Use of magnesium in bareroot pine nurseries

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.

Use of calcium in bareroot pine nurseries

South

2022

Use of sulphur in bareroot pine and hardwood nurseries

South

2023

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.

Zinc fertilization in bareroot pine seedbeds

South

2023

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.