Correlation of Nitrogen Soil Tests With Nitrogen Uptake by the Tobacco Plant

Greenhouse and laboratory studies were conducted on soils collected from 37 Wisconsin tobacco fields to evaluate their capacity to supply nitrogen for two successive tobacco crops. Correlation analyses were made between the nitrogen content of each crop and the nitrogen determined by the various soil tests on the samples taken before the first crop. Highly significant correlation coefficients of 0.97 and 0.90 were obtained for soil nitrate nitrogen and Aspergillus niger tests, respectively. However, these tests were not significantly correlated with nitrogen uptake by the second crop, no doubt a result of depletion of the nitrates by the first crop. Similar results were obtained by dividing the soils into Prairie and Gray‐Brown Podzolic groups, except that a highly significant coefficient was obtained between the Aspergillus niger test and nitrogen uptake by the second crop for the Prairie soils. The tests which determined all or a portion of the organic nitrogen correlated at significant or highly significant levels with the nitrogen content of the second crop but not by the first crop. This lack of consistency between crops was undoubtedly due to the pronounced effect of the higher content of nitrate nitrogen in the soil prior to the first crop. Highly significant correlation coefficients were obtained between total soil nitrogen and each of the following: alkaline permanganate nitrogen (0.95), percentage organic matter (0.99), nitrification rate (0.65) and the amount of ammonia nitrogen extracted by various concentrations of sulfuric and hydrochloric acids (0.59 to 0.71).