THE EFFECT OF PLANTING DATE AND SEEDING RATE ON UPLAND AND LOWLAND SWITCHGRASS ESTABLISHMENT AND DRY MATTER YIELD

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1 THE EFFECT OF PLANTING DATE AND SEEDING RATE ON UPLAND AND LOWLAND SWITCHGRASS ESTABLISHMENT AND DRY MATTER YIELD Chengjun Huo, Jim Stein, Josh Pittman, and Twain Butler Abstract Switchgrass (Panicum virgatum L.) is a warm-season perennial grass that has potential for biofuel, forage, and wildlife use. However, it is slow to establish due to small seed with low seedling vigor, which limits its widespread use. Utilizing the optimal planting date and seeding rate may improve establishment. The objectives of this study were to determine the effects of planting date (fall, winter and spring) and seeding rate (2-10 lb PLS/acre) on upland (Cave-in-Rock) and lowland (EG1101) switchgrass ecotypes establishment and dry matter (DM) yield in subsequent years. The split-plot RCBD experiment with four replications was conducted on a Dale silt loam at a research farm of the Noble Foundation near Ardmore, OK. Main plot consisted of three planting dates (September, February, and May) and subplots consisted of a factorial arrangement of five seeding rates (2, 4, 6, 8, 10 lb PLS/acre) and two switchgrass ecotypes (upland and lowland). For lowland switchgrass, September planting had greatest seedling count (36 seedling/ft 2 ) but winter killed and produced lowest DM yields (85, 173, and 0 lb/acre) in 2007, 2008, 2009, respectively, compared to February (1010 lb/a, lb/acre, and lb/acre, in 2007, 2008, an 2009 respectively) and May (1401, 10696, and lb/acre in 2007, 2008, 2009, respectively). There were no yield differences between February and May planting dates in all three years. For upland switchgrass Cave-in-Rock, there were no consistent differences in seedling number or DM yield among September, February, and May planting dates. As seeding rate increased, seedling counts and DM yield generally increased the first season, however there were no differences among seeding rates in the second or third season after establishment. Based on these data, lowland switchgrass should be planted at 2 lb PLS/acre in February or May, and upland type should be planted at 2 lb PLS/acre in fall, winter or spring in southern Oklahoma. Introduction: Switchgrass (Panicum virgatum L.) is currently being researched as a potentially viable biomass source in biofuels production. Although established stands of switchgrass tend to be persistent small seed size, and slow, erratic germination can result in inconsistent or slow establishment (Hsu and Nelson 1986; Aiken and Springer 1995; Hintz et al., 1998; Evers and Parsons 2003). Planting date has been observed to affect establishment in terms of both soil moisture and weed competition (Smart and Moser 1997). Due to the costly nature of switchgrass seed (Vogel 1987), increases in seeding rate to increase stand success and density can become economically prohibitive, thus limiting use of switchgrass for biofuel production (Vassey et al., 1985). Previous studies have documented the influence of switchgrass planting date and seeding rate on establishment and yield (Vassey et al., 1985; Hsu and Nelson 1986; Vogel 1987; Smart and Moser 1997). Vassey et al. (1985) in eastern Nebraska suggest that highly productive switchgrass stands can be obtained during the establishment year. These results were achieved through mid-april to early May planting dates and seeding rates of 3 lb PLS/acre when Atrazine was used for weed control. No significant differences were observed for the lowest seeding rate as compared to other rates for year 2 yields (Vogel

2 1987). In Columbia, MO, results indicated optimal planting dates for switchgrass between late April and mid-may due to increased emergence and reduced risks of temperature and soil moisture stress (Hsu and Nelson 1986). Late-spring and early-summer planting dates were not effective due to unfavorable soil moisture conditions and competition from annual grass and broadleaf weeds (Smart and Moser 1997). Smart and Moser (1997) recommended earlier spring planting dates in Lincoln, NE as opposed to late April and May. Although these studies have documented the influence of planting date and seeding rate on establishment and yield for Missouri and Nebraska, there is limited information concerning areas further south. Subsequently, the objective of this study conducted in southern Oklahoma, was to compare three planting date and five seeding rate. Materials and Methods: Experiments were conducted on the Samuel Roberts Noble Foundation Dupy research Farm near Ardmore, OK, USA (34 17'N latitude, 96 60'W longitude, 342 m elevation). Site characterization included soils consisting of a Dale silt loam (fine-silty, mixed, superactive, thermic Pachic Haplustoll) with average ph of 6.8. Average soil P and K concentrations were 246 and 564 mg kg -1, respectively. The experiment was arranged as a completely randomized block design in a split-plot arrangement. Main plot consisted of three planting dates (September, February, and May) and subplots consisted of a factorial arrangement of five seeding rates (2, 4, 6, 8, 10 lb PLS/acre). Two switchgrass ecotypes, lowland (EG1101) and upland (Cave-in-Rock) switchgrass were each drilled on 14-inch row spacings into a conventionally tilled seedbed with a plot size of 10 x 20 ft. During each growing season, plots were fertilized in May with 50 lb N/acre. Weed control measures were implemented through the application of 0.4 oz/acre cloransulam (FirstRate) and 1.0 qt/acre glyphosate (Credit) prior to switchgrass emergence, followed by 2 pt/acre Atrazine (Atrazine 4L) and 2 pt/acre 2, 4-D amine (Weedar 64) post-emergence in the establishment year. Seedling counts at 30 DAP, winter survival for September planted switchgrass, and DM yield of weed-free switchgrass were recorded in the establishment year. Dry matter yields were recorded for two subsequent years. Plots were harvested for DM yield in August and October in 2007, June and October in 2008, and November in Dry matter yield was determined by collecting a six ft wide cutting which extended the length of the plot to five inch stubble height. Subsamples from the cutting were obtained for DM determination and dried at 140 o F to constant weight. Total yield was determined by combining yields across all harvests each year. The remaining uncollected plot area was removed to the target residual stubble height. Statistical analyses were performed using SAS Proc GLM (SAS Institute, 2002), and least significant differences were calculated at α=0.05. Results and Discussions: Seedling Establishment. Of the planting dates observed, September plantings produced the highest success rate for seedling establishment at 30 DAP, with a mean seedling count of 36 seedlings/ft 2 for EG1101 and 43 seedlings/ft 2 for Cave-in-Rock (Table 1). May planting dates produced moderate rates of seedling establishment at 11 seedlings/ft 2 for EG1101 and 18 seedlings/ft 2 for Cave-in-Rock. Decreased seedling counts observed for May plantings could be attributed to competition from warm season grassy weed species which were not effectively controlled by herbicide applications. Additionally, 0 seedling/ft 2 was observed for both varieties in February plantings due to marginal soil

3 conditions for germination (Figure 1) and early spring freeze damage. The highest number of established seedlings for EG1101 (30 seedlings/ft 2 ) occurred at 8 lb PLS/acre seeding rate (Table 1); similar observations were recorded for Cave-in-Rock, with 35 seedlings/ft 2 occurring at of 10 lb PLS/acre seeding rate. There were no differences in seedling count among seeding rates of 2, 4, and 6 lb PLS/acre for either variety of switchgrass. Switchgrass survival. Winter survival for September planted plots was recorded in early spring the following season. Although total stand failure was observed for the EG1101, Cave-in-Rock winter survival averaged from 5 to 58 % (Table 2) among seeding rates. This suggests upland switchgrass varieties may express a greater cold tolerance than lowland varieties when established in autumn. Dry matter yield. Dry matter yield varied by planting date in all years (Table 3). EG1101 planted in February and May had similar DM yields which were greater than September planting date yields in all years. There were no differences in DM yield of Cave-in-Rock among planting dates in 2008 or However Cave-in-Rock planted in February had lesser yield (38 lb DM/acre) than the September and May planting dates (455 and 339 lb DM/acre, respectively) in Seeding rate had no effect on Cave-in-Rock DM yield in any year (Table 3). Dry matter yield of EG1101 was only affected by seeding rate in 2008, in which the seeding rate of 2 lb PLS/acre had the least yield (4363 lb DM/acre) compared to all other seeding rates (avg lb DM/acre). Based on these results, it is recommended that lowland switchgrass EG1101 be planted at 2 lb PLS/A in winter or spring, while upland switchgrass Cave-in-Rock can be planted in fall, winter, or spring at 2 lb PLS/A in southern Oklahoma. Literature Cited: Aiken, G.E., and T.L. Springer Seed size distribution, germination, and emergence of 6 switchgrass cultivars. Journal of Range Management 48: Evers, E.W., and M.J. Parsons Soil type and moisture level influence on Alamo switchgrass emergence and seedling growth. Crop Science 43: Hintz, R.L., K.R. Harmoney, K.J. Moore, J.R. George, and E.C. Brummer Establishment of switchgrass and big bluestem in corn with atrazine. Agronomy Journal 90: Hsu, F.H., and C.J. Nelson. 1986a. Planting date effects on seedling development of prennial warm-season forage grasses II. seedling growth. Agronomy Journal 78: Hsu, F.H., and C.J. Nelson. 1986b. Planting date effetcts on seedling development of perennial warm-season forage grasses.1. field emergence. Agronomy Journal 78: Smart, A.J., and L.E. Moser Morphological development of switchgrass as affected by planting date. Agronomy Journal 89: Vassey, T.L., J. R. George, and R.E. Mullen Early mid and late-spring establishment of switchgrass panicum-virgatum cultivar Cave-in-Rock at several seeding rates. Agronomy Journal 77: Vogel, K.P Seeding rates for establishing big bluestem and switchgrass with preemergence Atrazine applications. Agronomy Journal 79:

4 Figure 1. Monthly rainfall amounts for the growing seasons, and 30-yr average rainfall amounts at Ardmore, OK. Table 1. Seedling count for switchgrass at 30 days emergence in planting, at Ardmore, OK. Treatment EG1101 Cave-in- Rock Planting date Seedling/ft Sep. 37 a 43 a Feb. 0 c 0 c May 11 b 18 b Seeding rate 2 7 c 10 b 4 8 c 13 b 6 13 bc 20 ab 8 30 a 23 ab ab 35 a Means within treatment and column followed by the same letter do not differ at the P=0.05 significant level

5 Table 2. Switchgrass survival for Sep. planting in planting, at Ardmore, OK. Treatment EG1101 Cave-in-Rock Seeding rate % Winter survival a 26 ab 4 0 a 51 a 6 0 a 58 a 8 0 a 7a 10 0 a 5a Means within treatment and column followed by the same letter do not differ at the P=0.05 significant level Table 3. Switchgrass dry matter (DM) yield of the planting in the 2007, 2008, and 2009 growing seasons, at Ardmore, OK. EG1101 Cave-in-Rock Planting date lb DM/acre Sep. 85 b 173 b 0 b 455 a 4315 a 4539 a Feb a a a 38 b 3433 a 4069 a May 1401 a a a 339 a 4380 a 4846 a Seeding rate a 4363 b 9381 a 286 a 3405 a 3505 a a 6980 a 9613 a 268 a 3719 a 4636 a a 8266 a a 235 a 4204 a 5063 a a 7881 a a 242 a 3605 a 4337 a a 7566 a a 352 a 4663 a 4986 a Means within treatment and column followed by the same letter do not differ at the P=0.05 significant level