Soybean [ Glycine max (L.) Merr.] is a leguminous plant with high nutritional and medicinal value. The goal of this research was to determine the optimal concentration of nitrogen, using Hoagland nutrient solution, which will enhance the productivity of soybeans. The specific objective of the study was to assess the effect of variation of nitrogen concentration on soybean growth and leaf chlorophyll concentrations. Soybeans were grown under three soil nitrogen amendments: low, medium, and high concentration of Hoagland nutrient solution and a control group. Soybeans were grown under controlled environmental conditions in the Biotronette ? environmental chamber. Temperature of the environmental chamber was regulated at 27 ℃ and the photoperiod was set to 10 L: 14D. Soybeans grown in the low treatment group had the highest growth rate (1.03 ± 0.03 cm/day) compared to the control, medium, and high treatment groups. During the first chlorophyll analyses, the control group had the highest total chlorophyll concentration (216.25 ± 4.09 μg/mL/g). During the second chlorophyll analyses, the low treatment group had the highest total chlorophyll concentration (102.81 ± 14.54 μg/mL/g). Although no finding was statistically significant between groups, the low nitrogen treatment conditions had a trend towards producing more favorable physiological outcomes on soybeans.
The soybean [Glycine max (L.) Merr.] plant is a member of the Leguminoceae family which includes other le- gumes such as peas, beans, lentils, peanuts, and other podded plants [
Soybeans, as with all legumes, are well recognized as excellent sources of dietary protein [
Soybeans are a unique source of the isoflavones, genistein and diadzein [
Nitrogen is an essential mineral macronutrient required in the greatest amounts by plant [
Previous studies comparing sources of nitrogen for soybeans suggest that nitrogen fixation, facilitated by Bradyrhizobioum japonicum, is ideal for soybean growth and productivity [
The goal of this research was to determine the optimal concentration of nitrogen, using Hoagland nutrient so- lution, which will enhance the productivity of soybeans. The specific objective of the study was to assess the ef- fect of variation of nitrogen concentration on soybean growth and leaf chlorophyll concentrations. The findings from this study will contribute vital information on the ideal concentration of nitrogen required for optimum soybean productivity.
This is an experimental study with three treatment groups (low, medium, and high) and a control group. The three treatment groups’ designation was based on variation of nitrogen concentrations using Hoagland nutrient solution. Four replicates, containing two plants per replicate, were assigned to each group: control group, and low, medium, and high treatment groups to maintain the statistical validity of the data.
Soil was prepared by using the ratio of 5:2:8:1. Five pots of potting soil, two pots of garden soil, eight pots of top soil, and one pot of river sand were mixed thoroughly for homogeneity and to give the soil a loamy quality. The soil mixture was then placed into 16 plant pots (~2 lbs capacity), with four pot replicates for each of the three treatment groups and the control group.
Soybean seeds were washed with five percent Clorox® bleach for approximately five minutes to eliminate con- taminants. Five seeds were sown in each pot and 100 mL of distilled water was added to each pot and left under room conditions (26˚C). As seedlings started sprouting, the plants were thinned to two plants per pot and were ready for the experiment.
The Hoagland nutrient solution [
The concentration of the compounds for the low treatment group is the standard concentration for the Hoag- land Nutrient Solution [
The nutrient solution was applied to the soil on two occasions separated by a 7-day interval. The first nutrient application occurred 7 days after seeds were sown. In the first nutrient application, 50 mL of distilled water was added to the control and 50 mL of the low Hoagland nutrient solution, 50 mL of the medium Hoagland nutrient
Compounds | Control (ppm) | Low (ppm) (Standard) [ | Medium (ppm) (Modified) | High (ppm) (Modified) |
---|---|---|---|---|
Ca (NO3)2 | 0 | 1653 | 3310 | 6611 |
KNO3 | 0 | 506 | 1011 | 2022 |
KH2PO4 | 0 | 326 | 326 | 326 |
MgSO4 | 0 | 493 | 493 | 493 |
Trace Elements Constituents: H3BO3—2.8 gm/L MnCl2∙4H2O—1.8 gm/L ZnSO4∙7H2O—0.2 gm/L CuSO4∙5H2O—0.1 gm/L NaMoO4—0.025 gm/L | 0 | 4.93 | 4.93 | 4.93 |
FeEDTA Constituents: EDTA∙2Na—10.4 gm/L FeSO4∙7H2O—7.8 gm/L KOH—56.1 gm/L | 0 | 74.3 | 74.3 | 74.3 |
solution, and 50 mL of the high concentrated Hoagland nutrient solution was added to each pot in the low, me- dium, and high treatment groups, respectively. A week later, a second 50 mL of the nutrient doses were applied to each pot similar to the first nutrient application. On the same day of the second application, 50 mL of distilled water was added to each of the 16 pots to ensure the soil remain moist.
Following the first application of the nutrient solutions to the soil, plant pots were transferred into the Biotro- nette® Environmental chamber for photoperiod and temperature regulation. Temperature was regulated at about 27˚C and photoperiod was regulated at 10 light (L): 14 dark (D) hours because soybeans are short day plants [
Three plant growth measurements were taken on days 7, 17, and 31 after sowing of the soybean seeds. Plant growth rate per day was calculated by dividing the average plant growth per treatment group by the number of days until the last plant growth measurement (31 days after seeds were sown).
Soybean leaves were collected twice for the chlorophyll analysis using the method outlined by Einhellig and Rasmussen [
[µg Chlorophyll a/mL solution = (13.70) (Absorbance [A] at 665nm) ? (5.76) (Absorbance [A] at 649nm)
[µg Chlorophyll b/mL solution = (25.80) (Absorbance [A] at 649nm) ? (7.60) (Absorbance [A] at 665nm)
Due to variation in the weight of the soybean leaves used for chlorophyll analysis, chlorophyll concentration of the soybean leaves was calculated per gram using the formula:
Chlorophyll a concentration = [µg Chlorophyll a/mL ÷ weight (g)]
Chlorophyll b concentration = [µg Chlorophyll b/mL ÷ weight (g)]
Data analysis was performed using IBM SPSS Statistics for Windows, Version 19.0. Armonk, NY: IBM Corpo- ration. Analysis of variance (ANOVA) was used to compare the differences between the means in the three treat- ment groups and the control group. Data are expressed as mean values ± standard deviation (SD).
Soybean growth was measured on three occasions as described in the experimental section. The data on soybean growth rate and 31-day growth are presented on
Chlorophyll a, chlorophyll b, and total chlorophyll were assessed twice as described in the experimental section. There was no statistically significant difference between chlorophyll a, chlorophyll b, and total chlorophyll in ei- ther the first or second set of chlorophyll analysis as depicted in Tables 3 and 4. There was a general decline in the leaf chlorophyll concentration in the second chlorophyll analysis when compared to the first chlorophyll analysis as depicted in Tables 3 and 4 and Figures 1 and 2.
Control | Low | Medium | High | P-Value | |
---|---|---|---|---|---|
Growth Rate (cm/day) | 0.935 ± 0.05 | 1.038 ± 0.03 | 0.959 ± 0.07 | 0.928 ± 0.11 | 0.147 |
31-Day Growth (cm) | 28.975 ± 1.40 | 32.175 ± 0.96 | 29.725 ± 2.07 | 28.775 ± 3.31 | 0.147 |
Control | Low | Medium | High | P-Value | |
---|---|---|---|---|---|
Chlorophyll a Concentration [µg/mL/weight (g)] | 82.62 ± 2.93 | 81.36 ± 2.38 | 83.71 ± 8.12 | 77.75 ± 12.63 | 0.723 |
Chlorophyll b Concentration [µg/mL/weight (g)] | 133.63 ± 2.27 | 131.51 ± 7.97 | 116.65 ± 33.02 | 125.531 ± 20.25 | 0.633 |
Total Chlorophyll [µg/mL/weight (g)] | 216.25 ± 4.09 | 212.87 ± 8.67 | 200.36 ± 38.23 | 203.28 ± 32.85 | 0.791 |
Control | Low | Medium | High | P-Value | |
---|---|---|---|---|---|
Chlorophyll a Concentration [µg/mL/weight (g)] | 34.80 ± 2.59 | 38.36 ± 5.53 | 36.09 ± 3.86 | 36.40 ± 8.75 | 0.847 |
Chlorophyll b Concentration [µg/mL/weight (g)] | 55.28 ± 4.55 | 64.45 ± 9.04 | 61.56 ± 7.39 | 65.14 ± 12.43 | 0.411 |
Total Chlorophyll [µg/mL/weight (g)] | 90.08 ± 7.03 | 102.81 ± 14.54 | 97.65 ± 11.23 | 101.54 ± 21.14 | 0.610 |
The results of chlorophyll a, chlorophyll b, and total chlorophyll from the first set of chlorophyll analysis are presented in
The results of chlorophyll a, chlorophyll b, and total chlorophyll from the second set of chlorophyll analysis are presented in
In our study, there was no statistically significant difference observed between the treatment groups when eva- luating growth rate and 31-day growth. There was however, a trend to higher growth rate in the low treatment group. A study by Sabaratnam and colleagues evaluated growth characteristics of soybean subjected to different concentration of nitrogen as relative growth rate (RGR) [
Another study by de Veau et al. assessed leaf area of soybean grown under three different nitrogen regimens [
In our study, we observed no statistically significant differences between the treatment groups in the first and second chlorophyll analyses. In the first chlorophyll analysis, the control and low treatment groups had the highest total chlorophyll concentration compared to the medium and high treatment groups although this finding was not significantly different between the groups. In the second chlorophyll analysis, the low treatment group had the highest total chlorophyll concentration compared to the control, low, and medium treatment groups. Overall, when assessing the cumulative concentration of leaf chlorophyll from the two chlorophyll analyses, there was a trend to increase in leaf chlorophyll concentration in the low treatment groups compared to the con- trol, medium and high treatment groups.
Sabaratnam et al. in their study observed a significant reduction in chlorophyll a and total chlorophyll content in soybeans treated with higher concentration of NO2 (0.5 ppm) compared to soybeans treated with lower con- centrations of NO2 (0.1, 0.2, and 0.3 ppm) and in the control group [
deVeau et al. in their study assessed the leaf chlorophyll content of the soybean grown under three different nitrogen regimens [
Certain limitations are applicable to our study. First, we did not evaluate the effect of variation of nitrogen on soybean photosynthetic rate. Second, this study is susceptible to a type II error and may not have adequate pow- er to detect a statistically significant difference between the three treatment groups and the control group. Our future research will focus on the photosynthetic rates of soybean under different concentrations of nitrogen and its impact on overall yield.
This study evaluated the effects of variation of nitrogen concentration, using Hoagland nutrient solution, on soybean growth and leaf chlorophyll concentrations. There was no statistically significant difference between groups when assessing growth rate, 31-day growth, and leaf chlorophyll concentration. This study, however, pro- vides some positive evidence to support that supplementation of soybean with low concentration of nitrogen (based on Hoagland nutrient solution) may produce relatively ideal physiological outcomes for soybeans.
Thanks to the National Science Foundation for sponsoring this research project and financial support (HRD- 0102620). Special thanks to Dr. Murty Kambhampati, Professor of Biology, for providing mentorship and re- sources for this experiment.