Agronomy Journal Grow Your Career With ASA
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

Published in Agron J 98:198-205 (2006)
DOI: 10.2134/agronj2005-0131
© 2006 American Society of Agronomy
677 S. Segoe Rd., Madison, WI 53711 USA
This Article
Right arrow Abstract Freely available
Right arrow Figures Only
Right arrow Full Text (PDF) Free
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in Web of Science
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Web of Science (2)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Ross, J. R.
Right arrow Articles by DeLong, R. E.
Right arrow Search for Related Content
PubMed
Right arrow Articles by Ross, J. R.
Right arrow Articles by DeLong, R. E.
Agricola
Right arrow Articles by Ross, J. R.
Right arrow Articles by DeLong, R. E.
Related Collections
Right arrow Soybean
Right arrow Nutrient Management
Right arrow Plant Nutrition
Right arrow Production Agriculture

Production Papers

Boron Fertilization Influences on Soybean Yield and Leaf and Seed Boron Concentrations

Joni R. Rossa, Nathan A. Slaton*,a, Kristofor R. Bryeb and Russell E. DeLonga

a Dep. of Crop, Soil, and Environmental Sciences, 1366 W. Altheimer Drive, Fayetteville, AR 72704
b Dep. of Crop, Soil, and Environmental Sciences, 115 Plant Science Building, Fayetteville, AR 72701

* Corresponding author (nslaton{at}uark.edu)

Received for publication May 3, 2005.

   ABSTRACT
TOP
 NOTES
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Soybean [Glycine max (Merr.) L.] is considered relatively insensitive to B deficiency. However, B deficiency has recently become a common nutrient deficiency of soybean in northeast Arkansas. Field studies were conducted on four alkaline silt-loam soils in northeast Arkansas to determine the influence of B application time and rate on soybean growth, tissue B concentration, and seed yield. Boron fertilizer was applied at 0, 0.28, 0.56, 1.12, and 2.24 kg B ha–1 near the V2 or R2 growth stages. Boron fertilization had no significant effect on soybean yield at one site but increased seed yields from 4 to 130% at three sites. At the most responsive site, B application at V2 increased yields by 13% compared with applications at R2. In contrast, at a site where leaf B concentrations were sufficient for soybean receiving no B, B applied at the R2 stage significantly increased seed yields by 5% compared with V2 B applications. Trifoliate leaf B concentrations at the R2 stage increased as B rate increased. Seed B concentrations also increased as B rate increased. Boron applied at the R2 stage resulted in equal or greater seed B concentrations than B applied at the V2 stage. Application of 0.28 to 1.12 kg B ha–1 during early vegetative or reproductive growth was sufficient to produce near maximal yields. The expected severity of B deficiency plus fertilizer and application costs associated with B fertilization should be considered when selecting the most appropriate B fertilization strategy.

Abbreviations: BD, bulk density • COVN, Covington Farm • HALL, Hall farm • MORY, Moery farm • PTBS, Pine Tree Branch Station • SOM, soil organic matter


   INTRODUCTION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
BORON is an essential micronutrient for plants. Some plants are more susceptible to B deficiency and toxicity than others. Soybean is considered relatively insensitive to B deficiency (Martens and Westermann, 1991; Touchton and Boswell, 1975). However, research with soybean has reported negative, positive, or no yield responses from direct applications of B fertilizer (Freeborn et al., 2001; Rerkasem et al., 1997; Reinbott and Blevins, 1995; Schon and Blevins, 1990; Touchton and Boswell, 1975; Touchton et al., 1980; Woodruff, 1979). Oplinger et al. (1993) reported that 0.28 kg B ha–1 applied foliarly numerically increased soybean yields by 3% when averaged across 29 trials conducted on B-sufficient soils in the Midwest. Individual trial results usually showed no significant differences among yields between the unfertilized control and soybean receiving B. Touchton et al. (1980) noted that soybean yield responded positively and nominally to B fertilization at three of nine site-years in Georgia and suggested that environmental conditions probably influence whether soybean responds positively or not at all to B fertilization. Although environmental conditions may play an important role in soybean response to B fertilization, soybean leaf B concentrations reported by Touchton et al. (1980) were sufficient (>25 mg B kg–1). Soil chemical (e.g., soil pH and organic matter content) and physical (e.g., texture) properties also influence B availability to plants and have likely contributed to the inconsistent soybean response to B fertilization (Moraghan and Mascagni, 1991).

In Arkansas, before 2001, B was not recognized as a growth- or yield-limiting nutrient for soybean production, and no recommendations for B fertilization of soybean were available to growers. In 2001, B deficiency of soybean was first diagnosed in several counties in northeast Arkansas (Slaton et al., 2002) and has been observed every year since, making it the most common nutrient deficiency of soybean reported in Arkansas. The soybean-producing areas of Craighead, Cross, Greene, Jackson, Lawrence, Poinsett, Randolph, St. Francis, and Woodruff counties that are west of Crowley's Ridge produce about 403 000 ha of soybean annually (AASS, 2004), which accounts for roughly one third of the Arkansas soybean production area. A large portion of the Arkansas soybean hectarage is irrigated with ground water high in Ca and Mg bicarbonate, rotated with flood-irrigated rice (Oryza sativa L.), and grown on silt-loam soils that have low organic matter, low clay content, alkaline soil pH, and shallow topsoil, all of which have been recognized as soil conditions conducive to B deficiency (Martens and Westermann, 1991). Boron deficiency symptoms have been observed 4 to 6 wk after soybean emergence during vegetative growth and during reproductive growth. The only published record of B fertilization field research with soybean in Arkansas was made by Al-Molla (1985), who reported a 15% yield increase from the application of granular B at the R1 soybean stage (Fehr and Caviness, 1977) in Poinsett and Craighead counties.

Several studies have reported that soybean (Touchton and Boswell, 1975), cotton (Gossypium hirsutum L.) (Roberts et al., 2000), peanut (Arachis hypogaea L.) (Davis and Rhoades, 1994), and alfalfa (Medicago sativa L.) (Mortvedt and Woodruff, 1993) yields may respond positively to pre-plant incorporated or postemergence foliar applications of B. Boron application rate, rather than application strategy, seems to be the most important factor determining the response of crops grown on B-deficient soils. Compared with the unfertilized control, Touchton and Boswell (1975) reported that soybean yields were increased from 0 to 4% from application of 0.28 to 1.12 kg B ha–1 and reduced by 6 to 10% from 2.24 kg B ha–1. Woodruff (1979) reported that soybean yields at one site were 77% greater than the unfertilized control when 0.56 kg B ha–1 was applied to the soil from the V4 to V8 growth stage. The trifoliate leaves of the unfertilized control contained only 10 mg B kg–1, which is below the critical level of 20 mg B kg–1 (Mills and Jones, 1991). The literature suggests that soybean with low tissue B concentrations (<20 mg B kg–1) generally respond positively to B fertilization and that B fertilization of soybean with sufficient concentrations of tissue B may have no benefit, slightly increase, or may reduce soybean yields.

Much of the B fertilization research conducted with soybean has examined B fertilization for the purpose of increasing soybean yield potential by increasing branching (Schon and Blevins, 1990), pod set (Reinbott and Blevins, 1995; Weaver et al., 1985), and various physiologic processes that may contribute to higher seed yields (Reinbott and Blevins, 1995), especially for soybean grown in high-yielding environments (Touchton et al., 1980). Preventing B deficiency has not been cited as a primary reason for studying B fertilization of soybean, presumably because widespread B deficiency of soybean, similar to the recent occurrence reported in Arkansas (Slaton et al., 2002), is uncommon. Because B deficiency of soybean in Arkansas often occurs before the onset of reproductive growth and tissue B concentrations of soybean grown in northeast Arkansas are often low (Mozaffari et al., 2003), research-based B fertilization recommendations are needed to assess the proper timing and rates of B application for preventing significant seed yield losses. The objective of these field studies was to determine the effects of foliar B application time and rate on soybean growth, B concentration in trifoliate leaves and seed, and grain yield. We hypothesized that (i) soybean yields would increase with B fertilization, (ii) B applied during early vegetative growth would increase soybean yield more than B applied during early reproductive growth on B-deficient soils, and (iii) increasing B rate would increase leaf and seed B concentrations.


   MATERIALS AND METHODS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Site Description
Four field experiments were conducted in 2003 to evaluate soybean response to B fertilization. Experiments were established on a Calhoun silt loam (fine-silty, mixed, active, thermic Typic Glossaqualfs) at the Pine Tree Branch Station (PTBS) in St. Francis County, AR (35°7' N lat; 90°57' W long); a Crowley (fine, smectitic, hyperthermic Typic Albaqualfs)–Hillemann (fine-silty, mixed thermic Albic Glossic Natraqualfs) silt-loam complex on the Moery farm (MORY) located in Cross County, AR (35°18' N lat; 90°50' W long); and the two remaining sites were on Henry (coarse-silty mixed active thermic Typic Fragiaqualfs) silt loams on the Covington (COVN, 35°41' N lat; 90°43' W long) and Hall (HALL, 35°39' N lat; 90°44' W long) farms in Poinsett County, AR. The COVN field had shown B deficiency symptoms in 2001, the last year soybean was grown. Boron-deficient soybean had not been documented at PTBS but had been observed in the general vicinity. For the other two sites, B deficiency of soybean had been observed in nearby fields.

Rice was grown the previous year at all sites except PTBS, which followed soybean. Soybean was drill-seeded (18-cm wide drill-row spacing) into conventionally tilled seedbeds at all sites except HALL, which was seeded with a no-till drill into the previous year's rice stubble. The cultivar and selected dates of agronomic significance for each site are listed in Table 1. Phosphorus (20 kg P ha–1 as triple superphosphate) and K (60 kg K ha–1 as KCl) fertilizers were applied to all plots to ensure these nutrients were not growth-limiting factors. For all sites, soybean was flood-irrigated on an as needed basis. In general, seeding rates, fertilization, and pest management practices closely followed University of Arkansas Cooperative Extension Service recommendations for irrigated-soybean production at all sites (University of Arkansas, 2000).


View this table:
[in this window]
[in a new window]
  		Table 1. Summary of planting, foliar B fertilizer application, and sampling and harvest dates of soybean for Covington (COVN), Hall (HALL), Moery (MORY), and Pine Tree Branch Station (PTBS) sites.

 
At the COVN site, 1.12 kg B ha–1 as granular B was blended with P and K fertilizers and broadcast to the field area surrounding the study site. At the HALL site, the grower foliar applied 1.12 kg B ha–1 by airplane about 10 d before the R1 soybean growth stage to the area surrounding the study. No B fertilizer was applied to the fields surrounding experiments at the PTBS and MORY sites.

Fertilizer Treatments
Each experiment was arranged in a randomized, complete-block design with a split-plot treatment structure where B application rate was the main plot factor and application time was the subplot factor. Each treatment was replicated six times. Each plot was 4.0-m wide by 6.1-m long, contained 20 soybean rows, and was separated from adjacent plots by a 50-cm wide alley that contained no soybean plants.

Boron fertilizer (Solubor DF [mixture of H3BO3, Na2B4O7·5H2O, and Na2B10O16·10H2O]; 175 g B kg–1; U.S. Borax Inc., Valencia, CA] was applied at rates of 0, 0.28, 0.56, 1.12, and 2.24 kg B ha–1 at the V1 to V3 growth stage (hereafter referred to as V2 stage) or at the R1 to R2 stage (referred to as R2 stage). The V2 applications were made 9 to 28 d after seeding, and the R2 applications were made 26 to 35 d after the V2 application (Table 1).

All B fertilizer treatments were sprayed with a CO2 backpack sprayer calibrated to deliver 94 L ha–1. Howard et al. (2000) showed that buffering foliar-applied B solutions to a pH of 4.0 improved cotton lint yield compared with the check and unbuffered B solutions. Therefore, B solutions applied at the R2 stage were buffered to a pH range of 4.3 to 4.5 using Buffer Extra Strength (Helena Chemical Co., Collierville, TN). Eight milliliters of Buffer Extra Strength were required to reduce the solution pH to 4.4 for every 0.28 kg B ha–1 increment applied.

Soil and Plant Sampling and Measurements
Before B fertilizer was applied at the V2 stage, one set of composite soil samples was collected from the 0- to 10-cm depth in the unfertilized control plot from each replicate. Each composite sample consisted of eight 1.9-cm diameter cores. Soil samples were oven-dried, crushed to pass through a 2-mm sieve, and extracted with Mehlich-3 solution (Mehlich, 1984). Mehlich-3 extracts were analyzed for B, P, K, Ca, Mg, and Zn by inductively coupled atomic plasma spectroscopy (ICPS) (Soltanpour et al., 1996) (Table 2). Soil water pH was determined in a 1:2 soil/water (w/v) ratio. Soil organic matter was determined by weight loss-on-ignition (Schulte and Hopkins, 1996). The mean values of selected soil properties are listed by site in Table 2.


View this table:
[in this window]
[in a new window]
  		Table 2. Mean (n = 6, sample depth 0- to 10-cm) values for soil water pH, soil organic matter (SOM), bulk density (BD) (n = 30, sample depth 0- to 12-cm), particle size analysis, and Mehlich-3 extractable soil nutrients for Covington (COVN), Hall (HALL), Moery (MORY), and Pine Tree Branch Station (PTBS) sites.

 
A second set of soil samples (n = 30) was collected 5–8 wk after planting from each plot in the first, third, and sixth replicate blocks for the determination of bulk density (BD) and particle-size distribution. A 4.8-cm diameter soil core was collected from the 0- to 12-cm depth for BD. Soil cores were oven-dried at 70°C for 48 h and weighed (Blake and Hartge, 1986). Soil cores were subsequently crushed and sieved through a 2-mm mesh screen for determination of sand, silt, and clay proportions using the hydrometer method (Arshad et al., 1996).

Before B was applied at the R2 stage, 10 whole plants and 20 recently matured trifoliate leaves (i.e., top two nodes of the main stem) were randomly collected from each unfertilized control and treatments that received B at the V2 stage (Table 1). Whole plants were cut 2 cm above the soil surface and grouped into a single composite sample for each plot. Because visible differences in growth were noted among treatments at the HALL site, plant height and node number were recorded for each of the 10 whole plants. All tissues were dried at 60°C, weighed (whole-plant samples), and ground to pass through a 1-mm sieve. A 0.25-g subsample was digested with concentrated HNO3 and 30% H2O2 for elemental analysis as described by Jones and Case (1990). Digests were analyzed for elemental concentrations using ICPS.

At or after the R7 growth stage, 10 whole plants were randomly collected from each plot as described for the R2 stage. Pods on each composite plant sample were counted, summed, and removed from the stalk; stalks and pods were dried; soybean seeds were threshed from the pods; and the seeds were weighed. Dried stalks plus pods were weighed, ground, and digested as described previously. Four soybean seeds were weighed, and seeds were digested and analyzed as described previously.

A 9.0-m2 area from the middle of each plot was harvested for grain yield with a small plot combine. The grain weight and moisture content of each harvested sample were determined. Grain yield was adjusted to a uniform moisture content of 130 g kg–1 for statistical analysis.

Statistical Analysis
Data from the four sites were analyzed together. Data collected from plant samples collected at the R2 stage were analyzed with a split-plot treatment structure where location was the main plot factor and B application rate was the subplot factor. Seed yield, pod number (10 plants–1), and B concentration data collected at maturity were analyzed as a split-split-plot design where location was the main plot factor, B application rate was the subplot factor, and B application time was the sub-subplot factor. Analysis of variance procedures were conducted with the PROC GLM procedure in SAS (SAS Inst., Cary, NC). Mean separations were performed by Fisher's protected least significant difference at a significance level of 0.05.


   RESULTS AND DISCUSSION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS
 REFERENCES
 
Visual Observations
No visual symptoms of B deficiency or growth responses to B fertilization were observed for soybean grown at PTBS. Boron deficiency symptoms during vegetative growth and a vegetative growth response to B fertilization (at V2) were observed only at HALL. The HALL site was also the only site that was seeded no-till into an undisturbed seedbed. Soybean not receiving B at the V2 stage showed dramatic B-deficiency symptoms by 5 wk after emergence. Symptoms of B deficiency included stunting, swollen nodes, and death of the terminal growing point; also, the youngest leaves were small; exhibited interveinal and marginal chlorosis; and eventually became thick, dark green, and cupped downward. The youngest leaves of soybean receiving B at the V2 stage were generally a lighter green color and larger than leaves of B-deficient plants. Soybean receiving 0.56, 1.12, and 2.24 kg B ha–1 were taller and had more nodes than soybean receiving 0.28 and 0 kg B ha–1 (Table 3). The rice straw and the lack of tillage may have contributed to the early-season B-deficiency at HALL. Boron contained in undecomposed rice straw may reduce the amount of plant-available B in no-till situations.


View this table:
[in this window]
[in a new window]
  		Table 3. Soybean node number and plant height at the R2 growth stage as influenced by B rate applied at the V2 growth stage for the Hall site.

 
Boron-deficiency symptoms were also observed at the COVN and MORY sites at the onset of reproductive growth, but foliar symptoms were subtle, with plants showing no visual differences in height or color. Whole-plant weights (10 plants plot–1) at the R2 stage were significantly (P < 0.0001) different among sites but were unaffected by B rate or the site x B rate interaction. The average whole-plant weights at the R2 stage for MORY was 128 g, which was 32, 61, and 65 g greater than mean plant weights from the HALL, PTBS, and COVN sites, respectively.

By maturity, visual differences among B treatments were apparent for soybean at COVN, HALL, and MORY. The symptom common to all three sites was delayed senescence of leaves. Delayed leaf senescence has not been previously cited as a B-deficiency symptom of soybean. Boron-deficient cotton is reportedly difficult to chemically defoliate (Keogh and Maples, 1969; Shelby, 2000). Complete defoliation (i.e., maturity) of soybean receiving no B ranged from 8 to 14 d later than soybean receiving >0.28 kg B ha–1 with soybean at COVN showing the most dramatic differences among treatments. Although soybean receiving 0.28 kg B ha–1 tended to defoliate before the unfertilized control, defoliation was not as rapid as observed for the greater B rates. Boron rate appeared to be the most important factor influencing leaf senescence as few differences were noted between application times for B rates >0.28 kg B ha–1.

Delayed leaf senescence was the only symptom observed at MORY. However, at COVN, plants receiving no B also contained twisted pods with no seed, small pods with shriveled seed, and fewer pods on the upper one-half of the stalk. Plant height was not measured at maturity, but height differences among B treatments were apparent only for soybean at HALL. Mature plant weights were significantly (P < 0.0001) different among sites following the order of HALL = MORY > PTBS = COVN.

Based on the time of appearance and severity of B-deficiency symptoms, sites ranked from the most to least severe B deficiency followed the order of HALL > COVN > MORY > PTBS (none). The HALL site was ranked as having the most severe B deficiency because of its expression during early-season growth. The lack of more dramatic symptoms during reproductive growth was attributed to drift of B solution sprayed (1.12 kg B ha–1) via airplane to the surrounding field by the grower. Although B applied to the field was not directly sprayed on the plots, all trifoliate leaf samples showed high concentrations of B (>45 mg B kg–1) about 1 wk after the field was sprayed suggesting that a portion of the B solution drifted across the plots and may have been enough to allow for plant recovery. At harvest, the presence or absence of B deficiency symptoms among B treatments suggested that growth and yield differences would occur at COVN, HALL, and MORY, but not at PTBS.

Tissue Boron Concentration at R2 Stage
Boron concentration data from all sites, except HALL, were analyzed together. The HALL data were excluded due to the B contamination of tissues mentioned previously. The site x B rate interaction was significant for the trifoliate (P = 0.0057) and whole-plant (P < 0.0001) B concentrations at the R2 growth stage (Table 4). Within each site, the numerical trifoliate leaf and whole-plant B concentrations generally increased as B application rate increased. However, the magnitude of the increase varied among sites. For both tissues, the greatest range of B concentrations among B rates occurred at the COVN site, and the smallest range occurred at the MORY site. Although the reasons for the different responses are not known, they may be related to soil physical and chemical property differences. For example, the COVN soil had the lowest clay and soil organic matter contents of the two sites (Table 2) and showed the greatest yield response to B fertilization. Soils with greater amounts of clay and soil organic matter may retain more plant-available B and be less responsive to B fertilization (Jin et al., 1988; Goldberg, 1993; Yermiyahu et al., 2001).


View this table:
[in this window]
[in a new window]
  		Table 4. Soybean whole-plant and trifoliate B concentrations at the R2 growth stage as affected by the site x B rate (applied at the V2 stage) interaction for the Covington (COVN), Moery (MORY), and Pine Tree Branch Station (PTBS) sites.

 
Mean trifoliate leaf B concentrations of the unfertilized controls from the COVN and MORY sites were B deficient, whereas trifoliate leaf B concentrations for PTBS were above the 20 mg B kg–1 critical concentration (Mills and Jones, 1991). Application of 1.12 kg B ha–1 for COVN and 2.24 kg B ha–1 for MORY were required to raise the trifoliate B concentrations above 20 mg B kg–1. Application of 2.24 kg B ha–1 at the V2 stage never increased tissue B concentrations beyond the established toxic concentration of 60 mg B kg–1 (Mills and Jones, 1991). Although trifoliate and whole-plant B concentrations were not statistically compared, data suggest that when B availability is low, as shown for B application rates <1.12 kg ha–1 at COVN and MORY, trifoliate leaf B concentrations is slightly lower than whole-plant B concentrations. Sherrell (1983) reported that the whole and upper portions of B-deficient lucerne (Medicago sativa L.) contained equal B concentrations, but, when B was sufficient, upper-plant portions often contained greater B concentrations. The data also suggest that trifoliate leaves or whole plants can be sampled to determine plant B status at the R2 stage.

Stalk Boron Concentrations at R7 Stage
Averaged across B rates and application times, stalk B concentrations at maturity differed significantly (P < 0.0001) among sites. Statistically, PTBS (20.4 mg B kg–1) had the greatest and COVN (12.6 mg B kg–1) had the lowest mean B concentrations, compared with the HALL (15.3 mg B kg–1) and MORY (15.2 mg B kg–1) sites (LSD0.05 = 1.3 mg B kg–1).

The B rate x application time interaction, averaged across the four sites, was significant (P = 0.0063) for stalk B concentration at or after the R7 stage (Table 5). Within each application time, stalk B concentration generally increased as the B application rate increased. Application of 0.28 and 0.56 kg B ha–1 at the R2 stage increased stalk B concentrations more than B applied at the V2 stage. Stalk B concentrations were similar between application times for rates >0.56 kg B ha–1. Others have also reported that tissue B concentrations increase as B rate increases (Schon and Blevins, 1990; Al-Molla, 1985; Touchton et al., 1980; Woodruff, 1979).


View this table:
[in this window]
[in a new window]
  		Table 5. Mature soybean stalk B concentrations, averaged across sites, as affected by the B rate x application time interaction.

 
Seed Boron Concentrations at Maturity
The site x B rate x B application time interaction was significant (P = 0.0005) for soybean seed B concentration (Fig. 1 ). The MORY site showed that seed B concentrations were similar for like B application rates regardless of application time. At COVN, the B fertilizer rates >0 kg B ha–1 applied at the R2 stage always increased soybean seed B concentrations compared with the same B rates applied at the V2 stage. At HALL, 1.12 kg B ha–1 applied at the V2 stage resulted in a significantly greater seed B concentration than 1.12 kg B ha–1 applied at the R2 stage. However, B that drifted from the surrounding field may have influenced seed B concentrations at HALL. At PTBS, the seed B concentration from the 1.12 kg B ha–1 applied at the R2 stage was significantly greater than 1.12 kg B ha–1 applied at V2. At all sites, soybean seed B concentrations tended to increase as B fertilizer rate increased up to 1.12 or 2.24 kg B ha–1. Soybean seed B concentrations reported by Touchton and Boswell (1975) and Reinbott et al. (1997) were >25 mg B kg–1, which is greater than the maximum concentrations found for seed at the PTBS site. Touchton and Boswell (1975) also reported that seed B concentration increased nonlinearly as B rate increased, but B application time did not influence seed B concentration. Data from the COVN site indicates that B applied during early reproductive growth is transported more efficiently to developing seed compared with B applied during early vegetative growth when B deficiency is severe.



View larger version (27K):
[in this window]
[in a new window]
  		Fig. 1. Mature soybean seed B concentrations as affected by the site x B application rate x application time interaction for the Covington (COVN), Hall (HALL), Moery (MORY), and Pine Tree Branch Station (PTBS) sites. The LSD0.05 = 3.6 to compare means for application times within same B rate and site. The LSD0.05 = 3.3 to compare means for two B rates with same site. The LSD0.05 = 2.9 to compare means at different sites.

 
Soybean seed from the unfertilized control at COVN and HALL contained B concentrations less than the 10 mg B kg–1 critical concentration suggested by Rerkasem et al. (1997). For soybean seed harvested from COVN, 2.24 kg B ha–1 applied at V2 was required to increase the seed B concentration above 10 mg B kg–1. In contrast, only 0.56 kg B ha–1 was required when B was applied at the R2 stage. The 0.56 kg B ha–1 rate applied at either stage raised the seed B concentrations to a sufficient B level at the HALL site. Application of B to soybean intended for seed production can increase seed B concentration, which may be of direct value for soybean seeded in B-deficient soils and warrants further investigation. Rerkasem et al. (1997) reported that B-deficient soybean seed had low germination and when seeded into a B-deficient soil, plants produced lower yields due to fewer pods and seeds per pod than soybean grown from B-sufficient seed.

Pod Number per 10 Plants
Soybean pod number (per 10 plants) was affected by B application time (P = 0.0103), averaged across sites and B rates, and the site x B rate interaction (P = 0.0359) (Table 6), averaged across B application times. Soybean receiving B at the V2 stage (615 pods [10 plants–1]) produced greater pod numbers compared with B applied at the R2 stage (560 pods [10 plants–1]). Schon and Blevins (1990) reported foliar applications of 0.56 and 1.12 kg B ha–1 at the flowering stage increased the number of soybean pods per branch, with the optimal B rate being 0.56 kg B ha–1.


View this table:
[in this window]
[in a new window]
  		Table 6. Number of pods per 10 plants as affected by the site x B application rate interaction, averaged across B application times, for the Covington (COVN), Hall (HALL), Moery (MORY), and Pine Tree Branch Station (PTBS) sites.

 
In general, pod numbers were greatest for soybean at MORY and lowest at PTBS and COVN (Table 6). Within each site, pod numbers were similar among B application rates for COVN, MORY, and PTBS. Significant differences among B application rates occurred only at HALL. For HALL, soybean receiving no B produced significantly more pods than soybean receiving B. Although pod numbers among B rates at the COVN site were statistically similar, soybean that received B produced a numerically greater number of pods than the unfertilized control. These data suggest that B fertilization does not always increase total pod number per plant but may influence another component of yield, such as seed number per pod as reported by Rerkasem et al. (1997).

Seed Yield
Soybean seed yield was affected by the site x B rate (P < 0.0001) (Table 7), averaged across B application times, and site x application time (P = 0.0110) (Table 8), averaged across B rates, interactions. Seed yield was not affected by the three-way interaction (site x B rate x application time, P = 0.2711), suggesting that the B rate and application time effects acted independently. Among sites, soybean yields were greatest at PTBS and HALL and lowest at COVN (Tables 7 and 8). For COVN, late planting was likely the main reason for low yields (Beatty et al., 1982). The B-deficient soybean plants produced shriveled and deformed seed, which is a characteristic of B-deficient soybean seed (Rerkasem et al., 1993), and was likely a factor depressing soybean seed yield of the unfertilized control at COVN.


View this table:
[in this window]
[in a new window]
  		Table 7. Soybean seed yield as affected by the site x B application rate interaction, averaged across B application times, for the Covington (COVN), Hall (HALL), Moery (MORY), and Pine Tree Branch Station (PTBS) sites.

 

View this table:
[in this window]
[in a new window]
  		Table 8. Soybean seed yield as affected by the site x B application time interaction, averaged across B application rates, for the Covington (COVN), Hall (HALL), Moery (MORY), and Pine Tree Branch Station (PTBS) sites.

 
Soybean seed yield differed significantly among B application rates within a site at COVN, HALL, and PTBS (Table 7). Yield increases from B fertilization ranged from 111 to 130% for COV, 5 to 14% for PTBS, and 4 to 10% for HALL. Application of 2.24 kg B ha–1 did not reduce soybean yields. Depending on the site and when averaged across B application times, near maximal soybean yields were produced by applying 0.28 to 2.24 kg B ha–1. For COVN, B application rates ≥0.28 kg B ha–1 significantly increased soybean yields compared with the unfertilized control. At HALL, MORY, and PTBS, the yields of soybean receiving B fertilizer were numerically greater and occasionally statistically greater than yields of soybean receiving no B. Compared with the unfertilized control, application of 1.12 kg B ha–1 for HALL and 0.56 and 2.24 kg B ha–1 for PTBS significantly increased soybean yields.

Application of >0.28 kg B ha–1 at MORY numerically increased soybean yields by 5 to 9%, but the greater numerical seed yields were not statistically greater than the unfertilized control when evaluated at the 0.05 (Table 7) or 0.10 probability levels (LSD0.10 = 246 kg ha–1). Specific reasons for the lack of significant yield increases from B fertilization at MORY are not known, the harvested yield was also lower than expected. Tissue concentrations of other essential elements at the R2 stage were sufficient for normal to high soybean yields. Irrigation frequency or other pest problems (e.g., nematodes, cultivar selection, disease, etc.) that were unnoticed may have limited soybean yield and response to B fertilization. Rerkasem et al. (1993) showed that soybean cultivars differ in susceptibility to B deficiency. Slaton et al. (2004) reported that DP 5915 RR, the cultivar planted at the MORY site, generally contained lower trifoliate B concentrations than 13 other cultivars evaluated on B-sufficient soils in Arkansas. Perhaps this soybean cultivar has a lower B requirement and is less susceptible to B deficiency than other cultivars.

Soybean yield response attributed to B application time varied within each site (Table 8). Time of B application did not effect soybean yields at HALL and MORY. Soybean yields at COVN were greatest when B was applied at the V2 stage, but for PTBS soybean yields were 5% greater when B was applied at the R2 stage. The variable soybean yield responses among sites to B application time and rate may be partially attributed to the degree of deficiency at each site. At COVN, the most responsive and B-deficient site, soybean yields were 13% greater when B was applied at the V2 stage. At the HALL site, soybean yield response to B application time, rate, or both may have been reduced from B applied to the surrounding field, which apparently drifted across the research plots. Had B drift not occurred at HALL, reduced vegetative growth (Table 3) due to early-season B deficiency suggests that early application of B would potentially have been more beneficial for grain yield at this site too. When B deficiency symptoms were absent, as at PTBS, B application time was either less important or more beneficial when applied at the onset of reproductive growth.


   CONCLUSIONS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
REFERENCES
 
Boron fertilization significantly increased soybean seed yields in three of four field studies by 4 to 130% above soybean receiving no B. When B deficiency was severe, early-season B fertilization prevented B deficiency and increased seed yields more than B applied during early reproductive growth. Although not conclusive, the data also suggest that application of B at the onset of early-reproductive growth to soybean with sufficient B concentrations may nominally increase seed yields. No single optimum B application rate was consistently identified by these studies, but application of 0.28 to 1.12 kg B ha–1 was generally adequate to produce near maximal seed yields. Soybean responded differently to B fertilization among the four sites, which contained different cultivars and management systems, but were grown on soils with similar chemical and physical properties.

Routine soil testing with the Mehlich-3 extractant is not able to distinguish between B-deficient and sufficient soils making tissue analysis the preferred method of identifying fields that may require B fertilization at the onset of reproductive growth. Low trifoliate B concentrations do not guarantee a significant yield increase from B fertilization but provide some evidence about the plant's B nutritional status. Boron applied at the onset of reproductive growth may be less convenient and more expensive compared with applications made pre-plant or during early vegetative growth because other fertilizers or crop protectants compatible for blending or mixing B with are seldom applied late in the growing season. Research should be continued to develop a soil property-plant response database, which may be useful for correlation of routine soil-test results with plant response to B fertilization so that B-deficient soils can be identified.

Boron fertilization increased B concentration in trifoliate leaves at the R2 stage and in soybean stalks and seed at maturity. When B deficiency was severe, B applied at the onset of reproductive growth was translocated to developing seeds more efficiently than B applied shortly after soybean emergence. The B concentration of soybean seed can be increased through fertilization and might be a means of improving crop tolerance to early-season B deficiency. Further research should be conducted to investigate whether seed with sufficient to high B concentrations can be planted to reduce the risk of B deficiency. Also, if tissue analysis is more accurate for identifying B-deficient soils than soil analysis, a better understanding of seasonal B uptake and tissue B concentrations of soybean is warranted. Although the current critical trifoliate leaf B concentration at the R2 growth stage of 20 mg B kg–1 seems to be reasonably accurate, tissue B concentrations from earlier growth stages may be correlated with plant response to B fertilization. Collection of soybean tissue samples during vegetative growth would allow a wider window of time for samples to be analyzed and growers to make timely foliar applications of B before seed yield losses attributed to B deficiency occur.


   ACKNOWLEDGMENTS
 
Appreciation is extended to the Arkansas Soil Test Review Board, U.S. Borax Inc., and Potash and Phosphate Institute/Foundation for Agronomic Research for financial support of this research. Special thanks are extended to the growers and county Extension Agents for their assistance in furnishing labor, land, and resources for this research.


   NOTES
TOP
 NOTES
ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Contribution of the Univ. of Arkansas Agric. Exp. Stn.


   REFERENCES
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 




This article has been cited by other articles:


Home page
 jashsHome page
S. Mishra, S. Heckathorn, J. Frantz, F. Yu, and J. Gray
Effects of Boron Deficiency on Geranium Grown under Different Nonphotoinhibitory Light Levels
J. Amer. Soc. Hort. Sci., March 1, 2009; 134(2): 183 - 193.
[Abstract] [Full Text] [PDF]

This Article
Right arrow Abstract Freely available
Right arrow Figures Only
Right arrow Full Text (PDF) Free
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in Web of Science
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Web of Science (2)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Ross, J. R.
Right arrow Articles by DeLong, R. E.
Right arrow Search for Related Content
PubMed
Right arrow Articles by Ross, J. R.
Right arrow Articles by DeLong, R. E.
Agricola
Right arrow Articles by Ross, J. R.
Right arrow Articles by DeLong, R. E.
Related Collections
Right arrow Soybean
Right arrow Nutrient Management
Right arrow Plant Nutrition
Right arrow Production Agriculture

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
The SCI Journals Crop Science Vadose Zone Journal
Journal of Natural Resources
and Life Sciences Education		 Soil Science Society of America Journal
Journal of Plant Registrations Journal of
Environmental Quality		 The Plant Genome