity at the nursery stage. On the other hand, many saplings in the CF treatments at the rates of 5 g and 10 g died in the field due to their spindly shoot form and low photosynthetic activity in the nursery, even though the saplings that survived showed on adequate growth. Therefore, the application of slow-release type CRF in the nursery was considered to be feasible and suitable for successful establishment of a dipterocarp plantation in the field. Ectomycorrhizal fungus present in the nursery would sustain and be correlated with P uptake of the saplings after transplantation.

Growth and nutritional response of hardwood seedlings to controlled-release fertilization at outplanting

Hardwood bareroot seedlings typically undergo transplant shock immediately following afforestation planting associated with moisture or nutrient stress. Broadcast field fertilization at outplanting with readily available nutrients has shown limited capacity to reduce nutrient stresses. Furthermore, the rapid nutrient release characteristic of broadcast fertilization leads to high levels of nutrient leaching and may stimulate growth of competing vegetation more than target trees. Application of controlled-release fertilizer (CRF) in the outplanting hole could be a useful alternative to help improve fertilizer use efficiency and alleviate competition problems associated with broadcast fertilization, thereby promoting early regeneration success of outplanted seedlings. We tested growth and nutritional response of black walnut ( Juglans nigra L.), white ash ( Fraxinus americana L.), and yellow-poplar ( Liriodendron tulipifera L.) to 6 rates (0, 15, 30, 45, 60, and 75 g plant −1) of polymer-coated CRF applied to the root zone at outplanting in southern Indiana, USA. Fertilizer release was evenly distributed between years 1 and 2. Seedling survival was above 85% for all treatments. Compared to non-fertilized seedlings, the 60 g seedling −1 rate accelerated mean height and root-collar diameter (RCD) growth by 52 and 33% in year 1 and 17 and 21% in year 2. Nitrogen (N) and potassium (K) uptake were increased 40 and 30% at the 60 g rate compared with controls. Height and RCD growth were greater by 543 and 200% in white ash and 300 and 233% in yellow-poplar, relative to black walnut. Uptake of N and K was increased by 79 and 22% in yellow-poplar and 93 and 56% in white ash, compared to black walnut. Results suggest CRF has potential to improve early establishment success of hardwood afforestation plantings.

Co-situs application of controlled-release fertilizers to alleviate iron chlorosis of paddy rice grown in calcareous soil

Co-situs is the placement with one application of a sufficient amount of controlled-release fertilizer for an entire growing season at any site, together with seeds or seedlings, without causing fertilizer salt injury. An experiment was conducted to find an efficient method for ameliorating Fe deficiency in two rice cultivars (cv. Tsukinohikari and cv. Sasanishiki) grown in a calcareous soil (pH 9.2, CaCO3 384 g kg−1), which was poor in organic matter (0.1 g kg−1) and available Fe (3.0 μg g−1 soil). The field treatments consisted of co-situs application of the following fertilizers: 1) controlled-release NPK fertilizer (CRF-NPK) containing no micronutrients; 2) controlled-release NPK fertilizer containing micronutrients (CRF-M1); and 3) controlled-release NPK fertilizer containing micronutrients (CRF-M2). The main difference between CRF-M1 and CRF-M2 was that the former had larger granules than the latter. All the fertilizers were placed in contact with the roots of rice seedlings at transplanting time. Plants in the CRF-M1 and CRF-M2 treatments had similar lengths, number of stems, leaf age, and leaf color (SPAR value) during the cultivation period. By contrast, plants from the CRF-NPK treatments grew poorly, showed severe chlorosis symptoms of Fe deficiency, and all died on 30 DAT. Plants of both cultivars accumulated more macroand micronutrients with the CRF-M2 treatment than with the CRF-M1 treatment. The grain yield of cv. Tsukinohikari was 0.0, 1,910, and 2,160 kg ha−1 for the CRF-NPK, CRF-M1, and CRF-M2 treatments, respectively, and 0.0, 2,490, and 2,860 kg ha−1 for the same treatments for cv. Nihonbare. Chlorosis due to iron deficiency was successfully ameliorated and world-average grain yields were obtained with the co-sites application of both controlled-release fertilizers.

Effects of controlled-release fertilizer on growth and ectomycorrhizal colonization of pot-grown seedlings of the dipterocarp Dryobalanops lanceolata in a tropical nursery

The effects of the application of controlled-release fertilizer on the growth and ectomycorrhizal colonization of pot-grown seedlings of the dipterocarp species Dryobalanops lanceolata were studied in a nursery in Sarawak, Malaysia, to produce a sufficient number of healthy dipterocarp seedlings to reforest degraded tropical lands. Samples of a forest soil were mixed with an equal volume of river sand following a typical practice in the Niah Forest Research Station nursery. About 1.4 kg of the soil mixture was placed in plastic bags. Either a 700-day (80% elution of the ingredients at 20°C) controlled-release fertilizer (CRF, N: P : K = 12: 14: 12) or a chemical fertilizer (CF, N: P : K = 15 : 15 : 15) was applied at the rate of 2,5, and 10 g per pot. After 16 months of cultivation, mycorrhizal colonization and photosynthetic activity of the seedlings were evaluated, and the nutrient concentration and dry mass were analyzed. Application of ten grams of CRF resulted in the enhancement of the biomass, leaf development, photosynthetic activity, nutrient status, and ectomycorrhizal formation of the seedlings. It is expected that the CRF treatment can be used practically for dipterocarp seedling production in tropical nurseries.

Influence of fertilization application and growing substrate on container-grown woody ornamentals

Five fertilization systems and seven types of growing substrates were tested with two woody plant species with different nutritional demands (Thuja occidentalis, Pyracantha coccinea) grown in two-litre containers. The experiment was repeated in two vegetative seasons. Application of controlled release fertilizer (CRF) was proved the most reliable; it gave good or at least average results in dependence on used growing substrates. Significant differences between application of CRF and other fertilization systems were with Pyracantha plants. System using slow release fertilizer with additional nitrogen fertilizing also showed good results. Systems based only on liquid feeding were less reliable, with some substrates they showed very good results; with others (peat substrate, peat bark substrates with wood components) they were bad. Similar results were achieved with top dressing of granulated fertilizer. Evaluating the substrates good results were obtained by using mixtures of peat with components with higher content of nutrients – peat bark substrates, peat bark substrates with compost and non-peat mixtures of composted bark, wood fibres and compost. Significant differences between these types of substrates and peat one or peat bark substrate with wood components were both with Thuja plants and especially with Pyracantha plants, which have higher demand for nutrients. The experiments showed that peat based substrates amended with alternative components or non-peat substrates can bring better results than the peat ones.

Effect of Controlled-Release Fertilizer Application Rates on Bedding Plant Growth In Substrates Containing Compost

Growth of ‘Accent Orange’ impatiens (Impatiens wallerana Hook.f) and ‘Blue Rhea’ salvia (Salvia farinacea Benth.) plants were compared in substrates containing 0, 30, 60, or 100% compost made from biosolids and yard trimmings and fertilized with 13N-5.7P-10.8K Nutricote (type 100 plus minors) top-dressed at transplanting at 0.5, 1, 2, or 4 g per pot (6, 12, 24, or 48 kg·100 m−2). Initial substrate cation exchange capacity (CEC), pH, electrical conductivity (EC), nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) were greater in substrates containing 30, 60 or 100% compost than in substrates containing 0% compost. Shoot dry mass of impatiens and salvia plants increased as fertilizer application rate increased in all substrates. Final impatiens and salvia substrate EC concentrations also increased as fertilizer application rate increased from 0.5 to 4 g in all substrates. There was no difference in impatiens or salvia shoot dry mass among the substrates when plants were fertilized with 0.5 g. However, shoot dry mass of impatiens plants fertilized with 4 g increased as the percentage of compost in the substrate increased. The shoot dry mass of salvia plants fertilized with 4 g increased as the percentage of compost increased to 60% but then decreased. At the low fertilization rates, substrates containing compost made from biosolids and yard trimmings did not appear to supply sufficient nutrients to increase plant growth beyond that achieved in 0% compost. However, at higher fertilization rates, Nutricote apparently augmented the nutrients provided by substrates containing compost and increased plant growth beyond that achieved in 0% compost.

USE OF CONTROLLED RELEASE FERTILIZERS AND NITRIFICATION INHIBITORS TO INCREASE NITROGEN USE EFFICIENCY AND TO CONSERVE AIR ANDWATER QUALITY

Field trials on controlled release fertilizers (CRF) and a nitrification inhibitor (NI) were conducted in order to show their potential to increase N use efficiency (NUE) and to conserve air and water quality. For this purpose, flood irrigated barley grown on a clay soil (Colorado, USA), center-pivot irrigated potato grown in a sandy field (Colorado, USA), and corn grown on a loamy soil at a large scale lysimeter (Fukushima, Japan) were selected. NI (dicyandiamide) and CRF (polyolefin coated urea) were capable of reducing N2O emissions from urea applied to the barley field by 81 % and 35 %, respectively. Total N fertilizer losses averaged 15 and 10 % in the NI and urea treatments, respectively. On the other hand, those from the CRF treatment averaged only 1.9 %, indicating that CRF showed the highest potential to increase N use efficiency. The trials in the potato field demonstrated that CRF could markedly increase NUE and tuber yields. A single basal application of CRF at planting (N rate, 112 kg ha−1) produced tuber yields comparable with those of traditional fertilizer applications (112 kg N ha−1)by basal dressing, 90 kg N ha−1 by topdressing and 67 kg N ha−1 by 8 fertilizations). The urea and CRF plots in the corn fields showed similar N2O emission patterns, having two high emission periods following the basal and topdressed N applications in the urea plots and the enhanced N release from a short linear formulation and a long sigmoidal formulation in the CRF plots, respectively. However, the total N2O emission value of the CRF plots was almost one third of that of the urea plots. The plant recovery of CRF N was almost two times of that of urea N. Finally, the authors discussed that contributions of CRF and NI to conserve air and water quality are basically due to maximizing NUE and reducing the N fertilization rate.

Effect of Reclaimed Wastewater on the Growth and Nutrient Content of Three Landscape Shrubs

Abstract An experiment was set up to determine the effects of treated municipal wastewater irrigation and fertilization on growth, leaf morphological characteristics, chlorophyll content, and ion uptake of three container-grown landscape shrubs characterized by different growth habits (Abutilon ‘Kentish Belle’, Viburnum tinus ‘French White’, Weigelia florida ‘Bouquet Rose’). The study was conducted in Tuscany (Central Italy) in a typical landscape plant production area. One-hundred plants per species were watered with treated sewage effluent from the nearby wastewater treatment facility (RW) and 100 with well water after ponding (WW) from the nursery where the research plots were located. Fifty plants per species and within each irrigation treatment received controlled-release fertilizer application at transplant and 50 received no fertilization. The experiment showed no major limitations to the use of sprinkle-irrigated wastewater for container-grown landscape plant production and a general, positive, influence on growth of the plants. However, the species under observation showed a different behavior in response to the effluent irrigation for all the parameters considered. Weigelia was the most responsive and Abutilon the least. The influence of fertilizer addition at transplanting was less evident and the combined effect of RW and fertilization was rarely found and seemed to be species-specific.

Effect of Split Fertilizer Application and Irrigation Volume on Nitrate-Nitrogen Concentration in Container Growing Area Soil

Abstract Outdoor-grown, containerized, Aronia melanocarpa (Michx.) Ell. and Rhododendron ‘Roseum Elegans’ were grown atop soil-filled boxes that had been recessed into a grassed field in separate studies. Aronia were fertilized with either a single application of controlled-release fertilizer (CRF) or a split application of CRF separated by 36 days. Rhododendron were supplied a single application of CRF and either a standard or excessive irrigation volume on each irrigation day. Soil samples were taken in 30 cm (12 in) layers to a depth of 90 cm (36 in) beneath containers at 14-day intervals and soil NO3-N concentrations were determined. Accumulation of NO3-N was immediate in the 0—30 cm (0–12 in) layer for both species with accumulation of NO3-N in the deeper soil layers occurring later. Split application of a CRF was somewhat effective at reducing NO3-N accumulation at specific times and in specific soil layers, but reductions were not as substantial as studies on NO3-N concentrations in leachate have indicated. The large irrigation volumes used in the irrigation volume study resulted in NO3-N moving rapidly through the soil profile beneath containers.

Mid-Season Reapplication of Controlled Release Fertilizers Affect ‘Helleri’ Holly Growth and N Content of Substrate Solution and Effluent

Abstract The objective of this study was to determine how a mid-season CRF (controlled release fertilizer) reapplication to container-grown Ilex crenata ‘Helleri’ Thunb. affected growth, substrate solution N content, and the amount on N leached compared to a single early season CRF application (control). ‘Helleri’ holly liners were initially fertilized (March 7) with an 8 to 9 month CRF, Osmocote 18N-2.6P-9.9K (18-6-12), or a 12 to 14 month CRF, Osmocote 17N-3.1P-9.9K (17-7-12). A subset of plants received a CRF reapplication (half rate) of the respective Osmocote formulation on July 19, August 2, or August 16. In addition, 12 plants received a water soluble fertilizer solution (WSF) with each irrigation starting on July 19. All effluent was collected and analyzed for N. Substrate solution N and electrical conductivity (EC) levels (via the pour-through method) and foliar N concentrations were determined every two weeks. Throughout the experiment, plants were irrigated with an irrigation amount that resulted in an ≈ 0.25 leaching fraction (LF). Plant width was determined on November 1. Plant width values were higher for the first and second reapplication and WSF treatments for both formulations than the control. However, in terms of commercial size grades, plants of all treatments were in the same grade. Thus, there was no economic advantage to reapplying CRF. We concluded that CRF reapplication was not necessary when substrate solution N and foliar N values were ≥ 20 mg N/liter and ≥ 2.3%, respectively. Irrigating at a LF of 0.2, the mid-season CRF application increased the amount of N lost from containers by 42% compared to a single, early season CRF application.

Reducing nitrogen leaching‐losses from containerized plants: The effectiveness of controlled‐release fertilizers

Abstract To evaluate the effectiveness of controlled‐release fertilizer (CRF) for reducing nitrogen (N) leaching‐losses from containerized greenhouse crops, three experiments were conducted where CRFs were applied in different ways and compared to water‐soluble fertilizer (WSF). In each experiment, ‘First Lady’ marigold (Tagetes erecta L.) plants in 0.5‐liter pots of a soilless growth medium were fertilized with the same amount of ? from 20N‐4.3P‐16.6K WSF, Osmocote 14N‐6.2P‐11.6K CRF, or Nutricote 14N‐6.2P‐11.6K CRF fertilizers. The volume of irrigation water applied to all treatments was the same in each experiment. Nitrogen content, as NH4‐N and NO3‐N in container leachates, and plant growth were measured and used to compare WSF with CRFs incorporated in the growth medium, or as applied to the surface, in either one large application or two small doses. A single large application of CRF at planting resulted in as much or more ? leaching than the regular application of WSF. Effectiveness of CRFs in limi...

Early growth of planted western hemlock in relation to stock type and controlled-release fertilizer application

Four types of western hemlock (Tsugaheterophylla (Raf.) Sarg.) nursery stock, differing in size, morphology, and root growth capacity were planted on a clear-cut forest site on Vancouver Island, British Columbia. The stock types were: (i) 1-year-old, plug-rooted seedlings raised in 36-cm3 containers; (ii) as (i) but transplanted to a bareroot nursery for 1 year; (iii) 1-year-old, bareroot seedlings raised in 1000-cm3 containers; (iv) as (iii) but raised in containers coated on the inside with copper paint to inhibit lateral root elongation upon contact with the container wall. Survival and growth of seedlings with and without fertilization at planting with 50 g of a slow-release (Nutricote®, 12-month release at 25 °C) N–P–K fertilizer were observed for 3 years. Neither stock type nor fertilizer had a statistically significant (P < 0.05) effect on seedling survival. At planting, plug seedlings were significantly (P < 0.01) shorter and smaller in stem volume than the other stock types. These differences were no longer evident by the end of the third growing season because of more rapid growth by the plug stock. The largest differences between the plugs and the other stock types in height and diameter relative growth rates occurred during the first growing season. Fertilization significantly (P < 0.01) increased height and stem volume relative growth rates of all stock types during the first growing season. During the third growing season fertilization had a significant (P < 0.01) negative effect on height, and diameter and stem volume relative growth rates of all stock types, but not on absolute rates. At the end of three growing seasons, fertilized trees remained significantly (P < 0.01) larger in all stock types than in the controls.