The Importance of Subsoil Phosphorus to Agronomic Crops

During the last few decades several investigators have suggested that the subsoil is an important source of plant nutrients. For the most part, these claims were based on excavation studies which indicated that the root systems of some agronomic crops penetrated the subsoil to considerable depths. These studies, however, gave no information as to the actual amounts of subsoil nutrients removed by the crops, and little progress was made in this direction until the development of radiotracer techniques.