Early Soybean Growth Research Articles

New Strains of Trichoderma with Potential for Biocontrol and Plant Growth Promotion Improve Early Soybean Growth and Development

New Strains of Trichoderma with Potential for Biocontrol and Plant Growth Promotion Improve Early Soybean Growth and Development

The silicon regulates microbiome diversity and plant defenses during cold stress in Glycine max L.

With climate change, frequent exposure of bioenergy and food crops, specifically soybean (Glycine max L.), to low-temperature episodes is a major obstacle in maintaining sustainable plant growth at early growth stages. Silicon (Si) is a quasi-essential nutrient that can help to improve stress tolerance; however, how Si and a combination of cold stress episodes influence plant growth, plant physiology, and microbiome diversity has yet to be fully discovered. The soybean plants were exposed to cold stress (8-10°C) with or without applying Si, and the different plant organs (shoot and root) and rhizospheric soil were subjected to microbiome analysis. The plant growth, physiology, and gene expression analysis of plant defenses during stress and Si were investigated. We showed that cold stress significantly retarded soybean plants' growth and biomass, whereas, Si-treated plants showed ameliorated negative impacts on plant growth at early seedling stages. The beneficial effects of Si were also evident from significantly reduced antioxidant activities - suggesting lower cold-induced oxidative stress. Interestingly, Si also downregulated critical genes of the abscisic acid pathway and osmotic regulation (9-cis-epoxy carotenoid dioxygenase and dehydration-responsive element binding protein) during cold stress. Si positively influenced alpha and beta diversities of bacterial and fungal microbiomes with or without cold stress. Results showed significant variation in microbiome composition in the rhizosphere (root and soil) and phyllosphere (shoot) in Si-treated plants with or without cold stress exposures. Among microbiome phyla, Proteobacteria, Bacteroidota, and Ascomycota were significantly more abundant in Si treatments in cold stress than in control conditions. For the core microbiome, we identified 179 taxa, including 88 unique bacterial genera in which Edaphobacter, Haliangium, and Streptomyces were highly abundant. Enhanced extracellular enzyme activities in the cold and Si+cold treatments, specifically phosphatase and glucosidases, also reflected the microbiome abundance. In conclusion, this work elucidates cold-mediated changes in microbiome diversity and plant growth, including the positive impact Si can have on cold tolerance at early soybean growth stages - a step toward understanding crop productivity and stress tolerance.

Seed Scarification and Day Length Effect on the Germination and Vegetative Growth of Soybeans (Glycine max)

Studies were carried out to determine the scarification and day length effects on the germination and early growth of soybean (Glycine max). Soil was collected from the biological garden of Yobe State University Damaturu. The soybean seed sample consists of two different treatments including scarified and unscarified seeds with two different levels of day length. A soybean of the tested varieties was sown in a polythene pot with a depth of half an inch. About two seeds mixed with a star dress were sown in each polythene bag. The data collected were analyzed using Genstat software 16 editions versus. Results of the experiments carried out indicate that, the seeds of soybeans have a highest rate of germination percentage when subjected to scarification treatment. From the obtained results, it can be concluded that, there is no effect of scarification on the germination of soybeans but there was significance in the effect of scarification on the vegetative growth in which the plants that were exposed to 12 hours day and 12 hours night grew faster than those exposed to 24 hours. It is therefore believed that the method of preventing dormancy can be used on soybeans in order to improve the growth and subsequent yield of the soybean crop.

Diamide seed treatment may protect early soybean growth stages against Helicoverpa armigera

In intensive soybean cropping systems, early-season pest insects such as lepidopteran larvae can seriously compromise crop establishment. Using a polyphagous global pest ̶̶ the Old World bollworm Helicoverpa armigera (Lepidoptera: Noctuidae), we determined the potential of seed treatments with diamide or neonicotinoid-carbamate mixture for systemic plant protection and residual efficacy against noctuid larvae. In controlled edaphoclimatic conditions, we infested differently aged soybean plants and recorded plant damage and insect mortality, growth, development, and fecundity to assess lethal and sublethal post-exposure effects. The seed treatments reduced plant damage by 50% during 1–7 days after plant emergence. The lowest damage (<25% defoliation) occurred on plants treated with chlorantraniliprole or cyantraniliprole. These diamides caused larval mortality >80% until 14 days after soybean emergence, which was the window of residual control efficacy. Carbofuran or thiodicarb + imidacloprid caused less than 50% larval mortality and minor plant protection against the larvae. There were sublethal effects on the growth, development, and fecundity of the insects surviving on plants of the insecticide seed treatments. The diamide seed treatments reduced the overall insect fitness for a longer time after plant emergence than did the other treatments. Therefore, soybean seed treatment with chlorantraniliprole or cyantraniliprole is potentially efficacious against noctuid larvae in the VE–V1 soybean growth stages (emergence until the first trifoliate), causing lethal and sublethal effects on the insects. Judicious use and effective resistance management for these systemic compounds are relevant as they are helpful for seed treatment and foliar applications against diverse targets.

Growth, photosynthesis and yield of soybean in ridge-furrow intercropping system of soybean and flax

It is of practical significance to control the excessive vegetative growth of soybean during the rainy season, which causes a reduction in yield. In this study, we adopted soybean flax ridge-furrow intercropping system in order to constrain soybean’s excessive vegetative growth by interspecific competition between intercrops and estimated the growth, photosynthesis and yield of soybean. Two-year-experiment was conducted in 2018 and 2019 in the experimental farm of KIM IL SUNG University. Soybean seeds were grown in ridges and flax seeds were in furrows between ridges. During the co-growth stage, the early growth of soybean intercropped with flax was depressed by interspecific competition. At 45 days after soybean sowing, just before flax harvest, the average height and stem diameter of intercropped soybean plant were 22.5 cm and 0.7 mm shorter than those of sole cropped soybean plant, respectively. At the reproductive growth stage, the height of intercropped soybean plant was still 18.5 cm shorter than sole cropped soybean, while other agronomic parameters, including leaf area index (LAI), dry matter per plant, photosynthetic rate and chlorophyll contents, were greater for intercropped soybean. This led to higher yield of soybean (118.5%) and land equivalent ratio (LER) (203.5%) in ridge-furrow intercropping, as compared to sole cropping. Our results suggest that ridge-furrow intercropping system can be an effective way to constrain soybean’s excessive vegetative growth during the rainy season and improve soybean seed yield and LER.

Quantifying Effects of Excess Water Stress at Early Soybean Growth Stages Using Unmanned Aerial Systems

Low-gradient agricultural areas prone to in-field flooding impact crop development and yield potential, resulting in financial losses. Early identification of the potential reduction in yield from excess water stress at the plot scale provides stakeholders with the high-throughput information needed to assess risk and make responsive economic management decisions as well as future investments. The objective of this study is to analyze and evaluate the application of proximal remote sensing from unmanned aerial systems (UAS) to detect excess water stress in soybean and predict the potential reduction in yield due to this excess water stress. A high-throughput data processing pipeline is developed to analyze multispectral images captured at the early development stages (R4–R5) from a low-cost UAS over two radiation use efficiency experiments in West–Central Indiana, USA. Above-ground biomass is estimated remotely to assess the soybean development by considering soybean genotype classes (High Yielding, High Yielding under Drought, Diversity, all classes) and transferring estimated parameters to a replicate experiment. Digital terrain analysis using the Topographic Wetness Index (TWI) is used to objectively compare plots more susceptible to inundation with replicate plots less susceptible to inundation. The results of the study indicate that proximal remote sensing estimates above-ground biomass at the R4–R5 stage using adaptable and transferable methods, with a calculated percent bias between 0.8% and 14% and root mean square error between 72 g/m2 and 77 g/m2 across all genetic classes. The estimated biomass is sensitive to excess water stress with distinguishable differences identified between the R4 and R5 development stages; this translates into a reduction in the percent of expected yield corresponding with observations of in-field flooding and high TWI. This study demonstrates transferable methods to estimate yield loss due to excess water stress at the plot level and increased potential to provide crop status assessments to stakeholders prior to harvest using low-cost UAS and a high-throughput data processing pipeline.

Identification of QTL for Tolerance to Flooding Stress at Seedling Stage of Soybean (Glycine max L. Merr.)

Flooding stress is a serious problem in soybean production, causing a remarkable yield reduction. The onset of rainy season during the early growth of soybean in Korea and some other parts of the world potentially subjects soybean plants to flooding stress. The objective of this study was to map quantitative trait loci (QTL) for flooding tolerance using a recombinant inbred line (RIL) population derived from a cross between ‘Danbaekkong’ (flood-tolerant) and ‘NTS1116′ (flood-susceptible) cultivars grown in a plastic house for two years. The plants were flood-stressed at the V1-V2 stage by ponding about 10 cm water from the soil surface. Leaf chlorophyll content and shoot dry weight were measured under control and flooded conditions to map the QTL. The genetic map was constructed using 1689 polymorphic markers obtained from the 180K Axiom® SoyaSNP markers used for genotyping the population. Ten QTL with 3.39−5.14 logarithm of odds scores and 8.1−30.7% phenotypic variations (PVE) were identified on seven chromosomes. One QTL on chromosomes 6 and 15 and two QTL on chromosome 7 were detected at least in two different environments causing up to 30.7% PVE, suggesting their potential applications in the breeding of flood-tolerant soybeans. The results could be useful in further exploring the genetic basis of flooding tolerance and developing tolerant cultivars of soybean.

Phosphorus fertilizer optimization is affected by soybean varieties and placement strategy

Soybean (Glycine max (L.) Merr.) response to phosphorus (P) fertilization can vary by fertilization strategy, tillage system, and soybean variety. The objectives of this study were to access possible differences in soybean productivity and P fertilizer efficiency as affected by contrasting soybean varieties and P fertilizer placement. The effects of two soybean varieties and six P fertilizer placements on soybean shoot dry weight, P uptake, apparent P recovery, seed P concentration, seed yield, P removal, and partial P balance were investigated in four sites in Kansas, during the 2014 and 2015 growing seasons. Band fertilizer applications increased the apparent P recovery at the soybean V3 growth stage and increased the shoot dry weight up to 9.13 and 12.9% compared to broadcast and control, respectively. Likewise, the band fertilizer treatments increased the P uptake by 30% compared to the control plots. On the other hand, the P concentration in soybean tissue at the R3 growth stage was higher under broadcast treatments. Yield differences were observed between variety selection only and varied by site. The good soil drainage variety increased the P removal by the seed on 5 and 6.9% at Ottawa 2015 and Scandia 2014, respectively, compared to the poor soil drainage variety. In general, band-applied treatments resulted in P fertilizer optimization during early soybean growth whereas broadcast treatments optimized fertilization efficiency during the soybean reproductive stage. The lack of soybean yield response to P fertilization suggests that P was not the limiting factor for yield response in this study.

Quantitative trait loci mapping for flooding tolerance at an early growth stage of soybean recombinant inbred line population

AbstractFlooding stress causes a significant yield reduction in soybean. The early growth of soybean in Korea coincides with the rainy season, potentially exposing to flooding stress. Greenhouse experiments were conducted to map the quantitative trait loci (QTL) for flooding tolerance in soybean and to identify and investigate candidate genes near the QTL hot spots. Flood stress was imposed at V1–V2 stage on a recombinant inbred line population (‘Paldalkong’ × ‘NTS1116’), and leaf chlorophyll content (CC) and shoot dry weight (DW) were measured under control and flooded conditions. The genetic map was constructed using 180K Axiom® SoyaSNP markers. The QTL were analysed under control and flooded conditions as well as for index (ratio of CC or DW under flooded to control, CCI and DWI) and flooding tolerance index (FTI, mean of CCI and DWI). A total of 20 QTL with LOD scores 3.59–19.73 causing 5.8%–33.3% phenotypic variation were identified on nine chromosomes. Chromosomes 10, 12 and 13 harboured relatively more stable QTL. Results of this study could be useful to further understand the genetic basis of soybean's flooding tolerance and applied in breeding programmes.

Optimizing organic cover crop-based rotational tillage systems for early soybean growth

Cover crop-based rotational tillage (CCBRT) practices continue to be adopted on organic farms across the globe. In these systems, fall-planted cover crops are mechanically terminated in the spring and used to suppress weeds and eliminate the need for tillage and cultivation in the soybean (Glycine max L.) phase of the rotation. However, challenges remain as to maximization of soybean yields due to later planting dates of soybean and delayed early soybean growth. In this study, soybeans were planted into cereal rye (Secale cereale L.) using two strategies (planting at Zadoks’ stage 45 and 69), with termination with the roller-crimper occurring at Zadoks’ stage 69 for each rye variety which differed in their time to maturity. The impacts of cover crop variety and planting strategies were compared through measurements of (1) cover crop biomass; (2) the regrowth of cover crops; (3) soybean plant populations; (4) weed densities and biomass; and (5) soybean nodulation. Biomass production of each cover crop differed significantly by year, ranging from 7907 kg DM ha−1 to 11,466 kg DM ha−1. Significant differences in weed densities and weed biomass were found between rye varieties and control treatments across the different planting strategies. Soybean nodulation was suppressed by CCBRT management, potentially impacting early soybean growth. Soybean yields were equivalent from both the earlier vs. late maturing varieties of rye. Soybean yields varied across planting strategies of soybeans when cereal rye reached Zadoks’ stage 45 versus stage 69, with greater or equivalent yields of the early planting strategy beans in 2016 and lower or equivalent yields in 2017. Further work must be conducted to understand the benefits and risks of earlier planting of soybeans in the CCBRT system and to develop best management practices to promote early soybean growth.

Characterizing interactions between Fusarium graminearum and Fusarium virguliforme on early soybean growth and development

Fusarium graminearum and Fusarium virguliforme are two fungal pathogens that can infect soybean [Glycine max (L.) Merr.] early in the growing season. A greenhouse experiment was conducted to determine if the presence of both pathogens resulted in an increased negative impact on early soybean growth compared with each pathogen alone. Treatment factors consisted of four inoculation treatments: a non-inoculated control, inoculation with F. graminearum only (FG), inoculation with F. virguliforme only (FV), and a combination of both pathogens (FG + FV). As well, three soybean cultivars (CH2105R2, P92Y51 and ‘Sloan’), and three seed treatments (a control, mefenoxam + fludioxonil, and fluxapyroxad) were evaluated. Results indicated FG + FV did not result in increased root disease, a decrease in shoot growth, or reduced root growth compared with FG and FV. The FV inoculation treatment exhibited more root disease severity compared with FG, but there were no differences between the two inoculation treatments for the other below-ground measurements, as well as all above-ground measurements. Fungicide seed treatment did not reduce root disease severity or lead to increased early soybean growth compared with the non-treated control. Cultivar differences were the primary factor which influenced early-season soybean growth. Because there was no evidence of an increased effect between presence of F. graminearum and F. virguliforme, these results suggest management decisions for both pathogens can remain separate for soybean growers in Wisconsin, but management of F. virguliforme should take priority over F. graminearum due to its prevalent cause of soybean sudden death syndrome.

Biological control of Heterodera glycines by spore-forming plant growth-promoting rhizobacteria (PGPR) on soybean

Heterodera glycines, the soybean cyst nematode, is the most economically important plant-parasitic nematode on soybean production in the U.S. The objectives of this study were to evaluate the potential of plant growth-promoting rhizobacteria (PGPR) strains for mortality of H. glycines J2 in vitro and for reducing nematode population density on soybean in greenhouse, microplot, and field trials. The major group causing mortality to H. glycines in vitro was the genus Bacillus that consisted of 92.6% of the total 663 PGPR strains evaluated. The subsequent greenhouse, microplot, and field trials indicated that B. velezensis strain Bve2 consistently reduced H. glycines cyst population density at 60 DAP. Bacillus mojavensis strain Bmo3 suppressed H. glycines cyst and total H. glycines population density under greenhouse conditions. Bacillus safensis strain Bsa27 and Mixture 1 (Bve2 + Bal13) reduced H. glycines cyst population density at 60 DAP in the field trials. Bacillus subtilis subsp. subtilis strains Bsssu2 and Bsssu3, and B. velezensis strain Bve12 increased early soybean growth including plant height and plant biomass in the greenhouse trials. Bacillus altitudinis strain Bal13 increased early plant growth on soybean in the greenhouse and microplot trials. Mixture 2 (Abamectin + Bve2 + Bal13) increased early plant growth in the microplot trials at 60 DAP, and also enhanced soybean yield at harvest in the field trials. These results demonstrated that individual PGPR strains and mixtures can reduce H. glycines population density in the greenhouse, microplot, and field conditions, and increased yield of soybean.

Peningkatan Populasi, Pertumbuhan dan Serapan Nitrogen Tanaman Kedelai dengan Pemberian Azotobacter Penghasil Eksopolisakarida

Nitrogen-fixing Azotobacter is widely used as biofertilizer in sustainable agriculture. The bacteria produce exopolysaccharide which might have a significant role in enhancing soybean nitrogen uptake and growth. The objective of this research was to obtain growth media of Exopolysaccharide–producing Azotobacter; and increase shoot and root growth as well as nitrogen uptake of soybean var. Anjasmoro at early vegetative phase following inoculation of Azotobacter chroococcum liquid. Research consist of two phase, 1) determination of organic-based media for A. chroococcum liquid inoculant production, and 2) pot experiment for application of liquid inoculant on soybean. The first experiment was performed in a series of batch fermenter consisted of several organic media for 72 hours. The second experiment was set in completely randomized design consisted of three density of liquid inoculant. The results verified that the best media which induced exopolysachharide production of A. chroococcum was 1% molase enriched with 0.1% NH4Cl. Liquid inoculant clearly enhanced population of Azotobacter in soybean rhizosphere, plant height, roots dry weight and N uptake of 21 day old soybean. This research implied that A. chroococcum might be used as biofertilizer at early growth of soybean. Keywords: Azotobacter chroococcum, biofertilizer, liquid inoculat

Evaluating the Interaction Between Chelated Iron Source and Placement on Phosphorus Availability in Soybean

In agriculture, chelating agents are used to supplement micronutrients, such as iron (Fe). However, little research has been conducted at the field-scale level to evaluate chelating agent effects on phosphorus (P). The objectives of this study were to evaluate three commercially available chelated Fe sources on early soybean growth and nutrient uptake. The study was conducted at six locations in 2014 and 2015. The experimental design was a randomized, complete block with a factorial treatment arrangement. The two factors included fertilizer source and fertilizer placement. The fertilizer sources were P only, EDTA-Fe, HEDTA-Fe, and one glucoheptonate product, Cee*Quest N5Fe758 (CQ-758), with two fertilizer placements, in-furrow with seed contact and surface band at planting. Results show soybean yield was affected by chelate source and placement. Greater yields occurred with application in-furrow at Scandia in 2014 and 2015, but in-furrow was superior at Rossville in 2015. Increased yields also occurred with applications of EDTA and HEDTA. However, further analysis of tissue and grain may show chelate effects on nutrients.

Dual Cropping Winter Camelina with Soybean in the Northern Corn Belt

Sustainably balancing biofuel crop production with food, feed, and fiber on agricultural lands will require developing new cropping strategies. Double‐ and/or relay‐cropping winter camelina (Camelina sativaL.) with soybean [Glycine max(L.) Merr.] may be a means to produce an energy and food crop on the same land in a single year. A study was conducted between 2009 and 2011 in west central Minnesota to evaluate yields, seed quality, economics, and within‐field energy balance of winter camelina–soybean double‐ and relay‐cropping systems compared with a conventional monocropped full‐season soybean. Systems included methods to hasten camelina harvest (e.g., swathing and desiccating) to promote early soybean growth. Camelina seed yields were unaffected by cropping system and ranged from 1.1 to 1.3 Mg ha−1. Relay‐cropped soybean yields were greater than double‐cropped soybean and were 58 to 83% of that for the monocropped control. Seed oil and protein content of double‐ and relay‐cropped soybean were comparable to their monocropped counterpart and combined seed oil yield for the dual crop systems was as much as 50% greater. Net economic returns for the relay‐crop treatments were competitive with that of the full‐season soybean. Moreover, net energy of the relay‐crop treatments was generally as high as the sole soybean crop, but energy efficiency (outputs/inputs) was less due to greater inputs. Results indicate that dual cropping of winter camelina with soybean is agronomically viable for the upper Midwest and might be an attractive system to growers seeking a “cash” cover crop.

춘파호밀 리빙멀치가 잡초억제 및 콩 생산성에 미치는 영향

Establishment of mechanized soybean production system without herbicide is required for organic soybean production in recent. Effects of mechanized soybean planting with partial tillage between growing rye living mulch, which was sown in April or early May, on weed suppression, soybean early growth and yield were investigated with different rye sowing dates and locations in 2007 and 2008, respectively. Effect of rye living mulch on weed suppression at 40~50 days after soybean planting was high as much as 70~90% regardless of rye sowing dates. In particular, a strong suppression effect on the occurrence and growth of Echinochloa crus-galli which occupied 60~80% of total weed biomass was observed. Rye living mulch sown on April 9, of which biomass was more than that sown on April 27, inhibited soybean early growth severely and reduced soybean grain yield in 2007. However, soybean grain yield was no t reduced despite suppression of early growth of soybean plant by living mulch sown during from late April to early May compared with conventional planting. Rye sowing before late April was not proper considering tendency of weed occurrence in spring because of unfavorable changes in weed suppression, early growth and grain yield of soybean according to amount of living mulch.

Relationships between Soybean Yield, Soil pH, and Soil Carbonate Concentration

Soybean [Glycine max (L.) Merrill] often shows symptoms of iron deficiency chlorosis (IDC) on high pH, calcareous soils of the U.S. Midwest. The objective of this study was to assess the variation in soybean yield that could be explained by soil pH and carbonate concentration in Iowa fields. Color aerial images of soybean canopy taken from 2000 to 2002 from 12 fields having acid to calcareous soils were used to select 10 to 28 sampling areas 10 to 25 m2 in size to encompass significant variability in early soybean growth and IDC symptoms in each field. Representative areas 0.93 m2 in size were identified through field observations to collect soil samples and measure grain yield. Soil pH measured to a 15‐cm depth across fields ranged from 5.6 to 8.2 and calcium carbonate equivalent (CCE) ranged from 0 to 30%. Soil CCE varied from 2.5 to 30% as pH ranged from 7.7 to 8.2. Grain yield decreased with increasing pH and CCE in 9 and 11 fields, respectively. Soil pH and CCE explained 30 and 41% of the variability in relative yield across sites, respectively. An alkalinity stress index (ASI) that combined both measurements (pH + 0.14CCE) was developed based on the relative effects of each measurement on yield and explained 45% of the yield variability across sites. The index developed was a better predictor of soybean yield in fields with high‐pH soils than each measurement alone.

Absence of Interactive Responses of Early Soybean (Glycine max) Growth to Soybean Cyst Nematode (Heterodera glycines), Postemergence Herbicides, and Soil pH and Texture1

Farmer observations and previous studies indicated that reductions in soybean yield caused by the soybean cyst nematode (SCN) are greater when other stresses, biotic or abiotic, are present. Also, it has been reported that the effect of SCN on soybean growth depended on factors such as soil pH, soil texture, and herbicides. Although postemergence herbicides may adversely affect soybean metabolism, acifluorfen can reduce SCN infection. The objective of the present study was to determine the main and interactive effects of SCN egg population density (SCND), soil pH, soil texture, and the application of the herbicides acifluorfen, glyphosate, and imazethapyr on early soybean growth. Greenhouse studies assessed different combinations of these factors for 65 d after planting. No interactions were observed for any of the main effects. Soil pH and texture did not affect soybean growth. SCND was the only main effect that explained soybean growth reductions. The effect of SCND on soybean growth was exhibited as 15–50% decreases of leaf area index (LAI) and dry weight in all cases, but reductions in plant height also were observed. No relationship between SCND and the number of SCN eggs recovered at the end of the experiment was observed. Herbicides did not reduce soybean growth, although acifluorfen consistently caused the highest soybean injury reaching 18–20% from 1–14 days after application (DAA). At 50 DAA, acifluorfen injury was negligible, and soybean LAI and dry weight did not differ from the nontreated control. These results indicated that the effect of SCN on soybean growth was not directly affected by the other evaluated main effects. Therefore, trends observed in the field that suggested interactions between those factors are likely the result of other factors not considered in the present study or to more complex relationships between factors analyzed in the present study and other elements present in the field.Nomenclature: Acifluorfen, glyphosate, imazethapyr; soybean; soybean cyst nematode, Heterodera glycines Ichinoche.Additional index words: Herbicide injury, nematode infection.Abbreviations: AMS, ammonium sulfate; COC, crop oil concentrate; DAA, days after application; DAP, days after planting; LAI, leaf area index: MSO, methylated seed oil; PPFD, photosynthetic photon flux density; SCN, soybean cyst nematode; SCND, SCN egg population density.

Spurred Anoda (Anoda cristata) Competition in Narrow- and Wide-Row Soybean (Glycine max)1

The effect of spurred anoda competition in narrow- (35 cm) and wide-row (70 cm) soybean was studied in field experiments for 2 yr. Vigorous early soybean growth in narrow- compared with wide-row soybean resulted in lower radiation transmitted through the canopy, which can partially account for greater competitiveness of narrow-row than wide-row soybean. Soybean plant height was not significantly influenced by the row spacing. Relative yield total (RYT), which is the relationship between yield in mixtures and in monocultures of the crop or the weed and indicates resource complementarity, was equal to 1 with 12 spurred anoda/m2 in the year with less precipitation. Regardless of the row spacing, spurred anoda gave resource use complementarity with the crop (RYT > 1) in all other treatments; therefore, partial avoidance of competition in mixed species was evident. Soybean aggressivity, which takes into account the effect of competition on both the crop and the weed and indicates competitive ability, decreased...

The major Nod factor of Bradyrhizobium japonicum promotes early growth of soybean and corn.

Greenhouse experiments were conducted to evaluate the effect of Nod factor Nod Bj-V (C18:1, MeFuc) of Badyrhizobium japonicum on the growth of soybean and corn. Three-day-old seedlings of soybean and corn were grown in hydroponic solutions containing four concentrations (0, 10(-7), 10(-9) or 10(-11) M) of Nod factor. After 7 d of treatment, Nod factor enhanced soybean and corn biomass. Nod factor elicited profound effects on root growth resulting in 34-44% longer roots in soybean. More detailed analyses of the roots, using a scanner based image analysis system, revealed that Nod factor increased the total length, projected area and surface area of the roots and decreased the diameter of soybean roots, while it increased the total length of corn roots. Stem injection of soybean plants with 10(-7) M Nod factor resulted in increased dry matter accumulation. These results suggest that Nod factor, besides mediating early stages of nodulation, has more general plant growth-promoting effects.