Potassium fertilization in bareroot nurseries in the southern US: a review

This review covers most of the published literature on potassium (K) fertilization in bareroot seedbeds with the intent to concentrate on the southern United States. The timing and rates of K fertilization for bareroot seedlings are often based on logic and myths and, as a result, K recommendations vary considerably. Some recommend bareroot pine seedlings be fertilized with twice as much K as nitrogen (N) while others apply less than 100 kg ha-1. It was determined that several long-held claims about K fertilization are invalid. Nursery seedbeds do not need to contain four times as much available K as N and the belief that extra K fertilization will increase freeze tolerance or drought resistance of non-deficient seedlings is invalid. There are no data to support the claim that K fertilization increases root growth or assists in the formation of terminal buds. For sandy seedbeds, there is no need to apply K before sowing. Adding extra K during the fall does not increase seedling morphology or seedling performance when loblolly pine seedlings, at lifting, have more than 0.5% K in needles. A reduction of K fertilization can be achieved by reviewing foliar tests prior to K top-dressings

Is the recommended pH for growing hardwood seedlings wrong?

Two schools of thought address the optimum soil pH (measured in water) for growing hardwood seedlings in bareroot nurseries. One school uses nutrient surveys in non-fertilized forests to determine the best pH range for growing seedlings in fertilized nurseries. Some students of this school believe hardwood seedlings grow best at pH 6.0 to 7.5. In contrast, another school relies on research from pH trials to conclude that fertilized hardwoods can grow well in soils that range from pH 4.5 to 6.0. This article compiles some of the findings from seedbed and greenhouse trials and attempts to use data to dispel a few myths about the “optimum pH” for growing hardwood seedlings. Greenhouse trials suggest many fertilized hardwoods grow better in acid soils (pH 4-6) than in nearly neutral soils (pH 6.0-7.5). The optimal pH for growth differs among species and, therefore, it is a myth that all hardwood seedlings grow best at pH 6 to 7.5. Most nursery managers in the southern United States grow bareroot hardwoods between pH 4.8 and 6.0

Fertilizer trials for bareroot nurseries in North America

In North America, most tree nursery nutrition publications during the past two decades involved either container-grown stock or stock grown in greenhouses. In contrast, most bareroot nursery fertility trials in North America were published during the last century.  As a result, some bareroot fertilization recommendations have remained the same since 1980 and some practices continue to be based on myths and assumptions. The bareroot nursery industry in the USA might benefit if the next generation of graduate students will consider testing old and new theories about nursery fertilization.  Hopefully, they will discover new facts so that future fertilization regimes will be based on science. This paper provides various fertilizer trials that should be established in bareroot nurseries

Cost of inoculating seedlings with Pisolithus tinctorius spores

Although the production of commercial products of vegetative Pt (Pisolithus tinctorius (Pers.) Coker & Couch) inoculums has ceased in North America due to a lack of demand by consumers, the number of products that contain Pt spores has increased.  The quality, quantity and price of these products vary considerably.  The cost of inoculating 1,000 tree seedlings with Pt basidiospores can vary from $0.45 to more than$30.  The cost of treating with Pt spores is lowest when seedlings are inoculated in a container nursery using rates that are less than 0.4 mg per seedling.  However, with some products the cost to treat 1,000 bareroot seedlings is greater than 500 when spores are applied in the planting hole.  Three decades ago, 1 g of Pt spores could be purchased for 0.13 and now the price of 1 g can exceed $14. Although many research papers provide data on the biological response to inoculating seedlings with spores, few document the cost of inoculation. Commercial products that are marketed toward homeowners containing both ectomycorrhizal and endomycorrhizal spores are more expensive than products that contain only ectomycorrhizal spores.  In situations where survival and growth of seedlings are not increased, the benefit/cost ratio will typically be less than one

Irrigation in pine nurseries

This review provides information and opinions about irrigation practices in pine nurseries. Even when nurseries receive more than 15 mm of rainfall week-1, managers irrigate seedbeds to increase germination, increase seed efficiency, and increase root growth. In the southern United States, a 7-month old pine seedling in an outdoor nursery typically receives 2 to 6 kg of water supplied from either sprinklers (39 nurseries) or center-pivot irrigation (12 nurseries). Most nursery managers do not intentionally subject the crop to moisture stress, since most reforestation sites receive adequate rainfall, and many studies show that reducing root mass does not increase seedling performance. In fact, nursery profits can be reduced by more than $13,000 ha-1 when deficit irrigation reduces average seedling diameter by 1 mm. Although some researchers believe that failure to properly drought stress pine seedlings might increase outplanting mortality by up to 75%, research over the past 40 years does not support that myth. When pine seedlings average 5 mm (at the root-collar), water stress is not a reliable method of increasing tolerance to an October freeze event. In several greenhouse trials, researchers grew and tested seedlings that nursery managers would classify as culls (i.e., dry root mass < 0.5 g). Unfortunately, it is common for researchers to make irrigation recommendations without first developing a water-production function curve

Use of copper in pine nurseries

Copper has been used by nursery managers for more than 100 years to suppress fungi and as a fertilizer for more than 50 years. Consequently, nursery seedlings with copper deficiencies are rare, especially for broadleaf species. In many nurseries, soil contains <10 μg-Cu g-1 and in greenhouse trials, pine seedlings are relatively tolerant of soil levels with 35 μg-Cu g-1. A million bareroot pine seedlings may contain 50 to 100 g-Cu and, when soil tests indicate low copper levels, managers might apply 1 kg-Cu per million seedlings. In contrast, it may take only 15 g-Cu to produce one million container-grown seedlings. Copper fertilization is typically not required when 30 cm of applied irrigation water contains 0.1 μg-Cu g-1 (supplying 0.3 kg-Cu ha-1). This review highlights some of the past and current uses of copper in bareroot and container nurseries with a focus on deficiency and toxicity effects as well as the impact of various copper-based products and provides recommendations on ideal soil and foliar ranges

Effects of Fall Fertilizer Applications of Mitotic Index and Bud Dormancy of Loblolly Pine Seedlings

A series of studies examined the effects of fall fertilization with diammoniwn phosphate (DAP) on mitotic index and bud donnancy [as measured by mean days to budbreak (DBB)] of two half-sib seed sources of loblolly pine. The first study tested different rates of DAP (0, 67, and 202 kg Nlha), the second study compared DAP with ammoniwnnitrate, and the third study examined the effect of different application dates (September 28, October 19, and November 9). An increase in mitotic index of unfertilized seedlings was observed during October and was due to developmental activity which follows initial budset. Differences in mitotic index were observed between families in all three studies.Overall, the Georgia family has a higher mitotic index, but in one study, the Virginia family had higher values in the spring. Both families tended to reach a minimum level of mitotic index at the same time (mid- to late December). However, the Virginia family reached maximum rest (as measured by days to bud break) about 1 to 2 weeks prior to the Georgia family. Fertilization with DAP in the fall (after bud set in September) did not delay the progression of the bud dormancy cycle as measured by days to bud break in a greenhouse. The overall effect of fall fertilization on increasing the mitotic index was temporary and only lasted for about three weeks after fertilization. These findings indicated that a direct relationship may not exist between the bud dormancy cycle and mitotic index

Root Growth Potential and Field Survival of Container Loblolly Pine Seedlings Fall Fertilized with Nitrogen

Two studies investigated the effects of fall nitrogen fertilizer applications on the root growth potential (RGP) and field performance of container loblolly pine seedlings (Pinus taeda L.). The seedlings were sampled at 4 chilling levels ranging from 100 to 550 hours (0 to 8\u27 C). Seedlings propagated for the first study may have had a hidden nutrient deficiency and therefore the fall diammonium phosphate (DAP) application at rates of 202 kg N/ha and 67 kg N/ha increased RGP 43% and 32%, respectively. The growing season mineral fertilizer application rate was increased in the second study which may explain why nitrogen applications at 202 kg N fall/ha did not increase RGP. In general, RGP increased as exposure to chilling hours increased. Fall fertilization increased total seedling weight. Analysis of covariance indicated that RGP may be a function of total seedling weight and not a direct response to fertilizer treatment or chilling level. For the first study, survival was not significantly affected by the fall DAP treatments

Should forest regeneration studies have more replications?

When it comes to testing for differences in seedling survival, researchers sometimes make a Type II statistical error (i.e. failure to reject a false null hypothesis) due to the inherent variability associated with survival in tree planting studies. For example, in one trial (with five replications) first-year survival of seedlings planted in October (42%) was not significantly different (alpha = 0.05) from those planted in December (69%). Did planting in a dry October truly have no effect on survival? Authors who make a Type II error might not be aware that as seedling survival decreases (down to an overall average of 50% survival), statistical power declines. As a result, the ability to declare an 8% difference as “significant†is very difficult when survival averages 90% or less.  We estimate that about half of regeneration trials (average survival of pines <90%) cannot declare a 12% difference as statistically significant (alpha = 0.05).  When researchers realize their tree planting trials have low statistical power, they should consider using more replications.  Other ways to increase power include: (1) use a one-tailed test (2) use a potentially more powerful contrast test (instead of an overall treatment F-test) and (3) conduct survival trials under a roof

Forest Nursery Practices in the Southern United States

Over the past five decades, researchers in the southern United States have been working with nursery managers to develop ways to reduce the cost of producing seedlings. In this regard, the Southern Forest Nursery Management Cooperative (at Auburn University in Alabama) has helped reduce hand-weeding costs and losses due to nematodes and disease. As a result, nursery managers are able to legally use a variety of registered herbicides and fungicides for use in pine and hardwood seedbeds.  Other changes over the last three decades include a reduction in the number of nurseries growing seedlings, a reduction in the number of seedlings outplanted per ha, an increase in the number of container nurseries, an increase in the average production per nursery, an increase in production by the private sector, growing two or more crops after fumigation, the development of synthetic soil stabilizers, applying polyacrylamide gels to roots and the use of seedling bags and boxes for shipping seedlings