When the going gets tough: Responses of Sorghum bicolor L. (cv. Tegemeo) seedlings to soil penetration resistance

Summary

Sorghum bicolor L. (cv. Tegemeo) seedlings were grown for nine days in soil at field capacity packed to give a uniform penetration resistance (PR) of either 0.25, 1.00 or 1.75 MPa. Root biomass was not significantly affected by soil PR treatment. However, as PR increased to 1.75 MPa, the diameter of the seminal root axis increased by 52% whilst its length decreased by 30%. Shoot growth, in terms of oven dry (OD) weight and photo-synthetic area, was reduced in both the 0.25 MPa and 1.75 MPa treatments compared to the 1.00 MPa treatment. A reduced nutrient, water or oxygen supply to the roots were discounted as possible causes of the root and shoot responses to soil PR. It is suggested that the changes in root morphology between treatments were a direct result of the changes in soil PR. For shoot growth, in the 0.25 MPa treatment it is suggested that shoot growth was reduced as a result of an increase in the carbon sink strength of the roots.