Howard M. Taylor

PENETRATION OF COTTON SEEDLINGN TAPROOTS AS INFLUENCED BY BULK DENSITY, MOISTURE CONTENT, AND STRENGTH OF SOIL

PENETRATION OF COTTON SEEDLINGN TAPROOTS AS INFLUENCED BY BULK DENSITY, MOISTURE CONTENT, AND STRENGTH OF SOIL HOWARD TAYLOR;HERBERT GARDNER; Soil Science

The Role of Rooting Characteristics in the Supply of Water to Plants1

Publisher Summary The chapter discusses both axial and radial resistances to water flow from midway between roots located deep within soil to the xylem at the land surface. The chapter discusses idealized patterns for cotton, a taprooted dicotyledonous plant, and maize, a fibrous-rooted monocotyledonous plant. Water uptake by cotton plants grown in a rhizotron compartment was modeled. In the analysis it was assumed (1) that the radial resistance to water flow from the midpoint between roots to lumen of the xylem was a function only of volumetric water content of the soil layer—that is, the radial resistance-water content relations did not vary with root age or with soil depth and (2) that axial resistance was negligible. The total quantity of water available at any one time for withdrawal by a plant increases with available soil water content and with volume of soil occupied by its roots. Plant species differ greatly in the shape and size of their root systems and in their water extraction patterns. The characteristic rooting pattern of each species is genetically controlled but environmentally modified.

DIFFERENCES IN WATER UPTAKE RATES OF SOYBEAN ROOTS ASSOCIATED WITH TIME AND DEPTH

We developed a model of water uptake by soybean root systems. The model incorporated soil, root-soil contact, and radial and axial resistances to water flow. Parameters for the model were developed from field experiments conducted during the 1979 growing season on Ida silt loam, a loess soil, at Castana, Iowa. The specific water uptake rate decreased from 0.23 to 1 x 10-4 cm3 H2O cm-1 root day-1 as the soil water became depleted in a particular layer. The average conductivity of the soil-root system decreased linearly with age of plant. The water potential decrease along the vertical axis at the 20-cm depth was 0.0615 bar cm-1 when the transpiration rate was 1 cm day-1. A simulation of water uptake, based on a solution of the water flow equation with a sink term and performed with the aid of a differential equation solver DGEAR, tracks the seasonal withdrawal of water in a reasonably accurate manner.