Developing Scenarios for Switchgrass in High Yielding Irrigated Environments.

Developing biofuels such as switchgrass (Panicum virgatum) presents a challenge in irrigated regions such as California.  Biofuels must compete economically with a wide range of high value specialty food crops as well compete for scarce water resources.  However, there are 12.3 million hectares of irrigated ‘lower-value’ crops (forages, grains, agronomic crops) that could contribute to biofuels, if a series of agronomic and economic factors are satisfied. These include very high yield potential, development of multiple-uses such as forages, ability to utilize wastewater, flexibility in water use, water and N-use efficiency, and provision of environmental services.  The potential of switchgrass was evaluated from 2007 through 2009 in statewide trials testing variety adaptation, N-use, cutting schedules, and yield potential.  Seeding year yield of switchgrass varieties planted June, 2007 in 4 irrigated CA environments ranged from 1.3 to 13.9 Mg ha^-1 and first full season (2008) yields ranged from 11.2 to 41.2 Mg ha^-1, with highest yields in southern irrigated regions. Several Alamo-type varieties were killed by frost at Tulelake, CA.  Significant differences between varieties were seen at all locations.  Nitrogen response in the first full season was negligible to moderate, with the most response in the second harvest.  Cutting schedules will have large effects on whole-system viability, presenting complex interactions with N-use, irrigation strategies, utilization patterns, and crop management.  The success of switchgrass in high-yielding environments like California may depend upon multiple-use scenarios (forage-biofuel), very high yield potential, high efficiency of N and water use, and other factors such as environmental services and use of wastewater.