Defoliation Management Affects Productivity, Leaf/Stem Ratio, and Tiller Counts of ‘Performer’ Switchgrass

Abstract

Core Ideas Defoliation management resulted in a wide range of plant responses that varied by year, with deleterious responses more evident in the second year. Greater leaf/stem ratios occurred with more frequent defoliation treatments. Frequent defoliations such as every 3 wk should maintain a stubble height of at least 40 cm, defoliation frequencies ≥6 wk to 20‐cm stubble height, and ≥9 wk to 10 cm stubble height are warranted to ensure stand persistence. ‘Performer’ switchgrass (Panicum virgatum L.) was released in 2006 by the USDA‐NCSU forage program because of its greater digestibility compared to standard cultivars grown in the southeastern United States. Forages with greater digestibility have potential to positively impact animal responses, however, defoliation management can influence its productivity and persistence. The objectives were to determine the effect of the factorial combination of four defoliation heights (DH) (clipped to 10, 20, 30, and 40‐cm) and four defoliation frequencies (DF) (clipped every 3, 6, 9, and 12 wk) on productivity, leaf/stem ratio, and tiller counts. The experiment was conducted in 2016 and 2017 at the Central Crops Research Station, Clayton, NC. The 16 treatments were allocated in a complete randomized block design replicated four times. In 2016, total dry matter (DM) yield ranged from 4.2 to 13.1 Mg ha−1 being greatest for the 9‐ and 12‐wk DF at 10‐ and 20‐cm DH and lowest for all DH at 3‐wk defoliation frequency. In 2017, the DM yield range was wider ranging from 0.5 to 14.0 Mg ha−1 with lower tiller counts for the 10‐ and 20‐cm DH, 3‐wk DF treatments. Leaf/stem ratio was greater for the more frequently defoliated treatments in both years. ‘Performer’ switchgrass is a productive forage and on the basis of total DM harvested, leaf/stem ratio, and tiller counts, frequent defoliations such as every 3 wk to 40‐cm stubble height, ≥6 wk to 20‐cm stubble height, and ≥ 9 wk to 10 cm stubble height, are warranted to ensure stand persistence.

Harvest Management Effects on Canopy Height and Light Interception of ‘Performer’ Switchgrass and its Relationship with Weed Infestation

“…A detailed description of plot management was provided by Bekewe et al (2018). A 50-by 51-m area of well-established (>8 yr) 'Performer' switchgrass was used for this experiment.…”

“…In addition, they reported that overutilization of the grass at the start of the growing season, such as clipping monthly for three consecutive months starting in May, resulted in lower yields, lower tiller numbers, and weed infestation, to the point that weeds shaded the switchgrass tillers. Bekewe et al (2018) indicated that frequently defoliated treatments had lower DM yield and required clipping to greater stubble heights to ensure productivity and persistence of 'Performer' switchgrass. Working with 'Alamo' switchgrass, Seepaul et al (2014) reported concurrent lower canopy heights at harvest and lower total herbage mass for treatments that were frequently clipped to a stubble height of 5 cm.…”

“…A previous study by Bekewe et al (2018) concluded that, after 2 yr of imposing defoliation treatments, there were three defoliation thresholds that ensured the persistence of 'Performer' switchgrass. A previous study by Bekewe et al (2018) concluded that, after 2 yr of imposing defoliation treatments, there were three defoliation thresholds that ensured the persistence of 'Performer' switchgrass.…”

“…A previous study by Bekewe et al (2018) concluded that, after 2 yr of imposing defoliation treatments, there were three defoliation thresholds that ensured the persistence of 'Performer' switchgrass. Clipping every 3 wk to 40-cm stubble height resulted in DM yield of 4.4 Mg ha −1 , ³6 wk to 20-cm stubble resulted in DM yield of 7.1 Mg ha −1 , and ³9 wk to 10-cm stubble resulted in DM 10.9 Mg ha −1 (Bekewe et al, 2018). Clipping every 3 wk to 40-cm stubble height resulted in DM yield of 4.4 Mg ha −1 , ³6 wk to 20-cm stubble resulted in DM yield of 7.1 Mg ha −1 , and ³9 wk to 10-cm stubble resulted in DM 10.9 Mg ha −1 (Bekewe et al, 2018).…”

“…In situations where weed suppression by crop competition is the goal, what is being managed is light (McLachlan et al, 1993;Holt, 1995). Data on productivity responses for 'Performer' have been previously reported (Bekewe et al, 2018); therefore, the objectives of this study were (i) to characterize and compare canopy height and light interception of cultivar 'Performer' of switchgrass as a function of a wide range of defoliation management treatments, (ii) to determine canopy cover and frequency of weeds as a function of the treatments imposed, and (iii) to draw relationships among canopy height, light interception, and weed infestation responses measured in this study and previously reported productivity measurements. We hypothesized that weed infestation will be greater in treatments with lower switchgrass canopy light interception and lower canopy heights before and after clipping.…”