Top and Root Relations of Field‐Grown Soybeans1

Abstract

AbstractField data describing both the top and root growth of soybeans [Glycine max L. (Merr.)] at different morphological stages are very limited. Such quantitative data are essential for analyzing or simulating growth patterns of whole soybean plants.Soybean top and root growth studies were conducted at the Western Iowa Experimental Farm on Ida silt loam soil [fine, silty, mixed (calcareous) mesic family of typic Udorthents]. Plant height, dry matter distribution of above‐ground plant parts, leaf area index, root length, and root dry weight distribution were measured at different physiological stages.Top‐root ratio of soybeans was 3.8 when the plants were in stage V6, and the ratio increased to 9.0 by the time that the plants reached stage V15R2. From the root length and leaf data, the total length of roots required to supply water and nutrients to each m2 leaf area was calculated. These root lengths increased from 630 m/m2 leaf area when the plants were in V6 stage to 1,190 m/m2 at V13R2 stage then decreased to 345 m/m2 at stage V15R2 as the soil dried. Root length in a specific layer decreased whenever soil was drier than —2 bars or volumetric water content was below 16%.Plant height and leaf area were positively correlated (r = 0.95). Most of the leaf area was concentrated in the upper portions of the soybean canopy when leaf area was maximum.