Published online 8 January 2009
Published in Agron J 101:120-123 (2009)
DOI: 10.2134/agronj2008.0123
© 2009 American Society of Agronomy
677 S. Segoe Rd., Madison, WI 53711 USA
Main-Stem Node Removal Effect on Soybean Seed Yield and Composition
Shawn P. Conleya,*,
Palle Pedersenb and
Ellsworth P. Christmasc
a Dep. of Agronomy, Univ. of Wisconsin, 1575 Linden Dr., Madison, WI 53706
b Dep. of Agronomy, Iowa State Univ., 2104 Agronomy Hall, Ames, IA 50011-1010
c Dep. of Agronomy, Purdue Univ., 815 W. State St., West Lafayette, IN 47907
* Corresponding author (spconley{at}wisc.edu).
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ABSTRACT
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Hail injury to soybean [Glycine max L. (Merr.)] is common across the United States. Currently, U.S. hail adjusters use procedures that assume that yield reductions caused by stem cutoff and defoliation or defoliation without stem loss is similar during the vegetative development period. Our hypothesis was that seed yield will be affected by timing of node removal in vegetative soybean and that main-stem node removal will influence seed composition. Research was conducted in Indiana and Iowa from 2003 to 2005 to test if removing 0, 20, 40, 60, 80, or 100% of nodes at V2, V6, or R3 development stages affects seed yield and grain composition. In Indiana, imposing node removal at the V2 stage resulted in 15.9% greater yield than imposing at the V6 stage. In Iowa, imposing node removal at the V2 stage on the average resulted in 24.9 and 46.1% greater seed yield than imposing node removal at the V6 or R3 stages, respectfully. Seed mass was 7.7% greater when comparing the V2 to the V6 node removal timing in Indiana. In Iowa, seed mass decreased 7.0% when 60% of the nodes were removed at V6 and 5.6% when 20% of the nodes were removed at R3. Soybean oil content was only affected by extreme node removal treatments while protein content was unaffected. Our results indicate that the soybean development stage that node removal occurs must be considered when estimating soybean seed yield loss and that an oil content adjustment is not needed to properly compensate growers for economic losses caused by node removal.
Received for publication April 18, 2008.
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INTRODUCTION
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HAIL DAMAGE is common across many soybean producing areas in the United States (National Crop Insurance Service, 2008, Acres insured-NCIS Premium Line; unpublished internal document). Since 2003 the National Crop Insurance Service has paid claims on an average of 2.3 million acres of soybean per year at an average cost of $53.5 million. With increasing global temperatures, more extreme and unpredictable weather patterns have been suggested; therefore; grower risk for severe hail damage may increase (Kajfez Bogataj, 2005).
Soybean yield loss associated with hail injury varies with injury timing and the type and severity of injury. Yield reductions associated with plant injury tend to be greater during reproductive development stages than during vegetative development stages (Weber, 1955; Fehr et al., 1983; Conley et al., 2008). Hunt et al. (1994) concluded that removal of leaf area delayed the time to achieve a critical leaf area index of 3.5, thus limiting light interception and dry matter accumulation. Haile et al. (1998) and Singer (2001) reported similar observations.
The effect of defoliation coupled with loss of main-stem nodes during vegetative development is not well understood. Fehr et al. (1983) found that removing a portion of the main stem decrease seed yield, but defoliation without stem removal at the same development stage had no significant effect on seed yield. Hintz and Fehr (1990) found that complete defoliation during vegetative development at V3 and V6 did not reduce seed yield, however stem removal did lower seed yield. In contrast Hintz et al. (1991) reported that yield loss was similar between stem removal and defoliation treatments when removed in the mid- to late-vegetative development stages of indeterminate cultivars.
Soybean is the most valuable oilseed crop in the world and the value of seed is determined based on the seed composition. Today, more than one-third of the world's edible oils and two-thirds of the world's protein meal are derived from soybeans (Golbitz, 2004). Agronomic decisions can affect seed yield and composition but often at a lower level than cultivar selection (Osler and Carter, 1954; Pedersen and Lauer, 2003; Temperly and Borges, 2006).
Data from many of the previously described studies have been incorporated into current crop insurance adjustment tables (Fehr et al., 1983; Hintz and Fehr, 1990; Hintz et al., 1991). United States hail adjusters using these procedures assume that yield reductions caused by stem cutoff and defoliation or defoliation without stem loss is similar during the vegetative development period (National Crop Insurance Services, 2007). Lack of information on current cultivars and production practices exists regarding multiple levels of stem cut-off during either vegetative or reproductive development stages. In addition, no work has been documented on the impact of stem cut-off on seed composition. Our hypothesis is that seed yield will be affected by timing of node removal in vegetative soybean and that main-stem node removal will influence seed composition. The objective of this study was to determine the effect of node removal on yield and seed composition of vegetative- and reproductive-stage soybean.
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MATERIALS AND METHODS
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Field experiments were conducted in 2003 to 2005 at the Purdue University Agronomy Center for Research and Extension located near West Lafayette, IN and at the Iowa State Agronomy Farm located near Ames, IA. The soil was a Chalmers silty clay loam (fine-silty, mixed, superactive, mesic Typic Endoaquolls) at West Lafayette and a Clarion fine loam (fine-loamy, mixed, superactive, mesic Typic Haplaquolls) at Ames. The experimental design at both locations was a randomized complete block factorial with four replications. Treatments were a factorial arrangement of development stage of main-stem node removal (V2 and V6 at West Lafayette and V2, V6, R3 at Ames; Fehr and Caviness, 1977) and percent main-stem node removal (0, 20, 40, 60, 80, and 100%). Plot size of the experimental unit was 3 by 7.6 m.
The soybean cultivar AG3701 (Monsanto Company, St. Louis, MO) was planted no-till at 4-cm depth in six rows spaced 38-cm apart at West Lafayette using a Great Plains no-tillage drill (Great Plains Mfg. Inc., Salina, KS). At Ames, the soybean cultivar AG2905 (Monsanto Company, St. Louis, MO) was inoculated with Bradyrhizobium japonicum (EMD Crop Biosciences, Milwaukee, WI) and was planted in four rows spaced 76-cm apart at 4-cm depth using a John Deere MaxEmerge planter (John Deere, Moline, IL). At Ames, tillage was accomplished by chisel plowing in the fall and field cultivation twice in the spring before planting. AG3701 and AG2905 are indeterminate soybean cultivars.
Soybean was planted in the first week of May each year at both locations. Plots were over-seeded to assure adequate populations for the various treatments. Shortly after emergence, soybean seedlings were hand thinned to a final population of 330,000 plants ha–1. At each node removal timing, the total number of nodes per plot was calculated by multiplying the number of plants per plot by the average number of nodes per plant. Nodes above the unifoliate node were counted only if the trifoliolate at that node was considered open (Ritchie et al., 1994). Then, knowing the total number of nodes per plot, we randomly imposed the node removal treatments (0, 20, 40, 60, 80, and 100%) on each plot using hand clippers. Plants were cut at various heights and the number of nodes removed was noted until the removal equaled the assigned number for that plot treatment. For the purposes of this experiment no plants were cut below the cotyledon node, as plant death would occur; therefore these nodes were not factored into the node removal calculations.
Weed control was accomplished at both locations with 1.12 kg a.i. ha–1 of glyphosate [N-(phosphonomethyl) glycine] applied two times each season. Escaping weeds were removed by hand. All fertility management practices were conducted according to Purdue University and Iowa State University recommended practices (Gerber et al., 2008; Sawyer et al., 2002).
Data Collected
Seed yield was calculated by harvesting the center 1.5 by 7.6 m of each plot. Seed was harvested using a Wintersteiger plot combine (Wintersteiger Int., Kollmering, Germany) at West Lafayette and an Almaco plot combine (Almaco, Nevada, IA) at Ames. Seed yield was adjusted to a moisture content of 130 g kg–1. Following harvest a subsample of seed from each plot was collected to calculate seed mass (g 100 seeds–1) and seed oil and protein content (g kg–1). Oil and protein concentrations were determined by near-infrared spectroscopy at the Purdue University and at the Iowa State University Grain Quality laboratory.
Statistical Analysis
Experimental error variances were heterogeneous between West Lafayette, IN and Ames, IA therefore; location-specific analyses were conducted. All of the data were subjected to an analysis of variance using the PROC MIXED procedure of SAS (SAS Institute, Cary, NC). The level of significance was defined at P 
0.05. Mean comparisons were made using Fisher's protected LSD test. All effects except replicates and years were considered fixed in determining the expected mean squares and appropriate F tests in the analysis of variance. Seed yield was regressed on percent main-stem node removal using the REG procedure of SAS. Linear, quadratic, log-linear, and the Gompertz models were compared. Model selection was based on model significance, maximization of the coefficient of determination (R2), and an assessment of the residuals.
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RESULTS AND DISCUSSION
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Environment—West Lafayette and Ames
Environmental conditions differed among years at West Lafayette and Ames (Table 1
). Average air temperatures were lower in August 2004 than in 2003 or 2005 at West Lafayette and Ames. Early season (April through June) rainfall was greater in 2004 at West Lafayette; whereas August rainfall was greater in 2004 and 2005 than 2003 at Ames. The favorable environmental conditions in 2004 likely contributed greatly to the state record soybean yields that were achieved in Iowa and Indiana during that year (National Agriculture Statistics Service, 2008).
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Table 1. Mean monthly air temperature and total rainfall at West Lafayette, IN and Ames, IA in the 2003–2005 soybean growing seasons.
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West Lafayette, Indiana
Main-stem node removal x node removal timing interactions were significant for seed yield (P < 0.0001). Seed yield decreased as percent node removal increased at each removal timing, but regression analysis indicated a nonlinear response to percent main-stem node removal at V2 soybean (P < 0.0001) and a quadratic response at V6 soybean (P < 0.0001) (Fig. 1
). Seed yield was reduced when 
60% of nodes were removed at V2 soybean and when 40% of nodes were removed at V6 soybean. Coefficient of determination values indicated a strong relationship between seed yield and percent main-stem node removal at each node removal timing.
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Fig. 1. Percent main-stem node removal and node removal timing effect on soybean seed yield at (A) West Lafayette, IN and (B) Ames, IA averaged across the 2003–2005 soybean growing seasons.
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Main-stem node removal x node removal timing interactions were also significant for oil content (P = 0.0013). Soybean oil content was not affected when nodes were removed at V2 soybean; however, oil content decreased 6.1 to 8.3% when 100% of the nodes were removed at V6 soybean (Table 2
). Percent node removal treatments did not affect seed mass or protein content; however averaged over node removal treatments seed mass was 7.7% greater at the V2 (12.7 g 100–1 seeds) than the V6 node removal timing (12.4 g 100–1 seeds).
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Table 2. Effect of main stem node removal imposed at selected stages of development on seed mass and percent oil content at Ames, IA and West Lafayette, IN averaged across the 2003–2005 soybean growing seasons.
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Ames, Iowa
Main-stem node removal x node removal timing interactions were significant for seed yield (P < 0.0001). Seed yield decreased as percent node removal increased at each removal timing, but regression analysis indicated a linear response to percent main-stem node removal at V2 soybean (P = 0.0005), a nonlinear response at V6 soybean (P < 0.0001), and a quadratic response at R3 soybean (P < 0.0001) (Fig. 1). Seed yield was reduced when 80% of nodes were removed at V2 soybean, 40% of nodes were removed at V6 soybean, and when 20% of nodes were removed at R3 soybean. Coefficient of determination values indicated a strong relationship between seed yield and percent main-stem node removal at each node removal timing.
Main-stem node removal x node removal timing interactions were also significant for seed mass (P = 0.009) and oil content (P = 0.0197). Seed mass was not affected when nodes were removed at V2 soybean; however seed mass decreased when 60 and 20% or more of the nodes were removed at V6 and R3 soybean, respectively (Table 2). Soybean oil content was lowered 3.1% when 100% of the nodes were removed at V2 soybean and 3.6% when 80% of the nodes were removed at V6 soybean. Node removal at R3 soybean did not affect soybean oil content. Percent node removal or node removal timing treatments did not affect protein content.
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DISCUSSION
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Our data confirm that soybean development stage affects the yield response to percent node removal. These results differ from those reported by Hintz and Fehr (1990) and Hintz et al. (1991), both of whom stated that stage of soybean development was not a critical factor in estimating yield loss from stem cut-off and defoliation during mid- to late-vegetative development of indeterminate cultivars. Our differences may partially be due to greater yield potential in today's elite soybean cultivars. Frederick et al. (1991) reported a 31 and 9% yield increase when comparing modern vs. old cultivars in an irrigated vs. drought-stressed environment, respectfully. Frederick et al. (1991) attributed the yield increase to a greater number of pods and increased vegetative biomass in the modern cultivars. Based on our treatments it is speculated that yield losses from node removal at late vegetative and early reproductive development stages will accrue greater yield loss as we directly affected the pod formation sites (i.e., nodes) and decreased vegetative biomass and leaf area.
Seed mass was 7.7% greater when comparing the V2 to the V6 node removal timing at West Lafayette. At Ames, seed mass decreased 7.0% when 60% of the nodes or greater where removed at V6 and 5.6% when 20% of the nodes or greater where removed at R3. These results differ from those reported by Hintz and Fehr (1990) where they found no differences in seed mass between node removal timings.
Soybean oil content response to percent node removal varied among node removal timings and locations, but in general oil content decreased only slightly as percent node removal increased. These results are similar to those reported by McAlister and Krober (1958) where they reported a 1.3% reduction in oil content when 80% of leaves were removed at R4 (full pod) soybean. In contrast, Conley et al. (2008) found that soybean seed oil content increased 1.7% when 75% of plants were removed at the V3, V6, R1, and R3.5 soybean development stages. The treatments in this experiment and the Conley et al. (2008) experiments however, differ greatly. In this experiment nodes were physically removed from individual plants. The physical removal of nodes reduced the total node number per area which lead to significant plant injury (both main-stem and leaf area loss) and stress. In contrast, Conley et al. (2008) removed whole plants from the plant canopy. Whole plant removal would modify the soybean canopy in a different manner than in this experiment. In both cases, however modifying the soybean canopy altered light penetration, yield components, and seed composition. Although significantly different, the results of this experiment suggest that such small changes in oil content due to node loss do not necessitate additional price premium adjustments to properly compensate growers for economic losses due to hail damage.
Protein content was not affected by percent node removal and only slightly affected by node removal timing at West Lafayette. These results are similar to those reported by Conley et al. (2008).
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CONCLUSIONS
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Our results demonstrate that soybean seed yield response to percent main-stem node removal treatments differ between early to mid-season vegetative and reproductive node removal timings. This suggests that separate yield loss equations may be required to accurately predict soybean seed yield loss estimates. Our results also suggest that an oil content adjustment is not needed to properly compensate growers for economic losses due to node removal that occurs during the vegetative and early reproductive developmental stages of soybean.
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ACKNOWLEDGMENTS
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The author's thank hail adjusters from Indiana and Iowa for helping with the node removals and the National Crop Insurance Service, Purdue University Agricultural Experiment Stations, and the Iowa State Agricultural Experiment Stations for financial support.
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NOTES
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All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher.
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ABSTRACT
INTRODUCTION
