A test was conducted at ten farm locations in the flue-cured tobacco producing area of North Carolina for 3 consecutive years with the P₂O₅ treatments applied to the same plots. The six treatments were 0, 22.5, 45, 67.5, 90 or 180 kg P₂O₅ per hectare. The concentration of P, K, Ca and Mg was determined in the tissue of whole tobacco plants 5 and 7 weeks after transplanting. The concentration of reducing sugars (RS), total alkaloids (TA), N, P, K, Ca. Mg, RWA, and NRA was determined in the cured leaf. Responses to the six P₂O₅ rates were found mainly at the test location where the initial available soil P level was very low. The concentration of Ca in whole plants increased as P₂O₅ increased up to 45 kg per ha. for each sampling. At a location very high in P availability, P in the whole plant 7 weeks after transplanting increased as P₂O₅ increased up to 180 kg per ha., whereas K at the 5th week after transplanting decreased with P₂O₅ rates higher than 45 kg per ha. Analyses of the cured leaf from all locations showed no effect of added P₂O₅ Although location and year effects were significant (probably due to rainfall amount and distribution) for most of the characteristics studied, the P₂O₅ rates generally produced consistent results across the diverse years and locations since, in general, no significant Year x P, Location x P or Location x Year x P interactions were measured. It is concluded that as a result of previously high amounts of P₂O₅ application it is now possible to use smaller amounts and that 45 kg/ha of P₂O₅ are adequate to produce good marketable tobacco leaf.

(Full article published with kind permission from "Tobacco International")