PORE SIZE DISTRIBUTION AND ROOT GROWTH RELATIONS OF RICE IN ARTIFICIALLY SYNTHESIZED SOILS

Abstract

Growth responses of a rice root system to particle and pore size distributions were assessed in eight soil mixtures artificially synthesized from separated clay, silt, and sand-sized quartz powders, under a controlled optimum, submerged (3 ± 1 centimeters) soil temperature regime of 37–25°C. Moisture retention characteristics were utilized for calculating the average macropore size and effective pore size densities of the soils The pore frequencies were maximum at 15–19 microns in finer soils—clay, silty clay, silt, silty clay loam, and clay loam—and at 19–24 microns in coarser soils—loam, sandy loam, and sand. With the decrease in clay and a corresponding increase in sand or silt content, the average macropore size of the soils appreciably increased. The highest rice root growth was recorded in silty clay loam, followed closely by that in sandy loam. Larger radii for maximum pore frequencies and of average macropore in sandy soils and greater mobility of particles in silty soils as compared with that in clayey soils contributed to higher root and shoot growth. In clay, silty clay, and clay loam soils, rice root growth was highly restricted, and the roots could penetrate only to an average soil depth of 14 centimeters.