Use of a Dead‐Load Technique to Determine Axial Root Growth Pressure1

The axial root growth pressures generated by cotton (Gossypium hirsutum L.) and pea (Pisum sativum L.) seedlings under different ambient oxygen concentrations were determined by a dead‐load method in which individual roots encased in plaster of paris blocks were loaded differently. Each seedling root could either elongate or not elongate depending on the applied force. The average values agreed well with those reported by Taylor and Ratliff (1969) using a different method. The average root pressures exerted by cotton and peas in an atmosphere of 21% oxygen and at —l/3‐bar matric potential were 11 and 12 bars, respectively, and individual values ranged from 8 to 15 bars. Root growth pressures were similar at 8 and 3% oxygen with peas. However, a 3% oxygen level reduced the root growth pressure of cotton to 5 bars. No significant differences were apparent between results obtained at —1/3‐ and —l/10‐bar matric potential around the root tips.