Switchgrass ( Panicum virgatum L.) biomass, which is of a good quality in the middle of summer, when cool-season grasses are unproductive, is a very important source of forage. This study measured the influence of the date of first harvest and cutting height on the first and regrowth yields of switchgrass cultivars Blackwell and Cave in Rock. The experiment was conducted in Blacksburg, VA, USA on a Groseclose-Poplimento soil to determine the influence of four dates of harvest and two cutting heights on the yield of switchgrass in 1990, and the influence of the treatments in previous years on the yields in 1991 and 1992. The first yield of both cultivars increased as the date of first harvest was delayed and the cutting height reduced. The regrowth yield of both cultivars declined as the date of first harvest was delayed. A shorter cutting height caused reductions in vigour and yield potential in the second year, whilst in the third year the harvested yield was only 40–50% of that obtained from previously unharvested stands.

In this exercise the student learns to use growth analysis to interpret the increased yield from plant species with varying growth rates during the fall growing season. The student is instructed in the collection of data and the calculation of various growth analysis formulae, including mean relative growth rate, mean net assimilation rate, and mean crop growth rate. The student also learns how to organize his data into tables and how to interpret his results. Additional index words: Net assimilation rate. Relative growth rate. Alfalfa, Reed canarygrass, Orchardgrass. T TNDERSTANDING the principles involved in plant growth requires a systematic approach using the tools of mathematics, physics, and other sciences along with a common sense knowledge of biological variability. This teaching resource illustrates the method of interpreting plant development ref erred to as "growth analysis." The exercise can be used jointly with a series of related problems in a crop science course (8, 9). 1 Contribution of the Department of Agronomy, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061. Associate Professor and Professor of Agronomy, respectively.

Projected economic benefits of renewable energy derived from a native prairie grass, switchgrass, include nonmarket values that can reduce net fuel costs to near zero. At a farm gate price of $44.00/dry Mg, an agricultural sector model predicts higher profits for switchgrass than conventional crops on 16.9 million hectares (ha). Benefits would include an annual increase of $6 billion in net farm returns, a $1.86 billion reduction in government subsidies, and displacement of 44-159 Tg/year (1 Tg = 1012 g) of greenhouse gas emissions. Incorporating these values into the pricing structure for switchgrass bioenergy could accelerate commercialization and provide net benefits to the U.S. economy.

The objective of this study was to investigate the influence of water stress conditioning on the photosynthesis response of switchgrass (Panicum virgatum L.) and tall fescue (Festuca arundinacea Schreb.) to moisture deficiency. Tillers of the two species were grown in the same, controlled, environment and were subjected to three conditioning water stress cycles, or were kept well watered. After drought conditioning all plants were subjected to moisture deficiency while photosynthesis and leaf water potential were monitored. Measurements were taken between –0.8 and –4.0 MPa and the rate of water stress was 0.49 MPa/day. The conditioning of switchgrass produced a 26% reduction in the photosynthesis rate during drought, while that of tall fescue produced a 57% reduction in photosynthesis. Both species maintained elongation and photosynthesis down to lower leaf water potentials after drought conditioning than before conditioning. The conditioning water stress cycles decreased the leaf conductance, mesophyll resistance and transpiration of tall fescue plants after rewatering. The leaf water potential of conditioned switchgrass plants was lower upon rewatering after three conditioning water stress cycles than the leaf water potential of non-conditioned plants, while the leaf conductance, mesophyll resistance and transpiration of conditioned and non-conditioned tillers were equal. These data indicate an improvement in the drought tolerance of tall fescue and switchgrass plants, emphasize the importance of knowing the previous water stress history of the plants in moisture deficiency experiments, and help to choose proper irrigation management for switchgrass and tall fescue.

Switchgrass (Panicum virgatum L.) shows potential as a sustainable herbaceous energy crop from which a renewable source of transportation fuel and/or biomass-generated electricity could be derived. In 1992, a new research program focused on developing switchgrass as a biomass energy feedstock was initiated by the U.S. Department of Energy in five of the southern United States. The multifaceted, multi-institution research addresses breeding for improved biomass yields, regional field tests, cultural practices, physiology and tissue culture. Recent progress is highlighted in this paper. Preliminary results from the breeding program indicate that recurrent restricted phenotypic selection could lead to development of new cultivars. A technique for regenerating switchgrass plants via tissue culture has been proven and new populations of regenerated plants have been established in the field. Performance trials at three regional cultivar testing centers in Virginia, Alabama and Texas have shown that ‘Alamo’ switchgrass has higher biomass yield and broader adaptability than other cultivars tested. Research on management practices designed to maximize biomass yield has shown that multiple harvests of switchgrass may reduce total seasonal yields in some instances and that responses to fertilizer inputs vary with the environment. Seed dormancy often retards rapid establishment of competitive stands of switchgrass. Our research has indicated that seed dormancy can be modified, resulting in increased seed germination and a greater number of switchgrass plants. Research on the physiology of switchgrass has shown that lowland and upland ecotypes differ in photosynthetic rate but not in respiration rate. Findings in each of these areas can contribute to development of switchgrass as a sustainable bioenergy crop. Future research will address molecular biology techniques for exploiting genetic variation, explore canopy architecture and carbon allocation patterns affecting biomass yield, elucidate key factors in successful establishment of switchgrass and provide technology transfer that facilitates scale-up of switchgrass production for commercial energy production.

Switchgrass (Panicum virgatum L.) has been proposed as a model species for biomass fuel production. To better manage switchgrass as a biofuel crop, knowledge of its morphological development in several environments would be useful. This study was conducted to determine how morphological development of switchgrass varies in different field environments and to relate development to soil moisture status and other meteorological indicators. An established stand of 'Alamo' switchgrass at Stephenville, TX (32°13'N, 98°12'W ; 399 m elevation), was sampled weekly or biweekly from April to September in 1991 and 1992. Field plots of Alamo and 'Cave-in-Rock' were established at Stephenville in 1992 and sampled 17 times during 1993. Established field plots of Alamo and Cave-in-Rock at Blacksburg, VA (37°11'N, 80°25'W ; 610 m elevation) were sampled at 11 dates in 1992 and 9 dates in 1993 from May to September. Maturity stage at each harvest was determined according to a maturity scale developed at Stephenville. Morphological development and apical meristem elevation of both cultivars were closely related to cumulative degree days (DD, base 10°C) at each location. The developmental patterns were similar among years and were not affected by differences in soil moisture or rainfall distribution at Stephenville. Cave-in-Rock and Alamo matured about 4 wk earlier at Stephenville than at Blacksburg. The duration of the vegetative period was about 300 DD shorter at Blacksburg than at Stephenville for both Alamo and Cave-in-Rock. The close association of morphological development with DD in different environments could simplify morphological development models ; however, the models would need to be location specific, because the timing and duration of phenological events differed as switchgrass cultivars were moved southward or northward.

The authors have investigated cutting and N management strategies for two biofuel feedstock candidate species -- switchgrass (Panicum virgatum) and weeping lovegrass (Eragrostis curvula). Each was no-till planted in 1987 at three sites underlain by Davidson or Cecil soils. Three N levels (0, 50, or 100 kg/ha) were applied, and the plots fertilized at each level were harvested either twice (early-September and early-November) or only in early-November. The results with lovegrass suggest 50 kg N/ha is nearly optimal and that two cuttings provide more biomass than one. For switchgrass, when averaged across sites and years, 50 kg N/ha produced a slight yield advantage over no added N, but 50 kg was not different from 100 kg. In 1989 and 1990, more biomass was available in early-September harvests (9.6 Mg/ha) than in early-November (8.3 Mg/ha). Apparently the plants translocated significant portions of their biomass below ground during the last few weeks of the season. In 1991, we harvested only in early-November. Plots that had been cut in early-September in the previous three years had lower yields (7.6 Mg/ha) than those that had been cut only in early-November (9.4 Mg/ha). The delayed cutting permitted more growth on a sustained basis -- presumably because of conservation of translocatable materials. This poses an interesting dilemma for the producer of biomass. In additional studies, the authors found no advantage in double-cropping rye (Secale cereale) with switchgrass; at low input levels, rye yields were low, and rye lowered switchgrass yields. Other studies showed double-cropping with winter-annual legumes such as crimson clover (Trifolium incarnatum) may have potential. The timing of herbicide treatment of the legume is critical.

Accurate delivery of solutions from a sprayer or of seed and fertilizer from ground-driven spinner spreaders requires accurate travel speeds. The objective of this note is to provide plans for building your own inexpensive electronic speedometer. Where the applicator is mounted on wheels, an accurate speed can be maintained using a computerized bicycle speed indicator and small magnets secured at equal intervals around the spokes. Insulated wire connects the magnetic sensor to a computerized digital display unit mounted within view of the operator. The computerized display is calibrated for the diameter of the wheel by settings in the operator's manual. The indicated speed is 10 times the actual speed. Speed is updated each second and displayed to the nearest 0.1 km h-1. The computer unit and materials can be purchased from local suppliers and assembled in a few hours. Evaluation of performance was made by four subjects under several conditions. When considering subjects and conditions, the standard error of travel speed was 0.056 km h-1 when operating the unit at a target of 3.22 km h-1 (2.0 MPH). This means that a range of 3.16 to 3.28 km h-1 could be achieved 95% of the time while intending to travel at 3.22 km h-1.

Tall growing, perennial, warm-season grasses that produce 65 to 75% of their yield in mid-summer may provide needed summer grazing; however, establishment is often slow and inconsistent when compared to cool-season grasses. Improved establishment would make these warm-season grasses less vulnerable to annual weed competition. No-till plantings of switchgrass (Panicum virgatum L.) and caucasian bluestem [Bothriochloa caucasica (Trin.) C. E. Hubbard] were made at Blacksburg, VA (37-degrees 11' N-degrees 80-degrees 25' W, 610-m elevation) on a Groseclose loam soil (clayey, mixed, mesic Typic Hapludult). Eight experiments included carbofuran (2,3-Dihydro-2-dimethyl-7-benzofuranol methylcarbamate) at 0 and 1.1 kg a.i. ha-1 and atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) at 0, 1.1, and 2.2 kg a.i. ha-1 in all possible combinations. Seedling growth, leaf appearance rates, seedling weights, density, leaf elongation rates, and heights were measured. Yields of weed-free perennial warm-season grasses were determined in the year of planting and the year after planting. Carbofuran at 1.1 kg a.i. ha-1 placed in the row with the seed at planting enabled seedlings to develop faster, elongate more rapidly, and provided more and heavier seedlings than without carbofuran. In the year after seeding, yields of warm season grass were higher where carbofuran was applied at seeding in seven of eight experiments. Atrazine reduced herbage yields as well as population, weight, development, and leaf elongation rate of seedlings in the seeding year. Atrazine at 1.1 kg a.i. ha-1 was not detrimental to either grass in the second year of the study. Atrazine at 2.2 kg a.i. ha-1 appeared to injure switchgrass more than caucasian bluestem. Yields in the year after planting further confirmed these observations. Atrazine at 1.1 kg a.i. ha-1 increased yields over untreated controls. However, in one of four switchgrass experiments, yields of grass treated with atrazine at 2.2 kg a.i. ha-1 were lower than controls the year after planting. A yield reduction was observed in two of four caucasian bluestem experiments. All stands were nearly pure with planted species the year after planting. Carbofuran and atrazine at 1.1 kg a.i. ha-1 was considered the best recommendation for establishment of switchgrass and caucasian bluestem under the conditions of the experiment.

Current recommendations for grazing alfalfa ( Medicago sativa L.) include grazing for a few hours or days when plants are near a haycut stage. This study investigated the influence of continuous grazing of ‘Arc’ alfalfa by steers ( Bos taurus L.) during spring (38 d), summer (26 d), or both on plant growth, potato leafhopper ( Empoasca fabae Harris) population, and subsequent hay yields. Three grazing and one nongrazed treatments were imposed during 1986 and 1987 on Groseclose silt loam (clayey, mixed, mesic Typic Hapludults). Treatments included: (i) spring grazing started when alfalfa height was approximately 10 cm, followed by three hay harvests; (ii) hay harvested twice, followed by summer grazing that started when alfalfa height was approximately 15 cm, followed by one hay harvest; (iii) both spring and summer grazing as described above with hay harvested after the second and fourth growth cycles; and (iv) nongrazed with hay harvested four times. No grazing was imposed during 1988 when hay was harvested four times to measure the influence of previous grazing. In 1986 and 1987, hay yields following spring grazing (6.61 Mg ha −1 ) were not different than those for nongrazed (6.47 Mg ha −1 ). Fall hay yields following summer grazing (1.39 Mg ha −1 ) and spring plus summer grazing (1.34 Mg ha −1 ) treatments were lower than for spring grazing (1.85 Mg ha −1 ) or nongrazed treatments (1.80 Mg ha −1 ). Grazing had no influence on root total nonstructural carbohydrates at the end of Year 2. Grazing for 2 yr by any treatment had no effect on yields during Year 3 when alfalfa was harvested four times for hay. Potato leafhopper density increased during regrowth following summer grazing to a level of 11.5 insects per sweep that required insect control, whereas little buildup occurred following hay harvest during the same growth period. Our data show that grazing, begun in spring or summer at a young vegetative stage, can continue for a time equal to a growth cycle in either or both seasons of at least 2 yr with no detrimental effect on alfalfa hay yield in Year 3.

Cool-season perennial grass productivity falls sharply during hot, dry summer weather. This summer slump has been observed at many locations in the USA, especially in the Southeast. Perennial, tall-growing, warm-season forage grasses produce abundant herbage during the summer and could make a contribution to Southeastern forage systems. However, the relatively long period commonly required to produce grazable stands of warm-season grasses is problematic. Before these warm-season species can be incorporated into a summer forage system, problems with establishment must be investigated. Field research was undertaken to evaluate the influence of limestone, P, and carbofuran (2,3-dihydro-2,2,-dimethyl-7benzofuranyl methylcarbamate) in the establishment of switchgrass (Panicum virgatum L.) using no-till procedures. Plantings were made both in 1985 and 1986 into a killed sod in Blacksburg, VA, located at 37-degrees 11' N-degrees 80-degrees 25' W at 2000-ft elevation. The soil was a Groseclose loam (clayey, mixed, mesic Typic Fragiudult) with a fragipan at 17 in. Treatments included granular carbofuran at 0 and 1 lb/acre placed in the row with the seed, limestone at 0 and 2 ton/acre, and P at 0 and 44 lb/acre in all possible combinations. Limestone and P were broadcast 26 wk prior to planting. Seedling growth rate and leaf appearance rate were recorded through the sixth-leaf stage of development. Seedling weights, populations, and heights were determined at the sixth-leaf stage of development. Leaf elongation rates were measured for leaves 7, 8, and 9. Yields of forage and percentages of switchgrass in the harvested herbage were determined in the year of planting and the year after planting. The data indicate that carbofuran application increased nine of 12 measurements in the year of seeding. Yields the year after planting were significantly higher in the carbofuran plots than the control plots in both years. Phosphorus application increased yields in the 1986 harvest of the 1985 planting but no effect was observed in the 1987 harvest of the 1986 planting. Limestone had no effect the year after seeding in either experiment. Carbofuran applied at planting in the row with the seed and P applied prior to no-till planting in areas with low P soil test levels are considered good recommendations for establishment of switchgrass.

Fall establishment of alfalfa (Medicago saliva L.) in locations such as southwest Virginia (37 ° N, 80 ° W, and 600 m elevation) is often not possible by conventional methods because of the difficulty in meeting currently recommended planting deadlines. This usually results from unfavorable weather, a need to utilize a previous crop for an extended time, or the removal of a corn crop for silage. The objective of this study was to establish a recommended date for late‐season no‐till alfalfa planting as an alternative to conventional methods so that plantings need not be delayed until the following spring. Alfalfa was planted on 1, 10, 20, 30 September, and 10 October 1982, 1983, 1984, and 1985 using conventional and no‐till procedures. Soils were Groseclose (clayey, mixed, mesic Typic Hapludults) with 3 to 7% slopes. Excellent stands were achieved by mid‐December from both conventional and no‐till procedures regardless of planting date. Seedling survival during the winter decreased with delay in planting after 1 September, with less loss occurring with no‐till than conventional plantings. Each 10‐d delay in planting after 1 September caused a 6.8‐d delay in first harvest date the following spring beyond the mid‐May cutting date resulting from the 1 September planting. These data support a recommendation that no‐till planting can be made 3 wk later in the growing season than is possible with conventional methods. This extra latitude will allow flexibility when unavoidable delays in planting may occur and where the previous crop cannot be removed early enough to permit successful conventional planting.

Successful establishment of no‐till alfalfa (Medicago sativa L.) in spring and late summer is limited by soil moisture, weed competition, and disease. Thistudy tested an alternative planting time that partially avoids these problems. Vegetation was suppressed with fall‐applied herbicides and plantings were made in late winter (early March). Plantings were made into Typic Hapludult and Typic Fragiudult soils. All areas received 2,4‐D [(2,4‐dichlorophenoxy) acetic acid] in late August, but this could have been omitted if no broadleaf weeds had been present. A no‐herbicide treatment was included as a check. Herbicide suppression included glyphosate [N‐(phosphonomethyl) glycine] at 3.4 kg ha−1 on 1 October, paraquat (1, l′‐Dimetyl‐4, 4′‐bipyridinium ion) applied once on 1 October or 1 November at 0.56 kg ha−1, or a split paraquat application with 0.56 kg ha−1 applied 1 October and 0.28 kg ha−1 applied 15 November. Treatments were harvested three times in the year of establishment and four times in the year after seeding. Excellent seedling emergence occurred from all treatments in each year, so yield differences were due to success of weed suppression by herbicides. No‐till alfalfa planted in early March resulted in vigorous seedlings where original species in the sod were suppressed the previous fall. Vigor and productivity of plants established without herbicide was not satisfactory. Percentage alfalfa in the harvested herbage and yields in both harvest years tended to be higher for the split application of paraquathan other treatments even though this was not always significant (P ≤ 0.05). The split paraquat treatment was more consistent between sites and years than the glyphosate or single paraquat treatments. These results suggest that in environments similar to the test site (37 ° N, 80 ° W, and 600‐m elevation) high yielding alfalfa stands can be established using fall applications of a split paraquat treatment, followed by late‐winter planting with a no‐till drill.

Herbaceous biomass crops have the potential to capture solar radiation and store energy as a renewable fuel resource. Establishment procedures that can be used successfully without damage to the environment are essential. The objective of this research was to develop procedures to establish perennial, warm-season grasses, such as switchgrass (Panicum virgatum L.) and lovegrass (Eragrostis curvula L.), without tillage and preparation of a fine seedbed. Two applications of paraquat spaced 3 weeks apart or a single application of glyphosate can be used to suppress sod before no-till plantings. Carbofuran applied in the row at 1.1 kg ha−1 with the seed increased seedling vigor and populations. Application of 1.1 kg ha−1 of atrazine when seedlings began to emerge provided post-planting weed suppression. Weed encroachment occurring in years after establishment was halted by 2 kg ha−1 of simazine applied before first growth in the spring. These data provide guidelines for successful establishment of herbaceous perennial, warm-season grass biomass crops.

Defoliation management of forage species in the northern USA is related to total nonstructural carbohydrate (TNC) concentrations. These energy compounds are closely related to winter survival, stand persistence, and subsequent productivity of stands. Influences of early spring defoliation on TNC concentrations of switchgrass (Panicum virgatum L.) during recovery growth in the humid USA have not been reported. This field study was conducted to observe influences of defoliation time and intensity on TNC concentrations during recovery growth when switchgrass was grown without or with N fertilization (120 kg N ha−1). The experimental site was a Webster‐Nicollet soil complex (fine‐loamy, mixed, mesic Typic Haplaquolls‐Aquic Hapludolls). Defoliation treatments at 2‐wk intervals in 1984 and 1985 consisted of early‐, mid‐, and late‐spring defoliation, each at moderate or severe intensity. Nitrogen fertilization reduced TNC concentrations for all defoliation treatments. Accumulated TNC concentrations remained lower after 3, 6, and 9 wk of recovery growth for 120 compared with 0 kg N ha−1, but relatively little difference was observed among defoliation treatments in TNC concentrations by mid‐October. Severe defoliation at early, mid, and late spring generally contributed to lower TNC concentrations during recovery growth compared with moderate defoliation. However, TNC concentrations 6 to 8 wk or less after spring defoliation were at a relatively high concentration for most defoliation treatments, which suggests that herbage utilization in mid‐ to late‐July should not seriously weaken stands. Lower TNC concentrations in mid‐October of 1985 compared with 1984 suggest that both weather conditions and defoliation management influence TNC concentrations in stem bases of switchgrass.