Soybean Root Morphology and K Uptake 1

When roots are grown in media of high mechanical strength, such as in sand rather than solution, root diameter increases. Little is known of how root morphology affects nutrient influx. The objective of this research was to determine if changes in root morphology created by changing growth media affected K influx into the root. Soybean ( Glycine max L. Merr.) plants were grown in solution culture and in sand continuously leached with nutrient solution. Both were in a controlled climate chamber. Shoot weights were similar for both treatments. Root weight per pot and root radius were greater )(0.22 vs. 0.17 mm) for sand‐grown plants than for solution grown plants. Root lengths per pot were similar. Increased root radius was due to an increase in radial size of the cortical cells. Radius of the stele was not affected by treatment nor was number of cortical cells in a cross‐section of the root. Imax (maximum influx) for K influx was 55% greater for sandgrown roots than for solutiongrown roots. The Michaelis constant (Km) and the level of K in solution where net K influx was zero (Cmin) were not influenced by treatment. Soybeans had greater root weight when the roots encountered adverse growing conditions. When the data for increased root radius and Imax were used in a mathematical model to predict K uptake, increasing r, from 0.17 to 0.22 mm increased predicted uptake 21% and increasing Imax from 4.6 to 7.1 pmoles cm −2 Sec −1 increased predicted uptake 35%.