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 NO 3 . 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 NH 4 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 NO 3 . 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 641

Improved fertilizer management systems for hurley tobacco (Nicotiana tabacum L.) are needed to reduce the detrimental effects of large applications of fertilizer, such as fertilizer‐induced soil acidity and Mn toxicity. Field studies were conducted at several locations in Kentucky during 1980 to 1986 to examine the response of tobacco to rates and methods (band vs. broadcast) of application of N‐P‐K fertilizer. Response to banding N‐P‐K fertilizer varied widely among experimental sites and was related to level of NH4OAC‐extractable soil K. At low soil K levels, greater dry matter and cured leaf yields occurred most often for broadcast compared with banded fertilizer. These effects probably resulted from factors affecting the efficient use of K by the plant, including the greater numbers of roots in contact with fertilizer in broadcast treatments. At high soil‐test K levels, greater growth and yield occurred more often from band treatments (as opposed to broadcast). This probably resulted from a reduction in toxic Mn levels and fertilizer salt injury, and from a more favorable balance between K and other nutrients in band treatments. A linear regression revealed that yields from band and broadcast treatments were equal when initial soil‐test K measured 248 kg ha−1. In soils testing high in P and K, the content of plant Mn increased linearly with rate of N‐P‐K fertilizer in broadcast treatments, whereas it was unaffected by fertilizer rate when the fertilizer was banded.