Development, Quality, Growth, and Yield of Two Diverse Switchgrass Cultivars Receiving Nitrogen Fertilizer in Indiana

2019-01-03T20:18:18Z (GMT) by Brooke A. Stefancik
Switchgrass (Panicum virgatum L.) is an important warm-season perennial grass in livestock systems and has been extensively researched as an herbaceous energy crop. Objectives of this series of studies were to compare morphological development, compositional quality, crop growth, and yield of a recently developed biofuel cultivar ‘Liberty’ to an improved forage cultivar ‘Shawnee’ in multiple Indiana environments. Pure stands of each cultivar were sampled in the field at Trafalgar and Roann, Indiana in 2016. In 2017, samples were collected at Trafalgar, Roann, and Lafayette, Indiana. Samples were collected weekly during the early season and every other week in the late season with development determined by use of the Mean Stage Count (MSC) and Mean Stage Weight (MSW) system.
In the morphological development study, MSC and MSW were linearly related to both GDD and DOY for both years. ‘Liberty’ growth lagged behind ‘Shawnee’ throughout the whole growing season by approximately seven days. Prediction equations for MSC and MSW were developed based on accumulated GDD and DOY for Trafalgar and Roann in 2017. The prediction equations for MSC as predicted by GDD explained from 84 to 93 percent of the variation in MSC across locations for ‘Shawnee’ and between 90 to 94 percent of the variation for ‘Liberty’. For MSW, ‘Shawnee’ and ‘Liberty’ prediction equations explained from 84 to 93 percent and 90 to 95 percent of the variation as predicted by GDD across locations, respectively.

In the compositional quality study, samples from every other sampling date were ground and analyzed using near-infrared reflectance spectroscopy (NIRS). Increasing nitrogen fertilizer caused a higher nitrogen concentration at a given MSC. The 0 kg N ha-1 fertilizer rate dropped below 10 mg g-1 nitrogen by MSC 2.2, whereas the 134 kg N ha-1 fertilizer rate had greater than 10 mg g-1 until MSC 2.7. ‘Liberty’ had increased Neutral Detergent Fiber (NDF) concentration as compared to ‘Shawnee’. For whole-plant samples, ‘Liberty’ averaged 727 mg g-1 NDF as compared to ‘Shawnee’ which averaged 718 mg g-1. ‘Liberty’ had 18 mg g-1 higher acid detergent fiber (ADF), on average, as compared to ‘Shawnee’. Acid Detergent Lignin (ADL) was not different among nitrogen fertilizer treatments. Stem-plus-sheath material accounted for a higher percentage of NDF, ADF, and ADL, in whole-plants as MSC increased, as compared to leaf blades. ‘Shawnee’ had higher IVDMD as compared to ‘Liberty’ and the biggest differences occurred around MSC 2.9. At MSC 2.9, ‘Shawnee’ whole-plant IVDMD was 448 mg g-1 and ‘Liberty’ whole-plant IVDMD was 430 mg g-1. Whole-plant ash concentration decreased as MSC increased.

For the study that evaluated crop growth and yield, differences in grams m-2, mass tiller-1, and tiller number per unit area were analyzed in response to growing degree days (GDD) and day of year (DOY). Number of tillers had a negative linear response to GDD and DOY for both years, whereas, mass tiller-1 had a positive linear response to GDD and DOY for both years. Grams m-2 responded quadratically to GDD and DOY. Generally, ‘Liberty’ had 20 percent higher mass tiller-1 and lower number of tillers per m-2 at the end of the season as compared to ‘Shawnee.’ Addition of nitrogen fertilizer generally increased mass tiller-1 and grams m-2. Roann, the northern most site, also had highest tiller numbers at the beginning of the season and decreased faster than at the central Indiana sites. ‘Liberty’ yielded 8.8 percent higher than ‘Shawnee’ across locations, nitrogen rates, and sampling years. Addition of nitrogen fertilizer did not conclusively increase yield. Grams m-2, mass tiller-1, and tillers per sample area helped explain some yield differences. For example, ‘Liberty’ had increased yield as compared to ‘Shawnee’, and ‘Liberty’ also had higher mass tiller-1 with no differences in tiller number between cultivars. While additions of nitrogen fertilizer increased grams per tiller, yield was not significantly increased with added nitrogen fertilizer. Therefore, these measures should not stand alone as a predictor of yield differences between cultivars. Switchgrass is a bunchgrass and has inherent difference in numbers of plant and tillers per plant within a plot, which may not be truly represented by one crop growth parameter alone.

This study confirms that switchgrass has great potential as a forage and biofuel crop in Indiana with low nitrogen fertilizer requirements and high yield. Understanding how switchgrass morphological development, compositional quality, growth, and yield responds in Indiana environments across locations, years, and nitrogen rates will help guide the future switchgrass management decisions of producers and researchers.