The capacity of a native prairie grass, Andropogon scoparius (little bluestem), to grow successfully in an extremely P deficient soil of central Wisconsin was investigated. This grass is invading ridges, but not depressions, of abandoned fields of Poa pratensis (Kentucky bluegrass). Ridge soils contain less available phosphorus than depression soils. The yield and P absorption of Andropogon and Poa were compared when grown in the low P soil and in nutrient sand culture at various levels of added P. The former consistently outyielded the latter at all levels of P in both soil and sand cultures. Andropogon, which exhibited less yield response to increasing P supply than did Poa when grown in the P deficient ridge soil, was able to absorb much more P from ridge soil. It also utilized absorbed P more efficiently in producing plant dry matter when grown under extreme P stress in sand culture. The critical P concentration for Andropogon was lower than for Poa.