Switchgrass Growth Research Articles

Evaluating changes in switchgrass physiology, biomass, and light-use efficiency under artificial shade to estimate yields if intercropped with Pinus taeda L.

There is growing interest in using switchgrass (Panicum virgatum L.) as a biofuel intercrop in forestry systems. However, there are limited data on the longevity of intercropped bioenergy crops, particularly with respect to light availability as the overstory tree canopy matures. Therefore, we conducted a greenhouse study to determine the effects of shading on switchgrass growth. Four treatments, each with different photosynthetically active radiation (PAR) levels, were investigated inside the greenhouse: control (no shade cloth, 49 % of full sunlight), low (under 36 % shade cloth), medium (under 52 % shade cloth), and heavy shade (under 78 % shade cloth). We determined the effect of shading from March to October 2011 on individually potted, multi-tillered switchgrass transplants cut to a stubble height of 10 cm. In the greenhouse, there was a reduction in tiller number, tiller height, gas exchange rates (photosynthesis and stomatal conductance), leaf area, above- and belowground biomass and light-use efficiency with increasing shade. Total (above- and belowground) biomass in the control measured 374 ± 22 compared to 9 ± 2 g pot−1 under heavy shade (11 % of full sunlight). Corresponding light-use efficiencies were 3.7 ± 0.2 and 1.4 ± 0.2 g MJ−1, respectively. We also compared PAR levels and associated aboveground switchgrass biomass from inside the greenhouse to PAR levels in the inter-row regions of a range of loblolly pine (Pinus taeda L.) stands from across the southeastern United States (U.S.) to estimate when light may limit the growth of intercropped species under field conditions. Results from the light environment of loblolly pine plantations in the field suggest that switchgrass biomass will be significantly reduced at a loblolly pine leaf area index between 1.95 and 2.25, which occurs on average between ages 6 and 8 years across the U.S. Southeast in intensively managed pine plantations. These leaf area indices correspond to a 60–65 % reduction in PAR from open sky.

Effect of different levels of nitrogen deficiency on switchgrass seedling growth

Switchgrass (Panicum virgatum L.) is a warm-season rhizomatous perennial grass that can tolerate diverse abiotic stresses while yielding relatively high biomass, and is considered a leading biofuel feedstock for marginal lands. Nitrogen (N) is crucial for the growth and development of switchgrass, and its tolerance to low N supply and high N use efficiency are very important for its production under poor conditions. The large-scale planting of switchgrass on marginal lands could be an effective approach to solving the problem of feedstock supply for biomass energy. This study used a hydroponic experiment to evaluate the effect of N deficiency on switchgrass seedlings. Three N treatments (0, 0.15, and 1.50mmolL−1 Hoagland's solution) and six cultivars were used, three of each ecotype (upland and lowland). The results showed that biomass, leaf area, root surface area, net photosynthesis, and total chlorophyll content significantly decreased under low N treatments compared with those in full strength Hoagland's nutrient solution. However, once established, all plants survived extreme N stress (0mmolL−1) and, to some extent, were productive. Cultivar Kanlow performed best of the six cultivars under stress. Significant interactions between stress treatment and cultivars showed that breeding for cultivars with high yield and superior performance under N deficiency is warranted. The lowland outperformed the upland ecotypes under stress, suggesting that lowland cultivars may survive and be productive under a wider range of stress conditions. However, given the better adaptability of lowland ecotypes to hydroponic cultivation, further study is needed.

Evaluation of Salinity Tolerance and Genetic Diversity of Thirty-Three Switchgrass (Panicum virgatum) Populations

Switchgrass (Panicum virgatum) is a warm-season C4 grass that is a target lignocellulosic biofuel species. Salt stress is one of the major limiting factors for switchgrass growth in many regions. The objective of this study was to examine relative salt tolerance and genetic diversity among 33 switchgrass populations. Seeds of each population were planted in cone-tainers and grown in a greenhouse. Two months after establishment, the switchgrass were grown in half strength Hoagland’s nutrient solution with either 0 mM NaCl (control) or half strength Hoagland’s nutrient solution with 250 mM NaCl (salt stress treatment) for 24 days. Salt stress tolerance was determined based on a variety of parameters including leaf electrolyte leakage (EL), chlorophyll content (Chl content), leaf photochemical efficiency (F v/F m), photosynthetic rate (P n), stomatal conductance (g s), and transpiration rate (T r). Significant differences in salt stress tolerance were found among the 33 populations. Based on the P n and salt tolerance trait index (STTI), lowland populations AM-314/MS-155, Kanlow, TEM-LoDorm, Alamo, and BN-13645-64, as well as upland populations T-2086, T-2101, BN-11357-63, and BN-12323-69 were classified as salt tolerant. In contrast, upland populations BN-18757-67, 70SG0021, Summer, 70SG0016, T16971, Dacotah, Turkey, 70SG003, and Pathfinder were classified as salt sensitive populations. Sequence-related amplified polymorphism (SRAP) marker analysis was employed to determine the genetic diversity among the 33 switchgrass populations. UPGMA cluster analysis showed that salt tolerant switchgrass populations TEM-LoDorm, Alamo, Kanlow, BN-12323-69, AM-314/MS-155, T2101, BN-11357-63, T-2086, and BN-13645-64 clustered into one group, indicating that these salt tolerant populations may have a similar genetic background.

Effects of Irrigation Regime, Organic and Inorganic Mineral Source on Growth and Yield Components of Switchgrass (Panicum virgatum L.) in Upland and Lowland Conditions in Sokoto, Nigeria

The effects of organic, inorganic fertilizer and irrigation regime on yield parameters of P. virgatum in upland and lowland areas in Sokoto geoecological region of Nigeria were assessed. Four levels of nitrogen (0, 25, 50 and 75 kg N ha(-1)), three rates of farmyard manure (0, 5 and 10 t ha(-1)) and three irrigation regimes (w2, w4 and w6) were set up as a split -plots design. Farmyard manure and irrigation regimes were combined and allocated as the main plots, while nitrogen rates were assigned to the sub-plots and each replicated three times. Results revealed that raising nitrogen rate from 50 to 75 kg N ha(-1), farmyard manure rate from 5-10 t ha(-1) or irrigation intervals from 2 to 4 days did not show a significant (p > 0.05) increase in yield components evaluated. Dry matter accumulation was significantly (p < 0.05) affected by irrigation regime in both seasons and locations and 2 day interval irrigation had the highest dry matter yield. A significant interaction between nitrogen and manure application was observed only at upland in 2008/2009 and a combination of 75 kg N ha(-1) and 10 t ha(-1) manure produced the highest values in all the parameters evaluated. The study suggest that 50 kg N ha(-1) with 5 t ha(-1) of farmyard manure and 2 day irrigation interval gave the highest yield. A combination of 50 kg N ha(-1), with 5 t ha(-1) of farmyard manure and 2 day irrigation interval were found to be optimum for growth and yield of Switchgrass under both lowland and upland conditions in Sokoto geoecological zone of Nigeria.

Loblolly Pine Age and Density Affects Switchgrass Growth and Soil Carbon in an Agroforestry System

Loblolly Pine Age and Density Affects Switchgrass Growth and Soil Carbon in an Agroforestry System

Evaluation of intercropped switchgrass establishment under a range of experimental site preparation treatments in a forested setting on the Lower Coastal Plain of North Carolina, U.S.A.

There is growing interest in using switchgrass (Panicum virgatum L.) as a biofuel crop and for its potential to sequester carbon. However, there are limited data on the establishment success of this species when grown as a forest intercrop in coastal plain settings of the U.S. Southeast. Therefore, we studied establishment success of switchgrass within experimental intercropped plots and in pure switchgrass plots in an intensively managed loblolly pine (Pinus taeda) plantation in eastern North Carolina. Pine trees were planted in the winter of 2008, and switchgrass was planted in the summer of 2009. Establishment success of switchgrass was measured over the growing season from May to October 2010, and quantified in terms of percent cover, height (cm), tiller density (number of tillers m−2), leaf area index and biomass (Mg ha−1). At the end of the growing season, pure switchgrass plots were taller than the intercropped treatments (114 ± 2 cm versus 98 ± 1 cm, respectively), but no significant treatment effects were evident in the other variables measured. Switchgrass biomass across all treatments increased from 2.65 ± 0.81 Mg ha−1 in 2009 to 4.14 ± 0.45 Mg ha−1 in 2010. There was no significant effect of distance from the pine row on any switchgrass growth parameters. However, we anticipate a shading effect over time that may limit switchgrass growth as the pines approach stand closure.

Growing season greenhouse gas flux from switchgrass in the northern great plains

Abstract Switchgrass ( Panicum virgatum L.) is being evaluated as a bioenergy crop for the northern Great Plains. Field measurements of CO 2 , CH 4 , and N 2 O flux are needed to estimate the net greenhouse gas (GHG) balance of this biofeedstock. The study objective was to determine effects of recommended Nitrogen (N) fertilization (67 kg ha −1 of N applied) and unfertilized switchgrass on growing season soil-atmosphere CO 2 , CH 4 , and N 2 O flux using static chamber methodology. Mean hourly CO 2 flux was greatest during periods of active switchgrass growth and was similar between N fertilizer treatments ( P = 0.09). Mean hourly N 2 O flux was consistently greater under N fertilization than without N throughout the growing season. Overall, N fertilization of switchgrass affected cumulative growing-season N 2 O flux (27.6 kg ha −1 ± 4.0 kg ha −1 vs. 86.3 kg ha −1 ± 14.3 kg ha −1 as CO 2 equivalents (CO 2 eq) for 0 kg ha −1 and 67 kg ha −1 of N applied, respectively; P 2 or CH 4 flux ( P = 0.08 and 0.51, respectively). Aboveground biomass production was greater with N application (6.8 Mg ha −1 ± 0.5 Mg ha −1 dry matter) than without N (3.2 Mg ha −1 ± 0.5 Mg ha −1 ) ( P − 1 harvest yield as CO 2 eq) for switchgrass production was similar between N treatments (0.71 vs. 0.44 for 0 kg ha −1 and 67 kg ha −1 of N applied, respectively; P = 0.18).

Growth promotion and colonization of switchgrass (Panicum virgatum) cv. Alamo by bacterial endophyte Burkholderia phytofirmans strain PsJN

BackgroundSwitchgrass is one of the most promising bioenergy crop candidates for the US. It gives relatively high biomass yield and can grow on marginal lands. However, its yields vary from year to year and from location to location. Thus it is imperative to develop a low input and sustainable switchgrass feedstock production system. One of the most feasible ways to increase biomass yields is to harness benefits of microbial endophytes.ResultsWe demonstrate that one of the most studied plant growth promoting bacterial endophytes, Burkholderia phytofirmans strain PsJN, is able to colonize and significantly promote growth of switchgrass cv. Alamo under in vitro, growth chamber, and greenhouse conditions. In several in vitro experiments, the average fresh weight of PsJN-inoculated plants was approximately 50% higher than non-inoculated plants. When one-month-old seedlings were grown in a growth chamber for 30 days, the PsJN-inoculated Alamo plants had significantly higher shoot and root biomass compared to controls. Biomass yield (dry weight) averaged from five experiments was 54.1% higher in the inoculated treatment compared to non-inoculated control. Similar results were obtained in greenhouse experiments with transplants grown in 4-gallon pots for two months. The inoculated plants exhibited more early tillers and persistent growth vigor with 48.6% higher biomass than controls. We also found that PsJN could significantly promote growth of switchgrass cv. Alamo under sub-optimal conditions. However, PsJN-mediated growth promotion in switchgrass is genotype specific.ConclusionsOur results show B. phytofirmans strain PsJN significantly promotes growth of switchgrass cv. Alamo under different conditions, especially in the early growth stages leading to enhanced production of tillers. This phenomenon may benefit switchgrass establishment in the first year. Moreover, PsJN significantly stimulated growth of switchgrass cv. Alamo under sub-optimal conditions, indicating that the use of the beneficial bacterial endophytes may boost switchgrass growth on marginal lands and significantly contribute to the development of a low input and sustainable feedstock production system.

SWITCHGRASS AND INTERMEDIATE WHEATGRASS ABOVEGROUND AND BELOWGROUND RESPONSE TO NITROGEN AND CALCIUM

Calcium (Ca) and nitrogen (N) treatments (2, 8, and 32 mg L−1) were investigated on aboveground and belowground growth of switchgrass (Panicum virgatum L.) and intermediate wheatgrass [Thinopyrum intermedium (Host) Barkworth & D.R. Dewey] in a greenhouse experiment. Switchgrass (cultivars ‘Sunburst’ and ‘Dacotah’), and intermediate wheatgrass (cultivar ‘Reliant’) aboveground and belowground biomass were harvested and analyzed to determine total biomass, macronutrient concentrations, and forage quality. Intermediate wheatgrass biomass followed a positive response to increasing N and Ca while switchgrass response to N and Ca treatments varied by cultivar. Increased Ca supplementation rates from 2 mg L to 32 mg L−1 increased aboveground Ca concentrations of 113% and 257% for switchgrass and intermediate wheatgrass, respectively. Calcium had little impact on measured cell wall characteristics with the exception of hemicellulose content in intermediate wheatgrass. Further investigation on intermediate wheatgrass yield response to Ca under field conditions is warranted.

MicroRNA Expression Analysis in the Cellulosic Biofuel Crop Switchgrass (Panicum virgatum) under Abiotic Stress

Switchgrass has increasingly been recognized as a dedicated biofuel crop for its broad adaptation to marginal lands and high biomass. However, little is known about the basic biology and the regulatory mechanisms of gene expression in switchgrass, particularly under stress conditions. In this study, we investigated the effect of salt and drought stress on switchgrass germination, growth and the expression of small regulatory RNAs. The results indicate that salt stress had a gradual but significant negative effect on switchgrass growth and development. The germination rate was significantly decreased from 82% for control to 36% under 1% NaCl treatment. However, drought stress had little effect on the germination rate but had a significant effect on the growth of switchgrass under the severest salinity stress. Both salt and drought stresses altered the expression pattern of miRNAs in a dose-dependent manner. However, each miRNA responded to drought stress in a different pattern. Salt and drought stress changed the expression level of miRNAs mainly from 0.9-fold up-regulation to 0.7-fold down-regulation. miRNAs were less sensitive to drought treatment than salinity treatment, as evidenced by the narrow fold change in expression levels. Although the range of change in expression level of miRNAs was similar under salt and drought stress, no miRNAs displayed significant change in expression level under all tested salt conditions. Two miRNAs, miR156 and miR162, showed significantly change in expression level under high drought stress. This suggests that miR156 and miR162 may attribute to the adaption of switchgrass to drought stress and are good candidates for improving switchgrass as a biofuel crop by transgenic technology.

Biosphere-atmosphere exchange of volatile organic compounds over C4 biofuel crops

Significant amounts of ethanol are produced from biofuel crops such as corn and, in the future, likely switchgrass. The atmospheric effects of growing these plant species on a large scale are investigated here by measuring the plant-atmosphere exchange of volatile organic compounds (VOCs). Field grown corn and switchgrass emit VOCs at flux rates of 4.4 nmolC m−2 s−1 (10−9 mol carbon per square meter leaf area per second) and 2.4 nmolC m−2 s−1, respectively. Methanol contributes ∼60% to the molar flux but small emissions of carbonyls, aromatic compounds and terpenoids are relatively more important for potential air quality impacts. Switchgrass can act as a sink for carbonyls and aromatic compounds with compensation points of a few hundred pptv. In switchgrass moderate drought stress may induce enhanced emissions of monoterpenes, carbonyls and aromatics. Per liter of fuel ethanol produced, the estimated VOC emissions associated with the biomass growth of corn (7.8 g l−1) or switchgrass (6.2 g l−1) are in the same range as the VOC emissions from the use of one liter gasoline in vehicle engines. VOC emissions from the growing of biofuel crops can therefore be a significant contributor to the VOC emissions in the life cycle of biofuels. The VOC emissions from corn and switchgrass are small compared to those of tree species suggested as biofuel crops. Due to their reactivity with respect to OH the emissions from corn and switchgrass are not likely to have a significant impact on regional ozone formation.

Review and Model-Based Analysis of Factors Influencing Soil Carbon Sequestration Beneath Switchgrass (Panicum virgatum)

A multi-compartment model was developed to summarize existing data and predict soil carbon sequestration beneath switchgrass (Panicum virgatum) in the southeastern USA. Soil carbon sequestration is an important part of sustainable switchgrass production for bioenergy because soil organic matter promotes water retention, nutrient supply, and soil properties that minimize erosion. A literature review was undertaken for the purpose of model parameterization. A sensitivity analysis of the model indicated that predictions of soil carbon sequestration were affected most by changes in aboveground biomass production, the ratio of belowground-to-aboveground biomass production, and mean annual temperature. Simulations indicated that the annual rate of soil carbon sequestration approached steady state after a decade of switchgrass growth while predicted mineral soil carbon stocks were still increasing. A model-based experiment was performed to predict rates of soil carbon sequestration at different levels of nitrogen fertilization and initial soil carbon stocks (to a 30-cm depth). At a mean annual temperature of 13°C, the predicted rate of soil carbon sequestration varied from −28 to 114 g C m−2 year−1 (after 30 years) and was greater than zero in 11 of 12 simulations that varied initial surface soil carbon stocks from 1 to 5 kg C m−2 and nitrogen fertilization from 0 to 18 g N m−2 year−1. The modeling indicated that more research is needed on the process of biomass allocation and on nitrogen loss from mature plantations, respectively, to improve our understanding of carbon and nitrogen dynamics in switchgrass agriculture.

Salinity Effects on Germination and Plant Growth of Prairie Cordgrass and Switchgrass

Identifying bioenergy crops that can be produced successfully on marginal lands, such as those affected by salinity, reduces the pressure to produce energy crops on land that would otherwise be used to produce food crops. In this paper, the degree of salinity tolerance of “Red River” prairie cordgrass (Spartina pectinata Link) and “Cave-in-Rock” switchgrass (Panicum virgatum L.) was determined by evaluating seed germination, plant growth, ion uptake, and leaf anatomical feature responses in saline conditions. Red River seeds retained 50% of germination potential under high salinity up to 300 mM NaCl, whereas Cave-in-Rock seed germination was reduced by 80% at 300 mM NaCl. Red River seedlings survived up to 500 mM NaCl, while more than 30% of Cave-in-Rock did not survive above 100 mM NaCl in greenhouse experiments. Red River produced more biomass and second-generation tillers and had a greater root and shoot biomass ratio than Cave-in-Rock under all salinity ranges. Sodium accumulation in shoots of Cave-in-Rock increased with increasing salinity, whereas Red River maintained a low level of sodium in biomass through salt-gland exclusion. The increasing rate of selectivity coefficient for potassium over sodium in Red River was higher than in Cave-in-Rock with increasing salinity. Although seed germination and plant growth decreased as salinity increased, Red River retained its potential of seed germination and to produce new tillers and biomass under salinity stress.

Determining the impact of climate and soil variability on switchgrass (Panicum virgatum L.) production in the south‐eastern USA; a simulation study

AbstractSwitchgrass (Panicum virgatum L.) is a perennial warm‐season grass native to North America. The species is currently being evaluated as a potential feedstock for bioenergy. Growth and yield of switchgrass vary substantially due to weather and soil conditions. The objective of this study was to determine the impact and implications of weather, climate, and soil variability on switchgrass production in the south‐eastern USA using a crop simulation model. We simulated switchgrass growth and yield as a function of weather, soil, and crop management with the Agricultural Land Management Alternative with Numerical Assessment Criteria (ALMANAC) model. The model was first evaluated with switchgrass data from five field experiments conducted throughout Alabama. Subsequently, switchgrass growth and yield were simulated for climate and soil conditions representing the Tennessee River Valley region of northern Alabama and Georgia. Based on the simulations, we evaluated switchgrass production potential in this region under different climate and land‐use scenarios. Weather data from the 1950s, 1960s, and 1980s were included to account for the climate variability during the twentieth century. The average annual simulated switchgrass yield across the region was significantly (P &lt; 0.05) higher for the 1950s (13 740 kg d.m. ha−1) and the 1980s' climate (14 162 kg d.m. ha−1) than for the 1960s' climate (12 492 kg d.m. ha−1). The annual production potential for the region ranged from 64 977 and 83 915 metric t due to spatial variability in climate and soil conditions. Using results and implementing the approach from this study can help plan switchgrass‐based bioenergy systems. © 2011 Society of Chemical Industry and John Wiley &amp; Sons, Ltd

Nitrogenous fertilizer effects on soil structural properties under switchgrass

Nitrogen (N) fertilization is needed to sustain the biomass yield of switchgrass ( Panicum virgatum L., Poaceae) as a biofuel feedstock and, consequently, may influence the potential for soil quality improvements through soil organic carbon (SOC) sequestration. Therefore, the objective of this study was to assess how inorganic N application to switchgrass affects soil structural properties, which may feed back to affect the sustainability of biomass production. Soil was sampled at depths of 0–5, 5–10, and 10–15 cm in April and November 2008 during the fifth year of switchgrass growth in Milan, TN. Nitrogenous fertilizer was applied as NH 4NO 3 at rates of 0, 67, and 202 kg N ha −1 y −1 beginning in the second year. Root weight density (RWD), root length density (RLD) and SOC concentration were measured under different N treatments as factors potentially influencing soil structural properties. Measured soil structural parameters included soil moisture characteristic curve (SMCC), and aggregate stability through wet-sieving. At 0–5 cm depth, spring RWD (3.8 mg cm −3) was significantly lower with 202 kg N ha −1 application compared to 0 and 67 kg N ha −1 (14.1 and 17.0 mg cm −3, respectively). Although fall RWD did not vary among N treatments, RLD under 202 kg N ha −1 (7.1 cm cm −3) was less than half of that at 0 kg N ha −1 (15.7 cm cm −3). The SOC concentration was greater in both fertilized treatments than in the unfertilized treatment. Although SMCC varied somewhat between seasons, it did not exhibit any consistent trends attributable to N application. The proportion of macroaggregates for 0–10 cm depth were significantly greater in the 0 and 67 kg N ha −1 treatments than in the 202 kg N ha −1 treatment. These data suggest that excessive N application to switchgrass could have negative impacts on soil structural properties by reducing root biomass and length, crucial determinants of soil structure despite an increase in SOC.

Adaptability evaluation of switchgrass ( Panicum virgatum L.) cultivars on the Loess Plateau of China

In the study, the growth traits, photosynthesis and morphology characteristics of several cultivars of switchgrass ( Panicum virgatum L.) have been assessed the yield potential and adaptability in diverse environments (Yangling, Dingbian of Shaanxi province, Guyuan of Ningxia) on the Loess Plateau of China. Alamo was the best adapted switchgrass cultivar for biomass production in Yangling with dry matter (DM) yields of 44.22 t/ha; Illinois USA and Cave-in-Rock grown at Guyuan had DM yield of 10.59 t/ha and 9.36 t/ha, respectively. Similarly, Cave-in-Rock in Dingbian performed better than others except the lowland cultivars (Alamo and Kanlow), which could not overcome cold stress at Guyuan and Dingbian. Moreover, Cave-in-Rock and Nebraska 28 has the highest photosynthesis rate which reflects its high productivity. Nebraska 28 and Pathfinder shown strong drought tolerance due to their higher WUE. It appears that the upland cultivars with high ploidy (e.g. 8 n) would have better establishment than lowland varieties there. Optimal mown management seems to enhance the growth and productivity of switchgrass. Morphological characteristics were further studied using light-and scanning electron microscopy (SEM). Silica particles, vacuole size and other traits in switchgrass tissues (stem, leaf and root), as well as trichomes (leaf) showed that Cave-in-Rock and Pathfinder had larger stoma area, up to 824.4 μm 2 and 770.1 μm 2, respectively. Silica particle length was the longest in Pathfinder and shortest in Cave-in-Rock. There was a highest density of silica particles in cv. Forestberg, and lowest in Cave-in-Rock and Pathfinder. The morphological characters seemed to be associated with their ploidy levels and the arid habitat from which they were selected. Therefore, if switchgrass is to be introduced and extended on the Loess Plateau of China, Cave-in-Rock and other upland cultivars with a high chromosome ploidy might be optimal choices for biomass plants.

Nutrient Leaching and Switchgrass Growth in Mine Soil Columns Amended With Poultry Manure

AbstractIn Pennsylvania, land disturbance from 150 years of extensive coal mining and intensive animal production that produces manure nutrients in excess of crop needs have degraded ecosystems and water quality. Excess manure could be used in mine reclamation, but the large application rates requir

Simulating Switchgrass Growth and Development under Potential and Water‐Limiting Conditions

Anticipating a demand for switchgrass (Panicum virgatum L.) as a source for biofuel production, a crop simulation model of this crop can be a component of a biofuel decision support system. The objective of this effort was to develop and test a model for switchgrass, based on robust empirical relationships between plant behavior and the environment. The model simulates date of annual growth initiation (AGI), anthesis, aboveground biomass, leaf area index (LAI), and water balance components with a daily time step for crops grown under potential and water‐ limiting conditions. Daily weather data (solar radiation, maximum and minimum temperature, and rainfall), soil available water‐holding capacity (AWHC), and the fraction of AWHC at the date of AGI (FAWHC‐AGI) are required inputs. Two cultivar‐specific parameters, the maximum rate of development at the optimum temperature (Rmax) and maximum LAI (MAXLAI), synthesize differences in development and growth between cultivars. Tested against 10 independent data sets, the model generated good predictions of date of anthesis (root mean square error [RMSE] = 3 d) and aboveground biomass (RMSE = 1.5 Mg ha−1).

Effect of soil depth on phytoremediation efficiency for petroleum contaminants

Biodegradation of organic contaminants in soil may be enhanced by the presence of vegetation. Evaluating the effect of soil depth on phytoremediation efficiency may provide researchers and regulators with a clearer understanding of contaminant clean-up. A column study with polycyclic aromatic hydrocarbons (PAHs) and diesel-contaminated soil was conducted over a 147-day period of switchgrass (Panicum virgatum) growth. Analysis of the contaminants and plant biomass was conducted along with microbial enumeration at three soil depths in 49-day intervals. Remediation proceeded rapidly near the surface of the soil (0–20 cm) for both vegetated and unvegetated columns, but the effect of vegetation relative to an unvegetated control only was significant in the lower soil depths. Contaminant dissipation in the 20–40 and 40–60 cm layers was not significantly different between vegetated and unvegetated soil.

Establishment and Seedling Growth of Big Bluestem and Switchgrass Populations Divergently Selected for Seedling Tiller Number

Selection at the seedling stage in grass breeding would be extremely useful if seedling traits are correlated to desired agronomic traits. The objective of this study was to evaluate seedling morphological development, plant growth, and field establishment of big bluestem (Andropogon gerardii Vitman) and switchgrass (Panicum virgatum L.) populations that were developed by divergent selection for seedling tiller number while selecting for high shoot weight. Six populations were evaluated: (i) ‘Pawnee’ big bluestem base, (ii) ‘Pathfinder’ switchgrass base, (iii) big bluestem multiple tiller, (iv) big bluestem single tiller, (v) switchgrass multiple tiller, and (vi) switchgrass single tiller. Field plots were seeded in spring 1999 and 2000 in a Kennebec silt loam (fine‐silty, mixed, superactive, mesic Cumulic Hapludolls). Plants were excavated and evaluated during the growing season for shoot weight, root weight, and morphological stage of shoot and root systems. There were no major population differences in shoot weight, root weight, and morphological root stage. Shoot stage was higher for multiple tiller populations than single tiller populations 6 wk after emergence. Stand counts for all populations exceeded 10 seedlings per linear m of row, which is considered an acceptable stand density, and there were no consistent differences among populations. Populations divergently selected for seedling tiller number did not differ in ability to become established under field conditions because root systems apparently were not altered by the selection for seedling tiller number and weight. These results suggest that selection for high shoot weight did not improve seedling vigor in the field.