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Excess-Base and Excess-Base/Nitrogen Ratio of Various Crop Species and Parts of Plants¹

The primary objective of this study was to determine how various crop species differ in their cation-anion balance and thus in their effects on soil reaction and on the acidifying effects of N fertilizers on the base status of soils. Samples of 27 species of cereal, grass, legume, and miscellaneous field and vegetable crops were collected from a wide range of environmental conditions in the field. The plants were analyzed for total N, nitrate N, and excess-base (EB); and calculations were made of excess-base/organic N ratios (EB/N). Similar determinations were also made on the principal plant parts of 13 crop species.

Marked differences were found in the excess-base of the various crop species. The average EB ranged from 30 meq/100 g for wheat (Triticum aestivum L.) to 213 meq/100 g for tobacco (Nicotiana tabacum L.). In general, monocotyledons were lower in EB than dicotyledons. Likewise, crop species showed distinctive differences in EB/N ratios, ranging from 0.24 for cabbage (Brassica oleracea capitata) to 1.09 for buckwheat (Fagopyrum esculentum).

Samples of a given crop species grown under a wide range of environmental conditions showed considerable range in EB and EB/N ratios. For most crop species the coefficients of variation of EB/N ranged from 10 to 20%.

The principal plant parts of a given crop species showed in many instances moderate to large differences in EB and EB/N. Thus, differences in the proportion of plant parts in different samples may affect the EB and EB/N of a given species.

The significance of the differences in the EB/N of various crop species in modifying the effect of N fertilizers on soil acidity is discussed.

Key Words: Acid-base balance • Cation-anion balance • Species differences • Growth stage • Nitrogen fertilizers • Nitrification • Denitrification • Soil Acidity

² Professor of Agronomy and Graduate Assistant in Soils, respectively.

Received for publication April 26, 1972.