Soybean Density Research Articles

SCAG: A Stratified, Clustered, and Growing-Based Algorithm for Soybean Branch Angle Extraction and Ideal Plant Architecture Evaluation.

Three-dimensional (3D) phenotyping is important for studying plant structure and function. Light detection and ranging (LiDAR) has gained prominence in 3D plant phenotyping due to its ability to collect 3D point clouds. However, organ-level branch detection remains challenging due to small targets, sparse points, and low signal-to-noise ratios. In addition, extracting biologically relevant angle traits is difficult. In this study, we developed a stratified, clustered, and growing-based algorithm (SCAG) for soybean branch detection and branch angle calculation from LiDAR data, which is heuristic, open-source, and expandable. SCAG achieved high branch detection accuracy (F-score = 0.77) and branch angle calculation accuracy (r = 0.84) when evaluated on 152 diverse soybean varieties. Meanwhile, the SCAG outperformed 2 other classic algorithms, the support vector machine (F-score = 0.53) and density-based methods (F-score = 0.55). Moreover, after applying the SCAG to 405 soybean varieties over 2 consecutive years, we quantified various 3D traits, including canopy width, height, stem length, and average angle. After data filtering, we identified novel heritable and repeatable traits for evaluating soybean density tolerance potential, such as the ratio of average angle to height and the ratio of average angle to stem length, which showed greater potential than the well-known ratio of canopy width to height trait. Our work demonstrates remarkable advances in 3D phenotyping and plant architecture screening. The algorithm can be applied to other crops, such as maize and tomato. Our dataset, scripts, and software are public, which can further benefit the plant science community by enhancing plant architecture characterization and ideal variety selection.

No yield benefit from starter fertilizer in soybean no‐till planted into rolled‐crimped cereal rye

AbstractNo‐till planting organic soybean [Glycine max (L.) Merr.] into rolled‐crimped cereal rye (Secale cereale L.) can improve soil health while decreasing labor and fuel costs, but yield declines from tillage‐based production hinder wider adoption. In addition to soil moisture depletion, nitrogen (N) tie‐up in cereal rye biomass and cool soil temperatures under mulches may contribute to yield differences by decreasing N availability early in the production system before the onset of biological N fixation. A field experiment was conducted to determine if starter fertilizers could increase early‐season soybean growth and subsequent yields. Over five site‐years in New York and Wisconsin on organically managed land, soybeans were no‐till planted into rolled‐crimped cereal rye and four treatments were applied in a randomized complete block design: feather meal, poultry litter, and sodium nitrate starter fertilizer treatments supplied at 28 kg N·ha−1 and a zero fertilizer control. Early‐season growth, weed biomass, soybean biomass, soybean density, and soybean yield were compared among treatments. The relationships between soybean yield and these other variables were also explored. Some differences among treatments were observed in early‐season growth, but the results were inconsistent and only found in two site‐years. Soybean yield did not differ between the control (2664 kg·ha−1) and any treatment (feather meal: 2760 kg·ha−1, poultry litter: 2812 kg·ha−1, and sodium nitrate: 2769 kg·ha−1), though greater cereal rye biomass and soybean density were associated with higher yield. The results suggest that soybeans in organic cover crop‐based no‐till production do not consistently respond to starter fertilizer.

Optimizing organic no‐till planted soybean with cover crop selection and termination timing

AbstractResearch is needed to develop and optimize agroecological practices that can replace unsustainable managementand increase agricultural diversification. Field experiments were conducted in Maryland and New York to assess the effect of cover crop cultivar selection and cover crop termination soybean [Glycine max (L.) Merr.] planting (roll‐plant) date on cover crop growth stage, biomass, and reseeding; weed biomass; and soybean density and yield in organically managed no‐till planted soybean production. Twelve winter cereal cultivars—four each for barley (Hordeum vulgare L.), cereal rye (Secale cereale L.), and triticale (× Triticosecale Wittm. ex A. Camus.)—were seeded at equivalent densities and terminated at four roll‐plant dates. Although many cover crop cultivars had not yet reached the recommended growth stage for adequate termination (anthesis) at the earlier roll‐plant dates, greater soybean yields and similar cover crop reseeding, compared with later dates, were observed. Weed biomass was low across treatments despite cover crop biomass production below the recommended threshold of 8 Mg ha−1. When pooled over cultivars, triticale performed as well as cereal rye in terms of biomass production, weed suppression, and soybean yield. Within each species, differences in weed biomass and soybean yield were observed among cultivars, but inconsistent across site‐years. Results from this research also show that planting soybean before cover crop anthesis can help maximize yield. Farmers can improve management in cover crop‐based no‐till planted soybean by selecting regionally adapted winter cereal species and cultivars that perform well across a range of outcomes, rather than focusing exclusively on biomass production.

Cereal rye mulch biomass and crop density affect weed suppression and community assembly in no‐till planted soybean

AbstractThe use of multiple ecological weed management tactics may be an effective solution to weed management challenges associated with reducing tillage. An experiment was conducted to assess how soybean Glycine max (L.) Merr. density and cereal rye Secale cereale L. mulch biomass affected weed suppression and community assembly in no‐till production. Soybean was planted at five rates from 0 to 74 seeds m−2, and five cereal rye mulch levels were established from 0 to 2 times the ambient cereal rye biomass within each site–year. We assessed the effects of soybean density and cereal rye mulch biomass on weed suppression, weed community composition, and the functional structure of weed life cycle, emergence timing, seed weight, height, and specific leaf area traits. Weed suppression was influenced by a synergistic interaction between soybean density and cereal rye biomass. The functional dispersion (FDis) of all weed traits, when combined, was reduced by increased soybean density and mulch biomass, suggesting that high treatment intensities induced trait convergence. However, soybean density and cereal rye biomass had differing effects on the FDis and composition of individual traits, suggesting that these management practices represent unique filters during weed community assembly. Mulch biomass had a larger effect on annual weed suppression and weed community composition than soybean density. Farmers who utilize high biomass cover crop mulch for weed management may experience shifts in weed community composition toward an increased proportion of perennials and weeds with later emergence, heavier seeds, and shorter stature. Increasing soybean density may reduce perennial weed biomass, making it a valuable complement to high cereal rye mulch biomass. As such, weed management in no‐till soybean is enhanced by combining multiple practices, which can enable synergistic weed suppression and the management of diverse weed functional groups.

Effects of Soybean Density and Sowing Time on the Yield and the Quality of Mixed Silage in Corn-Soybean Strip Intercropping System

Intercropping is a cropping strategy that makes efficient use of space, nutrients, and soil. A 2-year field trial was conducted in 2019 and 2020 to study the effects of different soybean sowing times (9 days before corn sowing (ST1), 0 days at corn sowing (ST2), and 9 days after corn sowing (ST3), respectively) and densities (120,000 plants ha−1 (PD1), 150,000 plants ha−1 (PD2), and 180,000 plants ha−1 (PD3), respectively, and the planting density of corn was 60,000 plants ha−1 constantly) on total yield and on mixed silage quality in corn-soybean strip intercropping system. The yield decreased with an increase in soybean planting density. Before ensiling, the total dry matter (DM) content increased with an increase in soybean planting density, while that of crude protein content decreased with sowing time. The interaction of planting density × sowing time was significant for neutral detergent fiber and water-soluble carbohydrate (WSC) content. After ensiling, the WSC content of PD2ST3 (4.90% DM) was the highest. The PD1 (4.51%) had a higher content of ammonia–nitrogen to total nitrogen than that of PD2 and PD3. The lactic acid content of PD2ST3 (3.14% DM) was the highest. In general, better silage quality and a higher total yield were obtained when soybean was sown at the planting density of 150,000 plants ha−1 after 9 days of corn sowing.

Glyphosate-resistant Italian ryegrass (Lolium perenne ssp. multiflorum) control with preemergence and postemergence herbicide programs

AbstractA field study was conducted twice in Elizabeth, MS, at on-farm sites in 2010–11 and 2011–12, and twice in 2012–13 at Mississippi State University’s Delta Research and Extension Center in Stoneville, MS, to evaluate glyphosate-resistant (GR) Italian ryegrass control and crop response to fall treatments followed by postemergence herbicide treatments in winter and/or spring. Italian ryegrass was controlled ≥92% and 61% following S-metolachlor and tillage 77 d after fall treatments (DA-FT), respectively. S-metolachlor fall treatment provided 33% greater control than clethodim winter treatment at 21 d after winter treatments (DA-WT). Tillage fall treatment followed by (fb) clethodim winter treatment fb paraquat spring treatment provided similar control (93%) to treatments containing S-metolachlor fall treatment fb a winter or spring herbicide treatment (≥93%) 24 d after spring treatments (DA-ST). Greatest soybean and corn density and yield were also observed following programs containing S-metolachlor fall treatment. Sequential postemergence herbicide treatments were not required to increase corn and soybean density and yield when S-metolachlor was used as a fall treatment. Growers have the best opportunity to maximize GR Italian ryegrass control when S-metolachlor fb a winter or spring herbicide treatment is used.

Elk (Cervus elaphus) grazing reduces volunteer soybean density

Management of glyphosate resistant volunteer soybean can be challenging and costly in other glyphosate resistant crops. This study examined the effect of elk (Cervus elaphus) grazing on volunteer soybean (Glycine max) management. Volunteer soybean density was assessed in four fields grazed by elk and three without elk in western Manitoba, Canada. This study determined that elk grazing of soybean stubble significantly reduced soybean volunteer density in the following crop. These results demonstrate that winter elk grazing can be an effective management technique for volunteer soybeans.

Co-application of thifensulfuron with glyphosate accentuates soybean injury

Three trials (two in 2019 and one in 2020) were completed at the University of Guelph, Huron Research Station near Exeter, ON, to determine if the co-application of thifensulfuron with glyphosate accentuates soybean injury in glyphosate-resistant (GR) soybean. At 1, 2, 4, and 8 weeks after treatment (WAT), thifensulfuron (6 and 12 g a.i.·ha−1 representing the 1× and 2× rate, respectively) applied POST with no adjuvants caused up to 5% soybean injury. The addition of a non-ionic surfactant + UAN to thifensulfuron increased soybean injury to up to 24%. There was no decrease in soybean density, dry biomass, height, and yield, except soybean dry biomass was reduced up to 22% with the addition of adjuvants to thifensulfuron at the 2× rate. Glyphosate (1800 and 3600 g·ha−1 representing the 1× and 2× rate, respectively) applied POST caused no adverse effect on soybean injury parameters evaluated. The co-application of glyphosate + thifensulfuron at the 1× and 2× rates, without additional adjuvants, caused a synergistic increase in soybean injury at 1, 2, 4, and 8 WAT, and a synergistic decrease in dry biomass and height. All other interactions were additive. The co-application of glyphosate + thifensulfuron at the 1× and 2× rates, with additional adjuvants, produced a synergistic increase in injury at 1 (1× and 2× rate), 4 (1× rate), and 8 (1× rate) WAT in soybean. All other interactions were additive.

High Seeding Rates and Low Soil Nitrogen Environments Optimize Weed Suppression and Profitability in Organic No-Till Planted Soybean

No-till planting crops into rolled-crimped cover crops can improve soil health while reducing labor and fuel requirements compared with traditional tillage-based production. However, little information is available to help farmers optimize the management of organic no-till planted crops. Weed suppression, crop yield, and profitability were assessed across soybean [Glycine max (L.) Merr.] seeding rates and soil nitrogen environments in an experiment conducted at two sites in central New York. Soybeans were no-till planted into rolled-crimped cereal rye (Secale cereale L.) at 0, 185,000, 371,000, 556,000, and 741,000 seeds ha−1. Three rates (0, 63, or 125 kg ha−1) of sodium nitrate (15-0-2) were applied across seeding rates to create different soil nitrogen environments. When pooled over sites, the lowest weed biomass occurred at the highest soybean density in the lowest soil nitrogen environment. An interaction was observed between soybean seeding rate and nitrogen treatments on weed communities. Soybean yield increased asymptotically with crop density and was not affected by nitrogen or site treatments. When pooled over nitrogen treatments and sites, partial returns to the soybean seeding rates were maximized at $2,238 ha−1 with 527,800 seeds ha−1. Results suggest that crop density is an important lever for optimizing weed suppression and crop yield in organic no-till soybean, and that managing for low soil nitrogen conditions may further enhance weed suppression while maintaining high yields.

Soil‐residual herbicides: Is there a trade‐off between waterhemp control and soybean injury?

AbstractThe perceived risk of pre‐emergence (PRE) herbicide injury negatively affecting soybean [Glycine max (L.) Merr.] grain yield may cause growers to select herbicides and/or rates that, consequently, reduce waterhemp (Amaranthus tuberculatus (Moq.) J.D. Sauer] control. Research was conducted over 3 years with flumioxazin and sulfentrazone to evaluate the influence of herbicide rate and mixture on waterhemp control and soybean injury, density, development, and grain yield. In a year with limited rainfall, waterhemp control was >90% up to 9 weeks after planting (WAP) and soybean injury never exceeded 7% from all treatments. In years with more adequate moisture, reduced rates of either flumioxazin or sulfentrazone applied with any mixture herbicide provided similar waterhemp control (>95%) to a full‐labeled rate of flumioxazin or sulfentrazone applied alone at 3 WAP. A full‐labeled rate of flumioxazin or sulfentrazone in mixture with fomesafen + S‐metolachlor provided the greatest and most uniform waterhemp control (>90%) at 9 WAP. When applied at full‐labeled (1x) rates, soybean injury at 3 WAP from flumioxazin‐ and sulfentrazone‐based treatments ranged from 8 to 18% and 2 to 6%, respectively. Similar trends among treatments were observed for soybean density. Despite early‐season injury, treatments applied at a 1x rate did not reduce grain yield. However, applicators should be cognizant of spray boom overlap as 2x rates increased the extent of yield loss by up to 10 bu acre–1. Soybean injury at 9 WAP was a more accurate predictor of grain yield loss (R2 = .51) than injury at 3 WAP (R2 = .14).

Effect of planting density and row spacing on the yielding of soybean (Glycine max L. Merrill)

The paper presents the effect of planting density and row spacing on the growth, development and yield of soybean, cv. Merlin, under very diversified thermal and humidity conditions in the north-central part of Poland. The field experiment was performed in 2016–2019. Three planting densities were applied (70, 90 and 110 seeds per 1 m<sup>2</sup>) with two row spacing (16 and 32 cm), in 4 replications. Under good humidity and thermal conditions in 2016 and 2017, the yield of seeds and protein in soybean was 3.3 times higher than if exposed to extreme drought and accompanying high air temperatures in 2018 and 2019. The highly diversified thermal and humidity conditions also contributed to a significant decrease in the effect of the factors applied on the structural yield components, leaf area index and dry matter of nodules. As a result, no need of increasing soybean density was observed; along with row spacing, it should be chosen according to the region.

Soybean density and Palmer amaranth (Amaranthus palmeri) establishment time: effects on weed biology, crop yield, and economic returns

AbstractKnowledge of crop–weed interference effects on weed biology along with yield penalties can be used for the development of integrated weed management (IWM) tactics. Nevertheless, little is known about the beneficial effects of soybean [Glycine max (L.) Merr.] density, an important aspect of IWM, on late Palmer amaranth (Amaranthus palmeri S. Watson) establishment time. Two field experiments were conducted in 2014 and 2015 to investigate how various soybean densities and A. palmeri establishment timings in weeks after crop emergence (WAE) affect height, biomass, and seed production of the weed but also crop yield in drill-seeded soybean. Soybean density had a significant impact on dry weight and seed production of A. palmeri that established within the first 2 wk of crop emergence, but not for establishment timings of the weed 4 wk and later in relation to crop emergence. Differential performance of A. palmeri gender was observed, regarding greater biomass production of female than male plants under crop presence, and merits further investigation. Grain yield reductions were recorded at earlier A. palmeri establishment timings (i.e., 0 and 1 WAE) compared with 8 WAE establishment timing in 2014 and 2015. High soybean densities resulted in greater soybean yields compared with low soybean density, but no grain yield benefits were observed between medium and high soybean densities. Crop budget analysis revealed the benefits of moderate seeding rate (i.e., 250, 000 seeds ha−1) increases in comparison to lower (i.e., 125,000 seeds ha−1) or high (i.e., 400,000 seeds ha−1) on crop revenue, net income returns, and breakeven price. Earlier A. palmeri establishment timings (i.e., 0, 1, and 2 WAE) resulted in lower crop revenue and net income returns compared with later establishment timings of the weed.

Flumioxazin effects on soybean canopy formation and soil-borne pathogen presence

AbstractRapid crop canopy formation is important to reduce weed emergence and selection for herbicide resistance. Field experiments were conducted in 2017 and 2018 in Fayetteville, AR, to evaluate the impacts of PRE applications of flumioxazin on soybean injury, soybean density, canopy formation, and incidence of soil-borne pathogens. Flumioxazin was applied at 0, 70, and 105 g ai ha−1 to predetermined flumioxazin-tolerant and -sensitive soybean varieties. Flumioxazin at 70 g ha−1 injured the tolerant and sensitive varieties from 0% to 4% and 14% to 15%, respectively. When averaged over flumioxazin rates, density of the sensitive variety was only reduced in 2017 when activation of flumioxazin was delayed 7 d. Compared to the tolerant soybean variety, flumioxazin at 70 g ha−1 delayed the sensitive variety from reaching 20%, 40%, 60%, and 80% groundcover by 15, 16, 11, and 5 d, respectively. No delay in canopy closure (95% groundcover) was observed with either variety. Consequently, no yield loss occurred for either variety following a flumioxazin application. Flumioxazin did not impact root colonization of Didymella, Fusarium, Macrophomina, or Rhizoctonia. Pythium colonization of the soybean stem was increased by flumioxazin in 2017, but not in 2018. Increased injury, delays in percent groundcover, and an increase in Pythium colonization of soybean following a flumioxazin application may warrant the need for other soil-applied herbicides at soybean planting. Alternatively, soybean injury and delays in percent groundcover following flumioxazin applications can be mitigated through appropriate variety selection; however, comprehensive screening is needed to determine which varieties are most tolerant to flumioxazin.

Effects of aphid-resistant soybean on nontarget herbivores in Minnesota

The use of aphid-resistant soybean varieties containing Rag genes can provide an effective pest management strategy against soybean aphid (Aphis glycines Matsumura). However, the compatibility between soybean containing Rag genes and the management of other potential soybean pests (i.e., nontarget herbivores) is poorly understood. Therefore, our goal was to (1) assess the efficacy of pyramided (Rag1+Rag2) aphid-resistant soybean for reduction of soybean aphid populations, and (2) determine if aphid-resistant soybean affects populations of nontarget herbivores under field conditions. To accomplish these goals, field experiments were conducted in southeast Minnesota from 2015 to 2017 for a total of five site-years using whole-plant counts to assess soybean aphid densities and sweep-net sampling to estimate nontarget herbivore densities in plots of near-isoline soybean with Rag1+Rag2 (i.e., resistant) or no Rag genes (i.e., susceptible). Plant genotype (i.e., resistant or susceptible) affected seasonal abundance of soybean aphid, with fewer soybean aphids on aphid-resistant than susceptible soybean. Furthermore, plant genotype affected seasonal abundance of bean leaf beetle (Cerotoma trifurcata Forster), green cloverworm (Hypena scabra Fabricius), and potato leafhopper (Empoasca fabae Harris). Aphid-resistant soybean was associated with increased seasonal abundance of bean leaf beetle and reduced seasonal abundance of potato leafhopper and green cloverworm. The abundance of these herbivores was also associated with seasonal abundance of soybean aphid as a covariate. Results presented here confirm the efficacy of aphid-resistant soybean with Rag1+Rag2 against soybean aphid and show that aphid-resistant soybean can influence the seasonal abundance of nontarget herbivores in soybean. However, the magnitude of impacts of aphid-resistant soybean on nontarget herbivores was relatively small and likely of little-to-no agronomic significance, which suggests compatibility of aphid-resistant soybean with management of other potential pests.

Do Weeds From Seeds or Regrowth in Coexistence Periods Alter Biochemical and Yield Characteristics of Soybeans?

The objective of this study was to evaluate changes in soybean secondary metabolism and soybean yield components when subjected to coexistence periods with volunteer corn and established horseweed (Conyza spp.) regrowth. Two field experiments were conducted in the agricultural years 2015/2016 and 2016/2017 at Passo Fundo University, Passo Fundo, Rio Grande do Sul, Brazil. Experiment I was conducted in the agricultural year 2015/2016 in order to establish periods of coexistence between soybean and corn. The treatments consisted of two soybean densities in the main plots (175,000 and 350,000 plants ha-1) and different periods of coexistence between soybean and corn in the subplots. Experiment II was conducted in the agricultural year of 2016/2017 in order to investigate the interference of regrowth horseweed during coexistence periods with soybean. The total phenols, flavonoids, saponins, soybean yield components and seed yields were evaluated. Volunteer corn that initiates growth after the V4 soybean stage and horseweed regrowth during cultivation do not adversely affect secondary metabolism, seed yield or soybean yield components.

Corn Yield Loss Due to Volunteer Soybean

The widespread adoption of glyphosate-resistant corn and soybean in cropping rotations often results in volunteer plants from the previous season becoming problem weeds that require alternative herbicides for control. Corn yield losses due to season-long volunteer soybean competition at several densities in two growing seasons were used to define a hyperbolic yield loss function. The maximum corn yield loss observed at high volunteer soybean densities was about 56%, whereas, the incremental yield loss (I) at low densities was 3.2%. Corn yield loss at low volunteer soybean densities was similar to losses reported for low densities of velvetleaf and redroot pigweed, with 10% yield loss estimated to occur at 3 to 4 volunteer soybean plants m−2. Several herbicides, including dicamba with or without diflufenzopyr applied at the V2 growth stage of volunteer soybean, provided > 90% control, demonstrating several economical options to control volunteer glyphosate-resistant soybean in glyphosate-resistant corn. Reevaluation of control recommendations may be needed with commercialization of other genetically modified herbicide-resistant soybean varieties.

Effect of Drill-Seeded Soybean Density and Residual Herbicide on Palmer Amaranth (Amaranthus palmeri) Emergence

Palmer amaranth is the most troublesome weed of soybean in the southern United States. Field experiments were conducted at two Arkansas locations to determine the effect of drill-seeded soybean density on Palmer amaranth emergence. Experimental factors were multiple soybean seeding rates planted on a 19-cm-wide row spacing and the presence or absence of a PRE residual herbicide (flumioxazin plus pyroxasulfone). Soybean groundcover was measured throughout the growing season and daily soil temperature was recorded in selected soybean densities. In the absence of a PRE residual herbicide, at least a 1.7-fold reduction in Palmer amaranth emergence occurred when soybean were present. Differences in Palmer amaranth emergence occurred among soybean densities for both locations, suggesting the value of crop canopy in preventing Palmer amaranth emergence in the absence of an effective residual herbicide. In plots treated with the PRE herbicide, no difference in Palmer amaranth emergence occurred among soybean densities, except for the absence of soybean. Achievement of 95% groundcover by soybean reduced daily soil temperature fluctuations, which in turn reduced Palmer amaranth emergence. For both locations, soybean grain yields were greatest at the highest seeding rate (617,500 seed ha−1). In the presence of flumioxazin plus pyroxasulfone applied PRE, greater grain yields occurred compared to the absence of a PRE herbicide at both Fayetteville and Marianna. Based on this research, an effective PRE-applied residual herbicide has more influence on Palmer amaranth emergence than soybean density, and Palmer amaranth germination and emergence are dependent upon daily soil temperature fluctuations, which is a function of soybean density.

Potential Synergistic Effects of Cereal Rye Biomass and Soybean Planting Density on Weed Suppression

Increasing crop density is a cultural weed management practice that can compliment the use of cover crops for weed suppression. In this research, we created a range of cover crop biomass and soybean densities to assess their weed-suppressive ability alone and in combination. The experiment was conducted in 2008 and 2009 in Maryland and Pennsylvania using five levels of cereal rye residue, representing 0, 0.5, 1.0, 1.5, and 2.0 times the ambient level, and five soybean densities ranging from 0 to 74 seeds m−2. Weed biomass decreased with increasing rye residue and weeds were completely suppressed at levels above 1,500 g m−2. Weed biomass also decreased with increasing soybean density in 2 of 4 site–years. We evaluated weed suppression by fitting an exponential decay model of weed biomass as a function of rye biomass and a hyperbolic model of weed biomass as a function of soybean density at each of the five tactic levels. We multiplied these individual tactic models and included an interaction term to test for tactic interactions. In two of the four site-years, the combination of these tactics produced a synergistic interaction that resulted in greater weed suppression than would be predicted by the efficacy of each tactic alone. Our results indicate that increasing soybean planting rate can compensate for lower cereal rye biomass levels when these tactics are combined.

Effects of plant density of intercropped soybean with tall sorghum on competitive ability of soybean and economic yield at Otobi, Benue State, Nigeria

Field experiment was conducted for three years to evaluate the influence of plant population density of intercropped soybean with sorghum on its competitive ability and economic yield at Otobi, Benue State, Nigeria. The experiment was laid out in split-split plot with three replications. The main plot treatment comprised of cropping systems with two levels (sole cropping, intercropping), while the sub-plot treatment was soybean variety at three levels (TGX 536-O2D, Samsoy 2, TGX 923-2E) and the sub-sub-plot treatment was plant population density of soybean at three levels (200,000 plants/ha; 333,000 plants/ha and 400,000 plants/ha). Planting intercropped soybean at 333,000 plants/ha gave significantly higher seed yield than planting at 400,000 plants/ha, which in turn had greater seed yield than planting at 200,000 plants/ha during the three years of experimentation. Increased density of soybean beyond 333,000 plants/ha in the intercrop reduced sorghum yield. The results showed that all the intercrop combinations had land equivalent ratio (LER) and area- time equivalency ratio( ATER) above unity (1.63 - 1.97) and (1.41 - 1.47),respectively, under all the densities of soybean tested, suggesting a considerable benefit for intercropping soybean with sorghum. LER figures decreased with increase in soybean density. ATER was highest at 333.000 plants/ha, suggesting higher productivity at this density. Aggressivity values were consistently negative at 200,000 plants/ha with a mean value of -0.25 and it was inconsistent at 333,000plants/ha and 400,000 plants/ha. The competitive ratio of soybean increased (0.76 - 1.15) with increasing density of the soybean in the intercrop combinations, indicating higher competitiveness at higher densities than the sorghum component. The competitive ratio of sorghum had the opposite response (1.23 - 0.76). Relative crowding coefficient (K) was inconsistent at all densities, while land equivalent coefficient (LEC) was above 0.25 indicating intercrop advantages for all combinations. ‘Soybean yield equivalent’ was also highest at 333,000 plants/ha (1.70) implying general suitability of soybean to intercropping at this density. Dominance analysis revealed that sole crop treatments were dominated. Intercropped soybean planted at 333,000 plants/ha and 400,000 plants/ha gave significantly higher net benefits than those planted at 200,000 plants/ha. Marginal analysis showed that planting soybean at 333,000 plants/ha gave the highest marginal rate of return and this was 2825%.These results suggest that growing soybean under intercropping at Otobi is biologically efficient at 333,000 plants/ha and more profitable. Key words: Intercropped soybean, density, competition, Otobi.

Determining the Optimal Timing of Foliar Insecticide Applications for Control of Soybean Aphid (Hemiptera: Aphididae) on Soybean

Field experiments were performed over 3 yr to examine the impact of insecticide application timing to control soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), populations and to prevent soybean yield losses. Experiments were conducted in early and late-planted soybean, Glycine max (L.) Merr. Insecticide applications were made based on soybean growth stages. In 2001, applications were made at V1, V3, R2, and R3 growth stages; in 2002 and 2003, applications were made at R2, R3, and R4 stages. Additional treatments consisted of an unsprayed control and a multiple spray treatment that received insecticide applications at 7-10-d intervals. Soybean aphid densities were recorded throughout the growing season, and yields were measured. Soybean aphid populations varied considerably across years and planting dates. In general, late-planted soybean exhibited higher aphid pressure than early planted soybean, and experiments in 2002 had lower aphid numbers than those in 2001 and 2003. The multiple spray treatment significantly increased yield over the control in four of the six experiments, the exceptions being 2002 late planted and 2003 early planted. This suggests that soybean aphid populations were not large enough to cause yield losses in these two experiments. The R3 spray treatment increased yield in three of the six experiments (2001 late planting, 2002 early planting, and 2003 late planting), the R2 spray treatment increased yield in two of six experiments (2001 and 2003 late plantings), and the V1 application increased yield over the control in the 2001 late-planted experiment. Results suggest that when aphid populations are high insecticide applications made at R2 and R3 plant stages are most effective in preventing yield loss.