Effects of soil ph,nitrogen source,phosphorus, and molybdenum on early growth and mineral nutrition of burley tobacco

Abstract

Previous research has indicated that P application may influence plant Mo nutrition, and that both P and Mo are influenced by soil pH. This is of interest, since Mo is deficient in some soils and because large quantities of acidifying nitrogenous fertilizers are commonly applied in production of burley tobacco (Nicotiana tabacum L.).

Burley tobacco was grown in two experiments using Maury silt loam soil (Typic Paleudalfs) to determine the influence of soil acidity, form of N applied, and P application on plant growth and mineral nutrition. The studies were conducted in the greenhouse so that high root densities would develop and the data primarily reflect rhizosphere effects.

Ammonium application depressed rhizosphere pH 0.4 to 0.6 pH units. Nitrate nutrition raised soil pH less than 0.1 pH unit. Plants supplied NH₄ exhibited slower early growth than plants supplied NO₃. Several significant interactions involving soil pH, N source, P, and Mo occurred. In the first experiment, plant P was not affected by form of N applied, while in the second experiment NH₄ application resulted in higher plant P concentration, both in presence and absence of applied P. Application of NH₄ also increased plant weight in the second experiment. Plant P concentration was influenced by pH, being greatest at pH 6.2 and decreasing as pH levels decreased or increased. Plant Mo concentration did not differ among forms of N at pH 5.4, but at pH 7.2 was three times greater in the presence of NO₃. When Mo was applied, P addition enhanced plant Mo concentration, but when Mo was not applied, P addition did not increase Mo concentration. This effect of P on Mo occurred only in the presence of N and was greater in the presence of NH₄ than NO₃. These observations suggest that enhancement of plant Mo nutrition by P application may be dependent on adequate levels of N being present.