The form of nitrogen taken up by plants (e.g., ammonium, nitrate or N fixation) strongly influences the overall ratio of cation to anion uptake, which in turn affects the alkalinity of the ash after combustion of the organic material in plant tissues.  Ash alkalinity was measured in foliage from intensively cultivated crops (corn, wheat, soybeans, alfalfa) as well as native plants including C3 and C4 grasses in a successional field and deciduous forest trees and forbs from the forest understory, all growing on similar soils. 

Results/Conclusions

Among the crops, large differences in ash alkalinity were observed, with corn and wheat showing very low ash alkalinity, soybeans having intermediate values, and alfalfa being relatively high (the latter two are potential nitrogen fixers).  The grasses and trees were intermediate in ash alkalinity.  Forbs from the forest understory varied over a large range but included species with the highest ash alkalinity values that were measured (Impatiens, Mayapple, Virginia Creeper).   The potential of these measurements as indicators of nitrogen nutrition is considered in light of what is known about ash alkalinity, nitrogen cycling in these soils, and the ecology of these particular species.