Nature of Work: Wulpak is a processed wool fiber product that has been used as mulch in container nursery production. In studies conducted at MHCREC, Fletcher, NC in 2000, when Wulpak was applied at rates calculated to provide the same amount of nitrogen as the standard fertilizer products, controlled release fertilized plants produced from 200 to 400% more growth during the experiment than those receiving only Wulpak. Data indicated that available nitrogen from Wulpak was released during the first two weeks of the experiment. For some, but not all, species a superior root system seemed to develop where Wulpak was top-dressed, possibly because of temperature and water stress modification by Wulpak as a mulch.

The objective of the test was to determine whether Wulpak as a fertilizer source can be a benefit to plant growth when standard controlled release fertilizers are used. To evaluate this, Wulpak was applied at label recommended rate of 45 g. per gallon pot. The controlled release fertilizer Wilbro 19-5-12 was applied at the rate of 1.5 g N (21 g actual fertilizer)/gallon pot/month which was statistically the best rate in the 2000 tests. Additional treatments were 0.25 times that rate and 0.50 that rate, with or without Wulpak used as a mulch. There was also an unfertilized and unmulched treatment.

All plants were potted from commercially grown plugs into standard MHCRS pine bark based nursery potting medium and placed under overhead irrigation on the crushed rock container research pad at MHCRS, Fletcher on May 8, 2001. Wulpak mulch was applied to the appropriate treatments following irrigation then the appropriate rate of fertilizer was applied over the Wulpak mulch.

Following the first complete irrigation, VTEM measurements were taken from representative plants of each species. Readings from these same plants were taken 24 hrs later, 7, 14, 21, 28, 35 and 42 days after initial fertilizer application (data not shown). The experiment was terminated when plants reached salable size on July 6, 2001 which was 7 weeks after the initiation of the experiment. Fresh weight was determined by severing plants at the surface of the growing medium and immediately recording fresh weight for each plant. There were seven plants per treatment and four replicates.

Results and Discussion: Mulch may help to retain moisture, a cooler rootball and suppress weeds. However, none of these values were measured directly. It is impossible to separate moisture and temperature from fertilizer performance so we report what happened in terms of growth but do not speculate as to why it happened.

Wulpak alone resulted in more growth than no fertilizer but growth equal to only about that achieved with 0.25 of the standard controlled release fertilizer (Table 1). This suggests that Wulpak has some value in producing growth over not applying Wulpak at all.

Significance to the Industry: Wulpak may have some value as a fertilizer. If a grower is using Wulpak for mulching value anyway, no more than the 0.5 rate of controlled release fertilizer needs to be used for Buddleia 'Nanho Purple' and Eupatorium fistulosum 'Carin.' However, when growing the ornamental grass Panicum virgatum 'Prairie Skies,' the full rate of fertilizer application with Wulpak resulted in increased growth over the full fertilizer rate alone. Therefore, a higher application rate of the fertilizer may be worth exploring.

Acknowledgments: Thanks to both Wilbro and North Creek Nurseries for their support of this research.

Table 1. Fresh weight (grams) of selected plants grown in trade gallon pots with the addition of Wulpak and or Wilbro 19-5-12 controlled release fertilizer.

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North Carolina State University