Nitrogen Fertilization of a Canaan Valley Seed Source of Balsam Fir

Special Circular 159

Conclusions and Recommendations

Results of these studies indicate that plantings of the Canaan Valley seed source of balsam fir growing on sites having a relatively wide range of internal soil drainage can benefit from nitrogen fertilization. Of the traits measured or evaluated in the study, differences between fertilized and unfertilized trees were statistically significant only for foliage colors of the upper surfaces of needles of trees. However, other traits, including weights of foliage samples, color of the lower surfaces of needles and, to some extent, needle lengths and numbers of lateral limbs on terminal shoots, were also consistently better on trees that had received N applications. However, there appeared to be little or no effect on terminal shoot growth. In general, there were no consistent differences between trees fertilized with 100, 200, and 300 pounds of N/acre.

As described in the Methods section, applications of N were made in 1993, 1995, and 1996 for the two studies established in 1993 (Wooster 1 and Pomerene 1) and in 1996 for the three studies established in 1996 (Wooster 2 and Pomerene 2 and 3). Although differences between years in measurements/evaluations were not analyzed statistically, overall benefits from N fertilization appeared to last for at least two and possibly three years, as evidenced by consistently higher measurements or ratings for fertilized than for unfertilized trees in 1994 and 1997 for Wooster 1 and Pomerene 1 and in 1997 for Wooster 2 and Pomerene 2 and 3.

Even where there were beneficial effects of N fertilization, there was still wide variation in growth and foliage characteristics of individual trees between and within study areas. As discussed, part of that variation was probably related to internal soil drainage. Variations were probably also related to genetic differences between and within individual half-sib families of trees, and N fertilization will not overcome all of that variation.

These studies were confined to N fertilization only. As discussed previously, both study sites at Wooster had overall fertility that was more than adequate for even the more demanding Christmas tree species that are grown in Ohio. However, at the Pomerene Forest Laboratory, potassium levels were low for all three of the study sites and two, Pomerene 1 and 2, also had relatively low pH (Table 1). Without a better data base for Canaan fir, it is unclear how this may have affected overall growth and foliage characteristics of trees on those sites. Completion of the soil-site studies now in progress, plus additional sampling of grower-owned plantations, should help to establish minimum soil fertility levels needed for good performance on a variety of sites.

Based on results of the studies reported here, these recommendations are made for nitrogen fertilization of established plantings of "Canaan" fir:

• Nitrogen fertilization will probably not significantly increase lengths of terminals and other shoots of trees growing on most sites. However, the beneficial effects of fertilization on foliage characteristics, including colors of the upper and lower needle surfaces and foliage weights, appear to be effective for at least two years. Therefore, fertilization with approximately 100 pounds of actual N per acre could be confined to one or two applications late in the rotation. This would improve the quality of visible foliage on trees at the time of harvest and reduce costs related to early and more frequent applications.

• Based on results from this and other studies at OARDC, application of fertilizer to three- to four-foot-wide bands along the rows of trees should be as effective as broadcast applications to plantations. This will not only reduce the costs of N fertilizer but also would not promote vigorous growth of grass and weeds between rows.

• Application of soluble nitrogen sources such as ammonium nitrate, urea, sodium nitrate, etc., to first-year plantings of trees is not recommended, particularly for bare-rooted seedlings. Research at OARDC has shown that high salt concentrations in the soil following fertilization can lead to loss of regenerating roots, with resulting poor growth and/or mortality of trees.

• Although not a part of this study, some type of effective weed control around trees is essential if the benefits of N applications are to be fully realized. Research in Ohio (Brown, 1980; Brown et al., 1989; Evans, 1981; Heiligmann et al., 1985) found that use of chemicals, shallow cultivation, and mulches were equally effective in providing effective weed control in Christmas tree plantings, while mowing alone did not give the desired level of control. Those studies also found that strip and/or spot applications around trees were as effective as complete area control.