LEPA differs from other types of low-pressure nozzles and heads in several ways. Generally, it operates at lower pressures and has higher irrigation-water application and distribution efficiencies, which result in lower net water loss and energy use (Fipps and New, 1991). This system can also be set up to apply fertilizers and pesticides.
Another promising technology involves using spectral radiometers that analyze crop color (Scharf et al., 2001). These can be mounted directly on fertilizer applicators and used to control variable-rate nitrogen applications. Systems that utilize sensors to assess color and health of crop plants, as well as variable-rate nutrient applications based on soil management zones and aerial photography, should find success with multiple types of feedstocks. Perennial feedstocks such as switchgrass or other native grasses would be in the field longer and thus should provide a greater opportunity to apply PA technologies. However, the application of technologies for efficient production of cellulosic biofuel will be determined by the economics of the specific production system.
Biotechnology innovations can be important in at least three areas. The first and obvious one is in improving biomass feedstock development through molecular biology/genetic engineering as well as traditional crossing and selection of plants. This has long been done with a focus on optimization for food, but now there is a need to broaden the focus to optimizing for biofuels production. Currently, major companies are screening their corn germplasm for ethanol production efficiency (i.e., gallons of ethanol per bushel of corn), and work is progressing to transfer identified traits into commercial varieties (Mark Alley, Virginia Tech, personal commun., July 20, 2007).
By optimizing for fuel as opposed to food, researchers can create biomass feedstocks that have a higher nitrogen-use efficiency, increased drought and water-logging tolerance, and improved root distribution characteristics—technologies that can be applied to both corn and cellulosic feedstocks. It should be noted that corn has a head start in this area in the form of a 15-year history of biotechnological development while even the basic tools of biotechnology for cellulosic crops remain in their infancy. An example of this can be seen in the rate of yield gain, in which corn yields increased at a rate of about 2.5 bushels per acre per year during this 15-year period (Troyer, 2006).
Second, this new molecular genetics knowledge can be incorporated