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Seeding rate recommendations for wheat (Triticum aestivum L.) are often 150–450 seeds m−2. However, we hypothesize that wheat grown with high resource availability (i.e., fertility and moisture) can maximize yield under considerably lower rates. Our objectives were to explore winter wheat response to low populations under high resource availability using yield‐contest fields as a case study. A factorial experiment evaluated four wheat varieties (i.e., Joe, WB‐Grainfield, Langin, and LCS Revere) exposed to five seeding rates (50, 100, 150, 200, and 250 seeds m−2) during five seasons in commercial wheat fields managed by yield‐contest winning producers near Leoti, KS. Fields were silt‐loam soils with high available water‐holding capacity, long‐term history of manure application with non‐limiting fertility, and adopted a sorghum [Sorghum bicolor (L.) Moench]–fallow–wheat rotation. Plant density ranged from 26 to 341 plants m−2 and yield ranged from 3.2 to 6.8 Mg ha−1. Water use efficiency of 19.5 kg ha−1 mm−1 suggested no management limitations to yield. Quadratic models portrayed the grain yield–plant density relation well, with 95% of the maximum yield reached at 68 to 91 plants m−2 for crops sown at the optimum date (4 out of 5 years), and at 312 plants m−2 for a late‐sown crop. Greater fall temperature accumulation reduced the relative yield between the maximum and minimum seeding rates. There was no variety × plant density interaction and Langin was the most consistent yielding variety across environments. Optimum plant density for winter wheat in environments with high resource availability may be considerably lower than current recommendations. Core Ideas: Winter wheat response to plant density depends on resource availability.Under high resource (fertility and moisture), winter wheat response to density relied on fall temperature.Note that 68–91 plants m−2 reached 95% maximum yield in four out of five seasons under optimum sowing time.Note that 312 plants m−2 reached 95% maximum yield in one out of five seasons with late sowing.Current seeding rate recommendations could be lowered for intensively managed fields. [ABSTRACT FROM AUTHOR]

Nitrogen fertilizer application and increasing planting density have been recognized as essential measures to achieve higher wheat (Triticum aestivum L.) yields. However, inadequate management practices often lead to poor culm quality and lodging. We hypothesized that optimizing culm characteristics could be a feasible approach to improving both lodging resistance and yield. In this study, field experiments involved five nitrogen levels (0, 180, 240, 300, and 360 kg ha−1) and three planting densities (225, 375, and 525 × 104 ha−1). Two wheat cultivars with different lodging resistance were selected and their culm morphological characteristics, biochemical components, field lodging rate, and yield in different treatments were measured. We found that field lodging rate in wheat was negatively correlated with yield, and there was a contradiction between increasing spike number and lodging resistance. Culm carbohydrate accumulation affected field lodging rate by regulating culm quality rather than the center of gravity height. Compared with Xinmai 26, Xinhuamai 818 had higher culm carbohydrate accumulation, which increased the breaking strength and yield by 14.2% and 17.0%. Nitrogen application and planting density had significant effects on yield and lodging resistance. Compared with N0 treatment, increasing nitrogen application rate improved yield of 67.2%–83.2% by increasing spike number and grain number per spike, and the N2 treatment showed the largest increase. Planting density had little effect on yield. Reducing planting density can increase the culm carbohydrate accumulation and enhance lodging resistance. Compared with D3 treatment, the culm breaking strength was increased by 27.6% under the D1 treatment. This study determined that the optimal combination of nitrogen and density for improving wheat lodging resistance and yield is 240 kg ha−1 and 225 × 104 ha−1. This combination enhances culm breaking strength by increasing carbohydrate accumulation and achieves high yield by increasing grain number per spike, 1000‐grain weight, and stabilizing spike number. [ABSTRACT FROM AUTHOR]

Tissue culture, aeroponics, and hydroponics have improved the production of first‐generation potato (Solanum tuberosum L.) minitubers in Ethiopia. However, some minitubers may be very small (<5 g) and would probably fail to survive in open‐field conditions. Thus, they are usually replanted in screenhouses in pots as single tubers/hills. The impact of pot size and number of minitubers that can be feasibly planted per pot to obtain optimal yield with little impact on progeny tuber size require investigation to optimize indoor seed potato production. Consequently, a screenhouse experiment was conducted at Adet Agricultural Research Center, Amhara, Ethiopia, between 2020 and 2021 to investigate the effect of seed density and different pot sizes on a number of tubers harvested per pot, per planted minituber, and average tuber weight (g). Experimental treatment factors were potato variety at two levels, pot size at three levels, and seed density at five levels. Five replications per treatment combination, each with four pots, were used. Analysis of variance, with seed density up to cubic component as single‐degree polynomial contrast, showed that the assessed variables were not significantly (P ≤ 0.05) affected by potato variety. All two‐ and three‐way factor interactions except pot size by seed density for the number of tubers harvested per planted minituber were not significant (P ≤ 0.05). Pot size significantly (P ≤ 0.05) affected the number of tubers harvested per pot and per planted minituber but not the average tuber weight. All the assessed variables were significantly (P ≤ 0.05) affected by seed density. The number of tubers harvested per pot increased significantly (P ≤ 0.05) with increasing pot size and seed density. Polynomial regression showed that linear and quadratic components of seed density as a predictor of the assessed variables were significant (P ≤ 0.05); however, its polynomial components did not significantly (P ≤ 0.05) interact with main treatment factors. The estimated optimum seed density from the derivatives of the polynomial functions was five tubers per pot. The predicted minimum average tuber weight was 18.5 g, which is appreciably high for good open‐field minituber survival. Meanwhile, the 10‐L pot produced significantly (P ≤ 0.05) more minitubers than other pot sizes; however, it had the lowest production efficiency per unit area of screenhouse and per kilogram of culture substrate. Thus, 2‐ and 6‐L pots, each planted with five minitubers, irrespective of the potato variety are recommended to maximize productivity of minitubers and screenhouse space with little or no impact on progeny tuber size. Core Ideas: Tissue culture, aeroponics, and hydroponics have improved production and availability of potato minitubers in sub‐Saharan Africa.Some minitubers, however, may be very small and unable to survive well in open fields and are thus sown in pots in screenhouses.Tuber yield in pots in screenhouse conditions was affected by pot size and planting density but not potato variety.The number of minitubers harvested per pot increased with increase in pot size and seed planting density.The optimum seed density at planting was estimated at five minitubers per pot irrespective of potato variety and pot size. [ABSTRACT FROM AUTHOR]

Era studies are important to understand historical changes in maize (Zea mays) germplasm and estimate genetic gains, yet information for short‐season maize hybrids is limited. Here, we determine grain yield genetic gain in Bayer short‐season hybrids (100–105 days) and investigate indirect changes made on 17 secondary traits, including yield components (kernel number, weight, and shelling efficiency), and grain quality traits (oil, protein, starch, ethanol, moisture, and test weight). We evaluated 40 maize hybrids released from 1980 to 2020 across 18 environments in the US Corn Belt. Plant density and N‐fertilizer were held constant within each environment. Results indicated a linear increase in grain yield (from 11.1 to 15.3 Mg ha−1, 105 kg ha−1 year−1, or 0.8% year−1) with no sign of a plateau. The increase in grain yield was attributed more to increased kernels per m2 (0.57% year−1) than kernel weight (0.23% year−1). Grain protein concentration decreased until the late 2000s and plateaued thereafter, while starch and ethanol concentration increased until the early 2000s and plateaued thereafter. However, the total amount of protein, starch, and ethanol increased linearly from 1980 to 2020. We concluded that maize breeding for increased grain yield has indirectly affected many traits at different rates and directions. Our results are encouraging for future progress in grain yield increase, update genetic gain information to 2020 for short‐season hybrids, and can inform plant breeders, crop physiologists, agronomists, and crop modelers. Core Ideas: We measured 18 plant traits of 40 maize hybrids across 18 experiments in the US Midwest.Grain yield linearly increased by 105 kg ha−1 year−1 from 1980 to 2020.Kernels per m2 increased at twice the relative rate compared to kernel weight.Protein concentration decreased up to 2008 and remained unchanged until 2020.Grain moisture at harvest, test weight, and oil concentration remained unchanged. [ABSTRACT FROM AUTHOR]

Alfalfa (Medicago sativa L.) intercropping with maize (Zea mays L.) silage is being developed in the northern United States to improve the profitability and environmental sustainability of forage production. This study, conducted under rainfed conditions in Wisconsin and semiarid irrigated conditions in Idaho, compared the establishment of alfalfa and dry matter yield of four intercropping systems to three conventional systems. The former systems included alfalfa interseeded at planting or the vegetative emergence (VE) stage of maize and grown with or without prohexadione growth retardant. The latter systems included alfalfa seeded in spring, summer‐seeded after barley (Hordeum vulgare L.), or late summer‐seeded after maize silage. Spring seeded and interseeded alfalfa in Wisconsin also received foliar fungicide and insecticide during establishment. During alfalfa establishment, yield of intercropped maize silage was 1.8‐ to 4.4‐fold greater than spring‐seeded alfalfa. Compared to spring‐seeded alfalfa, interseeded alfalfa had similar or somewhat lower stand density but similar first cut yield the following year, provided that intercropped maize was harvested near September 1 to allow ample alfalfa fall regrowth. Shifting interseeding from maize planting to the VE stage decreased early‐season alfalfa growth, but improved maize silage yield, with minor effects on alfalfa fall growth, stand density, and first cut yield. Prohexadione application had little impact on establishment or yield of interseeded alfalfa. While having high plant density, alfalfa seeded after barley or especially maize had less fall growth and low first cut yield. Overall, alfalfa establishment and yield of intercropping systems compared favorably with conventional systems. Core Ideas: Delaying alfalfa interseeding until the vegetative emergence stage improved maize silage companion crop yield.During alfalfa establishment, intercropped maize silage had up to 4.4‐fold greater yield than solo‐seeded alfalfa.Early harvest of maize silage improved fall growth and first cut yield of interseeded alfalfa after establishment.Interseeded and spring solo‐seeded alfalfa had comparable stand density and first cut yield after establishment.Summer solo‐seeded alfalfa had relatively poor fall growth and first cut yield after establishment. [ABSTRACT FROM AUTHOR]

One of the main challenges of using low plant densities in restrictive and variable environments is to maximize the use of resources in better‐than‐expected years. In this context, tillering could be an alternative to increase reproductive and vegetative plasticity. The objectives of this study were to (a) characterize the correlation between environmental conditions, tiller traits, crop grain yield, and grain yield advantages due to tillers; (b) determine the grain yield response to tillering (i.e., grain yield difference between tillered and nontillered crops) for a wide range of environments; and (c) to evaluate the effect of tiller presence on grain yield of the main shoot, considering its effect on the apical and subapical ears. Tillered and nontillered crops were evaluated under rainfed conditions during two seasons (2018–2019 and 2019–2020). These experiments were carried out at 11 sites in the southern Argentinean Pampas, varying sowing date (22 Oct. to 5 Dec.), plant density (2–3 plants m−2), genotype (AX7784 and AX7761), and soil depth. Grain yield (3.2–11.9 Mg ha−1) was correlated with tillers productivity, mainly explained by postflowering precipitations. The contribution of tillers to grain yield was more proportional than their consequent yield depression at the main shoot. Tillers either increased (3 sites) or maintained (8 sites) grain yield, and their contribution increased as the environment improved without any detrimental effect in the most restrictive environments. Tillering has the potential for increasing resource (radiation, water, nitrogen) use efficiency under low plant density strategies adopted for restrictive environments. Core Ideas: Tillers either increased (3 sites) or maintained (8 sites) crop yield.Grain yield was correlated with tillers productivity, mainly explained by postflowering precipitations.Tiller contribution to grain yield was greater than the consequent yield depression of the main shoot.Tiller contribution to yield increased as the environment improved (high yield).Tillering has the potential for increasing resource use efficiency under low plant density strategies. [ABSTRACT FROM AUTHOR]

Genetic improvement in maize (Zea mays L.) grain yield is associated with improvements in dry matter accumulation during the grain‐filling period and the ability to maintain partitioning to the grain (i.e., harvest index) when grown at higher plant population densities. Although several attributes have been identified that lead to improved dry matter accumulation during the grain‐filling period, the attributes that have enabled the maintenance of harvest index at higher plant population densities remain elusive. Using the Ontario ERA hybrids that represent five eras of genetic improvement in Ontario, we examined genetic improvement in several attributes associated with sink establishment and partitioning to the grain. We show that the number of florets on an ear initial is not influenced by plant density, nor is there any evidence of a genetic improvement in floret number. There has been genetic improvement, however, in the ability to support kernel set at a lower threshold level of dry matter accumulation and to more efficiently set kernels at lower dry matter accumulation levels, such as those experienced at higher plant densities. Genetic improvement is evident for reduced plant‐to‐plant variability for dry matter accumulation, grain yield, kernel number, and plant growth rate around silking, but most notably for grain yield. Finally, we show that genetic improvement in reduced plant‐to‐plant variability for grain yield is the result of the lower threshold dry matter levels required for seed set and the improved resource utilization, which has led to greater stability of individual plant performance in a stand. [ABSTRACT FROM AUTHOR]

Studies at a regional scale suggest that although maize (Zea mays L.) yield increased substantially, sensitivity to water deficit also increased concurrently with crop improvement. This study assessed changes in yield and yield stability after two decades of breeding by evaluating two cohorts of hybrids released by the AQUAmax program and comparing them to a non‐AQUAmax control. Studies were conducted in 2019 and 2020 seasons at four sites under well‐watered, moderate and severe stress conditions. Plant densities varied from 2.5 to 12.5 pl m−2. AQUAmax hybrids yielded more than non‐AQUAmax hybrids under water deficit conditions with the magnitude of the difference dependent on plant density. The sensitivity in yield across environments with a wide range of total crop evapotranspiration (350–800 mm) was lower for AQUAmax than non‐AQUAmax, so both yield and yield under stress conditions (yield stability), were enhanced for AQUAmax hybrids. The median differences between observed yields and the 80% quantile yield–evapotranspiration front were 379 for AQUAmax and 427 g m−2 for non‐AQUAmax hybrids. We conclude that deliberate selection of hybrids for yield performance under water deficit underpinned the sustained improvement in yield stability after two decades of drought breeding. Future research should focus on understanding the root causes for the suboptimal utilization of drought tolerant maize for the diversity of environments at a regional scale. Core Ideas: Yield improvement for drought is critical to enable a circular bioeconomy.Maize susceptibility to drought at regional scale is increasing with crop improvement.Genotype × management technology (G×M‐tech) is not the root cause of the higher instability.Socioeconomic factors and policy may underpin suboptimal use of G×M‐tech at regional scale. [ABSTRACT FROM AUTHOR]

Switchgrass (Panicum virgatum L.) breeders use spaced‐seedling plots for evaluations of biomass yield, but prior studies are ambiguous about the relationship between performance in spaced plots and commercial seeded sward performance. This study used a split‐plot incomplete block design to evaluate 52 half‐sib switchgrass families across two years to determine the correlations among four different plot types (including seeded swards) and four individual plant traits. Plots (1.62 m2) that contained 3, 6, and 18 plants had mean yields of 5.92, 8.04, and 11.06 Mg ha–1, respectively, while seeded‐sward plots had a mean of 5.37 Mg ha–1. In a mixed‐model analysis including family‐, year‐, and plot‐type interactions with a spatial‐spline correction, the largest proportion of family variance was accounted for by the main family effect (48%), while the plot type‐by‐family effect was only 17% of family variance. These results indicate that spaced‐plant plots are reasonable surrogates for biomass performance in sward conditions. Yield reliability was 0.50 across all plot types with a mean of 0.46 for individual plot types. Surrogates for sward yield varied due to genetic background of the families. Yield of families derived from the Liberty cultivar (n = 32) had genetic correlations with winter survivorship scores (0.66). Diverse lowland ecotype families (n = 20) had genetic correlations with plant height and heading date. This study highlighted a major difference in performance among the plot types, specifically that seeded swards have depressed yield due to high plant density. This should encourage further research for the mechanism behind this difference in performance. [ABSTRACT FROM AUTHOR]

Datura stramonium L. (jimsonweed) from the Solanaceae family is widely used in traditional medicine due to its medicinal properties. This paper investigated the effect of three levels of urea fertilizer (60, 120, and 180 kg ha–1) and three levels of planting density (6, 10, and 14 plants m−2) on the grain alkaloids, chlorophylls a and b content, carotenoids, anthocyanins, and grain and biological yields. A factorial experiment as a randomized complete block design was carried out at the Research and Education farm of Isfahan Agricultural and Natural Resources and Training Center in IRAN in 2018 and 2019. Significant differences were detected between urea levels and plant density for leaf chlorophyll content, carotenoids, and anthocyanins at the 1% probability. Also, hyoscyamine alkaloid levels and scopolamine content are affected by the urea levels at the 1% probability. Moreover, the relationship between phytochemical characteristics and alkaloids with the grain and biological yields in D. stramonium is investigated by path analysis. The results showed that grain yield, hyoscyamine alkaloid levels and scopolamine content is significantly improved by 6 plants m−2planting density and 180 kg ha–1 urea. Core Ideas: The effect of plant density and urea levels on the content of tropane alkaloids in Datura stramonium L. was investigated.The effect of physiological traits and tropane alkaloids on grain and biological yields were further studied by path analysis.Grain yield is significantly improved by 6 plants m−2 planting density and 180 kg ha−1 urea. [ABSTRACT FROM AUTHOR]

Successful field establishment begins with superior plant genetics, quality seeds, land preparation, sowing depth, weed control, and moisture. Our research examined the field‐establishment plant density of six populations of little bluestem [Schizachyrium scoparium (Michx.) Nash] and three selection generations at three locations over a 3‐yr period. Recurrent selection was used to develop C1 and C2 populations from six improved C0 populations (NU1, NU2, UC1, UC2, UO1, and UO2). In Cycle 1, open‐pollinated seeds from each C0 population were geminated in water of −0.8 MPa potential for 7 d. For each C0 population, seeds that germinated in 7 d were selected to create six C1 populations. Cycle 2 selection was identical to Cycle 1, except that C1 populations were used to create the six C2 populations. Plant density (number of plants m‒2) was determined using a frequency grid method at 30, 60, and 90 d after planting (DAP). The plant density of little bluestem varied with location (L), population (P), selection generation (G), DAP, L × P, L × G, P × G, and L × DAP interactions (P <.01). Averaged over generations and DAP, plant density averaged 7.6, 6.6, 6.5, 7.1, 6.6, and 7.1 plants m‒2 among populations NU1, NU2, UC1, UC2, UO1, and UO2, respectively. Averaged over populations and DAP, plant density averaged 5.9, 6.6, and 8.2 plants m‒2 for generations C0, C1, and C2, respectively. Thus, recurrent selection for increased laboratory seed germination in simulated dry conditions results in greater establishment plant densities of little bluestem. Core Ideas: Field establishment of little bluestem was enhanced by selection.Recurrent selection for greater laboratory seed germination improved field establishment.Rapid seed germination and seedling development is an important attribute for native grasses. [ABSTRACT FROM AUTHOR]

In intercropping systems, interspecies interaction intensity has an important effect on water consumption. However, how interspecies interaction intensity reduces water consumption in intercropping is still unclear. The effects of interspecies interaction intensity in wheat (Triticum aestivum)–maize (Zea mays) intercropping system on water consumption characteristics, root length density, and grain yield were examined. A 3‐yr field experiment was conducted to evaluate three root interaction intensities: complete belowground interaction (W/M, without root barrier), partial belowground interaction (NW/M, nylon mesh barrier), and without belowground interaction (PW/M, plastic sheet barrier), with two plant densities of maize (45,000 plants ha−1, M1, and 52,500 plants ha−1, M2) in wheat–maize intercropping system. During co‐growth period of wheat and maize and independent growth of maize, evaporation was reduced by W/M and with increased maize plant density. Root length density of maize was inhibited by intercropped wheat during the co‐growth period. Root length density of maize in the W/M treatment was increased by 14% in 2014 and 45% in 2015, compared with the NW/M treatment, and increased by 26% in 2014 and 119% in 2015, compared with the PW/M treatment, expect for 2016, during maize independent growth. Moreover, there was a negative correlation between evaporation and root length density of maize. Grain yield was increased by W/M2 treatment. Increasing interspecies interaction intensity can decrease evaporation by increasing the root length density of intercropping crops. Core Ideas: With increased maize plant density, evaporation was reduced by complete belowground interaction.Root length density of maize was increased by complete belowground interaction.Root length density of maize was negatively correlated with evaporation. [ABSTRACT FROM AUTHOR]

Long‐term selection in maize (Zea mays L.) favored single‐stalked phenotypes limiting vegetative growth. However, reduced plant densities create conducive environments to the expression of vegetative branches called tillers. Tiller expression has motivated discussions about its yield effect in variable environments, but tiller research is lacking for modern corn genotypes. The objectives of this study were to (a) quantify the relative importance of management, environment, and interactions on the yield effect of tiller expression for two modern genotypes; (b) understand effects of observed tiller density, plant density, and their interaction on yield; and (c) identify key environmental determinants of yield response to tiller density in modern genotypes. In 10 environmentally diverse site‐years across Kansas, tiller presence and removal were evaluated in two commercial corn hybrids (P0657AM and P0805AM) across three target plant density levels (25,000, 42,000, and 60,000 plants ha−1). Yields were increased or unaffected by greater plant densities and tiller presence within site‐years. Environments varied in yield responsiveness to tiller density, but fine‐tuning plant density was needed to maximize yields. Sites with yields most responsive to tiller density were characterized by good soil properties and photothermal quotient values (e.g., soils with high organic matter and climates with greater solar radiation and cooler temperatures). Favorable growing conditions can be exploited by plasticity traits such as tillering in unpredictable environments with annually variable optimum plant densities while limiting potential yield loss and producer risk due to disproportionate plant density. Core Ideas: Tiller presence never reduced yield in evaluated environments and plant densities.In favorable scenarios, corn tillers have plant density compensation potential.Plant density adjustment was necessary to maximize yield for all environments.Corn tillers have plasticity potential to optimize defensive management strategies. [ABSTRACT FROM AUTHOR]

Exploitation of plant density tolerance in sweet corn (Zea mays L.), including the use of density‐tolerant hybrids at plant densities that optimize economic returns (hereafter called economic optimum plant density), has the potential to improve profitability. Multiple experimental approaches, including artificially created root lodging events in field trials and natural root lodging events in growers' fields, were used to determine if economic optimum plant densities, compared with current plant densities, increase incidence of root lodging in sweet corn. An artificially created root lodging experiment over multiple years showed the environment in which sweet corn is grown is far more important to the effects of root lodging than plant density. In trials with natural root lodging events, results showed commercial sweet corn hybrids differed greatly in their susceptibility to root lodging, with some cultivars tolerant across all plant densities. Across 16 experimental comparisons of sweet corn response to plant density where natural root lodging was observed, including seven environments and 11 commercial hybrids, there was no difference in root lodging between current and economic optimum plant densities. Factors other than plant density dominate the crop's potential for, and recovery from, root lodging in growers' fields, namely, the hybrid and the environment in which the crop is grown. Core Ideas: Optimizing economic plant density of density‐tolerant sweet corn improves profitability.Environment and hybrid have much greater effect on root lodging than plant density.Compared with current plant density, economic optimum plant density does not increase root lodging incidence. [ABSTRACT FROM AUTHOR]

Turf‐type perennial ryegrass (Lolium perenne L.) success depends on adequate turfgrass quality and economical seed yield. In most breeding programs, spaced plants are the initial unit of selection in which observations of related individuals dictate the selection of superior germplasm for further testing. Therefore, spaced plants must be predictive of seed production and turfgrass growing environments. This study investigated the effectiveness of standard (three plants m−2) and competitive (23 plants m−2) spaced‐plant nurseries as selection environments with respect to two sward environments as well as applying a novel image analysis technique for several key traits. Seed production, turfgrass, and the two spaced‐plant growing environments were tested at two locations in Minnesota. Turfgrass quality traits were measured in 2017 and 2018 and seed production traits were measured in 2018. Automated image analysis was able to predict the traditional visual scoring values at both locations for crown rust (Puccinia coronata f.sp. lolii) severity [Pearson's correlation (rp) > 0.79, P <.001], winter injury (rp > 0.89, P <.001), and turfgrass texture (rp > 0.88, P <.001). Increasing the competition among spaced plants altered the plant phenotype and improved accuracy for vegetative biomass, crown rust severity, seed yield, and, at one location, turfgrass quality. There was no benefit of increasing competition for several traits such as genetic color, fertile tillers, and spikelet number. Although the competitive design was not useful for all traits, pragmatically, the competitive design used less space and often made measurements and observations easier for bunch‐type grasses. [ABSTRACT FROM AUTHOR]

Drought tolerance and rapid post‐stress recovery are critical survival strategies for turfgrass management in areas with limited rainfall and irrigation. This study sought to determine whether elevated CO2 could improve drought tolerance in rhizomatous Kentucky bluegrass (Poa pratensis L.) by protecting rhizomes from stress damage and promote regrowth and regeneration of daughter plants from rhizomes upon rewatering. Plants (cv. 'Baron') were grown at elevated CO2 concentration (800 μl L−1) or ambient CO2 concentration (400 μl L−1) for 28 d and then exposed to well‐irrigated conditions (control) or drought stress by withholding irrigation for an additional 28 d, followed by rewatering in growth chambers. Elevated CO2–treated plants had significantly higher leaf relative water content, visual quality, and membrane stability during drought compared with ambient CO2–treated plants. Rhizome nodes of elevated CO2–treated plants maintained significantly higher viability and lower content of abscisic acid and auxin under drought stress. In response to rewatering, plants previously exposed to drought stress under elevated CO2 exhibited increased growth of new shoots measured as total shoot biomass and daughter‐plant biomass, and an increased number of rhizomes, as well as greater canopy density compared with plants at ambient CO2. This study suggested that elevated CO2 concentration was able to protect rhizomes from drought damage and reactivate rhizomes for regeneration of new plants when drought was relieved by irrigation. [ABSTRACT FROM AUTHOR]

Prolonged seedling age (PS) caused by delayed transplanting frequently occurs in double‐season rice (Oryza sativa L.), leading to a significant grain yield loss. However, it is not clear whether optimizing the seeding rate in the nursery and planting density in the field could compensate for this yield loss. Field experiments with two seedling age, two planting density, and two seeding rate treatments were conducted in the early and late growing seasons of 2013 and 2014 in Wuxue County, Hubei Province, China. Increasing the planting density significantly increased grain yield but couldn't completely alleviate the negative effect of PS on grain yield in both early and late growing seasons. Reducing the seeding rate in the nursery significantly increased the grain yield in both seedling age treatments in the late season with an average of 4.4% across treatments and years. There was a significant interaction effect between seedling age and seeding rate on grain yield in the early season, suggesting that yield loss could be significantly mitigated by reducing seeding rate. In conclusion, optimizing seeding rate and planting density could partially compensate for the yield loss caused by PS. Core Ideas: Prolonged seedling age resulted in significant yield loss which was greater in late season.Increasing the planting density couldn't completely mitigate yield losses in both years.Lowering the seeding rate significantly compensated for yield loss in early season. [ABSTRACT FROM AUTHOR]

Xinjiang is currently the most dominant cotton (Gossypium hirsutum L.)‐growing region in China and possesses abundant radiation resource. The cultivation techniques such as wide and narrow row‐spacing and high density are widely adopted to obtain high cotton yield in the region. However, the region is facing some problems including poor light transmittance in the field and low exploitation for light resources under the current planting pattern which impedes further growth in cotton yields. Therefore, it is essential to develop some cultivation practices to increase radiation use efficiency (RUE) and cotton yields in Xinjiang. Here we conducted a field experiment to quantify the effects of row spacing pattern and plant density on RUE, intercepted photosynthetically active radiation from May to August (IRAR5–8), and lint yield during 2017 and 2018. In this study, we designed two row‐spacing configurations (R1, wide and narrow configuration, 66 cm + 10 cm; R2, uniform row‐spacing configuration, 76 cm) and six plant densities (4.5, 9.0, 13.5, 18.0, 22.5, and 27.0 plants m−2). The RUE, lint yield, and number of bolls were higher in R2 than R1 by 4.1–5.9, 2.5–4.8, and 9.1–14.2%, respectively. The RUE significantly increased with plant density, but lint yield stabilized at 18.0 plants m−2. Moreover, RUE had more significant positive effects on boll number and lint yield. Overall, we found that R2 combined with optimal plant densities (13.5–18.0 plants m−2) would be an effective strategy to achieve higher RUE and yields in the Xinjiang cotton system. Core Ideas: The 76‐cm, uniform row‐spacing significantly improved RUE, TBN, and lint yield of cotton in Xinjiang.The increase in the yield was mainly attributed to the increase of TBN rather than boll size or lint percentage.Lint yield would be stabilized when plant density increased to 18.0 plants m−2.The RUE had more significant positive effects on TBN and lint yield than IPAR5–8. [ABSTRACT FROM AUTHOR]

Solar radiation is an important environmental factor affecting maize (Zea mays L.) root and shoot growth and grain yield. This study was conducted in Qitai and Yinchuan, China, in 2018 and 2019. The maize cultivars of XY335, ZD958, and DH618 and planting densities of 7.5 × 104 (D1) and 12 × 104 plants ha−1 (D2) were adopted under shading levels of 15 (S1), 30 (S2), and 50% (S3) with natural light as the control (CK). The results showed that averaging all shading and density treatments over the 2 yr, shading reduced the grain yields of XY335, ZD958, and DH618 by an average of 40.4, 39.2, and 35.6%, respectively, compared with the CK. The effect of solar radiation on the root dry weight was greater than that on the shoot dry weight, which resulted in a decrease in root/shoot ratio with increasing shading level. The quantitative analysis results showed that for every 1‐MJ m−2 decrease in solar radiation, the root dry weight, shoot dry weight, and root/shoot ratio decreased by 0.1938 g m−2, 1.3517 g m−2, and 0.0103 × 10−2, respectively. According to this quantitative relationship, it was helpful to select cultivars and planting density with suitable root characteristics under different solar radiation conditions in different regions. From the aspects of shoot and grain yield, DH618 was more shade resistant, and its root system rapidly adjusted to compensate for shoot growth and yield formation when solar radiation decreased. Such cultivars should be given attention in future production and breeding. [ABSTRACT FROM AUTHOR]

Identifying the agronomic optimal plant density (AOPD) for maximum grain yield is essential to develop enhanced management strategies for maize (Zea mays L.) production. In this study, we used a boundary‐line method to examine the yield response of maize to plant density in China, based on the metadata (2783 data points) gathered from 157 recent studies during 2000–2017. We found the AOPD was 8.5 × 104 plants ha−1 in Northeast China, 9.3 × 104 plants ha−1 on the North China Plain, 10.5 × 104 plants ha−1 in Northwest China, and 8.0 × 104 plants ha−1 in Southwest China. Compared with current practices, potential grain yield with these AOPDs was improved by 13–20% for these major maize regions of China. Across regions, AOPDs were similar for spring‐planted (9.2 × 104 plants ha−1) and summer‐planted maize (9.3 × 104 plants ha−1) systems, although grain yield at the AOPD was 7% greater for the spring‐planted maize system. For different productivity environments, we found that high‐yielding plots obtained a yield of 18.2 Mg ha−1 at an AOPD of 11.6 × 104 plants ha−1, whereas in general productivity plots, 39% lower grain yield was achieved with a 19% lower AOPD (9.4 × 104 plants ha−1). In summary, this study illustrated AOPDs with modern maize hybrids for different productivity environments, cropping systems, and regions. Further study is needed to investigate the possible influence of agronomic factors such as lodging risks by increasing plant density. [ABSTRACT FROM AUTHOR]

Kernel set response to plant density was examined in terms of physiological processes underlying kernel set in temperate (Te), tropical (Tr), and temperate × tropical (TeTr) maize (Zea mays L.) hybrids. Four field experiments were performed in a subtropical environment, and treatments combined two new and popular commercial hybrids of each group of germplasm background with five plant densities (2–30 plants m−2). Determinations included plant growth rate (PGRS) and topmost ear growth rate (EGRS) during the period bracketing silking, grain yield, and its components. In all hybrids, kernel number was the main grain yield component contributing to grain yield variations across densities. When grown in a high‐yielding subtropical environment, all hybrids exhibited increased kernel number per area with increasing plant density from 5 to 11 plants m−2. There was not a clear trend among groups of germplasm background in the number of kernel set at each plant density, but distinctive physiological processes underlying kernel number per plant (KNP) were evident between Te and Tr hybrids. Across plant densities, the KNP/PGRS ratio was larger and PGRS was lower in Te than in Tr hybrids. Larger KNP/PGRS in Te than in Tr hybrids were associated with greater prolificacy al low plant density and larger EGRS. In TeTr hybrids instead, there was not a common physiological process underlying kernel set, since genotypes representing this group shared traits similar to those of Te and Tr genotypes. [ABSTRACT FROM AUTHOR]

This study quantified sunflower (Helianthus annuus L.) water use efficiency for seed (WUEg) and for oil yield (WUEo) and their components (i.e., evapotranspiration [ET], seed and oil yields) in response to plant density increments and studied, in particular, the underlying processes relevant to the responses of crop ET to plant density (i.e. water uptake pattern, intercepted photosynthetically active radiation [iPAR], and soil water depletion profile). Sunflower was grown at 3, 6, and 9 plants m−2 in Season 1 and at 2, 3 and 6 plants m−2 in Season 2. Measurements included (i) soil water content and iPAR during the whole growing season, and (ii) seed and oil yield at physiological maturity. Crop ET was estimated by means of a water balance, and it was analyzed during three different periods (i.e. vegetative, critical period for seed set, and seed filling period). Increasing sunflower plant density from 2 to 9 plants m−2 did not modify seasonal ET, but it changed the water uptake pattern through the season; it increased ET during the vegetative period by depleting more water from deep soil layers (i.e., 41–140 cm), but it reduced ET during the seed‐filling period. Increments in plant density increased seed and oil yield in accordance with significant iPAR increments, whereas harvest index remained stable. Sunflower WUEg ranged from 4.8 to 9.4 kg ha−1 mm−1, WUEo ranged from 1.8 to 4.5 kg oil ha−1 mm−1 across plant densities, and they were positively and closely associated with seasonal iPAR. [ABSTRACT FROM AUTHOR]

Interseeding alfalfa (Medicago sativa L.) into native grasslands can enrich forage nutritive value, but successful establishment in semiarid regions is limited by chronic water deficit. The objective was to evaluate establishment and stand development of two upright‐type alfalfa cultivars, 'WL 440HQ' (WL), 'NuMex Bill Melton' (NM), and prostrate‐type 'Falcata'–'Rhizoma' blend (FR), interseeded into mixtures of four native grass species at 36‐ or 71‐cm row spacing near Lubbock, TX. Average emergence was 265, 216, and 175 seedlings m−2 for WL, NM, and FR, respectively; however, the WL stand declined faster than the FR and NM stands during seedling and crown development stages (P < 0.01). The upright‐type cultivars maintained a greater crown density and ground cover compared with FR at both row spacings (P < 0.05). Alfalfa seedling or crown density fitted against time (d) with exponential models revealed an initial sharp decline followed by a slow rate of decline after establishment. At the end of 3 yr, row‐spacing results converged to similar levels for plant density (6.5 crowns m−2) and alfalfa cover (23.5%). This indicates significant seed cost savings with the wider row spacing at that level of stand establishment. Interseeding adapted, upright‐type cultivars at wide row spacing can produce a desirable level of alfalfa establishment in a semiarid grassland of the southern Great Plains. [ABSTRACT FROM AUTHOR]

Nitrogen is an essential element for maize (Zea mays L.). Farmers in developed countries most often apply more N fertilizer than necessary, which reduces N use efficiency (NUE). Improving radiation and N distribution, and thus the NUE of modern maize production systems with high plant density, is of great significance. In this study, field experiments were conducted in 2014 and 2015 in Xinjiang, China, using hybrid maize cultivar DH618 with high density. In addition, a synthesis analysis was conducted using data from 95 publications to observe N characteristics under different yield levels and compare the experimental results with existing studies. The relationship between radiation and N distribution in the canopy of high‐yield maize was also assessed. Nitrogen uptake was significantly correlated with grain yield. However, N uptake per unit grain yield and grain N concentration at maturity decreased as grain yield increased. The positive correlations between radiation and leaf and stalk N concentrations at silking showed that N concentration at silking increased as the height of the canopy layer increased because of increased radiation in the canopy. These results indicate that maize hybrids with erect upper leaves and high post‐silking N uptake can coordinate and optimize the distribution of radiation and N in different canopy layers and thus improve NUE and yield under high‐density production. [ABSTRACT FROM AUTHOR]

Knowledge of planting density and lodging resistance is essential to developing effective cropping systems. This study determined (i) the lodging resistance of different genotypes of oilseed flax (Linum usitatissimum L.) under different planting densities, and (ii) the effect of density on lignin content and related enzyme activities in different genotypes in Northwest China. We hypothesized that (i) lignin content and related enzyme activities varied with different planting densities, and (ii) a planting density of 750 x 104 grains ha-1 increased the lignin content and related enzyme activities of stem tissues and improved lodging resistance. The characteristics of oilseed flax from three different cultivars-'Dingya 23'(V1), 'Jinya 10'(V2), and 'Neiya 9'(V3)-were evaluated under different planting densities. Results indicated that increasing plant density increased the phenylalanine ammonia-lyase (PAL) and tyrosine ammonia-lyase (TAL) activities but decreased the 4-coumarate:CoA ligase (4CL) activity and lignin content of a high-lodgingresistance cultivar. However, increasing plant density decreased the PAL and TAL activities but increased the 4CL and lignin content of a low-lodging-resistance cultivar. We conclude that plant density affected the plant lignin content by regulating the 4CL activity. Flax seed yield increases with density were mainly due to increased lignin content, bending strength, and regulated PAL, TAL, and 4CL activities. The study concluded that optimizing planting density could play an important role in crop lodging resistance and grain yields in the northwest of China. [ABSTRACT FROM AUTHOR]

Cover crops can provide ecological services and improve the resilience of annual cropping systems; however, cover crop use is low in corn (Zea mays L.)--soybean [Glycine max (L.) Merr.] rotations in the upper Midwest due to challenges with establishment. Our objective was to compare three planting methods to establish cover crops (winter rye [Secale cereale L. 'Rymin'], red clover [Trifolium pretense L. 'Medium'], hairy vetch [Vicia villosa Roth], field pennycress [Thlaspi arvense L. 'MN-106'], and a mixture of oat [Avena sativa L.], pea [Pisum sativum L.], and tillage radish [Raphanus sativus L.]) (MIX) in corn at the seven-leaf collar stage. Planting methods included directed broadcast into the inter-row (DBC), directed broadcast with light incorporation (DBC+INC), and a high-clearance drill (DRILL). The DRILL method achieved greater fall biomass than DBC for all species except pennycress, and DRILL and DBC+INC increased red clover and hairy vetch spring biomass compared with DBC. Cover crops did not affect corn grain or silage yield and reduced yield of the subsequent soybean crop by 0.4 Mg ha-1 (10%) only when poor termination of hairy vetch occurred at one site. Cover crops with >390 kg ha-1 of spring biomass reduced soil nitrate- N compared with the no-cover control. These results support that cover crops can be interseeded into corn at the seven-leaf collar stage in the upper Midwest to reduce soil nitrate-N while maintaining corn and subsequent soybean yields; however, effective cover crop termination is critical to avoid competition with the subsequent soybean crop. [ABSTRACT FROM AUTHOR]

Maize (Zea mays L.) yield potential has not undergone genetic improvement during the hybrid era, yet substantial genetic improvement has occurred for tolerance to high plant population densities. As many crops including maize are approaching yield plateaus, it may be necessary to exploit other means of increasing grain yields. In this study, we examine potential reasons for why this occurred. Using a four-way breeding cross representing the commercial germplasm pool, we demonstrate that the lack of genetic improvement in yield potential is not due to the two attributes being antagonistic. We then demonstrate that the lack of genetic improvement in yield potential is not due to density-tolerant genotypes being higher yielding at modern conventional plant densities. We show that physiological differences in partitioning dry matter to the grain (i.e., harvest index [HI]) are present in a set of genotypes with contrasting yield potential and density tolerance genotypes. However, a higher or a lower HI is not associated with yield potential either. Finally, we show that the density-tolerant genotypes exhibit a static kernel set efficiency (KSE), meaning that regardless of the plant growth rate at silking (pGRS), the number of kernels formed per unit dry matter fixed is constant. Surprisingly, the hybrids with high yield potential possess a dynamic KSE and are capable of sustaining kernel set at higher levels when pGRS is low. Given our findings, there is no apparent biological or genetic explanation for genetic improvement in only density tolerance during the hybrid era. [ABSTRACT FROM AUTHOR]

Continued yield increases in modern commercial maize (Zea mays L.) hybrids will require increased plant density, improved nitrogenuse efficiency, and breeding for a hybrid's potential yield response to this management. The objective of this study was to determine the genetic variation of commercial hybrids in response to plant density and nitrogen (N) fertilizer levels to assist breeding programs to select hybrids with high yield stability or adaptability to crop management. From 2011 to 2014, 101 hybrids were grown in eight different environments at two planting densities (79,000 and 110,000 plants ha-1) and three N rates (0, 67, and 252 kg N ha-1). Broad-sense heritability increased with increased N rate and plant density. Increased plant density altered yield from -0.60 Mg ha-1 to +0.58 Mg ha-1 under high N conditions, whereas the yield response to increased N ranged from +4.47 to +5.64 Mg ha-1. Hybrids that combined above-average yield under unfertilized and low-N conditions exhibited greater-than-average yield stability across environments under high-N conditions. Hybrid yield stability variance was larger under high-N than under low-N conditions because of greater genotype x environment interaction. Hybrids that were adaptable to high plant density and N conditions exhibited greater-than-average yield potential and yield variation across environments. Selecting hybrids with both high yield and yield stability may be difficult, as yield under lower N levels and yield increases with high N fertilization were negatively correlated. [ABSTRACT FROM AUTHOR]

Siberian wildrye (Elymus sibiricus L.) is a globally important cool-season forage grass for semiarid regions. However, its seed yield is often low or inconsistent. As previous studies examined the effects of row spacing and P and N levels on seed production of Siberian wildrye separately, this study was focused on the combined effects of four row spacings (30, 45, 60, 75 cm), four P application levels (0, 60, 90, 120 kg P ha-1), and four N application levels (0, 30, 60, 90 kg N ha-1). Treatments were established within a split-split-plot factorial arrangement, with main plots arranged in a randomized complete block design with four replicates. The field experiment was conducted on a Lithic Haprendoll soil type at the Guyuan farm in Hebei Province, China, during the 2010, 2011, and 2012 growing seasons with no supplemental irrigation. Narrow row spacing improved seed yield by increasing fertile tillers m-2, with 30 cm being the optimal row spacing. Phosphorus application increased seed yield by increasing spikelets per fertile tiller, with 90 kg P ha-1 being the optimal P application level. Nitrogen application had no significant influence on seed yield in any year. Path analysis structural equation modeling revealed that spikelets per fertile tiller and fertile tillers m-2 had significant and direct path coefficients with variances in seed yield. The best management practices for optimal seed yield of Siberian wildrye was 30-cm row spacing, 90 kg P ha-1, and no additional N beyond 109 g kg-1 available soil N under rain-fed conditions with annual rainfall <300 mm. [ABSTRACT FROM AUTHOR]

Hybrid era and management practices like nitrogen (N) rate and plant density influence canopy traits and their correlations with grain yield, kernel number, and kernel weight in maize (Zea mays L.). A four site-year study was conducted employing two N rates (55 and 220 kg N ha-1) with three plant densities between 54,000 and 104,000 plants ha-1 for two newer hybrids (2005) and two older hybrids (1967 and 1975). Hybrids varied in anthesis--silking interval, specific leaf nitrogen (SLN), specific leaf area, and leaf greenness (soil plant analysis development [SPAD] readings), but not in leaf area index (LAI) at silking. Consistently higher kernel weight in newer hybrids (15% in 2012, 23% in 2013) across management treatments was related to their higher SLN at silking and green leaf number retention during grain filling. The threshold LAI at silking for maximum kernel number for 2005 hybrids (averaging 3917 kernels m-2) occurred at 4.0 m² m-2, compared with 3.28 m² m-2 for the 1975 hybrid (3893 kernels m-2), and kernel number declined when LAI exceeded 3.43 m² m-2 for the 1967 hybrid. Higher leaf biomass, leaf N content, and therefore higher SLN at silking in newer hybrids contributed to greater green leaf retention during grain filling. Applying more N weakened correlations between grain yield and canopy attributes, including leaf retention in both years and yield correlations with leaf biomass, leaf N content, LAI, and SLN in 2013 (more favorable weather). Grain yields for all hybrids in 2013 had higher correlations with LAI at silking and during grain fill when grown at higher densities. [ABSTRACT FROM AUTHOR]

Prediction of fertile tiller number (FTN) is important for predicting crop leaf area development and provides an avenue to identify genotypes with specific adaptation to variable environments. However, previous tillering prediction models in sorghum [Sorghum bicolor (L.) Moench] were limited to only a few genotypes. This study aimed to develop an approach to predict FTN for a large number of genotypes grown in multiple environments. A set of 756 genotypes from 17 diverse families of a backcross-derived, sorghum nested association mapping population were evaluated in test cross combinations with a single female tester. Plants were grown in five environments, but not all genotypes were included in all environments. One of the environments was space planted for expression of tillering propensity. Three predictors of tillering were considered: tillering propensity, incident radiation per unit thermal time during the tillering stage, and plant density. These represent the genotypic, environmental, and management effects on FTN, respectively. Based on these predictors, a robust model was developed for 125 genotypes grown in the spaced planting and all four test environments (R2 = 0.85, n = 500). For the independent set of remaining genotypes, the model predicted FTN in each of the four test environments with an accuracy and precision close to that for the training set (R2 = 0.69–0.74). The implications for crop improvement of this predictive capability of FTN are discussed in relation to the opportunities for assessing genetic and management options for specific adaptation, and for removing confounding effects in the analysis of breeding trials. [ABSTRACT FROM AUTHOR]

A correction is presented to the article "The effect of different levels of urea and planting density on the phytochemical characteristics, alkaloids, and yield of the medicinal plant jimsonweed (Datura stramonium L.)."

High plant density of maize (Zea mays L.) reduces the stalk quality of the basal internodes and increases stalk lodging. The objective of this experiment was to explore the mechanism by which plant density influences basal internodes. The morphological, mechanical, anatomical, and biochemical characteristics of the third basal internode were compared at three plant densities. High plant density increased internode length due to an increase in the rate of rapid elongation. High plant density decreased the duration of internode thickening and dry matter accumulation, causing the diameter and dry weight per unit length to decline. However, rind penetration strength (RPS) did not increase rapidly until after the termination of rapid morphological growth. The mid-to-late stage of dry matter accumulation was critical for RPS formation. The rapid increase in RPS was closely related to cellulose and lignin accumulation. High plant density reduced the rates of cellulose and lignin accumulation, which was adverse to the formation of cortex tissue and RPS. High plant density caused rapid elongation, thickening, and structural carbohydrate accumulation to begin and end earlier. These results indicate that measures should be implemented as early as possible in the growing season to increase lodging resistance at high plant density of maize. These measures need to reduce the rate of rapid internode elongation and increase the rate of rapid cellulose and lignin accumulation. [ABSTRACT FROM AUTHOR]

Cowpea [Vigna unguiculata (L.) Walpers] is a major crop legume for the Sahelian zone in Africa. An accurate simulation of the growth and yield for cowpea that considers the environment would be a robust tool for evaluating improved management and plant genetics. The objective of this study was to parameterize a simple model framework to describe cowpea leaf area development. To obtain field data in divergent environments, leaf area development was measured for four genotypes at two sites: Patancheru, India, and Bambey, Senegal. In addition, the effect of plant density was tested at Patancheru. Leaf area development was considered in two steps: the increase in main stem node number as a function of temperature (i.e., phyllochron) and plant leaf area as a function of main stem node number. The difference in phyllochron values among genotypes was not significant at Bambey, but one genotype at Patancheru significantly diverged from the others. Also, there was a plant density effect at Patancheru, especially for genotype Suvita-2. An allometric power function, used to calculate plant leaf area based on the number of nodes, required two parameters: PLAPOW, the exponent in the function, and PLACON, the linear multiplier of the equation. Determination of the two parameters at Patancheru showed a genotype effect in both site and plant-density effect. To examine the practical impact of genotypic differences and density effects in light interception and shading, estimated leaf development parameters were used to calculate light interception. There was very little variation in light interception resulting from the observed range in leaf phyllochron, PLAPOW, and PLACON and in density responses among the cowpea genotypes. The results of these experiments showed that, in most cases, a single set of parameters can be used to describe light interception by cowpea leaf canopies. [ABSTRACT FROM AUTHOR]

Breeding for higher grain yield in maize (Zea mays L.) using increased selection densities has produced varieties that are adapted to grow at higher population densities. While the effects of density on final grain yield and plant phenotypes are well known, how density affects the early-season growth of the plant has been less studied. The objective of this experiment was to examine the effects of high planting density on the growth of stalk, tassel, and ear shoots in unselected Iowa Stiff Stalk Synthetic (BSSS) and Iowa Synthetic Corn Borer No. 1 (BSCB1) and in populations that have been selected for high grain yield via a reciprocal recurrent selection program. The selected and unselected populations were planted at four densities ranging from 3.23 to 12.92 plant m-2 in six environments near Ames, IA, over 3 yr. Increased planting density affected plant organ growth timing differently in BSSS and BSCB1. High-density delayed stalk biomass accumulation in BSCB1 but not BSSS and delayed ear shoot and tassel biomass accumulation in BSSS but not BSCB1. Differences in biomass accumulation and partitioning between unselected populations were generally not observed between selected populations, suggesting that selection caused a convergence in growth patterns between the populations. Increased density lowered maximum growth rates for all plant organs, but reduction in growth rate as a result of density occurred at higher density in selected populations than unselected populations. [ABSTRACT FROM AUTHOR]

Identifying an optimal plant density is a critical management decision for corn (Zea mays L.) production. The main objectives of this study were to: (i) investigate the grain yield responses to plant density (yield-density relationship), (ii) identify best fitted yield-density response curves, and (iii) explore genotype (G) x environment (E) interaction effect on yield-density response models. Analysis was conducted on meta-data (124,374 observations) gathered from 22 US states and 2 Canadian provinces, diverse sites (E), for years from 2000-2014 on multiple hybrids (G). Yield data were further grouped into four yield environments (low [LY], <7 Mg ha-1; medium [MY], 7-10 Mg ha-1; high [HY], 10-13 Mg ha-1; and very high [VHY], >13 Mg ha-1 yielding groups). Primary outcomes from this analysis were: (1) strong G x E interaction; (2) a quadratic model best fitted yield-density relationship; (3) four contrasting yield-density responses identified as dominant in each yield productivity environment, i.e., a declining, a constant, an increasing, and ever-increasing type; (4) the yield productivity environment varied for the different corn comparative relative maturity (CRM) groups, i.e., the LY environment for long-maturing hybrids matched with a MY or HY environment for short maturing hybrids; and (5) maximum yielding plant density (MYPD) was lower but maximum yield was greater for long- versus short-maturing hybrids. In summary, optimal plant density should be decided based on detailed G x E analysis of production conditions that include factors such as CRM, yield productivity environment (weather-soil x management practices), and site information. [ABSTRACT FROM AUTHOR]

Increased adaptation to high plant density has been an important factor in improvements in grain yield in maize (Zea mays L.). Despite extensive public literature on variation and improvement in plant density response among maize varieties, much less public information is available on effects of environment and genotypé environment interactions (G X E) on plant density response for grain yield in maize. The present study was conducted to quantify environment effects and G X E effects on plant density response for maize grain yield. A set of 57 synthetic populations, synthetic X inbred line crosses, and synthetic X synthetic population crosses were evaluated across a five year period including 17 individual location-years. The data in this study were an unbalanced combination of multiple experiments that included 370 pedigree-environment combinations with each containing at least four planting densities and two replications per environment in most cases. G X E accounted for 26% of total genetic variance (genetic variance plus G X E variance) in linear regression coefficients and 39% of variance in quadratic regression coefficients in the regression of grain yield on observed plant density. Variance in G X E for linear and quadratic regression coefficients resulted in variation in optimal densities among varieties being highly specific to individual environments. Average plant density responses varied widely among environments with average optimal plant densities ranging from 5.6 to 9.1 plants m-2. [ABSTRACT FROM AUTHOR]

previous research has shown that progress in genetic yield potential is associated with adaptation to agronomic planting density, though its genetic basis has not been addressed before. In the current study, a wheat (Triticum aestivum L.) association mapping initiative (WAMI) panel of 287 elite lines was assessed for the effects of plant density on grain yield (YLD), 1000-kernel weight (TKW), and grain number (GNo) in yield plots consisting of four evenly spaced rows. The YLD and GNo of inner (high plant density) rows compared with outer rows (low plant density) indicated a consistent pattern: genotypes that performed best under intense competition (inner rows) responded less to reduced competition (outer rows) while being generally the best performers on aggregate (inner plus outer rows). However, TKW was not affected by plant density. To identify the genetic loci, an adaptation to density index (ADi) was computed as the scaled difference in trait values between inner and outer rows. results on biplot analysis indicated that ADi was correlated with YLD in high-yielding environments, suggesting that it is a component of high yield potential. Genotyping of the WAMI panel was done through 90K Illumina Bead single nucleotide polymorphism (SNp) array. Association mapping employed using 18,104 SNp markers for ADi identified a major locus in chromosome 3B at 71 cM that explained 11.4% variation in ADi for YLD and GNo. Functional marker for ADi will enable identification of the trait in early generations--not otherwise possible in spaced plants typical of pedigree breeding approach--and to select parents for hybrid development. [ABSTRACT FROM AUTHOR]

Seeding rates (SRs) and row-spacing widths (RSWs) in perennial ryegrass (Lolium perenne L.) seed production are variable and the impacts of these factors on perennial ryegrass seed yield and plant growth characteristics are not well characterized. Experiments were conducted during 2010 and 2011 in first-year seed production fields near Roseau and Roosevelt, MN, where five SRs (1.3, 2.6, 5.2, 7.8, and 10.4 kg pure live seed [PLS] ha−1), three RSWs (10, 20, and 30 cm), and three N rates (67, 112, and 157 kg N ha−1) were evaluated in a split-split plot design under nonirrigated conditions. The 30-cm RSW resulted in 45% greater stem rust incidence, 8% fewer fertile tillers, and up to 2% greater 1000-seed weight (TSW) vs. the 10-cm RSW. For every unit of N applied, N increased biomass by 4 to 25 kg ha−1, fertile tillers by 3.7 tillers m−2, and seed yield by up to 4.7 kg seed ha−1, depending on environment. The 7.8 and 10.4 kg PLS ha−1 SRs combined with the 10-cm RSW, 157 ha−1 N rate, and other management factors, nearly eliminated weeds (<2% weed cover) compared with with wider RSWs and lower SRs. Weed cover was always inversely correlated with early-season vegetative cover (EVC). Seeding rates of 2.6 kg PLS ha−1 and greater resulted in similar seed yields suggesting that early-season plant density is not as important for seed yield as other management factors such as N rate, which significantly improved seed yield in three environments.

Multispecies competition effects of Xanthium strumarium L. and Datura stramonium L. have not been characterized in maize (Zea mays L.). Such information would be useful in developing an integrated approach to managing these two problematic weeds. Field experiments were conducted during 2 yr to evaluate multiple weed species interference of X. strumarium and D. stramonium at the total densities of 0, 4, 8, 12, and 16 plants m-2 (alone, and all possible combinations of the two weeds) with maize. Crop yield was associated with the density of D. stramonium and X. strumarium and decreased severely with increasing weed density. The maximum maize yield loss (63%) occurred when 12 X. strumarium and 4 D. Stramonium plants m-2 were allowed to compete with the crop. The total weed density (expressed in X. strumarium equivalent density) required to cause a 5% maize yield loss was about 0.50 and 0.56 plants m-2 in 2006 and 2007, respectively. Total canopy leaf area index and crop yield were reduced more strongly by competition with X. strumarium than with D. stramonium. Averaged over multispecies populations, X. strumarium contributed 84 and 67% of the total weed biomass in the first and second years, respectively. Owing to the high competitive ability and biomass production of X. strumarium in mixed crop and weed communities, it should be given a greater priority for control than D. stramonium in maize. [ABSTRACT FROM AUTHOR]

Genetic improvement in kernel filling characteristics has been an important contributor to hybrid maize (Zea mays L.) yield increases. However, changes in kernel filling characteristics have not been evaluated within the context of recurrent selection programs. The objective of this study was to determine if rate and duration of kernel filling and their interaction with plant density changed with long-term recurrent selection for agronomic performance in the Iowa Stiff Stalk Synthetic (BSSS) population. Populations selected for improved grain yield and agronomic performance were compared with the unselected base population, BSSS, at average final plant densities of 4.7 and 6.6 seeds m-2 at two locations near Ames, IA in 2009 and 2010. Treatments were replicated three times per location in a split plot design. Selected populations had a longer period of kernel filling but did not have a higher rate of kernel filling. Selected populations also had reduced final kernel weight at higher plant density, whereas unselected populations did not differ in final kernel weight. Reduction in final kernel weight at high plant density in selected populations suggests that increases in grain yield at high plant density in selected populations resulted from components of grain yield other than final kernel weight. [ABSTRACT FROM AUTHOR]

Research on the effects of seeding rates (SDR) and row spacing (RS) on soybean [Glycine max (L.) Merr.] seed composition is almost nonexistent. The objective of this research was to investigate the effect of SDR and RS on soybean seed protein, oil, fatty acids, sugars, and minerals using four soybean cultivars (P 93M90 and AG 3906, maturity group[MG] III; P 94B73, MG IV; and V 52N3, MG V) tested in 2006 and 2007. Seeding rates for P 93M90 and AG 3906 ranged from 247,000 to 592,800 seeds ha-1 and for P 94B73 and V 52N3 ranged from 60,000 to 180,000 seeds ha-1. Row spacings were 38 and 76 cm. Protein, oleic acid, sugars, P, and B concentrations increased with the increase of SDR in P 93M90 and AG 3906. However, after the maximum concentrations of these constituents were reached, a decrease was observed at the highest SDR. This trend was mainly observed in 2006 and depended on RS. In 2007, the opposite trend of protein and oleic acid concentrations was observed, where the protein and oleic decreased with SDR. In cultivars P 94B73 and V 52N3, results showed that protein concentration increased with SDR in 2006 and 2007 for both 38 and 76 cm RS. Oleic acid increased and linolenic acid decreased with SDR in 2006. The different trends of protein and oleic concentrations between years may be due to temperature and drought stress differences. This research showed that SDR and RS can alter seed constituents, and the magnitude of this effect depended on cultivar and environmental factors, especially temperature and drought. [ABSTRACT FROM AUTHOR]

A broad range of U.S. maize (Zea mays L.) germplasm was evaluated for plant density tolerance (PDT) to identify potential sources of favorable alleles and to obtain a better understanding the underlying genetics involved. Thirty-two hybrids created using a set of inbreds representing parentage of key heterotic subgroups were evaluated at plant densities ranging from 47,000 (19,000 plants per acre [ppA]) to 133,000 plants ha-1 (54,000 ppA). Forty-eight phenotypic traits from five categories (photosynthetic capability, plant architecture, growth responses, source- sink relationship, and general stress tolerance) as well as grain yield were evaluated in three environments that differed for levels of soil moisture availability. The relationship between plant density and grain yield was assessed for each hybrid, with a wide range of responses observed. Five hybrids showed substantial tolerance to plant densities ≥116,000 plants ha-1 based on grain yield performance. Phenotypic trait correlations revealed a subset of traits associated with grain yield across plant densities, with all five categories of traits implicated directly; the subset included leaf angle, upper stem diameter, leaf area required to produce a gram of grain, kernel rows per ear, days to canopy closure, barrenness, kernels per plant, kernel length, leaf number, upper leaf area, staygreen, zipper effect, kernels per row, and anthesis- silking interval. Analysis of gene action for grain yield across plant densities emphasized the prominence of additivity, the increasing importance of nonadditivity as plant density and environmental stress levels increased, and genotype by environment interaction. This work paves the way for further characterization of PDT through quantitative trait locus mapping and candidate gene approaches. [ABSTRACT FROM AUTHOR]

Increasing seed yield and quality of key cool-season perennial grasses is an important component of meeting China's environmental, food security, and urban beautification goals. Determining a suitable seed producing region and developing best management practices for this region with specific, high priority grasses will contribute to the availability of seed for reducing desertification, increasing livestock production, and improving urban living conditions. Previous research in other areas has addressed various agronomic practices on some grasses, but none has evaluated optimal row spacings for producing high yields of high quality seed in conditions similar to the Hexi Corridor, currently a major seed producing area in China for other seed crops. We compared our field trials in this area with those of other regions in China and the world to determine if this area would be suitable as a grass seed production center. Five important perennial, cool-season grasses {[Elymus kamoji (ohwi) S.L. Chen, slender wheatgrass [Elymus trachycaulus (Link) Gould ex Shinners ssp. Trachycaulus], smooth bromegrass (Bromus inermis Leyss), Siberian wildrye (Elymus sibiricus L.), and Chinese sheepgrass [Leymus chinensis (Trin) Tzvel]} were evaluated from 2010 to 2012 under four row spacing treatments (30, 50, 70, and 90 cm). Results showed all five grasses have potential for high seed production in this region, with yields equivalent to or significantly higher than other areas. Optimal row spacing for Elymus kamoji and smooth bromegrass was 30 cm while a 50 cm row spacing was better for seed production and weed control for slender wheatgrass, Siberian wildrye, and Chinese sheepgrass. This work will allow multinational seed companies, development agencies, and government program directors to better evaluate the potential economic sustainability of grass seed production in this region compared to importing seed from other regions of the world. [ABSTRACT FROM AUTHOR]

Improved plant N utilization and partitioning is critical for future improvements in maize (Zea mays L.) grain yield (GY). The overall research objective was to gain understanding of the physiological mechanisms underpinning biomass (BM), N uptake partitioning, and GY processes during the reproductive period for two maize hybrids grown at varying plant density (PD) (low is 54,000 plant ha-1, medium is 79,000 plants ha-1, and high is 104,000 plants ha-1) and N inputs (low is 0 kg N ha-1, medium is 112 kg N ha-1, and high is 224 kg N ha-1) over four site- years. At the community level, maize GY was maximized in both genotypes at the medium PD and highest N rate. At maturity, grain harvest index improved as the whole-plant N uptake increased following a linear-plateau model and, for N allocation, both grain and shoot N concentrations increased similarly as BM increased. Around flowering (±15 d), dry mass and N partitioning rates were unmodified by treatment factors. Treatment factors only marginally influenced potential kernel number near flowering. Allometric analyses confirmed a lack of treatment impact on whole-plant N uptake and N remobilization coefficients. Greater reproductive- stage N uptake was associated with superior ear strength (kernel number and weight) and late shoot N remobilization, but GY was also positively related to vegetative-stage N uptake. Future research should identify genotypic variation for overcoming the documented N uptake trade-off mechanisms (vegetative-stage N uptake vs. shoot N remobilization) as related to the maize GY improvement process. [ABSTRACT FROM AUTHOR]

From a physiological perspective, field studies that quantify the influence of plant density (PD) and N rate on biomass (BM) and N uptake are needed to build more functional partitioning models for maize (Zea mays L.). The overall goal was to quantify the effects of maize hybrid (two genotypes), PD (low = 54,000; medium = 79,000 and high = 104,000 pl ha-1), and N rate (low = 0, medium = 112 and high = 224 kg N ha-1) on the organ-specific dry mass and N allocation, and on the resource capture (ratio of leaf area index [LAI] to BM), and resource use efficiency (ratio of N uptake to LAI) parameters, during the vegetative phase at four site-years. Allometric analyses revealed that the resource capture was primarily affected by the PD, and the resource use efficiency by the N rate. The stoichiometry between leaf and stem dry mass was unaffected by the treatment factors, but no isometry was documented (greater BM to the stem than leaf). The N rate primarily modified the leaf and stem N concentrations (0N vs. 112- 224N). With respect to resource use efficiency, modifications in the leaf N content per unit of LAI were joint outcomes of changes in leaf mass and %N (N concentration). In contrast, physiological changes in the stem N content per unit of LAI were more dependent on changes in the stem %N (greater N storage capacity) rather than in the stem mass. Intensifying competition with neighboring plants reduced per-plant mass similarly in both leaf and stem structures, and improving N supply was proportionately more beneficial in maintaining plant mass and stem %N at high PD during vegetative growth. [ABSTRACT FROM AUTHOR]

Increasing interest in deploying multiple types of sensing instruments for agricultural plotlevel observations has created a need for simple, high-clearance vehicles that can be easily maneuvered through crops while minimizing damage due to wheel traffic. We describe a simple cart built from a 2-m-wide by 1.2-m-long steel frame that was welded onto two bicycle frames at a height providing 1 m of vertical clearance. Instruments such as radiometers and infrared thermometers are attached to the frame via arms that are secured with U-bolts. A large, horizontal surface allows mounting data loggers, batteries, or computers. The cart is easily maneuvered by one person on level ground or by two persons on terrain with furrows, berms, or other obstacles. Design sketches and lists of materials are provided in an electronic supplement. The basic design is readily modifiable for different interrow spacings and sensor positions. [ABSTRACT FROM AUTHOR]

Under field conditions water is often inadequate for satisfactory seedling establishment. This research investigated the field emergence and plant density of two lines (AB-medium and CD-tall) of sand bluestem (Andropogon hallii Hack.) and three generations of selection (Syn-0, Syn-1, and Syn-2). Populations AB-medium Syn-1 and AB-medium Syn-2 were developed from AB-medium Syn-0 using two cycles of recurrent selection for increased seed germination at a low water potential. Similarly, CD-tall Syn-1 and CD-tall Syn-2 were developed from CD-tall Syn-0. Our objective was to verify if the increase in seed germination of selected populations would also lead to an increase in field emergence and plant density. Field testing involved planting the six lines in a randomized block design replicated four times at three locations over a 3-yr period. Field emergence and plant density were determined using a frequency grid method at 30, 60, and 90 d after planting (DAP). Percentage field emergence and plant density varied only with sand bluestem line (P < 0.01), generation of selection (P < 0.01), and number of DAP (P < 0.05). Field emergence averaged 52.5, 57.4, and 61.1% for generation Syn-0, Syn-1, and Syn-2, respectively. Plant density averaged 13.8, 15.2, and 16.1 plants m-2 for generation Syn-0, Syn-1, and Syn-2, respectively. Therefore, selection for increased seed germination in sand bluestem also resulted in greater field emergence and higher plant density. [ABSTRACT FROM AUTHOR]

Sunflower (Helianthus annuus L.) production systems in semiarid regions often have poor seedling emergence and patchy stands leading to lower yield. We hypothesized plant spacing was positively related to individual plant yield and this relationship would strengthen as water deficits increased. In a 2-yr study in Colorado, individual plant spacing and associated seed was measured for different irrigation treatments. Highly significant positive linear and second-order polynomial regressions of individual plant spacing and yield (p < 0.001) were observed for all irrigation treatments in both years. However, given highly variable individual plant yield with spacing, regression explained no more than 16% of the variation. No consistent pattern in linear regression slope, y-intercept, or R2 values among irrigation treatments were noted, thereby not supporting the expectation that the relationship would be greater as water deficits increased, although rainfall events may have confounded the results. Leverage plots showed similar results as the regression equations but indicated plant spacing explained yield variation more than irrigation treatment. Regression tree analysis further confirmed that plant spacing was more important than irrigation treatment in explaining final plant yield. These results suggest there is a cost to final yield per unit area where large spacing results in lower yields even though these plants have the highest yields per plant of any spacing classes. [ABSTRACT FROM AUTHOR]

The plant density at which maize (Zea mays L.) hybrids achieve maximum grain yield has increased throughout the hybrid era while grain yield on a per plant basis has increased little. Changes in plant characteristics including flag leaf angle, anthesis-silking interval, plant height, tassel branch number, and total number of loaves have been characterized in comparisons of commercial hybrids representing different eras of hybrid maize production but have not been studied extensively in a temperate maize recurrent selection program. The objective of this experiment was to determine if direct selection for grain yield and agronomic performance in the Iowa Stiff Stalk Synthetic (BSSS) population has indirectly improved adaptation to high plant density. Material from an unselected base population, BSSS per Se, was compared to four selected populations per se at four plant densities ranging from 38,300, to 95,700 plants ha1. Treatments were replicated twice in each of two locations in 2 yr and arranged in a split plot design with plant density as whole plot and breeding population as subplot treatment. Selected populations had reduced anthesis-silking interval and fewer tassel branches. Increasing plant density increased anthesis-silking interval in the base population whereas increasing plant density did not increase anthesis-silking interval in the most advanced populations. These results demonstrated that selected populations were better adapted to high plant density than the unselected base population. [ABSTRACT FROM AUTHOR]