Submitted to: Agronomy Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/21/2000
Publication Date: 7/20/2001
Citation: Muir, J.P., Sanderson, M.A., Ocumpaugh, W.R., Jones, R.M., Reed, R.L. 2001. Biomass production of 'alamo' switchgrass in response to nitrogen, phosphorus, and row spacing. Agronomy Journal. 93(4):896-901. Interpretive Summary: Sustainable production of bioenergy crops requires optimizing fertilizer inputs to reduce fossil fuel inputs to the system. This research determined how much nitrogen and phosphorus fertilizer is necessary for growing switchgrass as a bioenergy crop in the southcentral U.S. Our data indicated N fertilizer and rainfall (particularly growing season rainfall) controlled switchgrass production in the southcentral USA. About 168 kg N ha-1 maximized switchgrass biomass production in most years in this region. On average over all sites, experiments, and years, 168 kg N resulted in nearly 13.4 Mg biomass production ha-1 yr-1. The plots that received no N deteriorated over time, indicating that sustainable switchgrass biomass production is not feasible without N fertilization. Sustainable production of switchgrass in both north and southcentral Texas may not require P fertilizer. The soils at both sites were low in plant-available P, yet the eyearly application of P to the soil did not increase biomass production at any of the rates studied.
Technical Abstract: Management practices for biomass production of bioenergy grasses may differ from management for forage. We determined the yield and stand responses of 'Alamo' switchgrass (Panicum virgatum L.) to N and P fertilizer as affected by row spacing. Alamo was established at Stephenville and Beeville, TX, in 1992. Five rates each of N (0, 56, 112, 168, and 224 kg ha-1) and P (0, 9.8, 19.6, 29.4, and 39.2 kg ha-1) were applied to plots during 1992 to 1998 at Stephenville and 1993 to 1995 at Beeville. Three row spacing treatments (18, 36, and 54 cm at Stephenville; 25, 51, and 102 cm at Beeville) were applied as subplots. Biomass production was determined each year in late summer or early fall. Tiller density and tiller mass were measured during 1993 to 1996 at Stephenville. Biomass production was not influenced by P at either location. Biomass production did not respond to row spacing at Stephenville, but at Beeville the response to N was greater in narrow rows than wide rows during the establishment year only. Yield responses to N were quadratic in 5 of 7 yr. at Stephenville and linear at Beeville. A maximum yield of 22.5 Mg ha-1 occurred during 1995 at Stephenville at 168 kg N ha-1. Tiller density and mass increased as row width increased. Tiller mass also increased with increasing N fertility at Stephenville. Average biomass production at 168 kg N ha-1 yr-1 was 14.5 Mg ha-1 yr-1 at Stephenville and 10.7 Mg at Beeville. Nitrogen use efficiency was greatest at Stephenville and greatest, 108.6 averaged across 7 years, for the first increment of applied N. Biomass production without applied N tended to decline over the years. Switchgrass biomass production was not sustainable at Stephenville without the application of at least 168 kg N ha-1 yr-1 and may not be sustainable as far south as Beeville, Texas.