Switchgrass cultivar, yield, and nutrient removal responses to harvest timing

Authors: ASHWORTH, AMANDA - Orise Fellow; ALLEN, FRED - University Of Tennessee; BACON, JENNIFER - University Of Tennessee; SAMS, CARL - University Of Tennessee; TYLER, DONALD - University Of Tennessee; GRANT, J - University Of Tennessee; Moore, Philip; Pote, Daniel

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/24/2017
Publication Date: 10/5/2017
Citation: Ashworth, A.J., Allen, F.L., Bacon, J.L., Sams, C.E., Tyler, D.D., Grant, J.F., Moore Jr, P.A., Pote, D.H. 2017. Switchgrass cultivar, yield, and nutrient removal responses to harvest timing. Agronomy Journal. 109(6):2598-2605. Available: https://dl.sciencesocieties.org/publications/aj/articles/109/6/2598.

Interpretive Summary: Harvest timing and switchgrass variety can have a significant impact on yield, but switchgrass growers in the southeastern USA need research-based information to identify the best switchgrass cultivar and fall harvest time to help them maximize long-term yields with minimal nutrient inputs in their region. To provide the necessary data, a research team from USDA-ARS and the University of Tennessee compared nutrient removal and yields from eight switchgrass cultivars (two upland and six lowland) and four late-season harvest dates at two research sites in Tennessee. They found that yield was greatest from lowland cultivars, especially when switchgrass was harvested in early November; but nutrient removal did not vary across harvest dates because nutrient concentrations in the crop declined as yield increased. Although early (mid-September) harvesting in the southeastern USA is not likely to increase nutrient removal, it may decrease biomass yields by 20-30% compared to later harvest dates. This study is of interest to scientists, extension personnel, biomass industry specialists, and agricultural producers because it provides management strategies for southeastern switchgrass producers to support high yields with minimal nutrient loss.

Technical Abstract: Finite nutrients, such as P (phosphorus) and K (potassium) are remobilized post-growing season in herbaceous feedstocks such as swichgrass (Panicum virgatum L.) as a function of environmental signaling and genotype. However, harvesting early during the maturation process may result in yield reductions. Therefore, it is necessary to target harvest dates that maximize yield while minimizing nutrient removal per cultivar. The objectives of this study were to compare multi-year yield data from the eight widely used and experimental upland and lowland switchgrass cultivars in Tennessee, and determine for the southeast region i) which harvest timing provides maximum yield; ii) effects of harvest timing on overall P and K removal (in leaves and stems); and, iii) how results are affected by switchgrass cultivar. Among all post-senescence harvests, yields peaked early-November (13.2 Mg ha-1), which was greater than all other harvests (P<0.05), with mid-October and late-October not differing from one another. Because yields reached an asymptote early-November, P and K removal did not vary across harvest dates (despite both P and K concentrations declining mid-October). Lowland varieties, on average, yielded 3.9 Mg ha-¹ more biomass annually than upland entries, suggesting lowland varieties are better suited to environments in the Southeast. Due to lower yields, P and K removal was lower for upland cultivars (Blackwell and C62), compared to that of lowland cultivars. Consequently, switchgrass can be harvested as early as mid-September without removing greater amounts of P and K, although variations may occur between upland and lowland cultivars.