Information is limited about phosphorus (P) fertilization effects on soybean seed composition. A field experiment was conducted to investigate the effects of P application rates on the concentrations of various fatty acids, protein, and oil in soybean under no-tillage on low and high testing P soils at Jackson and Milan, Tennessee from 2008 through 2011. Five P rates 0, 10, 20, 30, and 40 kg ·P ·ha -1 plus the recommended P fertilizer rate based on soil P testing results were arranged in a randomized complete block design with four replicates. Protein, oil, and fatty acid concentrations in seed responded differently to P fertilization. In general, protein concentrations were enhanced but oil levels decreased with increased P application rate. Palmitic and oleic concentrations responded positively to P application rate up to a certain level. However, the response of linolenic acid concentration was inconsistent (negative or positive). Stearic concentration was not influenced by P fertilization. Application of 10 kg·P·ha -1 resulted in higher production of protein and palmitic, oleic, and linolenic acids than zero P and the higher P application rates as well on the P deficient soil. Excessive P application rates could lower seed yield and the quality of some attributes in seed. In conclusion, linoleic acid concentration, a key quality attribute in soybean seed for human and animal consumption, can sometimes be enhanced by P fertilization; the indigenous soil P level and P application rate should be taken into account in breeding soybean cultivars with low linolenic acid level.
Soybean [Glycine max (L.) Merr.] is traditionally grown for protein and oil in the seed. Soybean seed grown in the United States contains approximately 41% protein and 21% oil on a dry weight basis [
Soybean seed quality attributes are affected by both genetics [
Although nutrient management effects on soybean seed yield and protein and oil concentrations have been examined in previous studies [
With the increased interest in eliminating trans fatty acids in the diets of Americans, soybean breeders continue to place more emphasis on developing varieties which can produce seed with elevated levels of desired fatty acids such as oleic acid. If a market premium is offered for specific seed quality attributes, soybean growers will need information on how to improve their seed quality. The main objective of this study was to evaluate P application rate effects on the concentrations and production of palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, protein, and oil of soybean under no-tillage on low to high testing P soils.
The P fertilization effects on seed quality attributes and yields of soybean were investigated in a small plot field experiment that was conducted on the University of Tennessee’s West Tennessee Research and Education Center at Jackson and University of Tennessee’s Research and Education Center at Milan from 2008 to 2011. The fields used for this study were classified as Memphis silt loam at Jackson and Dexter loam at Milan, which had been under continuous no-till production for more than 10 years before experiment establishment. The previous crop was soybean at both locations in 2007.
A randomized complete block design was used with six P treatments repeated four times at both locations each year. The first five treatments consisted of the following five P application rates: 0, 10, 20, 30, and 40 kg∙P∙ha−1 (equal to 0, 20, 40, 60, and 80 lb P2O5 a−1). The last treatment was the recommended P application rate based on soil P testing results every year. The recommended P rates for Milan were 22, 0, 10, and 0 kg∙ha−1 and the rates for Jackson were 15, 0, 0, and 10 kg∙ha−1 for 2008, 2009, 2010, and 2011, respectively. The P fertilizer was uniformly applied on the soil surface by hand as triple superphosphate (0N-20P-0K). Plots were 9.1 m long and 3.0 m wide. A full season soybean “Pioneer 94M80” crop was no-till planted in 76-cm rows at both locations in all four seasons. No winter crop was grown in any year in this study. The planting dates were 6 May 2008, 12 May 2009, 6 May 2010, and 11 May 2011 at Jackson and 23 May 2008, 20 May 2009, 13 May 2010, and 2 June 2011 at Milan. A uniform rate of potash fertilizer was applied as needed according to the soil K testing results each year [
Soybean yields were determined at maturity with a plot combine by harvesting the center two rows for the entire plot length from each plot on 29 September 2008, 21 October 2009, 21 September 2010, and 30 September 2011 at Jackson and 2 October 2008, 19 October 2009, 20 September 2010, and 30 September 2011 at Milan. The yields were adjusted to 130 g kg−1 moisture content.
A composite soil sample consisting of 10 cores was randomly collected at the 0-15 cm depth from each plot with a 2.5-cm diameter hand soil probe at Jackson and Milan before P treatments were applied on 3 March and 9 April 2008, respectively. After soil samples were air-dried, ground to pass a 2-mm screen, and thoroughly mixed, they were analyzed for basic properties by the University of Tennessee’s Soil, Plant, and Pest Center (Nashville, TN). Soil pH was determined in a 1:1 (soil:H2O) solution (Watson and Brown, 1998). Soil available NH4+, NO3−, P, K, Ca, and Mg were extracted with the Mehlich I method [
A composite soil sample was also taken from each plot at soybean harvest each year for soil available P which was determined with the same method as stated above. The specific sampling dates were 9 October 2008, 4 November 2009, 1 November 2010, and 1 December 2011 at Jackson and 28 October 2008, 5 November 2009, 5 October 2010, and 6 October 2011 at Milan.
A composite leaf sample composed of 20 most recently fully developed trifoliate leaves with petioles was randomly collected at approximately the V5, R1, and R3 growth stages from each plot at both locations in all four seasons for the determination of total P concentrations. The specific sampling dates were 8 July 2008, 26 June 2009, 14 June 2010, and 21 June 2011 at Jackson and 9 July 2008, 29 June 2009, 17 June 2010, and 13 July 2011 at Milan for V5; 16 July 2008, 6 July 2009, 21 June 2010, and 21 July 2011 at Jackson and 17 July 2008, 7 July 2009, 28 June 2010, and 25 July 2011 at Milan for R1; and 28 August 2008, 27 July 2009, 26 July 2010, and 1 August 2011 at Jackson; 29 August 2008, 23 July 2009, 28 July 2010, and 4 August 2011 at Milan for R3. A composite seed sample was taken at harvest from each plot at both locations during 2008-2010 for analyses of P concentrations. Leaf and seed samples were dried at 65˚C in a forced air oven for at least 3 d and then ground in a Wiley mill (Arthur K. Thomas Co., Philadelphia, PA) to pass a 1-mm screen. Total P in each leaf and seed sample was digested with nitric acid and hydrogen peroxide in a CEM MDS 2100 series microwave (CEM Corporation, Matthews, NC), and the digested solution was analyzed on a Thermo Jarrel Ash 1100 ICP [
Seed samples collected at harvest were also analyzed for protein, oil, and fatty acid concentrations at both locations during 2008-2010. Approximately 25 g of seed from each plot was ground with a Laboratory Mill 3600 (Perten, Springfield, IL) and analyzed with near infrared reflectance [
Analyses of variance were conducted for the concentrations and production of protein, oil, and fatty acids in each individual year at each location with the ANOVA procedure in SAS for Windows V9 (2) (SAS Institute, Cary, NC). A randomized complete block design with four replications was used for all these analyses. Data combined across the three or four years at each location were analyzed under a randomized complete block design with year as a random factor. Treatment or year means were separated with the Fisher’s protected LSD test if needed. Probability levels lower than 0.05 were designated as significant.
Weather conditions were different among the four years at Jackson and Milan (
According to the present Tennessee soil-test P interpretations, soil P fertility is categorized as low, medium, high, and very high for soybean when soil-test P concentration is 0 - 9, 10 - 15, 16 - 59, ≥60 mg P kg−1 (equivalent to 0 - 18, 19 - 30, 31 - 119, and ≥120 lb P a−1), respectively, with Mehlich I as the extractant [
Location | Month | Temperature | Rainfall | ||||||
---|---|---|---|---|---|---|---|---|---|
2008 | 2009 | 2010 | 2011 | 2008 | 2009 | 2010 | 2011 | ||
˚C | mm | ||||||||
Jackson | May | 19.9 | 20.5 | 22.2 | 19.9 | 174.2 | 191.0 | 566.4 | 211.8 |
June | 25.7 | 25.7 | 27.6 | 26.3 | 71.4 | 91.7 | 163.6 | 156.2 | |
July | 26.9 | 24.7 | 28.0 | 28.2 | 159.5 | 187.5 | 168.9 | 95.3 | |
August | 25.6 | 25.1 | 28.0 | 26.7 | 64.8 | 76.5 | 125.0 | 42.4 | |
September | 22.9 | 23.1 | 23.3 | 20.1 | 20.1 | 184.4 | 28.2 | 82.8 | |
October | 15.9 | 14.4 | 16.4 | 14.5 | 80.0 | 176.3 | 35.8 | 28.2 | |
Milan | May | 19.2 | 20.1 | 21.8 | 19.7 | 233.7 | 229.6 | 534.7 | 285.5 |
June | 25.3 | 26.0 | 27.5 | 26.4 | 38.6 | 56.4 | 82.0 | 172.7 | |
July | 26.5 | 24.6 | 27.6 | 27.9 | 79.2 | 200.9 | 150.6 | 36.1 | |
August | 25.1 | 24.5 | 27.8 | 26.4 | 18.8 | 56.6 | 50.0 | 29.0 | |
September | 22.5 | 22.4 | 23.1 | 21.0 | 9.9 | 119.9 | 9.1 | 259.3 | |
October | 15.1 | 13.9 | 15.9 | 14.6 | 65.0 | 207.8 | 48.5 | 27.2 |
two locations during November to December 2007, prior to the initiation of this study. Soil P concentrations before the treatment imposition in spring 2008 did not differ statistically among the plots assigned to the different P treatments, indicating that the two fields were generally uniform in soil P fertility prior to this study (
At Jackson, soil P levels did not differ among the P treatments after soybean harvest in the fall of 2008, 2010, or 2011 (
According to the boundaries of soil-test P with Mehlich I as the extractant for soybean in Tennessee [
Location | Treatmenta | 2008 | 2009 | 2010 | 2011 | |
---|---|---|---|---|---|---|
Pre-plant | Post-harvest | Post-harvest | Post-harvest | Post-harvest | ||
mg∙kg−1 | ||||||
Jackson | 1 | 26.9 | 21.4 | 17.1bb | 34.3 | 25.9 |
2 | 23.0 | 20.9 | 20.9b | 28.6 | 26.1 | |
3 | 28.6 | 23.8 | 18.1b | 30.4 | 20.5 | |
4 | 26.5 | 24.0 | 17.4b | 33.8 | 33.9 | |
5 | 28.8 | 28.1 | 29.4a | 31.4 | 30.6 | |
6 | 26.0 | 20.1 | 18.4b | 22.9 | 26.6 | |
Sigc | nsd | ns | * | ns | ns | |
Milan | 1 | 17.1 | 24.6 | 14.5 | 18.9 | 16.6d |
2 | 18.1 | 25.1 | 15.8 | 23.0 | 21.9bcd | |
3 | 16.5 | 27.3 | 15.3 | 20.4 | 28.0ab | |
4 | 14.6 | 28.6 | 17.6 | 13.8 | 26.3bc | |
5 | 20.4 | 30.0 | 19.8 | 18.6 | 35.1a | |
6 | 16.9 | 21.4 | 11.6 | 18.0 | 19.1cd | |
Sig | ns | ns | ns | ns | ** |
*Significant at 0.05 probability level; **Significant at 0.01 probability level. aTreatments 1, 2, 3, 4, and 5 were the annual P application rates of 0, 10, 20, 30, and 40 kg∙P∙ha−1, respectively; treatment 6 was the P fertilizer recommended rate based on soil P testing results every year. bMeans in a column within each location followed by the same letter are not significantly different at P = 0.05 according to the protected LSD. cSig, significance. dns, not significant at 0.05 probability level.
Phosphorus fertilization effects were occasionally significant on soybean leaf P concentrations at the V5, R1, and R3 growth stages in this study (
Campbell and Plank (2011) [
Location | Treatmenta | 2008 | 2009 | 2010 | 2011 | ||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
V5b | R1 | R3 | V5 | R1 | R3 | V5 | R1 | R3 | V5 | R1 | R3 | ||
g∙kg−1 | |||||||||||||
Jackson | 1 | 2.60 | 2.93 | 2.77 | 2.35bc | 2.76 | 3.21c | 3.40 | 3.57 | 3.50 | 3.81bc | 3.54b | 3.26 |
2 | 2.59 | 2.88 | 2.63 | 2.54b | 2.69 | 3.38abc | 3.61 | 3.66 | 3.29 | 3.48c | 3.58b | 2.97 | |
3 | 2.67 | 3.11 | 2.71 | 2.54b | 2.81 | 3.36bc | 3.40 | 3.79 | 3.54 | 4.15b | 3.63b | 3.46 | |
4 | 2.52 | 2.80 | 2.69 | 2.53b | 2.84 | 3.43ab | 3.83 | 3.99 | 3.42 | 4.13b | 4.07a | 3.37 | |
5 | 2.59 | 3.21 | 2.80 | 3.09a | 3.00 | 3.55a | 4.03 | 4.07 | 3.64 | 4.71a | 3.98a | 3.35 | |
6 | 2.59 | 3.09 | 2.76 | 2.72ab | 2.89 | 3.44ab | 3.49 | 3.88 | 3.51 | 3.80bc | 3.75ab | 3.29 | |
Sigd | nse | ns | ns | * | ns | * | ns | ns | ns | ** | * | ns | |
Milan | 1 | 2.26 | 2.66 | 2.88 | 2.48a | 2.23 | 3.50 | 3.75 | 3.48 | 3.39 | 4.33b | 4.18 | 2.62 |
2 | 2.37 | 2.72 | 2.80 | 2.53a | 2.40 | 3.99 | 3.87 | 3.74 | 3.37 | 4.30b | 4.24 | 2.87 | |
3 | 2.43 | 2.61 | 2.69 | 2.52a | 2.35 | 3.66 | 3.75 | 3.46 | 3.47 | 4.50ab | 4.21 | 2.76 | |
4 | 2.36 | 2.69 | 2.97 | 2.59a | 2.26 | 3.70 | 3.95 | 3.46 | 3.47 | 4.65a | 4.26 | 2.87 | |
5 | 2.43 | 2.67 | 2.75 | 2.64a | 2.31 | 4.13 | 4.13 | 3.70 | 3.35 | 4.40b | 4.20 | 2.80 | |
6 | 2.32 | 2.50 | 2.85 | 2.16b | 2.15 | 3.97 | 3.84 | 3.66 | 3.26 | 4.47ab | 4.35 | 2.73 | |
Sig | ns | ns | ns | * | ns | ns | ns | ns | ns | * | ns | ns |
*Significant at 0.05 probability level; **Significant at 0.01 probability level. aTreatments 1, 2, 3, 4, and 5 were the annual P application rates of 0, 10, 20, 30, and 40 kg∙P∙ha−1, respectively; treatment 6 was the P fertilizer recommended rate based on soil P testing results every year. bV5, 5-leaf growth stage; R1, beginning flowering stage; R3, beginning pod stage. cMeans in a column within each location followed by the same letter are not significantly different at P = 0.05 according to the protected LSD. dSig, significance. ens, not significant at 0.05 probability level.
At Jackson, soybean seed yield did not respond to P applications in any year or on the four-year averages (
At Milan, seed yield responded to P application averaged over the four years (
Significant responses of seed P concentrations to P applications were observed at both locations in 2010 only (
Overall, our results showed that soybean yields did not respond significantly to the P application rates at either location in this study. Soybean has been classified as a poor responder to P fertilization compared with other row crops although responses have been observed in low-testing soils [
Both protein and oil concentrations in seed differed among P application rates at Jackson in 2009 and 2010 and averaged over the three years (
It is well known that P deficiency reduces soybean leaf area and the number of leaves, nodes, and branches; P-deficient plants exhibit reduced carbohydrate supply to nodules and decreased nodule weight, number, and functioning, such as reduced nitrogenase activity of the nodule. Therefore, P fertilization increases N fixation when soybean is deficient in P, and thus enhances protein concentration in soybean seed.
Concentrations of the fatty acids in seed oil responded differently to P application rates at both locations (
Year | Treatmenta | Jackson | Milan |
---|---|---|---|
Mg∙ha−1 | |||
2008 | 1 | 2.45 | 2.28 |
2 | 2.55 | 2.37 | |
3 | 2.48 | 2.22 | |
4 | 2.49 | 2.33 | |
5 | 2.61 | 2.27 | |
6 | 2.51 | 2.29 | |
Sigb | nsc | ns | |
2009 | 1 | 2.42 | 2.92 |
2 | 2.59 | 2.91 | |
3 | 2.50 | 2.56 | |
4 | 2.46 | 2.90 | |
5 | 2.52 | 2.72 | |
6 | 2.61 | 2.73 | |
Sig | ns | ns | |
2010 | 1 | 2.74 | 2.71 |
2 | 2.63 | 2.99 | |
3 | 2.77 | 2.79 | |
4 | 2.83 | 2.80 | |
5 | 2.82 | 2.69 | |
6 | 2.82 | 2.70 | |
Sig | ns | ns | |
2011 | 1 | 2.08 | 2.14 |
2 | 2.19 | 2.23 | |
3 | 2.06 | 2.18 | |
4 | 2.03 | 2.21 | |
5 | 2.29 | 2.14 | |
6 | 2.01 | 2.22 | |
Sig | ns | ns | |
Average | 1 | 2.42 | 2.51abd |
2 | 2.49 | 2.63a | |
3 | 2.45 | 2.44b | |
4 | 2.45 | 2.56ab | |
5 | 2.56 | 2.45b | |
6 | 2.49 | 2.48b | |
Year | 2008 | 2.51b | 2.29b |
2009 | 2.52b | 2.79a | |
2010 | 2.77a | 2.78a | |
2011 | 2.11c | 2.19b | |
Sig | Trte | ns | * |
Year | *** | *** | |
Trt × Year | ns | ns |
*Significant at 0.05 probability level; ***Significant at 0.001 probability level. aTreatments 1, 2, 3, 4, and 5 were the annual P application rates of 0, 10, 20, 30, and 40 kg∙P∙ha−1, respectively; treatment 6 was the P fertilizer recommended rate based on soil P testing results every year. bSig, significance. cns, not significant at 0.05 probability level. dMeans in a column within each year, averaged over the four years, or averaged over the six treatments followed by the same letter are not significantly different at P = 0.05 according to the protected LSD. eTrt, treatment.
Year | Treatmenta | Jackson | Milan | ||||
---|---|---|---|---|---|---|---|
Seed P | Protein | Oil | Seed P | Protein | Oil | ||
g∙kg−1 | |||||||
2008 | 1 | 5.40 | 437 | 205 | 5.50 | 405 | 220 |
2 | 5.48 | 433 | 205 | 5.73 | 403 | 221 | |
3 | 5.55 | 431 | 203 | 5.55 | 407 | 220 | |
4 | 5.35 | 430 | 207 | 5.45 | 406 | 220 | |
5 | 5.53 | 432 | 205 | 5.50 | 404 | 218 | |
6 | 5.58 | 435 | 207 | 5.30 | 407 | 219 | |
Sigb | nsc | ns | ns | ns | ns | ns | |
2009 | 1 | 5.80 | 410cd | 244a | 6.04 | 412b | 228 |
2 | 5.80 | 433b | 225c | 5.90 | 441a | 225 | |
3 | 5.83 | 432b | 232bc | 6.05 | 438a | 225 | |
4 | 5.95 | 433b | 234b | 5.90 | 433a | 226 | |
5 | 6.01 | 441a | 233bc | 6.03 | 436a | 224 | |
6 | 5.90 | 436ab | 238ab | 5.84 | 440a | 224 | |
Sig | ns | *** | ** | ns | *** | ns | |
2010 | 1 | 6.66c | 445c | 198a | 6.22b | 420 | 202 |
2 | 7.09a | 448bc | 195ab | 6.20b | 421 | 203 | |
3 | 6.85bc | 446c | 199a | 6.51a | 422 | 201 | |
4 | 6.92ab | 459a | 190c | 6.39ab | 422 | 200 | |
5 | 6.85bc | 454ab | 191bc | 6.24b | 422 | 204 | |
6 | 6.80bc | 451bc | 199a | 6.30b | 423 | 203 | |
Sig | * | * | ** | * | ns | ns | |
Average | 1 | 5.96 | 431d | 216a | 5.92 | 412b | 217 |
2 | 6.12 | 438bc | 208d | 5.94 | 422a | 216 | |
3 | 6.08 | 436c | 212bc | 6.04 | 422a | 216 | |
4 | 6.07 | 441ab | 210cd | 5.91 | 420a | 215 | |
5 | 6.13 | 442a | 210cd | 5.92 | 421a | 215 | |
6 | 6.12 | 441ab | 214ab | 5.81 | 423a | 216 | |
Year | 2008 | 5.48c | 433b | 205b | 5.50c | 405c | 220b |
2009 | 5.88b | 431b | 234a | 5.96b | 433a | 225a | |
2010 | 6.86a | 450a | 195c | 6.31a | 421b | 202c | |
Sig | Trte | ns | *** | *** | ns | *** | ns |
Year | *** | *** | *** | *** | *** | *** | |
Trt × Year | ns | *** | *** | ns | *** | ns |
*Significant at 0.05 probability level; **Significant at 0.01 probability level; ***Significant at 0.001 probability level. aTreatments 1, 2, 3, 4, and 5 were the annual P application rates of 0, 10, 20, 30, and 40 kg∙P∙ha−1, respectively; treatment 6 was the P fertilizer recommended rate based on soil P testing results every year. bSig, significance. cns, not significant at 0.05 probability level. dMeans in a column within each year, averaged over the three years, or averaged over the six treatments followed by the same letter are not significantly different at P = 0.05 according to the protected LSD. eTrt, treatment.
Year | Treatmenta | Jackson | Milan | ||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
Palmitic | Stearic | Oleic | Linoleic | Linolenic | Palmitic | Stearic | Oleic | Linoleic | Linolenic | ||
g∙kg−1 oil | g∙kg−1 oil | ||||||||||
2008 | 1 | 110 | 41.1 | 249 | 566 | 68.7 | 116 | 43.3 | 238 | 556 | 48.2 |
2 | 110 | 40.9 | 249 | 554 | 72.4 | 113 | 43.2 | 247 | 557 | 51.5 | |
3 | 109 | 40.7 | 245 | 564 | 76.2 | 116 | 43.4 | 242 | 555 | 46.9 | |
4 | 106 | 41.1 | 248 | 561 | 71.7 | 112 | 43.3 | 249 | 554 | 46.5 | |
5 | 110 | 41.1 | 248 | 561 | 74.7 | 115 | 43.4 | 244 | 558 | 43.8 | |
6 | 110 | 40.7 | 245 | 566 | 75.5 | 115 | 43.5 | 245 | 553 | 46.3 | |
Sigb | nsc | ns | ns | ns | ns | ns | ns | ns | ns | ns | |
2009 | 1 | 112d | 40.5 | 227cd | 536ab | 107a | 117b | 392 | 228c | 540b | 90.6 |
2 | 144ab | 41.0 | 273ab | 528c | 78.9b | 136a | 387 | 276a | 552a | 109.0 | |
3 | 130c | 40.6 | 269b | 535abc | 80.7b | 129ab | 407 | 263ab | 540b | 93.5 | |
4 | 135bc | 40.6 | 282a | 531bc | 79.1b | 141a | 391 | 271ab | 539b | 104.0 | |
5 | 145a | 40.8 | 273ab | 541a | 79.9b | 135a | 391 | 262ab | 550a | 101.0 | |
6 | 144ab | 40.5 | 271ab | 538ab | 90.4ab | 142a | 391 | 256b | 546a | 98.4 | |
Sig | *** | ns | *** | * | * | * | ns | ** | * | ns | |
2010 | 1 | 93.4bc | 42.5 | 290bc | 539 | 65.0 | 99.0 | 43.5 | 274 | 555 | 67.9d |
2 | 95.0bc | 42.5 | 283c | 551 | 58.7 | 97.8 | 43.1 | 272 | 549 | 96.3a | |
3 | 101a | 42.6 | 278c | 540 | 68.9 | 101 | 42.3 | 265 | 565 | 87.3ab | |
4 | 91.2c | 42.8 | 307a | 534 | 62.9 | 98.9 | 43.1 | 278 | 560 | 80.7bc | |
5 | 94.1bc | 42.9 | 300ab | 533 | 71.3 | 98.0 | 43.2 | 276 | 555 | 76.6bcd | |
6 | 97.0ab | 42.4 | 298ab | 543 | 69.9 | 99.6 | 42.6 | 265 | 562 | 74.8cd | |
Sig | * | ns | * | ns | ns | ns | ns | ns | ns | ** | |
Average | 1 | 105c | 41.4 | 255d | 547 | 80.4 | 111 | 42.0 | 247d | 551 | 68.9c |
2 | 115a | 41.5 | 268bc | 544 | 70.0 | 115 | 41.7 | 265ab | 553 | 85.5a | |
3 | 113ab | 41.3 | 264c | 546 | 75.3 | 115 | 42.1 | 257bc | 553 | 76.9b | |
4 | 111b | 41.5 | 279a | 542 | 71.2 | 117 | 41.8 | 266a | 551 | 77.1b | |
5 | 117a | 41.6 | 274ab | 545 | 75.3 | 116 | 41.9 | 261abc | 554 | 73.6bc | |
6 | 117a | 41.2 | 268bc | 549 | 78.6 | 119 | 41.7 | 255cd | 554 | 73.2bc | |
Year | 2008 | 109b | 40.9b | 247c | 562a | 86.1a | 115b | 43.4a | 244c | 556a | 47.2c |
2009 | 134a | 40.7b | 266b | 535b | 73.2ab | 133a | 39.3b | 259b | 545b | 99.3a | |
2010 | 95.2c | 42.6a | 291a | 540b | 66.1b | 98.6c | 43.0a | 271a | 558a | 80.6b | |
Sig | Trte | *** | ns | *** | ns | ns | ns | ns | *** | ns | *** |
Year | *** | *** | *** | *** | *** | *** | *** | ** | * | *** | |
Trt × Year | *** | ns | *** | ** | * | ** | ns | ** | * | ns |
*Significant at 0.05 probability level; **Significant at 0.01 probability level; ***Significant at 0.001 probability level. aTreatments 1, 2, 3, 4, and 5 were the annual P application rates of 0, 10, 20, 30, and 40 kg∙P∙ha−1, respectively; treatment 6 was the P fertilizer recommended rate based on soil P testing results every year. bSig, significance. cns, not significant at 0.05 probability level. dMeans in a column within each year, averaged over the three years, or averaged over the six treatments followed by the same letter are not significantly different at P = 0.05 according to the protected LSD. eTrt, treatment.
three-year averages. Linoleic and linolenic acid levels showed significant responses to P applications in 2009 only. Linolenic acid concentration was reduced with P fertilization in 2009.
At Milan, P fertilization effects on the concentrations of palmitic and linoleic acids were significant and positive in 2009. Oleic acid responded positively to P rates in 2009 and averaged over the three years. Linolenic acid levels showed a significant and positive response to P application up to a certain rate in 2010 and on three-year averages. However, stearic concentration was not influenced by P application regardless of location and year in our study.
The fact that significant responses of several fatty acids to P fertilization in 2009 and 2010 but not in 2008 might be attributable to the accumulated treatment effects over the years at both locations. A larger number of fatty acids in response to P fertilization at both locations in 2009 might be partially resulted from the relatively lower temperatures in July 2009, because lower temperatures reduced soybean P uptake, and thus resulted in greater responses of fatty acids to P fertilization. On the other hand, very low rainfall in September at both locations in 2008 and 2010 might be in part responsible for no fatty acid response in 2008 and fewer significant responses of fatty acids in 2010 to P fertilization.
In general, palmitic and oleic acid concentrations responded to P fertilization positively when the responses were significant in our study. The responses of linolenic acid concentration were positive in 2009 at Jackson and positive in 2010 and on the three-year averages at Milan. There were significant differences in the concentrations of all fatty acids among the three years irrespective of location. It is interesting that protein, oil, and fatty acid concentrations sometimes responded significantly to P applications even when seed yield and/or seed P concentration did not respond to P fertilization.
Abbasi et al. (2012) [
Linoleic acid concentration is a key quality attribute in soybean seed for human and animal consumption because it is an important polyunsaturated fatty acid that cannot be synthesized by humans or animals [
Soybean breeders have endeavored to create new cultivars with lower linolenic acid concentration in the seed for value added cooking oil with improved health benefits [
Year exerted significant effects on protein, oil, and fatty acid concentrations at both locations in our study. The fact that the temperatures and rainfall were different among the four years at least partially explained the variability in P fertilization effects on the concentrations of protein, oil, and fatty acids among the three growing seasons.
Our results agree with those of Krueger et al. (2013) [
At Jackson, the production of protein, oil, and fatty acids were not affected by P fertilization in any year or on the averages over the three years except linolenic acid in 2009 which was reduced due to P application compared with the zero P control (data not shown). However, the year effects were significant on all the quality attributes except palmitic acid. Protein production was higher in 2010 than those in the other two years; while the production of oil and stearic, oleic, linoleic, and linolenic acids were all higher in 2009 than those in 2008 and 2010 (data not shown).
At Milan, the production of protein, oil, and fatty acids were not influenced by P fertilization in any year except palmitic and oleic acids in 2009 and linolenic acid in 2010 (
Basically the production of protein, oil, and fatty acids depend on the seed yield level and the concentrations of these attributes in the seed. Haq and Mallarino (2005) [
Year | Treatmenta | Protein | Oil | Palmitic | Stearic | Oleic | Linoleic | Linolenic |
---|---|---|---|---|---|---|---|---|
kg∙ha−1 | ||||||||
2008 | 1 | 921 | 501 | 57.9 | 21.7 | 119 | 279 | 24.2 |
2 | 955 | 524 | 59.2 | 22.6 | 129 | 292 | 27.2 | |
3 | 900 | 488 | 56.5 | 21.2 | 118 | 271 | 22.8 | |
4 | 949 | 514 | 57.6 | 22.3 | 128 | 285 | 23.8 | |
5 | 917 | 495 | 56.9 | 21.4 | 121 | 276 | 21.8 | |
6 | 930 | 501 | 57.6 | 21.8 | 123 | 278 | 23.1 | |
Sigb | nsc | ns | ns | ns | ns | ns | ns | |
2009 | 1 | 1205 | 665 | 77.8bcd | 26.1 | 152c | 359 | 60.1 |
2 | 1282 | 654 | 88.6ab | 25.3 | 181a | 361 | 71.0 | |
3 | 1123 | 578 | 74.0c | 23.5 | 152c | 312 | 54.2 | |
4 | 1253 | 656 | 92.5a | 25.6 | 178ab | 354 | 68.5 | |
5 | 1187 | 609 | 82.5abc | 23.8 | 160abc | 334 | 61.2 | |
6 | 1201 | 613 | 87.0ab | 24.0 | 157bc | 335 | 60.6 | |
Sig | ns | ns | * | ns | * | ns | ns | |
2010 | 1 | 1137 | 547 | 54.1 | 23.8 | 150 | 303 | 37.1c |
2 | 1256 | 606 | 59.3 | 26.1 | 165 | 333 | 58.9a | |
3 | 1174 | 560 | 56.3 | 23.7 | 149 | 316 | 48.9b | |
4 | 1180 | 559 | 54.1 | 24.1 | 155 | 313 | 45.1bc | |
5 | 1132 | 547 | 53.6 | 23.6 | 151 | 303 | 41.8bc | |
6 | 1141 | 549 | 54.6 | 23.5 | 146 | 308 | 41.3bc | |
Sig | ns | ns | ns | ns | ns | ns | ** | |
Average | 1 | 1088b | 571abc | 63.2b | 23.8 | 140c | 314ab | 40.5b |
2 | 1164a | 595a | 69.0a | 24.7 | 158a | 329a | 52.4a | |
3 | 1066b | 542c | 62.3b | 22.8 | 139c | 300b | 42.0b | |
4 | 1128ab | 576ab | 68.1a | 24.0 | 154ab | 317ab | 45.8b | |
5 | 1079b | 550bc | 64.3ab | 23.0 | 144bc | 305b | 41.6b | |
6 | 1091b | 555bc | 66.4ab | 23.1 | 142c | 307b | 41.7b | |
Year | 2008 | 929b | 504c | 57.6b | 21.8b | 123c | 280c | 23.8c |
2009 | 1209a | 629a | 83.8a | 24.7a | 163a | 343a | 63.0a | |
2010 | 1170a | 561b | 55.3b | 24.1a | 153b | 313b | 45.5b | |
Sig | Trte | * | * | * | ns | ** | * | *** |
Year | *** | *** | *** | ** | *** | ** | *** | |
Trt × Year | ns | ns | ns | ns | ns | ns | ns |
*Significant at 0.05 probability level; **Significant at 0.01 probability level; ***Significant at 0.001 probability level. aTreatments 1, 2, 3, 4, and 5 were the annual P application rates of 0, 10, 20, 30, and 40 kg∙P∙ha−1, respectively; treatment 6 was the P fertilizer recommended rate based on soil P testing results every year. Sig, significance. cns, not significant at 0.05 probability level. dMeans in a column within each year, averaged over the three years, or averaged over the six treatments followed by the same letter are not significantly different at P = 0.05 according to the protected LSD. eTrt, treatment.
found that protein and oil production responses to P fertilization tended to follow yield responses; P fertilization that increases soybean yield has infrequent, inconsistent, and small effects on oil and protein concentrations but often increases oil and protein production.
Phosphorus application rates had greater impacts on leaf P nutrition at the earlier growth stages. As P application rate went up, the increase in leaf P gradually slowed down. Protein, oil, and fatty acid concentrations in seed responded differently to P fertilization. In general, protein concentrations were enhanced but oil levels decreased with increased P application rate. Palmitic and oleic concentrations responded positively to P application rate up to a certain level. However, the response of linolenic acid concentration was inconsistent (negative or positive). Stearic concentration was not influenced by P fertilization. Application of 10 kg∙P∙ha−1 resulted in higher production of protein and palmitic, oleic, and linolenic acids than zero P and the higher P application rates as well on the P deficient soil. Excessive P application rates could lower seed yield and the quality of some attributes in seed. Our results suggest that linoleic acid concentration, a key quality attribute in soybean seed for human and animal consumption, can sometimes be enhanced by P fertilization, and thus appropriate P application may increase the market value of soybean production; the indigenous soil P fertility level and P application rate should be taken into account by soybean breeders in breeding for new soybean cultivars with low linolenic acid level since P can affect linolenic acid level in the seed.
This research was partially supported by the Tennessee Soybean Promotion Board. We thank Robert Sharp, James Warren, Jimmy McClure, and Jason Williams for their skilful technical assistance.
Yin, X.H., Bellaloui, N., McClure, A.M., Tyler, D.D. and Mengistu, A. (2016) Phosphorus Fertilization Differentially Influences Fatty Acids, Protein, and Oil in Soybean. American Journal of Plant Sci- ences, 7, 1975-1992. http://dx.doi.org/10.4236/ajps.2016.714180