Typic Udorthents Research Articles

Responses of soybeans to two row spacings and two soil water levels. I. An analysis of biomass accumulation, canopy development, solar radiation interception and components of seed yield

An experiment was undertaken to determine why seed yields from narrow-row (0.25 m) soybeans ( Glycine max (L.) Merr.) often are greater than those from the more traditional 1.0-m rows. Soybeans ( Glycine max (L.) Merr. ‘Wayne’) were planted on 15 May 1979, at Castana, IA, on a Typic Udorthents (loess) soil. Four treatments (nonirrigated and irrigated, 0.25-and 1.0-m row widths) were replicated three times. Plants were thinned to 160000 per ha. Plant heights, stage of development and biomass of plant organs (including roots) were measured as functions of time and treatment. Irrigation increased leaf area, total biomass, plant height, the number of vegetative nodes and crop growth rates but delayed reproductive development and did not affect seed yield. Irrigation increased the shoot-root ratio and plants growing in the 1.0-m row spacings had greater shoot-root ratios than those in the 0.25-m row spacings. The 0.25-m row spacings yielded an average of 2470 kg ha −1, while the 1.0-m row spacings yielded only 2108 kg ha −1. Radiation interception was greater at the narrow row spacing during most of the season. This difference in radiation interception during late seed development probably caused the differences in yield between these row spacings.

New Methods of Studying Soil Detachment due to Waterdrop Impact

AbstractAn improved and inexpensive raindrop tower 8.9 m in height was designed so that a single drop will hit a soil target area 1.6 cm in diameter. The soil used in this study was taken from the surface 15 cm of an Ida silt loam (mesic Typic Udorthents). The surface shear strength was altered by remolding the soil to three bulk densities and by equilibrating the cores to matric potentials of −5, −19, −38, and −62 mbars. The weight of soil detached from the impact of single water‐drops 3.0, 4.6, and 5.6 mm in diameter was closely correlated with the undrained soil shear strength as measured by the Swedish fall‐cone device. A correlation coefficient of 0.97 was found between splash weight and a linear function of the ratio of waterdrop kinetic energy to the soil shear strength. The fall‐cone method of determining soil shearing strength is rapid, inexpensive, and could be easily adapted to field use.

Relative Evaluation of Water Stress Indicators for Soybeans1

AbstractThe understanding of the relationships between changes in crop foliage to variations in the amount and status of soil water is at best incomplete. Since plant growth is directly affected by deficits of water in plants, and only indirectly by soil‐water deficits and atmospheric stresses, the importance of using plant measurements, rather than soil indices, is warranted and has led to this investigation. Field studies were conducted during 1976 on Ida silt loam [fine, silty, mixed (calcareous) mesic family of Typic Udorthents] at the Western Iowa Experimental Farm, Castana, Iowa, to evaluate three plant measurements (vis., stomatal conductance, leaf‐water potential, and leaf area) as water stress indicators for soybeans [Glycine max (L.) Merr.]. Stomatal conductance and leaf water potential were measured at 2‐hour intervals from 0600 to 2000. Stomatal resistance was measured with a diffusion porometer, with stomatal conductance taken as the reciprocal of leaf resistance. Leaf‐water potential was measured using a pressure chamber. Leaf area was measured with an electronic leaf‐area integrator.Daily means of stomatal conductance and leaf‐water potential measured several times during the growing season were closely related to changes in soil‐water potential. “Rate of leaf‐area expansion” which is defined as the change in average leaf area (leaf area/number of leaves) per plant over a period of time, also showed a close correspondence with soil‐water potential.Relative growth rates of soybeans showed a negative correlation with stomatal conductance, leaf‐water potential, and rate of leaf.area expansion. The three plant measurements should prove useful in explaining water‐deficit effects quantitatively under field conditions.

Comparison of Five Methods for Characterizing Soybean Rooting Density and Development1

AbstractMany methods are used to study plant root system development and function. Most methods are tedious and time‐consuming. Some require expensive, sophisticated equipment and frequently require highly trained operators. Few studies are published where several methods are compared for their time requirements, equipment needs, soil applicability, and validity of the results. This study determined usefulness of five methods for characterizing soybean (Glycine max (L.) Merr.) rooting depth and density in a loess [fine, silty, mixed (calcareous) mesic family of Typic Udorthents] soil. The methods were: (a) soil water‐depletion, (b) framed‐monolith and pinboard, (c) core‐sampling, (d) mini‐rhizotron, and (e) trench‐profile. Each method was used or attempted on several dates during the 1975 growing season. The soil water‐depletion method was fast, required only simple equipment, and provided satisfactory estimates of rooting depth but did not provide reliable estimates of rooting density. The framed‐monolith method was very time‐consuming, but provided quantitative estimates of rooting density with depth and could have provided rooting density estimates with distance from the row. The core‐sampling method was faster than the framed‐monolith method. Cores could be obtained either with a hand‐turned bucket auger or with a coring machine, but several profiles were required to obtain rooting density distributions with depth and distance from the row. The mini‐rhizotron method was fast, but did not provide accurate results, presumably because the mini‐rhizotrons were installed too late. The trench‐profile method provided semiquantitative estimates of rooting density with depth and distance from the row. The trench‐profile method was rapid and required no time‐consuming separation of live roots from debris of previous years. The hand‐augered core, soil water‐depletion, and the trench‐profile methods could be used through the entire growing season, but the framed‐monolith and the mechanized‐core methods were not satisfactory during a drought period because the soil column collapsed during sampling.

Top and Root Relations of Field‐Grown Soybeans1

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.

Use of Acrylic Plastic as Rhizotron Windows1

AbstractReliable cotton (Gossypium hirsutum L.) rooting densities (cm roots/cm3 soil) for bulk soil have been estimated previously from the number of visible roots in sandy soil immediately behind glass rhizotron windows. The present study determined whether soybean [Glycine max (L.) Merr. ‘Corsoy’] rooting densities could be estimated reliably in Ida silt loam (fine‐silty, mixed, mesic, Typic Udorthent) from the number of visible roots at the soil‐acrylic plastic windows of the Ames, Iowa rhizotron.Rooting density was evaluated as a function of soil depth and distance from the plastic‐soil interface in one compartment at the rhizotron. Fifty volumetric soil samples were collected at ten depths and at five distances from the interface. Roots were washed from the Ida silt loam soil. Root length contained in the sample was estimated using a laser modification of the Rowse‐Phillips root‐length instrument.Rooting density was substantially greater in the 2‐mm thick layers near the plastic‐soil interface than in bulk soil behind it. Acrylic plastic windows apparently are satisfactory for use in root growth boxes or rhizotron compartments for phenological or for comparative experiments, but glass rhizotron windows should be used in rooting density studies.