Taproot‐Elongation Rates of Soybean Cultivars in the Glasshouse and Their Relation to Field Rooting Depth¹

Abstract

Deeper rooting should improve soybean [Glycine max (L.) Merr.] water stress avoidance by increasing water uptake from deep soil strata. Because taproots are initially the deepest segment of soybean root systems, soybean genotypes with rapidly elongating taproots may have deeper root systems than genotypes with slowly elongating taproots. Taproot‐elongation rates of 105 soybean cultivars from Maturity Groups I, II, and III were measured in a glasshouse using clear plastic tubes filled with vermiculite and then inclined 15°. Taproot‐elongation rates within a maturity group differed among cultivars by as much as 1.3 cm/day. Seed weight within a seedlot and seed source also influenced the taproot‐elongation rate of a cultivar. Selected Maturity Group II cultivars with either faster or slower taproot‐elongation rates in the glasshouse were grown in the Ames rhizotron and in field plots. Excavation of rhizotron compartments 49 days after planting revealed that roots of faster elongators were 10 cm deeper than those of slower elongators. In field plots 56 days after planting, the faster elongating group was 9 cm deeper and had more roots at 150 cm than did the slower elongating group. The two groups did not differ significantly, however, 72 days after planting. The group of cultivars with faster elongation rates also depleted soil‐water below 120 cm slightly more than did the slower group.

Water deficits during reproductive growth of soybeans. II. Water use and water deficiency indicators

“…A more intense soil exploration can be expected under conditions of water deficiency (Maertens, 1986), but no agreement exists on the soil depth explored by soybean roots. Mayaki et al (1976), Kaspar et al, (1978Kaspar et al, ( , 1984; Willat and Taylor (1978) ;Reicosky and Deaton (1979); Hoogenboom et al (1987), found soybean roots at 1-2 m, and Maertens (1986) at 2-3 meters; but Cox and Jolliff (1987) reported little soil water absortion below 90 cm.…”

Role of Mineral Nutrition on Root Growth of Crop Plants – A Review

“…Soybean cultivars differ in their rate of downward growth during specific shoot development stages and in their maximum rooting depth on specific. Cultivars selected for rapid taproot elongation rates in a greenhouse trial were found to have greater rooting depths in rhizotron and field trials than cultivars selected for slow taproot elongation (Kaspar et al, 1984).…”

“…In a review of depth development of roots with time for 55 crop species (Borg and Grimes, 1986), it was shown that maximum rooting depth for most crop species was generally achieved at physiological maturity. Kaspar et al, (1984) noted that the rate of soybean (Glycine max L. Merr.)…”

Development and Growth of Crop Root Systems

“…Merr.) are diffuse-rooted, but the taproot elongation rate initially determines rooting depth and some cultivars have a more dominant taproot than others (Kaspar et al, 1984). White clover cultivars also show a range of relative dominance of taproots (Caradus, 1981) as do alfalfa cultivars (McIntosh and Miller, 1980).…”