Maturity Group VI Research Articles

Soybean test weight in relation to genotype, environment, and genotype × environment interaction in the Southern United States

AbstractTest weight (TW) is a unit of bulk density that is influenced by several factors, including both genetics and environment. A subset of the trials in the Uniform Soybean Tests—Southern States was used to correlate seed composition traits of oil and protein percentages, and seed weight (SW) with TW to investigate the interaction of these traits in multi‐environments for four different maturity group (MG) tests. The results indicate that environment (location and year combination) had a larger impact on TW than genetic effect in all MG tests. This difference was greater in the earlier MGs, compared to MG VI and MG VII. In all tests across four MGs, the genotype interaction with environment effect was significant, but practically was not as important as genotype or environment effects. Significant negative correlations between TW and SW (MG V, VI, and VII tests), and TW and oil (MG V and VI tests) were observed but not consistent in all environments within these tests. TW and protein correlations were inconsistent with a negative relationship in MG V but a positive relationship in MG VII. As anticipated, the inconsistencies in the relationships across MGs for TW and seed composition traits suggest that selection strategies for improving TW will differ across soybean breeding programs. In the future, a similar study using a diverse panel of cultivars that do not change from year to year may shed more light on the influence of seed composition and environmental conditions on TW.

Registration of USDA‐N6006 soybean germplasm combining high yield, flood tolerance, and elevated oil content

AbstractUSDA‐N6006 soybean [Glycine max (L.) Merr.] (Reg. no. GP‐527, PI 704140) is a conventional F4–derived early maturity group (MG) VI germplasm jointly released by USDA‐ARS and North Carolina Agricultural Research Service in 2023. USDA‐N6006 is the first MG VI, publicly released germplasm that combines flood tolerance with high‐yield lodging resistance, and elevated seed oil. Over 19 environments of the MG VI USDA Southern Uniform Soybean Trials (2017–2018), seed yield of USDA‐N6006 (3393 kg ha−1) was similar to high‐yielding lodging‐resistant check cultivars ‘NC‐Dunphy’ (3427 kg ha−1) and ‘NC‐Dilday’ (3475 kg ha−1). It matured 1 day earlier than NC‐Dunphy and exhibited similar lodging scores. Over 5 years of testing in North Carolina (2016–2019), USDA‐N6006 exhibited very robust flood tolerance. Mean flooding scores were numerically or statistically (p < 0.05) superior to the four flood‐tolerant controls at both V4 and R1 growth stages. USDA‐N6006 was not intentionally bred to be flood tolerant and identified as such only through an extensive screening of “in house” USDA breeding lines. USDA‐N6006 and most of its antecedents are unique in that they are derived from unreleased breeding lines developed at the flood prone Tidewater Research station in North Carolina. Inadvertent selection for flood tolerance may have been a part of the USDA's long‐term breeding effort to improve yield. Seed oil content of USDA‐N6006 (237 g kg−1) was similar to that of elevated seed oil cultivar NC‐Dilday, but significantly higher than NC‐Dunphy (228 g kg−1) in the Uniform Trials. Seed protein content and estimated meal protein contents of USDA‐N6006 (389 g kg−1 and 46.4%, respectively) were similar to that of NC‐Dunphy. USDA‐N6006 should be excellent parental stock for applied breeding in the southern United States.

Genetic mapping and confirmation of the Rdm3 locus underlying resistance to southern stem canker in soybean

AbstractSouthern stem canker (SSC) in soybean [Glycine max (L.) Merrill], caused by the fungal pathogen Diaporthe aspalathi, is a major disease in the southern United States. It can cause up to 80% yield loss in severely infected fields. Plant introduction (PI) 398469, a Maturity Group VI soybean accession from South Korea, is one of six known sources of resistance to SSC. To determine the genetics of the resistance provided by PI 398469, F2:3 and F5‐derived recombinant inbred line (RIL) populations were developed from a cross with the susceptible breeding line G81‐2057. Both populations were phenotyped in the greenhouse using a modified toothpick method. The SSC‐resistant and susceptible DNA bulks consisting of 20 resistant and 18 susceptible families were created from the F2:3 population and genotyped using the Infinium SoySNP50K BeadChips for a bulked segregant analysis (BSA). Based on BSA results, 22 Kompetitive allele specific polymerase chain reaction (KASP) markers were designed to genotype the RIL population. Quantitative trait locus (QTL) analysis identified qRdm_14, on chromosome (Chr) 14 with an R2 of 62%. Linkage mapping in the F2:3 population confirmed the presence of a QTL on Chr 14. F5‐derived RILs derived from G81‐2057 × Crockett were phenotyped for SSC resistance and genotyped with the KASP markers to examine the relationship between Rdm3 from Crockett and qRdm_14 from PI 398469. Both PI 398469 and Crockett carried realleles at the Rdm3 locus for resistance to SSC. The QTL and KASP marker information could be used to screen breeding lines for resistance to SSC.

Registration of USDA‐N6005 germplasm combining high yield, elevated protein, and 25% pedigree from Japanese cultivar Tamahikari

AbstractUSDA‐N6005 soybean [Glycine max (L.) Merr.] (Reg. no. GP‐442, PI 696388), is an F5–derived early maturity group (MG) VI germplasm jointly released by the USDA–ARS and North Carolina Agricultural Research Service in January 2021. USDA‐N6005 is a genetically diverse germplasm with 25% of its pedigree from Japanese cultivar Tamahikari and has high yield potential coupled with elevated seed and meal protein content. USDA‐N6005 is the first MG VI release derived from Tamahikari. In the USDA Uniform Tests–Southern States during 2017–2018, USDA‐N6005 yielded 102, 103, and 102% of the check cultivars NC‐Dunphy, NC‐Dilday, and NC‐Roy, respectively. It had significantly better lodging resistance (1.5) than NC‐Roy and NC‐Dilday (2.6 and 2.5, respectively). The seed protein content on a dry basis of USDA‐N6005 (424 g kg–1) was significantly higher than that of NC‐Dunphy and NC‐Dilday (392 and 383 g kg–1, respectively). The estimated meal protein content (49.0%) of USDA‐N6005 was significantly higher than that of NC‐Dunphy and NC‐Dilday (46.2 and 45.5%, respectively). Across the five environments of the 2016 USDA Preliminary Tests–Southern States, USDA‐N6005 yielded 100 and 102% of check cultivars AG6534 and NC‐Roy, respectively. This release should help to reverse the declining trend in genetic diversity and seed protein of U.S. soybean cultivars without negative impact on seed yield.

Registration of USDA‐N6003LP Soybean Germplasm with Low Seed Phytate

Soybean [Glycine max (L.) Merr.] meal is the main source of protein in poultry and swine rations worldwide. Phytate, the main storage form of phosphorous in soybean meal, is largely indigestible by monogastric animals and, thus, a major concern both for nutrition and for environmental pollution. USDA‐N6003LP (Reg. no. GP‐435, PI 689999) is a low‐phytate (LP) determinate, lodging‐resistant early maturity group (MG) VI soybean germplasm developed and released jointly by the USDA‐ARS and the North Carolina Agricultural Research Service. USDA‐N6003LP is derived from a backcross (BC1) between recurrent parent ‘NC‐Roy’ and LP donor line USDA CX1834. NC‐Roy is a high‐yielding MG VI cultivar adapted to the southern United States. USDA‐N6003LP has 60% lower phytate and 4.8 times higher inorganic phosphorus (Pi) contents in its seed than the seed of NC‐Roy. It matures approximately 5 d earlier and has larger seed size and better lodging resistance (P < 0.05) compared with NC‐Roy. Across 17 environments in the USDA Uniform Soybean Tests, Southern States and over four local yield trials in North Carolina, USDA‐N6003LP yielded 91 and 97% of NC‐Roy, respectively. Field emergences of this line in four tests in NC were 79 to 80% compared with 89 to 90% for NC‐Roy. USDA‐N6003LP is the first early MG VI LP germplasm release with good agronomic performance and relatively normal field emergence. It will be useful as parental stock for soybean breeders interested in developing LP soybean cultivars.

Phenology and Seed Yield Performance of Determinate Soybean Cultivars Grown at Elevated Temperatures in a Temperate Region.

Increased temperature means and fluctuations associated with climate change are predicted to exert profound effects on the seed yield of soybean. We conducted an experiment to evaluate the impacts of global warming on the phenology and yield of two determinate soybean cultivars in a temperate region (37.27°N, 126.99°E; Suwon, South Korea). These two soybean cultivars, Sinpaldalkong [maturity group (MG) IV] and Daewonkong (MG VI), were cultured on various sowing dates within a four-year period, under no water-stress conditions. Soybeans were kept in greenhouses controlled at the current ambient temperature (AT), AT+1.5°C, AT+3.0°C, and AT+5.0°C throughout the growth periods. Growth periods (VE–R7) were significantly prolonged by the elevated temperatures, especially the R1–R5 period. Cultivars exhibited no significant differences in seed yield at the AT+1.5°C and AT+3.0°C treatments, compared to AT, while a significant yield reduction was observed at the AT+5.0°C treatment. Yield reductions resulted from limited seed number, which was due to an overall low numbers of pods and seeds per pod. Heat stress conditions induced a decrease in pod number to a greater degree than in seed number per pod. Individual seed weight exhibited no significant variation among temperature elevation treatments; thus, seed weight likely had negligible impacts on overall seed yield. A boundary line analysis (using quantile regression) estimated optimum temperatures for seed number at 26.4 to 26.8°C (VE–R5) for both cultivars; the optimum temperatures (R5–R7) for single seed weight were estimated at 25.2°C for the Sinpaldalkong smaller-seeded cultivar, and at 22.3°C for the Daewonkong larger-seeded cultivar. The optimum growing season (VE–R7) temperatures for seed yield, which were estimated by combining the two boundary lines for seed number and seed weight, were 26.4 and 25.0°C for the Sinpaldalkong and Daewonkong cultivars, respectively. Considering the current soybean growing season temperature, which ranges from 21.7 (in the north) to 24.6°C (in the south) in South Korea, and the temperature response of potential soybean yields, further warming of less than approximately 1°C would not become a critical limiting factor for soybean production in South Korea.

Registration of G08PR‐394 and G09PR‐80 Soybean Germplasm Lines with Diverse Pedigrees

Increasing soybean [Glycine max (L.) Merr.] yield is a major goal of soybean breeding programs. Expanding the genetic diversity of the elite U.S. soybean gene pool is essential to maintain or increase the current rate of genetic gain for seed yield due to the current narrow genetic base of existing elite soybean germplasm. To increase the genetic diversity of southern U.S. soybean cultivars, two soybean lines—G08PR‐394 (Reg. No. GP‐380, PI 667741) and G09PR‐80 (Reg. No. GP‐381, PI 667742)—were developed and released by the University of Georgia agricultural experiment stations. G08PR‐394 is an F5 plant selection from ‘5601T’ × R01‐3637F and has 25% of its pedigree from a Japanese cultivar Misuzu Daizu (PI 423912). G08PR‐394 is a maturity group VI line that yielded 2, 4, and 20% greater than the seed yield of check genotypes: N6202, ‘Young’ and ‘N6201’. G09PR‐80 is an F5 plant selection from the 5601T × PI 157440 cross having 50% of its pedigree from a South Korean accession (PI 157440). G09PR‐80 is a maturity group V line that produced 95, 93, 87, and 84% of the seed yield of the check genotypes: ‘Dillon’, ‘Hutcheson’, JTN‐5503, and its elite parent 5601T. G09PR‐80 is resistant to bacterial pustule [caused by Xanthomonas campestris pv. glycines (Nakano) Dye] and southern root‐knot nematode [Meloidogyne incognita (Kofoid & White) Chitwood]. Based on their broad diversity and favorable yield potential, these lines could be used as parents to enhance genetic diversity and develop commercial cultivars.

Effects of Genetics and Environment on Fatty Acid Stability in Soybean Seed

Although seed oil production and composition are genetically controlled, changes of oil level and oil composition across genotypes and environments such as drought and temperature were observed. The mechanisms of how genotypes interact with environment, affecting oil production and composition, are still not well understood. The objective of this research was to investigate the effect of drought/water stress and temperature on soybean genotypes. Two soybean genotypes of maturity group (MG) II (PI 597411 B and PI 597408) and two of MG VI (Arksoy and PI 437726) were used. A repeated greenhouse experiment to study the effect of water stress and a repeated growth chamber experiment to study the effect of temperature were conducted. The results showed that both water stress and high temperature altered seed oil composition by increasing oleic acid and decreasing linoleic and linolenic acid concentrations. Severe water stress (soil water potential between -150 to -200 kPa) or high temperature (40/33℃, day/night) resulted in higher palmitic acid and lower stearic acid. Genotypes differed in their responses to water stress or temperature. Analyses of seed carbohydrates (glucose, fructose, sucrose, raffinose, and stachyose) showed a significant decline of glucose, fructose, and sucrose and a significant increase of stachyose concentration by water stress and high temperature. Analyses of natural abundance of δ15N and δ13C isotopes showed changes in sources of nitrogen and carbon fixation, possibly affecting nitrogen and carbon metabolism pathways. The research demonstrated that both water stress and high temperature altered oil production and composition, and this could be partially related to limited availability and movement of carbohydrates from leaves to seed. Further research to investigate the enzymes controlling fatty acids conversion and nitrogen and carbon metabolism is needed.

Resistance to Frogeye Leaf Spot in Selected Soybean Accessions in MG I through MG VI

Frogeye leaf spot (FLS) caused by Cercospora sojina Hara is a disease of soybean [Glycine max (L.) Merr.] that causes significant seed yield loss in warm, humid environments worldwide. The Rcs3 gene in soybean has been reported to condition resistance to all known races of C. sojina. The objectives of this study were to: (i) identify maturity group (MG) I to VI accessions resistant to C. sojina race 11 by field screening at two locations; and (ii) determine if the FLS resistance of the symptomless soybean accessions is likely to be conditioned by the Rcs3 allele. A total of 260 accessions including 12 differentials were evaluated for reaction to race 11 in field trials in Missouri and Illinois during 2009, and 20 accessions that did not develop symptoms were retested in 2010 to validate their resistance. The 20 accessions remained resistant and were tested for the potential presence of Rcs3 allele using molecular markers; and none was predicted to carry the Rcs3 allele. These accessions may contain novel loci for FLS resistance and may be used to broaden the base for developing soybean cultivars with frogeye leaf spot resistance. Accepted for publication 16 April 2012. Published 21 May 2012.

Soybean Seed Phenol, Lignin, and Isoflavones Partitioning as Affected by Seed Node Position and Genotype Differences

Factors controlling the production and partitioning of seed phenolics within soybean are not understood. Understanding these factors may justify selection for higher levels of seed phenolics because of their beneficial impact on human health and soybean defense mechanism against diseases. The objective of this research was to investigate the partitioning of seed phenolics (phenol, lignin, and isoflavones) along the main stem of soybean genotypes. A repeated green- house experiment was conducted on different soybean genotypes of different maturity and different stem archi-tecture (determinate and indeterminate). Genotypes were DT 97-4290, maturity group (MG) IV; Stressland, MG IV; Hutcheson, MG V; and Tracy-M, MG VI. Seed were harvested from top and bottom nodes at seed-fill stage (R6) and harvest ma- turity stage (R8). At R6, seed phenolic compounds (phenol, lignin, and isoflavones daidzein, genistein, and glycitein) were greater in the bottom seed than the top seed. This trend was observed in DT 97-4290, Tracy-M, and Hutcheson, but not in Stressland. Also, this trend was more obvious with daidzein and genistein isoflavones than glycitein. The maximum phenolic compounds were recorded at R8. The higher phenolic compounds concentration in bottom seed than in top seed was accompanied by higher cell wall boron (B) percentage and lower total B in bottom seed. The current research demonstrated that phenolic compounds partitioned differently between the top and bottom seed nodes. This trend cannot be generalized in soybean genotypes unless enough germplasm is tested. The partitioning of higher phenolic compounds concentration along the main stem would allow for single seed selection in the breeding program for higher levels of phenolic compounds and for accurate measurements of seed phenolics in breeding lines. The associa- tion of B trend with phenolic compound trend may suggest B involvement in phenolic metabolism, and support the structural role of B. Breeding for higher levels of phenolics, especially isoflavones, would benefit human health, pro- vide higher nutritional value of soy meal, and increase plant disease resistance.

Registration of R99–1613F, R01–2731F, and R01–3474F Soybean Germplasm Lines with Diverse Pedigrees

R99–1613F (Reg. No. GP‐372, PI 659987), R01–2731F (Reg. No. GP‐374, PI 659989), and R01–3474F (Reg. No. GP‐373, PI 659988) soybean [Glycine max (L.) Merr.] were developed by the Arkansas Agricultural Experiment Station, Fayetteville, AR and were released as high‐yielding conventional germplasm lines with 50% diverse pedigrees. R99–1613F is an F4 plant selection from the cross between ‘NK RA 452’ and PI 290126B. It is an indeterminate maturity group (MG) IV line with a yield potential similar to that of the popular Roundup Ready cultivar ‘AG4403’. R01–2731F is a determinate MG VI line derived from the cross ‘Caviness’ × PI 592947. Yield potential of R01–2731F is similar to or greater than conventional MG VI cultivar ‘Dillon’. R01–3474F was derived from Caviness × PI 594208. It is a determinate MG V line with a yield potential similar to that of the high‐yielding conventional cultivar ‘5601T’. These germplasm lines can be used as elite parents to improve yield and to enhance genetic diversity.

Application Timing of Harvest Aid Herbicides Affects Soybean Harvest and Yield

Research was conducted over 2 yr to evaluate soybean response to harvest aid herbicide treatments paraquat at 0.28 kg ai ha−1, paraquat with carfentrazone at 0.014 kg ai ha−1, and sodium chlorate at 6.72 kg ai ha−1. Indeterminate and determinate soybean cultivars were treated when moisture of seed collected from the uppermost four nodes of plants averaged 60, 50, 40, 30, and 20% (± 2%). For each soybean cultivar, the harvest aid treatment by application timing interaction was not significant, and data for harvest aid treatments were averaged. Application of harvest aid at 60% average seed moisture reduced yield for the maturity group (MG) IV indeterminate cultivar 15.4% compared with the nontreated; 100-seed weight was reduced 12.4%. Yield and seed weight were not negatively affected when harvest aid was applied at 50% average seed moisture and soybean was harvested 14 and 15 d before the nontreated control. Although planting date in the 2 yr for the indeterminate cultivar differed by 26 d, number of days from planting to harvest aid application at 50% average seed moisture was 112 and 116 d. For MG V and MG VI determinate cultivars, application of harvest aid at 60% average seed moisture reduced yield compared with the nontreated control 22 and 18.1%, respectively, and at 50% average seed moisture 15.6 and 4%, respectively; seed weight reductions of 8.9 to 33.3% accompanied the yield reductions of the two cultivars. Reduction in soybean yield and seed weight was not observed when harvest aid was applied at 40% average seed moisture, and harvest for the 2 yr was 8 and 9 d earlier for the MG V cultivar and 10 and 14 d earlier for the MG VI cultivar.

Response of soybean genotypes to different irrigation regimes in a humid region of the southeastern USA

Studies on irrigation scheduling for soybean have demonstrated that avoiding irrigation during the vegetative growth stages could result in yields as high as those obtained if the crop was fully irrigated during the entire growing season. This could ultimately also lead to an improvement of the irrigation water use efficiency. The objective of this study was to determine the effect of different irrigation regimes (IRs) on growth and yield of four soybean genotypes and to determine their irrigation water use efficiency. A field experiment consisting of three IR using a lateral move sprinkler system and four soybean genotypes was conducted at the Bledsoe Research Farm of The University of Georgia, USA. The irrigation treatments consisted of full season irrigated (FSI), start irrigation at flowering (SIF), and rainfed (RFD); the soybean genotypes represented maturity groups (MGs) V, VI, VII, and VIII. A completely randomized block design in a split-plot array with four replicates was used with IR as the main treatment and the soybean MGs as the sub-treatment. Weather variables and soil moisture were recorded with an automatic weather station located nearby, while rainfall and irrigation amounts were recorded with rain gauges located in the experimental field. Samplings for growth analysis of the plant and its components as well as leaf area index (LAI) and canopy height were obtained every 12 days. The irrigation water use efficiency (IWUE) or ratio of the difference between irrigated and rainfed yield to the amount of irrigation water applied was estimated. The results showed significant differences (P < 0.05) between IR for dry matter of the plant and its components, canopy height, and maximum leaf area index as well as significant differences (P < 0.05) between MGs due to IR. Differences for the interaction between IR and MG were significant (P < 0.05) only for dry matter of pods and seed yield. In general, seed yield increased at a rate of 7.20 kg for each mm of total water received (rainfall + irrigation) by the crop. Within IR, significant differences (P < 0.05) on IWUE were found between maturity groups with values as low as 0.55 kg m-3 for MG V and as high as 1.14 kg m-3 for MG VI for the FSI treatment and values as low as 0.48 kg m-3 for maturity group V and as high as 1.02 kg m-3 for maturity group VI for the SIF treatment. We also found that there were genotypic differences with respect to their efficiency to use water, stressing the importance of cultivar selection as a key strategy for achieving optimum yields with reduced use of water in supplemental irrigation

Soybean seed protein, oil, fatty acids, N, and S partitioning as affected by node position and cultivar differences

The mechanisms controlling the partitioning of seed composition constituents along the main stem in soybean are still controversial. Therefore, the objective of this study was to investigate seed protein, oil, and fatty acids partitioning in soybean cultivars along the main stem. The cultivars were DT97-4290, maturity group (MG) IV; Stressland, MG IV; Hutcheson, MG V; TracyM, MG VI. Seeds were harvested based on position on the plant (top nodes, middle nodes, and bottom nodes). At R8 (physiological maturity stage), DT97-4290, Hutcheson, and Stressland had higher percentage of protein and oleic acid and lower percentage of oil and linolenic acid in top node seed compared with bottom node seed. The increase of protein in top node compared with the bottom node across the two experiments ranged from 15.5 to 19.5%, 7.0 to 10.5%, 14.2 to 15.8%, 11.2 to 16.5%, respectively for DT97-4290, Hutcheson, Stressland, and TracyM. Except for TracyM, the increase of oleic acid in the top node ranged from 45.4 to 93%, depending on the cultivar. Conversely, the decrease in the top node seed ranged from 14.4 to 26.8% for oil and from 5.7 to 34.4% for linolenic acid, depending on the cultivar. The partitioning trend of seed composition constituents at R6 (seed - fill stage) was inconsistent. Except for Stressland, seed oleic acid was higher at R6 than at R8. The higher protein and oleic acid concentrations in the top node seed was accom- panied by higher activity of nitrate reductase activity, higher chlorophyll concentration, higher nitrogen (N) and sulfur (S) percentages in the fully expanded leaves at R5-R6 growth stage, and higher seed nitrogen (N) and sulfur (S) percentages in DT 97-4290 and Stressland. The current research suggests that the partitioning of seed protein, oil, and fatty acids in nodes along the plant depended on the position of node on the main stem, cultivar differences, seed N and S status, and tissue N and S partitioning. The higher nitrate reductase activity at the top nodes, accompanied higher protein and oleic acid, and the changes of oleic acid at R6 and R8 along the stem, were not previously reported, and need further investigation. The current knowledge is useful for soybean germplasm selection for desirable traits such protein and oleic acid, and for accurate measurements of seed composition constituents in breeding lines.

Profit-maximizing seeding rates and replanting thresholds for soybean: Maturity group interactions in the Mid-South

Considerable interest in adopting earlier-maturing soybean [ Glycine max (L.) Merr.] cultivars exists among producers in the Mid-Southern United States, as the potential for irrigation water savings and improved labor and equipment scheduling are attractive. Previous reports suggested that maturity group (MG) selection should depend primarily upon yield and not irrigation requirements, as irrigation savings generally did not offset lower yield of earlier MG. This research, however, did not account for differences in seeding rate recommendations. This report considered results from a conventional soybean (MG 00 to MG VI) population density trial (seeded at 10–100 seeds m −2) conducted at Fayetteville, AR for 3 years. The analysis revealed that planting soybean at the economically optimal seeding rate can lead to substantially different investment in seed (an average of $97 ha −1 for MG 00 vs. $27 ha −1 for MG VI). The results also indicated that later-maturing soybean exhibited greater flexibility in environments with plant establishment uncertainty, as the yield response to plant population density was less pronounced and investment in seed was lower compared to earlier-maturing cultivars. Later-maturing varieties did exhibit larger changes in optimal seeding rates over time than earlier-maturing varieties, however. Based on our results, a producer would be advised to examine yield potential of different MG soybean and to consider planting a range of cultivars within MG II–VI. Finally, while the numeric results of this research were location and cost specific, the analyses provided guiding principles for other regions with similar characteristics for crop establishment and replanting thresholds.

Soybean Development in the Midsouthern USA Related to Date of Planting and Maturity Classification

Soybean (Glycine max) is planted from late March through June in the midsouthern USA. Different developmental patterns that result from this range in planting dates will affect management decisions. Irrigated field studies were conducted at Stoneville, MS (33° 26′N) from 1979 through 2003 to determine effect of late March through June planting dates on developmental patterns of maturity group (MG) IV through MG VI soybean. In all plantings, time from planting to beginning bloom (R1) increased as MG increased from IV to VI. Time from R1 to full seed (R6; pod cavity filled) was sometimes but not always different among the MGs, and differences were always ≤ 7 days. The major difference in the length of growing season among cultivars of different MGs occured before reproductive development began regardless of planting date. Thus, performance of soybean cultivars of disparate MGs should not be affected by differences in time between stages of reproductive development, but rather by when the stages occur.

Reduced Seeding Rate for Glyphosate‐Resistant, Drilled Soybean on the Southeastern Coastal Plain

Seeding‐rate recommendations for narrow‐row (&lt;76 cm) soybean [Glycine max (L.) Merr.] on the southeastern Coastal Plain are almost double those of more traditional, wider row widths. A 2‐yr field study was conducted on a Dothan loamy sand soil to assess how main‐stem and branch yield fractions of four glyphosate‐resistant cultivars, ranging from maturity group (MG) V through mid‐MG VII, would respond to a lower‐than‐recommended seeding rate for narrow‐row culture. The cultivars Pioneer 95B32 (early MG V), Hartz 6255 (early MG VI), Delta and Pine Land 6880 (late MG VI), and Hartz 7550 (mid‐MG VII) were seeded at 370 000 seeds ha−1 and at the recommended rate of 620 000 seeds ha−1. Total seed yield of all cultivars was usually similar for the two seeding rates. Less seed yield from the main‐stem fraction with the lower seeding rate was usually compensated for by a higher seed yield from the branch fraction, except when insufficient rainfall occurred during critical periods of the growing season. Branch seed yield was more closely correlated with total seed yield at the low seeding rate (r = 0.675) than at the recommended seeding rate (r = 0.453) while the correlation between total seed yield and seed yield from the main‐stem fraction was similar for the two seeding rates (r = 0.579–0.613). In the absence of prolonged periods of drought stress, seeding rates for glyphosate‐resistant soybean grown in full‐season, narrow‐row systems can be reduced below current recommendations, thereby lowering seeding costs without decreasing seed yields.

Effects of soyabean leaflet inclination on some factors related to photosynthesis

Leaflet movement in soyabean (Glycine max (L.) Merr.) is considered to be an important physiological adaptation for intercepting sunlight for photosynthesis. Solar tracking may serve to increase plant production by maximizing light interception. The objective of this study was to determine the response of A (leaflet net assimilation rate), τ (stomatal conductance) and Ci (internal leaf carbon dioxide concentration) when penultimate fully expanded leaflet angles were changed. Soyabean (cv. Enrei, Maturity group VI) was planted at Niigata University, Japan, at two densities (25 and 16 plants/m2) in mid-May of 1992 and 1993. PFD (photon flux density), A, τ, and Ci were measured with a portable leaf photosynthesis instrument. The more towards vertical the leaflets were moved, the lower the PFD and A were. A measured at R5 showed no light saturation, but did show this at V13 and R3. While A measured at 09.00 h showed no saturation point, there was saturation at 12.00 h and 15.00 h at or less than 1500 μmol/m2/s. At R3 a high correlation (r = 0.89, P &lt; 0.01) was found between PFD and A for naturally oriented leaflets, but not for horizontal ones. These results suggest that leaflet movement is an adaptation to optimize A.

Long-Term Study of Planting Date Effects on Seed Yield in Soybean

Planting date in relation to subsequent crop development and yield are important determinants in realizing crop yield potential. This study was conducted to determine optimum planting dates for Oklahoma adapted maturity groups of soybean [Glycine max (L.) Merr.]. Effects of planting date on yield were investigated at Bixby, OK, in tbe Uniform Soybean Tests for Southern States. Field experiments were conducted from 1958 through 1994. Planting dates across years ranged between 10 May and 1 July, and were assigned to 5-d, planting intervals. Maturity groups IV, V, and VI were evaluated. Soil type was a Wynona silty clay loam (fine-silty, mixed, thermic Cumulic Haplaquoll). Significant interaction occurred between maturity group and planting interval for yield. Highest average yields produced by maturity group IV (2248 lb/acre) occurred with 9 to 18 May and 8 to 22 June planting intervals. Lowest average yields for maturity group IV (1524 lb/acre) occurred with 19 May to 7 June planting intervals. Highest average yields for maturity group V (2573 lb/acre) occurred with 14 to 18 May and 13 to 22 June planting intervals, and lowest average yields (1950 lb/acre) with 19 May to 12 June planting intervals. Maturity group VI produced highest average yields (2501 lb/acre) with 14 to 18 May, 3 to 7 June, and 13 to 22 June planting intervals. Maturity group VI yields for all other planting intervals averaged 2073 lb/acre. During the range of planting dates available from early May to early July, for maturity groups IV, V, and VI, definite optimum planting dates occur for highest yields. Knowledge of optimum planting dates can be one crop management tool applied to enhance crop productivity, facilitate cropping patterns, and better utilize environmental conditions. Problem Determining optimum planting dates for maximum seed yield is fundamental for successful crop production. This study was conducted to identify optimum planting dates based on seed yield for adapted maturity groups. Background Growers have a relatively long period between early May and early July for planting soybean in Oklahoma. Different maturity groups may produce different seed yields and change in relative rank for various dates of planting. This requires evaluation of maturity groups within planting dates and planting dates within maturity groups rather than considering either maturity group or planting date alone. Identification of optimum planting dates for different maturity groups would enable minimizing the effects that temperature, water stress and photoperiod may have on seed yield. Study Description This study was conducted from 1958 through 1994 on a Wynona silty clay loam at the Oklahoma Vegetable Research Station in Bixby, in the Uniform Soybean Tests for Southern States. Genotypes used each year were dependent upon entries in the Uniform Soybean Tests. Maturity groups IV, V, and VI were included. Maturity group IV contained both determinate and indeterminate genotypes. Maturity groups V and VI consisted of only determinate genotypes. All maturity groups were planted on the same date in a particular year, but planting dates changed from year to year. Planting dates ranged between 10 May and 1 July across the years. Planting periods between 9 May and 2 July were assigned to groups of 5-d intervals. Experiments were conducted under normal dryland conditions using cultural practices considered standard for the region. Seed yield was measured on each entry for the planting date in each year. Applied Questions Using genotypes representing maturity groups grown in Oklahoma, when are optimum planting dates for each maturity group? For each maturity group in this study, mid-May and mid- to late June plantings produced highest average seed yields. Lowest yields obtained for all maturity groups generally occurred for plantings between 19 May and 7 June. An exception was maturity group VI producing a high yield at the 3 to 7 June planting interval (Fig. 1). Figure 1Open in figure viewerPowerPoint Mean seed yield of each maturity group for each planting interval at Bixby, OK, from 1958 through 1994. What maturity groups produced highest yields for the various planting dates? For several planting intervals, maturity groups V and VI tended to produce higher seed yields than maturity group IV, but statistical significance did not exist at all planting intervals. Maturity group VI genotypes produced better seed yields than maturity group IV when planted in very late May or early June.

Yield and Risk Utilizing Short‐Season Soybean Production in the Mid‐Southern USA

Maturity Group (MG) V and VI soybean [Glycine max (L.) Merr.] grown in the mid‐southern USA often produce low yield. The objective of this study was to determine if yields could be increased and risk of production reduced by utilizing early‐maturing cultivars at early planting dates (short‐season system). Field experiments were conducted from 1992 through 1994 on Sharkey clay (very‐fine, montmorillonitic, non‐acid, thermic Vertic Haplaquept) to evaluate mid‐ April through early‐June planting dates (PD), row spacings of 75 and 100 cm, and irrigated vs non‐irrigated treatments for selected MG III, IV, V, and VI cultivars. The cultivars were MG III, ‘Williams (W) 82’; MG IV, ‘Asgrow (A) 4715’, ‘Northrup King Ringaround (RA) 452’, and ‘Riverside (RVS) 499’; MG V, ‘Deltapine (DP) 105’ and MG VI, ‘Davis’. Maturity Group and PD had large effects on soybean growth and yield, whereas row spacing and irrigation had small effects and were not important factors in yield determination at most PD. The optimal PD for MG III through V cultivars centered around early May. Yields of MG IV at early‐ to mid‐May PD were equal to or greater than their yields at April PD. In April plantings, MG IV, RA 452, and RVS 499, usually yielded higher than MG V and sometimes yielded higher than MG VI. Adaptation to early PD was related to length of growing season and plant size. Attaining harvest maturity in fewer than 120 d at an April PD or fewer than 108 d at a May PD reduced both plant height and yield. The risk for short‐season production was less than for plantings of MG V or VI cultivars because the short‐season system produced higher yields and there was no difference between the two systems in yield variation across years.