Comparison of fertilizers

Using advanced granule technology with industry standards in nursery containers

BY DR. HANNAH MATHERS, LUKE CASE AND JASON PARRISH

From 2007 to 2008, spring nitrogen prices increased by a third, phosphate prices nearly doubled, and potash prices doubled. Many factors continue to affect the fertilizer markets including a wide growth in demand, a decrease in capacity, especially in the U.S., increases in natural gas prices and record-high freight costs. The Anderson’s Company was interested in using the Advanced Granule Technology (AGT) for fertilizers to potentially create less expensive, yet effective, slow-release formulations for the nursery industry. Another saving in labour could be found in applying fertilizers in the fall versus the traditional spring application time. Application method was also examined in this experiment. Incorporation is reported to be the best method for nursery fertilizer applications. Topdressing increases fluctuation in temperature and inconsistent moisture (humidity) availability. On the surface of the container the fertilizer is subject to the day- and night-time temperature changes and drying effect of direct sunlight, which reduces availability of nutrients in the timetable that the plant requires. Topdressing also increases potential for fertilizers to be spilled onto the nursery floor and weed growth in the container. However, the practice of topdressing still occurs in many nursery operations.

Objectives
With this study, our objective was to assess experimental DG (AGT) formulations performance on container-grown ornamentals under nursery conditions, compared to standard nursery fertilizers using two application timings and methods.

Materials and methods
Three types of formulations were selected, a 3-4 month, 5-6 month, and 8-9 month, with two application timings, one application starting in the fall, and the other starting in the spring. Fertilizers consisted of three-, six- and nine-month formulations of 15-9-12 (15-4-10 actual) Osmocote Plus, three-month formulation of Harrell’s 16-6-13 (16-2.6-10.8 actual), six-month formulation of Harrell’s 16-6-11 (16-2.6-9.1 actual), nine-month formulation of Harrell’s 15-6-12 (15-2.6-10 actual), AGT 15-9-12 (15-4-10 actual) three-month formulation, AGT 15-9-12 (15-4-10 actual) six-month formulation, and two, nine-month formulations of 15-9-12 (15-4-10 actual), one with monoammonium phosphate (MAP), and the other with triple phosphate [or super phosphate(SP)]. The three-month formulations and triple phosphate formulations were not used in the fall trials.

The amount of fertilizer per container was determined by using the medium rate of the Osmocote formulations, and the other two types (Harrell’s and AGT) were put on at the same rate of the actual amount of nitrogen applied based on weight and formulation of the product. Four test locations were selected, two in Ohio and two in Ontario. The locations in Ohio were at Klyn Nurseries, Perry, and Decker’s Nursery in Groveport. The locations in Ontario were at Willowbrook Nurseries, Fenwick, and J.C. Bakker & Sons Ltd. Wholesale Nurseries (spring start only at Bakker) in St. Catharines. Species selected for testing consisted of Juniperus scopulorum ‘Wichita Blue, Buxus x ‘Green Velvet’, and Spiraea x bumalda ‘Goldmound’ from Willowbrook, Potentilla fruiticosa, Juniperus chinensis, and Thuja occidentalis from J.C. Bakker, Fothergilla gardenia, Ilex glabra ‘Shamrock’, and Juniperus horizontalis ‘Wiltoni’ from Klyn, Buxus x ‘Winter Gem’, Spiraea x bumalda ‘Goldflame’, and Microbiota decussata from Decker’s. Evaluations consisted of growth index at intervals throughout the trial, and pH and electrical conductivity (Ec) using the pour through method. Only growth index [(height+width)/2 or (height+width+width)/3 or height only depending on species] at the end of the trial will be presented. Visual ratings were also taken at Klyn based on a 1-5 scale with 1 being dead and 5 being perfectly healthy. Treatment means were separated using LSmeans in Proc Mixed with SAS (SAS, Inc., Cary, N.C.) software with α=0.05.

Results and discussion
Fertilizers behaved differently at each of the locations from the fall start, although at each location, a nine-month formulation was the best treatment for growth (Table 1). Across species, the best growth at Decker’s occurred with Harrell’s nine-month incorporated. At Willowbrook, Harrell’s nine-month top-dress gave the best growth and Osmocote nine-month top-dress was the best fertilizer at Klyn. By species, Buxus preferred the Harrell’s nine-month top-dress at Decker’s and Willowbrook. At Decker’s and Willowbrook, the Harrell’s nine-month formulation was preferred by all species (incorporated or top-dressed). At Klyn Nursery, Fothergilla and Juniperus showed superior growth with Osmocote nine-month top dressed; however, Ilex had the best growth with AGT six-month incorporated. In most instances, the AGT treatments provided average growth to not significantly different from the best treatments. It was in Buxus growth, however, that the AGT treatments performed below average with decreases growth. The nine-month MAP AGT formulation provided the worst growth for six of the nine species, including incorporated and top dressed applications.

Electrical conductivity values taken from Klyn in May and July 2009 indicate that all fertilizers fell within the desired range for controlled release fertilizers (0.2-1.0 dS/cm) (Fig.1 and 2). However, in May and July, the values indicate that the AGT fertilizers provided little, if any, increases in electrical conductivity which probably accounted for their poor performance in increasing growth. The pH values ranged from 5.2 to 6.6 in May and 5.2 to 7.1 in July. Normal pH values should be between 5.4 and 6.2 for soilless media. At both dates, the pH of the irrigation was above any of the fertilizer treatments. The AGT treatments provided the highest pH values next to water in May.

Averaged across species, the spring start Osmocote six-month top-dress formulation provided the best growth at J.C. Bakker and Klyn (Table 2). At Decker’s, the incorporated Osmocote nine-month formulation was the best, and at Willowbrook, the AGT six-month top-dress provided the best growth. When averaged across species, the AGT nine-month formulation (incorporated or top dressed) provided the worst growth at three of the four locations (Table 2). Only the Buxus, behaved similarly between Decker’s and Willowbrook growing best with the Osmocote nine-month top-dress formulation. The Juniperus species tested differently at three locations, but the species and cultivars were different between locations; however, at two locations, a six-month formulation was preferred. Spiraea also tested differently at the two locations where it was evaluated. At Decker’s, Spiraea performed the best with the Osmocote nine-month incorporated treatment, and at Willowbrook the AGT six-month top-dress provided the best growth. The AGT six-month top-dress treatment also provided the best growth for the Thuja at J.C. Bakker Nursery. For seven of the 12 species/cultivars, the AGT nine-month super phosphate treatments (incorporated or top-dressed) provided the worst growth, with incorporated worse than top-dress. When comparing super phosphate and monoammonium phosphate nine-month formulations, there is virtually no difference when topdressing, but when incorporated, the monoammonium phosphate formulation if far superior to the super phosphate formulation. The lowest visual ratings collected at Klyn and Decker’s for Juniperus, Buxus, and Spiraea occurred with the AGT super phosphate formulation. The AGT six-month top-dress treatment, however, was not significantly different from the best treatment for seven species/cultivars and provided the best growth for two species/cultivars.

Electrical conductivity values differed greatly between the three species tested at Klyn and all treatments provided Ec values above 0.2 dS/cm for all three test dates. At Klyn, pH values were above the desired range in most instances, with the lowest values recorded in May. The nine-month super phosphate AGT formulation provided the highest pH values in May for each of the species tested but were not above desirable.

 

Table 1. Growth index averaged across species of different fertilizer treatments from Decker's Nursery, Klyn Nursery, and Willowbrook Nursery planted in October 2008.

 

TREATMENT	DECKERS	KLYN	WILLOWBROOK
AGT 6 Mo.	50.3 cdez	38.2 b	30.1 e
AGT 6 Mo. Inc.	48.9 de	39.7 ab	33.8 cd
AGT 9 Mo. MAP	50.5 cde	38.5 ab	31.9 de
AGT 9 Mo. MAP Inc.	47.4 e	36.6 b	33.8 cd
Harrells 6 Mo.	54.9 ab	37.7 b	35.6 abc
Harrells 6 Mo. Inc.	51.9 bcd	36.7 b	3 2.9 cd
Harrells 9 Mo.	54.9 ab	36.1 b	37.1 a
Harrells 9 Mo. Inc.	56.6 a	36.7 b	37 ab
Osmocote 6 Mo.	53.2 abc	36.5 b	34.9 abc
Osmocote 6 Mo. Inc.	50.4 cde	37.9 b	36.7 ab
Osmocote 9 Mo.	49 de	42.6 a	33.8 cd
Osmocote 9 Mo. Inc.	51.4 bcd	38 b	34.3 bcd

z = Growth indexes followed by the same letter at each nursery are not significantly different, based on LSmeans (α = 0.05)

Conclusions
From these studies, it can be concluded that the AGT nine-month super phosphate formulation does provide detrimental effects to some species, especially when incorporated. The other AGT formulations, in most cases, perform better when top-dressed as opposed to incorporated. AGT formulations also gave better growth when top-dressed and applied in spring as opposed to fall application. For example, Spiraea and Buxus both performed better from AGT applications in spring. The top dressing of AGT formulations are comparable to industry standards in most cases. No winter injury was observed in fall up-shift and fertilization of plants.

The best treatments over species for the fall start were Harrell’s nine-month incorporated at Decker’s, Harrell’s nine-month top-dress at Willowbrook and Osmocote nine-month top-dress at Klyn. In the fall start by species Harrell’s nine-mo. top dressed performed well for Buxus and Spiraea and incorporated for Potentilla, Spiraea, Juniperus and Microbiota. Osmocote 9 mo. top dress was best for Fothergilla.

The best treatments in the spring start over species were Osmocote six-month top-dressed (Bakker and Klyn Nurseries), Osmocote nine-month incorporated (Decker’s) and AGT 15-9-12 (15-4-10 actual) six-month from The Anderson Co. (Willowbrook). In the spring start by species Osmocote nine-month performed well with Buxus, Spiraea and Potentilla. Osmocote six-month was best for Juniperus chinensis and scupulorum, Harrell’s six-month was best on J. horizontalis.  Osmocote six-month also performed well with Fothergilla and Microbiota. The AGT six-month performed well with Juniperus scupulorum and Spiraea.    

Dr. Hannah Mathers is an associate professor in the Department of Horticulture and Crop Science at The Ohio State University (OSU), Columbus, Ohio, and works under contract with the Ontario-based Vineland Centre for Research and Innovation to help the nursery and landscape industry with research initiatives, industry projects and extension activities. Luke Case is a research associate working with Dr. Mathers, and Jason Parrish is a graduate student at OSU.