Biological nitrogen fixation, 1924-1974.

Crop rotation was practiced in ancient times by alternating the use of leguminous and nonleguminous plants. The basis for the benefit derived from this practice was not understood, but it was observed empirically that crops were improved and the condition of the soil was maintained better with rotation than by continual cropping with nonleguminous plants. Rotation was recognized as good husbandry, but it remained for Boussingault to offer an explanation of the benefit in the 1830's. He established one of the earliest agricultural experiment stations and demonstrated in the greenhouse that clover and peas increased their nitrogen content when grown on sand that was virtually free of fixed nitrogen. His field experiments likewise supported the view that leguminous plants could use N. from the atmosphere. The observations of Boussingault touched off heated controversy and Liebig suggested that the observed increases in nitrogen in the leguminous crops arose merely because the large leaved leguminous plants were capable of extracting more ammonia from the atmosphere than were the smaller leaved control plants. Because Liebig could speak with authority in the area of organic chemistry, he apparently felt that this carried with it the privilege of speaking in the area of agricultural chemistry without the need to present experimental evidence in support of his postulates. It is hardly surprising that a French commission, assigned to the task of checking to see whether Liebig or Boussingault were correct, came to the conclusion that their fellow countryman in fact had demonstrated an increase in nitrogen in the leguminous plants.