Rooting Depth and Density of Corn and Sorghum Grown under Rainfed Conditions

Abstract

Corn variety Suwan 1 and sorghum variety KU 439 were sown into fine loamy typic Palequults under rainfed conditions in August 1984 at the Chiang Mai University Experimental Farm; a spacing of 25 x 75 cm was used for corn, and 10 x 75 cm for sorghum. Using the Frame Monolith method, rooting depth, root number and density were measured at 15 days after emergence (DAE) and at every subsequent 15 dyas during the grwoing period. Undisturbed soil samples were taken to determine soil bulk density and moisture content, and for root sampling.
During early growth, root penetration by corn was faster than sorghum. However, by 45 DAE root penetration had exceeded 100 cm by both crops. For each crop, root number and root density in the top-soil (0-10 cm) were at a maximum 45 DAE. Both parameters decreased rapidly with depth, the decrease being more marked in exceeded that for corn at depth, for the whole profile total root number for corn was greater than for sorghum. In corn, an exponential sissgmoid relationship described the relationship between root number and rooting density with depth, regardless of growth stage. In sorghum this type of relationship was observed only during early growth; in later growth a simple sigmoid association better described the relationship.
As moisture status throughout the soil profile was adequate for both crops, the root growth patterns defined reflected differences between the crops in association with the particular soil properties.