Table 1.
Characteristics of the soybean genotypes used in the study.
Table 2.
The characteristics of the experimental sites and field operations at Florence, SC, USA and Pendleton, SC, USA.
Fig 1.
The mesocosms used to grow soybean plants in the experiment.
Mesocosms were constructed of two stacked polyvinyl chloride (PVC) columns with an inside diameter of 15 cm. The height of the bottom and top columns were 46 and 25 cm, respectively. Each mesocosm was sealed at the bottom with a plastic cap, which had a central hole of 0.5 cm diameter for drainage. A diagram and a photograph of a mesocosm that contained a synthetic hardpan in between the top and bottom columns (A and B, respectively). The synthetic hardpan was made up of paraffin wax and petroleum jelly, and had a diameter of 20 cm and thickness of 2 cm. A diagram and a photograph of a mesocosm that did not contain a synthetic hardpan (C and D, respectively). The top and bottom columns along with the synthetic hardpan in between (if the mesocosm contained one) were tightly sealed together with a duct tape as shown in Fig 1B and 1D.
Fig 2.
Daily maximum (Tmax) and minimum (Tmin) temperatures from planting through the end of the season at Florence, SC, USA (a) and Pendleton, SC, USA (b). Temperature data were obtained from the National Centers for Environmental Information (NCEI) of National Oceanic and Atmospheric Administration (NOAA). Soybean genotypes were planted on 9 June 2017 at Florence and 8 June 2017 at Pendleton. The duration of the crop season was 188 and 161 d at Florence and Pendleton, respectively.
Fig 3.
Daily precipitation and irrigation from planting through the end of the season at Florence, SC, USA (a) and Pendleton, SC, USA (b). Precipitation data were obtained from the National Centers for Environmental Information (NCEI) of National Oceanic and Atmospheric Administration (NOAA). Soybean genotypes were planted on 9 June 2017 at Florence and 8 June 2017 at Pendleton. The duration of the crop season was 188 and 161 d in Florence and Pendleton, respectively. Irrigation involved application of 25.4 mm water at 35, 56, 69, 76, and 83 days after planting (DAP) at Florence and application of 25.4 mm water at 102 DAP at Pendleton.
Fig 4.
Seed yield of soybean genotypes grown at Florence, SC, USA under irrigated and non-irrigated conditions (Fig a and b, respectively) and at Pendleton, SC, USA (Fig c). Irrigated plots received 25.4 mm water at 35, 56, 69, 76, and 83 days after planting (DAP) at Florence and 25.4 mm water at 102 DAP at Pendleton. However, the genotype-by-irrigation interaction effect was not significant on yield at Pendleton. Therefore, data were averaged across irrigation treatments for this location. Bars represent least square means and error bars represent standard errors. Least square means with different letters are significantly different according to the LSD test at P < 0.05.
Table 3.
Analysis of variance results on effects of genotype, irrigation, their interaction (for the field experiments), presence of hardpan, and it’s interaction with genotype (for the controlled environmental experiments) for various traits measured in the study.
The field level measurements of root and shoot traits (total and fine root length, surface area, and volume, and shoot and root dry weights) were made only at one location (Florence, SC, USA).
Table 4.
Total root surface area, total root volume, and shoot dry weight of soybean genotypes evaluated under field conditions in Florence, SC.
Plants were grown under two irrigation treatments (irrigated and non-irrigated). Since the genotype-by-irrigation interaction effect was not significant on any of the below traits, main effects of genotype are presented.
Table 5.
Root and shoot traits of soybean genotypes evaluated under controlled environmental conditions.
Plants were grown in growth columns, and a synthetic hardpan (1 cm thickness) that simulate a compacted soil layer was imposed at 25 cm depth in half of the columns to test the genotypes for root and shoot traits under the presence and absence of a hardpan. Since the genotype-by-hardpan interaction effect was not significant on any traits, main effects of genotype are presented below.