Is the recommended pH for growing hardwood seedlings wrong?

Abstract

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 nonfertilized 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.

Abiotic factors impact on oak forest decline in Lorestan Province, Western Iran

“…Such a pH range is considered alkaline pH and is suitable for the availability of most nutrients to the roots 105 . Regarding soil chemistry, the most suitable pH range for root growth development is 6–7.5 106 . The center and north part of the study area have a more significant pH, while the south of the study area has a lower pH, which is more suitable for oak growth (Fig.…”

Use of sulphur in bareroot pine and hardwood nurseries

“…In 1980, about 29% of managers applied AS to pines during the summer while 68% applied AN (Marx et al 1984). Some managers applied AN since it was less expensive than AS while others relied on AS due to growth benefits (van den Driessche 1972;Morris 1979) plus the ability to lower soil pH and improve seedling quality (van den Driessche 1969;South and Davey 1983;South 2017).…”

“…Depending on species, cultural practices, and seedling age, a crop of 1-0 pine seedlings may remove approximately 5 to 10 kg of S (Flinn et al 1980;Boyer and South 1985;South 2018). Considering four consecutive crops of pine seedlings, it is estimated that around 24 kg ha -1 of S could be harvested, resulting in a potential decrease of 12 µg g -1 in soil S levels.…”

“…In addition, some S-rich proteins may offer resistance against herbivory (Zenda 2021). Lowering soil pH with S can reduce damping-off of pine seedlings in nurseries (South 2017) but applying 336 kg ha -1 of S did not reduce the incidence of root-rot at a nursery in Oregon (Johnson and Zak 1977). In some trials, fertilization with gypsum reduced Phytophthora infection (Messenger et al 2000) but it is not known if the effect was due to S or Ca.…”

“…There are several reasons why managers of bareroot nurseries apply S to seedbeds and seedlings. #1-increase soil acidity: When soil pH is too high for optimum growth, S rates of 800 to 1,100 kg ha -1 can lower soil pH at sandy nurseries (South 2017). In some cases, increasing soil acidity will reduce the risk of an Fe deficiency.…”