Zinc deficiencies are rare in pine seedlings with less than five documented cases in bareroot nurseries. One temporary deficiency occurred after soil was land-leveled (i.e., topsoil removed) and another occurred on a peat soil after more than 2,200 kg of agricultural lime was applied before sowing. Farmers also observe zinc deficiencies on (1) over-limed areas and (2) where Zn-demanding crops are grown on areas where topsoil was removed during land leveling. Since ZnSO4 is a naturally occurring pesticide, sometimes height growth increases are due to pest control. In pathogen-rich soils, pine growth may be improved more by the fungicidal effect than by a growth benefit from added sulphur and zinc. As a result, a pseudo-deficient response is possible when growth of non-deficient seedlings increases after treatment with large amounts of ZnSO4 or ZnCl2. In some trials, claims of a Zn deficiency have been made without supporting evidence from foliar tests or from tests using pathogen-free soil. Although fertilization with Zn increased seedling growth at pine nurseries in New Zealand, India, Russia, and Wisconsin, only at the Sweetwater Nursery in New Zealand did foliar tests prove a Zn deficiency.

During the 20th century, managers at sandy nurseries utilized sulphur (S) to lower soil pH and mitigate the risk of iron deficiency. During that time, however, applying S as a fertilizer was a rare event. At many nurseries, S in rain and irrigation water was sufficient to avoid visual deficiency symptoms. The S status of soil and foliage was typically unknown, and many researchers did not test for S due to the additional cost. Consequently, S became the most neglected macronutrient. While a few nursery trials demonstrated that elemental S reduced damping-off and increased height growth, a majority showed no benefit after applying S at rates lower than 100 kg ha-1.  Even so, by 1980, S-deficiencies occurred at bareroot nurseries in Alabama, Oklahoma, Virginia, Wisconsin, the United Kingdom, and likely in North Dakota and New York. The risk of a deficiency increases when N-only fertilizers are applied to seedbeds. Due to research, experience and the precautionary principle, several managers transitioned to using ammonium sulfate instead of, less expensive, N-only nitrogen fertilizers. After soil tests became affordable, managers began to ask questions about the need to apply S to seedbeds. Only a few hydroponic trials with small pine seedlings have been used to estimate “threshold” or “critical values” for foliar S.  Since an initial 1,500 μg g-1 S value is “unreliable” for pine seedlings, some authors lowered the value to 1,100 μg g-1 and even as low as 500 μg g-1 S. Others ignore all estimates based on total S concentrations and, instead, monitor only foliar SO4 levels.

When soil is moist and wind is at a gale force, the term used to describe blow down of old trees is windthrow. In contrast, toppling is a term used when planted pines lean more than 15° during the first decade after transplanting. Pines tend to topple more than other conifers and fast-growing species topple more than slow growing genotypes. Large areas of pine plantations have toppled before age 8 years. This paper describes some toppling events that have occurred in 18 countries and includes 16 questions about toppling.

Bareroot nursery managers may apply dolomite, gypsum, or Ca-nitrate to increase Ca in nursery soils. Although a few managers follow S.A. Wilde’s recommendations and maintain soil at levels of 500 to 1,000 μg g-1 Ca, there is no need to keep Ca levels this high.  In contrast, managers at sandy nurseries apply Ca when soil tests drop below 200 μg g-1 Ca. In fact, acceptable pine seedlings have been produced in irrigated soil with <100 μg g-1 available Ca. In plantations, asymptomatic wildlings grow when topsoil contains 17 μg g-1 Ca. In sandy soils, applying too much gypsum can result in a temporary Mg deficiency and too much lime will result in chlorotic needles. Managers apply Ca when foliar levels fall below a published “critical value.” The belief that the critical value for Ca varies by stock type is not valid. In fact, numerous “critical” values are invalid since they were not determined using growth response curves. Critical values determined for small seedlings using CaCl2 in sand are apparently not valid for use in bareroot nurseries.   At bareroot nurseries, the soil extractable Ca level can decline during a year by 30 μg g-1 or more. Harvesting 1.7 million pine seedlings may remove 20 kg ha-1 of Ca but irrigation can replace this amount or more. When water contains 5 mg l-1 Ca, 600 mm of irrigation will add 30 kg ha-1 Ca.  In some areas, 1,000 mm of rainfall will supply 7 kg ha-1 Ca. Even when a Mehlich 1 test shows no exchangeable Ca in the topsoil, pine needles on tall trees may exceed 2,000 μg g-1 Ca due to root growth in subsoil. There are few documented cases of deficient pine needles (<300 μg g-1 Ca) in irrigated nurseries in Australia, New Zealand, Scotland and in the Americas. Even when soil fumigation delays the inoculation of ectomycorrhiza, bareroot pines have adequate levels of Ca. Typically, foliage samples from pine nurseries contain at least 1,000 μg g-1 Ca. Samples from 9-month-old seedlings range from 300 to 11,000 μg g-1 Ca. Although the “critical value” for Pinus echinata foliage is not known, 1-0 seedlings with 300 μg g-1 Ca were not stunted and apparently grew well after ouplanting.

Pines with visible magnesium (Mg) deficiencies (i.e. yellow tips on needles) occur in bareroot nurseries throughout the world. The occurrence of “yellow-tips” is rare when soil pH is above 6.5 but they have occurred on sands (pH < 6.0) with less than 25 μg g-1 Mg.  If yellow-tips occur in the summer, the foliar content of yellow tips is usually less than 1,000 μg g-1 Mg. Some nurseries do not produce “yellow-tip” seedlings when irrigation water contains sufficient Mg. Factors favoring a deficiency include low soil pH, high calcium in irrigation water, frequent fertilization with nitrogen and potassium and applying too much gypsum. Although various Mg fertilizers are available, many nursery managers apply dolomite or potassium-magnesium sulfate before sowing seeds and a few also apply magnesium sulfate in July or August. Soil tests are used to determine when to fertilize before sowing and foliage tests determine when to apply Mg to green seedlings. Nursery managers who follow S.A. Wilde’s forest-based soil recommendations may apply magnesium sulfate to green seedlings even when seedbeds contain adequate levels of Mg.  When deficiency is minor, chlorosis on needle tips usually disappears before the fall equinox and, when applied at this time, Mg fertilizers have little or no effect on height growth.  This paper reviews some of the past and current uses of Mg in bareroot nurseries and highlights a need for additional research.

Nursery seedlings with visual boron (B) deficiencies are rare, especially for broadleaf species but they may have occurred in conifer nurseries in Florida, Oregon and the UK. Factors favoring a deficiency include high soil pH, high soil calcium and low soil moisture (i.e. withholding irrigation). Symptoms of a boron deficiency in pine include dead terminals, resin exudation from buds, dark green foliage, and terminal needles with less than 3 μg g-1 B. Chlorosis is an iron deficiency symptom but is not a boron deficiency symptom. At some nurseries (with more than 2% organic matter and more than 0.05 μg g-1 B in irrigation water), seedlings do not have a hidden hunger for B. As a result, there are no published trials that demonstrate a positive growth response from adding boron to managed nursery soils (when seedbed density is not reduced by boron). This review highlights some of the past and current uses of B in nurseries with a focus on deficiency and toxicity effects.

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.

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.

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.

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.