Root proliferation into soil zones rich in nutrients is an important mechanism ensuring effective exploitation of soil nutrients by plants. No studies have examined the effects of atmospheric CO₂ enrichment on cotton (Gossypium hirsutum L.) root distribution patterns as affected by localizing P in decreasing volumes of soil. Cotton plants were grown in a Troup Sand using 17.2 liter containers placed in open top field chambers under ambient (360 ppm) or enriched (720 ppm) atmospheric CO₂ conditions for 40 days. Equivalent amounts of P were added (150 mg P per kg of soil) to 100, 50, 25, 12.5, and 6.25 % of the soil volume; control containers with no added P were also included. Under extremely low P (controls), cotton was not responsive to atmospheric CO₂ enrichment. In treatments with both fertilized and unfertilized soil volumes, root proliferation was greater in the unfertilized soil due to elevated CO₂ conditions. Stimulation of root growth occurred in the P-fertilized soil fraction; the pattern of stimulation was similar under both levels of CO₂. Under ambient CO₂, cotton plants showed positive responses (shoot dry weight, and total root dry weight and length) to soil P when it was confined to relatively small proportions of the soil volume (12.5 and 6.25%). However, elevated CO₂ grown plants tended to respond to P regardless of its distribution in the soil.