Mean Stage Count Research Articles

Effect of growing degree days, day of the year, and cropping systems on reproductive development of Kernza in Kansas

AbstractReproductive growth and development of cool‐season grasses is primarily driven by air temperature and photoperiod. This study was conducted near Salina, KS, to model the effects of growing degree days (GDD), day of the year (DOY), and cropping systems on first‐ and second‐year intermediate wheatgrass [Thinopyrum intermedium (Host) Barkworth & D.R. Dewey] (IWG) in Kernza perennial grain production systems. In 2018 and 2019, GDD and DOY were highly correlated with reproductive growth and development (i.e., mean stage count, head meristem height, and leaf, stem, and head biomass fractions). Row spacing, fertilization, and intercropping with alfalfa (Medicago sativa L.) did not influence IWG reproductive growth and development. Across years, DOY more closely predicted reproductive stages than GDD, indicating a greater response to photoperiod than air temperature. After stem initiation, the fraction of total biomass allocated to leaves decreased, whereas stem and head biomass increased in response to GDD and DOY. At anthesis, stem biomass exceeded leaf and head biomass. Parameterizing GDD and DOY models for management in IWG dual‐purpose, Kernza grain production systems will require additional datasets from many locations and environments.

A Model to Identify Smooth Brome Elongation Using Correlation of Mean Stage Count and Accumulated Growing Degree Days

The US Fish and Wildlife Service (USFWS) uses the five-leaf developmental stage as a signal to the initiation of elongation in smooth brome (Bromus inermis Leyss.). In areas where certain plant community criteria are met, conducting a prescribed burn at elongation onset has reduced smooth brome populations. However, leaf stage identification presents USFWS managers with challenges due to the variability of smooth brome development in tallgrass prairies of the Northern Great Plains. The objective of this research was to develop an alternative method to determine when smooth brome populations reach the targeted 50% elongation by linking accumulated growing degree days and population-level plant phenological stages (mean stage count). We determined smooth brome phenological stages at sites in North Dakota, South Dakota, and Minnesota and calculated the corresponding number of growing degree days (using the base temperature of 0 °C). Linear regression models, correlating phenological stage and growing degree days, determined onset of elongation in the smooth brome population, regardless of leaf stage variation. The average accumulated growing degree days (1256 AGDD) and corresponding standard deviation (±155 AGDD) can be used to predict when 95% of smooth brome populations in northern tallgrass prairies reach 50% elongation. As part of USFWS Native Prairie Adaptive Management program, results will be used to assist management decisions regarding the timing of defoliation in an effort to enhance native plant communities where smooth brome is the dominant invader.

Developmental Morphology and Biomass Yield of Upland and Lowland Switchgrass Ecotypes Grown in Iowa

Sustainable development of the bioenergy industry will depend upon the amount and quality of bioenergy feedstock produced. Switchgrass (Panicum virgatum L.) is a model lignocellulosic bioenergy crop but critical information is lacking for improved management, growth, and development simulation model calibration. A field study was conducted near Ames, IA during 2012–2013 with the objective to evaluate upland (“Cave-in-Rock”, ‘Trailblazer’ and ‘Blackwell’) and lowland (“Kanlow” and “Alamo”) switchgrass ecotypes for harvest timing on morphology (i.e., phenology, leaf area index (LAI), and biomass yield). The experiment used a randomized complete block design, with three upland and two lowland varieties harvested at six dates annually. In both years, delaying harvest to later maturity increased biomass yield; lowland cultivars produced greater biomass yield (6.15 tons ha−1) than upland ecotypes (5.10 tons ha−1). Lowland ecotypes had delayed reproductive development compared with upland ecotypes. At the end of both growing seasons, upland ecotypes had greater mean stage count (MSC) than lowland ecotypes. “Cave-in-Rock” had greatest MSC and LAI, but did not produce the greatest biomass. Relationships were nonlinear between MSC and biomass yield, with significant cultivar–year interaction. The relationship between biomass yield and MSC will be useful for improving switchgrass, including cultivar selection, fertilizer application, and optimum harvest time.

Variation in the reproductive development of perennial ryegrass (Lolium perenne L.) cultivars

Abstract Plant breeding has manipulated the flowering behaviour of perennial ryegrass (Lolium perenne L.) by developing later-heading cultivars. However, the impacts of breeding on the intensity and temporal distribution of flowering are not known. This study compared the reproductive development of 23 perennial ryegrass cultivar/endophyte combinations. In the Waikato and Canterbury, two replicate plots were closed from grazing and tillers were collected every two weeks over a 10-week period during late spring and early summer. Plant development stage was determined for each tiller using a quantitative scale, which was then used to calculate the mean stage count of each cultivar. The rate and timing of reproductive development differed among cultivars. Mid-maturing cultivars matured earlier at both sites compared with late- and very late-maturing cultivars. While the intensity of flowering was similar between maturity groups, the temporal distribution of flowering varied: the late- and very late-maturing cultivars had lower proportions of reproductive tillers early in the season. Keywords: Lolium perenne L., reproductive development, flowering behaviour

Steer Consumption and Ergovaline Recovery from In Vitro Digested Residues of Tall Fescue Seedheads

ABSTRACTErgot alkaloids produced by the endophyte [Neotyphodium coenophialum (Morgan‐Jones and Gams) Glenn, Bacon, and Hanlin] of tall fescue [Lolium arundinaceum (Schreb.) Darbysh.] are a common problem faced by livestock producers. These toxins are concentrated within seedheads of tall fescue, which cattle were observed to selectively graze. There appears to be little research showing the extent to which alkaloids are released from developing seedheads during digestion. Therefore, the objectives of this study were to determine the amount at which tall fescue seedheads were removed by cattle and to estimate the amount of ergovaline that is released from these tissues. Seedheads from tall fescue pastures were monitored for consumption by steers during summer 2010. Samples were digested with a two‐stage procedure, and ergovaline concentrations were determined using high‐performance liquid chromatography. By mean stage count 3.91 (Day of Year 155), 60.7 ± 2.87% of seedheads within the pastures had been grazed, and 2 wk later increased to nearly 78.8 ± 0.82%. Ergovaline concentrations of seedheads increased throughout the season and were highest in mid‐June. The percentage of ergovaline released from seedheads collected in mid‐June was lower than earlier dates, but the difference was small. Results of this study indicate that high concentrations of ergovaline are released from tall fescue seedheads during the growing season, and management strategies should be aimed at controlling reproductive growth of the grass.

Fall dormancy and cutting frequency impact on alfalfa yield and yield components

The productivity and survival of alfalfa ( Medicago sativa L.) is strongly influenced by cutting frequency (CF), but there is a lack of knowledge of how cultivar differences in fall dormancy (FD) respond to CF. The yield components of alfalfa also are affected by CF, but it remains unclear which of the components are most affected and if this effect is similar between cultivars differing in FD. Our objectives were: (i) to evaluate the FD × CF interaction on alfalfa productivity (forage yield and yield components), and (ii) to determine relative importance of yield components in response to CF and FD. Treatments were a factorial combination of three alfalfa cultivars with different FD (3, 6 and 10) and three CF (20, 30 and 40 days intervals). Cultivars were sown on August 24, 2006 in rows 30-m long and 0.5-m apart in a randomized complete block with three replicates. The experimental period was two years where cutting frequencies were applied during 120 days of each year. At the end of each regrowth, forage yield, shoots m −2, mass shoot −1, height shoot −1, mass of shoots per centimeter and stage of maturity by the mean stage count (MSC) were measured. In both years, the FD × CF interaction on forage yield was not significant. Of the two factors used in this experiment, FD and CF, the latter had a greater effect on alfalfa performance reducing forage yield, yield components and survival at the 20-day CF. FD treatment had no effect on two-year total forage yield and alfalfa survival. Plants in the CF 20 treatment always had lower MSC than CF 40 and CF 30 treatments and FD 3 plants were always less mature at cutting than FD 6 and FD 10 plants. Our study provides evidence that: (i) in temperate areas, cutting management recommendations can be advocated for short-term stands of dormant, semidormant and nondormant cultivars alike; and (ii) the choice of cutting frequency by the farmer compared to the choice of FD is more important on productivity and survival of alfalfa. Shoot height −1 was the yield component that had the most impact on forage yield; therefore management practices, genetic improvements, and environment conditions that increase this yield component could improvement alfalfa productivity.

Resposta do capim-Mombaça a doses de nitrogênio e a intervalos de corte

The objective of the experiment was evaluate the response of Mombaça grass (Panicum maximun Jacq.) to three rates of nitrogen fertilizer (N) and two cutting frequencies. Forage yield (FY), density and the average weight of tillers and the mean stage count (MSC) were used as response variables. Nitrogen levels linearly affected DMY and MSC. The number of tillers increased up to 406kg ha-1. The MSC increased with the nitrogen fertilizer due to shoot elongation and development of reproductive tillers. For the 28-day interval, vegetative tillers had the greatest influence on DMY, while for the 42-day, the number of vegetative tillers decreased.

Developmental Morphology of Smooth Bromegrass Growth Following Spring Grazing

The timing of initial spring grazing of smooth bromegrass (Bromus inermis Leyss.) pastures affects regrowth potential and subsequent forage yield and quality. This study was conducted to quantify the effects of the timing of the initiation of spring grazing on these factors. A field experiment was conducted at the Rhodes Research and Demonstration Farm in central Iowa from April through July in 1996 and 1997. Treatments were an undefoliated control and four initial dates of defoliation that were applied weekly, beginning when one fully collared leaf per tiller was present. Defoliation was done using two mature cattle (Bos taurus) to quickly (12–24 h) graze the sward to a height of 5 to 10 cm. Regrowth was sampled weekly for 8 wk, staged, and analyzed for forage quality. Early grazing of smooth bromegrass pastures did not delay sward development. Initiation of grazing at the later dates caused short delays in both development and the ability to regrow rapidly, but allowed utilization of a larger quantity of forage for the initial grazing event, with minimally decreased forage quality. Sward development differed between years. Tiller density and mean stage count did not differ among treatments during the 7 wk after defoliation in 1996 but did so in 1997. However, by the end of 8 wk, development was similar for all treatments. On the basis of this study, initiation of grazing when one fully collared leaf per tiller was present, followed by an adequate recovery period before beginning rotational grazing would give producers an early start on pasturing with limited impact on sward yield and health.

Predicting Leaf/Stem Ratio and Nutritive Value in Grazed and Nongrazed Big Bluestem

Recent advancements in describing morphological development of perennial grasses have provided a useful index for identifying dates to harvest hay or graze pasture. The objective of this study was to determine the relationship between big bluestem (Andropogon gerardii Vitman) morphological developmental stage, days from 1 May, and accumulated growing degree days (GDD) and leaf/stem ratio, crude protein (CP), and neutral detergent fiber (NDF) in grazed and nongrazed swards. The grazing experiment was conducted in eastern Nebraska during 1997 and 1998. Six grazing treatments consisting of all combinations of two herbage allowances (22 or 66 kg of herbage dry matter per animal unit day) and three grazing dates (late May, early June, and mid‐June) were randomly assigned to seven paddocks (900 m2) in each of four blocks along with a nongrazed control treatment. Random samples consisting of 50 or more tillers were hand‐clipped weekly at ground level in each paddock beginning in late May and ending in early August. Morphological developmental stage of the samples were determined, and a mean morphological stage based on shoot count [mean stage count (MSC)] was calculated. Samples were hand‐separated to determine leaf/stem ratio and analyzed for CP and NDF. Regression analysis showed that good relationships were found between MSC (R2 = 0.61–0.81), days from 1 May (R2 = 0.45–0.76), and GDD (R2 = 0.44–0.74) and leaf/stem ratio in nongrazed big bluestem and high herbage allowance swards. All three were adequate predictors of nutritive value and leafiness, but MSC may be more useful to researchers who want a more descriptive measure of plant morphological development, particularly when comparing cultivars or species.

Predicting Forage Quality in Switchgrass and Big Bluestem

Predicting forage quality would help producers schedule hay harvesting to obtain desired hay quality. Our objective was to determine if growing degree day (GDD), day of the year (DOY), mean stage count (MSC), and mean stage weight (MSW) could be used to predict in vitro digestible dry matter (IVDDM), crude protein (CP), and neutral‐detergent fiber (NDF) of ‘Trailblazer’ switchgrass (Panicum virgatum) and ‘Pawnee’ big bluestem (Andropogon gerardii Vitman) grown in Nebraska and Kansas. This field study was conducted from 1990 to 1993 at Mead, NE on Typic Argiudoll soils and from 1992 to 1993 at Manhattan, KS on Aquic Argiudoll soils. Plants were sampled at 1‐wk intervals in 1990 and 1991 and at 2‐wk intervals in 1992 and 1993. They were morphologically classified as MSC and MSW and analyzed for IVDDM, CP, and NDF. Switchgrass IVDDM and CP were best predicted by GDD models, which accounted for 86 and 91% of the variation, respectively, whereas NDF was best predicted by MSC and MSW. Big bluestem IVDDM was best predicted by MSW and CP was best predicted by GDD, which both accounted for 90% of the variation. Mean stage weight accounted for 74% of the variability in big bluestem NDF. The DOY model adequately predicted forage quality due primarily to the determinate growth habit of these species. Morphological development accurately predicted forage quality in many instances. Although no universal parameter adequately predicted concentrations of IVDDM, CP, and NDF, it was possible to accurately predict quality with readily available environmental data and measures of plant maturity.

Field Use of an Ion-Specific Electrode to Measure the Potassium Concentration in Alfalfa

Methods for determining K deficiencies in alfalfa (Medicago sativa L.) are either imprecise, time-consuming, or expensive. New to the market are portable and inexpensive meters that use a K-specific electrode (KSE) to measure the K concentration of plant sap. Little research has examined the precision or accuracy of these meters for determining the K concentration in alfalfa shoots. The objective was to determine if the KSE meter could precisely and accurately estimate the K concentration in alfalfa shoots. Laboratory, greenhouse, and field experiments were conducted to test the KSE meter's ability to measure the concentration of K in aqueous solution and in alfalfa sap. Laboratory results showed that KSE meter readings are subject to interference from Cl−, SO2−4 and NO−3 ions. In greenhouse and field experiments, the KSE meter precisely estimated the K concentration in alfalfa shoots (R2s > 0.74) if readings were included in a multiple regression equation that also included sample moisture content or mean stage count and air temperature. Readings taken from fresh plant sap using the KSE meter were highly biased, with the readings being four to six times lower than those obtained by flame photometry. Readings from the KSE meter, if used with other variables in a multiple regression equation, would allow users to quickly assess the K status of alfalfa shoots for a relatively small investment.

Switchgrass Morphological Development Predicted from Day of the Year or Degree Day Models

We tested recently published linear equations for predicting developmental morphology of warm‐season perennial grasses on three cultivars of switchgrass (Panicum virgatum L.). Mean stage count (MSC, based on the Nebraska system) of ‘Cave‐in‐Rock’ and ‘Kanlow’ switchgrass was measured at Ames, IA, and MSC of Cave‐in‐Rock and ‘Alamo’ switchgrass was measured at Stephenville, TX, during 1995. Measured MSC was compared with MSC estimated from day of the year (DOY) or growing degree day (GDD; base of 10°C) equations. The DOY equation more closely estimated MSC for switchgrass grown at Ames than at Stephenville. The GDD equation did not work well for any cultivar at either location. The equations did not work as well in Texas, probably because of genotypic interactions with daylength and climate for developmental morphology. These results indicate that the DOY equation may be useful with some varieties of switchgrass in the central Great Plains.

Morphological Development of 2 Warm-Season Grasses in the Nebraska Sandhills

Morphological development of grasses has numerous implications to rangeland management including the timing and amount of herbivory. The objective of this study was to quantify the developmental morphology of prairie sandreed [Calamovilfa longifolia (Hook.) Scribn.] and sand bluestem [Andropogon gerardii var. paucipilus (Nash) Fern.] tiller populations. Tiller populations of these 2 grasses were studied for 2 years in the Nebraska Sandhills. Plant development was evaluated using a growth staging system which quantifies the development of tiller populations. A morphological growth index for each species was calculated from either the weighted average of tiller numbers reported as mean stage count (MSC) or tiller weight reported as mean stage weight (MSW) and correlated with the independent variables of growing degree days (GDD) and day of year (DOY). Correlation coefficients with the independent variables were greater than 0.97 for MSC and MSW within years and greater than 0.90 between years. Greater rainfall and warmer temperatures in 1991 increased the number of tillers in the more advanced morphological stages in prairie sandreed, but tiller weight rather than tiller number increased in more advanced stages of sand bluestem. A majority of the harvested tillers were vegetative throughout the sampling period but by the end of the growing season, a wide range of morphological stages were present. The use of grazing to prevent the formation of culmed tillers in these grasses may be unnecessary because of the high proportion of vegetative tillers and the wide range of morphological stages available for selection by livestock.

Tiller Demographics and Leaf Area Index of Four Perennial Pasture Grasses

AbstractDeveloping grazing systems requires basic information on the growth and development of adapted species. The objective of this field study was to determine seasonal tiller demographics and leaf area index (LAI) of intermediate wheatgrass [Thinopyrum intermedium (Host) Barkw. & D.R. Dewey], smooth bromegrass (Bromus inermis Leyss.), switchgrass (Panicum virgatum L.), and big bluestem (Andropogon gerardii Vitman) tiller populations. This study was conducted in 1992 and 1993 near Mead, NE, on a silty clay loam soil (Typic Argiudoll) as a randomized complete block. Monocultures were harvested six times each year for tiller demographics. Additionally, mean stage count (MSC), a quantified estimate of tiller population maturity, was determined at each harvest. The LAI was indirectly measured using a canopy analyzer at 7‐ to 14‐d intervals. Tiller density for all species generally declined as MSC increased. Tiller demographics were highly variable by year for intermediate wheatgrass and smooth bromegrass, which indicates that grazing management should be based on current tiller populations. Density of vegetative tillers declined most rapidly for smooth bromegrass, followed by intermediate wheatgrass, switchgrass, and big bluestem. Switchgrass and big bluestem tiller demographics were more uniform and predictable across years than intermediate wheatgrass and smooth bromegrass. The LAI for all species increased as MSC increased. Maximum LAI for intermediate wheatgrass, smooth bromegrass, switchgrass, and big bluestem in 1992 was 4.7, 5.1, 4.9, and 5.8, respectively. Integrating tiller demographics and LAI suggests that initial grazing readiness starts with smooth bromegrass in early spring, followed by intermediate wheatgrass in about 2 wk, switchgrass in late spring, and big bluestem in early summer.

Morphological Development of Switchgrass as Affected by Planting Date

AbstractLate‐spring and early‐summer plantings of warm‐season grasses often fail, due to dry soil conditions and competition from annual grass and broadleaf weeds. The objective of this study was to compare the morphological development of switchgrass (Panicum virgatum L.) planted in early, mid, and late spring in eastern Nebraska. This study was conducted in 1994 and 1995 at Lincoln, NE, on a Kennebec silt loam (fine‐silty, mixed, mesic Cumulic Hapludolls). ‘Blackwell’ and ‘Trailblazer’ switchgrass were planted in mid‐March, late April, and late May using a single‐row, precision grass‐seed cone planter to a depth of 0.6 to 1.3 cm at 98 pure live seed per linear meter of row in a split‐plot design. Twenty seedlings from each plot were excavated to a depth of 20 cm with a spade. Seedling morphological parameters measured were mean stage count root (MSCR) and shoot (MSCS), leaf area, shoot weight, and primary and adventitious root weight. Plots were sampled every 10 d following the first sample date. In 1994, seedlings from the March planting date were more advanced morphologically in MSCR and MSCS, had accumulated 2.5 times more leaf area, and about 3 times more shoot and adventitious root mass than the April planting date when sampled from late May to late June. In 1995, seedlings from the March planting date generally were more advanced morphologically in root and shoot development, had accumulated 2 to 12 times more leaf area, had 2 to 10 times more shoot mass, and had 2 to 33 times more adventitious root mass than the April or May planting dates at the sample periods from early June to mid‐July. We suggest that switchgrass should be planted in early spring instead of in late April and May, as suggested by previous research.

Predicting Developmental Morphology in Switchgrass and Big Bluestem

AbstractSwitchgrass (Panicum virgatum L.) and big bluestem (Andropogon gerardii Vitman) are important warm‐season grasses in livestock production systems in the central and eastern USA. The objectives of this study were to quantify the morphological development of ‘Trailblazer’ switchgrass and ‘Pawnee’ big bluestem and to evaluate day of the year (DOY) and growing degree day (GDD) as predictors of switchgrass and big bluestem morphological stage. Pure stands of each species were sampled at weekly intervals in 1990 and 1991 at Mead, NE, and classified as to mean stage count (MSC) and mean stage weight (MSW). Prediction equations for MSC and MSW were developed based on DOY and GDD. The validation study was harvested at 2‐wk intervals in 1992 and 1993 at Mead, NE, and Manhattan, KS, and classified as to MSC and MSW. Switchgrass and big bluestem MSC and MSW were related linearly in all environments. Linear DOY calibration equations accounted for 96% of the variation in switchgrass MSC across four environments, which indicates that switchgrass development was related to photoperiod and that general management recommendations could be based on DOY in the central Great Plains. Quadratic GDD calibration equations accounted for 83% of the variation in big bluestem MSC across four environments, which indicates that big bluestem development is more difficult to predict and management recommendations in the central Great Plains should be based on morphological development (which is best predicted by GDD). The comprehensive growth staging system gave repeatable results for quantifying the morphological development of switchgrass and big bluestem. The morphological development of switchgrass and big bluestem can be reliably predicted for adapted cultivars in the central Great Plains during years with near‐normal precipitation using DOY and GDD because of the determinate growth habit of these grasses.

Morphological and Climatological Predictors of Forage Quality in Tall Fescue

Forecasting quality losses of standing forage may aid producers when making harvest decisions. The objectives of this research were to compare morphological, climatological, and chronological models as predictors of forage quality in ‘Kentucky‐31’ and ‘All‐Triumph’ tall fescue (Festuca arundinacea Shreb.) receiving three N treatments; and test those models for their ability to predict forage quality. Pure stands of Kentucky‐31 and AU‐Triumph tall fescue were fertilized to meet University of Georgia (UGA) Cooperative Extension Service recommendations with all nutrients except N. Stands were divided into individual plots which received either 50, 100, or 200 kg N ha−1, and harvested weekly after initiation of spring growth. In 1990 and 1991, tillers were counted, staged for morphological development, and weighed. Samples were ground, scanned with a near infrared reflectance spectrophotometer (NIRS), and a subset was analyzed chemically to develop calibrations for forage quality. Near infrared spectrophotometric quality values were regressed with mean stage count, mean stage weight, growing degree days (MSC, MSW, and GDD, respectively) and calendar day, and regression equations were validated with samples harvested from plots in 1992 and 1993. The MSC and MSW equations had poor fit in AU‐Triumph (range of R2 from 0.28–0.35 and 0.58–0.61, respectively) and were not validated. Calendar day and GDD had predicted quality better (range of R2 from 0.76–0.90 and 0.74–0.87, respectively); validation statistics of those equations had intercepts equal to 0.0 and linear coefficients equal to 1.0 for in vitro dry matter disappearance (IVDMD) and occasionally for crude protein (CP), but not for neutral (NDF) or acid (ADF) detergent fiber.

Prediction of Alfalfa Chemical Composition from Maturity and Plant Morphology

To make informed harvest management decisions, producers need information on the chemical composition of alfalfa (Medicago sativa L.) forage. Our objective was to develop a fast and simple method for predicting forage chemical composition (crude protein, neutraland acid‐detergent fiber, and acid‐detergent lignin) using morohological characters. Five alfalfa cultivars werevaluated across a range of environments, growth cycles, and harvest maturities. The 15 morphological characters examined for association with chemical composition included number of nodes per plant, plant height, mean stage count (MSC), mean stage weight (MSW), and alternative stage of development descriptions. Simple regression analyses based on node number and plant height provided better prediction equations than when based on MSC or MSW. Multiple regression equations based on two and three morphological characters provided higher R2 and lower root mean squarerror (RMSE) values than did linear and quadratic models based on a single morphological character. Multiple regression of the two most easily measured characters, height of the tallest stem (MAXHT) and maturity stage the most mature stem (MAX), provided equations with RMSE values only slightly greater than those of the best two‐factor multiple regression models based on characters that are more difficult to measure. Thus, multiple regression techniques should improve the accuracy of predicting forage chemical composition, and the use of easily determined characteristicsuch as MAXHT and MAX may provide the best compromise between prediction accuracy and ease of use.