The acquisition of phosphorus byLupinus albus L.

Abstract

The maintenance of soil fertility is of prime importance in any agricultural system and an important component of this is nitrogen availability. In advanced agricultural systems, nitrogen availability to crops is usually maintained either by the application of nitrogen fertilizers, or by a system of ley farming in which a legume-based phase and a non-legume phase of varying periods are alternated. In more primitive agricultural systems, crops often consist of mixtures of legumes and non-legumes and this is thought to have enabled continuous cultivation of the land to occur over long periods without an associated decline in soil fertility, albeit at a low level of productivity14. Similarly, under pastures, which commonly consist of mixtures of legumes and non-legumes, soil nitrogen usually remains constant or increases with time. There are two ways by which nitrogen can be transferred from legumes to nonlegumes. The first is by the breakdown of the nitrogen rich plant as it or parts of it die, thereby releasing nitrogen to plants growing after the death of the legume. The second is by the secretion of nitrogenous compounds from the roots of the legume. This latter mechanism was elucidated by research conducted prior to 1934, and has been reviewed by Nicol13 who concluded that these compounds can be utilized by associated non-legumes. Subsequent work has generally supported this conclusion2'8,16'20'22 although it is recognized that species of legumes differ in their ability to transfer nitrogen17'21.