Soybean Planting Date Research Articles

Soybean yield is positively linked to organic matter, but planting date remains more influential

AbstractEstablishing connections between soil health indicators and crop performance will help ensure that tests recommended to farmers relate to outcomes of interest. This study assessed the relationship of soybean [Glycine max (L.) Merr] yield with three common soil health indicators: soil organic matter (SOM), permanganate oxidizable carbon (POXC), and autoclaved citrate extractable nitrogen (ACE‐N). These tests were assessed alongside other factors (soil test phosphorus, soil test potassium [STK], mapped clay, planting date, summer precipitation, and location). Soil samples were collected from 457 producer‐managed fields between 2019 and 2021 in Arkansas, Michigan, North Carolina, and Wisconsin. Planting date and yield were reported by producers, while mapped clay and rainfall were determined using publicly available data. Simple linear regression was used to assess the relationship between soil health indicators and yield: the natural log of SOM and POXC were positively associated with soybean yield (R2 = 0.07, p < 0.001; R2 = 0.03, p < 0.001), while ACE‐N was not (p = 0.872). Multiple linear regression was used to further test the relationship of SOM and POXC with yield, while accounting for other factors that contribute to soybean yield. Models explained 27% of variation in yield, with significant factors including SOM or POXC, soybean planting date, STK, and mapped clay. Based on standardized coefficients, planting date was the most influential factor associated with yield. Broadly, our results indicate that improvements in yield are linked to higher SOM, but management decisions like planting early are critical for achieving high yields.

Soybean planting date affects the relationships between soil test values and grain yield

AbstractMany soybean [Glycine max (L.) Merr.] growers in the US Midwest rely on soil test values for evaluating the crop's fertilizer needs. However, threshold values for Illinois were calibrated to soybean yield in the 1960s when the production systems and yield potential were much different than today. The objective of this study was to determine which and how well soil test values predict yield of unfertilized soybean. Preplant soil samples, collected from 133 trials across Illinois from 2014 to 2021, were analyzed for 14 chemical attributes and compared to unfertilized soybean grain yields from those same studies. Pearson correlation coefficients (r), principal factor analysis, and latent variable regression models were used to determine those soil attributes most closely associated with grain yield and yield components. The association of planting date and yield (r = −0.56) led to dividing the data set into five planting date groups. Soil fertility levels resulted in a strong correlation with yield for Late or Very‐late planting groups, but not for the Early or Very‐early groups. A factor analysis of soil attributes largely resulted in retention of two factors, identified as Soil Organic Charge and Soil Fertility, across the planting‐date groups. Regression of these factors with yield confirmed that soil fertility had a greater influence on grain yield for late‐planted soybeans than early‐planted and that these differences were associated with average seed weight. Therefore, positioning late‐planted soybeans in higher fertility fields and early‐planted soybeans in lower‐fertility fields could reduce the need for supplemental fertilization.

Soybean planting dates and maturity groups: Maximizing yield potential and decreasing risk in Louisiana

AbstractSoybean [Glycine max (L.) Merr.] producers in Louisiana began shifting to an early soybean production system (ESPS) in the early 2000s by planting earlier maturing varieties in April and May. Although this shift in planting practices has been supported by research elsewhere beginning in the mid‐1990s, there is minimum data focusing on the ESPS across Louisiana. The overall objective of this research was to evaluate the effect of planting date, maturity group (MG), and their combination across a comprehensive set of yield environments in the state of Louisiana to determine the combination of optimum planting date and MG for soybean production. We gathered field data from the 2013 to 2020 seasons originated from three Louisiana State University AgCenter research stations and four seed companies. A total of 428, 926, and 331 observations were analyzed from the Northeast, Central, and Southwest Louisiana regions, respectively. When including all data from across Louisiana, the optimum planting date was April 30. Breaking by regions, the average optimum planting date for the Northeast Louisiana region was April 9. The Central and Southwest results were divided by MG section, and the approximate optimum planting dates were April 15 and May 15, respectively. These results support the ESPS for the Northeast and Central Louisiana regions, but not for the Southwest Louisiana region. Optimizing planting recommendation is a critical component for supporting the development of varieties suitable for the southern production systems of the United States.

Planting date and dicamba‐based herbicide programs influence soybean production in the Southern Great Plains

AbstractThe interplay of management decisions involving soybean (Glycine max L.) planting date, herbicide programs, and herbicide application timings is critical to optimize soybean performance and weed control in Southern Great Plains soybean production systems. This research sought to evaluate soybean yield potential and the level of weed control as influenced by early‐, delayed‐, and late‐ planting dates and various combinations of preemergence (PRE), early‐postemergence (EPOST), and mid‐postemergence (MPOST) weed management programs. A field study was established in Bixby, OK in 2017 and 2018 under irrigated conditions and in Perkins, OK in 2017 under dryland conditions, consisting of three planting windows (early, delayed, and late) of XtendFlex soybean, with or without a PRE (chlorimuron + flumioxazin + pyroxasulfone + glyphosate + dicamba) combined with EPOST or EPOST + MPOST (glyphosate + dicamba) versus no in‐season applications. The gap in late‐planted soybean yield potential, compared to early‐planted soybean, was exacerbated in the dryland systems (1346 kg ha−1) versus an irrigated system (2311 kg ha−1). Use of PRE provided 60% weed control until MPOST and increased yields by 657 kg ha−1 and 457 kg ha−1 for delayed and late‐planted soybean, respectively. Late‐planted soybean with EPOST + MPOST provided up to 50% weed control, but lack of biomass production for cultural control reduced weed control by 29% compared to early‐ and delayed‐planted soybean. From an agronomic management standpoint, the time of soybean planting is influential on the success of weed control measures and soybean yields in double‐cropping system in the Southern Great Plains, particularly with late‐planted soybean.

Effect of ultra‐early, early, and normal soybean planting dates and rye cover crop on soybean grain yield

AbstractWith changes to climate and crop insurance, earlier soybean [Glycine max (L.) Merr.] planting dates need to be investigated. Additionally, the use of a cover crop prior to soybean is promoted as a sustainable practice though little is known about cover crop and ultra‐early soybean planting (prior to April 15). The objective was to evaluate soybean planting date and cereal rye (Secale cereale L.) cover crop termination timing on cover crop biomass, soybean plant population, and yield. The study was conducted in Northeast and West Central Ohio in 2021 and 2022. Treatments included three soybean planting dates (early April, late April, and late May) and three cover crop treatments (termination 1–2 weeks prior to planting or “early,” termination at or after planting or “late,” and no cover crop). Cover crop biomass increased as termination was delayed. Soybean planted in early April resulted in a yield reduction of 1.8 Mg ha−1 when planted into a cover crop compared to the no cover crop control. However, when soybean was planted in late April, grain yield was not different among cover crop treatments. Yield reduction associated with early April planting with a cover crop was likely due to low soybean plant population, especially in Northeast Ohio, where plant population was <55,000 plants ha−1 with a cover crop and >120,000 plants ha−1 without a cover crop. To maximize yield, soybean should be planted by the end of April in Northeast Ohio. In West Central Ohio, soybean can be planted in early April without a cover crop.

Soybean planting date and seeding rate effect on germinability and vigor of harvested seed

AbstractSeed is one of the most crucial inputs for soybean [Glycine max (L.) Merr.] production due to its influence on plant population, uniformity, and yield, as well as its cost as an input. Seeds of good quality have high germinability and vigor, providing an adequate stand with uniformly good growth and development even under adverse conditions. This study aimed to measure the effect of soybean planting date and seeding rate on harvested seed mass, seed germinability, and seed vigor. Seeds were collected from a field experiment during the 2020 and 2021 growing seasons at two locations in Ohio: Western Agricultural Research Station and Northwest Agricultural Research Station. The study was conducted using a split‐plot randomized complete block design (planting date–whole plot; seeding rate–subplot) with four replications. Standard germination and accelerated aging tests were conducted in the laboratory using seeds harvested from the field study. All four site‐years demonstrated that planting soybean very late (June 16–July 1) produced lower weight seeds than the other planting dates. Across planting date and seeding rate treatments, the harvested seed germinability was ≥94%. However, soybean planted in early June (June 1–June 15) had the lowest seed vigor results (64%–81%) compared to other planting dates (80%–89%). Rainfall at R7–R8 development stages is negatively correlated with the seed vigor. The results will help seed producers optimize seed production and quality and suggest avoiding planting in June to increase harvested seed vigor.

Effect of Infection Timing by Four Pythium spp. on Soybean Damping-Off Symptoms with and Without Cold Stress.

Pythium spp. cause damping-off of soybean, especially when soil conditions at or shortly after planting are cool and wet. Soybean planting dates continue to shift to earlier dates, so germinating seed and seedlings are exposed to periods of cold stress at a time which favors infection by Pythium, and seedling disease occurs. The objective of this study was to assess infection timing and cold stress on soybean seedling disease severity caused by four Pythium spp. prevalent in Iowa, namely P. lutarium, P. oopapillum, P. sylvaticum, and P. torulosum. Each species was used individually to inoculate soybean cultivar 'Sloan' using a rolled towel assay. Two temperature treatments (continuous 18°C [C18]; a 48-h cold stress period at 10°C [CS]) were applied. Soybean seedling age was divided into five growth stages (GS1 to GS5). Root rot severity and root length were assessed at 2, 4, 7, and 10 days after inoculation (DAI). At C18, root rot was greatest when soybean was inoculated with P. lutarium or P. sylvaticum at GS1 (seed imbibes water) and with P. oopapillum or P. torulosum at GS1, GS2 (radicle elongation), and GS3 (hypocotyl emergence). After CS, soybean susceptibility to P. lutarium and P. sylvaticum was reduced compared to C18 for inoculation at all GSs except GS5 (unifoliate leaf emergence). Conversely, root rot by P. oopapillum and P. torulosum was greater after CS compared to C18. Data from this study demonstrate that greater root rot, and consequently more damping-off, is likely if infection occurs at early germination stages before seedling emergence.

Soybean planting date and seeding rate effect on grain yield and profitability

AbstractTimely soybean [Glycine max (L.) Merr.] planting is ideal for maximizing grain yield. However, weather conditions often limit farmers’ ability to plant timely. The objectives of this study were to (a) measure the effect of soybean planting date and seeding rate on grain yield, (b) identify the agronomic optimum seeding rate (AOSR; the seeding rate where soybean yield is maximized), and (c) compare the net economic return of the base treatment (May 10 to 31 planting date and 370,000 seeds ha−1 seeding rate) to the other treatment combinations. The experiment was conducted in 2020 and 2021 in Ohio at the Western (WARS) and Northwest (NWARS) Agricultural Research Stations with a split‐plot randomized complete block design with four replications. The whole plot factor was four planting dates ranging from April 25 through July 1, and the sub‐plot factor was five seeding rates ranging from 123,500 to 618,000 seeds ha−1. When water was not limiting, soybean planted in April and May yielded 8% to 26% more than soybean planted late June. In general, planting in May resulted in a lower AOSR (247,000 to 303,000 seeds ha−1), compared to planting in June, where AOSR ranged from 430,000 to 618,000 seeds ha−1. Comparative net economic return was the lowest (from $237 ha−1 to $938 ha−1) when soybean was planted after mid‐June at 123,500 seeds ha−1. These findings can help farmers improve soybean grain yield by adjusting their seeding rate based on planting date to maximize profitability.

Spring-seeded winter rye living mulches enhance crop biodiversity and promote reduced tillage organic soybeans

As recognition increases of the benefits of reducing soil disturbance to preserve soil health, there is mounting interest in developing innovative methods of using cover crops as living mulches to control weeds in organic grain systems. Spring-planted winter cereal rye (Secale cereale L.) interseeded with soybeans (Glycine max. [L.] Merr.) is a promising, yet untested, living mulch system because rye exhibits vigorous growth in the early spring during the critical weed free period, but then dies back as the soybean canopy matures. The objectives of this study were to compare a rye living mulch system with a tilled “organic business-as-usual” control, and to understand the risks and benefits associated with delaying soybean planting date to manage the weed seed bank prior to establishment of rye and soybeans. Three treatments including (1) a June-planted rye and soybean living mulch system, (2) a June planted tilled control, and (3) a May planted tilled control, were compared in terms of weed prevalence and soybean grain yield in a randomized complete block experimental design with four replications implemented across 3 site years from 2019 to 2020. Interseeding rye as a living mulch resulted in consistently higher weed pressure as compared to tilled controls. Increased weed pressure in May- over June-planted controls in 2 of 3 site years indicate planting date influences weed dynamics. Rye biomass was positively correlated with soybean yield (R2 = 0.76, r = 0.87, p < 0.05) and negatively correlated with weed biomass (R2 = 0.63, r = −0.79, p < 0.05). Under optimal conditions where rye biomass was maximized, interseeding rye adequately suppressed weeds without reducing soybean yields as compared to tilled controls. However, under drier conditions with lower rye production, increased weed pressure and reduced yields emphasize the risks associated with living mulch systems.

Planting date and maturity group impact on soybean seed quality in the southeastern United States

AbstractThe impacts on soybean seed quality from shifting to using earlier soybean planting dates (PDs) and earlier‐maturing varieties in the southeastern United States are not well understood. The objective of this study was to determine the impact of diverse PDs and maturity groups (MGs) on soybean protein content, oil content, seed damage, and purple seed stain. Studies were installed across seven North Carolina locations in 2019 and 2020 to determine the impact of PD (mid‐March through mid‐July) and MG (2–7) on seed quality. Protein content declined as planting was delayed for the early MGs (2–5) but was stable across PD for the later MGs (6–7). It was observed that early‐maturing varieties (MG ≤5) had a lower protein content than the later‐maturing varieties (MGs 6–7). The oil content was greater in the early MGs (MGs 2–4) compared with the later MGs (MGs 5–7), with oil content and protein content having an inverse relationship. Seed damage was greatest when planting before late April with early MGs (MGs 2–4). Less purple seed stain was found in MGs 5–7 compared with the earlier MGs across all PDs. Further research is needed to understand how to minimize seed damage and purple seed stain as producers consider shifting to an earlier production system for the associated yield benefits in North Carolina and across the southeastern United States.

Sensitivity of soybean planting date to wet season onset in Mato Grosso, Brazil, and implications under climate change

Sensitivity of soybean planting date to wet season onset in Mato Grosso, Brazil, and implications under climate change

Detecting Recent Crop Phenology Dynamics in Corn and Soybean Cropping Systems of Kentucky

Accurate phenological information is essential for monitoring crop development, predicting crop yield, and enhancing resilience to cope with climate change. This study employed a curve-change-based dynamic threshold approach on NDVI (Normalized Differential Vegetation Index) time series to detect the planting and harvesting dates for corn and soybean in Kentucky, a typical climatic transition zone, from 2000 to 2018. We compared satellite-based estimates with ground observations and performed trend analyses of crop phenological stages over the study period to analyze their relationships with climate change and crop yields. Our results showed that corn and soybean planting dates were delayed by 0.01 and 0.07 days/year, respectively. Corn harvesting dates were also delayed at a rate of 0.67 days/year, while advanced soybean harvesting occurred at a rate of 0.05 days/year. The growing season length has increased considerably at a rate of 0.66 days/year for corn and was shortened by 0.12 days/year for soybean. Sensitivity analysis showed that planting dates were more sensitive to the early season temperature, while harvesting dates were significantly correlated with temperature over the entire growing season. In terms of the changing climatic factors, only the increased summer precipitation was statistically related to the delayed corn harvesting dates in Kentucky. Further analysis showed that the increased corn yield was significantly correlated with the delayed harvesting dates (1.37 Bu/acre per day) and extended growing season length (1.67 Bu/acre per day). Our results suggested that seasonal climate change (e.g., summer precipitation) was the main factor influencing crop phenological trends, particularly corn harvesting in Kentucky over the study period. We also highlighted the critical role of changing crop phenology in constraining crop production, which needs further efforts for optimizing crop management practices.

Influence of soybean management decisions on the subsequent rice crop's response to nitrogen

AbstractLittle is known about the effects of soybean [Glycine max (L.) Merr.] management practices on the success of the subsequent rice (Oryza sativa L.) crop. A study was initiated to determine how rice was affected by the preceding soybean crop's maturity group (MG) and planting date when grown in rotation on silt loam and clay soils. Optimum and late soybean planting dates and MGs (3.5, 4.7, 5.4, and 5.6) were followed by a rice crop. The results differed by soil texture, with the planting date and MG selection of the previous soybean crop more influential to the rice crop produced on a silt loam soil than a clay soil. Rice grown on a clay soil produced a higher grain yield when following a 5.4 MG soybean, whereas the planting date of a previous soybean crop influenced the soil‐N credits measured at rice emergence. On a silt loam soil, the interaction of both planting date and MG of the previous soybean crop influenced the maximal grain yield achieved by the rice crop. When soybean is planted during an optimum planting date, soybean MG has little effect on the successive rice crop. However, when the soybean crop is planted late, a determinate MG should be selected to achieve the highest rice crop total N uptake, maximal grain yield, and reduce the rate of fertilizer‐N needed to achieve 95% relative grain yield. Management techniques should be considered when implementing a soybean–rice rotation to maximize rice grain yield and overall farm profitability.

Integrated Weed Management Systems to Control Common Ragweed (Ambrosia artemisiifolia L.) in Soybean

As resistance to herbicides limits growers' weed management options, integrated weed management (IWM) systems that combine non-chemical tactics with herbicides are becoming critical. A 2 year integrated weed management (IWM) study was conducted at three locations in VA, USA. The factorial study evaluated: (1) soybean planting date (early or late planted) (2) with or without winter cover (cereal rye/wheat or no cover), and (3) with or without harvest weed seed control (HWSC). Prior to soybean planting in the first year, winter cover resulted in a 22% reduction in common ragweed density compared to no cover. At soybean harvest in the first year, the lowest common ragweed densities were in the late planted plots following winter wheat, and common ragweed aboveground biomass was reduced by 46 and 22% at two locations in late planted compared to early planted soybean. To evaluate the impact of the first year's treatments and HWSC, full season soybeans were planted across the trial in the second year. Prior to soybean planting in the second year, late planting in the first year common ragweed density was reduced by 83% at one location, but significant reductions were not observed elsewhere. When comparing winter cover to no cover, common ragweed densities were reduced by 31 and 49% at two locations and densities were similar at the third location. Harvest weed seed control reduced common ragweed density by 43% at one location compared to the conventional harvest plots but no significant reductions were observed at the other locations or at other rating timings. However, there was a significant location by planting date by winter cover interaction and the overall lowest common ragweed densities (4.1 to 10.3 plants m−2) were in the late planted plots with winter cover. This research indicated that winter cover, late planting, and HWSC can reduce common ragweed populations with late planting being the most influential. Therefore, double-cropping soybean after wheat is likely the most viable means to better control common ragweed using IWM as it combines both winter cover and late planting date.

Effects of Soybean Planting Date on Yield Loss From Defoliation

Soybean, Glycine max (L.) Merr., is planted during 3.5-4 mo across the Mid-South United States. Currently, no information exists regarding the effects of planting date on soybean yield loss from early season defoliation. In 2015 and 2016, to evaluate the effects of planting date on yield loss from defoliation, soybean were planted in field plots 2 wk apart from early April to mid-June, for a total of six planting dates. Each planting date included a nondefoliated control and a 100% defoliation treatment where leaves were manually excised at the V4 growth stage. Mean yield loss from defoliation varied across planting dates, with mid-April plantings having the least amount yield reduction, 573 kg/ha, and early-June plantings having the greatest yield reduction, 904 kg/ha. Percent yield reduction from defoliation increased as planting was delayed, suggesting that defoliation thresholds might need adjustment based on planting date and yield potential. However, more research is needed at lower levels of defoliation to accurately delineate such thresholds.

Analyzing corn and cotton producers optimal prevented planting decision on moral hazard

AbstractThe prevented planting provision U.S. crop insurance programs protects producers from financial losses and risk associated with delayed planting. This provision has recently undergone some changes due to concerns about moral hazard in this provision. However, little is known about the likelihood of moral hazard in prevented planting and how these changes impact this possibility. We compared the net returns and variability of net returns for the four prevented planting options available for a corn (Zea mays L.) and upland cotton (Gossypium hirsutum L.) producer assuming soybean [Glycine max (L.) Merr.] as a viable second crop. We determine the optimal prevented planting option using the current prevented planting coverage factor at three crop insurance coverage levels. We also show how reductions in the prevented planting coverage factor would change the optimal selection and moral hazard in prevented planting. Data were collected from non‐irrigated corn, upland cotton, and soybean planting date experiments located in Tennessee. Yield response functions to planting date for corn, cotton, and soybean were estimated and incorporated into simulation models to generate distributions of net returns. Risk neutral, profit maximizers would choose a late planting option over the full prevented planting payment, but as risk aversion increases, the full prevented planting payment was preferred. Reduction in prevented planting coverage factors will likely reduce the likelihood an insured producer chooses to not produce a crop and take the full prevented planting indemnity payment, despite planting during the late planting period or switching crops being more profitable options.

Soybean maturity group and planting date influence grain yield and nitrogen dynamics

AbstractManipulation of soybean [Glycine max (L.) Merr.] maturity group (MG) and planting date will increase the yield of a soybean crop while simultaneously influencing the potential soil‐nitrogen (N) credits. Variations in N returned to the soil by soybean can significantly affect the amount of fertilizer‐N needed for the subsequent crop. Four soybean MGs (3.5, 4.7, 5.4, and 5.6) were evaluated at optimal and late planting dates in Arkansas. Grain yield was significantly different among MGs in 2016 (P = .0012) and 2017 (P = .0004), with the 4.7 MG consistently yielding the highest at 3,232 kg ha−1. Plant total aboveground N uptake (TNU) increased with increasing grain yield (P = .0167) and was significantly higher when planted in an optimal planting window (P = .0004). The N removed from the cropping system through grain harvest (147–201 kg N ha−1) was significantly different among MGs in 2016 (P < .0001) and in 2017 was significantly influenced by the planting date × MG interaction (P = .0397). The net N returned to the soil through unharvested biomass (24–75 kg N ha−1) was not influenced by planting date (P = .7796) or MG (P = .3475); however, net N returned decreased as grain yield increased (P = .0522). An optimum planting date of a well‐adapted soybean MG produces the highest grain yield, TNU, and N removed from the cropping system, identifying a relationship that allows producers to achieve maximum profitability while minimizing inputs to the whole farm system.

Soybean in No-Till Cover-Crop Systems

Introducing agro-ecological techniques such as no-tillage systems with cover crops in rotations with soybean (Glycine max (L.) Merr.) could provide more resilience to changing climatic conditions and, at the same time, reduce soil erosion, nitrate leaching, and weed density in the main crop. However, there are challenges in introducing no-tillage techniques in crop systems in Europe as there is little quantitative knowledge about the agro-economic impact. The objectives of this study were to evaluate the agronomic and economic impacts of three soybean cropping systems involving a rye (Secale cereal L.) cover crop prior to soybean, i.e., two no-tillage systems; either herbicide-free with crimping the rye or herbicide-based without rye crimping and one plough-based in which rye was cut as green silage. The impacts of these cropping strategies were compared in a three-year cropping system experiment at a research station in north-eastern Germany with and without irrigation. The following parameters were measured: (1) cover crop biomass; (2) weed biomass; (3) soybean plant density; (4) soybean grain yield; and (5) gross margin of the cropping system. The results showed that all three soybean cropping systems can effectively suppress weeds. System (C), the no-tillage herbicide-based system, produced the lowest rye biomass and highest soybean yield; system (B), the no-tillage herbicide-free/crimped rye system, produced the highest rye biomass and lowest soybean yield compared to system (A), the standard cutting/plough-based system. The differences in rye biomass and soybean yield observed between the three systems could be mainly attributed to the timing of the cover crop termination and the soybean sowing date. The gross margin was highest in system (C), due to the high soybean grain yield. The low soybean grain yield in system (B) resulted in lower revenues and gross margins compared to systems (A) and (C), although system (B) could be economically attractive in organic farming with higher prices for organic soybean. In the particularly dry year 2016, gross margins were higher when soybean was irrigated compared to the rainfed cultivation, due to significantly higher grain yields. Before recommending the application of the no-tillage with cover crop technique for the conditions tested in north-eastern Germany, more investigations on the benefits and risks of this technique are needed. Further research needs to focus on maintaining a high rye biomass as well as on ensuring an early soybean planting date. Optimizing the crimping and drilling equipment is still required in order to develop good management practices for no-tillage herbicide-free systems in European conditions.

Minimizing competition between glyphosate-resistant volunteer canola (Brassica napus) and glyphosate-resistant soybean: impact of soybean planting date and rate

AbstractIn recent years, soybean acreage has increased significantly in western Canada. One of the challenges associated with growing soybean in western Canada is the control of volunteer glyphosate-resistant (GR) canola, because most soybean cultivars are also glyphosate resistant. The objective of this research was to determine the impact of soybean seeding rate and planting date on competition with volunteer canola. We also attempted to determine how high seeding rate could be raised while still being economically feasible for producers. Soybean was seeded at five different seeding rates (targeted 10, 20, 40, 80, and 160 plants m−2) and three planting dates (targeted mid-May, late May, and early June) at four sites across western Canada in 2014 and 2015. Soybean yield consistently increased with higher seeding rates, whereas volunteer canola biomass decreased. Planting date generally produced variable results across site-years. An economic analysis determined that the optimal rate was 40 to 60 plants m−2, depending on market price, and the optimal planting date range was from May 20 to June 1.

A Review of Soybean Yield when Double‐Cropped after Wheat

Core Ideas Relative to full‐season soybeans, the double‐crop soybean yield gap is delayed and full‐season soybean yields improved. As wheat yield improved, double‐crop soybean has lower probability of presenting greater yields than wheat. Previous wheat yield, and soybean planting date and maturity groups influenced the attainable yield for double‐crop soybeans. Soybean (Glycine Max L.) planted after wheat (Triticum aestivum L.) harvest in same season (double cropped [DC]) has the potential to increase productivity and sustainability. The objectives of this synthesis review were to (i) quantify attainable yield for DC soybean benchmarking against full‐season (FS) soybean; (ii) determine and build probabilistic response models on the effect of previous wheat productivity on DC soybean yields; and (iii) detect and rank factors influencing DC soybean yields via a decision inference tree analysis. A global database on DC soybean studies collected from 1976 to 2017 was divided into three data sets: (i) FS and DC soybean (n = 141 data points); (ii) wheat and DC soybean (n = 463); and (iii) production factors and DC soybean (n = 547). Analysis showed that the yield gap between FS and DC soybeans increased from ‐31 to 1160 kg ha−1 as FS yield improved from 1500 to 3000 kg ha−1. Even though the proportion of the variation accounted for wheat yields in the DC soybean/wheat yield ratio was low (R2 = 0.15), the probability of soybean yield being equal to wheat yield was 0, 20, 30, and 55% for wheat yields of ≥6, ≥4 and <6, ≥2 and <4, and <2 Mg ha−1. Inference tree analysis indicated that the major factor impacting success of the DC system was wheat yield followed by soybean planting date and maturity group.